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  [Illustration: THE OLDEST WOMAN IN THE WORLD AND HER SON

  Baba Vasilka is 126 years old, and her son Tudor is 101.
  They are peasants, and have lived all their lives in a
  little village in Bulgaria. They are typical examples of
  people who live to a great age by the use of soured milk,
  as it has been their principal food all their lives.]


                         The
                Bacillus of Long Life

  A Manual of the Preparation and Souring of Milk for
    Dietary Purposes, Together with an Historical
     Account of the Use of Fermented Milks, from
        the Earliest Times to the Present Day,
         and Their Wonderful Effect in the
           Prolonging of Human Existence

                         By
             Loudon M. Douglas, F.R.S.E.

               _With 62 Illustrations_


                 G. P. Putnam's Sons
                 New York and London
               The Knickerbocker Press
                        1911


                  _Revised Edition_


                    COPYRIGHT, 1911
                         BY
                  G. P. PUTNAM'S SONS


             The Knickerbocker Press, New York




PREFACE


This book has been designed with a view to meet an extensive demand for
definite data on the subject of Soured Milks. The author has had this
matter brought before him, times without number, by those inquiring for
authentic information on the subject, and he has therefore considered it
desirable to gather together such information as is available in
connection with ancient and modern practice. He has endeavoured to
present this to the reader in concise form.

The author is indebted to many friends for their assistance in getting
the book together, and would specially mention Dr. H. B. Hutchinson,
Bacteriologist, Rothamsted Experimental Station, for assistance in
connection with the bacteriology of fermented milks; Mr. Thomas Douglas,
of Wimbledon, who has assisted with the chemistry of the subject; Mr. S.
Javrilovitch, of Belgrade, Servia, for local information and
illustrations; Dr. Otokar Laxa, Bacteriologist, of Prague, Bohemia, for
general assistance; the editor of _Bacteriotherapy_, New York, U.S.A.,
for the use of the group of illustrations 30-44; the publishers of the
_Centralblatt fuer Bakteriologie_, Jena, for the group of illustrations
14-29; and many others, some of whom are referred to in the text.


  CONTENTS


  CHAPTER                                                    PAGE

     I.--INTRODUCTORY--HISTORICAL                               1

    II.--FERMENTED MILKS                                       15

   III.--THE CHEMISTRY OF MILK                                 47

    IV.--HANDLING OF MILK                                      68

     V.--THE BACTERIOLOGY OF FERMENTED OR SOURED MILK          84

    VI.--THE PREPARATION OF SOURED MILK IN THE HOUSE          125

   VII.--THE PREPARATION OF SOURED MILK IN THE DAIRY          139

  VIII.--SOURED MILK IN HEALTH AND DISEASE                    151

         INDEX                                                165




ILLUSTRATIONS


  FIG.                                                       PAGE

       THE OLDEST WOMAN IN THE WORLD AND HER SON   _Frontispiece_

       THE PASS OF BUKOVA                                       2

       KABYLES SOURING MILK                                     4

       THE HANDLING OF MILK IN THE PYRENEES                     8

       THE CONSTITUENTS OF MILK                                48

   1.--MICRO-PHOTOGRAPH OF A DROP OF WHOLE MILK                58

   2.--MICRO-PHOTOGRAPH OF SEPARATED MILK                      58

   3.--MICRO-PHOTOGRAPH OF CREAM                               58

   4.--PHOTOGRAPH OF TWO PETRI DISHES, WHICH HAVE BEEN
         INOCULATED WITH ORDINARY MILK                         60

   5.--THE CREAMOMETER                                         62

   6.--TESTING-GLASS FOR EXTRANEOUS MATTER IN MILK             62

   7.--LACTOMETER AND TEST-GLASS                               64

   8.--PASTEURISER                                             78

   9.--CONTINUOUS APPARATUS FOR THE PRODUCTION OF LARGE
         QUANTITIES OF SOURED MILK                             82

  10.--A MILK-FILLING APPARATUS                                90

  11.--SECTION THROUGH A KEPHIR GRAIN                          94

  12.--_Streptococcus lacticus_ (GROTENFELDT) GROWING ON
          LACTOSE-AGAR, STAINED BY GRAM'S METHOD               96

  13.--PHOTO-MICROGRAPH OF PREPARATION FROM ARMENIAN SOURED
         MILK (MATZOON)                                       106

  14.--GRANULE BACILLUS FROM YOGHOURT. SHREDDED PREPARATION
         OF A FRESH SKIM-MILK CULTURE                         110

  15.--GRANULE BACILLUS FROM YOGHOURT, CULTIVATED AFTER
         THE USUAL AGAR METHOD                                110

  16.--GRANULE BACILLUS FROM YOGHOURT. AGAR MILK SUGAR
         CULTURE                                              110

  17.--_Bacteria W._ FROM MILK, CULTIVATED TWENTY-FOUR
          HOURS                                               110

  18.--AGAR MILK SUGAR CULTURE. FROM THE ORIGINAL BULGARIAN
         YOGHOURT                                             112

  19.--AGAR MILK SUGAR CULTURE. SURFACE COLONY OF GRANULE
         BACILLUS FROM CALF'S STOMACH                         112

  20.--AGAR MILK SUGAR CULTURE. DEEP-LYING COLONY
         OF GRANULE BACILLUS FROM CALF'S STOMACH              112

  21.--AGAR MILK SUGAR. COLONY OF _Bacterium W._ FROM
         YOGHOURT                                             112

  22.--TWO COLONIES OF _Bacillus Acidophilus_ FROM CALVES'
         MANURE                                               114

  23.--BEER-WORT GELATINE                                     114

  24.--SHREDDED PREPARATION OF BULGARIAN ORIGINAL YOGHOURT    114

  25.--GRANULE BACILLUS FROM YOGHOURT. CULTIVATED IN SKIM
         MILK IN TWENTY-FOUR HOURS                            114

  26.--_Bacteria W._, AGAR MILK SUGAR CULTURE                 116

  27.--_Bacteria acidophilus_ FROM CALVES' MANURE             116

  28.--MUCUS FROM CALF'S STOMACH INOCULATED INTO MILK AFTER
         EIGHT TRANSFERRINGS                                  116

  29.--DIPLOSTREPTOCOCCUS FROM YOGHOURT. PURE CULTURE IN
         SKIM MILK                                            116

  30.--PHOTO-MICROGRAPH OF PREPARATION MADE FROM YOGHOURT,
         SHOWING YEAST CELLS                                  118

  31.--PHOTO-MICROGRAPH OF SMEAR FROM GREEK CURDLED MILK
         CALLED "GIAOURTI"                                    118

  32.--PHOTO-MICROGRAPH OF SOURED MILK INOCULATED WITH
         A TABLET CONTAINING VIABLE AND PURE CULTURES OF
        _Bacillus bulgaricus_                                 120

  33.--PHOTO-MICROGRAPH OF MILK INOCULATED WITH A FERMENT
         TABLE IN WHICH _Bacillus bulgaricus_ IS NO LONGER
         VIABLE                                               120

  34.--PHOTO-MICROGRAPH OF SMEAR OF CULTURE OF _Bacillus
         bulgaricus_                                          122

  35.--_Bacillus bulgaricus_, SHOWING THE CULTURES
          IN ENGLISH COW'S MILK                               124

  36.--PHOTO-MICROGRAPH OF PURE CULTURE OF _Bacillus
         bulgaricus_                                          124

  37.--PHOTO-MICROGRAPH OF SMEAR OF COMBINED CULTURE
         OF _Bacillus bulgaricus_ AND _Bacteria
         paralacticus_                                        124

  38.--PHOTO-MICROGRAPH OF SMEAR OF ONE-MONTH CULTURE
         OF _Bacillus bulgaricus_                             126

  39.--PHOTO-MICROGRAPH OF CULTURE OF _Bacillus bulgaricus_
         IN MALT                                              126

  40.--PHOTO-MICROGRAPH OF SMEAR FROM MILK THAT HAD BEEN
         ALLOWED TO SOUR SPONTANEOUSLY                        126

  41.--PHOTOGRAPH OF AGAR CULTURE, INOCULATED WITH A LACTIC
         POWDER                                               128

  42.--PHOTOGRAPH OF TEST-TUBES OF STERILE MILK, INOCULATED
         WITH A TABLET PREPARATION SAID TO CONTAIN PURE
         CULTURES                                             128

  43.--PHOTOGRAPH OF TEST-TUBES OF STERILE MILK, EACH TUBE
         HAVING BEEN INOCULATED WITH A TABLET OF A
         PREPARATION SAID TO CONTAIN PURE CULTURES            128

  44.--PHOTOGRAPH OF TEST-TUBES OF STERILE MILK INOCULATED
         WITH A TABLET OF "LACTOBACILLINE"                    130

  45.--APPARATUS OF "LE FERMENT" CO.                          129

  46.--SOURED MILK APPARATUS OF THE MAYA BULGARE COMPANY,
         LIMITED                                              130

  47.--LACTIC FERMENTS, LIMITED, APPARATUS                    131

  48.--MESSRS. ALLEN & HANBURY'S SOURED MILK APPARATUS        132

  49.--VIRONELLE APPARATUS FOR SOURING MILK, MADE BY
         MESSRS. CLAY, PAGET & COMPANY, LIMITED               132

  50.--"LACTOBATOR" MADE BY MESSRS. CHARLES HEARSON & CO.,
          LIMITED                                             140

  51.--MESSRS. HEARSON & COMPANY'S "LACTOBATOR"               142

  52.--EDGAR'S "LACTOGENERATOR," SOLD BY THE DAIRY SUPPLY
         CO., LIMITED                                         143

  53.--APPARATUS OF THE WILLOWS REFRIGERATING CO., LIMITED    144

  54.--"LACTO" APPARATUS OF THE DAIRY OUTFIT CO., LIMITED     145

  55.--STERILISING APPARATUS FOR STERILISING MILK ON
         THE LARGE SCALE                                      146

  56.--ANOTHER METHOD OF STERILISING (DAIRY SUPPLY
         CO., LTD.). AN AMERICAN APPARATUS FOR PREPARING
         SOURED MILK                                          148

  57.--AN AMERICAN APPARATUS FOR PREPARING SOURED MILK        149




THE BACILLUS OF LONG LIFE




CHAPTER I

INTRODUCTORY--HISTORICAL


The milk industry is one of the oldest known to mankind, and it is
difficult to imagine a time when milk in one way or another did not form
a part of the diet of the human race. There is a good deal of evidence
to show that in Paleolithic and Neolithic times, cattle were part of the
possessions of the nomadic races; and, according to the Vedas, the
manufacture of butter was known in India 1500 years B.C.

In the eastern part of Europe, milk has always been looked upon as one
of the principal kinds of food, but not necessarily the milk of cows,
as, from ancient times to the present day, the milk from camels,
buffaloes, sheep, and goats has been used indiscriminately throughout
the East.

According to Layard,[1] "the Bedouins do not make cheese. The milk of
their sheep and goats is shaken into butter or turned into curds; it is
rarely or never drunk fresh, new milk being thought very unwholesome, as
soon by experience I found it to be, in the desert. I have frequently
had occasion to describe the process of making butter by shaking the
milk in skins. This is also an employment confined to women, and one of
a very laborious nature. The curds are formed by boiling the milk, and
then putting some curds made on the previous day into it and allowing it
to stand. When the sheep no longer give milk, some curds are dried, to
be used as a leaven on a future occasion. This preparation, called
_leben_, is thick and acid, but very agreeable and grateful to the taste
in a hot climate. The sour milk, or _sheneena_, a universal beverage
amongst the Arabs, is either buttermilk pure and diluted, or curds mixed
with water.

  [Illustration: THE PASS OF BUKOVA.--During the revolution
  of 1904, a number of Turkish soldiers, just before
  traversing this pass, were given coffee containing "cafe"
  by a Bulgarian coffee-seller, or keeper of a small khan.
  Whilst in the pass the poison began to take effect, and
  they realized that they had been poisoned. Fortunately for
  them, a peasant with three horses loaded with Yoghourt
  (soured milk) had taken advantage of their escort. The
  soldiers ate freely of the Yoghourt, which counteracted
  the effects of the poison.]

"The camel's milk is drunk fresh. It is pleasant to the taste, rich, and
exceedingly nourishing. It is given in large quantities to the horses.
The Shammar and Aneyza Bedouins have no cows or oxen, those animals
being looked upon as the peculiar property of tribes who have forgotten
their independence, and degraded themselves by the cultivation of land.
The sheep are milked at dawn, or even before daybreak, and again in the
evening on their return from the pastures. The milk is immediately
turned into leben, or boiled to be shaken into butter. Amongst the
Bedouins and Jebours it is considered derogatory to the character of a
man to milk a cow or sheep, but not to milk the camel. The Sheikhs
occasionally obtain dates from the cities. They are eaten dry with bread
and leben, or fried in butter, a very favourite dish of the Bedouin...."

The practice is now the same as it was in scriptural times, when milk
was looked upon as the principal article of diet, and throughout the
Scriptures there are copious references to milk in different forms, some
of which are of peculiar interest at the present day.

It may be noticed, for example, that milk is absent from the sacred
offerings amongst the Hebrews, and this was ascribed by the late
Professor Robertson Smith to the fact that all ferments were excluded
from presentation at the altar,[2] it being recognised that, owing to
the hot climate, milk of all kinds became rapidly sour, and in this way
came to be looked upon as only fit for consumption when in that
condition. It has been suggested that the prohibition referred to is on
the same level as the prohibition of the use of blood, "as milk has
sometimes been regarded as a kind of equivalent for blood, and
containing the sacred life."[3] To this day the wandering tribes of
Arabia consider the milk of their camels and flocks more refreshing when
it has been slightly fermented or soured by being poured into a
milk-skin on the inside of which are still sticking sour clots from the
previous milking, and there shaken for a brief period; but this slightly
soured milk (the _Oxygala_ of Pliny) is known widely in the East simply
as leben (milk). The name is also applied to what we term buttermilk.[4]

  [Illustration: KABYLES SOURING MILK

  In the north of Africa the use of soured milk is common,
  and the illustration shows Kabyles shaking a skin full of
  milk so as to sour it. The skin has previously been used
  for the same operation, and, as a consequence, clots of
  milk are left from the previous day's use, and thus
  fermentation is set up.]

