



Produced by Roger Frank








THE CHILDREN’S LIBRARY

NATURAL WONDERS




[Illustration: The Robin Moth]




THE CHILDREN’S LIBRARY

NATURAL WONDERS

By

EDWIN TENNEY BREWSTER

Garden City — New York

DOUBLEDAY, DORAN & COMPANY, INC.

1928




COPYRIGHT, 1912 BY DOUBLEDAY, PAGE & COMPANY.

ALL RIGHTS RESERVED.

PRINTED IN THE UNITED STATES AT

THE COUNTRY LIFE PRESS, GARDEN CITY, N. Y.




PREFACE


No small part of our fundamental knowledge concerning the world of
nature has been put into shape for comprehension by children, time
out of mind. “The Swiss Family Robinson” is half natural history,
even if not always of an especially convincing kind; and science of
all sorts, good and bad together, makes up no small portion of Jules
Verne’s uncounted tales. “Cousin Cramchild’s Conversations,” if
there had been such a book, would have embodied the Victorian idea
of what every child should know about his universe; while of actual
books, we elders recall at once Abbott’s “Science for the Young,”
and the half dozen contributions to juvenile knowledge of John
Trowbridge and “Arabella Buckley.” Even the great Ostwald, within
the decade, has made a child’s book on chemistry after the old
conversational form.

In school, moreover, between his geography and his nature study, the
modern child becomes acquainted with not a little modern science,
while in most of our states a detailed acquaintance, by no means
always scientific, with his own physiology is required by law of
every public school pupil. One thing with another, today’s child of
eight or ten is supposed to know a little of physics and of biology,
together with a good deal in a general way of earth science and the
elements of human physiology.

Naturally, there are excellent texts and reading books in all these
fields. So far as I am aware, however, the present work is the first
attempt to set before young readers some knowledge of certain
loosely related but very modern topics, commonly grouped together
under the name, General Physiology. It is, in short, an attempt to
lead children of eight or ten, first to ask and then to answer, the
question: What have I in common with other living things, and how do
I differ from them? Incidentally, in addition, I have attempted to
provide a foundation on which a perplexed but serious-minded parent
can himself base an answer to several puzzling questions which all
children ask—most especially to that most difficult of them all: By
what process of becoming did I myself finally appear in this world?

How far I have succeeded with either task, I leave to the mothers
who shall read this book aloud.

E. T. B.

Andover, Massachusetts




NATURAL WONDERS

CONTENTS

  Chap. I — How The Chicken Gets Inside The Egg
  Chap. II — Some Other Sorts of Eggs
  Chap. III — Little Fishes in The Brook
  Chap. IV — Of Plants’ Eggs
  Chap. V — What Little Boys And Girls Are Made Of
  Chap. VI — More About Living Bricks
  Chap. VII — How Much Of Us Is Alive
  Chap. VIII — How We Grow
  Chap. IX — How We Grow Up
  Chap. X — How We Grow Old
  Chap. XI — Why We Grow At All
  Chap. XII — Things That Do Not Have To Be Learned
  Chap. XIII — Why We Like Certain Things
  Chap. XIV — Animals’ Games
  Chap. XV — Some Instincts Of Chicks And Kittens
  Chap. XVI — Certain Stupidities Of Animals
  Chap. XVII — How We Differ From The Animals
  Chap. XVIII — Something More About Speech And Thinking
  Chap. XIX — Why Most Of Us Are Right-Handed
  Chap. XX — Where We Do Our Thinking
  Chap. XXI — Where Some Of The Animals Do Their Thinking
  Chap. XXII — What Plants Know
  Chap. XXIII — What Plants Can Do
  Chap. XXIV — Some Plant-Like Doings Of Animals
  Chap. XXV — The Five Senses And The Other Five
  Chap. XXVI — Eyes
  Chap. XXVII — Seeing And Believing
  Chap. XXVIII — Some Other Senses
  Chap. XXIX — The Sight And Hearing Of Ants
  Chap. XXX — Ants’ Noses
  Chap. XXXI — Some Other Eyes And Ears
  Chap. XXXII — Having Senses And Using Them
  Chap. XXXIII — Seeing In The Mind’s Eye
  Chap. XXXIV — Ear Minds And Others
  Chap. XXXV — Living Automobiles
  Chap. XXXVI — Air And Fuel
  Chap. XXXVII — Men In Glass Boxes
  Chap. XXXVIII — Of Sugar And Other Poisons
  Chap. XXXIX — Snake Venoms And Others
  Chap. XL — Of Measles And Rusty Nails
  Chap. XLI — The Great War
  Chap. XLII — More About The Great War
  Chap. XLIII — Living Apothecary Shops
  Chap. XLIV — What Becomes Of The Tadpoles
  Chap. XLV — Nature’s Repair Shop
  Chap. XLVI — Little Monsters
  Chap. XLVII — How The Animals Keep Their Tools Sharp
  Chap. XLVIII — Why The Blood Is Salt
  Chap. XLIX — Horses’ Fingers
  Chap. L — How The Elephant Got His Trunk
  Chap. LI — Something Nobody Understands




ILLUSTRATIONS

Frontispiece

  The Robin Moth

Full Page Illustrations

  How the Chicken Gets Inside the Egg

  Seeds That Have Plumes and Wings

  The Star-fish Has Eyes on His Arms; The Slug Also Has Eyes on His
  Horns; The Snail Has Eyes on His Two Longer Horns

  Lymph Cells or White Blood Corpuscles

  Extinct Reptiles Which Look Like a Mixture of Alligator, Rhinoceros
  and Kangaroo but Their Bones Were More Like the Bones of Birds

In the Text

  A Sea-Urchin

  Eggs of Perch After Egg Laying

  Salmon with Yolk Sac

  The Bean Egg Changes to a Bean Plant

  Living Bricks Which Make the Skin of a Leaf

  Cells of the Inner Tree Pulp

  Cells of the Outer Skin of a Leaf

  Cells of a Pond Scum Much Enlarged

  Three Sorts of Infusoria Much Enlarged

  Some Jelly-fish Grown on Stalks and Some Swim About in the Sea

  The Cob Is the Mother of the Corn

  Pollen Grains Much Enlarged

  A Right-handed Person Has All His Thinking Spots on the Left Side of
  His Brain

  A Sea-anemone

  More Common Infusorians, Much Enlarged

  The Leaf Has a Spiral Joint on Which to Turn

  Optical Illusions

  Optical Illusions

  Optical Illusions

  Optical Illusions

  Optical Illusions

  Ear of a Mole Cricket on the Front Leg

  Back of the Frog’s Eyes Are the Ear Drums

  A Newt

  The Leaves Take in Air Through Breathing Holes

  In Place of Lungs, Insects Have Breathing Holes

  The Minute Animal Which Causes the “Sleeping Sickness”

  The Caterpillar Changes into a Moth

  Accidents to Growing Fish Eggs

  A Two-headed Turtle, a Crab with an Eye on One Side and a Feeler on
  the Other, and a Child With Two Great Toes on Each Foot

  The Fangs of a Rattlesnake

  Early Man Scratched Pictures of the Mammoth on Pieces of Its Own
  Bones

  The Elephant Has Lost the Front of His Face

  Our Single-toed Horse Has Been Made Over from a Four-toed One




I

How the Chicken Gets Inside the Egg


There is no more fascinating sight to be seen anywhere than an
incubator full of eggs just as the chickens begin to hatch out. You
look through the little glass window in the side and see, at first,
only rows of clean white eggs, dozens upon dozens of them, looking
as if they were all ready to go into the family ice-chest or to be
made into omelets for breakfast.

But they are not. First you begin to hear faint scratchy sounds.
Pretty soon, here and there, a hole breaks through the broad end of
an egg, and a tiny bill sticks out. The little chick is packed so
tightly into the egg that it can move only its head. So it pecks and
pecks; and stops to rest; and pecks again; and the hole in the shell
gets larger and larger; until by and by, the egg cracks open, and a
brand-new chicken draws its first long breath and looks out into the
world.

After that, the chick usually takes a long rest, for it is pretty
tired. When it feels better, it begins to move its legs and wings,
and a half-hour or more after it first began work, it gets clear of
the shell and stands up on wabbly legs, wet, bedraggled, weary, as
disconsolate looking a little object as can well be imagined.
Shortly, however, the feathers, which at first were plastered tight
to the skin, dry off and fluff out, the legs get steady, and soon
there is running about a rolypoly yellow chick, seemingly at least
twice as large as the egg which held him only an hour before. Truly
it is a wonderful sight, five hundred eggs turning into little
chicks in an incubator, for all the world like the kernels of corn
changing to pop-corn in the popper.

But wonderful as it is to see the way a chick comes out of an egg,
it is still more wonderful to see the way it gets in. A fresh,
new-laid egg has no chick inside. After it has been kept warm three
weeks, it has—all ready to come out. The question is how the chicken
got there.

Many different men have studied this question. For the most part,
they have started a dozen or more eggs at once, and then taken them
one by one and two or three hours apart, and cautiously broken them
open to see what was inside. Sometimes, however, a student of eggs
carefully cuts away the shell on one side, until he has made a hole
about the size of a ten-cent piece. Over this he cements a sheet of
glass as thin as paper, so that he can look through this tiny window
into the egg, and see the chick grow.

This is really easier than it sounds. The yolk, as everyone must
have noticed in hard-boiled eggs, does not stay in the middle of the
egg, but always floats to the upper side. The chick, too, always
forms on the upper side of the yolk; and when the egg gets turned
over, the yolk rolls round like a barrel in the water and brings the
chick to the upper side. So the chick, until it grows big enough to
be a tight fit, always lies crosswise of the egg, on the upper side
of the yolk just under the shell.

At first, of course, there is no chick at all, but only a round
white fleck hardly larger than the head of a large pin, on the side
of the yolk where the chick is by and by going to be. Before the end
of the first day after the egg is laid, this little fleck has become
somewhat oval in outline and an eighth of an inch across. Through
its center runs a whiter line, as thick as heavy basting cotton and
a sixteenth of an inch long; about half as large, that is, as an “l”
or a figure “1” in the type on this page.

This is the beginning of the chick. Only it has hardly yet begun to
be a chick, for it has as yet neither head, tail, wings, legs, eyes,
nose, mouth, heart, stomach, brain, nor any other parts. It is in
short, only a tiny line of chicken substance, which is now to begin
to be made into a chicken.

Early in the second day of incubation, the little white line begins
to get thicker on the end where the head is going to be. The brain
and spinal cord appear first; later in the day there is the first
sign of eyes and ears. At about the same time, the heart begins to
form, and the minute blood vessels to grow out into the yolk like
the first roots of a tiny plant. Before the end of the second day,
the heart has begun to beat, and the blood vessels have begun to
absorb the yolk to feed the growing chick. The yolk, in its turn,
feeds on the white; for as everybody knows, the yolk and the white
of an egg are stored up food, on which the little bird can live and
grow until it is old enough to get out of the egg and shift for
itself.

At the beginning of the third day, or a few hours before, the chick,
which has been lying on the yolk face down (only it hasn’t any face
yet), turns over on its left side. It is getting to be a big bird
now, a quarter of an inch long and as thick as a good sized pin.
Next, the brain grows rapidly; and so do the eyes, though these are
not so large as the eyes of the finest needles. Now too, the nerves
begin to form; also the lungs, the stomach, liver, and other organs
of digestion; and there are beginnings of a tail, though without
feathers.

During the fourth day, there are signs of a mouth. Legs and wings,
looking just alike, begin to bud out from the body. Another day, and
one can tell which is which; while now there appear beginnings of
the skull and of the place where the back bone is going to be.
Meantime, the little bird has become more than a half-inch
long—though it does not yet look the least bit like a bird, but more
like a large “?” mark. There is still no front to the body, and the
heart, beating merrily away, hangs out in the yolk.

With the second week, the little chicken does begin to look
something like a real bird. The bones begin to harden; while on the
tip of what has been just an ordinary nose appears a speck of chalk,
which will by and by harden into a bill. The claws begin to grow;
and there are signs of feathers, each one still enclosed in the
little transparent sac in which it forms.

At the end of two weeks, the white of the egg is all used up; and
the little bird, which has been lying crosswise of the egg, now
turns to bring its head toward the broad end. The yolk, too, is
getting small; and on the nineteenth day, the chick pulls the last
remnant into its little tummy, and begins to close over the hole. At
about the same time also, he pecks through into the large air space
which one sees in the broad end of an egg, when he eats it,
hard-boiled, at a picnic. For a week or more, he has been breathing
by means of a sort of gill, much like that of a fish, only that
instead of being on the side of the head like a fish’s it grows out
from the middle of the stomach on a long stalk and spreads over the
inside of the shell. So the chick breathes through the shell, which
is full of minute holes almost too small to be seen. But after the
last bit of yolk has been taken in, this gill shrivels up and drops
off, and the chick breathes with its lungs like the rest of us.

At the end of three weeks, there is nothing left of the egg but the
shell and a tea-spoonful of water. The chick, which began life the
size of a pin head, now fills the shell jam full, with only just
room enough to peck the hole that lets him out. On the twenty-first
day of his imprisonment, out he comes.

[Illustration: How the Chicken Gets Inside the Egg]




II

Some Other Sorts of Eggs


All birds lay eggs. Some are brown or white like the hen’s egg; some
are green, some buff, some blue; many are speckled. Some, like the
eggs of the screech owl, are almost as round as marbles; not a few
are so pointed at one end as to be fairly pear-shaped. The
hummingbird’s egg is the size of one’s finger tip, the ostrich egg
is as large as one’s head. But all alike they have shell and yolk
and white; and by and by, a little bird inside. Only sometimes, like
the chick, the little bird hatches out with feathers grown, and only
needs to dry off and get its breath, before it is ready to run about
and pick up a living for itself; and sometimes, like the little
robin, it has no feathers, cannot stand up on its legs, and has to
be fed by its parents, like a human baby.

Snakes and turtles have eggs also, very much like birds’ eggs. Like
these, they have white and yolk; and the little reptile grows in the
egg almost exactly like the little bird. For curiously enough the
turtles, snakes, lizards and crocodiles, tho they look so very
different from birds, are really very like them. They all have large
eggs, with large yolks; and the little animal begins at a point in
the side of the yolk, and does not, for a long time, fill the entire
egg.

Oddly enough, there does not seem to be much connection between the
size of an animal and the size of its egg. Big birds, to be sure,
have big eggs; and little birds have little eggs. But a great
crocodile, fifteen or twenty feet long and able to bite a man in
halves, is hatched from an egg no larger than that of a goose. The
little salt water minnow, or killifish, which is only as long as
one’s finger, has very large eggs, for a fish, almost as large as
small blue berries, and quite as large as the eggs of salmon and
trout which grow to be a hundred times heavier. But cod fish, which
sometimes are almost as large as a man, and the great sturgeons,
which are as long as three men and as heavy as a horse, have eggs
not much larger than the periods on this page, smaller even than
those of a tiny ant. As for the little sea creatures, star-fish,
sea-urchins, and the like (which to be sure, are quite as large as a
hummingbird or a wren) their eggs are but fine dust, which cloud the
water and are too small to be seen at all.

However, the smaller the eggs, the more of them there are, to make
up. While some birds lay only two eggs at a time, and few more than
a dozen, some fishes lay a hundred or more, the cod a hundred
thousand, and the sturgeon two or three million.

[Illustration: A Sea-Urchin]

Sometimes, when one is poking about in the brooks in the spring of
the year—as every boy and girl should do, for it is great fun—one
happens upon masses of transparent jelly half as large as one’s
head, full of tiny black dots. These black dots, which are just
about the size of the o’s in this book, are the eggs of frogs. If
instead of being in round masses, they are in long strings, a yard
sometimes in length, then they are almost always the eggs of toads;
but if they occur neither in masses nor in strings, but separately,
then they are the eggs of newts.

It seems strange that a frog should be able to lay a mass of eggs
and jelly forty or fifty times larger than the frog itself. The real
egg, however, is only the dark speck; and this when it is first laid
has only a thin coating of jelly, hardly thicker than paper and
nearly dry. As soon, however, as it touches the water, this dry
jelly begins to swell, and goes on swelling and swelling for three
hours until it is a hundred times larger than it was to start with.

These balls of frog’s eggs look, then, very much like tiny hens’
eggs with black yolks, broken into a bowl ready for cooking. They
really are not quite this; because the frog’s eggs have no shell and
no white, being simply yolk and nothing else. In fact, the only
sorts of eggs that do have white are those of birds and reptiles;
while few others have shells either. The jelly of frog’s eggs is not
“white,” because it is not meant for the little frog to eat, but to
keep other creatures from eating him. Besides this, it helps to keep
the little chap warm.

You will recall that the little chick begins as a tiny dot on one
side of the yolk, and keeps growing larger and larger until it uses
up both yolk and white and fills the entire shell. Not so the little
frog. Always, from the very beginning, it is as large as the egg. It
is the egg, in fact. You can see that the egg is dark above and
light below just as the tadpole will be, and the frog after him. At
first, however, the baby tadpole does not have any parts or members.
He gets in proper succession, eyes, ears, backbone, brain, skin,
tail, and the rest; but he does not grow any larger until he hatches
out, wriggles his way thru the jelly, and begins to eat.

At first the tadpoles are very tiny, only a quarter of an inch in
length; and they cling in tufts to the under side of the water
plants. After that, I suppose, everybody knows what happens.

There is still another curious difference between hens’ eggs and
frogs’. When a frog lays an egg, that egg is nothing else but just
egg—the little frog has not begun at all to form inside it. But when
a hen lays an egg, while there is no little creature in that either,
still the egg has already begun to get ready to turn into a chick.
Some animals go farther than this, so that when their eggs are laid,
the little creature is already formed inside, and so has only the
last part of his growing left to be done outside. Certain fishes,
certain reptiles, and various other animals besides, actually put
off laying the eggs until so late that the young is all ready for
hatching. Such eggs are laid and hatched at the same time, or even
hatched first and laid afterwards.

All the four-footed creatures which have fur and hair, horses,
cattle, dogs, cats, monkeys, and the like, manage in this way. And
because this kind of egg doesn’t get knocked about, it does not need
to have either hard shell nor thick jelly to protect it, but only a
thin skin. For this reason, and because the egg hatches a few
moments before it is laid, people are apt to miss it entirely, and
so to get the idea that these animals have no eggs at all. But they
have—one egg for each little animal.

We pretend that the bunny rabbits at Easter are hatched from the
 Easter eggs. They really are hatched out of rabbits’ eggs.
No one notices the remnants of the rabbits’ egg, because what little
there is soon dries up to almost nothing, or else the old mother
rabbit eats it. Besides, one has all one can do to look at the new
bunnies. Nevertheless, all little animals come out of eggs, puppies,
colts, lambs, calves, kittens, every kind of living creature that is
big enough for you to see, and a good many besides that are so small
that you have to look for them with a microscope.




III

Little Fishes In The Brook


Of all eggs, the most interesting, I think, are the fishes’. Nearly
all of these are pretty small, little round whitish globules like
sugar pills. Some, like the eggs of trout and salmon which one finds
in the gravel banks of rapid streams, are as large as fair-sized
beads. Many, like the eggs of sea fish which float near the surface
of the ocean, would go thru the eye of a darning needle.

The point, however, which makes them especially interesting is that
so many of them are like tiny glass marbles. The membrane around
them is so clear, and the substance of the egg itself so
transparent, that with a magnifying glass, one can look right thru
the egg, and see the little white fleck inside grow from nothing at
all to a real fish, long enough to reach clear round the egg and lie
with its tail almost in its mouth.

Some eggs are much clearer than others. The clearest are, at first,
like clear glass, so that they can not be seen at all under water.
Soon, however, a tiny vague white spot begins to form on the lower
side. Then one can make out that the egg is covered with a rather
thick membrane, that within this is a narrow, clear space filled
with water, while within this and still smaller, floats the tiny
yolk which is the real egg that is going to become the little fish.

[Illustration: Eggs of Perch after Egg Laying.]

The white spot on the yolk is not itself fish, but only fish stuff,
which is being made ready to turn into fish by and by. The spot
grows larger and thicker, until it looks like a round dab of putty
stuck on the side of a marble. When this cap has grown until it is
about half as much in diameter as the egg itself, it thins in the
middle and thickens at the edges, until it forms a ring. A very
strange thing, thereupon, happens to this ring. It begins to grow;
and as it grows, it keeps slipping farther and farther round the
egg. Soon it has become a band round the middle of the egg. Then as
it moves along still farther to the other side of the egg, it has,
of course, to grow smaller in order to fit. So it does, and the
extra length taken in at one point in the ring, forms the body of
the little fish. The head has already begun to form from a
thickening at one side of the ring before it passed the middle of
the egg. The two sides of the ring form the two halves of the body.
But the tail being easier to make, does not grow out until much
later.

Now there is a head and a body; but the only difference is that the
head is bigger. Neither has any parts. There are no eyes, ears,
nose, or mouth in one; nor any fins, backbone, stomach, nor scales
in the other. These all appear later, much as in the chick—eyes,
ears, brain, and heart early; fins and tail, scales and the whole
front of the body not until long afterwards.

Many learned men have spent their entire lives in studying the way
in which all these various parts form in the young animal, and a
most strange and fascinating study it is, quite worth any man’s
spending his life on. If I were to tell all that is known about the
least part of one fish, the tale would fill up this entire book and
leave no room for anything else. I shall, therefore, tell about the
eyes only—partly because they are interesting and important organs;
but more because they happen to be parts of the body which form in
the same manner in all animals that have a backbone, whether they
are fishes, frogs, birds, four-footed beasts, or human beings. The
eyes with which you, my reader, are reading this page, grew in the
way I shall describe, as I have myself seen it in the egg of cod and
sea-bass.

In general, the part of the body to form earliest is the brain. Next
after that come the eyes. These begin as two buds which grow out one
on each side of the brain where the head is going to be. Each is a
hollow, bubble-like affair on a short stalk; as much as anything,
except for size, like a hollow rubber ball stuck on a pencil stub.
One would think that this hollow ball would simply change into an
eyeball; but it doesn’t, for Nature rarely does things simply.
Instead, one side of the eye-bud folds in, as you might push in a
hollow rubber ball with your finger, until it forms a cup. This cup
is the eyeball. The sides grow out until the hole narrows down to
the dark opening in the middle of the eye which we call the pupil.
Various kinds of eye-stuff grow over the edge and form the interior
parts of the eye; other tissues on the outside thicken the walls and
form the transparent cornea in front; and while the pupil is still
large, a portion of the substance which is later to become the skin,
buds into the eyeball to form the lens of the eye. The reason, then,
for this round-about process, this doubling in of the original eye
bud to make a cup, which afterwards closes down to the eyeball we
finally use, is to get various substances inside the eye, and
finally to leave a pupil for the light to enter.

[Illustration: “Salmon With Yolk Sac.”]

Thus far, like the little chick, the little fish has had no front to
its body. It lies on the yolk, curled round it like a child with the
stomach ache hugging a pillow. By and by the tail grows out free of
the yolk. The head also lifts clear, and the lower jaw has room to
form. Last of all, the sides of the body grow completely round the
yolk, and put it where it will do the most good.

Now the fish is ready to hatch. For some time it has been giving
occasional wiggles inside the egg membrane; finally it breaks thru
and floats out. It is a tiny helpless creature, still more than half
yolk. It cannot swim, but floats, belly up, and mouth wide open, not
yet able so much as to close its jaws.

From this time on, the fish grows rapidly, living on the yolk, which
grows smaller and smaller. At first the little creature floating on
its back can only give an occasional wiggle. As the yolk becomes
more manageable, the fish wiggles more. Soon it turns for a moment
on its side, then clear over; and by the time the last of the yolk
has disappeared, it is swimming right side up and has begun to eat
the still tinier water creatures which are its food. At this stage,
if it is a fresh water fish, it begins to be visible in the shallows
in schools of minute, but veritable, fishes a quarter inch long and
mostly eyes.




IV

Of Plants’ Eggs


The plant’s egg is, of course, the seed. We commonly say that the
plant grows from the seed. And so it does. Yet this is not exactly
true either, because the ripe seed is already a little plant, folded
up tight and packed away in a hard case, like a chick inside its
shell.

If one takes, for example, an ordinary bean or a peanut, peels off
the shell and opens it carefully, it separates into two halves, held
together by a little nodule at one end. These two halves, which
together form pretty much the entire bean, are really two fat
leaves. They are the yolk of the bean egg, on which the new bean
plant is going to feed until it has grown leaves and root, so that
it can pick up a living for itself out of the earth and air.

The rest of the new plant is the little nodule which lies between
these seed-leaves. Curled up against the outside of the seed, like a
puppy’s tail between its legs, is a short fat root; while hidden
away between the seed-leaves is the next pair, tiny leaves almost
too small to see, but real leaves nevertheless.

So the bean is an egg. Not a new-laid egg, but an egg with a little
plant inside, all ready to hatch out and grow.

[Illustration: The bean egg changes to a bean plant.]

If instead of cooking and eating the bean, we plant it in the
ground, or in wet sawdust or blotting paper, it soon hatches out.
The shell drops off, the seed-leaves first take in water and swell
and then shrink away to nothing as the growing plant eats them up.
The little root grows down, the little leaves grow up, the whole
plant turns green and begins to climb the bean pole.

All seeds, then, are eggs just ready for hatching. They are like
fish eggs, however, rather than like birds’ eggs, because the little
fish and the little plant both save most of their yolk to use in
getting a start in the world after they are hatched out. But the
birds, you will recall, because they have large eggs and plenty of
room inside, keep on growing till the yolk is all gone, and then
hatch.

The little plant, as you might expect, gets inside its seed almost
exactly as the little bird or frog or fish gets inside its egg. The
“string beans” which we eat in the summer are fat pods stuffed out
with bean-stuff to be used in making seeds. There are tiny beans
inside, which are new-laid bean eggs, and so have no little plant
inside, but only bean-stuff. The little bean plant, starting from
nothing, forms one part after another, like chick and fish.

But where does the egg come from in the first place? The bean egg
forms in the pod, too small at first to be seen at all, and keeps
growing until it is big enough to begin to form the new plant. In
exactly the same way, the mother fish, and the mother frog, and the
hen, have a sort of pod inside them. First this pod stuffs and
fattens itself out with egg-stuff, like a string bean. Then some of
it turns into little eggs, too small to be seen. These grow and
grow, like the beans in the pod, while the pod shrinks away. Only
after they have grown a great deal, do they begin to form little
beans, or fish or chicks inside.

[Illustration: Seeds that have Plumes and Wings]

First of all, in short, the bean pod begins as a minute speck and
grows into a proper pod. Then the bean inside this pod begins as a
minute speck, and grows into a proper bean. Then the new bean plant
inside this bean begins as a minute speck and grows into a proper
bean plant, ready to be hatched out and shift for itself. So part of
the mother plant becomes pod, and part of the pod becomes bean, and
part of the bean becomes little growing plant. So it is with little
fishes and little birds and little rabbits and puppies and kittens
and all the rest of the little animals that you know.




V

What Little Boys and Girls are Made Of


  “What are little boys made of, made of?
    What are little boys made of?
  Snaps and snails and puppy dog’s tails;
    That’s what little boys are made of.
  What are little girls made of, made of?
    What are little girls made of?
  Sugar and spice and all that’s nice;
    That’s what little girls are made of.”

So says the old nursery rhyme. It has this much truth in it, that
little boys and little girls are far from being alike, and it isn’t
worth while to try to make either one over into the other. What
little boys and girls are really made of, and all other living
things as well, is a much longer story.

Oddly enough one can tell this story more simply by telling first
about little star-fish and sea-urchins, and what they are made of.
Star-fishes’ and sea-urchins’ eggs (for the two creatures are really
very much alike, for all they look so different) are much like the
eggs of fishes. They are round and transparent, and so minute that
they look like fine red dust in the water. Naturally, therefore, few
people ever see them at all.

Each of these eggs is a tiny drop of fluid substance with a very
thin skin round it. It is in fact, not unlike a toy rubber balloon,
filled with thin jelly mixed with oil, and set floating in the
water.

This then is the young egg, before there is any sign of a growing
creature inside. One would perhaps expect to see the oil and jelly
mixture change gradually into a star-fish. Instead of this, however,
this little balloon-like affair splits squarely in two, and makes
two little balloons just alike, which lie side by side and more or
less flattened against one another, like two soap bubbles blown from
the same pipe. In about a half hour, each of these balloons or
bubbles, “cells” as they have come to be called, has divided again;
so that now there are four. The four soon become eight; the eight,
sixteen. In the course of a few hours, there are hundreds, all
sticking together and all very minute; so that the whole mass looks
like the heap of soap bubbles which one blows by putting the pipe
under the surface of the soap suds.

So the first single cell of the new laid egg, small as it was, has
become several hundred still smaller. These, however, are not yet
star-fish, but only star-fish-stuff, arranged in a little pile like
a heap of bricks, and all ready to build into a star-fish.

Now if a man is building a house out of bricks, he piles the bricks
near where the house is going to be; and then he takes them, a few
at a time, and cements them into his wall. Not so the star-fish
house. This has to be built right in the living brick pile. It is as
if we dumped a heap of bricks in a field, and then each brick of its
own accord got up and went to its proper place in the house. The
little ball of cells which is the egg, begins to swell, and fold,
and move. It pushes out one part here, and doubles in another there.
The cells divide rapidly in one place, and form a thick solid bunch;
in another they spread to a thin sheet. By and by, there is a little
creature; not indeed a star-fish, but something with a stomach and
an outside skin, and between the two, certain nondescript cells,
which later on are going to make the hard skeleton and the muscles.
After this, the cells still keep on dividing, but instead of getting
smaller and smaller, they wait each time they divide till they grow
to full size again. Thus the baby star-fish grows. And by growing
fast in some places, and slowly in others, and in still others not
growing at all, it changes at length into a veritable star, altho no
bigger than a grain of sand.

All eggs change into little animals in this same way. The hen’s egg
yolk is such a cell—a thin skin filled with oil and jelly. The
frog’s egg is another, with one side  black. The fish egg is
like the others, with an especially clear jelly that one can easily
see into. Frog eggs and star-fish eggs and sea-urchin eggs, most
sorts of eggs in fact, split fairly in two the first time they split
at all, the whole yolk divides and the little animal, from the first
moment when there is any at all, is always as large as the egg. But
birds’ eggs, most fish eggs, and some other sorts too, are so loaded
down with fat that the egg does not divide clear thru, but as I have
already explained, only at a tiny spot on one side where the jelly
is thickest. But whether this pile of minute cells which is the heap
of little animal bricks, is a small spot on the side of a large egg
or the whole of a small one, it all comes to the same thing in the
end. When the proper moment arrives, the living cell bricks move to
their appointed stations, and the new creature begins to form.

Now we know what little boys and girls are made of. They are built
of enormous numbers of these living bricks which we call cells, just
as other living creatures are. All of us, men or animals, trees,
bushes, or grass, were once, each of us, just one single round cell
which divided, and divided, and divided again, until it became a
vast number. Out of this vast number the new plant or animal builds
itself.

If it is an animal like ourselves, this body stuff, before it
becomes a body, is a round ball. A furrow doubles in along the place
where the back is to be, and becomes the spinal cord. A rod strings
itself along underneath this, and becomes the backbone. The front
end of the spinal cord grows faster than the rest, becomes larger,
and is the brain. The brain buds out into the eyes. The outer
surface of the body, not yet turned into skin, buds inward and makes
the ear. Four outgrowths come down from the forehead to make the
face. The limbs begin as shapeless knobs, and grow out slowly into
arms and legs. Sometimes these make a mistake at their ends, and
split into six fingers or toes instead of the customary five. Then
if the little creature is a human baby, the Doctor has to cut one of
these off; but if it’s a kitten we say it has double paws and will
be a good mouser—tho really I don’t suppose it makes the least
difference.

Most of our growing, then, is just the increase in numbers of these
little living bricks. There is a spot at the bottom of each
finger nail where the nail cells are dividing and pushing out the
finger nail. The white spots in the nail do not mean that one has
been telling white lies, as some people say. They come because one
happens to bruise the soft “root” of the nail where the nail cells
are new and easily hurt like the soft flesh of a little child.

When we were very much younger than we are now we had no teeth. As
biting-time drew near, the cells of the thin skin which lines the
mouth began to multiply so rapidly where the two gums touch one
another that they soon formed a thick ridge growing back into the
jaw. A little later, and this ridge continued to grow at twenty
separate points while it stopped growing everywhere else. Soon these
twenty growing points opened up into twenty pockets. From the bottom
of each pocket grew up a tooth; while from the side of each there
budded out another pocket in which, when the baby is eight years or
more old, the second teeth form. But the three back teeth in each
side of a man’s jaw, tho they come late and are the largest he has,
really belong to the first milk set, the rest of which he lost as a
child.

Even the hair grows by the division of cells at the inner end of the
little bulb which you see on the end of the hair when you pull it
out and look at it against white paper. Just between hair and skin
is a spot which is neither hair nor skin, where all the growing of
the hair is done.

So we are not built like a cement or a wooden house, but like a
brick one. We are made of little living bricks. When we grow it is
because these living bricks divide into half bricks, and then grow
into whole ones again. But how they find out when and where to grow
fast, and when and where to grow slowly, and when and where not to
grow at all, is precisely what nobody has yet made the smallest
beginning at finding out.




VI

More About Living Bricks


The largest of these living bricks is the yolk of an ostrich egg;
since this is, of course, like all eggs before they begin to grow, a
single cell. The smallest known are certain of the bacteria and
germs which float about in the air, and are so minute that they
cannot be made out even with the strongest microscopes. All one can
see is that there is something there; something which if placed a
thousand in a row, would still not reach across a grain of dust.

Few cells, however, are as small as bacteria on the one hand, nor
anything like as large as the yolks of birds’ eggs on the other.
Many are just comfortably visible to the unaided eye. But the great
mass of cells which make up our own bodies, the bodies of other
animals, and of plants are a little too small to be made out with a
common pocket lens, tho an ordinary microscope shows them with ease.

While the egg yolk is dividing to form the first hundred or more
living bricks out of which the little animal is to be built, the
cells are all about alike, generally round except where they are
flattened against one another. As soon, however, as they begin to
move about into place to build the new animal, they begin themselves
to change. Some remain small; others grow large. Some grow out into
long strings, and become muscle fibers or nerve. At one point, many
thousands together swell up with oil and become fat. At another,
more thousands build themselves about with hard lime phosphate, and
become bones and teeth. Those which form within them little brown
granules, give the color to hair and skin. The blood is  red
by the coin-shaped cells which float in it. In certain parts of the
eye, on the other hand, the cells have to remain perfectly clear and
colorless, else the light could not come thru and we should never
see truly.

When an animal is very young indeed, long before it is ready to
leave the egg, the whole outer surface of its body is covered with a
single layer of these cells. They are packed closely together, and
flattened against their neighbors so that the sheet of cells is not
unlike, on a small scale, the marble floor of a public building or
the block pavement of a city street. Like other living cells, these
grow, and divide. They cannot grow sidewise, for the space is
already filled; nor inward for that way lies the entire body. So
they split off a piece of their outer ends. Then they do it again,
and yet again; until the outer skin of the body, from being one
layer of cells in thickness has become many.

Only the original inner layer, however, grows and divides. The split
off ends dry up to a roundish cracker shape, grow hard and homy, and
become the thin outer skin of the body, which we run pins and
needles under, and pull off or scrape off when we “bark” our shins,
without hurting. This part of the skin is dead. It gets rubbed off
by our clothes, or soaks off in the bath tub and has to be scrubbed
off the sides. But as fast as it is removed on the outer surface, it
grows again from the living bottom layer. No matter how old one
gets, this lower layer of the skin continues to split off the outer
ends of its cells, just as it did before there was any proper skin
at all. Most parts of the body grow thruout their mass; but the skin
grows only on the inner side.

On the palms of the hands and the soles of the feet the skin grows
very rapidly and is especially horny. When one works with his hands
more than he is accustomed, the first effect is to wear the skin
thin and sore, or to pull it loose from the bottom layer and make
blisters. In the end, however, the rubbing only makes the live skin
work faster, until it builds great homy callouses that no work can
wear thru. But when our boots do not fit and rub in one spot, this
also starts up the live skin to working hard. First thing we know,
we have a corn. For a corn is only an especially hard and thick
callous, where the living skin made a mistake and grew too much in
one little spot.

Each finger nail and toe nail is a sort of corn. It grows from a
fold of skin, forming from the bottom layer like any skin, but it is
especially homy, even more horny than the hardest callous. The hair,
also, is a sort of corn. The skin doubles in to form a minute
pocket; and at the bottom of this pocket this same living under
layer of the skin grows into a narrow shaft of cells, dry and dead
and homy like skin and nails.

The horns of animals, too, are only thick hard skin. Sometimes they
have a core of bone inside, but the outside is just a special sort
of skin. Wherever we go in the body, there we find some special sort
of cell. They may be large, small, thick, thin, long, round, soft,
hard. They may build this, that, or the other thing around them.
They may have this, that, or the other thing inside. But in one way
or another the whole body, from head to heels, is built of these
cells and their products.

[Illustration: Living bricks which make the skin of a leaf. Five pairs
of these are the lips of breathing holes.]

It is the same way with the plants. They too are built of these
living bricks. Each leaf and blade of tree or grass is covered with
a sheet of colorless cells one layer deep, which one can often peel
off from the green pulp underneath. The green pulp, in turn, is a
rather loose pile a half dozen thick, of roundish brick-shaped
cells, each containing scattered grains of green coloring matter.
The solid wood of a tree is only the thick walls of long slender
cells, overlapping at the ends and packed tightly together. These
cells lie lengthwise of the tree; that is why wood splits with the
grain so much easier than it cuts across it.

[Illustration: Cells of the inner tree pulp. The rings show that the
tree is three years old.]

[Illustration: Cells of the outer skin of a leaf. At the bottom is
the mouth of a breathing hole.]

I have already said that at the time of year when the tree is
growing rapidly, these woody cells are large; but when the tree is
growing slowly, they are small. So each year there is a change from
large cells formed in the spring to smaller ones grown in the fall.
The next year, the living substance of the cell moves off to the
growing region next the bark, and leaves the old wood cells empty.
These, therefore, never change; and because the large cells and the
small ones do not look quite alike, we see the annual rings of wood
in the tree trunk, as thick as card board, which give us the light
and dark lines in our furniture and our hard wood floors. From these
one can tell, not only how old the tree is, but also what were its
good years when it grew rapidly, and what its poor seasons when it
hardly grew at all. If a drought came along any summer, or if
insects one year ate off all the leaves, that too shows in the wood.
But trees which grow in the tropics, where they keep growing the
whole year thru, do not have annual rings.

While some cells of the tree form wood and some green pigment,
others in the bark produce cork, as one can see nicely in the thin
layers of cork in the bark of an elm. The cells of juicy fruits
swell up with water, and form sugar and various flavoring matters
and pleasant acids. Where the animal cells swell up with oil and
become fat, the plant cells swell up with starch grains and become a
potato or the thick seed-leaves of a bean. But other cells form gum,
rosin, turpentine, pitch, and the various oils and the like,
pleasant or bitter, which we use for food and medicines.

So the plant, like the animal, is just a great mass of different
sorts of these living bricks, and of the various substances which
they form within and around them.

Naturally it takes millions upon millions of these living bricks to
build up the body of a man or an apple tree, still more of a whale
or one of the giant redwood trees of California. Many humbler
creatures, on the other hand, both animals and plants, contain
comparatively few. Our common green pond scums, for example, which
tho they are plants, have neither leaves nor stems nor roots, are
like single long lines of tiny green barrels set end to end. Our
common sea-lettuce is a sheet of cells only one layer thick; while
other sea-weeds and water plants are but bundles of a score or more.
Often the fewer such bricks there are, the larger they are; even at
times, to a half-inch in thickness and an inch or more in length.

[Illustration: Cells of a pond scum much enlarged. The green living
substance flowing from one to another unites to form an egg or spore.]

A vast number of plants and animals, moreover, are single cells.
Such among plants are the yeasts with which most of us make our
bread, and a few of us brew our beer. Such also are the hundreds of
different sorts of bacteria, which tho some of them are the germs of
various catching diseases, are for the most part useful enough. But
of these we shall learn more by and by. The green spots and patches
on the bark of old trees and fences, and sometimes even on damp
earth, are due to enormous numbers of minute plants, green with the
same green pigment as the leaves of the largest tree; while the
green tint of the gray lichens on rocks and tree trunks is caused by
similar single-celled plants which grow among the white fibers of
the lichen proper. Besides these, there are many like plants which
float about in fresh water, each a single cell.

[Illustration: Three sorts of infusoria much enlarged.]

The diatoms which one finds in the mud at the bottom of ditches and
mud-puddles, tho they have shells and move about, are usually
counted among plants; but the water of most ditches and puddles
swarms with amoebas, infusoria, animalcules of various sorts, most
of them large enough to be made out with the unaided eye when seen
in a tumbler against the light, and each a single cell.

Many animals, then, and many plants are just one single cell and no
more. Many others, like pond scums and sea-lettuces,—which are
plants,—and sponges and jelly-fishes,—which are animals,—are
composed of many cells, but all pretty much alike. But the animals
and plants which we know best, kittens and oak trees and horses and
grass, and the creatures we know best of all which are ourselves,
are made up of many cells, and many different sorts—skin and bark
and wood, flesh and fat and leaves and hair and all the rest, so
many that it would take half an hour merely to write them all down.

[Illustration: Some jelly-fish grow on stalks and some swim about
in the sea.]

These “cells” then, are the living part of every plant and animal. Each
of them became by the splitting in halves of an older cell; each of
these in turn by the splitting in halves of a still older cell, until
we get back to the egg which is the great-great-great-grandfather of
them all. But the egg itself arose by the splitting of still another
cell, which, of course, was part of the parent’s body. This came from
yet another, and so on back to the beginning of life on this earth, tho
nobody knows how long ago that was.

So the living flesh of us has always been alive. Most of it will
die; but some of it will live on in our children and our children’s
children, until the and of the world.




VII

How Much of Us Is Alive


How much of a tree is alive? Certainly not the outer bark. That
falls off in dry scales, or can be scraped off down to the white
layers within, and the tree be none the worse. Certainly not the
wood. One often comes across old trees that have lost limbs or been
carelessly pruned, which are entirely decayed out on the inside, so
that nothing is left but a thin shell next the bark. Yet these trees
grow as vigorously as ever, and bear leaves and fruit like a solid
tree. The bark is dead; and the wood is dead. Between the two is a
thin layer, perhaps a quarter inch thru, which is alive. On one
side, it is changing into dead wood. On the other side, it is
changing into dead bark. The new wood is alive, and the new bark.
Between them is something neither wood nor bark, but just living
tree-stuff. The green leaves also are alive, and the green twigs,
and the blossoms, and the growing buds. But at least half of every
living tree is already dead; while the larger and longer lived a
tree is, the smaller proportion of it is alive at one time.

How much of a hen’s egg is alive? Not the shell, for that is mostly
just chalk. Not the white, for that is merely the little chicken’s
pantry shelf where it keeps the food on which it is to grow. The
living part of the egg is the yolk—unless somebody boils the egg and
so kills it. Sometimes, too, the egg dies, as any living thing may;
then we usually find it out.

Even we ourselves are not all alive. I have already pointed out that
our hair and nails are not alive at all, and that our outer skin,
the thin skin, that is, which we tear off when we bark our shins, is
fully alive only on the inside. Our “bark” in fact, is very like a
tree’s. Each has a soft, thin, living layer on the inside, which
grows, hardens, dies, forms a water-tight layer over the rest of the
body, cracks into scales, and drops off. Where one forms cork, the
other forms horn. Indeed the cork stoppers of our bottles are made
from nothing more than an especially thick corky bark of a certain
kind of oak, like the especially thick and homy soles of all
bare-footed savages and some bare-footed little boys.

“The blood,” we say, “is the life.” And yet the blood itself is
dead. The watery part is just soup; water and salt and fat and
jelly. The minute, coin-like, red blood corpuscles carry the oxygen
of the air from the lungs all over the body. But there are similar
oxygen-carriers, likewise dead, in bottles in the drug-stores. The
corpuscles are dead cells alive once, and like the hard skin cells,
a great deal more useful dead than alive.

As for our teeth, the hard white enamel on the outside is just about
as much alive as a clam shell. The baby tooth, as I have already
explained, is formed in a little pocket in the gum. The inner part
of the tooth grows up from the cells at the bottom, very much as a
hair grows out from the bottom of the still smaller pocket where it
starts. In fact, the tusks of pigs and the long front gnawing teeth
of squirrels and rats are still more like hairs, for they keep
growing from the root, and wear off at the outer end. The tooth
pushes thru the gum; and as it goes by, the cells at the sides of
the pocket and on top plaster it with a coating of enamel.
Therefore, as most of us find out to our cost, this enamel once
destroyed, can never grow again. Once clear of the pocket where it
was formed, it has to last us the rest of our lives; and little boys
and girls who don’t keep their teeth clean when they are young, have
to put up with something not nearly so good when they are grown up.

The inside of the tooth is not quite so dead as the outside—one
sometimes gets the impression during a visit to the dentist that it
isn’t dead at all. The tooth, inside the enamel, is mostly bone; and
bone is mostly lime, like clam-shells, mortar and chalk, plaster,
and the great boulders and ledges of rock in a limestone country.
The rest of the bone is living substance, scattered cells far apart
from one another with long roots, that look as if they had grown out
into the bone like tree roots into the soil. Really, however, it is
the other way. Before there were bones, there were bone cells. These
build themselves round with the hard bone substance, pushing their
neighbors away and leaving only the long root-like strands of living
substance. It is thru these root-like living strands that we feel
the dentist’s auger bore into the solid tooth. But cutting the outer
enamel does not hurt at all simply because no part of that is alive.

We are, then, built of living bricks, but of living bricks set in
dead mortar. We saw that the great trees, complex and long lived,
have more wood and bark and other dead substances in them than the
shrubs, herbs, and grass. These in turn are less alive than the
lowly water plants and yeasts and molds which have no wood or bark
at all. The same is true of animals. The jelly-fishes and infusoria
have neither skin, hair, bones, nails, nor blood, and are pretty
much all alive. So the more a creature’s life is worth, the less of
it is alive.

Even the living cells themselves are not wholly alive. The thin
living jelly always contains water and salt, which are—just water
and salt. Fat cells contain drops of oil, which are simply stored up
food material, no more alive than the oil in an oil can. Plants, on
their side, store up their food largely as starch, no more alive
than that in a package from the grocers. Besides oil and starch,
some cells contain gum or rosin or saliva or milk or sweat, which
they pour out from time to time. These substances, too, can hardly
be considered more alive while they are in the body than when they
are outside.

So the living substance is the cell jelly. Everything outside the
cell is dead; many cells even are dead, while not a few, even while
alive, contain so much dead stuff within them, that there is more
oil in a young hen’s egg than there is chick, and more starch than
corn-plant in a grain of corn.




VIII

How We Grow


By “we” I mean all living things, trees and grass and dogs and cats
and boys and girls. For as you, my reader, have I hope already
discovered, we who have the breath of life in us are a good deal
alike, whether we are oaks or men. We don’t look much alike, to be
sure. But when we consider the things that are not alive—the stones
and stoves and bats and balls and such—and see how very different we
are from these, then we get some idea of what being alive is, and
understand how being alive makes us blood-brothers with everything
else that is alive also.

Now things that are alive usually do more or less growing. We have
already learned something of this growing of little creatures in the
egg—how the eye buds out as a ball and afterwards folds into a cup,
how the limbs sprout out from the body as shapeless lumps which only
gradually turn into hands or feet or wings. We have learned
something of the way the bones grow, and the skin, and the hair, and
the nails. Now we have to learn something more about the way a
little child or a little tree grows up to be a big one.

The tree, we already know, grows larger round only between bark and
wood. It grows taller only at the tips of its branches. The solid
wood, once formed, does not change. If then, you drive two nails
into the trunk of a little tree, say a foot apart and one above the
other, even if that tree should grow to be a hundred feet high,
those two nails would remain just where they were, a foot apart and
just the same height from the ground as before. The little tree
looks so much like the big one, that one cannot help thinking that
it has simply grown thruout, so that the same branch which was once
at the height of one’s head has now been lifted to the height of the
house eaves. But this is not the fact. The lower branches of the
little tree have died and dropped off; what are now the lower
branches of the large tree, were once the top twigs of the little
one, which have always been at the same level where they now are.
The top branches of the large tree, as the tree grows still larger,
will in their turn become, first the middle branches, then the lower
ones, then will drop off entirely.

Now this growing at one end which looks like growing thruout is
pretty common in our own bodies. We have seen how the hair grows at
the inner end only, and the nails likewise, and the skin. Ignorant
people will tell you that cutting off the ends of your hair, or
singeing the ends; and that smearing various messes on the outside
of your skins will change the quality of either. Don’t you believe
them. After wood and skin and hair and teeth are once grown, all we
can do is to protect them. Really to affect their growth for good or
ill, we have to do something to the growing end.

The bones also grow in spots. The child’s leg bones and arm bones
and finger bones do not simply swell up to become the man’s. The
head of each bone, the rounding end, that is, where it touches the
next, grows on the outside. But the shaft does its growing chiefly
at two spots, one at each end where the shaft joins the head.

The bony part of the tooth, on the other hand, starts as a
paper-thin sheet, but full sized. The living cells which build the
hard bone, lie on the inside of this shell. They keep building on
more bone on the inner surface, pushing themselves toward the middle
of the tooth, until the tooth wall is so thick that only a narrow
space is left in the center. But their long roots which they leave
behind, still reach thru to the outer surface of the bone, ready to
ache when there is occasion. Meantime, the outside of the tooth
pocket, as we have learned, has been plastering on enamel on the
outside of the shell, and pushing itself farther and farther away.

A plant’s roots, like its branches, grow at the tips; and the nerves
in our own bodies grow in somewhat the same way, beginning at the
inner end, and somehow finding their way thru and around the other
tissues of the body, till they find the place to which they were
sent. But the muscles and the fat grow thruout their mass, like
dough being raised for bread. Most of the hollow tubes of the
body—the blood vessels, for example, and the red lane down which our
breakfast goes—grow in this way. But the hollow bones, as they grow,
are taken down on the inside to enlarge the hollow, and built up
again on the outside with old material and new to enlarge the shaft.

Even the blood grows, the watery portion coming from the food we eat
and the water we drink; but the red and white corpuscles which float
in the watery part, are made in special factories in the body (some
of them in the marrow of the bones) and turned loose in the blood
stream.

Growing, you see, tho easy to do, is by no means so simple as it
appears.




IX

How We Grow Up


Ten years from now, you who are reading these sentences will be
grown up. Once you were little pink and white babies, all soft and
sweet and clean. And because you were soft and unresisting, you grew
at a tremendous rate. At first you probably doubled your weight in
six months. Then it took three years; then six or eight. By the time
you are twelve, you probably will be half as heavy as you ever will
be. In all the rest of your lives, you will do no more growing than
you did in the first 180 days of them.

You will grow, too, as you have grown, by fits and starts. Sometimes
you will shoot up like sunflower stalks. Sometimes, again, you will
stop growing large, and begin growing hard. You will not seem to be
getting bigger; but you will be getting stronger. Then, when you
start growing again, you will perhaps find that you really can’t do
so much as you could when you were a year younger, nor do it so
well.

So you will keep on, sometimes growing large and sometimes growing
hard, but almost never both at once, until you come to the full
stature of men and women, and your soft baby flesh that couldn’t
lift its head from the pillow has changed to tough muscle and hard
bone. That is, of course, supposing that you have taken care of
yourselves. If you haven’t—why then it may be different.

This growing up is so common an affair, so many of us do it, puppies
and calves and kittens and little rabbits and baby birds, that we
usually forget how wonderful a matter it is. Wonderful indeed it is;
yet hardly less strange is it that after we have grown a while, then
we stop. Yet our hair, as we know, doesn’t stop, nor the skin, nor
the nails. Sometimes parts of the body which have hardly grown at
all in youth, start up and grow in middle life. But the parts of the
body which count, the parts which if they did grow would make us
larger, these somehow know enough to stop.

It is not so with some other living creatures. A tree does not stop
growing so long as it lives; nor does a fish. The big oak or the big
trout may have grown faster than the little one; most likely it has
simply been growing longer. We call any creature adult when it is
large enough to have children of its own. But the oak bears acorns
and the trout lays eggs, and then keeps on growing till it is ten,
twenty, fifty times bigger than it was when it first had little
ones. It is as if the cat, when her kittens were growing up, kept on
growing along with them; and next year when there were more kittens
kept on growing nearly as fast as they; and kept on year after year
as long as it lived until it got to be as large as an elephant. And
still its kittens would be just kittens, no larger than before.

Many animals manage their growing this way. The star-fish egg, you
remember, is for size like a minute grain of dust, and the baby star
when he first hatches out is hardly bigger. After that, he eats all
he can get and grows as fast as he can, like any other kind of baby.

But suppose the little star-fish, as large say as a pin head,
doesn’t find enough to eat. Does he then starve? Not a bit. He
simply doesn’t grow. The eggs hatch out in the late spring within a
few weeks of one another, and the little stars which do not happen
upon a good boarding place, go practically without food all summer
long. They remain perfectly healthy; but they scarcely grow at all,
so that at the end of the summer they are still the pin heads that
they were six months before.

On the other hand, when a star-fish happens to be born where he can
find plenty of barnacles or small clams or mussels, he doesn’t do
much but eat, and grows to match. It may happen, then, that of two
stars, hatched on the same day, the one which has been well fed will
be no less than five thousand times larger than the other which has
gone hungry. Now a grown man is only about fifteen times as large as
a new-born babe. But this is as if two babies, each six months old,
should be, one no heavier than at birth, while the other weighed
twenty-five tons and was as large as a whale.

So you can’t judge by appearances. The star-fish that you pick up at
the shore may be a very young animal which has been well fed, or a
very old one which has gone on short rations, while a young star,
still growing, may be twenty times larger than his own great-grandfather.




X

How We Grow Old


After we grow up, we grow old. People say that we first grow up to
men and women; then we continue adults; then we grow old. Really,
however, we begin to grow old the day we are born; while we shall
never again grow old so fast as we did when we were babes in arms.

For growing old is simply growing hard. We begin life as squashy
little babies. Our bones are like green sticks. Our flesh is like
dough, only the softest cloth must touch our skins, and Nurse has to
hold her hand under our poor backs to keep our heads from dropping
off. Children are not squashy, but they are still soft. You can
pinch children. Sometimes you do. But you can’t pinch a grown man,
any more than you can pinch a board. Children are of course, much
harder than babies. All the same, if you put your fingers in your
mouths, or stand too much on one leg or slouch over your books or
shrug your shoulders up beside your ears when you play first base,
or sit on one foot when you curl up in the big chair in the library,
or do any other of the forty-leven things that somebody has to tell
you forty-leven times a day not to do, then you will pull your bones
all out of shape as if they were so much India rubber; and when you
grow up and your bones and muscles set, then you can’t get back into
shape again—tho you’ll wish you could.

For get hard you will. Then you will be grown up. When you are just
hard enough, you will be in the prime of life, able to work as
easily as you now play, and liking it, I hope, even better. But
still you will keep on getting hard; and when you get too hard, then
you are old.

So growing old is growing hard. And since the younger you are, the
faster you grow, you never grew old so fast as when you were a tiny
baby, and you never again will grow old so fast as you are growing
old now.

And the moral is, as the Duchess used to tell Alice, that since we
stay young and soft only a very short while, and grown-up and hard
most of our days, we’d better, as much as we possibly can, make the
short end of our lives help out the long one.

What I mean is this. While we are young, we are soft and plastic and
teachable. As we grow older, not only do our bodies harden, but our
minds also. We can do a great deal more after we are grown up than
we can while we are children; and I think we are, if less
light-hearted, on the whole quite as happy. But we shall be a great
deal less able to take up anything new. Let us, therefore, practice
while we are young those things which will bring us most happiness,
after we are too old to change.

For example, suppose a boy is fond of out-door games, as every
normal and healthy boy ought to be. He plays baseball all the
spring, tennis all summer, football thruout the autumn, and what
there is left of the year goes into ice hockey. He plays expertly,
has a glorious time; and he grows up manly and strong. This is as it
should be—so far.

But suppose the same boy, thru school and college and at work. There
is no more football for him, and no more ice hockey. For a few years
he may get an occasional game of baseball; if he is very lucky he
will get a little tennis. But tell me, boy who is reading this page,
how many of your father’s friends and associates ever play at all
the games at which you spend your spare time?

Now while we are supposing, let us suppose that this boy of ours,
instead of spending all his spare time at games, spent only half.
The other half he shall devote to sports which are not games. He
shall learn to ride a horse, to fish, to handle a sail boat, to
swim, row, paddle, to climb mountains, to take care of himself in
the woods, and above all to walk thru level country and enjoy the
sight of all he sees. By and by, this boy will grow up. In the
natural course of things, he will put away bat and ball and hockey
stick before he is thirty, but rod and saddle and oar will bring him
happiness and health almost to the end of his days.

There is a difference too in games. One plays football thru school
and perhaps in college—eight years at the outside. But one world’s
champion tennis player was well by forty; he must have played thirty
years. A golfer gets forty or fifty years of pleasure for the
trouble of learning his game. You may think you will learn the boy’s
game now, and the man’s game later. But you won’t. You will learn
the man’s game now along with the boy’s, or else you won’t learn it
at all. You will be too old to learn, and go gameless to your grave.

Or suppose a girl is fond of music, and learns to play, very nicely,
the banjo. It will be charming enough, summer evenings on the
porch—so long as one is young and has only a girl’s soul to express
in music. But by and by she will grow up to be a woman, and have
little children of her own. Will she get out her banjo Sunday
evenings and play for them hymns and solemn songs, or tinkle <DW53>
melodies for them when they are sick? Indeed she will not. She will
put that banjo on the top shelf of the spare bed room closet, and
wish she had spent her effort learning some other instrument more
worth while.

So it is with everything else. If, while we are young, we train our
ears to enjoy good music, and our eyes to love good pictures and
good furniture, cloudy landscapes and great trees, and our minds to
care for the important things of life, literature and religion and
art and science and politics and history, we shall still possess
growing sources of happiness longer after we have ceased to care to
read stories or to be able to play ball. A wise child will study the
happiest adults whom he knows, and learn to like and to do whatever
most helps to make them blessed.

However, I meant to tell about how we grow old, rather than how we
can best get ready to be so.

Oddly enough, most living creatures do not grow old. They simply
live along till some other creature comes along and eats them up, or
till the cold weather comes on and they freeze. A fresh egg is so
soft that it hardly holds together; a young chicken is as tender as
you please; while an old hen has to be boiled for days in order to
be eaten at all. But an old fish isn’t tough; neither is an old
lobster. Who ever heard a cook asking for little oysters, for the
sake of getting them tender and juicy, or a fisherman preferring
small fish? We like these the better, the older and larger they are.
All animals, before they hatch out of the egg, are very soft.
Afterwards they all grow larger and harder. But some stop growing
big and continue to grow hard; and some stop growing hard and
continue to grow big. The first sort grow old; the second do not.

Now when you come to think of it, about the only animals that grow
old are the four-footed beasts, ourselves, and the birds. But the
rate at which these various creatures grow old may be very different
indeed.

Let us take a new-born human baby, and a new-born puppy, and a
new-born mouse. All these are helpless little babies; and all three
start immediately growing up and growing old. But while it takes six
months for the human baby to grow to be twice as large as it was at
birth, the puppy doubles its weight in nine days; while the little
mouse, in the first twenty-four hours doubles its weight twice, so
that at the end of its first day of life it is already four times as
large as at the beginning.

At six months, the human baby, if he is very much up and coming, as
you no doubt, my reader, were, can just begin to sit up without a
pillow at its floppy back; it cannot walk a step, and it hasn’t a
tooth in its head. But a six months puppy is a wiggly little beast,
who runs away miles when he gets lost, chews up the family
overshoes, and is well on the way toward losing his milk teeth.
Meanwhile the mouse has grown up to be as large as he ever will be,
has children of his own and probably grandchildren.

At five years the mouse is dying of old age. The puppy has become a
sedate and middle-aged dog; but the baby is still a little child,
just beginning to go to school, and still some years from losing its
first tooth. At ten years, the child is young, the dog is old, and
the mouse has become ancient history.

You musn’t think that the larger animals live longest. A horse is as
large as six or eight men, but it is old long before a man first
votes, and the birds, which are in general much smaller than the
beasts, also in general live three, four, and five times as long.
Even the elephant, thought to be longest lived of all beasts, lives
no longer than we. But fish and turtles and crocodiles and
shell-fish and the like, which are neither beasts nor birds and grow
big without growing old, may outlive even parrots, elephants and
men.

I dwell upon this at some length because there is no doubt that just
as the dog grows old more slowly than the mouse, and the man grows
old more slowly than the dog, so some men grow old, more slowly than
others. Some people have used up their lives and are old at fifty or
sixty; some are still young and hard at work at seventy and eighty.
Now it rests partly with ourselves which we shall be. Five is not a
large number to multiply by. But five times your present age, my
reader, will take you well up to middle life. In no small degree, it
is for you to choose whether you will come to five times your
present age with the best part of your lives over and done with, or
with the best part still to come. What, in general, your fathers and
mothers are telling you is right and teaching you to do, will
contribute to the one result; what in general they are telling you
is unwise and wrong will doom you to the other. That indeed is how
we know that some things are right and others things are wrong.
People have tried, many times over, and found out, to their profit
or to their cost.




XI

Why We Grow At All


Did you ever stop to think how extremely convenient it is to have
two parents? Mama stays at home and takes care of the little
children, reads and sings to them, tells them stories, puts them to
bed, spanks them when they are naughty and kisses them when they are
good. Indeed, you couldn’t get on very well without Mama. Neither
could you get on very well without Daddy. Daddy doesn’t seem so
important as Mama; but if Daddy didn’t go to work every day, and
earn money for Mama and their little boys and girls, where would
house and food and clothes and birthday parties and music lessons
all come from?

Suppose there were no Mamas at all, but only just Daddies. Then of
course there would be no aunties, nor nurses nor cooks nor big
sisters nor kind ladies in the next house. There would be only just
men; and half the men would have to stay home from the office to
take care of the little boys of the other half, and then their work
wouldn’t get done, and there would be no end of trouble.

It would be almost worse if there were only Mamas and no Daddies.
For then all the Mamas would have to go out to work; and even when
they could earn enough to hire a nurse, which I am afraid would not
be often, the best of nurses isn’t like Mama. So it is really much
better as it is, when we have both fathers and mothers, one to work
abroad, and the other to work at home and take care of the children.

In fact, this arrangement is so much better than any other that
pretty much all the living world has adopted it. You know the ears
of corn which we buy in August and September and eat off the cob.
You know too how it comes from the shop, all wrapped up in soft
green husks, with the long silk hanging out of the end, that little
girls in the country use for dolls’ hair, and ridiculous little boys
try to smoke in pipes. The ear is the mother corn, and the kernels
wrapped snugly away in the green husk are her children. Or rather
they are her eggs, with the little corn plants inside, almost ready
to be dried over winter and be planted and start life for
themselves. Each kernel of corn has one fibre of silk, which is
joined to it at one end and hanging out of the ear at the other.

[Illustration: The cob is the mother of the corn. Its father is
the tassel.]

The ear, then, is the mother of the corn. Its father is the tassel
at the top of the stalk. From each branch of the tassel hang many
tiny brown bags, each about as large as a grain of rice, and each
filled with a very fine brown dust. This dust is called pollen. And
unless a grain of this pollen falls on each thread of silk of each
ear, then the kernel at the other end of the thread will never grow
to full size and never become a seed; but will always remain small
like the undersized kernels at the end of the ear. If the tassel is
cut off; or the silk pulled out; or the ear tied up in a paper bag,
then the ear forms no proper seed.

Sometimes, on an ear of sweet corn, one finds a few kernels, or a
single kernel only, that instead of being white like the rest, is
yellow. This means that somewhere in the neighborhood, it may be
miles away, somebody has planted a field of common yellow corn,
which we make into corn meal, but do not eat off the cob because it
isn’t sweet. A grain or two of pollen from this yellow corn has been
carried by the wind and fallen on the silk of an ear of sweet corn.
So the father of that particular kernel is yellow and its mother
white, and the kernel is  just as if a white woman had
married a <DW64> or an Indian.

Different plants manage these things differently. The ancient
Egyptians, who lived on dates much as we live on corn and wheat,
used to plant orchards of date palms as we plant orchards of our
fruits. Every year, at the time when the cultivated date trees were
in blossom, the Egyptian farmers used to go out into the desert, cut
branches from certain wild palms which never bore fruit, and carry
them in procession thru their date orchards. They did not know why
they did this. They only knew that if they omitted the ceremony for
a single year, that year they got no fruit. We know now, of course,
that the date-bearing palm is the female tree; and the wild palm
which doesn’t bear anything is the male. The procession with
branches thru the orchards simply brought in the pollen.

Most plants, on the other hand, not to take any chances, have seed
and pollen in the same flower. Many too, instead of relying on
accident and the wind to carry one to the other, are arranged so
that insects and humming-birds, in seeking food, shall make the
transfer. Some, few, however, like the willows, have seed and pollen
on separate trees.

[Illustration: Pollen Grains much enlarged.]

The water plants manage in much the same way. They, for the most
part, turn loose in the water what in them corresponds to the
pollen, and waves and currents carry it to the young seeds. The
simpler water animals, sponges and sea-anemones and shell-fish do
much the same. While the female sea-urchin or star-fish produces
eggs as small as dust, the male produces a still finer pollen-dust,
which we call milt or sperm. If one grain of this happens to float
against an egg, the egg at once begins to change to a young animal.
Otherwise after a week or so the egg dies and that is the end of it.
Of course, under these conditions, the chance of egg and milt
getting together is pretty slim, and the waste of eggs is enormous.
So the fishes, which can move about, have a much better plan. When
the female salmon, for example, swims up the rivers to leave her
eggs among the gravels in the swift water, the male goes along with
her. After she has laid her eggs and gone away, along comes her mate
and scatters milt over them. So the salmon egg is pretty sure to
grow; and the salmon can afford to have few eggs and larger, and so
give her little ones more yolk to live on and a better start in the
world.

The bees have a still better device. The single queen bee, as
everybody is supposed to know, lays all the eggs of the hive. When
the queen is young and the new swarm is just starting, she annexes
enough of this pollen-milt-sperm to last her the rest of her life,
and stores it up in a little sack. Then whenever she lays an egg,
all she has to do is to give this sack a squeeze, press out a little
of the contents, and start the egg growing into a new bee.

Strangely enough, however, altho this practice of having two parents
is so very common among both animals and plants, and so universal
among human beings, it is not, so far as we can see, at all
necessary. Potatoes are thick underground branches, and not seeds at
all. Yet we plant them and they answer exactly as well. Many lowly
creatures, like the yeasts, the bacteria, the infusorians of
stagnant water, and the like, never have anything resembling seeds
or eggs. There is a parent. The parent splits in halves. There are
two children. And where is the parent?

Among the common green plant-lice which swarm on the leaves in the
summer, the males all die early in the season. After that the
females go on laying eggs, and these hatch more females which lay
more eggs, for ten and twelve generations, before the cold weather
comes on and some of the eggs begin to hatch out males once more.
They get along exactly as well when each insect has only one parent,
as when it has two.

In the case of the queen bee, if while the egg is being laid she
squeezes the sack, then the egg hatches out a worker, which has
therefore, two parents. But if she does not, then the egg hatches
out a drone, which has only one. There are many other strange facts
of this sort, which have been known for a long time, but which
nobody has yet been able quite to understand.

Some facts still stranger have recently come to light. It has found
that in the case of many sea creatures, star-fish, sea-urchins,
shell-fish and others, that if the eggs are kept in common sea
water, but kept carefully away from any milt, they soon die, and
never grow up at all. But if any one of a considerable number of
substances is added to the water, sugar, salt, acids, and other
things, then the eggs, tho they still have only one parent, proceed
to grow into the proper sort of little sea creatures, just as if
they had two.

It is really a great mystery; the most that any one can say is that
the eggs are there, but something in the water, or the absence of
something, stops their growing. Add sugar, salt, acid, or milt and
they grow. In the case of the land animals, this something is
probably in the blood—for as you know, the blood is salt like the
sea, and in many other ways much like it.

At any rate, this is practically a most convenient arrangement. A
mother bird, for example, is herself born with all the eggs she is
ever going to lay already formed inside her. But something in her
blood keeps those eggs from growing bigger than pin heads. They
don’t grow into proper eggs, that can hatch into little birds, until
the mother bird gets a mate to help her build the nest, and to feed
the little birds when they come, and sometimes to feed her too. Then
some of them do grow up and hatch; and the two old birds take care
of them.

But as I said, it is all a very great mystery, which the wisest men
do not yet completely understand, and little boys and girls can
hardly expect to understand at all.




XII

Things That Do Not Have To Be Learned


So far in this book, we have been learning about the body. We know
something about the wonderful life-jelly of which all living things
are made—how it is itself the soft parts of plants and animals, and
how it builds for itself the hard shell and bones and wood, which
are its supports and its tools. We know, also, something about how
each particular animal or plant or human being starts as a minute
fleck of this life-jelly, grows to be, first a seed or an egg, and
then a full grown animal, a man, or a tree. We know, too, something
of the living bricks which build the bodies of living creatures; and
something of the difference between young creatures and old ones.
More than this, I trust, we have learned that all this curious
information is not to be looked at merely as something interesting
or amusing; but that like all the teachings of science, it is
something that will help us to live wisely. For as we come to know,
we ought also to learn to do; and while we are finding out something
about living things, we ought also to be finding out something about
living.

We have, I say, thus far been learning about our bodies. Now we
shall turn to a still more important part of us, and try to learn
something about our minds. Our bodies, we found, are very much
indeed like the bodies of animals and even of plants. Perhaps we
shall find that our minds also are like those of other living
things. Perhaps we shall find them to be something very different
indeed.

Most of us, I suppose, have seen at least one little baby. I don’t
mean a small baby merely, one that sits up in its carriage with a
pillow behind its back, and smiles up at you when you look in under
the hood. I mean a real little baby, a week or two old, that can’t
turn its head over on the pillow or put its hands anywhere in
particular, and instead of being nice and pink, is as red as a
little beet—for the little baby’s skin is so very thin that it uses
it to breath thru, to help out its poor little lungs, just as the
frogs and other water creatures which have lungs breath thru the
skin also. You know the size of baby I mean; if you haven’t had any
younger brothers and sisters, there must at least have been
something like it in the next house.

Now there are several very strange facts about such little babies,
of which by no means the least strange is this: If you take such a
very weak and tiny creature, just able to move its arms and legs,
and put a finger or a small stick across the palm of its hand, the
little one will grip so hard that you will have no small difficulty
in getting its fingers loose again. In fact, some babies will
actually allow themselves to be lifted in this way; and will hang by
their hands a minute or more before they will flop down again into a
helpless heap.

So here is one thing that the wee baby can do better than he can
when he gets to be older and a good deal stronger, and better
sometimes than he will ever be able to do it again. It is something,
too, that he did the first time he tried, didn’t have to learn,
didn’t have to practice, didn’t have to do anything but just be born
knowing how. Pity we can’t all get our geography lessons and our
piano practice done this easy way!

There are not a few other things which we all did exactly right the
first time, without ever being shown how, or practicing, or seeing
anyone else. For instance, when we were very young indeed, and very
small, about as young and small, in fact, as people ever get,
somebody gave us our first drink of water. We were not a day old
then; and we didn’t even know enough to look at the same point with
both eyes at once, but let them straggle off, one eye looking at one
thing and the other at another, so that both got generally mixed up
and couldn’t make out much of anything. But we knew all about
drinking. We shut our little mouths tight round the stopper of our
bottle, and sucked away like little steam pumps. The water went down
the front of our throats, crossed over to the back, and went into
our thirsty tummies. Meanwhile, our breath went in at our noses,
down into the back of our throats, crossed over to the front, and
went down our wind-pipes. But tho wind and water had to go crosswise
of the same passage, we never made a mistake, and opened or shut the
wrong lid for the wrong fluid, so as to let the air into our
stomachs or the water into our lungs. Which really, when you
consider how young we were, and how this was the first drink we ever
took, was decidedly clever of us.

An act of this sort, which we are born knowing how to do and do
right the first time without ever practising or being taught, is
called an instinct. Mighty handy, too, they are, these instincts.
Think what would happen to a baby that didn’t have the sucking
instinct, and couldn’t take a spoonful of water nor a drop of milk
till somebody had explained about drinking and showed him how to
swallow without letting it run down the wrong way. I don’t believe
there would be much chance of that baby’s ever growing up. To be
sure, the other instinct that makes the little baby grip so hard on
one’s finger, really, isn’t any particular use to him in these days.
Long, long ago, nevertheless, when our ancestors were wild men and
only half human, the little baby had to cling to its mother when she
ran thru the forest with the wild beasts chasing her. Then if the
little baby couldn’t hang on tight, it was pretty likely to get
eaten up. But the babies that clung to their mothers, while their
mothers were climbing a tree with both hands, and so couldn’t hold
on to them, these babies lived to grow up, and the memory of that
far away time still lingers in each little baby’s grip.

Some things are so important that one really has to know them. Did
you ever think why girls like to play with dolls and boys do not?
Why, on the other hand, boys can throw stones and girls cannot?
Girls like to play with dolls, because when they grow up to be women
and have real babies of their own, these babies have got to be
dressed and fed and washed and tended and taken care of when they
are sick. All this is very hard work indeed, about as hard and
trying work as anybody ever has to do; so that if your own
particular mama did not have a natural and instinctive love in her
heart for all babies, she would not have jumped up at night every
time you cried, no matter how cold and sleepy she was. If taking
care of little babies were just plain work, to be done no better
than other sorts of work are done, it would be pretty unpleasant for
the babies. So women are made to love babies so much that even when
they are little girls they like to play at taking care of doll
babies, in default of real ones. But boys and men, they don’t count;
so they do not have this taking-care-of-babies-and-dolls instinct.

But the boys and men can throw things, because before the invention
of guns (which really was not very long ago) and before men lived in
cities and planted crops, about the only way to get anything to eat
was to get out and throw something at an animal and kill it. Then,
too, when there was a war (and this often used to be most of the
time) the fighting had to be done with spears and swords, which had
to be thrown, or else used to strike and thrust with, which is
pretty much the same thing as throwing. So it happened that for ages
upon ages before our ancestors became civilized, while the women
stayed at home and took care of the children, the men went out and
threw things. And that is why today, girls like to play with dolls,
but boys like to hunt and fish; and why boys can throw stones, and
girls can’t.

Boys, then, are born with the throwing instinct. Throwing is as easy
for them to learn as walking. But girls haven’t it. For them
learning to throw is as hard as learning to walk on the hands. So we
see how both with walking and throwing, the inborn instinct makes
learning easy, tho it does not altogether take the place of
practice.




XIII

Why We Like Certain Things


We have seen that the reason why all proper little girls like to play
at taking care of dolls is that their mothers, and their grandmothers,
and their great-grandmothers, and their great-great-grandmothers, and
all other sizes of grandmothers for a thousand generations, and after
that for another thousand, and after that nobody knows how many more,
have all been taking care of real babies, until anything that looks
like a baby has become about the most interesting and precious thing
there is. We have seen also that boys learn to throw things easily, and
like to throw things because all the while that their many times
great-grandmothers have been taking care of the children, their many
times great-grandfathers have been throwing spears and javelins at
other people’s ancestors, or at things to eat running about on four
legs.

Every proper boy likes to hunt and fish and camp out and play Indian
because the most of mankind, up to a few centuries ago, have spent
their entire time in hunting, fishing, living in huts, and generally
playing Indians. Indians themselves, of course, play Indians all the
time; and up to the beginning of the Christian era, our own
ancestors, living in the wilds of northern Europe, were about as
wild as Indians, and did little except play Indians all their lives.
Who knows but that, a thousand years from now, after men have been
civilized for a long while, and been getting their livings many
years standing at benches or sitting at desks, all proper boys will
think it great fun to study out of a book indoors? Perhaps they may;
but I think it will be a long time first!

Every proper boy, too, when he gets old enough (and that is not so
very old) likes to play at games. Now pretty much all these games,
when you come to think of it, baseball, cricket, hockey, tennis,
golf, I don’t know how many more, all involve hitting a ball with a
stick. If we like to throw balls with our hands because our wild
forebears threw javelins and spears with theirs, can you not guess
at once that the reason why we like to strike balls with sticks is
that these same wild forebears had for so many ages been striking
things with clubs and swords? We like what our ancestors had to do.
If we cannot cut and thrust and hack and throw and strike at wild
animals in the chase or at other men in battle, at least we can do
it with a ball. So bat and ball are the boy’s dolls. He plays with
them for the same excellent reason that his sister plays with hers.

But why does every proper boy like to climb, and every proper girl
too, if she has lived in the country and had a proper chance? About
the first thing most of us did, as soon as we learned to creep, was
to head for the nearest stairs, and try to climb up. When we get a
little older, we cannot so much as set eyes on a fence or a shed
roof without wanting to be on top of it; while as for trees, who of
us, at a certain age, is satisfied until he has been to the top of
every tree in the neighborhood. As for climbing mountains, that is
one of the greatest games there is. So there is a climbing instinct
in us, as well as a throwing instinct and a hit-something-with-a-bat
instinct.

Now our wild ancestors who fished and hunted and played Indians for
a living probably did not do much climbing. But long before their
day we had certain still more ancient ancestors who were only half
human and lived in the trees; and long before these, in turn, were
still older ancestors who were not human at all, but regular apes
who had hands in place of feet, and could climb like monkeys. These
spent their lives in the trees; and in memory of them, each of us in
turn, before he is quite old enough to play bat and ball games, is
possessed to climb like a monkey, and climbs almost as surely and
well.

Some people say, too, that the reason why a drowning person throws
up his hands (the very worst thing he possibly could do under the
circumstances) is that, being quite crazy with fear, he forgets
completely his surroundings, remembers only the dim and far off time
when the tree-folk escaped danger by climbing up out of the way, and
reaches up for an imaginary branch which hasn’t been there these
many thousand years. Perhaps this is so; for my part, I believe it
is. At any rate, there is the wonderful grip of the new-born babe.
Where did he get it if not by climbing trees, or clinging to his
mother when she fled with him thru the branches?

Some people say also that the reason why we like to play
hide-and-seek is that our ape ancestors, and our half-human
ancestors, and our wild ancestors, and our half civilized ancestors,
down to considerably after the time when the school histories begin,
have spent no small part of their days stealing softly upon their
enemies and the wild creatures they were hunting for food, or else
hiding all mousey quiet while some enemy or wild beast is hunting
after them.

There are a few people even who say that the reason why we like to
go in swimming (we do like it, do we not?) is that in some sort of
dim way we remember a still more ancient forebear who lived all the
time in the water, who in short, was a veritable fish and did
nothing else but swim. I don’t believe this myself. Not that we did
not have such an ancestor—there doesn’t seem to be much doubt about
that. But it all happened so very, very long ago that it doesn’t
seem possible that there should be any trace of those days left.
Still who can tell?

At any rate, we like to do a vast number of things that our
forebears had to do whether they liked them or not; and if you can
think of any other reason than this why you like baseball and
hide-and-seek and climbing and dolls, I wish you would tell me.




XIV

Animals’ Games


Now that we know why boys play with balls and bats, and girls play
with dolls, let us see if we can make out why kittens play with
strings and puppies bark after wagons.

Perhaps you have already guessed. The grown up house cat and wild
cat get a living all or in part by hunting birds and mice. They
crouch close to the ground, creep slowly upon their prey; then seize
it with a rush. That is just what the kitten does when you drag some
small object slowly across the floor. The kitten doesn’t know why it
chases a spool on a string. Really, however, it is playing at
hunting small creatures, as its ancestors have hunted them in
reality for a million generations.

Puppies are different from kittens. They don’t care much about
spools and strings; but they like to run about over the fields and
chew up their owner’s shoes. Now the wild dogs, and their cousins
the wolves, do not go out alone and hunt small animals as the cats
do. They go in packs; and they hunt large animals, wild sheep, wild
oxen, deer, which they chase, sometimes, for days at a time. Spools
and strings, therefore, are too small potatoes for the puppy; he
chases wagons, automobiles and trolley cars, playing he is hunting
big game. He doesn’t creep up cautiously on a ball of yarn, not to
frighten it. Instead he barks at the top of his voice to call the
rest of the pack. He runs away to play with other dogs, because the
dogs and wolves are social animals; and when he chews up a rubber
boot, he is playing that the pack has killed a moose and he is
gnawing the great leg bone.