The use of milk-skins for the carrying of milk is not confined to one
country, as, while it is common all over the north of Africa, it is also
known in the Pyrenees and in some parts of the Balkan Peninsula, the
object being identical in each case; and when it is intended to make
butter from the milk, the skin is simply rocked between the knees until
the butter separates, a process of butter-making which was also used
after the introduction of earthenware churns.[5] Dried soured milk is
also used by the Arabs, and it is reconstituted when required by rubbing
it up with a little water, and it is known as _Meeresy_.[6] The ordinary
soured milk is the common article of diet, and is looked upon as being
necessary at every meal, and travellers frequently refer to the use of
this product, as a few references will show.

Charles G. Addison states: "A supper was brought in on a round tray. In
the centre was a huge pilaff of rice, and around it several small dishes
of stewed meats, grilled bones, sour clotted milk called _yaoort_,[7]
bits of meat roasted, etc....

"We retired into a tent to breakfast, where we found an immense bowl of
delicious fresh camels' milk, with thin hot cakes of unleavened bread,
baked upon the ashes, ready prepared for us. The principal food of the
Bedouins consists of flour and some camels' milk made into a paste,
boiled, and eaten swimming in melted grease and butter; boiled wheat
and beans dried in the sun and prepared with butter are a favourite
dish. They are all remarkably fond of butter and grease; the butter is
made in a goat-skin, suspended to the tent pole, and constantly shaken
about by the women."[8]

Burckhardt[9] says: "The provisions of my companion consisted only of
flour; besides flour, I carried some butter and dried leben (sour milk),
which would dissolve in water. It forms not only a refreshing beverage,
but is much to be recommended as a preservative of health when
travelling in summer. These are our only provisions." With regard to the
inhabitants of the Houran, Burckhardt relates that the most common
dishes of these people are _bourgoul_ and _keshk_. "In summer they
supply the place of the latter by milk, leben, and fresh butter. Of the
bourgoul I have spoken on other occasions; there are two kinds of
keshk--_keshk-hammer_ and _keshk-leben_. The first is prepared by
putting leaven into the bourgoul and pouring water over it. It is then
left until almost putrid, and afterwards spread out in the sun and
dried, after which it is pounded, and, when called for, served up mixed
with oil or butter. The keshk-leben is prepared by putting leben into
the bourgoul instead of leaven; in other respects the process is the
same. Keshk and bread are the common breakfasts. Towards sunset a plate
of bourgoul, or some Arab dish, forms the dinner."

Again, Taylor[10] says: "I received a small jug of thick buttermilk, not
remarkably clean, but very refreshing."

These references particularly refer to the East, from which it would
appear that soured milk was universally known in ancient times as it is
at the present day, and this remark applies not only to Egypt,
Palestine, and Arabia, but throughout Turkey and the Balkan States,
where the consumption of soured milk is equally common. It seems curious
that the use of this commodity should have been confined for centuries
to the East, as we shall see later on that its dietetic value is so
great that it is really a wonderful thing that no one has taken the
trouble to introduce its use to the Western nations until quite
recently.

  [Illustration: THE HANDLING OF MILK IN THE PYRENEES

  The handling of milk in the Pyrenees is, more especially
  in the villages, conducted in goat or sheep skins, in a
  similar way to the methods which prevail in Eastern
  Europe, and the picture shows a skin of milk on a small
  farm in the Pyrenees. The churning is very often performed
  by simply rocking the skin between the knees, acidity
  being induced by remnants of the previous day's milk;
  souring of milk is induced by the same method.]

A curious example of how the virtues of such an article may be
independently discovered by another nation is to be found in Lapland,
where reindeer's milk is the article used. "The reindeer's milk," says
Acerbi,[11] "constitutes a principal part of the Laplander's food, and
he has two methods of preparing it, according to the season. In summer
he boils the milk with sorrel till it arrives to a consistence; in this
manner he preserves it for use during that short season. In winter the
following is his method of preparation: The milk, which he collects in
autumn till the beginning of November, from the reindeer, is put into
casks, or whatever vessels he has, in which it soon turns sour, and, as
the cold weather comes on, freezes, and in this state it is kept. The
milk collected after this time is mixed with cranberries and put into
the paunch of the reindeer, well cleaned from filth; thus the milk soon
congeals, and it is cut out in slices, together with the paunch, to
effect which a hatchet is used, for no smaller instrument would perform
the office of dividing that lump of ice. It is then separated into small
pieces and eaten throughout the winter every day at noon, which is the
Laplander's dinner-hour. It must be presumed, as it is served up without
being brought to the fire, that this is ice-cream in the greatest
perfection: here are flesh and fruit blended with the richest
butyraceous milk that can be drawn from any animal; but, notwithstanding
the extraordinary fatness, which may be supposed to resist in a great
degree the effect of cold, this preparation, as our good missionary
remarks with a degree of feeling, as if his teeth still chattered whilst
he delivered the account, chills and freezes the mouth in a violent
manner whenever it is taken. The milk which is drawn late in the winter
freezes immediately after being drawn. This is put into small vessels
made of birchwood, and is considered by the Laplander as such an
extraordinary delicacy, that he reserves it as the most acceptable
present he can offer even a missionary. It is placed before the fire and
eaten with a spoon as it is thawed. When put by, it is carefully covered
up, because if the cold air gets to it afterwards, it turns of a yellow
colour and becomes rancid."

Amongst the peasants at the present day, soured milk is known as
_yoghourt_, a word which is spelt differently according to the locality
in which it is used. The method of preparation is practically the same
everywhere, and a short description of the process as now carried out
in one place would, with slight modifications, apply to the general
method adopted all over the East.

"The culture," says a correspondent at Varna, "which is used for the
preparation of yogourt, is known as 'Maya' or as 'Bulgarian Maya.' The
milk which is to be converted into yogourt must first be freed from all
bacteria by boiling and allowed to cool to the temperature of 45 deg. C.;
it is then inoculated with maya and maintained at an even temperature of
45 deg. C. during several hours. There are two kinds of maya, or ferment,
one known as sour, and the other as sweet maya.

"In Europe small stoves, made expressly for the purpose, are used to
maintain the milk at the proper temperature. In this country, however,
after the milk has been boiled, it is merely poured into a bowl and
allowed to cool to approximately 45 deg. C., then a tablespoonful of this
tepid milk is well mixed (in a small bowl apart) with a similar quantity
of maya, and the mixture, when it has become quite homogeneous, is added
to the bowl of tepid milk and stirred slightly. (One tablespoonful of
maya is sufficient to ferment one litre of milk.) A cover is then placed
on the bowl and the whole is enveloped in flannel and left in a warm
place for three hours in summer, and somewhat longer in winter.

"The process of preparation is complete when the mixture assumes the
appearance of a soft mass somewhat resembling cream cheese, but less
solid. The flannel is then removed, the bowl uncovered and placed in a
cool spot until needed for consumption. Of the yogourt thus prepared, a
tablespoonful is kept to serve as maya for the following day.

"The best yogourt is prepared from sheep's milk, the second quality from
buffaloes' milk, and the third quality from cows' milk. Yogourt forms an
almost daily article of diet with the natives in this country."[12]

With regard to the time stated for the fermenting process, it must be
noted that since the subject has been investigated so thoroughly, the
time required for fermentation has been found to be nearer ten than
three hours, but this will be dealt with in a subsequent chapter.

Historically it may be gleaned from the fragmentary references which we
have given, that soured milk has, from time immemorial, formed the
principal article of diet of a great many peoples, and the notable
feature in connection with it is, that in some countries where it is in
daily use, the age limit for human beings seems to be very much
extended, and it would appear that there is a direct connection between
the use of soured milk and longevity. In Bulgaria, for example, it is
stated that the majority of the natives live to an age considerably in
excess of what is recognised as the term of life amongst Western
nations, and inquiry has shown that in the eastern part of Southern
Europe, amongst a population of about three millions, there were more
than three thousand centenarians found performing duties which would not
be assigned to a man of sixty-five years of age elsewhere. It is quite
common to find amongst the peasants who live to such a large extent upon
soured milk, individuals of 110 and 120 years of age.[13]

In the ancient dairy practice, as we have seen, soured milk was the
principal product, and the extraordinary ages which are recorded of the
patriarchs, if translated into the modern denomination, would not appear
to be so imaginary after all, when it is considered that we have
thousands of examples at the present day of men and women enjoying quite
as long a term of existence. It has been noticed also, that while these
very old people are able to perform a certain amount of manual labour,
there is not the same tendency to the mental decay which is so prominent
and sad a feature amongst Western nations, at a period of about seventy
or eighty years of age. It would seem, indeed, as if the habit of living
long was well known in ancient times, and that, like many other of the
valuable arts and sciences, it fell under a cloud during the Middle
Ages, or, perhaps, the significance of the use of soured milk fell into
neglect, and, even after the revival of letters in the sixteenth
century, still remained obscure.

The discovery of micro-organisms in perishable products, which is
attributable to Anthony Van Leeuwenhoek, a Dutchman, whose vocation was
the polishing of lenses, and who lived between 1632 and 1723, altered
our point of view, not only of disease, but of all the functions carried
on by the lower organisms. Since Van Leeuwenhoek's time, the germ theory
has grown to vast proportions and has more especially been applied with
splendid results to the study of milk. As we shall see later, the
researches of modern investigators have led them to the conclusion that
micro-organisms play such an important part in the milk supply, that it
is impossible to carry it on safely without a knowledge of the
bacteriology of the subject. This view began to prevail about 1890, some
twenty years after Pasteur had shown what fermentation really meant.
Since that time, the progress in dairying has been continuous, and,
during recent years, attention has been directed to soured milk to such
an extent that it has become necessary for all who are interested in the
handling of milk and milk products to have a knowledge of the subject,
as it seems clearly demonstrated that, under proper direction, there is
every possibility of its forming an important element in the
prolongation of life.




CHAPTER II

FERMENTED MILKS


There is considerable variety in the number of soured or fermented
milks, and they are known by various names, such as Koumiss or Koomiss,
which is prepared from mares' milk; Keffir, which was originally
discovered in the mountains of the Caucasus, and which is prepared with
Keffir grains; Leben, an Egyptian product prepared from the milk of the
buffalo, cow, or goat; Matzoon, a soured milk which is prepared in
Armenia from ordinary cows' milk; Dadhi, an Indian preparation from
cows' milk. All of these owe their special characteristics to the fact
of their having undergone lactic and alcoholic fermentation.

"Milk left to itself," says Blyth,[14] "at all temperatures above 90 deg.
F. begins to evolve carbon dioxide, and this is simply a sign and result
of fermentation. If this fermentation is arrested or prevented, the fluid
remains perfectly sweet and good for an indefinite time. Besides the
production of carbon dioxide during decomposition, a certain portion of
milk sugar is converted into lactic acid, some of the casein and albumen
are broken up into simpler constituents, and a small proportion of
alcohol produced, which by oxidation appears as acetic acid, while the
fat is in part separated into free fatty acids, which ultimately unite
with the ammonia produced by the breaking up of the albuminoids. The
main fermentation of milk is a special kind which of late years has been
much studied, and is known as _lactic fermentation_. Accompanying lactic
fermentation there is nearly always a weak butyric and a weak alcoholic
fermentation."

One of the organisms causing _Butyric Acid Fermentation_ is a bacillus 3
to 10 mu in length, and about 1 mu in breadth. It has power of movement, and
when cultivated in gelatine, liquefies the gelatine, forming a scum on
the surface. When the bacillus is sown into sterile milk, the following,
according to Hueppe, are the changes:

"If the milk thus infected is incubated, on the second day a clear,
slightly yellow fluid is seen under the layer of cream; this fluid
increases from day to day, so that gradually a column of fluid is
formed which is quite clear above, but below is turbid; the casein, at
first thrown down in a firm coagulum, in the course of eight days begins
to be attacked, and by the end of two or three weeks most of it is
dissolved. The filtered fluid gives the biuret reaction; it contains
leucin, tyrosin, and ammonia; hence it is clear that the ferment acts to
some extent as a digestive of albumen. In advanced butyric acid
fermentation, the fluid is most offensive, and may have an alkaline
reaction."

Lactic acid was first isolated by Scheele in 1780 from soured milk, but
its exact constitution was not determined until later by Liebig,
Mitscherlich, Gay-Lussac, and Pelouze: "It is widely distributed in
nature, occurring in the sap of the vine and in most fermented liquids,
especially in soured milk; it is not, however, present in fresh
milk."[15]

In all the Eastern preparations referred to, the lactic fermentation is
produced, followed by alcoholic fermentation, which is due to the slow
decomposition of the milk sugar, the vinous fermentation being most
readily set up in milks which contain a larger relative proportion of
milk sugar and water, such as the milk derived from the mare, the sheep,
and the camel. As these fermented milks have different characteristics,
it is necessary to the thorough understanding of the process of
manufacture at the present day, to examine them in some detail.

_Koumiss._--The greatest of all the fermented milks is koumiss, and it
has been celebrated from the most ancient times until the present day,
as being the principal food of the wandering tribes of Khirgiz,
Bashkirs, Kalmucks, and Tartars, who inhabit the steppes of European
Russia and the plains of South, Western, and Central Asia. According to
Carrick, who has written an interesting volume on the subject,[16] the
nomads who inhabit these vast territories are shut up under the most
miserable circumstances during the winter time and at the advent of
spring they roam over the steppes from morning to night, usually in the
saddle. The milk yielded at such time by the mares is carefully
collected, and these nomads consume enormous quantities of it in the
fermented state, this habit having been in existence amongst them from
time immemorial. It is said that the Scythians, long before the
Christian era, used fermented mares' milk; and there are ornaments in
existence in Russia, of Scythian origin, which exhibit in detail the
preparation of koumiss from mares' milk. In historical times, the first
mention of koumiss was in the twelfth century, when it is referred to in
the Ipatof Chronicles. During the thirteenth century William de
Rubruquis, a French missionary, wrote about his travels in Tartary, and
he described how he had first become acquainted with koumiss, and how he
found it savoury to the palate. Subsequent to this, however, there is
very little mention of koumiss in Russian history, or, for that matter,
in any other, and the first really scientific contribution on the
subject was by Dr. John Grieve, who was a surgeon in the Russian army,
and who in the year 1784 sent a description of koumiss to the Royal
Society of Edinburgh,[17] of which he was a member, and the title of it
was, "An Account of the Method of Making Wine called by the Tartars
Koumiss, with Observations on its Use as a Medicine." Dr. Grieve
strongly advocated the use of koumiss as beneficial in cases of wasting
diseases, and subsequently it was adopted by the medical profession,
with the result that sanatoria for the treatment of pulmonary
consumption were established at Samara and other places in Russia, and
met with very great success; and at the present day such sanatoria are
carried on, but the bacteriology of the subject now being thoroughly
understood, the methods of preparation have been somewhat modified.