Of course, the puppy and the kitten do not know that they are
playing at hunting when they chase spools and bark at carriages, any
more than a boy knows why he likes to climb trees or hit a ball with
a bat. But you can see for yourselves that the difference between
the play of puppies and the play of kittens is just the difference
between the work of a grown cat who hunts small creatures alone, and
the work of a grown up dog who hunts large creatures in company.

Not many young creatures, such as we commonly see, do so much
playing as puppies and kittens, tho boys and girls do a great deal
more. In fact, the wiser any animal is when it grows up, and the
more it is able to do then, the more playing it does, and the more
interesting games it plays, when it is small. Calves and colts and
lambs do not play especially interestingly, because wild cows and
horses and sheep do not do much except eat, sleep, and run away from
something that threatens to eat them up. But young squirrels, kept
in cages, sometimes play at burying nuts in the floor of their cages
for their winter supply of food; and young beavers, kept as pets in
the house, have been said to play at building dams of chairs, canes,
and umbrellas, across the parlor floor. Always, however, no matter
how tame the grown animal is, the kitten plays at being a wild cat,
and the puppy plays at being a wild dog, and the little boy plays at
being a wild Indian; all because cats and dogs and men have been
tamed and civilized for only a short while, but ran wild for ages.

There is one game that we all play, children, kittens, puppies,
monkeys, and I don’t know how many other young creatures—and that is
make-believe fights. We do it with sticks and snow balls and wooden
swords; the little animals chase one another back and forth, and
pretend to bite and scratch in the fiercest manner, as if they were
fighting for their lives. Most animals do have to fight for their
lives, many times over; so did most men in earlier times, before we
had policemen and jails, and when everybody had to look out for
himself.

Did you ever notice that a kitten is ticklish in just the same
places that you are? You stroke the kitten’s back or head or legs,
and it is as pleased as can be. But you touch it along the front of
the body, or around the front of the neck, and at once it begins to
bite and scratch and protest its best. All creatures that can be
tickled at all are ticklish in the same places; and all these places
happen to be precisely the spots where the great blood vessels and
other important vital organs are close to the surface, and where,
therefore, a wound would be most deadly. So when little animals play
at fighting and pretend to bite one another, they bite hard enough
to tickle. They don’t like to be tickled any more than you do. So
they learn to protect those ticklish places in their play, and when
they get to be grown up and fight in earnest, they have already
learned not to get bitten in those spots where the bite would do
most damage.

So the young animal’s instinct is to play at doing whatever his
ancestors have been doing for work; and he has this instinct in
order that he may like to do when young what he must do when old;
and so have practice in doing it, and learn to do it well.
Unfortunately, as men become more and more civilized, they have
continually to do more and more new things, while they still persist
in liking to do the old ones. That, I suppose, is why some boys and
girls do not like to work.




XV

Some Instincts of Chicks and Kittens


It certainly is a most fortunate circumstance that all animals are
born with a natural instinct for doing the particular things which
they will have to do to make a living in the world. It would
certainly be most inconvenient if moles and rats had an instinct to
fly, and birds wanted to hide in drains and cellars; if cows thought
they must dive into the water to catch fish, and seals tried to come
ashore and graze in the pastures. As it is, each creature has the
particular set of instincts which make it want to do the things
which it can do best.

You remember what I told you in first pages of this book about the
little chick inside the egg. It lies quietly and grows, until it is
twenty-one days old. On the twenty-first day of its fife, for the
first time, the chick feels the instinct to peck. It has no idea why
it wants to peck, nor what will happen if it does. He only knows
that pecking against the inside of his shell is precisely the one
thing that he wants to do. So he pecks away—until, presto! out he
comes into a new and very much larger world.

By and by, after the chick has got rested and dried off, he staggers
up on his legs, and begins to look around him. His eye catches some
small object—peck! he goes again, and catches the bit in his mouth
the first time he tries, unerringly. It took you weeks to learn to
put your hand where you wanted it; in fact you couldn’t so much as
put your fingers in your mouth till you had tried many times. But
the chick is born with the pecking instinct, and hits at the very
first shot.

Yet the chick does not know what to peck at. He simply lets drive at
whatever chances to catch his eye—a bit of gravel it may be, or
something very nasty, or even a fleck of light on a blade of grass.
What is good to eat and worth pecking at, he has to learn by trying
just at you do. Neither does he know anything about drinking. In the
course of time, as he goes about pecking at all sorts of things, he
snaps at a dew drop on the grass or a sparkle of sun light on the
water in his drinking vessel. So he gets his first drink; and in the
course of time, he learns what water looks like.

Some day, perhaps, the chick will happen to walk into the water, not
seeing any reason why one should not walk on water just as well as
on land. Then he will think how very wet and unpleasant water is,
and out he will scramble as fast as possible. But if the chick were
a duck, tho he would not know anything more about water when he saw
it than a chick does, yet as soon as he felt the water on his legs,
that feeling would start up his swimming instinct, and away he would
go, swimming the first time he tried as well as ever he will. Yet a
duckling would sit on the edge of a pond till he grew up to be an
old duck before ever the sight of the water would make him want to
swim in it. The instinct starts up only when the duck gets its legs
wet. Either a duckling or a chick would sit down beside a dish of
water till they died of thirst, before they would try to drink, if
they did not make a start by pecking at something in the water or on
the bottom.

So you see the instinct does not tell the animal anything, it merely
starts him to doing something, from which he can learn more for
himself. It is just the same with us. We have an instinct to creep,
and after that to walk; these take us about so that we can see
things for ourselves. We have an instinct to climb; but we have to
learn for ourselves how much a branch will bear, and the difference
between poplar tree wood which will snap off and spill us out on our
heads, and apple tree wood which will not.

So you see that what animals know by instinct is always how to do
something. It may be how to swim, or how to fly, or how to build a
nest, or how to bite some other creature in the neck. Usually it is
some very simple act, that will simply give the creature a start in
life.

Did you ever see a kitten play with a mouse? The kitten’s instinct
is to chase any small object which is moving away from it—spool,
string, tail, ball, mouse, indifferently. The kitten sees the mouse
and runs after it. But the kitten will not hurt the mouse as long as
the mouse keeps still. You could put the mouse on the kitten’s head
and let it go to sleep there, and the kitten would never touch it,
so long as the mouse did not try to run away. But the minute the
mouse runs, away goes the kitten after it.

We say it is cruel of the kitten to torment the mouse as it does; to
let the poor frightened mouse think it has a chance to get away, and
when it tries to run, swooping down on it again. But the kitten
isn’t cruel. The kitten chases the mouse because it runs; plays with
it a few moments; then forgets all about it till it starts to run
again. But of course, the kitten is so large and rough compared with
a mouse, that sooner or later it is pretty certain to scratch the
little creature. Then for the first time, the kitten discovers that
there is meat inside the mouse, and that what it thought only an
amusing plaything is also good to eat. After that, the kitten
becomes a mouser.

It is something the same way with a dog. His instinct is to
pursue and bite large things that run away. If, therefore, you
run from a dog, he will run after you; and having started
running, he is pretty likely to bite. But if you pay no
attention to the dog, move only slowly, and do nothing to start
up his run-after-something-large-and-bite-it-in-the-legs
instinct, the dog will bark, but will not touch you.

One might go on at considerable length describing one after another
of the curious instincts of the various creatures we know. Many of
these, however, you can see for yourselves, just by watching young
animals, kittens, puppies, chicks, babies and the rest, and noticing
what they do all of their own accord, without ever being taught.

Of all these curious instincts, I know of nothing more curious than
the way in which the instincts of our common nesting birds play hide
and seek with one another thru the changing seasons of the year.
Each in turn comes to the fore, governs the birds’ conduct for a few
weeks, then dies down to give place to the next; but only to
reappear once more in its proper place during the following year.

When our song birds come north in the spring, one of the first
things they do is to pick out mates, and get to work building their
nests. We may be very sure that no young bird, hatched out the year
before and building her nest for the first time, has the remotest
idea why she is building it. She finds a spot in thicket, hollow
tree, or barn, which somehow looks right to her. Then she finds that
bits of string, hair, moss, wood, and the like, which she has never
bothered her head about before, suddenly become the most interesting
and attractive things in the world, and before she knows it, she is
building a nest; the same sort of nest that other birds of her sort
are building, tho it may be that she was brought up as a pet in the
house and has never seen a nest in her life before. When she is
older, and has built a great many nests, she will perhaps build the
least little bit better than she did the first time; but it will
take a pretty sharp eye to tell the difference. The bird who has
never seen a nest will always build the right size and kind at the
first trial, and build it almost as well as she ever will.

By and by there are eggs in the nest. I don’t suppose the bird knows
how they got there, and I am quite sure she doesn’t spend any time
wondering about it. The thing she cares for now is to sit on those
eggs; and the bits of string, hair, moss, and wood which once seemed
so valuable interest her no more.

Still she has not the least idea what the eggs are for. She merely
feels that her one desire is to settle down on top of them and sit
there; just as you, my reader, at night when you are tired and
sleepy, just plain want to lie down on something soft. A little
later, and instead of wanting to sit quietly on her nest, the mother
bird is possessed to rush round the country, picking up things to
eat and stuffing them into hungry little mouths. She can not
possibly know what it is all for. She just has a sort of hunger for
feeding her babies, as at other times she has a hunger for feeding
herself. But a few weeks later, she hasn’t the slightest interest in
these children of hers, doesn’t know them by sight, and is just as
likely to fight them away if they trouble her as if they were total
strangers. The hurry-round-and-find-something-to-feed-the-babies
instinct has served its purpose and gone back into cold storage.
Another instinct is taking its place, and pretty soon the birds will
be off for the south to spend the winter. Next year they will do the
same thing right over again. But how much they remember of what
happened the year before is just one of those things that I, among
others, would give something to find out.




XVI

Certain Stupidities of Animals


It is a good idea for boys and girls to keep pets. Often it is
rather hard on the pets; but the boys and girls get much happiness
out of their animal companions, and they learn a great deal about
the ways of animals besides.

Any of you who keep pets could, I have no doubt, tell me many
wonderful tales of the extraordinary intelligence of these horses,
dogs, cats, pigeons, cavies, mice, parrots, rabbits, squirrels, and
what not, which, according to their nature, share our hearth rugs or
our back yards. You who do not, have only to ask the man next door
who keeps a horse or a dog, or the woman on the other side who has a
cat or a parrot, to learn that animals are only just a little short
of human, and if they could only talk, would soon prove, as we say,
to “know more than most men.”

Now there is no doubt that many animals are extraordinarily clever.
I could easily fill this whole book with stories of their sagacity.
At the same time, they are often extraordinarily ignorant, and
sometimes extraordinarily stupid. And because you will always be
hearing abundant stories of their cleverness, I am going to tell you
sundry tales of their stupidity. Between the two, perhaps we shall
strike a just balance.

Let me begin by telling about my own dog, a white and brown collie,
whom I, in common with all owners of dogs, regard as uncommonly
intelligent. When I tie the dog up, I use a light chain, one end of
which runs on a long trolley wire fastened between the house and a
tree. This, by the way, is a good way to tie a dog, for then he can
run the length of his trolley wire and the length of his chain
besides, and yet not have to drag much weight or tangle up a long
chain. Very often, however, my dog, after running out beyond the
tree as far as he can go, starts to come back again on the other
side of the tree. Of course he can’t do it, for the chain is fast
about the trunk. Now what would you do, if you were tied up that
way, and found that your trolley wouldn’t work? I am sure you would
look at once to see whether you had not got your chain twisted round
the tree; and when you found you had, you would run round the other
way and untwist it. Of course you would, and you wouldn’t stop to
think twice. But my silly dog has never caught the idea. When he
first finds himself caught up short, he pulls and struggles. Then he
sits down and howls for me. I go out and walk round the tree the
other way. The dog follows me; and at once is free. I suppose I have
done this in exactly the same way fifty times. Yet the foolish dog
never has learned to do it for himself. And yet he is a wise dog—as
dogs go. I suppose the reason is that his wild ancestors never were
fastened up on trolleys, so there is no chain-untwisting instinct to
start him learning.

Or perhaps you think monkeys are especially wise little creatures.
Then consider this case: A man had a monkey, and was trying to find
out exactly what it did know. So he used to put the monkey’s food in
a box, lock the door with a key, leave the key in the lock; and
after many trials, taught the monkey to turn the key, open the door
and get his food. Then he tried taking the key out of the lock and
laying it down beside the door, to see whether the monkey would have
sense enough to pick it up. But the monkey didn’t. No matter how
hungry he might be, he would simply stand and wait until the man
picked up the key for him and put it in the lock. Then he would
unlock the door as usual and get his dinner. Fifty times in
succession the man picked up the key and put it in the lock, while
the monkey stood two feet away and watched every movement—but the
monkey never learned to do this simple act for himself.

Should you like to try for yourself an experiment that will show you
how little the wisest animal understands? Then get a wide-mouthed
bottle (a milk jar will do nicely), put in it a piece of fresh meat
or fish; hold it above the head of a hungry cat so that she will see
the food first thru the bottom; then set the bottle upright on the
floor, and watch the cat try to get the morsel out. She will
probably not go to work at all the way you would; and your way will
be decidedly the better.

Cats suggest <DW53>s; and <DW53>s, like cats, are commonly thought to be
especially clever little animals. So they are; but always with an
animal’s kind of cleverness, not our kind. Somebody who has been
studying <DW53>s more carefully than they have ever been studied
before, reports facts such as these: A <DW53> is taught to open a box
to get his food. The door of the box fastens with a bolt, and the
<DW53> has learned to pull the bolt and open the door as readily as
you or I could do it. The bolt is now changed over to the other side
of the door. The change completely baffles the <DW53>, who has to
learn his trick all over again, and that with almost as much
difficulty as when he learned it the first time. Even coming up to
the box from a different direction would throw the beast off, so
that he would boggle a long while over a door which he had been
unfastening with the greatest ease.

Another <DW53> was given a food-box with a door fastened by a simple
latch. The youngest child would have merely looked at the latch,
lifted it with his hand, and taken his food. But it was too much for
the <DW53>. He scratched and scrambled and hunted all over the box;
until in the violence of his efforts he fell off the top of the box
and landed on his head. As he stood on his head in front of the box,
pawing the air with all four legs at once, one hind foot chanced to
catch on the latch, lifted it, and opened the door. So Mr. <DW53> got
his dinner.

Next time he was hungry, what does he do but go and stand on his
head in front of the box, and paw the air with his hind legs, till
he hit the latch again, and got another dinner. In the course of
half-a-dozen trials, the <DW53> learned to put his paw in exactly the
right place, and give just the right push to open the door at once.
But all the time he continued to stand on his head to do it. It was
not until the twenty-eighth attempt and the twenty-eighth dinner,
that it occurred to the silly <DW53> that he could lift the latch just
as well standing right side up.

Still another student of animals has been testing rats. Now an old
rat is proverbial for wisdom; they laugh at cats, and it is pretty
nearly impossible to get them to go near a trap, unless they are
nearly starved. Let’s see, then, some things that a wise rat does
not know.

Rats, of course, are used to running thru holes in the walls of
houses, drain pipes, and the like, and are clever enough at finding
their way in such places. So this man made a set of passages, such
as a rat would naturally live in, and put seven rats in it. These
soon became at home, and would find their way at once thru the maze
of passages to the spot where their food was kept, running at full
speed. Then the man took a long straight passage with a sharp turn
at the end, and shortened it up by three feet. The next time the
rats were put in, they all started pell-mell for their food; but
when they came to the shortened passage, tho it was broad day light,
every one of the rats ran smash against the end wall; and it
actually took as long for them to learn that the length of the
passage had been changed, as it took to learn the way round in the
first place. But when the passage was made longer than before, the
rats ran their customary distance to the place where the side
opening used to be; then turned and butted into the side wall. This
they did time after time, and even after they had learned to turn at
the right point one day, they were just as likely to butt the wall
the next. Really, they did not seem able to think about the matter
at all.

But I am saving the strangest case for the last. This is about a
cow. The cow used to make a great deal of fuss for her owner because
she would not stand to be milked unless she were allowed all the
while to lick her calf. One day the calf died; then there was much
trouble, and no milk at all. But the farmer understood the ways of
cows. He took the calf’s skin, stuffed it with hay, and gave the
mother that to lick at milking time. To be sure, the stuffed calf
had neither head nor legs and didn’t look the least bit like a
calf—but it was all right to lick, and the mother cow licked it
contentedly and gave down her milk as before. One day, when the
tender parent was caressing her little calf at milking time, she
happened to unrip the seam where the skin was sewed up. The hay fell
out; and the mother cow, without the slightest surprise or
agitation, proceeded to devour the unexpected provender, and never
left off until the little hay calf had entirely disappeared down her
throat.

I understand that this practice of giving a cow the stuffed skin of
its calf is the regular thing in some countries, where the cattle
are wilder than with us. I am told also that a like device has to be
employed with camels. Each camel refuses to be milked, unless she
can have her little one to lick. But the natives are accustomed to
kill and eat the little camel, and give the mother its skin. This
answers exactly as well; but if they try to palm off another skin on
her, she knows the difference at once. Out of a hundred living
camel-calves or their stuffed skins, the mother camel will always
pick her own, and never be content with any other. Yet she doesn’t
bother her head over the difference between her live calf, and its
dead skin lacking legs and head, with the hay stuffing sticking out
of the seams! Truly, animals are as stupid about some matters as
they are wise about others.




XVII

How We Differ From The Animals


How do we differ from all other living creatures? Not in having
hands; the monkeys have four hands, and if hands were the test of
humanity, would be twice as human as we. Not in lacking coats of fur
or features; pigs and elephants have skins as bare as ours. Nor is
it that we walk on two legs; the birds do that, and the kangaroos.
The difference is not even in the fact that we have no tails; for
some of the apes also are as tailless as we are. Besides, when you
come to think of it, most animals do not have tails—insects do not,
nor clams and oysters, nor sea-anemones and star-fish, nor corals
and sponges, nor frogs and toads, nor jelly-fish; even the birds,
unless you count the feathers as part, do not have tails that one
could really wag.

After all, too, we human beings do have tails; or at least a string
of tail bones, an inch or more long, tucked away inside our skins.
This coccyx bone, as it is called, is the place where it hurts so
fearsomely when you sit down too hard on a pebble or a bicycle bar,
and it catches you in one little spot just at the end of the back
bone. When that happens, you may remember that the difference
between you and the animals is not altogether in tail bones. Once in
a while, too, men do have veritable tails, as large as a finger, and
round and curly like a pig’s.

The one essential difference between ourselves and all other
creatures on the earth is neither in hands nor skins nor legs nor
tails, but in talking. We can talk and the animals cannot.

But you say right off, parrots can talk. Oh, no, they can’t! Parrots
can speak, in the sense that they can say words; but that is a quite
different thing from talking. Dumb people, tho they cannot speak,
have no difficulty in learning to talk with their fingers. The
parrot can be taught to repeat words, whole sentences, even pieces
of poetry—but no parrot ever learns to talk about the things that he
is interested in. No parrot, for example, ever tries to tell about
the forest where he was born, nor his voyage to this country, nor
the animals he met in the store before he was bought. He, says
“Polly wants a cracker”; but he doesn’t say, “I want to get out of
this cage and fly about”; and no two parrots ever yet tried to
converse with one another.

How different it is with children. They try to talk long before they
can. They pick up words for themselves. They talk with one another;
and when they don’t know the word for something they want to say,
they make one up. Don’t you remember various words that you and your
playmates invented, that other people do not know the meaning of? In
short, we human beings have a talking instinct; just as birds have a
nest-building instinct, and squirrels an instinct for hiding nuts in
the ground.

So if we should take a lot of robin’s eggs, hatch them out in an
incubator, feed the little birds by hand and never let them see a
grown up bird or a nest, there is no doubt that when the proper time
came they would sing, build nests, and take care of their young,
much as if they had been brought up by their parents in the usual
manner. In the same way, if we should take a lot of tiny babies and
bring them up where they never heard a word of speech, there is
little doubt that when it became time for them to talk, they would
invent for themselves a language to talk with. Indeed, some people
think that the reason why there are so many different languages in
the world, hundreds and hundreds as there are, is because at various
times children have been lost, or all the old people of a tribe have
died, and the children having no one to teach them their parents’
tongue, have had to make up a new language for themselves.

But no animal could possibly do this. Whether because they lack this
strange talking instinct, or because they simply haven’t anything in
particular that they want to say, no group of animals has ever
invented a language, nor has any single animal ever learned to talk
our human speech. A parrot can utter words; a dog can understand
them. But somehow no creature except ourselves ever puts the two
together, and talks.

I don’t think we ever half realize what an advantage this being able
to talk is to us, nor how utterly helpless we should be without it.
Suppose for example you are lost in a strange city. You stop the
first passerby, and you say “I want to find such and such a street.”
“So many blocks up or down,” he answers, “so many to the right or
left”; and with one or two more simple questions from time to time,
there you are right on your doorstep.

But suppose your dog gets lost. He can not stop the next dog or man
he sees and say, “I belong to Mr. So-and-so on Such-and-such Street;
tell me how to get home.” All he can do is to look up into some
one’s face and whine; and that may mean equally well, “lam lost,” or
“I am hungry,” or “I want a drink,” or “The little boy that owns me
has gone into that house and I wish he’d hurry up and come out,” or
“I don’t like the place where I am living because there is a horrid
cat there that scratches me on the nose, and I wish I could go home
and live with you instead,” or “I know you have been in a meat
market, because I can smell the nice smell of the fresh meat, and I
wish I were going to have some for my dinner in place of dog biscuit
which I don’t like.”

All these ideas, and forty others like them, the dog would have to
express in precisely the same way, and leave to his hearer to guess
which one he might happen to mean this particular time. In fact,
about all the ideas that a dog can express are, “I want something
that I haven’t got,” “I am afraid I’m going to get something I don’t
want,” and “If somebody doesn’t look out, there’s going to be a very
dickens of a row here in about a minute.” What he may think beyond
these simple matters he has pretty much to keep to himself.

And did you ever think how extremely difficult it would be to learn
anything, lacking words to learn it with? You can tell the capitals
of the United States, or the chief rivers of Asia, or the kings of
England, because somebody who knew has told somebody else, and he
somebody else, until the information has at length filtered down to
you. Whatever you do not know and want to know, you can find out
from somebody who does know, either by asking directly or by looking
in a book where somebody has written it down. But a dog can find out
things only by seeing them for himself, and when he does find them
out, he has no way of telling any other dog anything about them.

No wonder that cow I was telling you about a short while ago was not
in the least surprised when her calf ripped apart and the hay fell
out. Why should she not think that all calves are stuffed with hay,
and are expected sooner or later to rip apart and provide hay for
their mammas’ supper? She has no way of finding out what calves are
made of inside. If you wanted to know, you would ask. She couldn’t.

I suppose a child going to school and asking questions at home and
getting them answered, as every child should, learns at least a
hundred times as fast as any animal can possibly learn. I suppose
too that a dog or cat, living in one place and doing about the same
things every day, learns in a year or two all that there is to be
known about his particular world, and so finds out nothing more all
the rest of his life. You learn for lessons something new every day,
you see new people, and visit new places, you have new things to
eat, and new clothes. But the animals always have the same clothes,
and the same things to eat. Most of them do not travel; if they do
sometimes make new friends, the new friends cannot tell them
anything. Think, then, how ignorant must be the rabbit shut up in
one pen, the cow confined to one pasture, the parrot always in the
same cage. They do the same things day after day; in a week they
have learned all there is to be known.

Of course, an animal cannot tell time nor count; for telling time
and counting require words. He cannot give names to anything, nor
remember anything by name, nor think about anything in words.
Indeed, it is pretty difficult, without words, to do any thinking at
all. We can learn, think, remember, plan, contrive, teach, ask
questions, answer them, because we have words to work with. The
animals have no words. Therefore, the wisest of them is like a child
of four.




XVIII

Something More About Speech and Thinking


We say commonly that we think with our brains. That is true; but it
is by no means the whole story. The brain has two halves, just
alike, exactly as the body has. In fact, the two sides of the brain
are even more precisely alike than the two hands.

Nevertheless, we do all our thinking with one side only. If we are
naturally right-handed persons, we do our thinking on the left side
of the head. If we are naturally left-handed, we do our thinking on
the right side. But we do not use both sides. Each half of the brain
governs the muscles of one side of the body; but the thinking is
done with one side only.

This very peculiar state of affairs is in some way or other
connected with our power of speech. The animals, who cannot use
words, do their thinking, so far as we know, equally on both sides
of their heads; and we have every reason to believe that if we did
not talk, we too should do our thinking with both sides.

Let us see if we cannot in part make out the reason for this
arrangement. Let us suppose you are using your mouth and tongue, not
to talk with, but to eat your breakfast. Each half of the brain, as
I have said, controls the muscles on one side of the body; and as I
dare say you have long ago been taught in school, a set of long
nerve fibers, like so many telephone lines, connects each muscle
with the proper region of the outer surface of the brain. You are,
we are supposing, at breakfast, and you take a bite of bread and
butter. At once, the two halves of the tongue telephone by way of
the nerves, each to its own side of the brain, “Something good to
eat, shall we chew and swallow?” Then each half-brain telephones
back, “Message received, stand by to chew, on signal; will call up
other side.” Then each side of the head rings up the other side and
says, “Bread and butter reported in my half the mouth; shall chew at
once. Are you ready to start? Go!” And away go the two sides of the
face working together.

Now of course I do not mean to say that this is literally what
occurs every time you attempt to do anything that requires both
sides of the body to act together. Nevertheless, something like this
really does happen. You know how a tiny baby cannot even look at the
same point with both eyes at once, but sends them straddling off,
one looking one way, the other another. It takes some days for the
two halves of the baby’s brain to learn to consult one another, and
to handle their two eyes in co-operation. So with any act that uses
two hands, or two feet, or a hand on one side of the body and a foot
on the other. The two halves of the brain have to call across to one
another, along certain nerve fibers which run back and forth between
the two, in order that the actions of the two sides of the body may
keep together. You can easily see that if one side of the brain
tried to open its side of the mouth, while the other side was trying
to shut its, you would probably have to start for school without
your breakfast.

Naturally, after the two brain halves have been living together for
a few years, growing up together in the same house, they learn to
work almost like one. Still this signaling back and forth does take
time. So long as we are merely eating, or walking, or shoveling
snow, the process goes on fast enough. But talking is a different
matter. When you are talking thirteen to the dozen, just as fast as
you can chatter, every several letter of every single word you utter
demands at least one change of position of tongue or lips or throat,
and generally of them all.

What would happen if the two halves of the brain had to stop to call
one another up and say, “Now I am on the point of starting to say
‘t’ with my half of the mouth. Are you ready with yours?” “Now I am
going to tuck on an ‘h.’ Are you ready with your side?” “Now go
ahead with the ‘e.’ Start.” It wouldn’t do at all. It’s altogether
too slow a way to get talking done. So by way of saving time, one
side of the brain has taken entire charge of the talking; for this,
one side only of the brain runs both sides of the mouth.

When we eat, then, both sides of the brain are in action. But when
we use the very same muscles for speaking, then we use one side of
the brain only. When we lift a weight with both hands, we signal to
the muscles from both halves of the brain. But when we play the
piano with both hands, the same side of the brain takes charge of
both. I am, for example, using a type-writer, and writing with both
hands. Only one half of my brain, however, has charge of the
writing. The other half simply side-tracks itself, stands aside, and
doesn’t meddle. But the minute I stop writing and start to put my
machine in its case, then the other half-brain switches on again,
and takes care of its side. If I should hurt my right hand, so that
I had to do all my writing with the left, the writing side of my
brain would still do all the writing, while the other side that
commonly manages my left hand would stand and look on. All these
very special, complex, rapid and difficult tasks, like talking,
writing, playing the piano, or running the type-writer, are done by
one side of the brain. The slow and easy things are done by both.

But the animals, who do not either talk or write or play musical
instruments, they use the two sides of their brains alike.




XIX

Why Most Of Us Are Right-Handed


We do our talking with one side of the brain only. But talking is
somewhat intimately connected with thinking. We ought to always, we
generally do, think before we speak; while much of our thinking, and
on the whole the most important part, consists in saying over words
to ourselves.

Speech and thinking, then, go so often together, that it becomes a
great convenience to get the thinking done also on one side of the
head only, and on the same side with the speech. It might have been
either side; it did happen to be the left. One cannot say why, any
more than why the heart should be on the left side and the liver on
the right, or why some snail shells curl one way and some the other.
But at any rate it is the left side.

Now I don’t know whether you have yet been taught in your school
physiology, if you have not yet you will be shortly, that the nerves
which run from the brain to various parts of the body, cross over to
the other side from the one on which they start. Thus the right side
of the brain controls the left side of the body; while the left side
of the brain controls the right side of the body.

But if the thinking is all done on the left side of the head, which
hand will act more quickly on the thought? Evidently, the right
hand; messages for that hand travel directly along the nerves,
crossing sides once. Therefore we are right-handed.

Some people, however, are born with the “speech center,” as it is
called, on the right side of the head instead of on the left. For
such persons the most direct path is to the left hand. These
persons, then, are naturally left-handed. The difference, therefore,
between a right-handed and a left-handed person is not so much in
the side of the body with which they have learned to act, as in the
side of the brain with which they have learned to think. But the
animals, who think on both sides alike, also use either forefoot
equally well, and are neither right nor left-handed.

This talking on one side of the brain has another curious result.
Did you ever stop to think why a right-handed batter stands with his
left side to the ball? Or why a driver of a horse sits on the right
hand end of the seat? Or why the engineer of a locomotive sits on
the right side of the cab, altho this position forces him to use his
left hand for the throttle valve? Or why you sight a gun or look
thru a spy-glass with the right eye? Or why you draw a bow with the
right hand on the string?

It is all on account of this same one-sided speech center. This has
made us right-handed; it has also made us right-eyed. We think much
in words; but we also think much about how things look. We think
most quickly concerning messages which come in on the thinking side
of the brain; and those are from the right eye, since the eye
nerves, like those from the hand, cross sides on the way. So hand
and eye and speech and thought all use the same side of the head;
and sight and thought and action follow one another most easily.
Being then right-eyed, we stand to bat, or sit to drive, or use gun
or bow or telescope, in the way which gives the better sight to the
better eye. But of course, naturally left-handed people are also
naturally left-eyed.

Some people, however, are as we say, ambidextrous; that is, they use
both hands about equally well, just as all animals do. Nobody,
however, is ever naturally ambidextrous. Sometimes the ambidexters
are people who have hurt the right hand, and had to learn to use the
left. More often they are persons naturally left-handed who have
been taught to use the right hand more than is natural in an effort
to make them right-handed, tho of course they really are just as
left-handed at ever, since no use of the other hand will change over
the speech center. But some ambidexters, oddly enough, are made so
by an injury to the sight of the right eye, if they were
right-handed to begin with, or to the left eye if they were
left-handed. Hand and eye have so often to work together and work
quickly, that one tends to use the hand on the side of the better
eye, even when that is the wrong side.

At any rate, tho it is an excellent plan to learn to do all heavy
work equally well on either side of the body and with either hand,
fine work and quick work and thinking work had better be done with
the hand that does it most naturally. This keeps writing, thinking,
speaking, memory, and the rest all close together, on one side of
the head, handy to one another, instead of scattering them about,
some on the wrong side of the body, some on the right.




XX

Where We Do Our Thinking


We think only on the left side of our heads—that is easy to say if
we are normal right-handed persons. If for any reason we have got to
thinking on the right side, that will, as I have explained, usually
result in making us left-handed.

Yet we do not use the whole of even one side of the brain. So far as
is known, we do not think at all with the front part of the head.
All our speaking and most of our thinking are done from a spot
hardly larger than a cart-wheel dollar, which lies on the side of
the head just above the left ear. At any rate, an injury to this
particular part of our brain puts a sudden stop to our ability to
think and speak.

When you put your left elbow on the table and lean your head on your
hand, your hand just about covers the only portion of the brain with
which you ever do any thinking at all; while only with the part that
lies directly under the middle of the palm, and is as I have said,
about the size of a silver dollar, do you ordinarily think very much
or hard. This thinking part of the brain lies on the outside, and is
just about as thick thru as the hand is.

But even this small thinking place in the brain is not all alike.
Directly over the ear, a place that you can almost cover with your
thumb, lies the most important part of all, the place where we
remember and handle words. At the bottom of this word spot, we
remember how words sound. An inch farther up and toward the back, we
remember how words look in print. A little farther up and forward
lies the “speech center,” from which, when we want to talk, we
direct the tongue and lips what to say. Thus we get our
word-hearing, our word-seeing, and our word-speaking centers close
together, so that when we speak we have close by and handy our
memory of what we have heard in words, and of what we have read.

Just below the place where we remember words, and a little forward
of it, lies the place where we remember other sounds which are not
words, such as the noises of bells and whistles, barking of dogs,
mewing of cats, all buzzings and creakings and gratings and
crashings, all laughing and crying. Every kind of sound which isn’t
either words or music is recognized and remembered here. Beyond this
spot, still farther forward and down, and just above the rear end of
the cheek-bone, is the place where we remember music. If we don’t
know anything about music, and can’t tell Yankee Doodle from Old
Hundred, then we don’t use this part of our brains at all. But if we
do know one tune from another, and know a good many to recognize
them when we hear them, here is where we do the knowing.

[Illustration: A right-handed person has all his thinking spots
on the left side of his brain.]

Back of the word-seeing part of the thinking spot, and reaching
pretty well round to the back of the head, lies the place where we
remember everything we see, except words written or in print. Above
the word-speaking part of the brain, or speech center, from which we
control the mouth, throat, lips, and tongue, which we use in
speaking, lie the various points from which we manage other parts of
the body. As you might expect, next the speech center lies the
center for the rest of the face and for the head and eyes. Above
that comes the center for the hand and arm. Still higher up, right
on the top of the head, comes the center for the legs. So whenever
we do anything with any part of the body, we have to signal the
proper muscles from the part of the brain that lies between the tip
of the ear and the top of the head. Close behind this region is the
spot where we feel everything that touches the skin; so that we can
make the movement and feel the results most handily.

So as you see, the surface of the brain is a sort of map or chart of
the entire body. Every muscle, every point on the skin, the eyes,
the ears, the nose, the tongue, every several organ which we
possess, has its own special spot on the surface of the brain,
somewhere above or behind the ear. Each half of the body is charted
on one side of the brain, a spot in one for each spot in the other.
But we who have to use these brains to think and remember with, as
well as to see and hear and feel with, and to control our muscles,
have chosen to do this thinking and remembering with the spot on the
left side of the head which corresponds to the muscles of the lips
and mouth and tongue, and to the eyes and ears and the right hand.
Thus we have everything convenient, all in one small spot on one
side of our heads, where we can get at everything with the least
trouble. But what the front part of the brain is for, is something
that nobody knows much about.

Certain very strange results follow from this practice of ours of
using only one side of the brain to think, remember, and speak with;
and using different parts of that for thinking and remembering about
different sorts of things. Once upon a time there was a workman who
was hit hard enough to break his skull, on the left side of his
head, pretty well round toward the back, and just over the spot
where, as I have explained, are stored up all the memories of things
seen. He seemed not seriously hurt; but when his wife came to see
him at the hospital, he did not know her. Neither did he know his
children nor his friends. In fact, he didn’t even know that they
were human beings. He had absolutely lost the memory of everything
that he had ever seen.

But the minute his wife spoke he knew her at once. Or if he could
feel of any familiar thing he knew what it was. All the while, he
could see perfectly well. His eyesight remained as good as ever, he
simply couldn’t remember that he had ever seen things before. The
plain seeing, he could do with either side of his head; and the left
side being hurt, he did it with the other. But the remembering that
he had seen the same thing before, he did with the left side only;
and when he could no more do it with that, he could not do it at
all. Yet his memory for sounds and the feeling of things was just as
good as ever; because the places where he did these sorts of
remembering were not under the place where he got hit. And the
moment the doctors lifted out the splinter of bone that was pressing
on his seeing-things spot, then he remembered wife, children,
friends, everything as before.

Here is another case, much like the first, and yet curiously
different: An educated woman, somewhat well along in years, went to
bed at night in ordinary health. During the night, however, a small
blood vessel burst and formed a tiny blood blister on the left side
of her brain, about an inch in front of the spot where, as I have
been telling, the workman was hit who couldn’t remember his wife
when he saw her. She had, in short, a sort of internal black eye,
just on the spot that she had been using for sixty years and more to
remember written and printed words.

She woke up in the morning, therefore, totally unable to read a
single word. She could see as well as ever, understand perfectly
every word said to her, speak and write without the least
difficulty—but she simply could not read. Give her a printed book,
she could count the letters in every word, draw them on paper, tell
which were tall, short, round, or square, see them in fact just as
well as before—but she no longer knew what they meant. It was
exactly as if she had never learned to read at all; and being much
too old to learn again, she never read another word as long as she
lived.

There is another accident which is so little uncommon that probably
every one who reads this book will some time in his life see an
example of it. This is a case where a blood vessel bursts on the
left side of the brain and wrecks the speech center. The person to
whom this happens, immediately forgets how to talk. If the blood
clot is small, so it presses upon the speech center and nothing
else, the victim of this sort of accident can read and write as
before, and understand all that is said to him. Oddly enough, too,
he can make any sound that he ever could, and repeat parrot-like any
words that he hears. But he cannot remember the meaning of words. He
is precisely like a man suddenly transported to a foreign country
where they speak a language which he never heard. His own language
has become to him like Chinese.

Strange indeed are the freaks of these accidents to the left side of
the head above the left ear. One man, a musician, finds that while
he can hear music as before, he hears it only as noise, and no
longer recognizes it as tunes. He has been hit low down on the side
over the spot where he keeps his music memory. Another, hurt a
little higher up, can hear noises as before, but cannot tell a
factory whistle from a church bell. Not that they sound alike; but
he has forgotten which is which. Occasionally, a watch-maker,
engraver, or other skilled artisan, will get an injury well up on
the side of his head at the place from which he manages his right
hand. Then he loses all his special skill of hand. He can still use
his right hand for ordinary acts, dressing, eating, shoveling coal;
but the power of doing thinking-things is gone. He has become like a
day laborer who has never learned a skilled trade.

There is a strange case of a business man who got a blood clot just
over his word-thinking spot, but toward the upper side so that while
it ruined his speech center and the place where he kept his memory
for the look of printed words, his memory for the sound of words
escaped. He could neither read nor write, nor speak a word; but he
could understand what was said to him. Curiously enough, he could
handle figures as well as ever, for the figure-remembering spot and
the figure-writing spot had escaped. So for seven years this man
kept on with his business. Every letter had to be read to him; and
all he could do in answer was to write down figures and point to
them. Meanwhile, he took lessons most diligently, trying to learn to
write and speak with the other side of his brain. But it was no use.

There was also a learned man, who in addition to his native
language, which was English, knew Greek, Latin, and French, and
could besides read music. After his accident, he could read his
native English only with the greatest difficulty, about like a child
of six or eight who can make out easy words, slowly; while writing,
he could scarcely read at all. French, he could read much better; as
well, say, as a high school graduate. Latin he could handle pretty
well; about like a boy just out of college. But Greek and music he
could read and write exactly as well as he ever could. The accident,
which had pretty well spoiled the place where he remembered his
native language, had only damaged the spot where he remembered his
French, had hardly touched the place where he remembered his Latin,
and had missed entirely the place where he kept his memory of music
and Greek.

You understand, of course, that when one of these very same
accidents occurs to a left-handed person, no matter how much it
damages his head on the left side, it does not destroy his speech or
memory. Or if the same thing happens to a right-handed person, on
the right side of the head, his speech and memory do not suffer. The
hurt has to be on the thinking side in order to affect the thinking.

When little children are hurt in these ways, at first they suffer
loss of speech or memory just as men and women do. But little
children, as I have already explained, are not hard and set like
grown up people. They can start over again, and learn to think,
speak, and remember with the other halves of their brains. But as
soon as any one gets too old and stiff to learn anything new, then
he is too old to learn an old thing over again on the other side.

Do you see now why you have to go to school five hours a day, and
sit on a hard seat studying still harder lessons, when you would
much rather sneak off and go in swimming? It is so that you may
build up these thinking spots in your brains. We are born with
brains like the animals, alike on both sides. Only slowly,
painfully, with much hard and disagreeable work, that we had a great
deal rather not do, do we manufacture a one-sided human brain. We
begin young, while the brain is still growing. With years and years
of work and study, we slowly form the thinking spots over our left
ears, which we are to use the rest of our days. When we are grown
up, we can no more form new thinking places on one side of our
heads, than we can form new thinking places on the other side, after
the old ones have been destroyed. The business man who lost his
ability to read, never learned to read again, tho he worked at it
six years, harder than any child ever studied. If he had put off
learning to read till his old age, he could never have learned at
all.

It does seem a long time that we sit on a piano stool doing our
daily practicing, and mighty little fun. Let us then remember that
all the while, we are making a time, tune, and harmony remembering
place just back of the left temple, and tying it up with the spot
farther up on the side of head from which we manage our hands and
fingers. It is slow work; but when once we get the job done, we
shall be able to enjoy and remember music with it for the rest of
our lives—forty, fifty, sixty years. Surely, this is cheap enough at
the price of a little daily practicing.

It really is a good deal as if we were born like a dog or a horse,
with head, body, and legs, but no hands, and had to make our hands
for ourselves. How we should work in such a case, building our
fingers, shaping our thumbs, and in every way getting the best
possible sort of hands to use thereafter. And what should we think
of any careless child who left off a finger or two, or was too lazy
to put on a proper thumb, and so had to be deformed and crippled all
the rest of his life.

But the thing which makes us different from dogs and horses, isn’t
half so much our hands, as it is the spot of brain substance which
we build for ourselves over our left ears. This spot looks like the
corresponding spot on the other side. But somehow or other, nobody
knows just how, our work and study and trying hard make that
particular patch more important for us than anything else in our
whole bodies. If we fail to build good thinking spots while we are
young, we shall be deformed and crippled for the rest of our lives.




XXI

Where Some Of The Animals Do Their Thinking


It really is a great advantage to us to bring all our thinking into
one small spot, where everything is handy to everything else. It is,
in fact, almost like the convenient little kitchens they have on
railway dining cars, where the cook can reach every dish and pan and
kettle, cupboard, stove, refrigerator, coal-bin, pantry, china
closet, and all, without shifting his feet or hardly even turning
round. If you want to understand how great this advantage is,
consider the case of some animals who not only have no words to
think with, but in addition, do their remembering and thinking, such
little as they do, at several different places or all over their
bodies.

There, for example, is the sea-anemone, such as one finds at the sea
side, in the salt water pools, after the tide has gone out.
Beautiful creatures they are, set solidly on thick muscular bodies,
and pushing out their long pink or yellow tentacles, a dozen or
twenty of them, sometimes, like the petals of a daisy. Only you must
be careful not to alarm this animal flower. If you do, sometimes if
you so much as let your shadow fall across him, in an instant he
will pull in those pretty tentacle-petals, and turn to a lump of
tough jelly, almost as hard, and not much more interesting, than
half a rubber ball; and there you will have to sit and wait and wait
for something to happen, only it never does, until somebody makes
you come in and change your shoes.

[Illustration: A sea-anemone.]

However, if you are careful, you can begin to feed this animal
flower with bits of meat or fish. Drop a morsel cautiously on one of
the tentacles, and he will reach out with the tentacles near by and
roll the food slowly over and over, until finally, with much
difficulty, he will get it into the center of the disk where his
mouth is. Then he will slowly open his mouth and work it in. In
short, the tentacles are the sea-anemone’s hands and fingers; but he
feeds himself clumsily enough, and cannot make any movement quickly
or certainly, except shutting up when he is frightened.

If you think you can fool the little animal by feeding him with
pieces of shell, or wood, or pebbles, or anything that is not food,
you will soon find out that he is wiser than he looks. These things,
which he cannot eat, he simply lets fall off his tentacles to the
ground. But real food he will eat and eat and eat, till he swells up
and up and up, and you think he is going to burst, only he never
does; and in time, if you do not get tired feeding him first, he
will take the food more and more slowly, and finally will refuse it
altogether.

Now if instead of feeding the sea-anemone with pieces of meat, you
press the meat against blotting paper so that the paper soaks up the
juice, and then feed the creature, sometimes with real meat,
sometimes with blotting paper and meat taste, at first he will
swallow both with equal avidity, not knowing apparently the
difference. After a half dozen trials, however, he will begin to
take in the blotting paper somewhat less rapidly than the meat. He
will continue to take the paper with more and more hesitation until
after some twenty trials or so, while he swallows the meat as
before, he will refuse to take the paper at all. He has learned the
difference.

All this time, you must have taken pains to offer the real food or
the imitation to the same tentacle, so that the same fingers shall
have stuffed the morsel into the mouth. If now, after the polyp has
thoroly learned the difference between meat and paper, on one side
of his mouth, you try feeding him in the same way on the other side,
you will discover that the new side knows nothing whatever about
what has been happening on the other. The anemone which has learned
to take meat and leave paper on one half of his body, still takes
them both on the other half, and it will take just as long to teach
the difference to the second side as it has already taken to teach
it to the first.

The reason for this peculiar behavior is simple. The sea-anemone,
instead of doing the remembering for his whole body, all in one
spot, as we do, spreads it out over a ring of brain which circles
the mouth, between the mouth and the base of the tentacles. He does
the remembering for each tentacle close to the base of the tentacle
itself. Each therefore remembers something of what has happened to
itself, something less of what has happened to its next neighbor,
still less of those beyond, and almost nothing at all of what has
happened to the tentacles clear over on the other side, a whole inch
away.

Even that much remembering, however, the tentacle-brain does not do
especially well. After the animal has learned his paper-meat lesson
thoroly one day, and can tell the difference straight off every
time, the next day he has as thoroly forgotten it. If he learns it
once more on the second day, he will as completely have unlearned it
again on the third, and will swallow paper and meat with equal zest.

So much then for animals who do their thinking in rings instead of
in spots. Now we shall see what happens to a creature who tries to
do his thinking all over his body.

I have already mentioned the infusoria which swarm by the thousands
in the water of ditches and puddles. They are decidedly small
animals, the largest of them no bigger than a pin head; and as I
explained before, they are remarkable in that each infusorian is
just one single cell. Most of them are free-swimming, that is, they
go about as they like thru the water as a fish does; but some grow
on stalks like flowers, tho even these can usually let go their
anchorage and float away to a new station.

[Illustration: More common infusorians, much enlarged.]

Small as they are, they feed on still smaller plants, the bacteria.
Nevertheless, they do not know their food either by sight, hearing,
taste, or smell. One hungry infusorian, looking about in search of
his dinner, will pass right by a mass of bacteria large enough to
feed him the rest of his life and not notice it. He will swim so
close as almost to graze the feeding ground, yet keep straight along
without turning or pausing, as if it were not there. The next
instant, he may run against some small particle which isn’t good to
eat at all, and swallow it down forthwith. In fact, the infusorian
simply swallows whatever happens to hit his mouth. If this happens
to be good to eat, why so much the better. If it happens to be only
a grain of dust or a fleck of shell, down it goes just the same; the
infusorian doesn’t know the difference.

When the infusorian, swimming straight ahead, runs into some
obstacle too large to swallow, it stops, backs off, turns a little
to one side, and goes ahead again. But he never takes any pains to
turn toward the side which will do the most good, or to notice
whether he turns enough to do any good at all. He is just as likely,
having run against the extreme end of some object, to turn exactly
the wrong way, so that he hits it next time fairly in the middle.
Then he backs off once more, turns again, and swims ahead. Perhaps
this takes him by; perhaps he butts the obstruction again at the
spot where he struck it first. Then he tries again, and yet again,
and in the course of time, usually manages to get by.

So the infusorian is a funny little machine, made so that when it
hits anything it backs off, turns somewhat, and goes ahead again. If
one is very clever with his fingers, as men who study creatures such
as these have to be, one can take a slender needle and touch the
infusorian on the front end—we cannot call it the head. Thereupon he
stops, backs, turns, and goes ahead. Touch him on his side. Again he
stops backs, turns, and goes ahead. Prick him from behind. Once
more, he stops, backs—right on to the needle which is pricking
him—turns, and goes ahead. Try heating the water. As soon as the
infusorian feels uncomfortably warm, he stops, backs, turns, goes
ahead. Try cooling it. The same process. Add to the water something
that the creature notices, acid for example. Still the same old
stop, back, turn, go ahead; tho often the next go-ahead sends him
straight into the drop of acid and burns him up.

So far as we can see, therefore, everything that the infusorian
feels at all, feels to him exactly like everything else. No matter
what it is he feels, nor on what part of his body he feels it, he
always acts in precisely the same way. It is, moreover, doubtful
whether one of these animals ever learns or remembers much of
anything, or in any other way ever finds out how to do anything
which he could not do about as well the first instant of his life.




XXII

What Plants Know


Of course, the plants do not really _know_ anything. Still they
usually act wisely; and that is practically just as good as knowing,
and often looks very much like it.

For instance, one sees little pine trees growing in a pasture. Each
year they send up a “leading shoot” a foot or more long, straight up
into the air, to become by and by the main trunk. Each year, also
from the point where the trunk ended the year before, there starts
out a whorl of little branches, a half dozen or so of them, some of
which will by and by become the main limbs. It is the same way with
the firs and spruces. If you haven’t seen these growing out of
doors, you have at least had them for Christmas trees in the house.

When these little trees grow in the pasture, pretty soon a cow comes
along and eats off the top so that there is no longer any leading
shoot to grow up into a trunk. What does the tree do then, but pick
out one of the side branches from the uppermost whorl, and turn that
up into a new leading shoot. So the tree gets a trunk in spite of
the cow. Somehow or other, nobody understands how, one of those
green tufts which was meant to grow into a horizontal branch,
changes its mind, turns up, and becomes the vertical trunk.

This may happen five or six times to a single tree—for when it isn’t
cows, then it’s wind, or insects, or something else, that kills the
bud that ought to grow up into the main trunk. So one finds often in
the woods, trunks of evergreen trees that grow up straight for a few
feet; then take a sharp turn to one side, and another straight run
of trunk; then another turn. Each of these turns means that
something has happened to the leading shoot, and that the tree, like
a very wise vegetable, has at once made another leading shoot out of
a side branch. But still the curve remains to show where the branch
had to change its mind.

It certainly is most clever of the tree. I for one, should like much
to know how that side branch finds out that something has happened
to the leader, and that it must step into the gap; and how the tree
decides which side branch it shall be that is to make the change.
Sometimes, indeed, the tree doesn’t seem to be able to decide, so
that two branches turn up instead of one; and after that, the tree
has a double trunk. Sometimes, too, when the leading shoot is weak
but still alive, a side branch turns up; and if the leader recovers
itself and grows up strongly again, there will be here also a double
trunk; but in such a case, one trunk will grow up straight, while
the other starts out with a turn. So the tree sometimes makes a
mistake, just as we all do. But it almost never makes so bad a
mistake as to have three branches turn up into trunks, tho as far as
numbers go, it might have six.

Another matter that all plants seem to understand is the difference
between up and down. At least they never make the mistake of sending
their roots into the air and their stems down. You recall the bean
plant that is inside the bean, with its little root and its tiny
stem and leaves tucked snugly away between the two big seed-leaves
which are most of the bean. You may plant the bean any way you like,
right side up or wrong side up, point the stem up and the root down,
or the stem down and the root up, put the bean flat on its side,
even plant it in one position for a while and then dig it up and
turn it over to another. It makes no difference what you do; that
little stem will twist round and grow up, and the little root will
twist round the other way and grow down, tho each has to travel half
way round the bean to do it. Somehow every seedling does tell which
from t’other.

Now the question is, does the plant grow up because up is up, or
because up is toward the light? The matter is easily settled. If we
plant a seed in a pot, pack the earth in solidly, put a screen over
the surface to keep the earth from falling out, and then tip the pot
upside down then if the stem wants to grow up it will have to grow
away from the light, and if it wants to grow toward the light it
will have to grow down. Thus we shall find out whether the plant
goes by light-and-darkness or by up-and-downness.

As a matter of fact, while nearly all plants are influenced by both,
for young seedlings just getting their start in the world, the
question of up and down is much the more important. So a seed
planted in an upside down pot, will grow its stem up into the dirt,
and its roots downward into the air.

So a plant knows in a way, up from down, as indeed it must, else a
tree would not be able to send a tall trunk straight up into the
air. Besides, when a tree happens to get uprooted, and yet lives,
the new part of the trunk which grows after the accident, does not
continue the direction of the old fallen portion, but turns and
grows straight up. You can see this sort of thing almost anywhere in
the woods.

The plant also, in a way, knows which way the light is falling on
it. Commonly, as everybody is supposed to know, the plant grows
toward the light. Yet the curious thing about it is that some parts
of some plants always grow away from the light. The leafless runners
of the strawberry geranium grow away from the light; but when they
begin to form leaves on their ends, then they change and grow toward
the light like other plants. The tendrils of many vines also, always
grow away from the light, while the leaves and, stems are growing
toward it. The reason is that by turning away from the light, they
turn back toward the rock or tree trunk or wall or trellis which
gives them support.

Thus the plant, that seems to know two things, is twice as well off
as the infusorian that knows only one.




XXIII

What Plants Can Do


As trees and vines and shrubs and bushes are wiser than they look,
so they can do more than we commonly suppose. We think of all plants
as merely sitting still and growing; but they really do much more.
Most ponds and ditches, the water squeezed out of bog moss, even
damp spots on rocks or the ground, often swarm with minute green
plants, that swim about quite as freely as if they were animals.
Some of these, single-celled, pear-shaped affairs, have two long
tails at the smaller end, with which they lash the water and so get
about as freely as do the equally small animals which live with
them. In fact, some of these little plants are so much like some of
the infusoria, which I have already told you about, that about the
only way to tell them apart is by the green color of the
vegetable—tho to be sure the plant is apt to have two tails, while
the animal has only one.

Then there are the so-called “diatoms” which live, absolutely
millions upon millions, in the slippery coating which covers the
sand and stones at the bottom of streams and ponds. These are
commonly counted among plants; but they have two shells like an
oyster and swim about freely—as an oyster does not, for all it is an
animal. Then too, there are the “slime moulds,” which at some times
of the year look like common puff-balls, and at other times change
into a soft jelly, and crawl away to find a new place to change back
into a puff-ball again.

In short, there is simply no end to the animal-like actions of the
simpler plants, for after all, plants and animals are a good deal
alike. To be sure, you don’t have any difficulty in telling a cow
from an apple tree, but that is because a cow is a very complex sort
of animal, and an apple tree is a very complex sort of plant. But
the simpler plants, which have neither stem nor twigs nor leaves nor
roots nor branches, and the simpler animals, which have neither
heads nor legs nor bones nor muscles nor skins, are naturally not
nearly so different from one another as apple trees and cows. And
when you come to the very smallest and simplest creatures, the
distinction between the two seems hardly worth counting. Some
animals grow on stalks, and some plants swim about or crawl. Many
plants are not even green; a few animals are. Once in a while, you
find the very same creature described as an animal in one book, and
as a plant in another.

However, I began to tell you about the animal-like actions of the
plants which we see more commonly, the ordinary trees and shrubs and
bushes, grass and house plants and the like.

We say that plants grow toward the light. They really do much more
than that. When a houseplant has stood for some time at a window, in
the same position, every leaf, as you know, is set to face the
light, so that as much sunshine as possible falls on the upper
surface of each. But if you turn the pot round, so that the leaves
face away from the light, within a day or two, every several leaf
will have skewed itself round toward the window again. So the plant
can move its leaves about as much as an animal can move its head;
only it moves very much more slowly. But the sunflower, grown out of
doors, can wag its head fast enough to keep up with the sun. Indeed,
it is called the sunflower, not so much because its blossom looks
like the sun, as because, in the morning at sunrise, it bends its
tip over toward the east so that the rising sun shall strike the
upper sides of its leaves, follows the sun around thru the sky all
day, and in the evening finds itself with all its upper leaves
facing west. Then in the night it nods back again ready for the next
sunrise.

Many leaves, if you notice them closely, have a soft bunch or
cushion, either where the blade of the leaf joins the stem or where
the stem of the leaf joins the branch or sometimes at both places.
This is the joint on which the leaf does its turning. The clover,
which is an especially active little plant has one of these joints
for each of its three leaflets.

[Illustration: The leaf has a special joint on which to turn.]

Not only the leaves of a plant, but the tendrils also, and the soft
green parts of the stem, and the slender tips of the roots, turn and
twist slowly, moving like the limbs of a very sluggish animal. Did
you ever wonder how the climbing vines, the beans, peas, morning
glories, woodbines, and the like, manage to find the poles and
trellises on which they grow? The seedling comes out of the ground
six inches or a foot away from the nearest support. Next thing you
know, it has grown straight for the support and begun to climb.

This is the way it manages to find its way. When the young shoot
first comes out of the ground it grows up straight like any plant.
Pretty soon, however, being but a slender vine, it begins to bend
over. Thereupon, it begins to sweep its tip slowly round in a
circle—hop and honeysuckle toward the left, bean and morning-glory
toward the right. As the stem grows longer, the circle gets bigger,
the tip reaches out farther and farther after a support. When at
length it does swing round against pole or trellis, it still keeps
on winding, and so continuing to grow, winds itself up toward the
top. If one pole is not high enough, when it reaches the top, it
again sweeps its long growing end round till it catches something
else and winds up that. Thus the vine finds its support in the first
place, having reached the top of that jumps across to another,
almost as if it could see where it was going.

The coiled tendrils of grape vines manage in the same way. They,
too, sweep round in a circle till they catch a support. Sometimes,
too, the tendril, instead of merely growing round an object,
actually closes down and grips it like a shutting hand.

[Illustration: A root much enlarged, shows cells and hairs.]

Or perhaps you have wondered how the roots of a plant manage to find
their way thru the soil, always picking out the cracks and openings
and never butting up against a pebble and having to stop. This is
the way it manages. Instead of growing straight forward, steadily,
the tip of the root grows out by perhaps the thickness of a sheet of
tissue paper. Then it pulls back again not quite so far. Then,
perhaps half a minute later, it grows out a little farther, and
again draws back. Meantime, the root tip is writhing and twisting
like an earth worm, only much more slowly. Whenever the moving tip
touches a pebble or a grain of sand, the growing region, which is
just back of the tip, grows a little faster on the side where the
touch came, and so throws the tip of the root away from the
obstacle. In this way, sooner or later, the root hits the open space
and grows thru. You see, it is almost exactly like the way in which
the infusorian gets by obstacles with its touch, back, turn, and go
ahead; except that where the plant grows the animal swims.

Not only the root-tips but all the soft, green, growing parts of a
plant are continually pushing out and drawing back, twisting,
turning and bending; only the movement is generally so very slow
that one can hardly make it out at all. Yet there are certain
“sensitive plants” which when touched, pricked, heated or cooled,
roughly handled, jarred, or in almost any other way made to sit up
and take notice, fold up their leaves or drop them.

All plants, however, give some sort of slow jump or twitch or bend
when anything is done to them. They are made sluggish with cold, put
to sleep with ether and chloroform, revived by water when they are
thirsty, even made uncertain of movement when beer is poured over
their roots; all of course, just about like an animal under the same
circumstances. Both alike move more feebly when they are tired; both
alike stop moving when they are dead.

The plant, in short, is a very sluggish animal, shut up tight in a
wooden box, so that only the ends of its roots and shoots stick out
where we can see them move. We know, however, that all the living
jelly of the plant does move, tho we cannot see it inside the wood.
To be sure, the plant moves only very slowly. A leaf will turn when
a lighted match is held near it; but if somebody held the same
lighted match equally near your nose, your jump would be something
like four thousand times quicker. Nevertheless, some of the slowest
animals are not a bit more rapid of movement than the quickest
plants. The fig tree and the fresh water clam, for example, are
equally slow to move when they are touched, but move they both do.

But we must not forget the turning of the plants’ leaves toward the
light, for that is, after all, the one movement of plants which we
have all seen for ourselves.

The curious thing about it is that the leaf turns, not because the
light falls on the leaf itself, but because the light falls on the
stem. If we cover the blade of the leaf, but let the light fall on
the stem, then the leaf will turn; but if we shade the stem and
leave the blade uncovered, then the leaf will not turn. Or in case
there is a joint in the stem where the turning takes place, as in
the clover leaf, then there is where the plant does its seeing.
Allow the light to strike the leaf, cover that spot only, and the
leaf is blind, but cover everything else, and the leaf turns as
before.

Nor is it only sunlight toward which the plant turns its leaves. The
great Darwin, who was one of the first to study this matter
carefully, had a plant that after being kept a long while in the
dark, screwed round its leaves to face a small lamp twelve feet
away. Some of the so-called “sensitive plants,” will start turning
toward a candle ten seconds after they first catch sight of it.

Oddly enough, however, the leaf will move in exactly the same way,
if instead of letting light strike the stem, one rubs salt on it, or
brings a hot wire near by. In fact, leaves, tendrils, and other soft
green parts will turn toward a red hot wire till they touch it and
are burned to death. So the plant is after all much like the
infusorian. It can do one thing, which is generally right; but it
does that one thing just the same, even when that is the worst thing
it possibly could do.




XXIV

Some Plant-Like Doings Of Animals


The plants, then, know enough to do two things—to grow up or down
with stem or root, and to turn toward the light or away from it.
This really, if you can call this knowing, is about all they do
know. Now I am going to tell you about some common animals which are
not much better off than the plants; which know up and down, and
know the direction of the sunlight, and know mighty little else.

Happy is the community which does not know the brown-tail moth.
Wherever it appears, it spreads like a pestilence, eating every
green leaf off a tree, and leaving it in mid-summer as forlorn and
bare as at Christmas time. A great tree that has taken a hundred
years to grow, the progeny of one moth will kill in three.

The brown-tail moths, their cousins the golden-tail moths, and
several other sorts of moths, lay their eggs in the late summer and
early fall. The little caterpillars hatch out that same season, grow
to be something like a quarter inch long, and spend the winter in a
cocoon-like nest which they spin for themselves much as does a
silk-worm or a spider. In the spring, having eaten nothing all
winter, they leave the nest, crawl to the ends of the branches, and
proceed to devour the new leaves.

But how does a little worm, no bigger round than a slender pin,
finding itself in the midst of a great tree, with nothing near it
but tough bark which it cannot eat, know in the first place that
there are fresh green buds anywhere, and how in the second place,
does it find its way to the tips of the twigs where the buds are?
The answer is, that it doesn’t. The little caterpillar knows no more
about buds and food and the way to them than the tree itself does.
It is simply built like a tree, so that when it first leaves its
nest, it always turns its head up, and when it has a choice between
light and darkness, turns toward the light.

So the caterpillar simply turns up and toward the light, just as a
plant would, and with no more intelligence than a plant has, and no
more idea what it is about. But of course, crawling up and toward
the light, sooner or later brings it to the outer ends of the
branches where its food is.

You can easily prove this by putting the young caterpillars in a
bottle, or a wide-mouthed jar. If you lay the jar down on the table
with the closed end toward the window, every caterpillar will crawl
to the closed end, and never a one will crawl back away from the
light to the open end and escape. You don’t need any cover; the
light holds them fast prisoners. But turn the jar round, open end
toward the window, and soon there will not be a caterpillar left in
it.

Suppose now, when your caterpillars are at the closed end of the jar
toward the window, you take some fresh leaves, from the tree on
which you found the insects (since these are presumably the sort
they eat) and put them in the open end of the jar away from the
window. The little caterpillars will stay where they are till they
all starve to death, before one of them will turn round and crawl
away from the light toward its dinner. They are even more helpless
than a plant, which can at least send its roots toward water, no
matter how the light comes.

Also, as I have explained, the caterpillars must crawl up. So they
cannot escape from an open jar placed mouth down. Neither can they
escape from an open jar placed mouth up; because when they come to
the lip of the jar, in order to go farther, they must turn head down
to crawl down the outside. But they cannot crawl head down so there
they must stay. Moreover, if you put food in the bottom of the jar
while they are at the top, they can never crawl down to get it. They
cannot turn head down, and they do not have sense enough to crawl
backwards.

There is, nevertheless, this difference between caterpillars and
plants. If the plant grows up and turns toward the sun at all, it
does so always; but the caterpillar changes its nature, and after it
has reached the buds and once fed, then the impulse to move upwards
and lightward, is no longer useful, and so in a large measure
disappears.

Still many sorts of caterpillars keep these willy-nilly turnings, until
they are full grown. Our common—our much too common—tent-caterpillar,
is accustomed to leave its tent during the warm part of the day, crawl
to the tips of the branches where its food is, eat until the cool of
the evening begins, and then return to its tent. In no sense, however,
does it go after its food, knowing what it wants. During the warm part
of the day, it simply becomes like a plant stem, head up, and crawls.
It has to head up, and it has to crawl. So in the end it reaches its
food, but it doesn’t know anything about how it gets there.

I have often on an early summer afternoon, when the caterpillars are
getting restless and just ready to start out, taken the tent,
inhabitants and all, and put it on top of a post or a smooth rock.
The caterpillars being disturbed, at once start to crawl away. They
start in all directions. In a moment, of course, they find
themselves crawling head down. That being against the rules, they
turn and crawl up again. In no possible way can a single caterpillar
get off the top of that rock or post, until the regular time for
them to knock off eating and go back to the tent. Then they have to
crawl down; and cannot crawl up if they try. So the chief difference
between tent-caterpillars and plants, is that while the plant always
turns its root down and its stem up, the animal turns its whole body
down at certain times of day, and turns its whole body up at certain
others. One can hardly say that either has any more sense, or
intelligence, or knowledge, than the other.

All caterpillars, while they remain caterpillars, have to crawl
toward the light. All caterpillars, also, after they have changed
into butterflies and moths, when they fly, have to fly toward the
light also. That is why the swarms of moths collect around the arc
lights on the streets, fly into lighted rooms thru unscreened
windows in the evening, circle about the reading lamp, or if the
light chances to be a candle with an uncovered flame, fly into it
and are burned.

People will tell you that the moth is curious, wants to see what the
light is. But he isn’t; any more than the leaf is curious to look
out of the window to see what is going on in the street. Both alike
simply turn toward the brightest light. The moth, having turned
toward the light, when he flies, flies toward it. If the leaf could
fly, it also would fly into the flame and be burned.

The reason why moths only fly into the lamp is that they are about
the only insects that fly at all while the lamps are lighted; most
other winged insects, also, head toward the brightest light. So do
vast numbers of other small animals, snails and crabs and various
water bugs, earth worms, leeches, infusoria, and even minute fishes
just hatched out of their eggs. But older fishes and all the larger
animals with fur and feathers, have more sense. They go where they
please and turn any way they like just as we do.

Many small animals, on the other hand, are like plant roots. They
have to head according to the light, but they head away from it, and
so move toward the darker places. In fact, it is rather the rule for
the young insect, before it gets its wings, to burrow like a root
and turn away from the light, but to turn toward it later after it
gets its wings.

Perhaps the strangest fact of all is that some water animals which
ordinarily head away from the light, turn round and head toward it,
as soon as a little acid is added to the water. Alcohol, even common
soda water or ordinary salt, has the same effect. But some salt
water animals which normally head lightward, if put into slightly
fresher water, promptly turn tail to the light. All of which shows
that the creature himself hasn’t much choice in the matter, and
probably doesn’t know much about it anyway, any more than if it were
a plant.

These turnings of plant or animal, toward the light or away from it,
up or down, the heading up-stream of many fishes, and the necessity
for crowding into cracks and corners of many insects and other small
creatures, all these are called “tropisms.” Tropism is merely the
Greek word for turning. I tell you the name, because we human beings
who have speech, if we want to think about a matter, have to have a
name for it to act as a handle for our minds to take hold of.

We see, then, that the various sorts of living creatures which we
have met thus far in this book, tho they are all made of much the
same sort of living jelly, have really quite different sorts of
minds. We ourselves, as you know, have reason, speech, intelligence,
feeling, and instinct. The animals most like ourselves, dogs and
cats and horses and the like, have also intelligence, feeling and
instinct. Animals very different from ourselves such as fishes,
insects, and the various strange sea creatures, have some
intelligence, some feeling, a few strong instincts; and besides
these, certain tropisms. But the simplest animals of all, and the
plants, have neither intelligence nor instinct, but only feelings
and tropisms.

All living things, then, plants and animals alike, have feeling. I
have already explained something about instincts and tropisms; and
told you, if not much about intelligence or reason, at least
something about speech. Now I shall tell you something about the one
thing which all living things have in common, and that is feeling.




XXV

The Five Senses and The Other Five


Traditionally, of course, we have five senses—sight, hearing, touch,
taste and smell. Yet we sometimes say that we are “frightened out of
our seven senses,” as if there were seven and not five. Really, the
number of our different ways of feeling is neither five nor seven,
as we shall now see by counting them up for ourselves.

Five at least we are sure of, the traditional five. There is no need
for anyone to tell us what our eyes, ears, and noses are for; nor
that we taste with our mouths as well as talk and eat, nor that we
feel touches anywhere over our skins. As to this last, however, I
don’t think we always realize how completely the sense of touch is
confined to the skin. Headaches, for example, we feel on the outside
of the head; the brain itself can be pinched, cut, burned, and
generally maltreated, and we not feel it so much as we feel a
pinprick on a finger tip.

Do you remember how, a few years ago, when you had not so many
things to do as you have now, you used to amuse yourself by whirling
rapidly round in one direction, till you were dizzy and could hardly
stand up. For a few moments, or till you whirled around in the other
direction, you lost your sense of right-side-up-ness; you didn’t know
sky from ground; and if you had been whirling especially fast or
long, you probably fell down flat, and couldn’t get up again. When
you dance, too, without reversing, by and by you get giddy, the
floor begins to curl up at the edges, and you become uncertain as to
which way is down.

The trouble is not with the eyes, because we get dizzy with our eyes
shut. We really have a sense of up and down, which is neither sight,
hearing, touch, taste nor smell; but a sixth sense. Its organ is a
portion of the inner ear, the so-called labyrinth; and it tells us,
not how things look or sound or taste or smell or feel, but whether
we ourselves are right side up. Too much whirling upsets this sense
of equilibrium, just as too bright a light dazzles the eyes, or too
loud a sound stuns the ears. A shark will swim with his head cut
off; but his ears being gone, he is as likely as not to swim upside
down.

There, then, are six senses. Let us see if we can find number seven.
While you are sound asleep at night, you do more or less turning
over in bed, so that in the morning, you are lying in quite a
different position from that in which you went to sleep. Yet altho
you remember nothing of what you did in the night, when you awake in
the morning, and before you open your eyes, you can tell exactly the
position of every arm, leg, or finger. You know just how much each
joint is bent. You have, in short, a sense of where the several
parts of your body are, which is none of the six senses which we
have recognized heretofore.

So, too, if you shut your eyes, and let some other person move any
member into another position, you feel it move, and know all the
while just where it is. Or suppose you are playing short-stop, and
fielding a hot grounder. Your eye is on the ball, and your mind on
the game; but your hands drop, and your back bends, and your knees
sink, all to precisely the right degree to bring your hands where
the ball is. You have a most accurate sense of where these hands
are, tho you neither see nor hear nor touch nor taste nor smell
them. A piano player relies on this same muscular sense, when
without looking at the keyboard he skips unerringly from one note
to another, never going too far nor stopping too short. In fact,
this muscular sense is really one of the most accurate of all our
senses. We can see a speck of dust much too small to feel; but a
person used to using a microscope or doing other nice work, can make
a movement with his fingers as small as the twentieth part of the
width of a hair—and that is a good deal smaller than any unaided
human eye can possibly see.

As you might guess from its name, this muscular sense is located
partly in the muscles. Still more, however, do we depend on the
joints. We do not feel one bone slip over the other, that would be
plain touch; but we know with extraordinary accuracy just how far
the joint has moved and just where it is at any moment.

Here then are seven senses; now for number eight. Take something not
too sharp, a tooth-pick will do, or the point of a lead pencil, and
touch the skin lightly on the back of the hand or on the forehead or
near the elbow. You feel, of course, the touch. Now move the point
ever so little, by the thickness say of a small pin, and touch
again. You probably feel the same touch as before. Continue this
touching, and before you have tried twenty times, you ought to
discover a spot where the point feels suddenly cold. In short, some
points on the skin feel pressure, which is the ordinary sense of
touch. But other points feel cold, which is a different sense, an
eighth sense, and not touch at all.

There is also a ninth sense, the sense of heat. If you are very
careful indeed, and notice very closely, you can find heat spots,
just as you found the cold spots. Only these are much harder to
locate, so that you will probably not be able to make them out.

One more sense is located in the skin besides these three. That is
the sense of pain. Tho to be sure other parts of the body feel pain
also—the muscles and joints when we have rheumatism, and the teeth
when we have the tooth ache. Pain is not touch. In the first place
it feels very different, and in the second place, it is quite
possible to lose one sense and keep the other. In certain diseases
of the nerves, the ordinary sense of touch remains as before, but
the sense of pain completely disappears. One can be pinched, cut,
burned, in the most violent manner, feel the touch of fingers or
knife or hot wire, and yet not feel the slightest pain. And the same
thing is true, after one has taken the right amount of ether or
chloroform; one isn’t asleep, and one can feel touches but one does
not feel pain—and a wonderful blessing it is sometimes.

I wonder whether many of you have ever heard of cocain, or had it
used on you when you got something in your eye, or had to have
something done to the inside of nose or mouth. (Only you musn’t call
it “co-cane,” in two syllables, as many people do and as it looks in
print, but “co-ca-in,” in three syllables; for it is extracted from
coca leaves, and the name is “coca,” with the “in” added on, like
strychnin, atropin, protein, and the names of so many drugs and
medicines). Cocain, then, looks a good deal like common salt, but
fit grain or two in a drop of water, placed anywhere where the skin
is thin, soaks thru to the ends of the nerves, and for ten minutes
or so, puts an end to all feeling there. If now we apply cocain to
the tongue in just the right strength, it takes away for the moment
all sense of pain, while it leaves the sense of taste as before, and
the sense of touch. One can bite his tongue and feel the bite, yet
it does not hurt. One can drop hot syrup on it, taste the sweet, and
yet not feel the burn. But if we make the cocain a little stronger,
then when the pain goes, the taste goes with it. One can feel
something in his mouth, but cannot tell sugar from salt; while a
drop of strong acid, tho it burned a hole in the tongue, would
neither taste sour nor hurt. A still stronger dose of the drug
suspends all feeling—pain, taste, and touch alike.

So pain is a different sense from touch, just as much as taste is.
Besides, if you take a sharp pin and make a line of pricks close
together, much as you did when hunting for cold spots, taking pains
to prick equally hard each time, you will be pretty sure to discover
certain points where the prick hurts much more than it hurts the
thickness of the pin away. This, of course, is a pain spot. Between
these you hardly feel the pain at all.

There are, then, in the skin, cold spots, hot spots, touch spots,
and pain spots, from two to three times as many of each as there are
fine hairs on the skin. Under each of these spots, is the end of a
nerve, either branching like a little bush or ending in a sort of
oval knob, much the shape of a foot ball. And just as the eye sees,
but doesn’t hear, and the ear hears, but doesn’t see, so each of
these nerve endings feels either pain, or cold, or heat, or
pressure, but only one of them.

How many senses have we then? At least ten, which is twice the
traditional five. Besides these there are thirst and hunger, which
are certainly feelings, tho neither sight, hearing, touch nor any of
the rest. Then there is that peculiarly unpleasant feeling which
comes to us after we have dined less wisely than well, or have been
rocked too fondly in the cradle of the deep, the sensation, I mean,
which we call “sickness” or nausea. This makes thirteen senses.
There are several more in addition to these, more or less vague
affairs, which for the most part tell us only what is going on
inside our own bodies.

If therefore, you ask how many senses we really have, I shall have
to say that we had better call it ten. At least we have ten well
defined sorts of feelings, which tell us what is going on outside
our bodies—and after all, that is what senses are for. These, then,
will be sight, hearing, touch, taste, smell, heat, cold, pain,
equilibrium, and the muscular sense. Each of these has its own
special place, in eye, ear, joint between two bones, or little spot
in the skin. If we lacked any one of these (as indeed many creatures
do) there would be something which it is important for us to know,
but which would be forever impossible for us to find out.




XXVI

Eyes


I am not going to tell you about the wonderful structure of the eye,
nor about how it works. That, if you have not learned something
about it already in your school physiology, you will get sooner or
later, certainly before you get thru the high school. This book is
mostly about things that you do not learn in school.

I have, however, told you something about how the eye grows, how it
buds out from the side of the brain, and then doubles in to form a
cup; and how this cup becomes at length the nervous portion of the
eye, the retina, which therefore, tho it lines the eyeball, is
really part of the brain; and how this retina somehow or other, in a
way that nobody understands, picks up the image of the things we
see, and sends it along the optic nerves to the part of the brain
which lies above the ear and round toward the back of the head. I
think you know also how these optic nerves cross over, just as most
of the other nerves do, so that the left eye reports to the right
side of the brain, and the right eye reports to the left side. You
know also how, in the end, both these reports get turned over to the
left side of the brain, and remembered there; so that while we see
with both sides of the brain, we remember what we have seen with one
side only.

Aside from these matters, there are various little points about the
eye which one can make out pretty well for himself. One of these is
the reflections from the front of the eye. You know, if you look
into a window in the day time, or try to look out of a window after
dark, or look into a glass tumbler, or at the face of a watch, or in
general, look at a glassy surface or at water, when it is lighter on
your side than it is on the other, instead of seeing thru quite
clearly, you see reflections from your side.

It is, naturally, the same with the glassy front of the eye. Look
into another person’s eye, or into your own with a mirror, and you
see reflections of windows, lamps, your own head, or any bright
objects. You ought to be able to find three reflections of each
bright spot. The largest, which is always right side up, is the
reflection from the clear glassy front of the eye which covers the
entire  part from which we call our eyes blue or brown or
gray or what not. If you look carefully, a little sideways, you will
be able to get a still smaller picture, coming from the front
surface of the lens of the eye, which lies just behind the round
black hole in the center of the  curtain. This also is always
right side up. But there is still another, always up side down,
which is the reflection from the back side of this same eye lens.
These last two, you can get also by looking at a common spectacle
lens, or by looking into the front of a camera.

For of course, the eye is really a little living camera. It takes a
little picture like that in a camera, always upside down, at the
back where the plate holder or the spool of films goes in a kodac.
We can actually see this picture at the back of an animal’s eye; and
what is more, people have sometimes taken out the lense of an ox’s
eye, and taken a photograph with it as if it were a lens of glass.
Indeed it is possible, tho the process is decidedly difficult, to
take an ox’s eye from the butcher’s shop, keep it in the dark, let
it look quickly at something bright, and then by treating it with
the proper chemicals, actually to fix on the retina, as on a camera
plate or film, the last object which the eye saw. There is a dark
pigment in the retina, called the visual purple, which changes color
in the light, and so forms the image.

But how this image or picture gets to the mind is another question;
a question, I am sorry to say, which nobody can altogether answer.
We do know, however, that there are nerve endings in the retina,
something like hot spots, cold spots, touch spots, and pain spots in
the skin, only of course very much nearer together. Probably there
are three kinds of these—red spots, green spots, and blue spots.
Each spot sees one color; and by combining these colors in all sorts
of ways, we build up the complicated pictures which we see. Still it
is by no means impossible that there may be, not three, but six
elements in our eye-pictures—white, black, red, yellow, green, and
blue. Nobody really knows; and it all shows how little, after all,
we have succeeded in finding out about ourselves, in spite of whole
lifetimes of study of many hundreds of scientific men. Who knows but
that some of you who read these pages may be the ones to discover
some of these things which all the world thus far has not been able
to learn.

There are still other curious facts about our sight which anybody
can make out for himself. If you take any  object, this book
for example, put it behind your head; and then slowly bring it round
in front, while you keep your eyes looking out steadily straight
forward, you will notice certain very peculiar facts. In the first
place, you will discover that you can see surprisingly far toward
the back of your head. A horse can see all the way round, and if he
did not wear blinders, could watch the people in the carriage behind
and the road which stretches out in front, along with everything in
between, all at once and about equally well. Many animals, in short,
can see clear round their heads. We can’t; we can see only about
half way round.

Then you will notice that you can see that something is there and
moving, while it is still so far round to the side that you cannot
at all make out either its shape or its color. Furthermore, you can
see the color perfectly well, long before you can make out the exact
shape. Indeed, you can make out the shape of ordinary letters well
enough to read them only when you hold them exactly in front of the
eye. The least little movement out of that one small spot mixes a
whole page to a gray blur; curiously too, you can make out blue and
green decidedly farther round toward the corner of the eye than you
can tell red.

In short, then, we can see movement considerably farther round
toward the backs of our heads than we can see color. We can see blue
farther round than we can see green and green farther round than we
can see red. But we cannot see shapes accurately, except right in
front of our noses.