An interesting account of koumiss is given by Clarke,[18] who says:

"Everybody has heard of koumiss, and the brandy which the Kalmucks are
said to distil from the milk of mares. The manner of preparing these
liquids has been differently related, and perhaps is not always the
same. They assured us that the brandy was merely distilled from
buttermilk. The milk which they collect overnight is churned in the
morning into butter; and the buttermilk is distilled over a fire made
with the dung of their cattle, particularly the dromedary, which makes a
steady and clear fire like peat. But other accounts have been given both
of the koumiss and the brandy. It has been usual to confound them, and
to consider the koumiss as their appellation for the brandy so obtained.
By other information I could gain, not only here, but in many other
camps which we afterwards visited, they are different modifications of
the same thing although different liquors; the koumiss being a kind of
sour milk, like that so much used by the Laplanders called _pina_, and
which has undergone, in a certain degree, the vinous fermentation; and
the brandy an ardent spirit obtained from koumiss by distillation. In
making koumiss they sometimes employ the milk of cows, but never if
mares' milk can be had, as the koumiss from the latter yields three
times as much brandy as that made from cows' milk.

"The manner of preparing the koumiss is, by combining one sixth part of
warm water with any given quantity of warm mares' milk. To these they
add, as a leaven, a little old koumiss, and agitate the mass till
fermentation ensues. To produce the vinous fermentation, artificial heat
and more agitation is sometimes necessary. This affords what is called
koumiss. The subsequent process of distillation afterwards obtains an
ardent spirit from the koumiss. They call it _vina_. In their own
language it bears the very remarkable appellation of _rack_ and _racky_,
doubtless nearly allied to the names of our East India spirit _rack_
and _arrack_. We brought away a quart bottle of it, and considered it
very weak bad brandy, not unlike the common spirit distilled by the
Swedes and other northern nations. Some of their women were busy making
it in an adjoining tent. The simplicity of the operation and their
machinery was very characteristic of the antiquity of this chemical
process. Their still was constructed of mud, or very coarse clay; and
for the neck of the retort they employed a cane. The receiver of the
still was entirely covered by a coating of wet clay. The brandy had
already passed over. The woman who had the management of the distillery,
wishing to give us a taste of the spirit, thrust a stick, with a small
tuft of camel's hair at its end, through the external covering of clay,
and thus collecting a small quantity of the brandy, she drew out the
stick, dropped a portion on the retort, and, waving the instrument above
her head, scattered the remaining liquor in the air. I asked the meaning
of this ceremony, and was answered that it is a religious custom to give
always the first drop of the brandy which they draw from the receiver to
their God. The stick having been plunged into the receiver again, she
squeezed it into the palm of her dirty and greasy hand, and after
tasting the liquor, presented it to our lips."

Another interesting account of the preparation of koumiss is given by
John M. Wilson in the _Rural Encyclopaedia_,[19] and it shows that the
methods in use about the middle of last century did not differ
materially from those which existed centuries before.

Wilson says: "Khoumese is vinously fermented mares' milk. Any quantity
of fresh mares' milk is put into wooden vessels; a sixth part of water
just off the boil is mixed with it; an eighth part of old khoumese or of
the sourest possible cows' milk is added; the mixture is kept from
fifteen to twenty-four hours, covered up with several folds of coarse
linen cloth and with a very thick board, and without being stirred or in
any degree disturbed, in a moderately warm place till it becomes
thoroughly sour, and sends up a thick mass to its surface; it is then
beaten and pounded and stirred till the curd is not only broken, but so
thoroughly mixed with the serum as to form a thick liquid; it next
remains covered and at rest during twenty-four hours more, and it is
finally put into a common butter churn and beaten and blended into a
state of perfect homogeneity. It is now fit for use; yet it acquires an
increase of given properties if it be allowed to stand for a few days,
and either then or now it would, if distilled, yield nearly one third of
its own bulk of a weak spirit which will bear to be rectified. Whenever
it is used it must be previously so agitated that its component parts
may be well mixed together, and it may be kept either in pans for
immediate use or in casks for more remote use; and if placed in a cool
cellar it will remain good during three or four months."

Mares' milk owes its peculiar fitness for making koumiss to its
containing a large proportion of sugar of milk, and readily undergoing
the vinous fermentation, and it possesses a general medicinal reputation
among the Tartars similar to that which asses' milk has partially
acquired in Britain. "That mares' milk will undergo vinous fermentation
and yield a certain quantity of spirit," says a writer in the _Magazine
of Domestic Economy_, "is not generally known, and it was reserved for a
nation of demi-savages to render this circumstance available as an agent
of health, as well as an agreeable and nourishing beverage. Every
educated person, however, has heard that the Tartars drink mares' milk,
though few know that this milk is taken on account of its specific
virtues alone, and not as a substitute for cows' milk, of which they
have abundance, and with which they adulterate mares' milk when scarce."
But the koumiss is reputed to be much more medicinal than the mares'
milk itself; and on account of its being free from all tendency to
curdle in the stomach, and of its possessing most of the nutritive power
of the milk in combination with native fermented spirit, it has been
strongly recommended by some persons as a remedy for most or all cases
of general debility, of nervous languor, and even pulmonary disease.

"Khoumese is called sometimes _koumiss_ and sometimes milk wine."

From these references it will be seen that koumiss is an alcoholic drink
made by the fermentation of mares' milk, but it is also frequently
prepared from the milk of the camel and cows' milk. It is stated that a
similar preparation to Russian koumiss is made in Switzerland from cows'
milk simply by the addition of a little sugar and yeast to skim milk;
"it contains more sugar and less lactic acid than Russian koumiss, and
on account of the much greater proportion of casein contained in cows'
milk, differs considerably from that prepared from mares' milk."
Suter-Naef gives the composition of a Swiss koumiss[20] manufactured at
Davos as follows:

                      In Grams.             Per Litre
                      Per cent.            (by weight).
  Water                90.346               1019.64 grams.
  Alcohol               3.210                 36.23   "
  Lactic acid           0.190                  2.14   "
  Sugar                 2.105                 23.75   "
  Albuminates           1.860                 20.99   "
  Butter                1.780                 20.09   "
  Inorganic salts       0.509                  5.74   "
  Free carbonic acid    0.177                  2.00   "

The ferments used in the preparation of koumiss are stated by Carrick to
be of two different kinds, artificial and natural.

"Of the natural ferments two have been resorted to. One is mentioned by
Grieve, which he borrowed from the Bashkirs of Orenbourg, and which
simply consists in the addition of one sixth part of water and one
eighth of the sourest cows' milk to fresh mares' milk; the other has
been employed, and was, if I mistake not, first recommended by
Bogoyavlensky. It is a very simple if rather a tedious method. New
mares' milk, diluted with one third its bulk of water, is placed in the
_saba_,[21] and while allowed to sour spontaneously, is continually
beaten up. This milk gradually undergoes the vinous fermentation, and in
twenty-four hours is converted into weak koumiss. The disadvantage of
this mode of commencing fermentation is obvious--viz., the great waste
of time in agitation. Hence it is only employed when no artificial
ferment is obtainable.

"In starting the process of fermentation in mares' or any other kind of
milk, therefore, an artificial ferment is more frequently employed than
a natural one. The former is used only for converting the first portion
of milk into koumiss; the latter is always resorted to afterwards.

"Of artificial ferments the variety is great, for besides all putrefying
animal matters which contain nitrogen--such as blood, white of egg,
glue, and flesh--certain mineral substances which act by souring the
milk are also capable of exciting fermentation.

"Now, many of the nomads, whose mares either give no milk or are not
milked in winter, commence the preparation of their koumiss in spring by
borrowing a ferment from the animal, mineral, or vegetable kingdom. Thus
a mixture of honey and flour is the favourite ferment with some races of
nomads; a piece of fresh horse-skin or tendon is preferred by others,
while a few resort to old copper coins, covered with verdigris, for
starting fermentation. In the choice of a ferment they are guided solely
by habit and tradition. As it would be useless, almost impossible, to
give a list of all the foreign substances that have been employed with
the view of converting mares' milk into koumiss, it will be best to
consider the simplest artificial ferments, and those most generally in
use.

"The simplest way is that recommended by Bogoyavlensky, and adopted and
modified by Tchembulatof.[22] It is prepared thus: 'Take a quarter of a
pound of millet-flour, add water to it, and boil it down to the
consistence of thick oatmeal porridge. Then heat separately, in another
vessel, eleven pints of milk to boiling-point, and allow it to cool
down. When its temperature has fallen to 95 deg. F., pour it into a wooden
bowl or tub, and add the boiled flour to it. The upper and open part of
the vessel is then covered with a piece of coarse linen, and left at
rest--at a temperature of about 99 deg. F.--from twenty-four to forty-eight
hours. The appearance of small bubbles, which keep bursting on the
surface of this liquid, combined with a vinous or acid odour, prove that
the ferment is ready. To this fermenting fluid twenty-two quarts of new
milk are gradually (_i.e._, every ten minutes) added, and the whole mass
is continuously beaten up for twelve hours. The temperature during
stirring should never be higher than 94 deg. F. The whole fluid soon begins
to ferment, and after twelve hours a not unpleasant koumiss is ready.
This should be filtered through a horse-hair or muslin sieve, after
which it is fit for drinking. This liquid is called weak koumiss; but a
limited portion of the lactine has undergone the lactuous and vinous
fermentations, and thus the percentage of alcohol is small. Koumiss at
an ordinary temperature remains weak for twelve hours after it has been
beaten up, and then gradually passes into medium.'"

Curiously enough, the richness of cows' milk in fat militates against
its being a good raw material for the making of koumiss, owing to the
production of small quantities of butyric acid, which follows upon the
fermentation, so that it is desirable, if koumiss is to be prepared from
cows' milk, that the fat should be first of all eliminated, so that the
separated milk will then approximate to the composition of mares' milk.

"The chemical changes," says Hutchison,[23] "which take place in the
milk under the double fermentation are not difficult to follow; the
lactic ferment simply changes part of the sugar into lactic acid, the
vinous ferment eats up a very small part of the proteid of the milk,
and, at the same time, produces from the sugar a little alcohol and a
good deal of carbon dioxide; the milk thus becomes sour, it effervesces
and is weakly alcoholic, but the lactic acid causes the casein to be
precipitated just as it does in the ordinary souring of milk, and the
casein falls down in flocculi."

As will have been noticed, it is an essential part of the process of
koumiss-making to keep the milk in a state of agitation during the
period of fermentation, a process which is intended to permit of oxygen
being taken up by the fermenting fluid, while, at the same time, the
casein is broken up into a state of fine division. The casein also, or
at least a portion of it, becomes very soluble, and after twelve hours
of fermentation the taste of the product is only slightly sour, and the
milk taste still remains. This taste, however, disappears in
twenty-four hours, owing to the rapid development of the lactic acid
organisms. After this lapse of time the sugar is entirely destroyed, and
the strong koumiss which results is a thin sour fluid which effervesces
briskly, and in this condition will keep for an indefinite period. "The
net change which has taken place in the original milk may be summed up
by saying that the sugar of the milk has been replaced by lactic acid,
alcohol, and carbon dioxide, the casein has been partly precipitated in
a state of very fine division, and partly pre-digested and dissolved,
while the fat and salts have been left much as they were."[24]

Violent stirring or agitation of the cultures does not seem to work so
much by supplying oxygen to the fermenting liquid, as by ensuring a
thorough distribution of the micro-organisms throughout the liquid, and
thus dividing the casein.

The greater number of the organisms are facultative anaerobes and oxygen
is not necessary. Again, koumiss put up in bottles on the first day is
regularly shaken although air is excluded.

_Keffir._--Keffir is a kind of fermented milk which has been in use in
the Caucasus for quite a long time, as koumiss has been in the steppes.
It differs from koumiss, however, in this respect, that it is prepared
from either sheep's, goats', or cows' milk. The process is started by
the addition of keffir grains to the milk, which is contained in
leathern bottles. These keffir grains are small solid kernels which are
kept in families and handed on from one generation to another.[25] The
grains are the origin of the ferment, as they disseminate in the milk
micro-organisms of a lactic yeast (_Saccharomyces kefir_ Beyerinck and
Freudenreich) and also the bacillus _Bacterium caucasicum_, which
develop rapidly and split up the milk sugar into carbon dioxide,
alcohol, and lactic acid. Small quantities of glycerine, acetic,
succinic, and butyric acids are also formed, the casein and albumen
being partly peptonised.[26] Keffir becomes slightly effervescent in
twenty-four hours, and in that time develops a small quantity of
alcohol, but after three days the amount of alcohol and lactic acid
is much increased.[27] It has been determined that the fermentation of
the milk is due to _Saccharomyces kefir_, and that the _Lactobacillus
Caucasicus_ does not take any part in the fermentation, a fact which
seems to be supported by the capacity of ordinary keffir for starting
the fermentation in fresh milk in the same manner as the keffir grains.
The use of this beverage seems to be universal throughout the Caucasus,
and travellers in these regions have frequently referred to it. Thus
Freshfield[28] states in one part of his book of travels as follows:

"The pig-faced peasant against whom we had at first sight conceived such
an unjust prejudice turned out a capital fellow. He brought us not only
fresh milk, but a peculiar species of liquor, something between
public-house beer and sour cider, for which we expressed the greatest
admiration, taking care at the same time privately to empty out the
vessel containing it, on the first opportunity." And again:

"The hospitable shepherds regaled us, not only with the inevitable and
universal airam or sour milk--if a man cannot reconcile himself to sour
milk, he is not fit for the Caucasus--but with a local delicacy that
has lately been brought to the knowledge of Europe--kefir. This may best
be described as 'effervescing milk.' It is obtained by putting into the
liquid some yellow grains, parts of a mushroom which contains a bacillus
known to science as _Dispora caucasia_. The action of the grains is to
decompose the sugar in the milk, and to produce carbonic acid and
alcohol. The grains multiply indefinitely in the milk; when dried they
can be preserved and kept for future use; its results on the digestion
are frequently unsatisfactory, as one of my companions learnt to his
cost."