Now curiously enough, all animals that can see at all, can see
something moving; tho they cannot see colors at all perfectly, nor
make out the shape of anything. Many lowly sea creatures have eyes
of this sort. A better kind of eye, like those of many insects, can
see colors, but not make out much about shapes; while certain ants
can see blue and green but are blind to red. Few indeed are the
creatures that can see anything like as clearly as we see, looking
hard at an object straight in front. Even a dog cannot do it, nor a
horse.




XXVII

Seeing and Believing


Even we ourselves, we human beings, by no means always see so truly
as we think we do. Take a look at this figure and say which of the
two lines in the south-west corner continues the single line in the
north-east corner. Then lay on a ruler or a strip of paper, and see
which line really does run clear across the figure.

[Illustration]

Or look at the figure below, and say which way the curved lines
bend. Then take a straight-edge and test them.

[Illustration]

Where, in this next figure, are the white bands widest, in the
middle or at the ends?

[Illustration]

Lay two strips of paper along the sides of a white band, one on each
side, so as to cover up the slanting lines. Where now is the band
widest?

Here is a square with some lines drawn across it. Are the lines
straight? Are they the same distance apart everywhere?

[Illustration]

Now I will add certain other lines to the same figure. Are the
original lines still straight and the same distance apart
everywhere?

[Illustration]

Or look at the B’s, H’s, S’s, 3’s, and 8’s on this page, that look
about the same size at top and bottom.

[Illustration]

Then turn them up side down and see what they really are.

[Illustration]

Or to take one more curious illusion, the lines of the figure on the
next page are really flat on the paper, where the printer put them.
But there is a point near the bottom of the page, about as far from
the line nearest the bottom as that is from the ones nearest the
top, where if you cover one eye and look at the lines with the
other, each line will appear to stand straight up from the paper
like a little post.

[Illustration]

Or possibly you think your eyes always report correctly concerning
colors? Then try looking at a landscape, with your head up side
down, so that the view appears under your arm or between your knees.
Are the colors the same as before. If not which is right?

Or try this experiment, take some brightly  object—paper,
cloth, or almost anything—in size anywhere between one and four
inches across, lay it on a sheet of white paper, put the two in a
strong light, and getting arm’s length or more away, stare steadily
at the  object for a half minute or so, until the eyes begin
to tire. Then whisk away the  object, continue looking at the
same place, and notice what you see on the white paper, where
nothing is. Or you can do what is really much the same thing, by
looking at a window up against the bright sky, and after a moment
turning away and shutting your eyes.

In all such experiments, one sees the outline of something that
isn’t there, but in a contrasting color. We have, as you will
recall, at least three sorts of color spots in the retina, red
spots, blue spots, and green spots. By looking at a bright red we
tire the red-seeing spots, so that everything looks blue-green. If
we look hard at bright green, we tire the green-seeing nerves, and
things look red-blue, which is purple. An eye tired of blue, sees
yellow.

The curious thing about this is that about one man in thirty and one
woman in three hundred is “born tired” to red. Such persons are said
to be red blind. Otherwise they can see as well as anybody; but red
things do not look  at all. None of us can see red far round
to the side out of the corner of the eye, as well as we can see
green and blue. Color-blind persons have the corner of the eye all
the way across, and cannot see red anywhere. They can see red
things; but they cannot see them red. Railway train men and masters
and pilots of vessels have to depend on red and green lights for
signals. Such persons, now-a-days, are carefully tested for
color-blindness; and all who cannot see red as the rest of us see it
have to find some other occupation.

Why do we have two eyes? We can see outlines exactly as well with
one; in fact, all the more difficult sorts of seeing, sighting a
gun, using a microscope or telescope are done entirely with one eye.
We can see colors exactly as well with one eye as with two. The only
thing that we can’t see well with one eye is distance.

Try with both eyes open to put your finger rapidly on various spots
arm’s length or so away. You can hit the mark every time. Now cover
one eye—always when you want to use one eye, don’t shut the other;
cover it, but keep it open. Also, by the way, if you are to use a
microscope or a gun, don’t shut either eye; learn to keep both open,
but to look with only one. With one eye only, then, try to put your
finger rapidly on various points which you did not look at until
after you had shut off the sight of the other eye. You can do it,
but much less quickly and certainly than with both eyes. The nearer
anything is, the more do the two eyes have to turn in, when both
look at it at once. After eight or ten years of practice, as most of
us have had, we learn to judge distances pretty accurately, just by
the feel of this turning in.

All these peculiarities of our eyes, the judgment of distance, the
different portions of the retina which see most clearly and which
see colors, the various ways in which the eye is deceived, and the
like, all these you can make out pretty easily for yourselves. There
remains, however, one especially curious matter which you will
hardly be able to discover, unless you take some little pains and
follow directions pretty closely.

This is the so-called blind spot. We have, as you have seen, in each
eye, a small spot in the center of the field of vision where the
sight is especially sharp. This is, in fact, the only part of the
eye that we can see to read with. Near this, between it and the
nose, is another spot, about the same size, with which we cannot see
at all.

We can prove this from the figure below.

[Illustration]

Hold the page about a foot in front of the face, as if you were
reading. Cover the right eye and look at the cross on the right, or
cover the left eye and look at the dot on the left. Keep looking
steadily but without too much effort, while you move the book back
and forth, bringing it nearer to the face, or trying it farther
away.

You should be able to find a distance at which the other mark, the
one at which you are not looking, entirely disappears. You can see
all round it, but the place itself is on the blind spot and is gone.

With some practice, one can make anything, not too large, disappear
in the blind spot. Boys in college, when they are studying about the
eye, sometimes amuse themselves in church by getting the clergyman
on the blind spot, and so blotting him out. It really is queer
enough. You cover one eye, and look with the other at the wall
behind the preacher a little toward the side on which your own nose
is. When you get just the right point to look at, the man simply
disappears. You see the wall and the pulpit and the chairs or what
not, on both sides. You hear the preacher’s voice. But the preacher
is gone. You don’t even see a black spot where he was. Or if you are
clever, you can cut off his head and leave his body; or cut off his
body and leave his head hanging in the air.

All this, however, requires more control over the body and more
steadiness of attention than boys and girls usually possess. I
should not have told you anything about the wicked students if I
were not sure that you will have forgotten all about the matter long
before you get old enough to try it.

Meanwhile, don’t forget that as there is a blind spot in each of
your eyes with which you simply cannot see what you know is there
all the while, so there are many other things in heaven and earth
which you cannot see, though they are there. Then don’t be too
certain, when you happen to be blind to what other people see, that
the people who do see are mistaken.




XXVIII

Some Other Senses


We really know far less about hearing than about sight. The eye is
where we can get at it, to look inside, and to see how it works. But
the ear, the inner ear that is, where the hearing is done, is set
deep inside the head, in the midst of a solid bone, the hardest
piece of bone in the whole body except the teeth. Nobody, therefore,
really understands how we hear.

We do know, however, that the ear is two different things. One part
of it is the organ of hearing—I am speaking always of the inner
ear—while another part, as I have already explained, is the
organ of the sense of equilibrium, the feeling of direction and
right-side-up-ness. But just how much of the ear goes for hearing,
and how much for right-side-up-ness, and exactly how either part
works, and especially just how we tell one sound from another, are
things that are still left for somebody to find out.

Nor do we know much more about smell. We know that the smelling is
done in the upper part of the nose, that the nerves of smell do not
cross over and report to opposite sides of the brain, as so many
other nerves do. But how we tell one odor from another, nobody
understands; and we are even farther away from understanding than we
are in the case of the eye.

We do, however, understand taste. At least we understand as much
about it as we do about sight; for the two senses are much alike.
There are four kinds of taste spots, scattered over the tongue and
the inside of the mouth, mostly on the tongue. Each of these gets
one kind of taste—salt, bitter, sour, or sweet. Oddly enough,
different people have these four sorts bunched in different parts of
the tongue, so that not all people taste the same thing in quite the
same place.

But you will say at once, we taste many things that are neither
sweet, sour, salt, nor bitter; there must be many more than four
tastes. There are not. What we commonly call tastes are really
smells. We smell things that are in the mouth, and think we taste
them.

If you don’t believe this, simply hold your nose. It is an old trick
to get somebody to close his nose tightly, and then while all sense
of smell is thus cut off, to bring into the room a piece of raw
onion, put it in the victim’s mouth, and ask him to guess what it
is. If the onion is not brought into the room until after his nose
is shut off, he cannot tell what it is that he is eating. For the
onion has almost no taste. But the moment one lets go his nose—then
he knows! There is no doubt that the onion has smell—enough and to
spare!

Almost any of the senses can be fooled. Put your finger on you
forehead; then move your head slowly from side to side so that the
finger, held motionless, slides over the skin. Your muscular sense
and your sense of equilibrium both testify that the head is moving
and the finger is still. Yet you can’t make yourself believe it. It
insists on feeling as if the head were still, and the finger moving.

Or try the senses of heat and cold. Take three dishes, one of hot
water, one of cold, and one of a mixture of the two that shall feel
neither warm nor cold but tepid. Put the fingers of one hand in the
hot water, and the fingers of the other hand in the cold water. Keep
them there a minute; then put them both in the tepid water. The
tepid water will feel hot to one hand and cold to the other. Really
it isn’t either. Perhaps, too, you have noticed, when you go in
bathing, that as you wade in, you feel the cold only at the surface
of the water where the skin was last wet. Hence the wisdom of going
in all over at once with a header.

Even the sense of touch, in general the most reliable of the senses,
can be deceived. When you are fishing and get a bite, where do you
feel it? Most fisherman feel the bite at the end of the line, as if
their nerves actually ran the length of the rod and down the string
to the hook! And when a ball player cracks out a long hit, I leave
it to all boys, if he doesn’t feel the place in the bat where it
hits the ball. Or to take a commoner example, when you touch your
hair, where do you feel the touch? In the hair itself where there is
no feeling at all, or in the scalp where it really is? Or once more,
if you hold the point of your nose between two fingers you feel one
nose; but if you cross the fingers, and then touch your nose between
the crossed parts, then you feel two noses.

Still on the whole, our senses are pretty reliable. The eleven
different sorts of feeling spots in eye, tongue, and skin, that tell
us about red, green, blue, heat, pressure, cold, pain, sweet, sour,
bitter, or salt, and the ears and nose which we don’t know so much
about, all these tell us, on the whole, the truth. Yet we never can
be quite sure; so that wise people, and especially wise boys and
girls, will beware of contradicting other people who chance to see,
hear, taste, smell, feel or believe, a little differently from
themselves.




XXIX

The Sight and Hearing Of Ants


So much then for our own senses, our sight, hearing, taste, pain,
and the rest of the ten, or as many more as one thinks it worth
while to count. The animals also have their senses, never
apparently, more than ours, oftentimes fewer, sometimes very few
indeed. So far as they have senses, these are like our own. But
since some animals haven’t any eyes, yet can see—a little; and some
haven’t any noses, yet can smell; and most of them haven’t any
skins, yet can feel; one may easily guess that their seeing and
smelling and feeling is not done quite in the same way that ours is.

I begin, then, with an animal that has eyes and can see, has no nose
and can smell, and does its hearing with its legs. This animal is
the ant. Of course, there are a great many different kinds of ants,
as there are a great many different kinds of human beings, and these
are by no means all alike. Some are black, some white, some yellow.
Some are, for size, like the smallest letters on this page; some are
more than an inch in length—and you can imagine their bite!
Naturally also, sight and hearing, taste and smell, are not quite
the same in them all.

Time would fail me to tell one half the strange ways of these
interesting creatures, the most interesting creatures, probably, in
all the world of little animals. Just as soon as you can, you must
get hold of the books of Fabre, M’Cook, Sir John Lubbock, or
Professor Wheeler, and read these strange things for yourselves—how
the ants live in cities underground, have workmen and soldiers,
carry on wars against their neighbors, raid their enemies’ nests and
make slaves of the captives, have plant-lice for cows, and milk them
of their sweet juice, and in return for this, feed and care for the
plant-lice and their young, pasturing them on the roots of plants,
and making no end of trouble for the farmers whose plants they are.

All this, I say, and many times more, no less fascinating, you can
read for yourselves in the proper books, not only about ants, but
about their cousins the wasps and bees as well. Just now, however,
we are concerned with how much the ant knows, and how he manages to
find it out.

Ants, in general, you must remember, live for the most part in total
darkness under ground. The workers, to be sure, leave the nest in
search of food, but the industries of the ant city, the storage of
food, the care of eggs and young, and the building of the city
itself, go on as if at the bottom of a mine. The queen ants, which
lay all the eggs for the colony, and the male ants, who like the
drone bees are gentlemen of leisure and don’t do much but loaf, are
for most of their lives like the vine tendrils which I have already
told you about. Whenever the light falls on them, they turn their
heads down stream to the ray; and so if they move at all, they have
to go toward the dark.

This, of course, holds them prisoners in the nest. But when at
certain times of the year, a new brood of males and females appears,
these ants, which, unlike the workers, have wings, suddenly become
like the leaves and stems of plants; they have to head toward the
light, and when they crawl or fly, they have to fly toward it. So
when the rays of the sun happen to strike the nest, and light up the
interior, out comes the swarm of winged males and females, leaving
the wingless workers behind. Away they fly toward the sunlight; and
those who are fortunate enough to find a suitable spot unhook their
wings, settle down to found a new colony and a new nest. Thereupon,
for the remainder of their lives, they turn their backs on the light
like a tree root. The rest, however, die, after they have lost their
wings, so that one sometimes finds great quantities of these
scattered about after the swarming.

The workers, on the other hand, who have to be in and out of the
nest about their business, do not have this tropism. They can take
the light sidewise, or end on, or any other way, just as we can. The
object of the tropism is to keep the males and females in the nest
until swarming time, and then to get them out. Really, could there
be invented a simpler or more effective way?

The worker ants can see. What is more, they can see colors.
Nevertheless, they do not usually see quite the same colors that we
see. For the most part they are red-blind, just as one man in thirty
is. But unlike the color-blind human being, many ants make up for
this red-blindness by seeing one or two other colors to which we are
blind.

Of course, you know the colors of the rainbow, beginning with red at
the bottom and running up thru orange, yellow, and green to blue at
the end. You see the same colors also in a dew drop, or in the light
which has come thru the corner of a square ink-well or the beveled
corner of a mirror. These are the so-called primary colors, by
mixing which all other colors can be made.

Now we, ourselves, do not all see the same rainbow colors. The great
Sir Isaac Newton, who made a special study of rainbow colors and
gave them their names, claimed to see seven—red, orange, yellow,
green, blue, indigo, and violet. I myself can see only six; that is
to say, I see only two colors beyond the green. More persons,
apparently, see six than seven. Try it for yourselves and see how
many you see.

The curious thing about the ants is that certain sorts, at least,
see the rainbow colors as many of us do—green, blue, indigo, violet;
and after that keep on still farther beyond this point, and see one
or two more colors, which we never see, and for which, naturally, we
have no names. Then, as I have said, to make it up, they are totally
blind to red, and nearly blind to yellow. Some ants go even farther
than this. They are totally blind not only to red and yellow, but to
all the colors which we see. They do all their seeing by means of
those two or more colors, farther out in the rainbow than the
violet, to which we human beings are totally blind.

There is a considerable practical convenience in this. The worker
ants, while they themselves run freely in and out of the nest, from
darkness to light, usually try to keep their eggs and young in the
dark. So when you turn over a stone and open into an ants’ nest, the
most that you get is a glimpse of piles of white eggs or larvae, and
a throng of workers skurrying about to drag them out of sight into
the ground. You really can’t see anything at all of the regular
daily life of the underground city.

But people who study ants simply carry them into a dark room, and
look at them by red light. Since the ants cannot see red, they think
they are still in total darkness, and so keep right on undisturbed
with their work as usual.

Doubtless, it has already occurred to you, that in this particular
the ant’s eye is very like a photographic camera. You who have
cameras, open your plates and films by red light, because the
sensitive chemicals are blind to red, and so treat red light as if
it were darkness. You probably do not know, however, that it has now
become the practice to take especially sharp pictures of small
objects thru a microscope by means of some of these colors which the
ants see and we do not. These colors do not come thru glass, and the
instruments have to be made of quartz; but they take beautiful
pictures in what seems to us total darkness, and what to an ant
would seem some familiar color, about which we know nothing.

On the whole, then, certain ants at least rather have the advantage
of us in seeing colors. We, on the other hand, more than make it up
when it comes to hearing sounds.

We ourselves, however, differ in this a good deal from one another.
Practically everybody who can hear at all, can hear all the notes of
a piano, from the big growly end up to the little squeeky end. You
young people can hear much shriller sounds than any on a piano; but
we old codgers, whose ears are getting stiff, do not hear shrill
sounds, even when we hear perfectly well those of lower pitch. The
squeek of a mouse is about the limit for most people. Some can hear
it, some can not. But cats can hear easily a mouse’s squeek, and
much higher sounds besides, such as no human being can hear at all.

But the ants are still more inferior to us than we are to the cats.
Some sorts which have been tested, can hear only two, and sometimes
only one, octave above “middle C” on the piano, tho this is only
half way up to the squeaky end of the key board. They hear well
enough up to that point, and then are deaf to all sounds beyond.

Ants, moreover, do their hearing thru their legs. We ourselves, do
something like this, when we grip one end of a stick in our teeth
and scratch the other end with a pin. Even a lead pencil will do for
the experiment; the sound is twice as loud when we shut our teeth on
the wood and hear the scratching thru the bones of the jaw, as it is
when we listen with our ears alone. Miss Helen Keller, completely
blind and deaf, managed nevertheless to enjoy music by holding a
music box in her hand, and feeling the jar; and she conversed in a
telegraphic alphabet by tapping with her foot on the floor, taking
the reply in the same way, by the jar, when anyone answers her.

The ants manage in much the same way. Stand an ant on cotton wool,
and he is totally deaf to all sound. No sound, high pitched or low,
can reach him thru the air. But put him on a hard surface, on his
legs, and he hears thru his legs, taking the jar much as Miss Keller
does. In fact, all sound is jar, either of air or of something else;
a fact which you can easily prove for yourselves by striking a bell,
and then touching a finger nail to the vibrating edge. Naturally we
hear best with ears; but lacking these, any part of the body will
make shift that can feel jars.




XXX

Ants’ Noses


Ants see, then, and hear. But their hearing is not at all good;
while they do most of their work in pitch darkness underground,
where they can not possibly see anything anyway. So they depend on
touch, and still more on smell. Smell, therefore, is their chief
sense, as sight is ours. So much thinking as they do, they do
largely with their “smell center.”

We in a strange country, find our way back home by remembering what
we saw on the way out. An ant gets home by following the smell of
its outward trail. We recognize our friends by sight, and know them
by the way they look. An ant recognizes its friends by touching them
with its feelers, as no doubt you have often seen ants do, and so
getting the familiar odor, smelling out each other’s claims to
acquaintance.

For the feelers or antennae are the ant’s nose. It feels with them,
and it also smells. As you can discover by looking at any ant, the
antenna is like some whips which have a stiff handle and a long
flexible lash fastened to its end. The handle sticks out sidewise,
and the lash is jointed so that it can be moved about freely.

Our common brown ant has eleven joints in its whip-lash. With the
joint at the tip it smells its nest. With the tenth joint it gets
the general odor of the colony to which it belongs. With the ninth,
it follows the scent of its own track. With the eighth and seventh,
it recognizes the helpless young which are its care. By means of the
sixth and fifth, it knows its enemies, the inhabitants of other ant
cities with which it is at war. What the remaining four joints next
the handle are for, is by no means clear.

An ant, therefore, which has had the outermost joint of its feelers
cut off, or has lost them in battle, does not know its own nest. One
that has lost the two outermost, does not recognize its fellows when
it meets them away from home. One that has lost the outermost three
joints, can not smell its own track and so can no longer find its
way home. If the seventh and eighth joints are gone, the ant no
longer has the slightest interest in the eggs and the helpless
young, which before the mutilation it would have fought to the death
to defend. Apparently, it no longer knows what they are; like the
men who wake up some morning with a little blood clot on the surface
of their brains over their left ears, who can see words but not read
them, and don’t know what their wives and children are. On the other
hand, ants from different nests, which have lost the whole of their
antennae down to the fourth joint, live together in perfect peace
and harmony. But ants from different nests, deprived of their
antennae only as far as the sixth joint, straightway start to
fighting like cats and dogs; and never leave off till they are all
killed or disabled.

Apparently then, the ant has enemy-smelling spots, and egg-smelling
spots, and track-smelling spots, and friend-smelling spots, and
nest-smelling spots, strung along in order on the lash-like part of
its feelers; so that when one of these sets of spots goes, that
particular sort of smell goes with it.

The ant, I say, depends greatly on smell. Probably it never knows
any of its fellows, or any of its young, separately as individuals.
It only knows that they have a certain familiar smell. At any rate,
ants taken from a nest, soaked in water with ants from another nest,
till they have taken on the foreign odor, and then returned to their
own nest, are promptly set upon and killed as if they were invaders.
But ants soaked in water with members of the colony, so that they
have the proper colonial smell, are received as brothers.

Each sort of ant has its own peculiar odor, so different from that
of other sorts that even the blunt human nose can tell them apart.
Each nest of ants, too, has a slightly different smell from that of
other nests of the same sort, so that each ant knows its own, tho
the differences are too small for us to detect. All the ants of a
colony are the children of the single queen, who lays all the eggs
for the entire ant city. All the ants of a hill, therefore, instead
of looking like their mother, smell like her. Each ant, then,
recognizes its own brothers and sisters, its mother, its mother’s
sisters, and the children of its mother’s sisters, who are its
cousins. All these have the familiar smell, and the ant treats them
as friends.

Ants from a related nest whose smell is nearly right, but not quite,
are received with suspicion, and not allowed to take any part in the
care of the young. Those whose odor is still less familiar are
dragged about and roughly handled, but allowed to live. But those
whose odor is entirely strange are promptly lynched, and their
bodies dragged away to the waste heap.

The odor of the queen ant remains the same thruout life.
Consequently, any ant will always recognize its own mother. But the
odor of the worker ants changes with age. An ant, brought up in a
nest, learns the queen odor, and the general nest odor, and the odor
of workers of its own age, and of all younger than itself, and of
all older than itself to which it is accustomed. But a young ant
taken away from its nest, and kept away for two months, will find
that its older sisters have meanwhile taken on a new smell. It
treats them therefore as enemies. Yet an ant, once familiar with the
odor belonging to any age, will remember it for at least two years.

There are some other peculiar results of the ant’s reliance on its
smell. Occasionally, in the fields and woods, one finds what are
called mixed nests of ants. Two different sorts of ants, which
ordinarily are mortal enemies, springing upon one another and
fighting to the death on sight, are found living together in
harmony, caring for each other’s young, and in all respects behaving
as if they were all of the same sort.

The way these arise is this: Two young queens, of different kinds,
starting their new colonies, happen to settle so near together that
the young workers mix with one another as soon as they are hatched
out. From their infancy, therefore, each sort knows the smell of the
other; and being used to it, thinks it quite the right and proper
thing. So the ants grow up together, while the odors change so
slowly with age that they never seem strange. Indeed, such nests
have been made in this way by students of the ways of ants, with as
many as ten different sorts in them, all living peacefully together.

When, however, such a nest is separated, and the two sorts of ants
kept apart for a few months, the mixed nest cannot be reformed. Each
sort of worker ant will recognize and care for the queen of the
other sort, and all young of the other sort of all ages up to the
time when the nest was split up. These the ant remembers. But all
workers older than this have, of course, taken on an unfamiliar
smell. The old friends have become enemies, to be slain on sight. So
each sort of ant befriends the young of the other, whose smell it
recalls, tho it has never known the individuals; while it fights to
the death its former friends of its own age, with whom it has been
working side by side, but whose odor has become strange.

Evidently then, an ant has no instinctive liking for any particular
smell. It simply has to learn a set of smells, and what they mean,
just as we have to learn our lessons. I think you will agree that
for ants living under ground, smell is on the whole the best sense
to tie to and do one’s thinking with. But for us, living upstairs in
the sunlight, sight is, I am sure, very much the most useful of all
the senses.




XXXI

Some Other Eyes and Ears


The rest of the insects are, in general, much like the ants. They
have their feelers or antennae, growing out in front of the head,
with which they both feel and smell. Most of them seem to taste
their food in their mouths. Nearly all have eyes.

As for ears, a good many insects, apparently, hear as the ants do,
without any regular ears, and just by feeling the shake of what they
happen to stand on. At least, nothing is known about their having
any regular ears; though it is quite possible that some of them hear
through their wings. Certainly, a tight hard wing, like a house
fly’s, when one wasn’t using it for flying, ought to make a very
decent sort of ear, one would think.

Grasshoppers and the like have proper ears. Though instead of being
where we have ours, on the sides of our heads, Grasshopper Gray
carries his ears on his hind legs, on the side of his great jumping
thighs; while the ear itself, instead of looking like a human ear,
is like a tiny drum—a tight thin head with a hollow underneath. Some
other insects have their ears on the side of their bodies, about the
middle. You can see these things for yourselves; they are not hard
to find.

[Illustration: Ear of a mole cricket on the front leg.]

Some of the jelly-fishes have ears, not at all good ones, but still
ears. Some also have eyes, not so good even as the ears, and not
good for much anyway. But the same kind of jelly-fish doesn’t have
both ears and eyes; whichever he gets, he goes without the other,
having apparently not sense enough to manage both. As for the
sea-cucumbers, they sometimes have more than fifty ears apiece, none
of them good for much.

Most all of these simpler sorts of ear are much like tiny rattles.
There is a hollow ball lined with nerves. Inside the ball is a small
hard ear-stone, or a number of smaller grains of ear-sand. When a
sound comes along, (for a sound is nothing but jar), it shakes the
rattle, so that the little stone inside bangs against the nerves.
Then the animal hears. In the cod fish these ear-stones are
unusually large, as large as the end of one’s thumb; children
sometimes call them lucky-bones, and use them for playings. We also
have these little rattles, two in each ear, with ear-sand. But
these, which are all there is to the ears of lowly creatures, are
only a small part of our hearing machinery.

[Illustration: Back of the frog’s eyes are the ear drums.]

You will find the ears of lobsters and crayfish, which are little
fresh water lobsters, just at the point where the smaller feelers,
which are double at the end, join the body. These, too, are merely
ordinary ear-rattles; you can make out the opening on the upper side
of the feeler. Of course, you know the ears of the frog—the big
spots on the side of the head, back of the eyes. These spots are the
drums of the ears; the real ear, much like our own, is inside. We
have such a drum, only it is at the inner end of the hole into the
ear, where it is much safer than it would be outside.

[Illustration: A newt.]

The fish’s ear you cannot find. That is inside; and the fish hears
through the bones of his head, just as we do when we hold a stick in
our teeth and tap the end, while we keep our ears stopped with our
fingers. But the long dark stripe which you see on many sorts of
fish, running from the place where the neck would be if fishes had
one, the whole length of the body to the tail, and also forward
across the head and around the eye, only you can’t make it out so
well there, this also is a sort of ear. In fact, the ear itself is
really a part of this “lateral line” very much improved—so much
improved that we human beings and the four-footed beasts and the
birds haven’t found it worth while to keep the lateral line at all.
But the newts and salamanders still have it.

As for eyes, of these also there are all sorts. The star-fish has
five, one at the end of each of its five arms, a tiny black dot. The
jelly-fishes, some of the commoner sorts at least, have their eyes,
such as they are, where the long tentacles join the center of the
bell underneath. Some of the worms have several hundred eyes; some
have a pair of eyes on each of the dozen or twenty joints of the
body. The leeches, the common blood-suckers which get on our legs
when we go swimming, have ten pairs of eyes, all on the front end.

Oysters, clams, and other “bivalves” have their eyes along the edge
of the shell. Many of the snails have them on stalks, which they can
pull back into the head or push out. The snail in Mother Goose, that

  “...put out her horns
  Like a little Kylo cow”

and frightened the four-and-twenty tailors, was really only putting
out her eyes to see these valiant heroes. Some of the shell-less
snails, or slugs, besides the eyes on the ends of their horns, have
a lot more, occasionally nearly a hundred, sprinkled over the back.

Such eyes, however, are really not good for much. They serve to tell
light from darkness. They let the creature know when a shadow falls
on him—which is usually the shadow of something on the point of
eating him up, so he gets warning and bolts. We ourselves can do as
much with our eyes shut tight; and that’s about all most eyes will
do wide open. There are not many really good eyes, till you get the
single pair of the animals with back bones.

[Illustration: The Star-fish Has Eyes on His Arms; The Slug Also Has
Eyes on His Horns; The Snail Has Eyes on His Two Longer Horns]

Still there is one very fair sort of eye, though not nearly so good
as ours, and that is the strange compound eye of the insects.

In general, the insects have either one, two, or three little eyes,
at the front of their heads, which they use, probably, for seeing
things close to them. Besides these, they have their two great
compound eyes, often many times larger than all the rest of the
head. The two together usually make almost a ball, and with them the
bee or wasp or moth or dragon-fly sees clear round the horizon,
above him and below him, all at once, and all equally well.

You know if you take a roll of paper, and look through it as if it
were a telescope, you see a small bright spot at the end. If you had
two such rolls, and could look through them both at once, you would
see two such spots. If you had a thousand or more such paper tubes,
and could look through all these at once, you would have something
very like the compound eye of an insect.

Our eyes, as you know, are cameras. They form real pictures at the
back, on the retina. But these compound eyes are not cameras, and
they do not form any pictures anywhere. Instead, the insect looks
out through one eye tube, and sees one spot of color; and through
another, and sees another spot; and through a third, and sees
another. Looking through some hundreds all at once, he sees a
corresponding number of hundreds of spots.

But even ten thousand such spots would make no such sharp picture as
we see in the small center of our field of vision where we see most
clearly. Flies and ants and bugs and grasshoppers see only as we see
things far round at the sides of our heads. They can see much
farther round than we can; but they can’t see nearly so well
anywhere.

So a fly never could see to read, even if he could ever learn. The
page of letters and the white paper would simply mix to a gray blur.
A fly cannot get through a netting with a half inch mesh, unless
there is a light behind it. Altho the holes are many times larger
than his body, he cannot tell hole from string well enough to fly
through. If you try to put your whole hand on a fly, or hit him with
one finger, you cannot do it. He sees something dark coming, and
stands from under. But you can often get him by bringing down the
whole hand slowly; and then, just as he is about to take flight,
dropping one finger on his back. He can see the whole hand against
the wall of the room; but he cannot see clearly one finger against
the others.

So on the whole, the fly does not really see much with his little
eye; in fact, taking, one thing with another, we boys and girls and
men and women probably see more distinctly, and make more use of our
eyesight, than any other creature that breathes.




XXXII

Having Senses and Using Them


All animals feel. So, too, do all plants. At least, all animals and
plants sometimes move when they are touched. So they must feel.
Whether they know that they feel or not, is another matter. Most
likely, all plants and all the lowest animals, feel as we feel in
our sleep, when we get tired of one position and turn over, or feel
cold and pull up the bed clothes, without knowing at all what we are
about. Somebody has said that the mind “sleeps in plants, dreams in
animals, and wakes in man,” and that is really just about the state
of affairs.

All animals except the very lowest also taste and smell. At least
they choose their food, as they couldn’t very well do if they did
not smell or taste it. Tho when you come to think of it, for an
animal living in the water, taste and smell are all the same thing.
The food is in the water, the creature’s mouth is full of water, and
its nose (if it happens to have one, as most water creatures do not)
is full of water also. So it doesn’t make much difference whether
you say that the creature tastes the water or smells it.

Most animals have eyes and can see. Not a few also, which have not
eyes, can still tell light from darkness. The earthworm, for
example, has no eyes at all, yet it always avoids bright light, and
keeps in its burrow when the sun is out. Neither has it ears, yet
when it is part way out of its hole, it will at once pull back again
when certain notes are sounded near it on a piano.

We might almost say that every bit of the life-jelly of which all
living things are made has itself all the five senses. All of it
seems to feel, and all in some faint way to see and hear, taste and
smell, move and remember. Besides this, the life-jelly makes itself
all sorts of eyes and ears, all sorts of mouths and noses, all sorts
of muscles and brains, in order that it may see and hear, smell and
taste, feel and move and remember better than it could do without
them.

But all this time that we have been thinking about ants, and
star-fish, and earthworms, we have been neglecting the creatures
which we really care most about, and certainly know best, the cats
and dogs and horses and rabbits and various pets of all sorts which
we know by name, and which in return we believe are fond of us.
These animals, the four-footed creatures with fur, and the birds,
are of all living things most like ourselves. They are most like us
in body, they are like us also in mind; and they have the same
senses that we have—five, seven, ten, a dozen or more, according as
we choose to count them.

They have, I say, the same senses that we have; but they use them
differently. Nothing, I think, is more striking about dogs, for
example, than the small use they make of their eyes. Often, indeed,
they seem half blind; they fail to recognize their own masters ten
yards away; get separated from them, and run round frantically,
smelling of everything in range; while all the while, the master can
see the dog perfectly well, and pick him out at a glance from a
dozen others. One would think that the dog would simply look round,
see his master, and join him.

I don’t think that they really are half blind. They probably can see
nearly as well as we. They simply don’t use their eyes, and depend
instead on their noses. Sight is the most important sense for us, as
it seems to be for the birds. But the beasts seem to depend most on
smell.

The tales we read about the scent of dogs, and especially of
bloodhounds, are often almost beyond belief. The bloodhounds, I
understand, are so-called, not because they are especially fierce,
in fact they seem to be on the whole a rather gentle sort of dog, as
dogs go, but because they are supposed to smell one’s blood, and to
be able to follow the smell almost anywhere. I suppose they really
do smell the perspiration; but they do it thru the sole of a heavy
boot, when one has simply walked along over the ground; and they
follow that inconceivably faint odor, hours after, and pick it out
from all other smells, even those of other people cutting across the
track.

Yet I sometimes think we make out the dog’s sense of smell to be
more wonderful than it is. The same dog that tracks footprints so
marvelously will nose round in all sorts of dirt as if he had no
sense of smell at all, and eat things that we would not have in the
house.

We also can do a little smelling. Anybody can smell the vapor of
bromin in the air when there is one part in two hundred thousand.
Hydrogen sulphid, which is the gas that makes the smell of rotten
eggs, will scent up 1,700,000 times its bulk of air. The least
little grain of musk will scent a room; as little as the fifty
thousand millionth of an ounce can be smelled by a good nose. Tea
and wine tasters (who of course are really tea and wine smellers)
can pick out the place where grapes or leaves grew, and the season
of the year. Wine tasters can tell one year’s vintage from another,
and distinguish between the top and the bottom of a single bottle.

No dog, probably, can smell anything like such small quantities of
these substances, or detect such minute differences. We smell musk
and wine and tea; he smells footprints. One can’t say that either
has a better nose than the other. Really, a good deal of the
difference between us and the animals is that we depend on sight and
hearing, because we can use these two senses to handle words. We can
see words, and we can hear words; we cannot taste or smell them. So
we get to relying on eyes and ears. But the animals, which don’t use
words anyway, they think more about smells.

There is still another way in which we are apt, I think, to
overestimate the senses of animals. We know, for example, that a
horse will find his way home on a dark night, when everything is
pitch black, and the driver cannot see his hand before his face. We
say that the horse must have wonderful sight to make out his way
under such conditions.

The real fact is, however, that the horse goes straight home thru
darkness and storm, not because his eyesight is good, but because it
is poor. He is at home in the night, because he does not see
especially well by day. Those of you who have read _The Last Days of
Pompeii_ (as everybody should, for it is a famous old story) will
remember that when, during the eruption of Vesuvius, the city was
darkened under the shower of ashes, so that the inhabitants wandered
about in the streets completely lost and quite unable to find their
way out, the blind girl was able to lead her friends straight to
safety. She had always lived in the dark, and could find her way as
well one time as another.

So it is with horses and other animals. They seem to see in the
dark, when they really hear and smell. A horse especially depends
for finding his way, on his muscular sense. While his driver is
noticing houses and trees and sign-boards, the horse is noticing so
long a pull up one hill, so much holding back down another, so much
level stretch between. The man is lost when he cannot see his houses
and sign-boards; but the horse’s hills and levels are still there.

You remember the rats that, when the passage in their maze was
shortened, kept running full tilt against the end wall; and then
when the passage was lengthened, kept turning too soon and butting
into the side wall. The rats were depending on their muscular sense.
They remembered their way as so long a straight run, then a turn.
They could run as fast by night as by day, because they didn’t do
much seeing either time.

We also depend on our muscular sense far more than we commonly
realize. Doubtless we all know how to button our coats. But how do
we know? We certainly do not know how it tastes, smells or sounds. I
don’t think we often remember how it looks. What we do remember is
the feeling of the buttons and the movements we make. But if we try
buttoning with the other hand, or put on a coat that buttons on the
other side, we feel as awkward as can be. We can see as well as
before; the touch has not changed; there never was any taste,
hearing, or smell. The difference is in the movements. The muscular
sense is learning something new.

How hard it is to bat on the other side, to use any tool the other
way round, or make any change which is strange to the muscular
sense. That shows how much we all rely on it. If we play the piano,
and remember pieces without the notes, it is by this muscular sense
that we do it. Our fingers seem to know the tune; and in a sense,
they really do. Surely, if a musician can find his way back and
forth over the keyboard thru a long piece of music, by means of his
muscular sense, it is not so remarkable that a horse should find its
way home over the road, or a rat scamper thru its holes, guided by
the same means. They don’t really see in the dark, they simply turn
on another sense. We have it also; but mostly we trust to our eyes,
instead.

There is another sense, too, on which animals are more given to
depending than we are, and that is the sense of equilibrium and
direction, which, as I have explained, has its seat in a part of the
inner ear. You know the game where you are blindfolded, turn around
three times, and then try to blow out a candle. If your
direction-sense is at fault, as it generally is, you turn too far or
not far enough, blow where the candle isn’t, and make everybody
laugh. Men who have to find their way about over a wild country,
explorers and the like, sometimes have this direction sense trained
to a wonderful degree. They simply cannot get lost anywhere. The
rest of us, who depend on street numbers and the sign-boards on the
lamp posts, don’t have much use for this sense, and so never really
learn to use it. Many animals depend on it a good deal. They find
their way home in truly marvelous ways; and we say it is “instinct.”
It really isn’t instinct, but just plain sight, hearing, smell, and
direction sense. Men who have practiced their direction sense can
find their way quite as well.

So in general, the animals haven’t different senses from ours, nor
on the whole better ones. But they use them differently; and
cultivate some senses which we let go to waste. For the most part,
the animals depend on smell far more than we. Smell is apt to be
their principal sense, as sight is ours. Because they don’t use
their eyes as much as we do, they notice and remember more of what
they learn thru their sense of direction and their muscular sense.
But a man who tries hard can usually beat any animal at his own
game.

The fact is, I suppose, that we, men and beasts and birds alike,
have all the senses there are, all that any sort of creature could
have anyway. Then each, according to his nature and habits, uses one
more than the rest, to think and remember with.




XXXIII

Seeing In The Mind’s Eye


Not all us human beings use our eyes, ears, and noses in the same
way, as a simple experiment will show.

Shut your eyes and think of the name of some familiar thing, like

  BREAKFAST TABLE.

What did you see in your mind’s eye? Some people see that breakfast
table just as clearly as if they were in the dining room with the
table itself before them. They see the cloth and the plates and the
food, the people at their places, the walls of the room, the
furniture, all just as sharp and bright and natural as if they were
looking at the things themselves. Others, more commonly, see the
room and table dimly. They do indeed have an inner picture, but it
is more like the picture one gets of things far round at the side of
the head, out of the corner of the eye. They have a general
impression, right as far as it goes; but they can’t see the patterns
on the plates, nor the position of each fork and spoon. Still other
persons, though there are not many of these, and children are almost
never this way, cannot see any mental picture at all. They have no
mind’s eye. They cannot see anything unless it is actually there.

People who can make such inner pictures are said to be eye-minded.
Children are especially this way. Sometimes, indeed, they have
difficulty in telling the difference between what they actually see,
and what they dream or imagine. Then sometimes, they get punished
for telling fibs.

Some people have this gift for making mental pictures to an
extraordinary degree. If they have a lesson to learn, they see the
page of the book before their inner eyes, and simply read off what
it says. I knew of a type-setter in a printing office, who was a
crack speller. He could spell anything. Give him a hard word, and he
simply saw in his mind’s eye his composing stick with the word set
up in type in it, upside down and backwards, as type is set by hand.
Then he simply read off the letters, and always got it right.

Some musicians, as I have explained, remember their pieces as if in
their fingers; but some see the inner picture of the notes, and read
them off as if from a real score. There is a story of a public
speaker, who in the midst of his speech stopped, hesitated, went
back and said something different. He explained afterwards, that
while he never read his speeches from a real manuscript, he did
always read them from an imaginary one which he saw before his
mind’s eye. This time, the manuscript that wasn’t there had some
words written in between the lines, so that he could not read them
easily.

Possibly you have heard of the truly wonderful performances of some
champion chess players. Chess is played on a board like checkers,
only it is a vastly more complicated game, with six different sorts
of “men” all moved in different ways. Nevertheless, many players can
play about as well when they do not see the board at all, as when
they do. They make a mental picture of the board, sit blindfolded,
and as the game goes on, they keep track of every move, as they are
told what it is, by altering their inner picture. Some of the best
chess players have played ten, fifteen, and even twenty different
games, all at the same time, blindfolded, and won them all against
as many separate players, each playing one game and looking at the
board. Such a champion player has to carry in his head the picture
of ten, fifteen, or twenty different boards, each with sixteen men,
scattered about over sixty-four squares, and all continually
changing. Yet they do this without ever making a mistake; just by
these inner pictures in the mind’s eye.

Some eye-minded people can see a picture on a blank sheet of paper
so clearly that they can mark over it with a pencil, and in this way
make most accurate and effective drawings. Some can picture to
themselves all four sides of a room at once, and imagine what is
behind them as easily as what is in front. Some do not even hear
directly what is said to them; but as each word is uttered, see the
same word printed before their mind’s eye, and then read it off.
There are those who say that they cannot wake up in the night and
think of the bright sun, without having their eyes dazzled!

Now it is a great advantage to be eye-minded. There is no easier way
of learning one’s lessons than by seeing books and maps and charts
and diagrams, whenever you want them, right in front of your eyes,
so that all you have to do is to look and see. The difference
between boys and girls who get their lessons almost without effort,
and those who get them only with the greatest labor, and then
promptly forget them again, is often in just this power of making
mental pictures. Some people can remember a page so clearly that
they can actually read off the first or last words of each line, or
read the printing backwards. Naturally, lessons come pretty easy to
such lucky people.

Then too, to be eye-minded is a great source of happiness. One sees
in the course of his lifetime, all sorts of beautiful and
interesting things. If he can, whenever he wishes, recall these as
mental pictures, almost as vivid as the reality, it is like seeing
the reality all over again. He always has with him a collection of
pictures, which though he cannot show to another, he can at any time
enjoy for himself.

The eye-minded person, moreover, has still another string to his
bow. Not only can he recall what he has seen; he can also imagine
things which he has not seen, and so tell in advance how they are
going to look. The engineer about to build a bridge, the architect
planning a house, the housekeeper deciding how she shall arrange a
room or set a table, the girl considering a new dress, the boy
laying out a ball field, all can work to vastly better advantage if
they can see exactly how everything is going to look, before they do
anything. It is a great deal easier to change things in one’s mind,
than after they get into wood and iron and cloth. No one can
possibly succeed as engineer, architect, designer, dress-maker,
milliner, and the like, unless he can make these pictures in his
mind’s eye, and see how things are going to be, before he wastes
time and material on the reality, Fortunately, this eye-mindedness
is easily cultivated. One has only to attend to his mental pictures,
and try to see all there is in them, to have them grow sharper and
more complete. In fact, children usually have so much of this
faculty that if they only kept what they have, instead of letting it
waste away from lack of use, they would be far better off when they
grew up than most grown-ups are. As we get older, we get to thinking
more in words, and we lose the knack of making pictures. All is, we
simply mustn’t.




XXXIV

Ear Minds and Others


Some persons are ear-minded. If you say to them

  BREAKFAST TABLE.

they don’t see any breakfast table at all. Instead they hear in
their mind’s ear the sound of dishes, the murmur of conversation,
and the clatter of knives and forks. When they have learned their
lessons, and stand up to recite, they hear an inner voice telling
them what to say. They cannot easily remember how places look on the
map; but they remember the songs of birds, the different whistles
and bells of their neighborhood, they like lectures and readings,
and when they have heard a tune once, they know it again. Such
people may find it hard to learn to read a foreign language, but
they make it up by learning easily to understand it when spoken.

Musicians are apt to be ear-minded. Mozart, for example, could
listen to a long piece of music, then go home and hear it over again
as many times as he liked in his mind’s ear, and so write it down at
his leisure. Beethoven, after he became stone deaf, used still to
write his magnificent symphonies, that took hours to perform, making
them up in his head and hearing them in his soul’s ear—violins, and
trumpets and cymbals and drums, each in its proper place, long after
his bodily ears had ceased to hear any noise.

Not many people are ear-minded; not nearly so many are as
eye-minded. Those that are, can always hear sweet music and pleasant
sounds, whenever they will, and recall the words and voices of their
friends. Surely there is much happiness in being ear-minded.
Whatever ear-mindedness one has, is well worth hanging on to and
improving.

More people are muscle-minded. Think of a

  BALL.

Do you see the ball in your mind’s eye? or do you hear the word ball
in your mind’s ear? or do you feel the ball in your fingers, and the
pull of your muscles as you throw? If the last, you are muscle, or
motor-minded, and you probably found yourself saying to yourself the
word ball.

Motor-mindedness, too, is a great convenience. It helps to make
games come easy, and dancing, and all sorts of gymnastics; it makes
it easy to carry oneself properly, to use tools, to be skillful with
one’s fingers, to play musical instruments. Motor-minded people are
apt to talk easily, and to learn readily to speak foreign languages.
Anything, in short, comes easy to them which involves doing
something.

Nearly all blind people are motor-minded. If they are also deaf,
then of course, they have to be so. I have seen a blind man get off
a street car, turn into his street, walk down the street as far as
his own gate, and there turn in without the least pause or
hesitation, any more than as if he could see. He couldn’t see. He
simply felt that he had walked just far enough. And he had.

Do you want to know which of the three possible sorts of minds your
mind happens to be? Then think of the street number of your house,
or the year in which Columbus discovered America. Did you look for
the figures, or listen for them, of try to say them to yourself? Did
you see 1492 printed out somewhere, or did you hear something say
it; or did you feel yourself saying it in your throat? In the first
case you are eye-minded; in the second, ear-minded; in the third,
motor-minded.

Most persons are mixed-minded. They have one principal sense, with
which they do most of their thinking; but where that is not
convenient to use, they employ another. Occasionally even, they use
the third. I am myself motor-minded. To learn anything, I say the
words over to myself. If anybody tells me anything, I cannot
remember it, unless I first say it over; and whenever I think of
anything, I say words about it to myself. I can Recognize tunes when
I hear them, but I cannot recall a tune, unless I fit it to some
words or sounds and think of myself as singing it. But I can think
of how things look, or imagine how things will look, much more
easily than I can think about how they sound; and I can, with some
effort, think how things look without starting to say anything about
them to myself in words. So I am also somewhat eye-minded.

Most of you will probably find yourselves, first eye-minded, then
motor-minded. That is, on the Whole, the most useful arrangement.
But the best sort of mind is one that can handle all three kinds of
ideas; and think about seeing, hearing, and doing all about equally
well. So you had better notice which you can’t do, and set about
learning to do it.




XXXV

Living Automobiles


If you will think back over what you have already learned in this
book, you will see that we began by finding out something about how
we men, the animals, and the plants come to have any such things as
bodies at all. We learned how the little chick forms inside the egg,
and the little plant inside the seed. We learned, too, about the
wonderful life-jelly or protoplasm of which all living things are
made; how it shapes itself into cells; how it builds these cells
into our various members, eyes and bones and hair and muscles; and
how the body changes, as we grow from youth to maturity, and from
maturity to old age.

Then, after we had learned something about this body of ours, we
turned to consider how we use it. We found about something of what
animals cannot do, and what they can do, and how they do it. We
learned how animals of various sorts, and plants as well, see and
feel and act; and we learned also something about how we ourselves
do our thinking, which is so very different, and so very much better
done, than that of any animal or plant.

Now we turn to a different matter. We have taken up being, and
doing, and thinking. Now we shall consider living. We shall learn
about how the body of the plant or animal feeds itself and keeps
alive, and how the different parts of it, the bones and skin and
leaves and bark, manage to get on with one another, and work
together like a well-made machine.

For, of course, the body is a machine. It is a vastly complex
machine, many, many times more complicated than any machine ever
made by hands; but still after all a machine. It has been likened to
a steam engine. But that was before we knew as much about the way it
works as we know now. It really is a gas engine; like the engine of
an automobile, a motorboat, or an airplane.

I don’t suppose that any boy, at least, needs to be told the
difference between a gas engine and a steam engine. In the one, we
build a fire under the boiler, and turn water to steam. Then the
steam goes thru a pipe to the cylinder, where it pushes the piston
back and forth, first on one side, then on the other, and so turns
the wheels.

In the gas engine, on the other hand, there is no boiler, no steam,
and no fire. A mixture of air and gasolene vapor flows into the
cylinder, cold. There it explodes, set off by an electric spark, and
the push of that explosion moves the piston and makes the wheels go
round.

We, I say, are not steam engines. We have neither boiler nor steam
nor fire. But each little working cell is like a little cylinder,
which takes up from the blood air and food, mixes them together
inside itself, waits with everything ready to go off, gets the
proper signal thru a nerve, then explodes and does something.

That’s the way a muscle does its work. It is a many-thousand-cylindered
engine. Each little fiber of the muscle is a cylinder; and each time you
lift your hand or move your foot there is a perfect battery of minute
explosions. You cannot hear them, for there is no pop—the muffling is
vastly better than any engine-builder ever devised. But you do feel the
heat; and if you move fast and hard enough, you have to stop to cool off
and get a drink.

The plants also are many-cylindered gas engines. They do not do so
much work as animals do, not so much running round and moving
things. But they do move, and certainly grow and lift themselves
high in the air. This much work they do by exploding their cells,
just as animals or automobiles do theirs. The growing plants take
their food out of the air thru their leaves; and they take also the
air itself in the same way. They mix these together inside their
cells; and when there is work to be done, growing, moving, or any
other sort, they explode a little of the mixture and do it.

[Illustration: The leaves take in air through breathing holes.]

Don’t think then that animals and plants and human beings are merely
like automobiles. They are automobiles. Their fuel is their food.
They mix it with air. They explode the mixture, and move. Anything
that does that is an automobile, and runs with a gas engine.




XXXVI

Air and Fuel


We are, then, gas engines. So we have to have air to mix with our
gasoline. The simpler water animals, such as sponges, which are
mostly holes, and all minute creatures, both animals and plants,
simply take it in directly into their cells where they are going to
use it. There is plenty of air in water—you can see it fizzle out
from the water in a drinking glass when you draw water from a faucet
in cold weather. The water creatures breathe this out of the water,
and die of suffocation if you put them in boiled water from which
the boiling has driven out the air.

Most animals which have blood, use this to carry the air to their
cells. For blood, whatever else it is, is nine-tenths water, and
will dissolve air like any other water. The insects, however, though
they have blood, do not use it to carry air. Instead, they have a
system of branching pipes running all over their bodies, and opening
at various points on the surface. You can often make these out
easily, a pair of openings for each joint, on the sides of
caterpillar’s body. These pipes carry the air everywhere over the
insect’s body, even to the feet, so that wherever there is a working
muscle, there also is the air for it to work with. Thus the insect
has no need of lungs, and has none; and therefore, I suppose never
gets out of breath, no matter how hard it works.

[Illustration: In place of lungs, insects have breathing holes like
a leaf.]

We human beings, and our four-footed cousins, all backboned animals
in fact, do not manage in any of these ways. We breathe the air into
our lungs. There, instead of dissolving it in the watery part of the
blood, we turn it over to the red corpuscles, which are especially
made to do this very thing and do it particularly well. These
minute, coin-like corpuscles carry the air all over the body, and
deliver it over to the cells as they need it. But of course, as you
must have already learned in school, the body handles only the part
of the air that it can use, the oxygen. The rest it lets go and
doesn’t bother with. That is where we have the advantage over other
automobiles, which can’t pick out the part they want but have to
take the air as it comes. Still it all comes to the same thing in
the end. With all animals the oxygen gets mixed with the fuel and
explodes.

Our fuel, moreover, is a good deal like gasoline. Gasoline, as you
know, is related to kerosene, benzine, paraffine, and the rest,
which are all products of rock oil. They are, then, themselves oils;
and gasoline is an oil.

We, too, eat oils; not, to be sure, mineral oils, but animal and
vegetable oils, olive oil and butter and cream and all sorts of
fats; for fats are merely oils that freeze at common living
temperatures and melt only after we get them stowed away.

We, then, burn many sorts of oil. We also burn bread and potatoes
and the like, starch and sugar and gums, which though not oils, are
much like them; really in a way, oils that are already about half
burned. These we finish up in our engines. On the whole, it’s much
more convenient than depending on one sort of fuel, and exploding
only gasoline.

I am not going to stop now to tell you the long story of how the
bread and potatoes and the rest of our food finally gets changed
over into a sort of sugar; and is as sugar, packed away in the cells
of our muscles and other tissues, mixed with the oxygen of the air,
and made ready to explode when the signal through the nerve touches
it off. The food is taken apart and put together again, combined and
separated, stored up when it isn’t needed, and used sometimes in one
way and sometimes in another. Different animals treat their food
differently after they get it swallowed; even different human
beings, eating the same food, do not always handle it quite the same
way.

Most of us take our food into our stomachs, but the earthworm crawls
through the earth, and at the same time lets a stream of earth crawl
through him, digesting what is food and leaving the rest behind as
he moves along. Amoebas sometimes flow round little water plants
many times longer than themselves, crawl along the stem, with the
stem sticking out front and back, and digest the juices as they go
along. The star-fish, which lives on oysters larger than himself,
turns his stomach inside out, sticks it into the oyster’s shell; and
after he has digested the oyster, pulls his stomach back again. A
dog will digest bones; and a cow will digest wood; while a fish will
swallow another fish nearly as long as himself, keep the tail, still
unswallowed, in his mouth while he digests off the head, and than
moves his meal up another notch.

There are all sorts of queer freaks, but the main point is that, in
the end, all our food gets built into the cells of our bodies; much
of it in the form of sugar, and that this sugar explodes as if it
were the gasoline vapor in a gas engine that some man has made. With
the force of these explosions, the body does its work; it keeps
itself warm with the waste heat.




XXXVII

Men In Glass Boxes


One curious thing about these explosion engines of ours is that,
when all goes well with our little insides, we get just exactly the
same amount of work out of each mouthful of our food, that we should
get, if we should dry the food, grind it to fine dust, and explode
the dust mixed with air in the cylinder of an automobile—as it would
be quite possible to do, if one wanted to take the trouble.

In fact, the United States Government, for several years, set people
to trying just this very thing, by way of finding out how much work
can be got out of various sorts of food, and out of which sorts a
man can get most for his money. They have a big glass box, as large
as a state-room on a steamer, with a bed in it and a table and
chairs, and also a stationary bicycle, on which one can ride without
moving, and so get his exercise. They put a man in this box, and
keep him there for a week. They weight carefully everything that he
eats and drinks; and each time he takes a meal they find out, by
drying some of the food and burning it and measuring the heat they
get from the burning, just how much that food is worth as fuel. Thus
they know how much exploding he ought to be able to do in his tiny
cylinders.

Then in addition, they keep track of all the air that goes into the
glass box, and find out just how much oxygen he uses up to explode
the food. They see also how much he heats up the air which comes out
of the box by the warmth of his breath, the heat of his body, and
the friction of the stationary bicycle when he exercises.

It always turns out that the man makes just as much heat out of the
food he eats as the same food would yield if dried and burned; and
that it takes just as much air to explode it in his body as it would
take to burn it in a stove. So the body is really an engine. It uses
up fuel like any engine; and gets the same amount of heat or work
out of its fuel as any other well-made engine would.

As a result of these experiments, and others like them, the United
States Department of Agriculture has issued a pamphlet, called
Bulletin Number 28, which tells, among other things, how much work
one ought to be able to do on one pound of almost any sort of food
that any civilized human being would ever think of eating. I trust
that every girl who reads this book, before she grows up, and goes
to keeping house, and has to feed a family, will get this little
pamphlet, or something else like it, and study carefully what
different foods are really good for. According to the United States
Government, a child can do more hard playing, and a man more hard
work, on one pound of bread, spread with four ounces of butter, than
eight pounds of broiled spring chicken; while ordinary dry crackers
and cookies are twice as nutritious as lean meat, and six times more
nutritious than oysters, lobster, and most sorts of fish.

Still, there is this most important difference between our living
engines and the engines which we build of brass and steel. When a
part wears out or breaks in an automobile, if it cannot be mended,
it has to be thrown away. But in the body, when a part of the
life-jelly wears out, as it is continually doing, we not only make
some new to take its place, but we use up the old stuff as fuel to
drive the engine.

In short then, some automobiles are built of steel and leather and
brass and rubber, and burn gasoline. And some are built of
life-jelly and burn sugar. The first sort, when it wears out, we
mend with more steel and leather and brass and rubber. The second
sort, when it wears out, we mend with more life-jelly, which we get
from the portion of our food that is neither sugar nor starch nor
oil, but the once living jelly of other plants and animals, which I
am sorry to say, we have to kill to get stuff for our own repairs.
The plants can make their life-jelly out of the air that they take
in thru their leaves and the water that comes in through their
roots. But we animals, from the least to the greatest, can get it
only by taking it away from something else. For my part, I feel
easier in my mind when I take away this life-stuff from some plant
like wheat or corn, than when I rob some breathing animal like
myself.




XXXVIII

Of Sugar and Other Poisons


Our bodies, therefore, and the bodies of all other animals, are gas
engines, which burn sugar by exploding it mixed with air. Most of
our food, to be sure, isn’t sugar, but bread and potatoes and
cookies and all sorts of nice things made of butter and flour, milk
and the like. But as I have already pointed out, the most important
portion of this food is either made over into our own life-jelly, or
else it is changed into sugar and exploded in our muscles.

Sometimes when the automobile goes by, one of the things you notice
is a very bad smell. This is largely the unburned and half burned
gasoline. Gasoline, when it burns clean, changes to water and to the
odorless and slightly tangy gas which we get in soda water, carbon
dioxid as it is called. When you burn gasoline, then, you get the
same products as if you boiled plain soda water.

Most things that burn, likewise, burn to carbon dioxid and water.
Wood does it, and coal, all kinds of oil that we burn in lamps, and
the gas that we burn for light and heat. So, too, do all sorts of
candles—paraffin, for example, or wax; and so, too, do the old
fashioned tallow candles which our great-grandmothers used to make.
Tallow, however, is a fat, except for its taste, like the fat we
eat. Practically, we eat nothing that we cannot also burn, when
dry—tho we do burn a good deal that we cannot eat.

Most of these burnable foods explode in the body, a good deal as
they burn outside. They form carbon dioxid and water—when you “see
your breath” on a cold day, you merely see the water in it that came
from your exploding muscles. If you eat largely only plain wholesome
foods, bread and butter, fresh vegetables, fruit, candy and cookies
and crackers, and all the various other foods that burn clean, they
will burn clear in your bodies, and you will yourselves be clean and
sweet as children ought to be. But if you have a taste for things
you ought not to have, and get them, then instead of good clean
water and carbon dioxid, you will explode to a lot of unwholesome,
poisonous, and smelly things, that are not at all nice outside the
body, and are still worse inside.

Unfortunately, we cannot live altogether on these clean-burning fats
and starches and sugars, which explode to carbon dioxid and water,
and leave nothing more behind than a wax candle when it burns. We
can’t make our life-jelly out of these foods. So we have to eat
also, eggs and milk and cheese and beans and peas and meat and fish,
some parts of which we can build to our life-jelly. But only about a
tenth part of our food needs to be of any of these life-jelly-making
sorts. The other nine-tenths should be the clean-burning things with
which we do most of our work and play.

But whatever the fuel with which we run our bodily engines, sooner
or later it gets used up and the waste products have to be blown off
into the air. Insects and automobiles, which take the air pretty
directly into their cells, blow off their waste gases directly into
the air again. The lowly creatures which breath the air in the
water, send their carbon dioxid back into the water again. But we
who have blood, use that to carry off our exploded sugar and other
things.

The water of the burned up food is simply added to the watery part
of the blood. The carbon dioxid becomes in the blood ordinary
cooking soda; the blood carries the soda to the lungs, and there it
changes to carbon dioxid again, exactly as it does when, as cooking
soda, or baking powder, you add it to flour and use it to raise
cake. Finally it comes out of the lungs with the breath, and that is
the end of it so far as we are concerned.

Still, we are not through with it yet; because the plants take in
thru their leaves the carbon dioxid that we animals breath out thru
our lungs, take it apart again, mix it up with water and other
things which they get thru their roots, and finally make it over
into wood, and into starch and sugar and the like which we animals
eat up once more. So if we eat the plants, the plants also eat us;
and the same stuff keeps getting used over and over again. And a
mighty convenient arrangement it is, too, since there is precious
little stuff to make living things out of in the world at best. Most
of the earth is just rocks.

However, I started to tell you something about the burnt up food and
exploded muscle-sugar, While it is still in the body, before blood
and lungs and skin and kidneys have combined to carry it away.

Did you ever stop to think why you are sleepy when night comes? You
play hard all day, running about until your legs are tired enough to
drop off. By and by, you begin to be sleepy, an hour or two it may
be before your proper bed time. You are tired in your legs. But you
are sleepy in your eyes. Your legs are not sleepy in the least; and
your eyes are not tired. How did the eyes find out that the legs had
been running hard and needed sleep?

It is these same waste matters in the blood. We run our legs off by
day; and by night time a hundred thousand little explosions in our
muscles have used up so much sugar and the rest, that the blood is
filled with the waste material, and the lungs cannot carry it off.

So it stays in the blood and poisons us—not badly, but just about as
much as if we had taken a small dose of laudanum or alcohol or any
of the large number of sleepy poisons, which kill one by putting him
to sleep so hard that he cannot wake up. Our “fatigue toxins” as we
call them (which is simply Latin for poisons that we make by getting
tired) poison us just enough to make us sleep. While we sleep we
don’t do much; less of these toxins are formed; the lungs and
kidneys have time to catch up with their work; pretty soon the blood
is clear again, and we wake up in the morning ready to do it all
over once more. We are made to stand a certain amount of poisoning,
and get over it. The trouble comes when we poison ourselves With
things that we put into our blood, that we might have kept out.

Did you ever think why, after you have been running hard for a long
time, your legs ache? Or why they stop aching when you sit down to
rest, but don’t stop at once? It is these same fatigue toxins. You
explode your muscle cells faster than the blood can wash away the
products of the explosions. So these accumulate. By and by, they
begin to poison the muscle, and you begin to feel the pain. If you
keep on working, as people have to sometimes in spite of weariness,
the ache and the poisoning gets worse and worse, till the muscle
simply refuses to work any longer.

If you stop to rest, the ache of weariness still continues. But
after a little, the blood stream washes the muscle clean. Then the
ache is gone, and you can get up and run again. Nevertheless, a
whole day’s play or work will so load up the blood with toxins that
it can no longer wash the muscle clean. Then you must take a longer
rest, go to sleep, and give time for the blood itself to clean up.

Perhaps you have noticed (if you haven’t, try it—only don’t lie on
the damp ground) that when your legs are tired, they rest and stop
aching much more quickly if you put your feet up higher than your
head. This is, of course, because the blood current coming from the
tired muscles, can run down hill, and so most easily drain off the
toxins which make the ache. So too, you can keep fresh much longer,
whether you are working or playing with the muscles, or sitting
still and working your brains over your lessons, if you stand up
properly and don’t slouch. When you slouch, you cramp your lungs.
The cramped lungs fail to clear the blood. The dirty blood fails to
wash brain or muscles clean, and you get tired sooner than you
ought. For the same reason, you tire more quickly in bad air. But if
you give blood and lungs a fair chance, they will do a lot of
resting for you while you are still at work.

But long before we get in the least tired, we get out of breath.
Poisons as before, only this time it is largely the carbon dioxid
that does the business. The muscle-sugar explodes, and forms the
carbon dioxid. The carbon dioxid leaks out into the blood; and the
blood, circulating thru the body, carries it to a certain nerve
center high up in the back of the neck. This in a sense tastes the
carbon dioxid, something as the tongue tastes it in a glass of soda
water.

When the nerve center in the neck tastes a little carbon dioxid, it
doesn’t say anything. But the moment the taste begins to get strong
(which is in less than a quarter minute after one starts running
hard) it telephones over the nerves to the lungs: “Here, here, here!
What is the matter with you fellows. Get busy. Breathe hard. This
blood is fairly sizzling with burnt up sugar!”

Thereupon the lungs get down to work. They breathe as hard and as
deep as they can; while the heart, which has also been telephoned of
the situation, beats harder and harder, to give the lungs all the
blood they can clean, and the working muscles all the blood they can
dirty.

If heart and lungs hold their own, nothing in particular happens.
But if we keep running on too hard, so that muscles poison the blood
faster than the lungs can un-poison it, then the nerve center which
is in the back of the neck interferes once more. When it cannot make
heart and lungs work faster, it calls off the muscle. Suddenly it
gives us such a feeling of loss of breath and suffocation, that we
simply cannot run another step. We have to stop. Then heart and
lungs catch up on their work.

Curiously enough, getting one’s “second wind” as we say, when the
lungs after pumping violently, settle down to working steadily once
more tho we still keep on running, and “getting in training” so that
we can do all sorts of exercises without getting winded, both these
highly desirable conditions depend in part on teaching this
“respiratory center” in the neck not to raise so much of a row when
it smells a little carbon dioxid in the blood. We train our muscles
to do their work; and we also train this nerve center not to get
rattled and turn on that feeling of suffocation until it absolutely
has to. We get it used to burnt muscle-sugar so that it doesn’t mind
the taste as it did.

So, as I say, we live only by just escaping being mildly poisoned.
But the curious thing about it is that among these various poisons
which would certainly kill us forthwith, if we did not promptly get
them out of our bodies, stands, of all things, sugar.

We eat a good deal of sugar in our food. We make a good deal more
out of other sorts of food. If we did not make sugar, and have it
always on hand in our blood, we could neither work nor live. And yet
thousands of persons, every year, die of nothing in the world but
sugar poisoning.

Sugar is so very poisonous that we have a special arrangement in our
livers for keeping down the amount that at any one time gets into
the blood. But for this, a box of candy, or a meal of bread and
potatoes would inevitably kill us within three hours. The blood of a
full grown man always contains about a quarter ounce of sugar, that
is to say, two ordinary lumps. If he has less than two lumps, he
begins to starve. If he has more than three or four lumps, his head
feels heavy and he cannot keep awake. He begins, in short, to be
poisoned. But any one who should get his blood half as sweet as he
takes a cup of tea or coffee, would promptly drop into a sleep from
which he would never wake up at all.

One thing then that the liver is for is to catch the sugar as it
goes by, after a meal, and store it up where it will do no harm.
Then it slowly feeds it out again, as the muscles use it up, always
keeping the amount in the blood at two lumps. But if we eat or make
more sugar than the liver can pack away, then the rest is changed
into fat and stowed under the skin and around the muscles. So we
store our food as fat, and use it as sugar—fat, luckily, being one
of the few things we make in our bodies that are not poisons.




XXXIX

Snake Venoms and Others


The life of any creature, man, animal or plant, is one long fight
against being poisoned. The poisons get us in all sorts of ways.
Some, like strong acids and caustics, actually destroy the flesh,
just as they would eat a hole thru the top of a stove, and we are
crippled or die for lack of a lining to our stomachs. A great many
poisons, like alcohol, ether, chloroform, the various alkaloids,
such as strychnin and atropin and cocain, which we use as medicines,
and nicotin, which is the alkaloid of tobacco, the poisons of many
toadstools, caffein (don’t call it caf-een, but caf-fe-in, like
co-ca-in) which we get in tea and coffee (and therefore ought not to
drink either till we are quite grown up) and half a thousand others,
mostly with names ending with “in” and the ptomains (again it’s
three syllables, to-ma-in) which form in fish and ice-cream that
have been kept too long, and poison whole families at once, all
these do not do any special harm in the stomach. But when they get
into the blood stream, they go straight for the nerves and upset
them. Ether, chloroform, and cocain, as we all know, begin by
paralysing the pain nerves. The pain sense is cut off from the
brain, so that no matter how much damage is being done, we don’t
know anything about it. And a mighty good thing it often is that we
don’t!

Other poisons attack the blood. The fumes from burning charcoal and
some sorts of gas that we use for lighting and cooking, lock the
oxygen of the air so tightly to the red blood corpuscles that are
carrying it to the cells, that the cells cannot get it away from
them. So the tissues die from lack of air, tho there is plenty and
to spare in the lungs and the blood—only the blood hangs onto it,
and the rest of the body cannot pry it loose. Snake poisons, also,
kill by attacking the blood, thus cutting off the supply of air.
These dissolve the blood corpuscles that carry the oxygen, and
literally “turn the blood to water.” Then the blood, having no
corpuscles, cannot carry oxygen to the cells of the body, and the
body dies of suffocation, tho the lungs take as much air as before.
Snake venom, therefore, does not do the least harm in the mouth or
stomach. One can suck the poison from the wound made by the snake’s
teeth, and spit out the poisoned blood, or even swallow some of it,
without the least danger. One could wash himself in rattlesnake
poison, and take no harm, so long as he kept a whole skin so that
nothing got into his blood.

Perhaps you know that pigs are the great enemies of rattlesnakes,
killing them and eating them up as if the serpents were so many
apple parings. The rattlesnakes bite the pigs. But the pig’s skin is
thick, and under it is a great layer of fat, in which there is
almost no blood. So when the pig gets a dose of poison under his
skin, enough to kill two or three men, he does not mind it at all.
The venom, shut up in the fat, works out into the blood so slowly
that the pig can make new blood corpuscles almost as fast as the
poison destroys the old ones. So at the worst, the pig feels only a
little discomfort. But the rattlesnake is safely tucked away in the
pig’s inside, where it will never do any more biting.

What I want you to remember, then, is this: All living things are
poisonous. We, ourselves, are continually manufacturing in our
bodies carbon dioxid, sugar, ammonia, and a score of other things,
any of which would soon put an end to us if we did not have a
special machinery for getting rid of them before they get a chance.
A great many plants produce also certain special poisons, strychnin,
nicotin, and the like, which would kill them if they made too much.
A few animals, too, like the snakes and some fishes and various
insects, manufacture poisons, which also would kill them. In
general, the blood of any animal is a poison to an animal of any
other sort, and always a poison of the same sort as snake venom
which does no harm in the stomach, but is fatal when enough is taken
into the blood. In general, then, each creature has some means of
getting rid of its own poisons, but the poisons of any different
sort of creature will kill it.




XL

Of Measles and Rusty Nails


Little boys sometimes get careless on Fourth of July. Perhaps they
let a cracker go off in their fingers. Perhaps they pull off a toy
pistol without noticing where it is aimed. Boys have been known to
do both these things.

When this happens someone is pretty likely to get a hole blown in
his skin. That of itself is not especially serious; the hole will
soon close again. But we are pretty certain to be dirty on the
Glorious Fourth, especially if we have been round the streets, in
the dust that people’s feet are stirring up. So when we blow holes
in our skin, we are pretty likely to blow dirt in also.

City dirt has a great many different things in it. Among them,
almost always, certain very small plants, far too small to be seen
except with a pretty strong microscope. These are, in fact, a
particular kind of bacteria. So we blow thru our skins, hole, dust,
and bacteria. The hole heals over, but the bacteria stay inside.

Being living plants, they grow in the blood—like mold in bread or
yeast in dough. Being living things, as they live, they make
poisons. It happens that this particular plant makes an especially
deadly poison, which goes straight for the nerves. Then the victim
has convulsions, and almost always dies within a few days.

This is, in fact, the dreaded tetanus or “lockjaw,” which used to
kill scores of boys and girls every Fourth of July. Sometimes, too,
one catches it by stepping on a rusty nail, not because the rust on
the nail does any special harm, but because a rusty nail is likely
to be a dirty nail also, with the tiny living plants mixed in the
dirt. We rarely get lockjaw from an ordinary cut with a sharp knife,
because such a wound bleeds freely and washes itself out. The
dangerous wounds are small deep holes and ragged tears, that give
the little living plants a chance to hide and grow.

All catching diseases are like Fourth of July lockjaw. Measles,
whooping cough, chicken pox, ordinary colds, grip, and many most
dreadful sicknesses of which people die, all such are caused by some
living thing which gets into our bodies, grows there, and living and
growing, poisons us with its waste products. Some of these plants
grow in the lungs, like that which causes consumption. In some, like
diphtheria, the growth is in the throat. In summer complaint, which
sickens the babies in the hot weather, the trouble is in the bowels.
Even some sorts of baldness are due to growing things at the roots
of the hair. Mostly, however, the plants grow in the blood. In any
case, the poisons they make get into the blood; and there they
poison the nerves, like the various alkaloids I told you about, or
else they attack the blood itself, as the snake venoms do.

[Illustration: The minute animal which causes the “sleeping sickness.”]

Some of these disease-making things, too, are not plants but
animals. Such, for example, is the minute creature that causes
malaria; and another that makes the dreadful “sleeping sickness”
that every year is killing thousands of wretched <DW64>s in Africa,
in spite of all that can be done to prevent it.

They get into our bodies in all sorts of ways. Some come in the
dust, when we breathe dirty air. Some come in dirty water. Some, a
great many, come in dirty food, on lettuce and celery that have been
carelessly washed, and especially in dirty milk. Some of the worst
of all among them, the germs of typhoid fever, are carried on the
feet of the common house fly, and planted all over the things that
we are going to eat. Rats and mice also carry diseases—in their fur,
on their feet, or even in their blood. So, too, do certain stinging,
biting, and sucking insects; and when they bite or sting or suck the
blood of some larger creature, they plant the seed of some disease
in his body, where it grows and flourishes until the animal sickens
and perhaps dies. No one, for example, ever catches yellow fever or
malaria unless he has been stung by a mosquito which has already
bitten somebody else with the disease. The mosquito picks up some of
these living germs in the blood of one person, and sows them in the
blood of the next; just as one might take seed from one field or
garden plot and sow it in another.

All the catching diseases, then, from ordinary colds to pneumonia,
and from measles and chicken pox to typhoid and scarlet fevers, are
nothing in the world but living plants or animals growing in our
bodies and poisoning us. We say that we catch the disease. Really
the disease catches us. The disease is a living thing, that in very
real sense, hunts for us, and catches us as a lion or a bear might
do, or a poisonous snake. If we could kill these lions, bears,
poisonous serpents, bacteria, and the rest, why then they wouldn’t
get a chance to kill us. Then we should all live to old age—unless
we poisoned ourselves, as I am sure some persons are quite foolish
enough to do, or met with some accident that we could not help. But
of course there are a few other diseases, like rheumatism and heart
disease and indigestion, where the trouble may be with ourselves and
not with any other living creature that gets after us.

Just to show you how one of these living, catching diseases manages
to get on, and when one victim dies, changes over to another, I am
going to tell you about something that I am sure you have already
heard of either in your history, or else in stories that you have
read about the Middle Ages, when the knights wore armor and the
yeoman fought with spears and bows.

In those good old times, every little while, whole cities would be
smitten with a terrible disease called the plague. Perhaps you
already know about the Great Plague of London in 1665, when seventy
thousand people perished, and the dead lay in the streets because
the living were too few to bury them. The same man who wrote the
story of Robinson Crusoe, wrote also a story of this great plague,
not a pleasant story, naturally, but one that you will want to read
later when you are older.

The trouble was nothing in the world but dirt and rats. The rats
lived in the dirt; and the minute, living plant that makes the
plague, lived in the blood of the rats. From them it got into the
blood of human beings. But so long as a city kept clean and free
from rats, it never had the plague. But when it let itself get
dirty, as ancient cities usually did, then it might lose a fifth of
its inhabitants in a few months.

As people, therefore, began to be more decent, the plague began to
disappear; and after about the time of our Revolutionary War, most
of Europe had become so clean and civilized that they had no more
plague there. But still it lingers in other parts of the world,
where there is more dirt, and where people, instead of putting their
waste tidily away in the bucket or burning it up, throw it out the
back door for rats to eat. Always, even now, the plague threatens
Asia. During the first ten years of this very civilized twentieth
century five million persons died of it in India alone.

And all because of dirt and rats and fleas. The rat lives in the
dirt. The fleas live on the rat, and when they bite the rat, get a
stomachful of blood, and with it some five thousand or so of the
little plants that cause the plague. Then the flea jumps off the
rat, on to a man, and bites him. Then a few of these five thousand
germs get into the man’s blood. By the next day, these few have
become millions. Within a week, often within two days, the man is
dead—simply poisoned. But if the man had kept his house clear of
rats and his skin clear of fleas, by keeping them both clean, he
would not have been poisoned at all.

I am sorry to say that since the year 1900, and even as late as
1909, there have been cases of the plague in one or two especially
dirty cities in the United States. So the National Government had to
interfere, to make them clean up and get rid of their rats.
Otherwise we might have had a terrible time; while as it was, some
three hundred people died—which is more human beings than most of us
know by name.

But you can’t have the plague without rats, and you can’t have rats
without dirt. So, therefore, every civilized government in the world
keeps men at work in its seaports, killing the rats that come in the
ships, lest they bring the plague from China or India, where they
don’t mind a little dirt.

There is another animal, dirtier even than the rat, and on the whole
rather more dangerous—and that is the fly. Wherever there is dirt,
there are pretty sure to be the germs of various diseases. If there
is anything the fly likes, it is dirt. He eats it; he wallows in it.
The dirt sticks to his feet, and the disease germs stick to the
dirt; for a fly is not nearly so much smaller than an elephant as a
disease germ is smaller than a fly.

Then the fly tracks over our food or falls into our milk. He may
carry a million germs on his body, and every time he puts down one
of his six feet he plants at least one. In forty-eight hours this
single one may have grown to sixteen thousand. Then some boy or girl
eats the food and is sick; or some baby drinks the milk and dies.




XLI

The Great War


The hardest battle we have to fight is with these living diseases.
They kill more people in each year than have perished at the hands
of the enemy in all the wars we have ever fought. During our war
with Spain, the flies alone killed in camp four times as many of our
soldiers as the Spaniards killed in battle. Every day of our lives
in war and in peace, we are fighting for our lives against these
unseen foes of pestilence and disease.

This is how we carry on the campaign. Our first line of defense is
keeping clean. Every city now-a-days has men who watch its water
supply. The surroundings of its ponds and reservoirs are carefully
guarded. If necessary, the water is filtered before it goes into the
street pipes. Always, if the city is half civilized, it filters all
its sewage before turning it into the rivers. Thus, if there are any
living animals or plants in the water, they get strained out. In
many houses, where the people are especially careful, they strain or
filter the water once more, or boil it till they kill every living
creature therein.

Then every city has other men to look after its milk. Because milk,
being good food for us, is good food also for other living
creatures; so that if one single germ gets into a bottle, it will
shortly grow to many millions, and play sad havoc with the family
that uses it. Careful people, too, do not depend on the city to keep
their milk clean, but see for themselves where it comes from;
especially if there are children, for children not only drink much
milk, but are peculiarly liable to catch the diseases which come in
it.

Careful people, in addition, look out that all their food is clean.
They see that none has been kept out where dust may fall in it,
where rats or mice may brush against it, or where flies may track
over it. In all these ways, the seeds of diseases may get sown in
our food. One ought to make sure that there are no rats, mice, or
flies in the house at all; and one ought to make sure also that all
raw foods, like lettuce and celery are thoroly washed, for these
often carry the eggs of certain animals, living eggs which will
hatch out inside anybody who swallows them, and not be at all to his
advantage.

That, then, is our first line of defense—keeping our food clean,
lest the enemy enter through our mouths. Our second defense is to
keep the air we breathe, clean and fresh and dust free, lest the
enemy attack us by way of our lungs, and we die of pneumonia or
consumption, or sicken of common colds and the grip. In all this, we
are like a country with a powerful navy which can prevent the enemy
from making a landing on its coast. So long as we keep these minute
foes out of our houses, and still more so long as we keep them out
of our cities, they cannot get near enough to us to do us any harm.

But when the enemy has broken through our first line of defense, and
begun to lay siege to our bodies, we still have a second line of
fortifications to protect us. One thing our skins are for is to stop
germs. So long as we keep a whole skin, it is pretty hard for many
sorts of germs to gain an entrance. And where the skin is thin, as
it is inside the mouth and nose, there is always a somewhat thick
and sticky mucous to catch the germs; while the eye has tears to
wash them out. We are like fortified cities; and we must not let the
enemy make a breach in the wall.