"It has been supposed," says Metchnikoff, "that the chief merit of
kephir was that it was more easy to digest than milk, as some of its
casein is dissolved in the process of fermentation. Kephir, in fact, was
supposed to be partly digested milk. This view has not been confirmed.
Professor Hayem thinks that the good effects of kephir are due to the
presence of alcoholic acid, which replaces the acid of the stomach and
has an antiseptic effect. The experiments of M. Rovigh, which I speak of
in _The Nature of Man_, have confirmed the latter fact, which now may be
taken as certain. The action of kephir in preventing intestinal
putrefaction depends on the lactic acid bacillus which it contains.
Kephir, although in some cases certainly beneficial, cannot be
recommended for the prolonged use necessary, if intestinal putrefaction
is to be overcome.... Professor Hayem prohibits its use in the case of
persons in whom food is retained for long in the stomach. When it is
retained in the stomach, kephir goes on fermenting, and there are
developed in the contents butyric and acetic acids, which aggravate the
digestive disturbances. Kephir is produced by combined lactic and
alcoholic fermentations ... and it is the lactic and not the alcoholic
fermentation on which the valuable properties of kephir depend; it is
correct to replace it by sour milk, that contains either no alcohol or
merely the smallest traces of it. The fact that so many races make sour
milk and use it copiously is an excellent testimony of its usefulness."

There are two methods given by Fluegge[29] for the preparation of keffir:

"In the first, the dry brown kefir grains of commerce are allowed to lie
in water for five or six hours until they swell; they are then carefully
washed and placed in fresh milk, which should be changed once or twice
a day until the grains become pure white in colour and when placed in
fresh milk, quickly mount to the surface--twenty to thirty minutes. One
litre of milk is then poured into a flask, and a full tablespoonful of
the prepared _koerner_ added to it. This is allowed to stand open for
five to eight hours; the flask is then closed and kept at 18 deg. C. It
should be shaken every two hours. At the end of twenty-four hours the
milk is poured through a fine sieve into another flask, which must not
be more than four fifths full. This is corked and allowed to stand,
being shaken from time to time. At the end of twenty-four hours a drink
is obtained which contains but little carbon-dioxide or alcohol. Usually
it is not drunk until the second day, when, upon standing, two layers
are formed, the lower milky, translucent; and the upper containing fine
flakes of casein. When shaken it has a cream-like consistence. On the
third day it again becomes thin and very acid. The second method is used
when one has a good kefir and two or three days to start with. Three or
four parts of fresh cows' milk are added to one part of this and poured
into flasks which are allowed to stand for forty-eight hours with
occasional shaking. When the drink is ready for use, a portion (one
fifth to one third) is left in the flask as ferment for a fresh quantity
of milk. The temperature should be maintained at about 18 deg. C., but at
the commencement a higher temperature is desirable. The grains should be
carefully cleaned from time to time and broken up to the size of peas.
The clean grains may be dried upon blotting-paper, in the sun, or in the
vicinity of a stove; when dried in the air they retain their power to
germinate for a long time."

_Leben._--In our earlier references to fermented milks in scriptural
times, we observed that alcoholic fermented milks were not permitted to
be presented at the altar. Such offerings, however, were quite allowable
amongst the ancient Egyptians, the Arabs and Carthaginians,[30] and from
remote antiquity these nations placed great value on this product.
Leben, which is peculiarly associated with Egypt, is a soured milk
prepared from the milk of buffaloes, cows, or goats. It is usually
prepared by the boiling of the fresh milk over a slow fire, after which
some fermented milk from a previous preparation is added to the warm
article, and the fermentation takes place rapidly and is considered to
be complete in about six hours.[31] The Egyptian leben is valued so
highly that it is offered in hospitality to the passing stranger, and it
is regarded as so much of a duty to present this milk, that in some
parts of Arabia it would be looked upon as scandalous if any payment
were received in return.[32]

_Matzoon._--Matzoon is prepared in Armenia in somewhat the same manner
as keffir is prepared in the Caucasus, and indeed it differs very
slightly from keffir in composition. Its use is universal in Armenia.

_Dadhi._--In India large quantities of fermented milk are used, under
the name of Dadhi, and its characteristics are not unlike the similar
products in Europe. The specific bacillus has been investigated by
Chatterjee,[33] who concludes that it is somewhat akin to the _Bacillus
bulgaricus_ and the bacillus of leben (_B. lebenis_). Dr. Chatterjee
gives a resume of his investigations which sums up the whole matter
thus:

"1. The fermented milk of India called Dadhi resembles in all essential
points the Bulgarian fermented milk as well as the leben and other forms
of fermented milk in use in the East.

"2. The causative element of the curdling process of Dadhi is a
streptothrix having characters similar to the _Bacillus bulgaricus_ and
_Streptobacilli lebeni_, and _Bacillus caucasina_ and the Long Bacilli
of Mazun, in (1) not growing in ordinary media; (2) producing a large
amount of lactic acid in milk; (3) producing, besides coagulation of
casein and splitting up the sugar of milk into lactic acid, no other
change in milk; (4) not producing any indol, nor peptone, nor
saponification of fat, nor formation of any gas.

"3. It differs from the above by showing peculiar pink-stained granules,
when stained with methylene blue and showing peculiarly convoluted
chains in glucose agar.

"4. The importance of the organism lies in the fact that, as in the case
of _Bacillus bulgaricus_, it kills all pathogenic non-sporing germs and
also destroys all proteolytic gas-forming bacilli in milk."

In the account of these investigations the following table is given,
showing the amount of lactic acid produced by different lactic acid
bacilli in one litre of milk, in terms of lactic acid--the culture
being kept at 37 deg. C.

  +--------------+-------+-------+-------+-------+-------+-------------------+
  | Name of the  | After | After | After | After | After |                   |
  |  Bacillus.   |   24  |   48  |  72   |  96   |  a    |    Remarks        |
  |              | Hours.| Hours.| Hours.| Hours.| Week. |                   |
  +--------------+-------+-------+-------+-------+-------+-------------------+
  | B. lactis    |  1.8  |  ...  | 10.08 |  ...  |  ...  | Observed by       |
  |  aerogenes    |       |       |       |       |       |  Hall and Smith   |
  |              |       |       |       |       |       |                   |
  | B. coli      |  1.8  |  ...  |  4.77 |  ...  |  ...  | Observed by       |
  |  communis    |       |       |       |       |       |  Hall and Smith   |
  |              |       |       |       |       |       |                   |
  | B.           | 12.8  | 16.5  | 20.2  |  ...  | 22    | Observed by       |
  |  bulgaricus  |  -.4  |  -.4  |  -.4  |  ...  |  -.4  |  Gabriel Bertrand |
  |              |       |       |       |       |       |  and Weisweller;  |
  |              |       |       |       |       |       |  the initial      |
  |              |       |       |       |       |       |  acidity of the   |
  |              |       |       |       |       |       |  milk was 4       |
  |              |       |       |       |       |       |                   |
  | Matzoon Long | 10.8  | 12.   |  ...  |  ...  |  ...  | Observed by       |
  |  staebschen B.|       |       |       |       |       |  Dueggeli          |
  |              |       |       |       |       |       |                   |
  | Strepto-     |2.61[34]  ...  |  ...  |  ...  |  ...  | Observed by       |
  |  bacillus    |       |       |       |       |       |  Rist and Khoury  |
  |  lebenis     |       |       |       |       |       |                   |
  |              |       |       |       |       |       |                   |
  | Streptothrix | 10.8  |  1.08 | 11.25 | 11.70 | 18.5  | Med. Coll.,       |
  |  dadhi       |       |       |       |       |       |  Calcutta         |
  +--------------+-------+-------+-------+-------+-------+-------------------+

In different parts of the world sour milk is consumed in great
quantities, and it is stated by Metchnikoff[35] that the chief food of
the natives of tropical Africa consists of soured milk, and in Western
Africa in the region south of Angola, the natives live almost entirely
on this product, there being a difference in the curdled milks produced
according to the nature of the microbial flora which is introduced.

It is stated[36] that in Servia, Bulgaria,[37] and Roumania there were
5000 centenarians living in 1896, and while many reasons are advanced
for such an abnormal condition of affairs, it seems fairly certain that
the sole reason why people in these districts live to such great ages is
because of their mode of living and the fact that they live very largely
on soured milk. The hygienic conditions throughout these countries are
not such as would give the population in the towns and villages any
special advantages in the prolongation of life, and while it may be
stated that a pastoral and agricultural life are likely to contribute to
longevity, these conditions would not account for a general tendency to
live long in the countries referred to, more than in any other
agricultural area. There are many countries throughout the world in
which the pastoral and agricultural existence is general, but it has
not been shown that in these countries life is prolonged. Hence the
conclusion has been forced upon investigators that the reason is to be
found not in the pastoral conditions, but in the habit which has existed
from time immemorial of consuming sour milk as a principal article of
diet.

There is no curtailment of the use of fermented milks in Eastern Europe,
and the methods of preparation at the present day are those which have
been carried out from time immemorial. A local observer states that in
Bulgaria yoghourt is made in nearly every household, especially in the
spring and summer. The method of preparation is very simple: The milk is
boiled until a quarter of its volume has evaporated, it is then cooled
to 45 deg. C. and the ferment added. This ferment is a portion of the
yoghourt of good flavour and is called "Maya" or "Zakvaska." The vases,
a kind of earthenware pot, are enveloped in woollen stuff or sheepskin
and placed in a warm place near the chimney. In ten hours the yoghourt
is made, and it is preserved in a cold place. The great reputation that
the yoghourt has acquired in Western Europe has caused this "Maya" to
become an article of commerce. It is sent out by rail hermetically
sealed in tinplate boxes. According to a Sophia chemist, the "Maya" is
employed in the following manner: For a litre of milk it is necessary to
take about 10 gr. of the ferment. This ferment is diluted with three
times the amount of water and put into a bowl previously heated with hot
water and dried. Into this bowl the milk, previously boiled and cooled
to a temperature of 75 deg. to 50 deg. C., is poured; it is then covered
over and put in a temperature of about 30 deg. C., and, in default of a
stove of constant temperature, the bowl is wrapped round with flannel or
a plaid, and left to curdle for eight to ten hours. It is then ready for
consumption. During winter, curdled milk keeps for several days, and in
summer it becomes sour in from twelve to twenty-four hours.

A similar food to the yoghourt is prepared in the Balkan mountains from
sheep's milk under the name of "Urgoutnik."[38] The milk is poured into
a goat-skin or sheepskin bag, and a little of the fermented milk added,
and is then left for some hours in a warm place. The milk consumed is
replaced by a fresh supply. In some of the Balkan countries, they are
not content with the fermentation of the milk, they add a little alum,
which, under the name of "typsa," is well known for this purpose. The
milk attains such a solid consistency that it can be put into a cloth
and carried to market.[39]

The various forms of sour milk which have been described in the
foregoing pages may be said to be of the traditional kind, and with the
light of modern knowledge, it has been possible to determine exactly
what constitutes the active principle in use in the milk consumed in
these countries, and, as we shall see, this principle has been applied
so that, at the present day, a pure fermented milk may be obtained in
any country, and there is every reason to believe that should such be
adopted as a general article of food, it would contribute to the
prolongation of human existence.

It is due to Metchnikoff, of the Pasteur Institute, that so much
prominence has been given to the use of fermented milks. He gave it as
his opinion[40] that senility was caused partly by auto-intoxication or
by the poison derived from putrefactive micro-organisms which inhabit
the digestive track. These organisms increase with age, and under
certain unhealthy conditions multiply enormously, particularly in the
large intestine. Having arrived at this knowledge, Metchnikoff set to
work to devise some means of combating the influence of these harmful
microbes, and set up the hypothesis that the tendency to longevity which
is exhibited in Eastern countries is due to the consumption of lactic
acid organisms in the shape of soured milk. These organisms are more
powerful than those of a putrefactive character and inhibit their
growth.

"In the presence of such facts," says Metchnikoff, "it becomes
exceedingly important to find some means of combating the intestinal
putrefaction which constitutes so incontestable a source of danger. Such
putrefaction is not only capable of producing diseases of the digestive
tube--_enteritis_ and _colitis_--but even of becoming a source of
intoxication of the organism in its most varied manifestations.

"It is some years since I proposed to combat intestinal putrefaction and
its injurious consequences by means of lactic ferments. I thought the
acidity produced by such microbes would be much more effective in
preventing the germination of putrefying microbes than the small
quantity of acids produced by _Bacillus coli_. On the other hand, I had
no illusion as to the difficulty sure to be encountered in any effort to
introduce lactic microbes into the intestinal flora which has been
preoccupied by a multitude of other microbes. To make surer of the
result, I chose the lactic microbe, which is the strongest as an acid
producer. It is found in the _yahourt_ (yoghourt), which originates in
Bulgaria. The same bacillus has also been isolated from the _leben_ of
Egypt; and it is now proved that it is found in the curdled milk of the
whole Balkan peninsula, and even in the Don region of Russia."[41]

It is a short step from considerations like these to the adoption of the
_Bacillus bulgaricus_ as the most potent of the various lactic organisms
which have been examined, and which is likely to play such an important
role in the destiny of the human race. The _Bacillus bulgaricus_ may
claim to be the Bacillus of Long Life.




CHAPTER III

THE CHEMISTRY OF MILK


_The Composition of Milk._--Like all other organic substances, or those
built up in connection with the life processes of plants and animals,
milk is of complex composition. It is also very liable to change--every
one is acquainted with its tendency to "go bad." This instability is
more or less inherent in all highly organised chemical compounds, and,
indeed, it seems to be necessary that the materials used in growth and
nutrition should be very plastic in a chemical sense, in order, _e.g._,
that the constituents, say of a plant, may easily be transformed into
the substances of the body of the animal which feeds on it.

The perishable nature of milk--the food of young and growing animals--is
therefore essential, so that it may be changed easily into the blood,
bone, muscle, etc., so abundantly required in the early stages of
existence.

Milk is a complete food, and, therefore, naturally it is not a simple
chemical compound, but a mechanical mixture of a number of substances.
The present state of chemical knowledge on the subject does not permit
of its composition being given in detail, but for practical purposes,
such as those of measuring its purity and food value, this is not
necessary.