So we must be careful not to neglect even small cuts, sores,
scratches, and the like, thru which the foe can enter. People
sometimes get most loathsome and dreadful diseases by drinking from
dirty cups when the skin of their lips is cracked in cold weather;
while the little plant that causes blood poisoning, often gets in by
way of a cut so small as to be hardly noticed. No child would ever
die of lockjaw, if he did not first cut or blow a hole in his skin.

Strangely enough, a great many of the lesser catching diseases of
children, measles and colds and the like, make their way into the
blood because of holes in the teeth. A hollow in a tooth gets filled
with food. A germ or two finds its way into this food, and grows
there till it becomes many millions. So naturally, an assault by an
army is more likely to be successful than an assault by a mere
handful. Merely by keeping the teeth and mouth clean, and by having
a dentist stop the holes in the teeth, one can cut down to less than
half, the number of days’ sickness in a year. Some people go beyond
this, and always after they have been in dust or bad air, wash out
their noses with some fluid that will dispose of any of the enemy
who have lodged there. In fact, people who have suffered almost
continually from colds and grin are sometimes cured at once and
completely, by merely a slight operation on the nose, which opens up
to the fresh air some hollow in which the besieging hosts were wont
to lurk.

Our second line of defense, then, is keeping skin and teeth and nose
clean and whole, that the enemy may have no place wherein to hide,
and no breach through which to enter. If this gives way, then we
must engage the enemy hand to hand.

Then it gets to be a pretty even thing between us. The invaders try
to poison us, and we try to poison them. We form an acid in our
stomachs—the same acid, by the way, that tin-men use to solder with;
one can buy it anywhere. Regularly, we use this to digest meat with;
but if any living things get into our stomachs, we give them a dose
of this acid, and usually bowl them over.

If they get by this, we poison them with bile. The bile is made in
that most useful organ, the liver, and is partly waste matter, more
or less hurtful to the body, which we are getting rid of. So since
we don’t want it to poison us, we use it to poison other living
creatures inside us.

That, then, is our third line of defense. If the enemy gets by that,
then the war has to be fought out in the blood. Even if we win, we
shall suffer damage, and very likely take to our beds and have to
call on the doctor for reinforcements.

The blood itself, good healthy blood, that is, will poison the
germs; for the blood of any sort of creature, as I have explained,
will poison any other sort. Besides that, we manufacture special
poisons with which to combat each special creature that makes a
special poison to assault us. So each side poisons the other, and
the battle becomes a question of which can kill the other first. In
one case, we are sick and recover; in the other case, we are sick
and die.

When the doctor takes a hand in the battle, he begins by giving us
food and medicine, to make us strong for the war. Sometimes, besides
these, he gives us something which, while it harms us a little,
harms the enemy a great deal more. In a few cases now-a-days, he
pumps into our bodies some of the blood of another animal, generally
a horse, which has been fighting the same disease, and so has its
hand in and can manufacture many times as much stuff to kill the
germs as we can. Many, many people have been saved by this means,
who otherwise would certainly have died.

In a few cases, too, small-pox especially, by means of vaccination,
long before the enemy attacks us, we can be loaded up with
ammunition to repel the invader when it does come. The vaccination
gives a mild form of the disease (not so very mild perhaps you
think, when your vaccinated arm gets nice and red); we defeat this
triumphantly, but we manufacture so much “anti-toxin” to do it with,
that for years afterwards we are all ready for the first germ that
shows its face in our blood, and slay him before he gets a chance at
us. The “anti-toxin,” as you know, is the substance which we make
with which to get back at the germs that are trying to poison us
with the “toxin” which they make.

But even the battle in the blood is not fought quite in the open. We
have, so to say, breastworks and rifle pits, where we can still make
a stand, even after the invaders have gained a footing in our
bodies.

Perhaps you have sometimes felt small roundish hard bunches as big
as a pea or a marble, under the skin at the side of the neck, under
the arm pit, or in the groin. Sometimes these swell up and get sore.
These nodules are the lymph glands. They surround the passages
through the flesh along which the invading germs are likely to come,
after they have burst through the skin. They are then like the
fortifications along a road over which the enemy is likely to march.
We can feel them only in certain places; but they are all over the
body, under the skin, and beneath the membranes of the lungs and the
digestive organs, wherever the body is most open to attack.

The garrison of these little forts are a peculiar sort of naked
cells, which having no walls or covering to hold them in, can change
their shape, reach out, and draw back again, as if they were
sea-anemones or polyps or some other sort of water creature, and not
part of our bodies at all. These cells are twenty or more times
larger than the bacteria. And when the bacteria or other germs come
along through the passages of the body on their way to the blood
vessels, these guardian cells of ours reach out and grab them, drag
them in, and devour them, like ogres that devour travelers who go by
their castles, over the high road. Only in this case, our sympathy
must be entirely on the side of the ogres.

But these lymph cells do not always stay in the lymph glands. When
they like, they let go their anchorage, and go floating off through
the blood, or through the lymph; for the lymph is only the watery
part of the blood without the red corpuscles, which doesn’t stay in
the blood vessels but soaks everywhere through the body, feeding and
moistening the cells. These lymph cells, or white blood corpuscles,
can go everywhere over the body, pushing and squeezing and elbowing
their way among the other cells or traveling in the open spaces
between them.

When the enemy enters the body, and begins to poison the blood, the
white corpuscles smell them, and at once begin to crawl toward the
smell, to reinforce their brothers in the particular lymph glands
which happen to be at the point of attack. You get a sliver in your
finger. The sliver opens a hole in your defense, and carries in some
hostile germs. If, therefore, your lymph cells did not come to the
rescue, you would inevitably die of blood poisoning. But they do
come to the rescue. The white “matter” or “pus,” which in a few days
comes out of the wound, is in large part the dead bodies of the
fallen enemy and of the defenders who have perished in the fight. So
in general, the invasion is stopped at the first lymph gland. A few
thousand white corpuscles fall in the war. The enemy is massacred to
the last man. And the body is saved.

Or else the foe get the upper hand; increase faster than the
defenders can kill them off; break through the defense; enter the
blood stream; invade the whole body; overrun the country; and put
the inhabitants to the sword.

[Illustration: Lymph Cells or White Blood Corpuscles]

All our lives long, every day of our lives, we keep up this fight
against disease. When measles does not threaten us, then it is
colds. The game, therefore, is to strengthen our outer defenses, by
keeping our food and houses clean, and our skins and teeth, and the
air we breathe. And while we are doing that, we ought also to keep
our bodies strong and resistant, with proper food and exercise and
sleep, ready to put up a good fight if the enemy should break in. We
know so much now about the causes of disease, that being sick or
keeping well is a good deal under our own control.




XLII

More About The Great War


We are not the only creatures who have to fight for our lives, every
day of them, against an ever-present but unseen enemy. All other
animals have to do the same, if they are big enough for any thing
else to live inside them. There are parts of this earth where no
cattle or horses can live, and where all the heavy work has to be by
machinery or by hand, because there are flies there which bite all
the larger animals, both wild and tame, and plant germs in their
blood. After that the tamed creatures, at least, almost invariably
die.

Animals, therefore, have their catching diseases just as we have.
Sometimes they are the same as ours; more often they are
different—things that dogs or cats or horses catch, and we do not.
Once, I remember, it must have been more than sixty years ago, all
the horses over entire states suddenly fell sick. One hardly saw a
horse on the street or anywhere; and because that was long before
the days of automobiles or trolley cars, people had to walk or to
drive oxen, and sometimes even to harness up cows. But after a few
months, the horses all either died or got well again. Those that got
well had their white blood corpuscles trained to fight that
particular germ; so there was no more serious trouble. But it would
make you laugh to see a span of cows haul a milk wagon.

There is a distemper that kills puppies. There is a chicken cholera
which wipes out whole flocks of hens. The monkeys in the menageries
succumb to colds and consumption, which they catch from the people
who come to look at them. When the plague enters a city, the cattle
and the various small animals of the house begin to die first before
the human beings, and thus often give them warning, and time to
flee. In all cases, some particular living and growing thing breaks
through into the blood, or gets a foothold somewhere in the body,
and begins to poison it. Then the invaders and the blood cells fight
it out—and the best man wins.

There is a disease called anthrax which attacks various animals,
ourselves and the birds among the number. A hen, for example,
fighting anthrax, will almost always win, if it is kept warm. The
lymph cells fight better when the blood is hot. But if the hen’s
feet are kept in cold water, then the anthrax wins. The cool blood
gives it the advantage.

That is how we and all other creatures catch cold. Mere cold would
never give us chills or grip or colds. But our being chilled, or
getting our feet wet, or sitting in a draught, just cools down some
part of the body enough so that the blood cells can’t fight quite so
well. Perhaps it is only for a moment; but in that moment the enemy
gets its footing. Some people say that the reason why a dog’s nose
gets hot when he is sick, and why human beings and animals have
fever when they have anything catching, is so that their bodies may
be well warmed up, and their lymph cells may do their fighting in
hot blood.

Nor is it only for human beings and animals that all these catching
things lie in wait. Plants have their troubles as well. Perhaps you
have noticed on wild cherry trees growing by the roadside, or on
plumb trees, that sometimes almost every tree in a clump, and even
every branch on a tree, will have a hard black lump, as large as
your fist, growing out of the bark. The tree is sick; sick with a
patching disease of trees called the black knot.

The disease itself is something like a mold. It breaks through at
the growing tip of the branch where the bark is new and thin. Thence
it grows down the branch sucking up the living substance of the
plant and killing everything as it goes. The “black knots” are the
fruiting of the invading plant, where it has broken through the bark
and is growing fine dust-like “spores,” which are its seeds and will
spread the trouble to neighboring trees. When a tree comes down with
this trouble, the only thing to do is to cut off every diseased
branch a foot or more below the lowest knot, and burn it up.
Possibly then, we may get ahead of the enemy, and so save the rest
of the tree.

Almost every cultivated plant has its diseases. The brown spots on
leaves and fruit of a pear tree are the plant’s measles. The hard
lumps in an apple are its mumps. There is a sort of black
scarlet fever of wheat, rust it is called, which destroys a million
dollars’ worth of grain each year. Some plants look wilted because
they need water; some, because they are sick and need medicine.

And they get medicine, too. Sometimes the plant-doctor gives it by
soaking the seeds in the remedy; sometimes by spraying it on the
leaves with a pump and a hose. In any case, the medicine is some
sort of poison that kills the living creature that makes the
disease, but does no special harm to the cultivated plant.

We even speak now of diseases of soils. Because there are minute
animals that get into soil and lessen its fertility so that no plant
will do well in it. Green-house keepers often bake their earth
before setting out plants in it, in order to cure it of any disease
that it may have caught while the last crop was growing; while a
healthy soil will catch a disease from a sick one, exactly as a
healthy animal or plant will do.

The fact that most diseases of men, animals, plants, timber, and
soils are living things is something that has not been known many
years. Indeed, it is only since the twentieth century came in, that
we have really made much of a start at finding out just what plant
or animal is responsible for the sickness of any other. It is only a
question of time, probably a few centuries at the outside, before we
shall have killed off all the common diseases. Then nobody can
possibly catch anything any more—measles, mumps, chicken pox, colds,
grip, diphtheria, scarlet fever, or anything else. There will not be
anything left to catch; and nobody will be sick any more, unless he
eats more than is good for him, or does something else that he might
just as well not have done.




XLIII

Living Apothecary Shops


Not only are the bodies of all except the very smallest animals and
plants at the same time gas engines and battlegrounds; they are also
living apothecary shops. Indeed, it is a pretty well stocked drug
store that has more different chemicals in it than a man and his
horse, and his dog, and the garden that he works in, all together,
manufacture every day of their lives.

Think to begin with, of all the different perfumes of all the
different flowers, and all the various tastes of all the different
vegetables which we eat, and of all the various spices and herbs
which we use for flavorings in our food. Think of all the different
coloring matters in flowers and leaves. Think of the tar, rosin,
pitch, maple syrup, turpentine, gum, varnish, shelac, india rubber,
tan bark, and the rest, that we get from a few trees alone. The
chemicals made by even the ordinary plants could fit out the shelves
of a fair-sized drug store.

We animals have vastly more different things inside us than any
plant. Every time we move a muscle, we manufacture soda water. Every
time we think, we turn a half dozen different chemicals into the
blood. We take a mouthful of cracker, which is mostly starch; and
straightway a ferment, or “enzyme,” in the mouth begins to turn the
starch into sugar. That is why a cracker or a potato tastes sweeter
and sweeter the longer one chews it. When the sugar gets into the
blood, another enzyme (the “y” is like “i,” and the word sounds like
en-zime) in the liver turns it back to starch again, so that it
stays there in the liver, and can’t get out. Then as you know, this
liver-starch slowly turns back to sugar again, and leaks out into
the blood to feed the muscles. In the muscles, still another enzyme
helps it to explode into carbon dioxid and water, only sometimes it
forms lactic acid instead, which is the acid of sour milk. Because
of these enzymes in the muscles, the gas engines which they are, can
run when only moderately warm, instead of needing to be too hot to
touch, like other engines when they are at work.

But if instead of making flour into crackers, or having the baker do
it, and then eating them, we had made the flour into bread with
yeast: then the yeast, which is a living and growing plant, would
have formed another enzyme, which in turn would have turned the
sugar in the bread into carbon dioxid and alcohol, and the carbon
dioxid would have puffed up the bread and made it light. That is
what yeast is for. The yeast of beer also, turns the sugar of the
grain into carbon dioxid and alcohol. The first of these gives us
the fizz, the second we use to poison ourselves with.

Even the color of our hair and eyes depends on an enzyme which
manufactures the coloring matter. People who have the enzyme, have
dark hair and brown eyes. People who haven’t it, have light hair and
blue eyes.

In fact, almost anything that any living part of the body has to do,
whether to take its food out of the blood stream and build it into
its own substance, or to do its work, or merely to grow, it
generally has to employ one or more of these enzymes to do it with.
These are, in fact, the tools of the living jelly, or protoplasm,
which makes our bodies and does our living for us. Without them we
could not live a single hour.

I suppose there must be hundreds, or perhaps even thousands, of
different chemicals and drugs and medicines and poisons and
antitoxins and enzymes forming all the time in different parts of
the body. The various organs put them to all sorts of various uses.
Among others, they employ certain of them as messengers, to carry
signals from one part of the body to another.

I have already explained that the head is one of the first organs in
the body to be formed. It gets a start, therefore, over the rest,
and a little baby’s head is something like four times as big as it
need be to fit its body. But the baby’s legs and arms, which started
late, are not nearly large enough to fit the rest of him. So the
limbs have to grow fast, and the head to grow slowly, in order to
come out right in the end. How do they know enough?

How fast little girls’ feet sometimes grow! At twelve they can wear
their mamma’s shoes. Then the feet stop growing and the rest of the
body catches up. Or when it is time for a boy’s voice to change, all
of a sudden, his Adam’s apple, where the voice comes from, starts
growing. In a few months it has increased from boy’s size to man’s,
and the voice has dropped to a deep, if uncertain, growl. Everywhere
throughout the body, the different parts start growing, and stop,
and keep along together, or get ahead of each other in the most
complicated fashion, but always right.

How they manage it, we do not altogether know. We do, however, know
that the different parts of the body do signal to one another by
means of these substances which they form within their cells, and
turn loose in the blood stream. In this way, each organ of the body
is able to send messages to the rest—“Start growing,” “Steady now,”
“Slow down,” “Stop”—as the case may be. You already know how a
working muscle signals to the heart and lungs, and how the blood
cells get wind of an invasion, by the altered smell or taste of the
blood, and rush to the point where the enemy has broken through the
defense, and the fight is on.

So in general, when a message has to go quickly from one part of the
body to another, it goes by way of the nerves. But when there is no
special hurry, or when the signal must go to some tissue or organ
which, like the blood corpuscles, has no nerve connection, then the
message has to go by way of the blood.

If then, our legs want to say: “We’re sitting on something hard and
sharp, please may we move,” they call us up over the nerves. If they
want to say: “We have been growing too fast, and it’s high time we
stopped and gave something else a chance,” they do it by turning
something into the blood. But if they want to say: “We’re so dead
tired that we simply can’t walk another step,” then as you know,
they use both methods—fatigue toxins and very dreadful aches.




XLIV

What Becomes Of The Tadpole’s Tail


The lymph cells, blood cells, white blood corpuscles, as they are
variously called, are a sort of standing army, always on duty to
repel invasion by any living germs of disease. In times of peace,
however, when there is no enemy to be set upon and devoured, they
have to work. All soldiers have to work when there is no fighting to
be done; and sailors on a battle ship have to keep it clean and in
order, row the captain about in his boat, and take turns paring
potatoes for the cook. So the cells in our blood are in this like
other fighting men.

Their particular work is to keep the body cleaned up, especially the
blood. Besides this, they take down and cart away any tissue or
organ or part of the body that is no longer any use.

There, for example, is the polywog’s tail, after he becomes a
frog—also his gills. The polywog, of course, is pretty nearly a
fish, with gills and tail, who breathes water. But Brer Frog is
pretty nearly a land animal. He breathes with lungs, tho not to be
sure especially good ones, so that he has to breathe thru his skin
also to help out. At any rate, he has lost his fishy gills, and no
longer has any tail.

Where has the tail gone? The white blood corpuscles have eaten it
up; and with it, a lot of other things, gills among the number,
which the tadpole has to have, but the frog has no use for.

The tadpole, as you know, has no legs. When they start growing (you
can see them under the skin, almost the first sign of the coming
change) these growing legs turn something into the blood which is a
signal to the blood cells to get to work eating up the tail. So the
blood cells do get to work. They devour the flesh, cutting into it
much as certain insects gnaw into wood, or a woodchuck digs a hole
in the ground. Then as fast as the blood cells take down the flesh
that is no longer useful, it is used again to build up the new legs.
So really the tadpole’s tail is used over to make the frog’s legs.

Much the same thing happens when a caterpillar turns to a butterfly.
The caterpillar, as you have no doubt often seen, shuts himself up
in a hard shell. Inside this coffin, or chrysalis, the body of the
caterpillar is taken to pieces, and changed over into a sort of
thick milk. Then out of this thick milk, the butterfly is formed.

[Illustration: The caterpillar changes into a moth.]

So the caterpillar does not become a butterfly simply by growing
wings. It is really almost a new creature, built up out of the
material of the old, as one might rip up an old coat and have it
woven into a rug; and we may be very sure that no butterfly ever has
the slightest recollection of the time when it crawled on a dozen
legs, and chewed leaves for its food.

We, too, grow and change like frog and butterfly. When we were, say,
four or five years old, we had twenty strong little white teeth,
each set firmly in the jaw bone on a stout root. By and by, these
teeth, one at a time, in pretty much the order in which they first
appeared, began to get loose. First we could wiggle the tooth a
little; then a good deal. By and by, it hung only by the thin skin
of the mouth, so that one good yank, or perhaps only the push of the
tongue against it, tore it out. Or possibly we bit into an apple,
and left the tooth behind.

Anyhow, the tooth hadn’t any root. The hard bone had gone, and with
it the soft nerve and blood vessel that used to be inside. There was
only the hollow cup that once was the crown of the tooth. The rest
had been eaten up, bone, nerve and all, by our blood corpuscles. We
needed larger teeth. Teeth, as I told you, once formed, cannot grow
any more. So the blood corpuscles chewed up the tooth, as much as
they could get at, and used the old stuff to build the new one. No
doubt they would consume the entire tooth, crown and all, and not
leave a shred behind, if only there were some way of holding the
last bit in place while they finished it off. That on the whole
would be pleasanter than having to tie a string round the tooth and
yank it out.

They do act that way with growing bones. The bones, as I have
already explained, grow much as a tree does, by adding on new stuff
to the outside. Meantime, since all bones are hollow, the hollow
also has to grow. The hollow grows by the taking down of the bone on
the inside, just as a tree might decay out at the heart, about as
fast as it grew under the bark. This, also, is the work of the white
blood corpuscles.

Then, too, the soft gristle of little children changes into the
solid bone of grown men. But the gristle never turns to bone. As
before, the gristle is taken out, eaten into, devoured, by these
living cells of the blood and lymph; and as fast as the gristle
disappears, the bone grows into its room.

Or sometimes it happens that two little boys find themselves not in
entire harmony, with the result that one little boy goes home with
one eye shut up; and the next day, and all the next week, that
particular eye is a most remarkable study in black and blue. That is
because, during the lack of harmony, something happened to hit one
little boy in the eye, and smashed up some of the little blood
vessels around it, so that the blood leaked out into the flesh.

Then the white blood corpuscles, which are themselves always leaking
out of the lymph spaces and blood vessels, and wandering round thru
the tissues, have to set to work to clean up that spilled blood. So
they actually eat up the flecks of blood; until by and by, the flesh
is all clean and white again, and the black eye is black and blue no
more. In general, whenever we meet with an injury or a wound of any
sort, these white blood corpuscles take a hand in the healing
process, eating away the damaged tissue, and allowing chance for
fresh growth.

The white blood corpuscles, then, live to eat. Like certain other
creatures who are always hungry, they sometimes eat things that they
had better have left alone. Sometimes, people’s hair turns white
suddenly—corpuscles have actually eaten up the color. Some people
even go so far as to say that the reason why we grow old (since, as
I have already told you, growing old is mostly growing hard) is
because these white blood corpuscles have gone crazy and eaten up
the softer parts of us, and left us only the hard ones to grow old
with. I don’t know whether this last is so or not. But at any rate,
these white blood corpuscles, which let go their hold on the places
where they grow, and go wandering off all over the body eating
everything in sight, would be likely to make this sort of trouble if
anything would; and the man who especially says it is so, probably
knows more about these matters than anybody in the world.




XLV

Nature’s Repair Shop


Of course, we get hurt in all sorts of ways—cuts, bruises, barked
shins, black eyes, once in a while a bad sprain or a broken bone.
Then the white corpuscles that are in our blood, and the growing
life-stuff or protoplasm which is in our flesh and bones, and all
this wonderful and mysterious life that is in us, take us in hand to
mend us up. The same power that made us, and that keeps us alive,
heals also our hurts. By and by, if we take care of ourselves, we
are once more as good as new.

The small and weak and lowly creatures, which cannot take care of
themselves as we can, and so are all the time getting into all sorts
of trouble, are able to repair damages even better than we. The
world is full of timid animals, which have neither teeth and claws
to fight with, nor armor for their defence, nor speed of foot or
cunning of brain with which to escape their enemies. But to make up
in part for this lack, many of these simple beings seem not to mind
at all such injuries as would <DW36> us for life; while they
recover completely, and that within a few days, from accidents which
would mean instant death to us.

A tiny lizard, for example, may at any moment have to scamper for
his life in search of an equally tiny crack in the rock, where it
may take refuge from some larger animal which wants it for
breakfast. Naturally, oftentimes, the lizard so hardly escapes being
“it,” that just as he whisks into safety, his pursuer snaps off his
entire tail.

A loss like this would kill most larger animals, but not the lizard.
He simply waits round for a week or two while a new tail grows, just
as good as the old one, so that he is as well off as before. The
same lizard has been known to lose his tail a dozen or twenty times,
and each time to grow a new one. Since, therefore, a lizard’s tail
is longer than his body, and nearly as large round, the animal must
have grown enough new flesh to make at least five or six whole new
lizards. Curiously however, the new tails, tho they look exactly
like the old one, always have a rod of gristle or cartilage inside,
in place of the regular backbone.

So too, with legs. A lizard that has had a leg bitten off,
straightway grows a new one. He will even grow a whole new eye, when
something happens to the one with which he happened to be born.

Yet oddly enough, the lizard, when he grows new legs and tails is
continually liable to make the strangest mistakes. He will grow a
new tail, when he hasn’t lost the old one, but only had a bite taken
out of it. Then he has two tails. Sometimes he makes even a worse
break than this, and grows out two new tails to replace the single
one which after all he didn’t quite lose. Then he has three tails,
which is at least one more than any proper lizard ought to possess.

It is the same, too, with legs. The lizard seems to get an idea that
his leg has been bitten off, when it has only had a piece taken out
of it. So he goes ahead to grow a new leg, and as a result, has
five. In fact, it is quite possible, to manufacture a lizard,
perfectly healthy and apparently happy, with eight legs and three or
four tails.

Perhaps you have heard that “the early bird catches the worm.” If
so, did you ever consider the transaction from the side of the worm?
If the worm happens to be retiring into his hole just as the hungry
robin catches sight of him, there is likely to be a tug of war
between the eater and the breakfast. The worm swells out the front
end of his body, and gets a grip on the sides of its hole, while the
bird digs its claws into the ground. Sometimes the worm lets go, and
gets eaten up. Sometimes he gets pulled in halves, and only the rear
end goes down the robin’s red lane.

The worm minds being pulled in halves just about as much as a train
of cars minds getting uncoupled. The front end calmly crawls away
into its hole, goes on eating dirt as usual, and pretty soon grows
itself a new tail as before.

But what becomes of the severed tail end, if by any chance the robin
fails to eat it up? That perhaps is the queerest thing of all. If
the front part that crawled away is short, say a third of the animal
or less, so that two-thirds of the worm at least is left in the tail
piece, then this severed tail grows a new head. So the one worm
becomes two. But if the tail piece is shorter, no more say than a
half the whole animal, then that tail, instead of growing a head,
grows another tail. In that case, the final result is one entire
worm, old head end and new tail; and two tails, one old, one new,
growing end to end. But of course, two tail ends, and nothing else
cannot very well make a living, and, the worm soon dies of
starvation.

There is, however, a smaller creature, the fresh water hydra, which
quite outdoes the earthworm, when it comes to growing on new parts.
The hydra is a very small sea-anemone, about as long as a pin is
thick, with a long slender stalk and a circle of long fingers or
tentacles round their mouths. One finds them growing on sticks and
water plants almost anywhere in ponds.

Cut off one of these fingers, and it grows again. Cut the entire
animal in halves as one chops thru the trunk of a growing tree, and
the root end grows a new head, and the head end grows a new; root,
and there are two new hydras in place of the one old one. Cut the
animal into three pieces, head end, root end, and a small bit out of
the middle of the stalk. The head end forms an entire new creature.
The root end forms an entire new creature. The middle piece, which
is neither head end nor root end, but just a little drum-shaped
snipped out of the stalk between the two, even that grows a new root
end and a new head end, and becomes an entire new creature, which in
time grows to be as large as the one out of which it was made.

It is, in short, as if when one ripped off the sleeve of a coat, the
coat grew a new sleeve; or when one pulled off the tail of the coat,
the coat grew a new tail; while the severed sleeve and tail each
grew new coats—pockets, buttons, collars, tails, sleeves, and all.

Our common star-fish, that we find in the salt water pools at the sea
shore after the tide goes out, also isn’t at all bad at mending
itself up after an accident. The five rays which grow out from its
center are continually getting broken off. So one finds often in the
water, star-fish with only four rays, or with four large ones, and
one smaller one just growing out to take the place of one which has
been lost.

But the lost ray, if something doesn’t eat it up, will grow a new
star-fish. From the broken end, four more little arms bud out like
those of a tiny star just getting its start in the world. The single
arm or ray, not only grows out the other five, but in addition forms
a new center for them to grow to, a new mouth, a new stomach, a new
nerve ring round the mouth which is the creature’s brain; and so one
thing with another forms a whole new star-fish with all its parts
complete. And all the while, of course, the severed arm cannot eat
anything, because it hasn’t any stomach. So it has to make the new
parts out of the old, as the tadpole builds its new legs out of its
old tail.

Still, I don’t know why any of these things are any more remarkable
than that the lizard and hydra and earthworm and star-fish should
have formed in the egg in the first place. That after all, is about
the most remarkable thing there is in this world.

Not a few animals, moreover, in addition to having this power of
mending themselves up after they have been injured, have also an
arrangement for getting themselves hurt in a convenient place. The
ray of a star-fish, for example, almost never breaks in halves.
Whenever the ray gets caught so that it has to come off, it breaks
close to the center, so that the whole arm comes off at once.

The crabs, such as one finds at the sea shore in salt water, have a
special place in each leg, close up to the body, where the leg is
meant to break off. The hard outer shell is turned back into the
flesh and makes a round plate of shell with a hole in the middle,
cutting right across the leg. Thru the hole run the nerves and blood
vessels, but the muscles come to the plate on each side and there
stop.

So when a hungry fish “catches a crab” by one leg, the crab digs his
claws into sand or sea weed and pulls. The fish backs water with his
fins and he pulls. Off comes the leg. Away goes the crab in safety.
The leg has pulled off at this plate of shell. No muscle has been
torn. The end of the stump is nicely protected; and all the injury
that has been done is to the small thread of tissue no larger than a
pin, which ran thru the hole in the center of the plate.

More than this, the stump is all ready to grow out again; and
actually grows out quicker, after the leg has been taken off at this
“breaking joint,” than if only a small piece had been taken off
lower down. Such breaking joints, where the wound is all healed over
before it is made, are somewhat common among animals, especially
among those which have a jointed shell on their outside.

Even here, however, there are some queer doings. Sometimes, after a
five jointed leg has been pulled off, the one which grows in its
place, tho just as large and just as long, has only four joints.
Some crabs, and the like, which have the big claws unlike on the two
sides, if they lose either one, instead of growing one like it in
its place, make a new claw like the one that belongs on the other
side. Also, if they lose an eye, they grow a new one; but if they
lose both the eye and the eye stalk on which the eye is set, then
instead of an eye, they grow a small feeler. Really, one does not
know which most to marvel at—their strange power of growing new
parts, or their crazy way of growing them wrong.

But of all living repair shops the most uncanny are certain little
flat worms, called planarians. These are a half inch or less in
length, and fairly common in some places at the sea side, tho they
are likely to be mistaken for snails which they much resemble.

Cut off the head of one of these creatures, and inside a week he
will grow another—eyes, brain, mouth, and all as good as before. Cut
off both head and tail, and still the creature will straightway fit
himself out with new ones. Split him fairly in two lengthwise of the
body, and each half will grow out a new half; and there will be two
planarians, each complete, where only one was before.

Or if one splits the body in halves from the neck down, then each
half body grows a new half, and there is a single head with two
bodies. Or on the other hand, if one splits the head in two and
leaves the body, each half head will become a whole one. Then we
shall get a double headed planarian, a sort of Y-shaped creature.

Sometimes, after the planarian has been split in two from the neck
backwards, and formed a Y upside down with two bodies and one head,
another head, or occasionally two new heads, eyes, brain and all
complete, grow out facing backwards in the fork of the Y. Indeed the
animal seems to have a sort of mania for growing new heads and tails
in all sorts of unbecoming places. If he gets a wound or cut almost
anywhere in the body, and the wound happens to open on the whole
backward, out of that wound or cut will grow a new tail in addition
to the one he already has. But out of such wounds as face forward,
there grow out complete new heads. As many as seven different heads
have thus been made to grow on a single planarian—some on the middle
of the back, some underneath the body, some even on the sides of the
tail, and all, no doubt, greatly to the embarrassment of their
owner.

As for cut off heads and tails, one might expect them to grow new
bodies and become whole animals again. They do not, however, unless
the pieces are pretty large. A head, cut off close behind the eyes,
grows out, not a body, but another head. So all there is to the
creature is two heads, joined neck to neck and looking in opposite
directions.

All the time these things are going on, while the worms are making
new heads, or bodies, or the two halves of one body are filling out
again, the creatures can get nothing to eat. How then do they manage
to grow? They live on their own flesh. The old fragment is taken
down and used to build the new. An entire worm, made from a half
worm, is no larger than the half from which it came. The animal,
instead of growing large, grows small.

Whether it also grows young again, is by no means clear. Apparently
it does. At least, a planarian that does not get enough to eat,
proceeds at once to ungrow, becoming gradually smaller and smaller,
till after a few months, it is no more than a fifteenth part of its
former size. Whether it really becomes a baby worm again or not, it
certainly looks like one, for it is a pretty small human baby that
is not more than one fifteenth as large as a grown man.




XLVI

Little Monsters


One usually thinks of monsters as large. They are always, I believe,
large and horrible in the fairy stories—giants and ogres and dragons
and winged horses and chimeras and three-headed dogs and I don’t
know what else, all most extraordinary to imagine as well as nice
and creepy to read about. Really, however, there is no reason
whatever why a monster should be large. It must be horrid, or
unusual, or misshapen, or quite out of the ordinary. Then it is a
true and proper monster, no matter how small it is. And as a matter
of fact, some monsters, as strange as any maker of fairy stories
ever invented, are too small to be seen at all, unless one looks for
them with a microscope.

The planarian worms that I have just been telling about are
monsters. If a two-headed calf is a monster, that people who go to
the circus will pay to see, then surely a planarian is a still
greater monster, with one extra head in the small of its back,
another on the side of its tail, and four or five more hanging on at
various places anywhere over its body; and this to say nothing of as
many superfluous tails stuck on anywhere between. You know already
that these monstrous planarians are formed because the worm, instead
of healing up a cut as he should, seems possessed to grow a new head
or tail out of it. I am going to tell you now how certain other
strange monsters come to be.

You remember that earlier in this book, almost in fact, at the very
first, I told you about how the eggs of all animals are, to begin
with, single cells; and how afterwards, when they begin to grow,
they split, first into two cells, then into four, then into eight,
and so on, until finally, the single cell of the egg has become the
hundreds and thousands which build the young animal.

Some of these eggs, especially those of certain of the small sea
creatures such as star-fish and sea-urchins and the like, are
extraordinarily tough. Indeed they have to be, else few of them
would ever live to grow up at all. It is quite possible to take
these eggs when the single cell has divided into two, and shake
these two apart into two separate half eggs. You might think that
each half egg would form a half animal. Instead, much like the
planarian cut in halves, it forms a whole animal, half size.

Or we can wait till there are four cells, and shake these apart.
Then we get four complete creatures, each quarter size. Or we can in
the same way make eight. Beyond that we cannot go. Eight animals out
of what was intended for one is all that egg can manage.

On the other hand, it is possible to take a half dozen eggs, which
ought properly to have made as many separate creatures, and make
them stick together into one gigantic egg, from which will hatch out
a single gigantic animal, as large as the six or eight together
which ought to have come from six or eight eggs.

Other strange things happen when the eggs, instead of growing in
ordinary sea water, are put into water which has just a little bit
more or less of something in it. For common sea water contains some
half dozen different kinds of salt besides the one kind that people
get out and use on the table and for cooking; and more or less of
any one of these makes a salt water which is not quite the same as
the salt water of the ocean. In fact, you must have noticed that
salt water made with ordinary table salt does not taste by any means
the same as ocean water.

[Illustration: Accidents to growing fish eggs result in all sorts of
double monsters.]

A different kind of salt water (not very different either, I doubt
if anybody could tell them apart by the taste,) sometimes makes a
lot of difference with the creatures that grow in it. A little more
of one thing, for example, makes little star-fish with their
stomachs hanging out of their mouths, instead of inside their bodies
where all proper stomachs belong. A little more of another, makes
the sea minnows which live in it have only one eye, and that right
in the middle of their foreheads like the single eye of the giant
cyclops that I trust you have all read about long ago in the story
of Ulysses. If you haven’t you certainly had better right away, for
it is one of the great stories of the world, and has been told to
children, and to grown men and women as well, for at least three
thousand years, and nobody knows how much more.

Then again, by making things a little different in another way, the
baby fishes grow like other proper fishes except that they do not
have any hearts. Naturally, however, these particular monsters do
not live to grow up. People make all sorts of strange creatures
now-a-days by doing something to the young eggs when the new animal
is forming.

Curiously too, all this sort of thing may happen to almost any egg
by accident. If the two halves of the young egg get separated
entirely, then the egg brings forth twin creatures so nearly alike
that it is almost impossible to tell them apart at all. But if the
two halves get only partly separated, the result is some sort of
double monster.

So there are two-headed chickens, and two-headed snakes, and
two-headed turtles, and two-headed calves. Sometimes only the tip of
the nose is double. Sometimes it is the whole head. Sometimes there
are two heads, four front legs, two hind legs, and one tail.
Occasionally there is one body with eight legs, because the legs
doubled and the body did not.

Just about as often, the doubling begins on the other end. Then
there are two tails; or four hind legs and two front ones.
Occasionally, two complete bodies are joined at one small region
only They just missed being a pair of common twins It all depends on
how well separated the first two cells of the egg happened to get.

[Illustration: A two-headed turtle, a crab with an eye on one side and a
feeler on the other, and a child with two great toes on each foot.]

The famous “Siamese Twins” were about like any other twins, except
that they were fastened together side by side by a band of flesh
under the arm. They lived to grow up, married, and travelled about
the country exhibiting themselves for years. Finally one died;
thereupon the other died almost immediately after. But as for that,
any twins, if they are markedly alike, are likely to die at about
the same time.

Often, too, only the buds which are forming the limbs get divided.
Then there are extra fingers or toes or claws or thumbs. Cats, for
some unknown reason, are especially apt to have double paws or extra
toes. Oddly enough, tho nobody knows why, this happens more commonly
on the front paws than on the hind ones.

So you see, the strange power which a few creatures have of making
new parts, or extra parts, like the tails of lizards or the heads of
planarians, belongs also to all creatures when they are very young.
Most of them lose the power as they grow old. But in some animals,
like crabs and earth worms and planarians, it lasts up to old age.




XLVII

How The Animals Keep Their Tools Sharp


One can not do much of anything without tools, so of course the
animals have to have them. But because they haven’t sense enough to
make tools as we do, or even sense enough to use such tools as they
find ready made—pointed sticks and sharp stones and shells and bits
of bone and the like—as our very savage and very stupid ancestors
used to do, the tools of the animals have to grow on them.

The horse’s front teeth are his mowing machine, with which he cuts
down the grass. His great flat-topped grinding teeth that lie in a
long straight row along each side of his jaw behind the place where
the bit goes, are his millstones with which he grinds his oats and
corn into meal. But the cheek-teeth of dogs and cats, which also lie
along the sides of their jaws, are not millstones, but knives; and
their front teeth, like their claws, are traps to seize their prey
and long daggers to stab them with. For the cats and dogs do not
grind corn; they kill things. They are butchers, not millers.

In fact, when you come to think of it, nearly all the larger animals
are either millers or butchers. Either they grind up plants for
food, as horses and cows and sheep and goats do; or else they hunt
and kill other living animals and devour them, as do the cats and
dogs and wolves and foxes and hyenas and such like. Naturally, these
two sorts of creatures have quite different sorts of tools—claws and
sharp teeth for one, hoofs and grinding teeth for the other. Tho for
some reason or other, pretty much all the animals that are strong
enough to do any work, are miller animals. All the horses, oxen,
ponies, donkeys, buffalos, elephants, camels, goats, llamas, and I
don’t know how many more, that any body can get any work out of, all
have hoofs and eat plants. The Eskimo dog, so far as I know, is the
only butcher animal that earns a living. The rest just lie round and
growl.

So the miller animals have to grind their food. Now millstones have
to be kept rough; and as fast as they wear smooth, the miller has to
“pick” out the grooves to make them rough again. In like manner, the
horses and cows and sheep would soon wear their teeth too smooth to
be of any use, if they did not have a way of making them once more
rough. In these grinding, millstone teeth, the hard enamel, instead
of being on the outside of the tooth as with us, is doubled into
folds and plates, and mixed in with the bone of the tooth like the
streak of fat and streak of lean in bacon, or like the two colors in
marble cake. So the bone wears down faster than the enamel, and
leaves the enamel standing up in sharp ridges. Thus the top of the
tooth is always rough and ready to do its grinding; and because
these teeth are pretty long, an inch or more, they last a long time
before they are worn out.

But the dogs and cats, which have teeth like ours, with the enamel
all on the outside, soon wear down their teeth so that they will no
longer cut. That’s why dogs and cats and the wild creatures like
them, are so short lived. They are built to grow up quickly and die
young, because there is no use in having them made to live longer
than their teeth will hold out. At least that’s one reason Why they
don’t live longer.

The elephants have a curious way of taking care of their teeth. They
have to take care of them, because the elephants live to be very
old—a hundred years—a hundred and fifty—some people say even two
hundred. Now a hundred years is a pretty long time for a tooth to
keep on grinding leaves and twigs and roots, so the elephant has to
save his teeth and make them last.

To begin with, he saves his front teeth by not having any. His two
great tusks are two upper front teeth grown out till they are not
teeth at all, but crowbars that the elephant uses to grub up roots
with. They have no enamel and no root. So they can keep growing at
the inner end as fast as they wear off at the outer. Being
especially hard bone, they last as long as the elephant does, and
get larger and larger as long as their owner lives. After that, they
get turned into piano keys and billiard balls.