A proximate analysis, in which, at least, some of the ingredients are
lumped together, is sufficient, and has been adopted everywhere by
analysts. On this basis the average composition of cows' milk may be
stated as follows:

                       Per cent.
  Water                  87.50
  Fat                     3.50
  Casein and albumen      3.65
  Milk sugar              4.60
  Ash                     0.75
                          ----
                        100.00
                        ------

The constituents other than water added together form the "total
solids," and they amount to 12.5 per cent.

                       Per cent.
  Water                  87.5
  Total solids           12.5
                         ----
                        100.0
                        -----

  [Illustration: THE CONSTITUENTS OF MILK
  In the illustration, a pint of milk is shown in a glass
  jar, and the various percentages of water, casein, sugar,
  ash, albumen, and fat, which make up its constituent
  parts, are shown in separate bottles, the percentage of
  each being stated beneath.]

Milk varies a good deal in composition; the different breeds of cows
give varying qualities. The Short-horn gives large quantities of milk of
rather poor analysis, while the Jersey yields smaller proportions of
very rich milk. During the period of lactation (the time which has
elapsed since the cow gave birth to a calf), care in milking, food,
health, etc., all have an effect on the quality of the milk.

The limits of variation may be stated as follows:

                            Per cent.     Per cent.
  Water                       87.5    to    82.5
  Fat                          2.5     "     6.0
  Casein and albumen           3.0     "     4.5
  Milk sugar                   3.5     "     6.0
  Ash                          0.6     "     0.8

These figures are extreme, and it is very seldom indeed that either the
minimum or maximum is reached. Indeed, by the regulation laid down under
Clause 4 of the British Sale of Food and Drugs Act of 1899, when the
percentage of solids not fat falls below 8.5 per cent., and fat under 3
per cent., it is assumed that the milk has been adulterated. This
regulation is a perfectly just one. While genuine milk may, in rare
instances, show figures as low as 7.1 per cent. of solids not fat, or
2.5 per cent. of fat, the right can hardly be claimed of supplying such
an abnormal article to the public as milk of proper quality, and the
dairyman who understands his business, and wishes to deal fairly with
his customers, can, by attention to the conditions enumerated above
which influence the composition of milk, entirely avoid the production
of such a low-grade article.

In the nutrition of both plants and animals large quantities of water
are needed. The solids must be supplied in solution or dissolved in the
assimilative processes, and this cannot take place without water, which
also conveys the dissolved solids to the various parts of the economy,
and in the case of animals removes waste materials. For the most part,
water passes through the body unchanged, but a certain proportion unites
chemically with the food materials and assists in their digestion. It is
therefore not surprising that seven eighths of milk is composed of
water. Blood contains a similar proportion, and this agreement
emphasises the fact that milk is a perfectly balanced food.

The fat of milk, which yields cream and butter, differs in some
important respects from other fats. Like these, it is made up chiefly
of stearin, palmitin, and olein, but, in addition, it contains an
abnormally large proportion of compounds of certain of the volatile
fatty acids. It is these which give to butter its agreeable flavour. By
the methods of Duclaux, the following is the approximate composition of
butter fat:

                                              Per cent.
  Stearin, palmitin, olein, and traces of
     myristin and butin                         91.50
  Butyrin                                        4.20
  Capronin                                       2.50
  Caprylin, caprinin, and traces of laurin       1.80
                                                -----
                                               100.00
                                               ------

Myristin occurs in nutmegs; butyrin in another combination flavours
pineapples and rum; caprinin is found in cocoanut fat, mutton fat, and
in the offensive odour given off by the goat (from which the name is
derived); caprylin is a by-product of alcoholic fermentation, and also
occurs in cocoa fat; laurin is found in sweet bay; from which it is
evident that there are some curious relationships in flavouring
materials.

Fats are very concentrated foods, furnishing a large amount of energy to
the body. At one time they were classed together with starch, sugar,
and other carbohydrates as heat-producers, but the distinction which
was drawn between the kinds of food which were thought solely to keep up
the temperature of the organism, and those which produced force in work
and other forms of bodily energy, has broken down, and by direct
experiment has been found not to exist. It is usually calculated that
one part of fat is equal in food value to about two and a quarter parts
of any of the other carbohydrates. Milk fat or butter is more digestible
than almost any other fat, and its importance therefore can readily be
realised. All the above constituents of milk fat are composed of
different proportions of carbon, hydrogen, and oxygen, but milk also
contains minute quantities of lecithin, a fat containing phosphorus in
addition. Lecithin is also found in the brain and nerve material of
animals, in the yolk of egg, and in several plants.

The nitrogenous constituents of milk--casein and albumen--are usually
estimated together, and they are reckoned as of equivalent food value.
The name protein is very commonly applied to the total of these bodies
in milk, or other animal and vegetable foods. They are composed of
different proportions of carbon, hydrogen, oxygen, and nitrogen, with
small quantities of sulphur, while casein contains phosphorus in
addition. Albumen exists to the extent of about 0.6 per cent. in milk.
It is very similar in properties to egg albumen. The coagulum which
forms on the surface of milk when boiled is largely composed of albumen.
Casein is combined with, and kept in solution by, lime, soda, and
calcium phosphate, and its amount averages a little over 3 per cent.

The remarkable property possessed by rennet, of curdling or coagulating
casein, is well known; rennet is an extract from the stomach of the
calf, and similar principles are present in the stomachs of man and
other animals, so that the coagulation of milk is the first process in
its digestion. If milk is gulped down in large quantities it is apt to
coagulate in lumps, and digestion is much interfered with, but if it is
taken hot and slowly, it coagulates in small pieces which are readily
attacked by the gastric juice, and milk is then one of the most
assimilable of foods.

Nature provides that the milk for young animals is supplied in finely
divided streams, so that coagulation takes place in the best possible
way.

The proteids are the most important constituents of food; they are
abundant in the blood, and build up the muscles, brain, nerves, and
other bodily structures.

Besides these mentioned, milk contains traces of another proteid of
similar composition called globulin.

The sugar of milk is not found anywhere else. It is a carbohydrate like
cane and grape sugar--that is to say, the hydrogen and oxygen they
contain are in the same relative proportions as in water. Milk sugar is
not so soluble or so sweet as the other sugars. It does not ferment with
ordinary yeast, but certain special yeasts which are made use of in the
preparation of keffir, koumiss, etc., have the power of transforming it
into alcohol. Its most remarkable property, however, is the facility
with which, under the influence of certain bacteria, it is changed into
lactic acid.

Every one is familiar with the souring of milk, but perhaps it is not so
generally known that there are great differences in the results obtained
in accordance with the conditions under which the souring takes place.
The skilled butter-maker, by keeping the milk in a cool and cleanly
dairy, obtains a sour milk of a characteristic and agreeable aroma and
taste, which beneficially affect the flavour of the butter produced. On
the other hand, if milk is kept in hot and dirty surroundings, the
development of acidity is accompanied by different bad tastes and
odours, and it becomes unfit for use as a food. In the first case, the
conditions are favourable to the maximum production of the lactic acid
bacteria, and these occupy the field, and largely prevent the
development of the other bacteria which are present--the survival of the
fittest in the struggle for existence. In the second case, the impure
surroundings swarm with the germs of many kinds of putrefactive
bacteria, and the high temperature assists these to gain the upper hand.
Again, the survival of the fittest, in the particular conditions. Even
in cool and cleanly surroundings injurious taints may develop,
especially if the milk has previously been subjected to a journey by
road or rail, as is the case in the modern creamery system, where the
farmers deliver their milk to a central creamery, where it is made into
butter. In such establishments it is the regular practice to kill the
germs, lactic and others, existing in the milk, by heating it to a high
temperature. This process is called pasteurising, after the great French
chemist and bacteriologist who invented it. Pure lactic cultures are
added to the pasteurised milk, and the souring process is under exact
control, with the result that butter of uniform flavour and quality is
produced. The same method is made use of in making the special sour milk
described in this book, with, of course, modifications in the apparatus
employed, to suit the smaller scale in which the manufacture is
conducted.

The ash is the mineral matter which is left when milk, previously dried,
is burnt in a crucible. It is a complex mixture, and, as we have seen,
it amounts to about 0.7 per cent. of the milk. The process of burning
destroys all the organic matter, and, at the same time, alters somewhat
the state of combination of the inorganic or mineral elements. Attempts
have been made from the analysis of the ash to reconstitute the
composition of the mineral matter as it exists in the milk. The best
known is that of Soldner, and the following is his calculation:

                                             Per cent.
  Sodium chloride                              10.62
  Potassium chloride                            9.16
  Monopotassium phosphate                      12.77
  Dipotassium phosphates                        9.22
  Potassium citrate                             5.47
  Dimagnesium citrate                           3.71
  Magnesium citrate                             4.05
  Dicalcium phosphate                           7.42
  Tricalcium phosphates                         8.90
  Calcium citrate                              23.55
  Calcium oxide, in combination with casein     5.13
                                              ------
                                              100.00
                                              ------

The presence of citrates will be noted in this analysis. Citric acid,
which gives to lemons their acidity, and is also found in other fruits,
has been proved to exist in milk to the extent of about 0.2 per cent.
When alkaline or earthy citrates are burnt or oxidised in the blood, the
citric acid is destroyed, and corresponding carbonates remain. No doubt
the function of citrates in milk is to furnish to the body the earthy
and alkaline carbonates which are required in certain of its parts.

The mineral constituents of milk have many important functions to
perform in the building up and nutrition of the bodily organism.
Phosphate of lime is the principal constituent of the skeleton, and the
blood must be richly supplied with the alkalies, earths, and acids which
are comprehended in the ash.

Milk contains traces of many other substances, the most important of
which are several enzymes which assist in its digestion.

_General Properties of Milk._--The appearance of milk is known to every
one; it ought to be a pure white opaque liquid, but very generally it is
tinted a cream colour with anatto to give it an added appearance of
richness. The average specific gravity is about 1.031; or, to put it
another way, while a gallon of pure water weighs exactly 10 lbs., a
gallon of milk weighs 10 lbs. 5 oz. It freezes at 31 deg. F. and boils at
about one third of a degree higher than water.

When milk is examined under the microscope, the fat is found to be
distributed through it in a multitude of minute globules varying in size
from 1/16,000th to 1/25,000th part of an inch, and occasionally they are
much smaller and also much larger.

Fig. 1 is a micro-photograph showing the fat globules in whole milk.
Fig. 2 is a micro-photograph of separated milk, and Fig. 3 a
micro-photograph of cream, all under high magnification (450 diams.);
from these figures the comparative number of fat globules present may be
seen.

  [Illustration: FIG. 1.--Micro-photograph of a Drop of
  Whole Milk, showing distribution of fat globules.
  (Magnified 450 diams.)]

  [Illustration: FIG. 2.--Micro-photograph of Separated
  Milk, showing the almost complete absence of fat globules
  as compared with whole milk. (Magnified 450 diams.)]

  [Illustration: FIG. 3.--Micro-photograph of Cream, showing
  agglomeration of fat globules. (Magnified 450 diams.)]

Fats distributed through a watery liquid in this finely divided
condition form together what is called an emulsion, in which the
particles of fat are kept apart by surface tension. The specific gravity
of milk fat averages 0.93, and compared with water weighing 10 lbs., a
gallon of fat would weigh 9 lbs. 5 oz. It is thus considerably
lighter than the other constituents, and when milk is left at rest, the
fat globules gradually rise to the top and float there, forming cream.
The difference in specific gravity between cream and milk is taken
advantage of in the mechanical separator, now so much used, and which
makes such a thorough separation between the two. Cream is an article of
the most varied composition, according to the ideas of the person who
produces it, but it ought to contain at least 20 per cent. of butter
fat, and may be made with a much larger percentage if necessary. When
cream is agitated in a particular way, as by churning, the surface
tension of the particles is overcome, and they run together into a mass
which forms butter.

The casein of milk is not held in solution in the ordinary sense, but in
a peculiar state of suspension called the colloidal condition,
practically the whole of it remaining behind when milk is filtered
through clay filters.

It is this state of suspension of the casein which makes milk opaque,
but the opacity is considerably increased by the emulsified fat.

The coagulation of the casein in milk by the addition of rennet has
already been referred to. Acids, either mineral or organic, also
precipitate it in the form of flakes. Skimmed milk is now largely used
for the preparation of casein by this method, and the washed and dried
precipitate is used very extensively in the arts for such varied
purposes as the manufacture of billiard balls, paints, cements, etc.

The clear liquid which separates when milk is curdled with rennet is
called whey, and contains the milk sugar and mineral salts. The sugar is
manufactured from it on a limited scale, and is used as an ingredient in
infant foods, and as a convenient medium in certain medical
preparations. In Sweden a kind of cheese is made from whey, but the
great bulk of it everywhere is used for feeding pigs.

The comparative composition of different varieties of milk is given in
the following table:

  -------------------------------------------------------------------------
             Human   Cow   Buffalo  Goat  Sheep   Mare   Ass Reindeer Whale
  -------------------------------------------------------------------------
  Water      88.32  87.75   82.57  86.34  81.08  90.38  90.30   67.7  60.47
  Fat         3.43   3.40    7.63   4.25   7.67   1.00   1.30   17.1  20.00
  Protein     1.55   3.50    4.69   4.40   6.08   1.98   1.80   10.9  12.42
  Milk Sugar  6.44   4.60    4.30   4.26   4.26   6.28   6.20    2.8   5.63
  Salts       0.26   0.75    0.81   0.75   0.91   0.36   0.40    1.5   1.48
  -------------------------------------------------------------------------
  Total     100.00 100.00  100.00 100.00 100.00 100.00 100.00 100.00 100.00
  -------------------------------------------------------------------------
  Specific   1.032 1.0315   1.033  1.033  1.038  1.034  1.033   ...   ...
   Gravity
  -------------------------------------------------------------------------

  [Illustration: FIG. 4 is a photograph of two Petri dishes,
  which have been inoculated with ordinary milk (A), and
  milk that has been subjected to sterilisation (B). The
  whitish bacterial colonies on A are due to enormous
  numbers of organisms, while B is quite free from such
  growth.

  For the production of a reliable lactic food, it is
  essential that certain precautions as to the treatment of
  the milk, and the maintenance of a suitable temperature
  during the growth of the lactic bacteria, should be
  observed.

  In the first place, milk immediately after extraction from
  the cow contains only a few organisms, but these multiply
  so rapidly that in a few hours the bacterial content may
  amount to many millions per ounce. In preparing a pure
  culture of any specific organism, then, care must be taken
  to destroy all the bacteria that have accidentally found
  their way into the milk, inoculating with the organisms it
  is desired to cultivate. This is best accomplished by
  heating the milk to the boiling-point of water for about
  thirty minutes, by which time almost all the undesirable
  bacteria have been killed.]