As the elephant spares his front teeth by not having any, he spares
his back teeth by not having many at a time. These are very large,
not quite as large as a leg of ham, but quite as large, often times,
as a loaf of bread.

The young elephant gets four of these big grinders, one on each side
of each jaw, and grinds away on them. After he has used these for a
few years and begun to wear them down, four new ones grow just
behind the first four. By and by, the first set gets worn out; then
the white blood corpuscles take down the roots, the crowns—what
there is left of them—fall off, and that is the end of that set. By
the time the elephant begins to get old, the second set of four
teeth has worn out, and a third set has come in. So a really old
elephant has only six teeth—the two tusks, if you call them teeth,
and four grinders.

The pigs do something the same. They hold back four very large
grinding teeth at the last end of the row, and don’t let them appear
till after the front grinders have been pretty well used up. So too
do we in a way. We don’t cut our “wisdom teeth” till we are past
twenty. Moreover, the wisdom teeth, which are last in the row, and
the eight grinders in front of them, two in each half of each jaw,
really belong to the milk set which we began to have when we were
babies. We don’t need them then. So we hold them back till we do,
though that isn’t for twenty years.

The rats, mice, squirrels, beavers, and other creatures that use
their front teeth as drills and chisels, have a pretty clever way of
keeping them sharp. You can easily see that a squirrel who puts his
teeth through the hard shells of nuts every time he gets a meal, or
a beaver who cuts through trees six inches across with his, or a
mouse or a rat, would use up any ordinary set of teeth in a few
weeks, and have to get on as best he could for the rest of his life
without any.

The grinding teeth of these creatures are like other grinders, that
last till they are worn down—and that’s all. But their four front
teeth, two in the upper jaw, two in the lower, are like the
elephant’s tusks. They have no roots, and they keep growing out from
the inner end as fast as they wear off at the outer. But in order to
have them held firmly in the jaw, having no roots, these front teeth
start way in at the back of the jaw close to the roots of the last
grinders. They grow out along the whole length of the jaw bone, past
all the other teeth, and come out at the front of the mouth. So the
front cutting teeth of mouse or rat or squirrel are about as long as
his legs, and start back almost to his neck. Besides this, they have
the hard enamel all in one plate at the front of the tooth, instead
of over the entire outside as we do. Then as the tooth wears down,
the bone wears fastest and leaves the enamel as a cutting edge,
always sharp.

The wild pigs do much the same thing with their four tusks. They
start them clear round at the back of the jaw, curve them past the
rest and bring them out at the sides of the mouth. Then they put two
together to make a tusk, and each grinds on the other and keeps it
sharp. But I don’t think that any animal ever does this sort of
thing with more than four teeth. He can make four grow all the time,
or two as the elephants do, or none. But the rest have to have
ordinary roots, and when they wear out, why that’s the end of them.

[Illustration: The fangs of a rattlesnake.]

But the sharks grow several rows of teeth at once, starting them
inside the mouth and letting them slide over the jaw in the skin.
These are not real teeth set in the bone, but only a sort of skin
teeth; and the shark grows them by the dozen, new ones as fast as
the old drop out. The snakes do much the same thing with their
poison fangs, and keep always at least one new pair folded down
behind the old ones, ready when these get pulled out. But snakes and
sharks don’t chew with their teeth, they only bite with them.

Now let’s see if you can’t find out for yourselves how it is that
pussy cat keeps her claws as sharp as needles. You can clip off the
points, but it will not be many days before she will make new ones,
just as sharp as the old. If you study the claw you will see how she
does it. The dog has the same device, only his nails are not so
sharp.




XLVIII

Why The Blood Is Salt


The blood is really salt. So is the sweat, as you can easily prove
by putting your tongue anywhere on your skin, after you have been
hot and sticky for a long time. And of course the tears are salt, as
no doubt you found out long ago, sometime when everybody was
especially horrid and they ran down into your mouth. In fact, pretty
much everything about the body is salty, for the reason that it is
all made of blood, which is itself pretty salt.

Now the blood is salt because the sea is. I much suspect that if the
ocean had always been fresh water, like the ponds and lakes, then
our blood, and the blood of all other animals, and all sweat and
tears and the like, would have been fresh also. For the sea and the
blood are salt with the same kinds of saltness. Their salt is mostly
the sodium chlorid which we use for table salt, and besides these,
there are calcium which makes limestone and lime and mortar and
plaster, potassium which makes potash and soft soap, and various
other metals including even gold. Altogether, sea water and blood
are extraordinarily alike, especially when you consider that there
are vast numbers of little animals in the sea that one can’t so
easily tell from the white corpuscles of the blood.

The reason for all this is that the simpler creatures of the ocean
do actually use the sea water for blood. Instead of having their
bodies shut up tight as we land animals have ours, so that nothing
gets into them unless we breathe or swallow, the inside of their
bodies is open to the sea water, and the sea water flows in and out
freely.

The sponges are like this. They take the water in through their
smaller holes, and let it out through the large ones. They breathe
the air that is in the water, and they turn their waste matter back
into the water again, just as if the water were their blood. Many
other creatures manage in this way, getting along without any
private blood of their own, and using the great common ocean
instead.

The rest of us have simply shut up our bodies and caught a little
bit of the ocean inside. We call this bit of ocean, blood; and we
have added various things to it. But still it is sea water, the same
old sea water that is the blood of the earth and of all the lowly
sea creatures that have no private blood of their own.

There are a great many other things also that we big land creatures
have and do for no other reason than that some small sea creature
began that way, and there has happened to be no special reason why
anybody should change.

For example, all fishes, as you know, breathe by taking water in
through their mouths and letting out again through a set of slits,
usually five in number, at the side of what would be the neck if the
fish had one. When the little fish is forming in the egg, at first
it does not have any of these “gill slits” and so has to breathe
through its skin. By and by, however, after the lower jaw has formed
and there is a mouth, these slits punch through and become the
convenient openings that we put a forked stick through when we go
fishing and so bring home our fish, instead of putting them in our
pockets, which is really a practice not at all to be commended.

So the little fish, while still in the egg, has these gill slits in
the side of his head because later, when he gets hatched out and
swims round, he is going to use them to breathe with. But the little
chick in the egg, after his lower jaw has begun to grow, also has
these same gill slits in the side of his neck, although when he
hatches out, he is going to breathe with lungs, and is never going
to have the least use for gills. So, too, do little puppies and
kittens and colts and calves and all the land animals that breathe
with lungs and haven’t the slightest use for any such holes.

Sometimes the hole doesn’t even break clear through. It starts from
the inside and comes out, and from the outside and goes in, but the
two tunnels never quite meet, and the hole never gets really open.
But whether the holes open through or not, they soon close up again,
and leave no sign that they have ever been there at all.

All except the first hole on each side, the one nearest the mouth.
That never closes again, but remains open and becomes the hole into
the ear. There is a hole in from the outside, as you know, the one
you used to put beans and pencils in, only you oughtn’t. And there
is another hole from the inside, beginning high up in the throat
just where you can’t see it, and running in till it almost joins the
other hole. Between the two is just a thin skin, which is the “drum”
of the ear, and if you get a hole in it you may never be able to
hear again. Because this drum never grew. It is the place that
remained after one tunnel came in from outside, and another from
inside, and the two didn’t quite meet.

So it comes about that all of us land creatures with backbones, who
breathe with lungs, start making gill slits which we can’t possibly
use. Then, because we have them on hand, we use the one farthest in
front for the hole of the ear, and close the rest up again. And we
take all that trouble—though it doesn’t trouble us much at the
time—just because various other backboned creatures, which live in
the water and don’t have lungs, had to make gill slits to breathe
with.

There are a lot of things of this sort—parts and organs and members
which one creature, while it is in the egg, makes and doesn’t use,
just because some other creature, when it grew up, had to have them.
You know what a short tail a hen or a turkey or a pigeon has—just a
stub of a tail, only just big enough to stick its tail feathers in.
But a little hen or turkey or pigeon, while it is still in the egg,
has a tail like other animals, long enough to wag.

There is a kind of salamander, which is unlike most salamanders,
efts, newts, and the like—these are all pretty much the same thing,
and you find them almost anywhere in the brooks and the ponds and
the damp woods. All of these that you are ever likely to see breathe
with gills like a fish, and can live in the water. Only instead of
having their gills covered over with a bony plate like the fish,
these creatures often have them outside, like a sort of lace collar
that hangs down at the side of their necks. Tom, the chimney sweep,
in Charles Kingsley’s famous tale, after he turned into a water
baby, had just such tufted gills so that he could swim under water
like any newt or eft, and if you haven’t read “The Water Babies,”
it’s certainly high time you did.

What I started to say is that this particular kind of salamander
lives on the land. So he doesn’t need gills and doesn’t have them.
But the little salamander, while he is still in the egg, has gills
like any salamander, though for all the use he can ever put them to,
he might just as well have been furnished with a pair of skates; for
by the time he hatches out of the egg, the gills have been taken to
pieces by his white corpuscles and the stuff used to make some other
part of the body.

All the same, if you break open the egg, take the little creature
out, and put him in the water while he still has gills, he will swim
away, and live under water as well as any water creature. But if you
wait till he hatches out of himself and has lost his gills, then if
you put him in the water, he will drown just as you would. So the
little salamander, that is going to spend his life on dry land,
still has gills while he is in the egg and has no use for them, all
just because other salamanders that live some of the time in the
water need gills to breathe with.

Then there are the snakes, which have lungs and breathe air like any
land animal. Only a snake is so very slender that there isn’t room
in him for two lungs side by side. So he has only one proper lung,
very long and thin, that runs from his neck pretty well down to his
tail. Nevertheless, the snakes still keep the other lung, small and
quite useless, tucked away beside the front end of the one they do
use. Other reptiles have two lungs, so the snakes have to have two
lungs also, though they can’t possibly use them both, and the other
which they don’t use, merely takes up room.

We human beings are just as bad as the rest. Every little while,
somebody comes down with appendicitis and has to be taken to the
hospital to have his “vermiform appendix” taken out. The appendix
isn’t the slightest use to anybody, we are better off without it,
but in cows and dogs and rabbits and kangaroos, and various other
animals, especially those that eat grass and leaves, it is a good
deal of use for helping to digest food. So we have to have it, to be
like the rest—and then pay the doctor to cut it off.

We don’t move our ears as horses and dogs and rabbits do. But still
the muscles are there; and people say that anybody who wanted to
take the trouble could learn to wag his ears like a baboon. Anyhow,
the muscles are there, though we don’t use them and other creatures
do.

We are said to have no fewer than one hundred and eighty such
useless things about us—all sorts of little things that are no use
to us at all and no use to half the animals that have them. But they
are useful to the other half, and we all have to be in the fashion.
Among these is a strange sort of single eye, set in the middle of
the head, so that we really have three eyes instead of two. Our
third eye is no bigger than a pea, and it lies tucked away between
the two sides of the brain, well inside the skull, where it cannot
possibly see anything. All the four-footed creatures have it. But in
none of them is it the slightest use, except in certain lizards,
especially in one in New Zealand, where it is a real eye placed in
the middle of the forehead between the other two. Several American
lizards also have this extra eye, though it isn’t good for much
seeing, among them the “horned toad” of California, which of course
isn’t a toad at all. So, just because a few lizards want three eyes
to see with, the rest of the four-footed animals and we human beings
have to have an extra eye that we don’t want, tucked away in pitch
darkness inside our heads.

But that’s the way things are managed—salt blood, and gill slits,
tails and gills in the egg and not out, extra lungs for the snakes,
and extra eyes for us all, like Little Three Eyes in the story. It’s
like the extra legs and tails on the lizard, and the extra heads on
the planarian. Nature gets started making things, and doesn’t seem
to be able to stop.




XLIX

Horses’ Fingers


The horse does have fingers—as one can easily see by counting up the
parts of his legs. Let’s start with the fore-leg, and begin at the
top next the body.

The sharp ridge just in front of the place where the saddle goes,
between that and the beginning of the mane, is mostly backbone, the
same part that we feel under our coat collars at the backs of our
necks. The horse’s shoulders, against which the collar rests when he
pulls his load, are mostly shoulder-blades, for the chest of all
four-footed beasts is narrow, and the shoulder-blades, instead of
being on their backs, as ours are, are at their sides. The upper
arm, between the shoulder and elbow is short, and is buried in
muscle so that one doesn’t notice it. So the first joint that shows,
where the fore-leg joins the body, is not the shoulder but the
elbow. The upper half of the arm is inside the skin.

The upper half of the horse’s fore-leg, then, is our fore-arm,
between elbow and wrist; and sure enough, that bone in the horse is
double just as it is in us, and in all animals that can twist their
hands round, tho the double bone isn’t the slightest use to the
horse. What we call the horse’s knee, then, is his wrist—and again,
like our wrists, it has a lot of little bones which make our wrists
supple so that we can bend them in all sorts of ways, but which also
are no use at all to the horse.

Then there is the horse’s shin—which isn’t shin at all, but the
palm-bone of the middle finger, which in us runs from the wrist to
the knuckle. The rest of the leg is the middle finger, with the
proper three joints, which every finger ought to have, and a
gigantic finger nail, which is the hoof. So the horse has a hand, and
a very large hand too; only he has lost all his fingers except one,
so that he really stands up and runs on the nail of his middle
finger. Nevertheless, the horse hasn’t quite lost the rest of his
hand; because along the sides of this middle-finger-palm-bone, which
we call the shin, lie two other little bones, too small to be any
use, which are the palm-bones of the first finger and the third. But
once in a long while a colt is born with two little hoofs on these
bones, so that it has three fingers instead of one. The rhinoceros,
on the other hand, has three fingers, all nearly the same size;
while the elephant keeps all five.

Now if you will notice the fore-leg of a cow, you will see that it
is just about like that of a horse, till you get down to the wrist.
Below that point, the cow, instead of having one palm-bone and one
finger, has two. Of course, then, it has two finger nails. The deer
has two fingers like the cow, and then two little ones besides, and
so does the pig. But the hippopotamus has all four fingers and lacks
only the thumb.

All of which, if you keep your eyes open, you can make out for
yourselves and more. Only I wish somebody would tell me why all the
animals that have horns at the side of their heads—cows and sheep
and goats and deer and buffaloes and I don’t know what all—have
either two fingers or four; and why the creatures that have one
finger, or three fingers, or all five, never have such horns. That
is something that nobody has yet been able to find out.

So much then for the horse’s hand—and what a whacking big hand it
would be, by the way, if it did have all five fingers instead of
only one! Let’s see what we can make out about the horse’s foot.

The thigh, as you can easily make out when the horse moves, starts
close up to the tail, and like the upper arm, is almost wholly
inside the skin. So the first joint that shows is the knee, and the
great muscles which, as you sit behind to drive, you see pulling you
along so strongly, are those of the calf of the leg. The joint that
comes nearest the driver’s feet, which we call the gambrel, is then
the heel. It certainly does look like a heel; and the rest of the
leg is the middle one of the five long bones of the foot, with the
middle toe on the end of it. So the horse stands on the end of his
middle toe, and his hind hoof is his middle toenail.

The cow, of course, keeps two toes with their foot-bones. The dog
has four. I don’t think a dog ever puts his heel down so as to stand
on the whole flat of his foot, except sometimes when he stands up to
beg. But cats and rabbits often do, when they want to stand up on
their hind legs to see as far as possible. Still they don’t do it
enough to have soles to their feet all the way back to the heel. But
the bears and the monkeys and a lot of other animals that can’t run
very fast, do put the whole foot down on the ground, and do have a
sole all the way back to the heel. In general, the faster an animal
can run, the more it stands up on its fingers and toes, the longer
its feet and hands are, the shorter its thighs and upper arms, and
the fewer fingers and toes it has. That’s why the horse, which I
suppose is about the fastest animal there is, has his fore-leg at
least half hand, and his hind leg mostly foot.

Some learned men devote their entire lives to making out just this
sort of correspondence between the various bones and muscles and
other parts of one animal, and those of others and of man. A most
fascinating game it is, too; and a game that everyone can play a
little, and keep on playing as long as he lives and keeps learning
more and more about animals.




L

How The Elephant Got His Trunk


According to the Just So Stories, in the high and far off times,
before any elephant ever had any trunk, there was a certain
Elephant’s Child who was afflicted with an insatiable curiosity. And
after this Elephant’s Child had been spanked for this same
insatiable curiosity by his tall aunt, the Ostrich, and by his tall
uncle, the Giraffe, and by his broad aunt, the Hippopotamus, and by
his hairy uncle, the Baboon, grievously and frequently, without
stopping, for a long time, he started out for the banks of the great
grey-green, greasy Limpopo River, to see what the Crocodile has for
dinner And the Crocodile caught the Elephant’s Child by the nose,
which was just a common nose and not a trunk at all, and pulled and
pulled and pulled, being minded to have Elephant’s Child for the
beginning of his dinner. And the Elephant’s Child spread out his
little four legs, and he pulled and pulled and pulled, until between
them, they stretched out the Elephant’s Child’s nose into the first
elephant’s trunk that ever was. So all other elephants have had such
trunks ever since.

This is Mr. Kipling’s story of how the elephant got his trunk. This
and several more like it of the Just So Stories, you must all read
for yourselves, for altogether they are about as good stories as
have been written by anybody this long time. Besides, something not
so very different from this adventure of the Elephant’s Child did
really happen. Only it didn’t happen in quite the same way; and
instead of there being one Elephant’s Child, there were many, many,
many, one after another for hundreds of years, each with a nose a
little more stretched out and a little more trunk-like than those
which came before it.

So what really happened is something like this: The elephant that
you feed peanuts to at the circus, now-a-days, is a strange sort of
beast, with his long trunk, his hairless body, his tall legs like
the stems of trees, and no front part to his jaws, so that he has
only his back teeth. The parents of the elephants that you see were
elephants like himself. So were his grand-parents; and their
grand-parents in their turn. But if you could go back a very long
time, back to the days when the first men appeared in Europe, you
would find that the elephants of those days were somewhat more like
other four-footed animals. For one thing, they had fur like other
animals, while instead of having only four grinding teeth in use at
once, they had nearly a full set as most other beasts have. These
are the great mastodons and mammoths, whose bones are still dug out
of the soil in the United States, in Europe, and in various other
parts of the world, and whose bodies have been found frozen in the
ice in Siberia, so well preserved that the dogs ate the flesh after
they were dug out. There are none of these left alive now, but we
still have the pictures of them which men long ago scratched on
pieces of bone or sketched on the walls of the caves in which they
lived before they knew enough to build houses.

[Illustration: Early man scratched pictures of the mammoth on pieces
of its own bones.]

Still older elephant-like creatures, whose bones we still find in
the ground, had front teeth, and very long muzzles, longer even than
the sharpest nosed dog, as long, let us say, as the bill of a duck,
a snipe, or any long-nosed bird. These, of course, had no trunks,
but snouts almost as long, with upper and lower jaw, and lips. Then
gradually, generation after generation, these long-snouted creatures
lost the front part of their jaws and their front teeth and their
under lips. They kept two upper front teeth, which grew very large
and became tusks. They kept also their long upper lip, without any
bones to hold it in place, so that it hung down and became a trunk.

[Illustration: The elephant has lost the front of his face except
his upper lip.]

So the elephant’s nose isn’t his nose only, but his nose and his
upper lip and part of the roof of his mouth. Next time you go to the
circus, you watch the elephant when he lifts his trunk so that you
can see the under side, and notice the rough cross markings that
other beasts have on the roofs of their mouths, and that you
yourselves can see in the mirror or feel on the roof of your own
mouth with your tongue. Then, when the elephant opens his mouth to
take a peanut, see whether his mouth doesn’t look as if his under
lip and the whole front of his jaws had been taken off just as I say
it has. But the proof of what I say, is there have been found near
Cairo, Egypt, the bones of the original elephant who didn’t have a
trunk, but did have a very long snout; and of other elephants
besides, the great-great-great-grandchildren of these, and the
great-great-great-grandfathers of the mammoths and mastodons, who
had begun to lose their long muzzles, and to turn their upper lips
into trunks.

It’s the same way with any other animal that is different from the
rest; his great-grandfather’s great-grandfather’s great-grandfather
many times removed wasn’t nearly so different from other animals as
he is. Take for instance, the horse. He is a good deal different
from other beasts, with his great size and speed, and his strange
single-fingered hand, and his strange single-toed foot, and himself
standing up on the nails of his middle fingers and toes.

[Illustration: Our single-toed horse has been made over from a
four-toed one.]

But out in Wyoming and thereabouts they dig out of the ground the
bones of old horses that had their middle finger nails and their
middle toe nails, which are their hoofs, considerably smaller than
our horses have them; while at the same time, the little splint
bones, which are the remnants of the fingers and toes next the
middle, are much larger than they are now-a-days. Still deeper in
the ground, are the bones of still older horses, which had three
hoofs on each foot, but the middle one was largest and the two at
the side did not touch the ground, just as they don’t in the deer.
These horses were only as large as the smallest ponies.

Lower in the ground, still, come the bones of yet older and smaller
horses, with three hoofs on each foot, all about the same size; but
the hoof has become more like a regular toe with a nail, about like
a pig’s, which are about half way between hoofs and toes. Buried
even deeper in the earth are the bones of horses no bigger than
large dogs, that look like horses, and yet look something like dogs
also, and something like sheep; which have four toes on their front
feet, that are real toes, only just beginning to turn into hoofs.
Last of all, there are the oldest horses of all, no larger than
cats, with four toes on their front feet, and the splint bone
belonging to the thumb, with claws like a dog’s that are not hoofs
at all, horses that had a tail like a dog’s, and looked almost as
much like a dog as like a horse, only it had grinding teeth and ate
herbs.

So gradually, one little change at a time, this creature that was
almost as much dog as horse, lost one toe after another, increased
in size, got up on his toes, and became a modern trotter. At the
same time, another animal that looked much like one of these little
dog-horses, only he was on the whole a little more like a dog, kept
on getting more and more dog-like, with smaller claws and sharper
teeth and slenderer nose, till he became something that was neither
dog nor wolf nor fox, but a general mixture of all three, with some
cat and some hyena thrown in.

They find out in Wyoming, also, the bones of another creature that
has been called “the father of cats”—_Patriofelis_ as they say it in
Latin. But the father of cats is also a great deal like a seal, and
something like an otter—at least he used to take readily to the
water, as our modern cats certainly do not.

In short, if any of us had lived in North America at a time not so
very long before the first human beings actually did live somewhere
on the earth, we should be surely put to it to tell one sort of
beast from another. The horses looked like dogs, and the dogs looked
like cats, and the cats looked like seals, and there were pigs that
looked like wolves, and camels that suggested sheep, to say nothing
of cows that you couldn’t tell from deer. Each beast used to be a
general mixture of all beasts, and only since there have been men in
the world have the beasts changed into all the various sorts which
we know.

[Illustration: Extinct Reptiles, which looked like a mixture of
Alligator, Rhinoceros and Kangaroo, but their Bones were more like
the Bones of Birds.]

The snakes used to have legs. In fact, a snake is not much more than
a lizard that has left off his legs for the sake of crawling into
smaller holes. But the snakes and lizards are much older than the
beasts; so that there were plenty of both in the world long before
there were horses and cows and dogs and cats and all the rest of the
beasts with fur—and still longer, naturally, before there were any
elephants or men.

The early birds, too, were a good deal like lizards. They had teeth
like a crocodile, and long tails with feathers stuck in the sides,
and tho they had wings like a proper bird, they had also claws on
their wings, which were really three-fingered hands with feathers
growing on them. But even our modern birds still keep the old lizard
scales on their legs, tho they have long ago changed them to
feathers on their bodies.

It is exactly the same with our own ancestors as with the ancestors
of any beast or bird or reptile. The bones of early men are still
found in the caves of Europe, mixed with the bones of the animals
which they ate, and buried in the earth and stone that have fallen
from the roof. These men were true and proper human beings, who
walked on their hind legs and, I suppose, talked. But they were not
quite such men as we are, for their skulls were a little flatter on
top, the bony ridges over their eyes were a little heavier and their
teeth a little larger.

These ancient men, like nearly all Indians before White Men came,
and for that matter, like our own prehistoric ancestors in Europe,
had no metal tools, and used only stone for hammers, axes, and
arrowheads. So there are found, all over Europe, vast numbers of
stone tools and weapons, cruder as they are older, until the very
earliest are only common pebbles that have been banged by use.

No skeletons are known of these early men, but only skulls, commonly
a good deal broken. So we do not know very much about these people.
But for the most part the hollow in the brain-case is just a trifle
larger over the left ear, as if even they had a speech center, were
right-handed, and could talk.

On the other hand, some very ancient apes had skulls and teeth more
like ours than any modern gorilla or chimpanzee ever has. So it
seems to be a general rule that, just as young animals and plants
tend to be more like one another than they will be when they grow
up, so very ancient creatures tend to be less unlike each other than
their present-day descendants are.




LI

Something Nobody Understands


Now, my reader, we have come to the last chapter of this book, which
is going to be the hardest chapter of all, and I think, the most
important. For though it is going to be about something that nobody
quite understands, and something that the more one thinks about, the
more he doesn’t understand it, nevertheless it is something that you
will have to think about many times in your lives hereafter, and you
might as well make a beginning. Besides, though you won’t understand
all that I am going to say—largely I am afraid, because I don’t
understand it myself—still I trust that you will remember some of
it; and by and by when you are sorely puzzled over these matters,
perhaps it will help you out.

If you will think back over what I have already told you in this
book about animals and plants, and recall also what you have
yourselves seen, and what you have learned about your own bodies and
the way they work, I think you will agree with me, that of all the
strange and wonderful things in this most strange and wonderful
world, a living thing is the strangest and the most wonderful.

Think, for example, how a little egg, no bigger, it may be, than the
head of a pin, with no help from outside, except perhaps a little
fresh air and a little warmth, just goes ahead and makes itself over
into a grown animal. Consider, too, how well it does the job—every
scale and feather and tooth and bone and gland and muscle and claw
and nail and blood vessel and nerve and hair, all just in the right
place, and just of the right size. When one builds a house, the
owner consults the architect, and the architect advises with the
contractor, and the contractor puts some of the work on the
sub-contractor, and the contractor and the sub-contractors direct
the workmen; and among them, in a year or so, they manage to get the
house together. But in the world of living things, one little fleck
of living protoplasm goes ahead all by itself, and builds a whole
living animal, sometimes in a few days. Yet there are more different
parts to be made and fitted together in one of your little fingers,
than in any common dwelling house, even tho you count the laths
behind the plastering and the shingles on the roof—yes, and the
nails that hold them on. As for your brains, they are, each one of
them, for complexity, like all the parts of all the houses in a
fair-sized city, with all the furniture, and all the tableware, and
all the pots and pans in all the kitchens thrown in for good
measure. If you think that a watch or a battleship is a complicated
affair, think what goes on in the brain of a tiny ant.

Think, too, how resourceful an egg is. It tries its best to grow
into a proper animal; but if somebody interferes, to prevent that,
then the egg goes pluckily ahead and makes the best it can of a bad
matter. If it gets jarred apart so that it cannot make one animal,
why then it makes two, or four, or eight. When it can make neither
one animal nor two proper and separate twins, it doesn’t give up,
but makes some sort of double monster, that at least manages to keep
alive. For my own part, I feel a sincere respect for eggs. I wish
more of us had their pertinacity.

After the egg has made itself into a grown animal, consider how well
fitted out that animal is. It has, usually, eyes, nose, mouth, ears,
sense of touch, of heat and cold, of taste, and the rest. It has
born in it the instincts to find its proper food, to find or build
its shelter, to take care of its young, to escape its enemies, and
in general to like the things which it is best for it to do. Yet if
it doesn’t happen to have these sense organs and instincts and the
rest, still it always has something nearly as good, and manages
somehow to get its living in the world.

Yet I sometimes think that the most extraordinary thing about living
things, both animals and plants, is the enormous number of different
kinds of them. There are some twenty different sorts of cats, of
various sizes from lions down; and twice as many different sorts of
dogs, wolves, foxes and other dog-like creatures. There are
thirty-two different kinds of willow trees in North America,
thirty-six different kinds of pine trees, Sixty-three different
oaks. As for insects, about three hundred thousand different sorts
have already been given names; and there are at least ten times as
many more that are still nameless. Do you know how many different
races of men there are that you can tell apart by their
looks?—Chinamen, <DW64>s, White men, Tartars, Eskimo, Indians,
Malays, Arabs, and I don’t know how many more, all alike in being
human, and yet all different.

Why there should be such a lot of different animals and plants and
men is something that nobody fully understands. We do know, however,
and know very certainly, that there haven’t always been all these
various sorts in the world. If we could go back a sufficient number
of thousand years, we should come to a time when, instead of twenty
sorts of cat, there were only ten. Back of that, was a still more
ancient time when there were only five. A long time before even that
early day, there was only _Patriofelis_, “the father of cats,” and
even he, as you know, was also a good deal like a seal.

So too there must once have been a “father of dogs” whose
descendants have changed, some into proper dogs, and some into
wolves, and some into foxes, and some into jackals, coyotes, dingos,
fennecs, and the rest of the forty-odd sorts of wild dogs—to say
nothing of all the various tame dogs, collies and terriers and
mastiffs and bull dogs and setters, that you can count up for
yourselves.

Once too, there was only one kind of man. He probably lived
somewhere in southern Asia, and spread out from there, till he
possessed the whole earth. Some of him went south-east into the
Pacific Islands, and changed into Malays and Australians. Some of
him went south-west into Africa and became <DW64>s. Some became
Persians, Egyptians, Hindus, and Arabs. Those that kept on further
and entered Europe turned various shades of white and became us. For
very few white men are really white—only certain Swedes and
Norwegians and Danes. The rest of us, who call ourselves white, are
merely not quite so black as our very-many-times-great-grandfathers
and our somewhat distant cousins, the <DW64>s.

Most of these early men, however, started north-east; and because
they couldn’t very well cross the great mountains and deserts in
central Asia, they ran round the eastern end, and then came back on
the other side. On their way, they turned to Chinamen and Japanese.
Those that got way up to the north under the Arctic circle became
Eskimos. Some of them crossed over by way of Siberia and Alaska (for
these countries have not always been as cold as they are now) and
turned into American Indians.

Then, after these people had got north of the great Asian mountains,
others of them turned west, and came clear across into Europe. In
fact, they came near to overrunning Europe during the last days of
the Roman Empire so that the famous Charlemagne had to fight them in
the eighth century, as you will learn when you study history in
school, or still better when you read stories of knights and
paladins of the early Middle Ages. So part of us white men came to
Europe, and then to America, directly from southern Asia. And part
of us came round by way of China and Tartary and Russia; tho now we
are all mixt up together so that no one can tell which from t’other.
Yet even now, whenever you get up in the gallery and look down on
the people’s heads, you can see that some white men have long,
egg-shaped heads and narrow faces, and some have round bullet-shaped
heads and broad faces. The long sort of head came straight up from
India, by way of Asia Minor; and the round sort came round the end
of the mountains and across central Asia. That’s the reason why, tho
we are all white men, we can’t wear one another’s hats.

That’s about the way it is with all kinds of animals and plants.
Each one starts somewhere, and spreads out in all directions as far
as it can, gradually changing as it goes, until from being one sort
of pine or oak, there come to be dozens, and instead of one kind of
cat or dog there are a score. On the whole, too, the latest kinds of
animals and plants are better than the earlier ones and there are a
great many more of them. This is what we call Evolution—but why it
all happens or what it is all for, Is just precisely “one of those
things that no fellah can find out.”

Still one can’t help thinking that if we men can make as many things
as we do out of iron—knives and saws and locomotives and bridges and
sky-scrapers and battle-ships and all sorts of wonderful machinery,
and make them better and better all the while, some wiser being than
ourselves might make other and still more wonderful machines out of
the life-jelly which we call protoplasm, and keep making them better
and better and more and more kinds of them as the ages have gone on.




INDEX

  Air, importance of clean, 276.
  Ambidexters, 121-122.
  Amoeba, 40;
    feeding of, 245.
  Ants, 194-209.
  Anti-toxin, 280.
  Bacteria, 31, 38, 71, 141;
    and disease, 266 and following, 274 and following.

  Bean, 20-23, 146.
  Bee, 70, 71.
  Birds, instincts of 96-98;
    lizard-like, 351.
  Blind spot, 186-188.
  Blood, 32, 43-44;
    growth of, 50-51;
    and air, 242 and following;
    waste matter in, 253 and following;
    poisons in, 263 and following;
    living creatures in, 268 and following;
    as defence, 279 and following;
    messages by way of, 294 and following;
    salt in, 329 and following;
    sea water as, 330 and following.
  Bones, of chick, 5;
    of fish, 16;
    growth of, 49-50, 300.
  Brain, of chick, 4, 5;
    of fish, 16;
    and speech, 114-118;
    centers in, 123-135;
    accidents to, 127-133;
    complexity of human, 357.
  Breath, why we get out of, 257 and following.
  Breakfast table, experiments in recalling, 228-229, 234.

  Camel, 106.
  Cat, 12;
    hunting instinct in, 86-87;
    and mouse, 94-95;
    and food in bottle, 102;
    double paws of, 320;
    teeth of, 321;
    sharp claws of, 328;
    feet of, 341;
    ancestors of, 350.
  Caterpillars, and moths, how find their way, 158-163;
    change to butterflies, 297 and following.
  Cells, 31-41, 238;
    of eggs, 25-27;
    of human beings, 27-29;
    of plants, 35-37;
    of bone, 45.
  Chick, hatching of, 1-2;
    growth in eggs, 3-6;
    instincts of, 91-93;
    gill slits of, 332 and following.
  Children, 24;
    growth of, 56-58, 61-64;
    best plays for, 58-60;
    grip of very young, 75-76, 84;
    swallowing of, 77;
    instincts of, 78-85, 93-94;
    compared with animals, 112-114.
  Cold, and heat, sense of, 169-170;
    experiments with, 191-192;
    how we catch, 286.
  Colors, how we see, 177, 183-185, 197-198.
  <DW53>, and box, 102-104.
  Corn, 66-68.
  Cork, 43.
  Cow, 12, 113, 246;
    and stuffed calf, 105-106, 112;
    limbs of, 340, 341.
  Crab, breaking joints of, 309 and following;
    eye of, 310, 319.

  Date palm, 68.
  Dog, 12, 61-62, 246;
    hunting instincts in, 86-88, 95;
    story of, 100,-101;
    advantage of speech to, 110,-111;
    sight and smell in, 220-222;
    teeth of, 321 and following;
    claws of, 328;
    feet of, 341;
    ancestors of, 349 and following.
  Dolls, why girls play with, 78-79.

  Ears, of chicks, 4;
    of fish, 16, 211-212;
    of beasts, 28;
    sixth sense in, 166-167, 189;
    of ants, 200-202;
    of other insects, 210;
    of jelly-fish, 211;
    of various animals, 211-213;
    making of, 332;
    muscles of, 336.
  Ear minds, 234-235.
  Egg, of hen, 1-6, 27;
    of other birds, 7-11, 22, 27, 31, 72-73;
    of reptiles, 7-8, 10, 12;
    of fishes, 7, 8, 12, 14-19, 22, 27, 70, 317;
    of star-fish and sea-urchins, 8-9, 24-27, 69-70, 72, 315, and
    following;
    of frogs and toads, 9-11, 27;
    of beasts, 12-13, 28;
    living portion of, 43;
    birds idea of, 97;
    effect of accidents to, 315 and following, 358 and following.
  Elephant, teeth of, 323 and following;
    trunk of, 343 and following.
  Enzymes, 291 and following.
  Evolution, 356.
  Eyes, 32;
    of chicks, 4, 5;
    of fishes, 16;
    how formed, 17-18, 28;
    images in, 175-176;
    as camera, 176;
    and color, 177-179, 183-185;
    object of two, 185-186;
    blind spot of, 186-188;
    of ants, 197-200;
    of various creatures, 214-215, 219;
    of insects, 215-217;
    black, 300 and following;
    third, 336.
  Eye minds, 229-233, 237.

  Fatigue, cause of, 255 and following.
  Fighting in play, 88-90.
  Finger nails, 29, 34, 43, 53.
  Fish, growth of, 53-54, 61, 70;
    feeding of, 246;
    monsters, 317 and following;
    gills of, 331.
  Flies and disease, 269-273, 274 and following, 284.
  Food, as fuel, 244 and following, 252 and following;
    importance of clean, 275.

  Games, best for children, 58-60;
    why children like, 81-85;
    of animals, 86-90.

  Hair, 80, 43, 58;
    whitening of, 301 and following.
  Head, of chick, 4;
    of fish, 16;
    early growth of, 293;
    shapes of human, 355.
  Horns, 34.
  Horse, 12;
    finds its way, 222-224;
    epidemic among, 284;
    teeth of, 321 and following;
    limbs of, 338 and following;
    feet of ancient, 348 and following.
  Hunger and thirst, sense of, 172.
  Hydra, result of injuries to, 307 and following.

  Insects, breathing of, 242 and following;
    and disease, 269.
  Instincts, 74-98, 101, 109.

  Jelly-fish, 40, 46.

  Leading shoot, 144-146.
  Life, length of in various creatures, 61-64;
    nature of, 239 and following.
    life-jelly, 25, 27, 46, 238, 249, 251, 303, 356.
  Light, growth and turning of plants toward, 147-148, 151-152,
  156-157;
    movement of animals toward, 159-164, 196-197.
  Liver, and sugar, 260;
    and bile, 278.
  Lizard, new legs and tails of, 304 and following;
    third eye of, 337.
  Lockjaw, 267 and following, 277.
  Lungs, of chicks, 5, 6, breathing by, 243 and following.
  Lymph cells, as defence, 280 and following;
    duties of, 296 and following, 303.

  Mammoth, 345.
  Man, ancient, 351 and following;
    early migrations of, 354 and following.
  Milk, importance of clean, 269, 275.
  Monkey, 12;
    and box, 101-102;
    and colds, 285;
    feet of, 341.
  Mosquitoes and disease, 269.
  Mouse, 61-62;
    and disease, 269;
    teeth of, 325.
  Muscles, growth of, 50;
    working of, 240.
  Muscle minds, 235-237.
  Muscular sense, 167-169, 191, 223-225.

  Nausea, 173.
  Nerves, of chick, 4-5;
    growth of, 50.
  Nose, and smell, 189-190;
    of ants, 203-209;
    bacteria in, 277-278.

  Pain, sense of, 170-172.
  Parents, advantage of two, 65-66;
    cases of one, 71-73.
  Parrots, 108-109, 113.
  Pigs, and rattlesnakes, 264;
    teeth of, 325 and following.
  Plants, as engines, 240-241;
    take food from air, 250, 254;
    sickness of, 286 and following.

  Rabbit, 12, 113, 341.
  Rat, and maze, 104-105;
    and disease, 269 and following;
    teeth of, 325.
  Reptiles, 63.
  Roots, growth of, 50, 146-147, 154-155.

  Salamander, 333 and following.
  Sea-anemone, 69, 136-140, 307.
  Second wind, 259.
  Seeds, of bean, 20-23;
    and pollen, 66-69.
  Shark, teeth of, 327.
  Sight, illusions of, 177-184.
  Skin, 32-34, 43, 53, 75;
    as defence, 276 and following.
  Snake, poison of, 262 and following;
    teeth of, 327;
    lung of, 335;
    limbs of, 350-351.
  Soils, diseases of, 288.
  Speech, 108-118;
    and brain, 114-118;
    and thought, 119-120.
  Speech centre, 120-124.
  Sponge, 242, 330.
  Squirrel, teeth of, 325.
  Star-fish, growth of young, 54-55;
    food of, 246;
    re-growth of, 308 and following;
    monsters, 315 and following.
  Sugar, as food, 244-245, 251, 253, 291;
    as poison, 259 and following.

  Tadpole, change of to frog, 296 and following.
  Tails, of human beings, 107-108;
    of birds, 333.
  Taste, 190-191, 218.
  Teeth, of children, 29, 325;
    growth of, 44-45, 49-50, 299 and following;
    importance of clean, 277 and following;
    as tools, 321 and following.
  Tickling, 89-90.
  Touch, errors of, 192.
  Trees, living part of, 42-43;
    growth of, 48-49, 53-54.

  Vaccination, 279 and following.
  Vine, climbing of, 153-154.

  Worms, feeding of, 245;
    repair of injuries to, 305 and following, 311 and following;
    monsters, 314.

  Yeast, 46, 71, 292.





End of Project Gutenberg's Natural Wonders, by Edwin Tenney Brewster

*** 