The milk of the cow differs a good deal from human milk, and where the
former is used for the feeding of children it is usual to add milk sugar
to it, and otherwise alter it to bring its composition more in harmony
with the human article. The high concentration of the milk of the
reindeer and the whale is noteworthy. Perhaps this may be due to the low
temperature conditions in which these animals live, necessitating strong
nutriment to enable their young to make proper progress in growth and
development. On the other hand, the milk of the ass is poor in quality,
and probably on this account it is more readily assimilated by those of
weak digestion, to whom it is sometimes recommended. Goats' milk is
richer than either cow or human milk, and its nourishing properties are
well known. The goat is usually free from tuberculosis and other
diseases which affect the cow, and its milk is therefore a very safe
article to use.

_The Analysis of Milk._--While the analysis of milk can only be made by
a competent chemist, there are a number of simple tests and observations
by which any intelligent person can obtain a fair idea of its quality.
The taste and smell afford some guide, as also the general appearance.
To judge of the latter, place some of the milk in a tumbler or other
clear glass vessel. If the milk is of good quality it will be quite
homogeneous and opaque. Any flocculent matter indicates either disease
in the cow or that the milk is old and bacteria have multiplied in it
and altered its composition. When the milk has stood long enough for the
cream to rise freely, the latter should form a perfectly homogeneous and
strongly defined layer on the top. The quantity of cream may be measured
in a creamometer, which consists of a small glass cylinder graduated at
the top (Fig. 5). It is filled with milk to the top graduation line, and
when the cream has risen, the percentage quantity of the latter which
has separated can be taken off.

  [Illustration: FIG. 5. The Creamometer]

The colour should be like that of porcelain, but, as already stated, it
is a common thing for the dairyman to add a small quantity of anatto or
an aniline dye of a similar shade, to give the milk a rich creamy tint.
If the milk is of a reddish colour this may be caused by blood from the
udder, although certain foods, such as beets, mangels, and carrots
sometimes give a similar tint. The milk given by cows immediately after
calving is called "colostrum" or "biestings," and is of a yellow or
yellow-brown colour. It is much thicker than ordinary milk, and
coagulates in boiling.

In dirty byres in which care is not taken in milking, quite considerable
quantities of hairs, pieces of manure, and other filth may get into the
milk. Usually the milk is strained by the dairyman, but sometimes this
is omitted or carelessly done. To test for dirt, a ribbed glass funnel
is useful. Get a piece of the finest muslin about twice the diameter of
the funnel, fold over twice, so that it becomes one quarter of its
original size; open one of the sections and place in the funnel; pass
the milk into this. It will run through quickly and some water may be
run into the funnel to clear away the last traces of milk. The filter
cloth can then be opened out and any dirt retained will become visible.
The apparatus is shown in Fig. 6.

  [Illustration: TESTING-GLASS FOR EXTRANEOUS MATTER IN
  MILK.

  FIG. 6.--A piece of muslin is folded as shown and a
  measured quantity of milk is passed through the funnel;
  from the sediment left in the muslin, the percentage of
  extraneous matter may be arrived at.]

If a glass funnel is not available, a very small jelly bag can be made
of fine gauze and used in the same way. The washing water should be used
in small quantities and directed to concentrating the dirt in the apex
of the bag. After washing, the latter can be turned outside in, to
permit of readier examination of the dirt. The bag should be well
washed in cold water, then boiled and dried, and is then ready for
future use.

The acidity of milk is a very useful guide to its age. Milk has the
curious property of being "amphoteric," _i.e._, it is both slightly acid
and slightly alkaline when fresh. As its age increases, however, so does
its acidity, and at a rate varying with the temperature and moisture
contents of the atmosphere in which it is placed. Old and acid milk is
heavily contaminated with bacteria, a proportion of which are likely to
be injurious to health.

  [Illustration: FIG. 7. Lactometer and Test Tube]

The simplest method of testing the acidity is to procure a few little
books of blue and red litmus test papers, and these can be had from any
philosophical instrument maker or laboratory furnisher. The strips of
test paper are torn out and dipped in the milk. When the milk is quite
fresh it will, owing to its amphoteric condition, change the red litmus
paper slightly blue, and the blue litmus paper slightly red. Old milk
changes blue litmus paper to a bright red because of its decided
acidity.

The above tests do not indicate if the milk is poor or rich, but this
can be determined by the lactometer, an instrument for ascertaining in a
simple way the specific gravity. The lactometer is shown in Fig. 7.

It is graduated usually from 25 deg. to 36 deg., corresponding to specific
gravities 1.029 to 1.038. It is graduated to degrees and half degrees.
Sometimes a thermometer is combined with the instrument. The specific
gravity rises as the temperature is lowered and decreases with increase
of temperature, so that it is important to make the test at the figure
at which the lactometer was graduated, which is usually 60 deg. F. Failing
this, an allowance has to be made for higher or lower temperatures. The
milk to be tested is well mixed, and placed in a deep vessel, and the
lactometer placed in it, holding it at first at an angle. It stands
upright and remains deeper or higher according to the specific gravity.
The reading is taken on the stem at the level of the milk. As the latter
is drawn up a little round the stem, about a half degree should be added
on to get the true figure. Thus, if the apparent reading is 31, the true
reading may be taken as 31.5. This is the average figure for good milk,
corresponding to a specific gravity of 1.0315; anything above this is
all to the good. Lower readings mean inferior quality, the latter being
proportionate to the lowness of the readings. The tests are most
conveniently made in a glass cylinder (Fig. 7), which may be purchased
with the lactometer. As there are many inaccurate instruments in the
market, it is necessary to go to a reputable maker, because an
unreliable lactometer is worse than useless.

The following table gives, in a condensed form, the allowances to be
made when the temperature is above or below the standard (60 deg. F.):

  ------------+----------------------------------------------------------
  Temperature.|               Reading of Lactometer.
  ------------+------------------------------------------------------------
     Degs. F. |
       40     | 23.5 24.5 25.5 26.4 27.3 28.2 29.1 30.0 31.0 31.9 32.8 33.7
       45     | 23.8 24.8 25.9 26.8 27.8 28.6 29.3 30.4 31.3 32.3 33.2 34.2
       50     | 24.1 25.1 26.1 27.0 28.0 29.0 29.9 30.9 31.8 32.8 33.7 34.7
       55     | 24.5 25.5 26.5 27.5 28.5 29.5 30.4 31.4 32.4 33.4 34.3 35.3
  ------------+------------------------------------------------------------
       60     | 25.0 26.0 27.0 28.0 29.0 30.0 31.0 32.0 33.0 34.0 35.0 36.0
  ------------+------------------------------------------------------------
       65     | 25.5 26.6 27.6 28.7 29.6 30.7 31.7 32.8 33.8 34.8 35.8  ...
       70     | 26.1 27.2 28.2 29.3 30.2 31.3 32.4 33.4 34.5 35.5 36.5  ...
       75     | 26.8 27.8 28.8 29.9 30.8 32.1 33.1 34.2 35.2 36.3  ...  ...
       80     | 27.4 28.4 29.5 30.7 31.6 32.8 33.9 35.9 36.1  ...  ...  ...
  ------------+------------------------------------------------------------

Thus if the thermometer indicates 40 deg. F., and the lactometer 29.1 deg.,
the true reading at the standard temperature of 60 deg. F. is 31 deg.,
corresponding to a specific gravity of 1.031. Intermediate figures can
readily be averaged. Care should be taken to wash the lactometer with cold
water under the tap, as otherwise the milk will dry on it and render it
inaccurate.




CHAPTER IV

HANDLING OF MILK


MODERN DAIRY PRACTICE

As we have seen, the dairy industry is a very ancient one, and has been
intimately associated with the development of civilisation.

Within historical times dairying has always formed a prominent feature
in connection with agriculture, and the use of milk in one form or
another has been common to every civilised nation.[42]

The greatest progress, however, in the study of milk has taken place
since about the year 1890, at which time the dairy industry seems to
have attracted the general attention of food specialists and scientific
investigators throughout the world. Since then it has been considered
worth while to enact laws in different countries with regard to the
regulation and control of the milk supply.

Since 1903 there has been an International Dairy Federation formed, and
it has held conferences at Brussels, Paris, The Hague, and Buda-Pest,
and in 1911 it will hold a conference in Stockholm. The Federation was
started in a very humble way in Brussels, and owes its origin, to a
large extent, to a distinguished Belgian agriculturist, Baron Peers of
Oostcamp, Bruges; but at the present day a general committee composed of
representatives of nearly every civilised nation has been formed, and
delegates from such countries attend the Congresses, which are held
every two years. The literature which has arisen out of these
International Congresses has been disseminated in different countries,
and has been instrumental in placing the dairy industry on a thoroughly
scientific basis.

_Milk Supply of the United Kingdom._--The milk supply of the United
Kingdom has steadily grown from year to year, and in relation to the
population works out at fifteen gallons per head. The manner in which
these figures are arrived at is shown in the following estimate:

  The population of the United Kingdom is now about
  45,500,000. The number of cows or heifers in calf or in
  milk in June, 1909, was 3,360,600; the number in 1910 was
  probably about 4,400,000.

  Of these about 300,000 were heifers that had not yet
  produced any milk. The actual milking class, therefore,
  comprised about 4,100,000 cows and heifers; of these,
  about 600,000 were heifers that calved in the winter and
  spring of 1909-10, and 300,000 were heifers that calved in
  the summer and autumn of 1910. The number of cows that
  produced two or more calves may be taken to be about
  3,200,000; of these about 600,000 should have produced
  their second calf in the winter and spring 1909-10, and
  would be milked as heifers in the summer and autumn of
  1910; the number of mature cows from which a full season's
  supply of milk was obtained during the twelve months from
  June 5, 1909, to June 4, 1910, was apparently about
  2,600,000. A large quantity of milk is yielded during the
  year by cows sold or lost during the twelve months before
  the census. Possibly ten per cent. of the milk produced in
  the twelve months from June, 1909, to June, 1910, was
  yielded by cows that were sold or lost before the census
  of June, 1910.

  It is estimated that the 3,200,000 cows (including the
  600,000 that up to the winter of 1909-10 were heifers)
  produced, on the average, 44 cwts. (480 gallons) of milk
  per head in the twelve months from June 5, 1909, to June
  4, 1910; the 300,000 heifers that calved in the summer and
  autumn, 30 cwts. (330 gallons) per head; the 600,000
  heifers that calved in the winter and spring of 1909-10,
  15 cwts. (165 gallons), making the total quantity of milk
  produced in the twelve months by cows and heifers on the
  farms, and that produced calves during the twelve months
  (June, 1909-1910), 158,800,000 cwts. (1,746,800,000
  gallons), or about 426 gallons per head, and about 400
  gallons per head for all the cows and heifers in milk or
  in calf in 1910. There remains to add the milk yielded by
  the cows that were sold during the twelve months, and of
  cows and heifers in feeding pastures that were milked
  during the twelve months, June to June, 1909-10, and which
  probably formed one tenth of the whole supply, making the
  total supply for the twelve months 176,444,000 cwts., or
  1,940,884,000 gallons. This equals 2 tons, or 440 gallons
  per head, crediting the whole supply to the 4,400,000 cows
  and heifers in milk or in calf in June, 1910. At 7-1/4d.
  per gallon the value of milk produced in the United
  Kingdom in the twelve months was L58,600,000. Including
  the value at birth of the calves, the total value of the
  produce of the milk-giving class would be about
  L62,000,000. The value of the milk, butter, cheese, and
  cream sold or consumed in farmhouses would be about
  L48,000,000, or equal to about 24 per cent. of the gross
  annual income of farmers.

  The average consumption of new milk is about 15 gallons
  per head of the population. During the twelve months of
  1911, the quantity required for this purpose will be about
  682,500,000 gallons, or about 35 per cent. of the total
  supply; calves will require about 10 per cent. of the
  supply; the quantity available for butter and cheese will
  equal about 55 per cent. of the supply.[43]

_The Milk Industry in the United States._--In the United States of
America, where the habits of the people are somewhat analogous to those
in the United Kingdom, it is estimated that the milk from five million
cows is annually consumed, which averages twenty-five and one half
gallons per year for each person, or equal to an ordinary sized
tumblerful each day.[44]

Such a vast industry, so intimately associated with the food of the bulk
of the people, naturally invites the closest study, and, as a
consequence, the literature on the subject, which has arisen during the
last twenty years, has been of a voluminous character, not only from the
point of view of practice, but from that of bacteriology, chemistry, and
hygiene.

A pure milk supply is essential to health, and it seems unfortunate that
the ordinary milk producer should, in a great many cases, take up an
antagonistic attitude to the scientific methods of handling milk. There
is a body of opinion being created, however, which is likely to alter
this attitude in the next generation, and this is attributable to the
fact that so much excellent work has been done at numerous dairy
colleges and institutes in all civilised countries that the dairy
industry is emerging from a period of rule-of-thumb procedure to its
proper place as one of the technical arts.

_Transmission of Disease in Milk._--It is not to be wondered at that the
handling of milk should now be regarded as a technical business, seeing
that milk-borne disease is one of the commonest with which we have to
deal.

The commoner diseases which have been transmitted by milk are scarlet
fever, typhoid, diphtheria, tuberculosis, sore throat epidemics. Others
of a more complex character have been traced to the same source of
infection, and the clearest possible evidence has been furnished of the
transmission of diseases by means of micro-organisms, which have
contaminated the milk supply.

It is therefore necessary to watch over the milk from the source of
supply to its consumption. It is primarily on the farm and in the
cow-house that methods of handling in a hygienic way should be insisted
on, as microbial contamination increases at a prodigious rate, and it is
the early microbe therefore which does the most damage.

The milk in the udder, for all practical purposes, may be assumed to be
sterile, and the contamination which takes place originates, therefore,
from external sources.

One of the principal means of infection is from hairs which fall from
the cow into the milk, and many of which are carriers of dangerous
micro-organisms.

There is also a certain amount of offensive dirty matter which may fall
into the milk-pail, and carry with it undesirable germs.

These impurities may, to a certain extent, be eliminated by good
straining, but a surer prevention is to have the cow-house perfectly
clean and free from dust, as dust specks are in many cases the vehicles
of disease germs. Cleanliness is, in fact, the essential feature in
modern dairying, not only in the cow-house, but in the milking utensils,
the drainage, etc., and, above all, the milker should be of cleanly
habits.

The flavours of milk sometimes arise from the absorption of
evil-smelling gases in the cow-house, or from a peculiar taint from
certain roots and feeding stuffs, and in such a case it is desirable
that aeration should take place in a fresh clear atmosphere, so that
oxygenation may have the effect of eliminating and destroying the
foreign odours and flavours which may be present. If this process of
aeration is carried out at blood heat, the result is generally highly
satisfactory.

_Milk Management._--There have been many excellent tables of rules
published for the management of dairies in different countries, but they
are necessarily framed within certain limitations which apply to all.
The following is an excellent set, which put concisely the conditions
necessary to be observed in the modern cow-house:

   1. The cow should be sound--no disease should exist in
        the animal.

   2. The feed should be good and free from aromatic
        substances. If these aromatic foods are used, they should
        be employed according to those methods which will not
        cause odours or flavours to appear in the milk.

   3. The cow should be groomed, and hair about the udder
        preferably clipped.

   4. The udder should be moistened during milking.

   5. The milker should be a neat, tidy person.

   6. The milker should be free from disease, and should not
        come in contact with any communicable disease.

   7. The milker's clothes and hands should be clean while
        milking.

   8. The pail should be sterilised.

   9. The stall should be such as to reduce the amount of
        disturbance of dust and dirt.

  10. There should be good light, good ventilation, and
         good drainage in the cow-house.

  11. The cow-house should always be kept clean.

  12. Feeding and bedding, unless moist, should be done
        after milking.

  13. A dustless milking-room is desirable.

  14. Milk should not stand in the cow-house.

  15. If milk is aerated, it should be done before cooling
        and in pure air.

  16. The sooner the milk is cooled after milking the
        better.

  17. Keep the milk as cold as possible when once
        cooled.[45]

The supply of milk is conducted, to a large extent, by towns' dairies,
which depend for their supplies upon the dairy farm in the country, and
it is obvious that a certain period of time must elapse, in the
generality of cases, before a town's dairy receives its supply in the
ordinary course, and this constitutes the greatest difficulty in modern
dairy practice, owing to the liability of the milk to absorb bacteria,
which during transit may multiply enormously.

The multiplying of bacteria in milk at different temperatures is easily
demonstrated, and the result of this has been stated in various forms
many times over. As a graphic means, however, of showing the increase
that takes place in the numbers of germs present, and the consequent
product of acidity, the table below by Conn may be given.

The consequent result of the increase in bacteria is the production of
lactic acid, which produces the souring so familiar in milk which has
been kept in the household at a high temperature.

  _Numbers of Bacteria per c.cm. in Milk kept at
             Different Temperatures._

  --------------------------------------------------------------------------
  Number  In 12   In 12    In 50    In 50 hrs. or at   No. hrs.   No. hrs.
  at     hrs. at hrs. at  hrs. at   time of curdling   to curdle  to curdle
  Outset 50deg.F. 70deg.F. 50deg.F. at 70deg.F.        at 50deg.F. at 70deg.F.
  --------------------------------------------------------------------------
  46,000 39,000 249,500 1,500,000   542,000,000            190        56
  47,000 44,800 360,000   127,500   792,000,000.36 hrs.    289        36
  50,000 35,000 800,000   160,000 2,560,000,000.42 hrs.    172        42
  --------------------------------------------------------------------------

What actually happens is that the lactic acid is produced by the
breaking up of the milk sugar, and the appearance of this sourness is an
indication that a period has been reached in the age of the milk which
may be described as being--unwholesome.[46]

It is necessary, therefore, for the town's milk dairy to be equipped in
such a way as to deal promptly with the milk supply.

We have seen that the milk should first of all be aerated at blood heat,
so as to liberate objectionable odours, after which it should be cooled
to as low a temperature as possible, by means of well water. When these
operations have been performed on the farm, milk should be sent as
rapidly as possible to the distributing towns' dairies, and should be
transported in refrigerated waggons, cooled preferably with ice, during
the journey. On arrival at the town dairy, it will be necessary to
pasteurise the milk--that is to say, the milk should be heated to such a
temperature as will destroy any pathogenic organisms which may be
present, and the pasteurising temperature should therefore be in excess
of the thermal death-point of all such organisms.

Pasteurisation owes its origin to Pasteur, and has become an adopted
method throughout the dairy industry, and there are many mechanical
devices termed "pasteurisers" (see Fig. 8) which are used for the
carrying out of this particular operation. The form of one of these is
that of a vertical jacketed cylinder with paraboloidal surface, around
which steam is made to pass, so as to maintain the temperature at about
176 deg. F. Milk is allowed to flow in at the bottom of the paraboloidal
surface, and is caught by mechanical agitating arms, which revolve at a
given speed, and by this action milk is distributed centrifugally over
the paraboloidal surface, and is forced out by the same action, at the
top of the apparatus, after being heated.

  [Illustration: PASTEURISER

  FIG. 8.--The milk enters from the bottom and circulates to
  the top of the inside cylinder, which is paraboloidal in
  construction. It is heated as it passes through the
  apparatus, and is discharged at the top at a temperature
  of 176 deg. F.]

The centrifugal action is sufficient to raise the milk some three to
four feet, through a tube, and this is taken advantage of so as to cause
the milk to flow over a conical cooler, described as a primary cooler,
and in which water is made to circulate. As the hot milk descends over
the conical cooler it gives up most of its acquired heat to the water,
and, in practice, is reduced in temperature to within 4 deg. of the
temperature of the water.

Below this primary cooler is fixed a cooler of the same size and shape,
which is termed a secondary cooler. In it, brine at a temperature of
about 35 deg. F. is circulated from a refrigerating machine, and, as the
milk falls over the secondary cooler, it is cooled to a temperature of
about 40 deg. F., when it may be looked upon as being pasteurised and free
from all pathogenic organisms, in which state it will keep for a
considerable length of time.

It is desirable that the milk should, as soon as possible after the
cooling takes place, be delivered to the consumers, and be kept under
cool conditions, either in bottles or in a closed vessel covered over
with muslin, so as to keep out specks of germ-laden dust.

Briefly speaking, the foregoing is an outline of what is carried on in
the ordinary dairy practice.

There are many modifications of this practice, such as the introduction
of regenerative heaters, so as to utilise a portion of the heat of
pasteurisation, which would otherwise be wasted.

In some cases, again, it is considered necessary to conduct the primary
and secondary cooling over coolers furnished with mantles, so that the
atmospheric bacteria which are everywhere present should be shut off
from the falling milk.

Ordinarily, however, the equipment for a town's dairy consists of:

1. Steam-boiler to generate steam for pasteurising, scalding, etc.

2. Motive power, which may be either a steam-engine, gas-engine, or
electric motor.

3. Refrigerating machine, which is used for supplying cold brine to the
secondary cooler. In many cases it is also used for cooling a room in
which the milk and cream are stored.

4. Milk-receiving tank.

5. Milk-strainer.

6. Pasteurising apparatus, and primary and secondary coolers.

Such a plant is necessary in order to conduct an ordinary town dairy
business in anything like a hygienic way, and is designed only for the
handling of milk intended for domestic consumption.

There are times when another plant might be necessary, such as a plant
for the separation of milk, or for utilising it for the production of
butter or cheese, such operations being subject to the fluctuations in
the milk supply.

It is sometimes desirable also to use up an excess of milk for cheese or
butter-making; hence it is necessary to provide such apparatus as has
been indicated.

_Preparation of Soured Milk._--The foregoing description has been given
in some detail, as showing the ordinary practice, and we now come to
consider how it can be modified so as to provide for the production of
soured milk. It may first of all be premised that within the next few
years the preparation of soured milk as an ordinary production of the
dairy will be universal, and will form a part of the ordinary dairy
practice. The apparatus, therefore, which is necessary is one of
considerable interest to all who are engaged in the dairy industry.

As will be seen from the chapter describing the preparation of soured
milk in the dairy, this process can be conveniently carried on, so as to
utilise the plant which is at present in general use. The milk can be
received in the same way, pasteurised and cooled to about blood-heat,
after which its preparation as soured milk is a very simple matter, and
only requires a certain amount of careful attention.

For the keeping of soured milk, a cold room cooled by a refrigerating
machine would be desirable, so as to maintain the fermented milk at a
low temperature and prevent over-fermentation.

Apparatus has been designed so as to handle soured milk on a large
scale, and one of the machines is shown on the illustration (see Fig.
9). It is simply a jacketed cylinder with a cover and an agitating gear.
The inside of the machine is nickel-plated, and there is an arrangement
whereby the cooling may be done rapidly, through a coil inside the
jacket, this coil being connected to the brine circulation of the
refrigerating machine.

  [Illustration: CONTINUOUS APPARATUS FOR THE PRODUCTION OF
  LARGE QUANTITIES OF SOURED MILK

  FIG. 9--This apparatus is made by the Dairy Machinery and
  Construction Company of Shelton, Conn., U S A. The milk is
  agitated inside a jacketed cylinder, where it is allowed
  to incubate at about blood heat. The milk can be rapidly
  heated and also rapidly cooled by means of this
  apparatus.]

The machine is filled with milk containing three per cent. of fat, which
has been previously pasteurised to about 190 deg. F., and cooled down to
about 90 deg. F.; at this point the pure culture of _Bacillus bulgaricus_
is introduced, and the agitator is kept working, so as to mingle it
thoroughly with the milk. The agitator is then stopped until the acidity
shows a test of 0.9 to 1.0 per cent., when the agitator is again
started, and cold brine from the refrigerating machine is turned on to
the cooling pipes, so that the product is thoroughly broken up, and
cooled down to 40 deg. F.

The milk is then transferred to a bottle-filling machine (Fig. 10),
poured into bottles and hermetically sealed, after which it is ready for
consumption. When it has to be kept for any time it should be placed
in a cold room where there is a temperature not higher than 40 deg. F.

The process, therefore, is a simple one, and lends itself to the
ordinary dairy business, without involving any great expenditure on
account of a new plant.




CHAPTER V

THE BACTERIOLOGY OF FERMENTED OR SOURED MILK


A CHAPTER FOR STUDENTS

During the last few years much work has been done in investigating the
action of various classes of organisms--bacteria, yeasts, and
moulds--upon milk and its products. While, however, the attention of the
dairyman has been chiefly directed to the propagation of acid-producing
organisms and the use of pure cultures of lactic acid bacteria in their
relation to butter and cheese making, a new sphere in micro-biology has
been disclosed by the study of the effects caused by the combined growth
of two or more different classes of organisms in milk and the consequent
production of lactic, alcoholic, and gaseous fermentations. The
simultaneous occurrence of these fermentative changes is responsible for
the formation of such beverages as keffir, koumiss, milk-wine, etc. It
has therefore become essential, in connection with the study of new
developments in the milk industry, that we should make a more intimate
acquaintance with the bacteriology of the ferments involved.

_Keffir_ (_kephir_, _kifyr_, _kiafyr_, _kephor_, _kyppe_) is the name
given to an acid, slightly alcoholic drink, which for many centuries has
been prepared by the nomadic tribes in the Caucasus. The characteristic
fermentation is induced by the addition of so-called keffir grains.
These are yellow or golden-yellow, warty, and furrowed flakes or
nodules, the former varying in size from that of a rice grain to that of
a bean, while the latter are often about an inch across and one eighth
of an inch thick. Bearing in mind the fact that the preparation of
keffir has been carried on for many centuries, it is not surprising that
the origin of these grains should be surrounded by myths.

The belief is prevalent among the Mohammedan tribes of the Caucasus that
keffir grains were, in the first instance, presented by Allah, as a sign
of immortality, to one preferred tribe. Others hold that, in past ages,
they were found by shepherds growing on a shrub in the Caucasian
highlands; while, according to Skolotowski,[47] they were originally
found adhering to the walls of an oaken vessel used for the preparation
of airam. This is a soured milk beverage similar to keffir, but
possessing a weaker alcoholic fermentation, and prepared from goats'
milk by the addition of pieces of calf's stomach. This would undoubtedly
serve to introduce various species of lactic acid bacteria, and will be
referred to in the portion dealing with soured milks. Keffir is prepared
by the Caucasians from cows', sheep's, or goats' milk, and the operation
is carried on in large leathern tubes or bottles. After the addition of
the grains or seeds to the milk the vessel is placed in a cool chamber,
and the fermentation is allowed to proceed for one or two days, by the
end of which time the normal fermentation is at an end. During this
period the keffir grains have increased enormously in size, assume a
bright yellow colour, and lose their sour buttery smell.

Previous to the removal of the fermented liquid, a portion of the bottle
is firmly bound from the rest by a stout cord, and the greater portion
of the remaining keffir is quickly removed for use, thus avoiding, as
far as practicable, any outside infection. After the addition of fresh
warm milk the cord round the end of the bottle is removed, and the old
and new milk thoroughly mixed for a time in order to ensure uniform
inoculation of the new milk for the next fermentation. During the winter
months the leathern vessels are often placed in the sunshine, so that
the temperature remains at 61 deg. to 65 deg. F.

The necessary agitation of the vessel is said to be supplied in the form
of kicks by passers-by or by the children during their play.

The beverage prepared in this way is so gaseous in character that it is
often blown forcibly from the vessel during removal, and possesses,
according to Podowyssozki,[48] a very acid taste.

During any interruption in the preparation of keffir in the above
manner, the grains are taken out, and after having been well washed in
clean water, are spread out on a clean cloth to dry in the sunshine.
They thereby assume a characteristic cheesy or buttery odour and become
rather darker in colour. Thorough desiccation is essential in order to
prevent subsequent mouldiness or disease of the grain.

In European countries the grains are subjected to a preliminary soaking
in water for five to six hours and then placed in four to five changes
of milk, each change having a duration of two to three hours. As soon as
the grains commence to rise to the surface of the milk, they may be used
for the actual preparation. To this end, a small quantity of the grain
is added to freshly boiled milk and allowed to stand for eight to twelve
hours at a temperature of 55 deg.-62 deg. F. with agitation of the flask
every two hours. By this time the milk, now known as Sakwaska, has become
abundantly inoculated with the organisms essential to the fermentation,
and after the removal of the grains, may be poured into well-corked
flasks for the secondary brew. The flasks should be kept at a lower
temperature for twenty-four to forty-eight hours, by which time the
product is ready for consumption.

According to the temperature and length of period to which this
subsequent fermentation is allowed to proceed, the resultant keffir is
more or less acid and gaseous. The grains may again be used for starting
a fresh portion of milk, and a regular supply obtained in this manner.
Well-fermented forty-eight-hours-old keffir should be an effervescent
beverage with prickling and acid taste and a consistency and smell
similar to sour cream. Large, persistent bubbles should form on the
surface of the liquid and the casein be present as an extremely fine
flocculent precipitate which remains suspended for a considerable time.

From the third day there ensues a gradual peptonisation of the casein.
If the temperature at which the secondary fermentation has occurred
should be higher than 72 deg. F., or if the milk has not been sufficiently
agitated, then the casein will be present in the form of porous small
flakes, which on shaking form a fine emulsion.

The chemical changes undergone by the milk during the preparation of
keffir are confined almost exclusively to the milk sugar. As already
stated, a slight peptonisation occurs in old samples, but this depends
very largely upon the method of preparation and purity of the culture.
Hammersten[49] and Essaulow[50] show, however, that this is not a
concomitant of normal fermentation. According to Hammersten, normal
keffir contains--

                            Per cent.
  Water                       88.26
  Fat                          3.35
  Casein                       2.98
  Lactalbumen                  0.28
  Peptones                     0.05
  Milk sugar                   2.78
  Lactic acid                  0.81
  Alcohol                      0.70
  Ash                          0.79

In no case should the acid be higher than 1.0 per cent., and the alcohol
more than 0.75 per cent.

_Biology of the Keffir Grain._--The first communication on the biology
of the keffir grain seems to have been made by Kern.[51] He regarded the
grain as a zoogloea composed of bacilli and yeasts, the latter being
regarded as the ordinary beer yeast (_Saccharomyces cerevisseae_), while
to the former he gave the name of _Dispora caucasica_. As the name
indicates, this bacillus possesses two polar spores, and germination of
these proceeded in the same manner as with _Bac. subtilis_. As, however,
pure cultures of the organisms were not made, and the descriptions and
illustrations made by Kern fail to show any distinctive characteristics,
it seems probable that accidental confusion with other organisms must
have occurred.

  [Illustration: A MILK FILLING APPARATUS

  FIG. 10--Where soured milk is handled on the large scale,
  a special filling apparatus for bottles is desirable, and
  the soured milk supply should be under cover as shown.
  This apparatus is made by the Dairy Machinery and
  Construction Company.]

Krannhals[52] succeeded in isolating ten different keffir bacteria among
which were several sporulating bacteria. Here too it is impossible to
attach any importance to the results, as the artificial preparation of
keffir, by means of these bacteria, was not attempted. Beijerinck[53]
studied the organisms constituting keffir grains and attached prime
importance to the occurrence of two organisms, viz., (_a_) a yeast,
_Saccharomyces kefir_, which was capable of inverting milk sugar by
means of an enzyme (lactase) and afterwards fermented the products with
the formation of alcohol and carbon dioxide, and also (_b_) a non-motile
non-sporulating bacterium, afterwards _Lactobac. caucasicus_. The
latter, when cultivated on gelatine, gave rise to tough warty colonies
about 1/40 in. diameter, and was regarded as one of the lactic acid
bacteria found in milk which has been incubated at 77 deg. to 90 deg. F.
and afterwards incubated at a higher temperature, 100 deg. to 104 deg. F.
Scholl[54] isolated three different organisms, of which a yeast inverted
milk sugar for the lactic acid bacteria, while _Dispora_ peptonised the
albuminoid matters.

Adametz[55] failed to isolate _Dispora_, and came to the conclusion
that ordinary lactic bacteria and yeasts played the most important part
in the fermentation.

Essaulow found in keffir grains six different organisms--yeast cells,
cocci, short thick bacilli, bent bacilli, long threads, and motile
bacteria. The two latter would seem to be _Bacillus subtilis_, while the
others may be regarded as _Bacterium acidi lactici_ (Hueppe), _Bacterium
aerogenes_, and _Streptococcus lacticus_ (Grotenfeldt). Pure cultures
were insufficient to produce keffir, while mixed cultures of _Bacterium
acidi lactici_ and yeasts were effective.

Freudenreich,[56] to whom we owe a record of very carefully executed
experiments, could not arrive at a satisfactory explanation of the role
of _Bacillus caucasicus_. This organism is described as being 5-6  mu long
and 1  mu thick, slightly motile, and possessing bright refractive spots
at the poles of the bacilli. It is extremely difficult to cultivate, and
forms flat, small greyish colonies of irregular outline. The bright
refractive spots above referred to are, however, granules taking the
usual stains quite readily, and not spores as supposed by Kern.

Freudenreich also found three other organisms--a yeast and two
streptococci. The yeast, to which he gave the name _Saccharomyces_
(Torula) _keffir_, forms small oval or roundish cells 2-3  mu wide and 3-5
 mu long. The optimum temperature would seem to be about 72 deg. F.; the
maximum 82 deg. F. This organism is unable to ferment milk directly, but is
able to decompose maltose and glucose with gas production. It does not
coagulate milk, but imparts to it a characteristic taste and is unable
to withstand desiccation for more than a few days.

Of the two streptococci isolated, _Streptococcus a_ resembles organisms
of the group _Streptococcus lacticus_ in appearance, but is able to
ferment milk, with weak acid and gas production, and is capable of
inducing coagulation.

  [Illustration: FIG. 11.--Section through a Kephir
  Grain--highly magnified.]

Contrary to what one would expect in an organism existing in keffir
grains, this streptococcus is as little able to withstand desiccation as
the above-mentioned yeast. _Streptococcus b_ forms smaller cells as well
as smaller colonies than _Streptococcus a_, but produces more lactic
acid and more gas, and retains its vitality after desiccation. The
relation of these four organisms is, according to E. von Freudenreich,
as follows: _Sacch. keffir_ is unable to ferment directly milk or
lactose, so that its growth must be preceded by that of _Streptococcus
b_. _Streptococcus a_ does not seem to play this part, but, unlike
_Streptococcus b_, is able to coagulate milk on its own account. By the
combined action of the yeast and the two streptococci, then, milk can be
coagulated, milk sugar inverted, acid and gas produced by the
streptococci, while gas and alcohol are formed by the activity of the
yeast. The role of _Bacillus caucasicus_ is unknown, but it would seem
to play a part in the formation of the keffir grain itself. By means of
mixed cultures of the above organisms Freudenreich was successful in
obtaining a fermented product possessing in all respects the
characteristic properties of normal keffir. On the other hand,
experiments to induce the formation of keffir grains gave negative
results, but in this respect the cultural characteristics of
_Lactobacillus keffir_ would seem to give promise of success in the
synthesis of the keffir grain. Fig. 11 is a photo-micrograph of an
extremely thin section through a keffir grain, after a preceding
treatment with saffranin. The matrix is composed entirely of long thin
bacilli (_Bacillus caucasicus_), while the peripheral portions, which
are more deeply stained, consist to a large extent of dense masses of
yeast cells with occasional streptococci. In a normal grain the latter
organisms are present on the surface or in the cavities and grooves of
the grain, and only to a less extent in the matrix. Nikolaiewa[57]
claimed to have isolated a hitherto unknown bacillus capable of
coagulating milk by acid production, _Bacterium caucasicum_, not
identical with, but related to Freudenreich's _Bacillus caucasicus_, and
also a torula. Although no experiments were carried out, Nikolaiewa
asserts that this organism forms the matrix of the grains. He was able
to produce a beverage resembling keffir, just as Freudenreich and
Essaulow did with entirely different organisms, but his product would
appear to have been slightly too acid and to have lacked the
characteristic aroma of the normal product. In the course of an
extensive series of experiments Kuntze[58] found the following
organisms:

  (_a_) True lactic acid forming bacteria, _Streptococcus
  acidi lactici_ (Grotenfeldt).

  (_b_) Bacteria of the group _Bacterium acidi lactici_
  (Hueppe) and _Bacterium lactis aerogenes_.

  (_c_) Various torula and yeast species.

  (_d_) Two species of butyric acid bacteria, _Bacillus
  esterificans_ and _Bacillus keffir_ (Kuntze).

His conclusions are: 1. In any case the presence of a yeast capable of
directly fermenting milk sugar is not essential. 2. The significance of
the presence of yeast lies in the fact that stimulation of the lactic
bacteria occurs; further, the yeast exerts a regulating influence upon
the rapidity of the fermentation proper. The variety is of minor
importance, provided always that the yeast does not produce an
unpleasant flavour. By the use of mixed cultures of _Bacillus
esterificans_, _Bacillus keffir_, and _Streptococcus acidi lactici_, and
a keffir yeast, Kuntze obtained a product that possessed to the fullest
degree all the characteristic properties of a normal keffir. In such
cultures he was successful in obtaining the formation of keffir-like
grains. Keffir fermentation is, according to Kuntze, the result of the
action of various organisms. During the initial stage butyric acid
fermentation takes place, but is prevented from becoming predominant by
the action of the keffir yeast. Simultaneously a true lactic acid
fermentation proceeds and eventually gives place to a subsequent
secondary production of butyric acid. Finally, then, we have a certain
amount of unison in the results obtained by Freudenreich, Essaulow,
Nikolaiewa, and Kuntze. These show that, for the production of a
characteristic keffir, specific organisms are not essential, provided
always that those used possess, either individually or collectively, the
essential capacity of acidifying, coagulating, and fermenting the milk.
For the growth of normal grains the presence of a matrix-forming
organism, such as _Bacillus keffir_, is indispensable.

  [Illustration: FIG. 12--_Streptococcus lacticus_
  (Grotenfeldt) growing on lactose-agar, stained by Gram's
  method. ( X 900 diams.)]

_Diseases of Keffir Grains._--According to the age and the previous
treatment to which keffir grains have been subjected, the vitality of
one or more of the organisms constituting the grain may have been
impaired. The results of Freudenreich have shown that _Saccharomyces
keffir_ and _Streptococcus a_ are unable to withstand desiccation for
more than a few days, and this is sufficient to account for the frequent
failures to obtain normal keffir from the grain. Further, grains succumb
to a mucilaginous disease; the cavities become filled with a slimy
fluid, and the grains are covered with mucilaginous matter. They lose
their elasticity and become brittle or mealy, but large grains appear to
be more subject to this fault than do the small ones. Such grains
should be disinfected by immersion for a short time in two per cent.
salicylic acid solution, followed by drying in the sun, whereby they are
completely regenerated.

Another disease consists in the predominance of certain butyric acid
bacteria which impart an unpleasant rancid taste to the keffir
(Podowyssozki). This is generally attributed to the use of rich milk, or
too high a temperature during preparation.

_Koumiss._--Another product of the combined action of lactic acid and
alcohol-producing organisms is called koumiss, kumys, milk-wine, lac
fermentation, or vinum lactis. In the steppes of Southern Russia and
Asia, as we have seen,[59] it is prepared chiefly from mares' milk, but
occasionally from that of camels and jennets. The name is said to be
derived from that of a tribe mentioned by Xenophon and Pliny, viz., the
Kumanen, by whom its preparation was practised. After the war with the
Tartars in 1215 its use was adopted by the latter people, and eventually
spread to the Turkomanen, Kalmucks, Khirgiz, Mongolians, etc.

Rubruck, in 1253, records the use of a fermented drink--kosmos--prepared
from mares' milk, and about the same time Marco Polo mentions the
occurrence of a milk-wine, chumis or chemius, among the Tartars. The
fact that the Tartars were seldom ill, and were almost invariably free
from lung troubles, led to an influx of visitors from surrounding
countries, until finally its use spread to Russia, Austria, and Germany.
At the present time the best koumiss is that produced in the province of
Orenburg; but specially equipped koumiss establishments, under the
control of physicians, exist in Odessa, Samara, Ufa in the Urals, and
other districts. The curative properties of koumiss have long been
recognised and its use is indicated in cases of indigestion, chlorosis,
scurvy, tuberculosis, etc.

Rubinsky states that, among the nomadic tribe, of Khirgiz and Kalmucks,
a special leathern bottle (Turssuk, Orroth, or Soaba) is used for the
preparation of koumiss, while wooden tubs (Tschiljak) similar in shape
to the old-fashioned churn are used by the Bashkirs, and in koumiss
establishments.

The fermentation is induced by the addition of koumiss to fresh mares'
milk, in proportions which vary according to the cleanliness observed in
the actual preparation. Where the process is carefully controlled, one
part of koumiss to ten parts of milk is often used, but where gross
infection from outside sources takes place one part of koumiss to three
parts of milk is taken. The mixture is stirred at frequent intervals,
and stored at a temperature of 73 deg.-90 deg. F. Weak koumiss is obtained
after twenty to twenty-four hours in winter and twelve to fourteen hours in
summer, but is scarcely ever consumed immediately, as it possesses a
strong purgative action.

It is generally poured into bottles (bottled koumiss); or allowed to
remain in the tubs (tschiljak koumiss); in the former case the
fermentation is anaerobic, in the second it is aerobic.

Storage of the koumiss upon ice or in a cellar is necessary since medium
koumiss is converted to strong koumiss in twelve to sixteen hours at
ordinary temperatures, while at the lower temperature this occurs only
in two to four days.[60]

According to Biel,[61] either old koumiss or the dried sediment from old
koumiss may be used for the initial inoculation. It may also be prepared
by the repeated inoculation of mares' milk with soured cows' milk until
a fermenting product is obtained. Koumiss may be prepared by a method
stated by Allik[62] to be in general use in the Caucasian
health-resorts. One part of beer-yeast is added to four to ten parts of
fresh mares' milk (according to the strength of product required), and
after thorough mixture of the two liquids the whole is allowed to
ferment at a temperature of 70 deg. to 72 deg. F. for two days. One part of
this first product is then added to five parts of fresh cold milk, and
allowed to stand three to four hours at 75 deg. to 77 deg. F. It is then
poured into bottles, and after the expiration of another three to four
hours is stored away in a cellar at about 45 deg. F. This koumiss may be
used at any time from one to five days (generally two to three) after
bottling according to the strength desired or prescribed in each
individual case.

The changes undergone during fermentation consist in a vigorous gas and
acid production accompanied by alcohol formation and coagulation of the
milk. The coagulum exists in an extremely fine state of division, and
the liquid froths violently on the bottle being opened. It has a full
pleasant acid taste, but should not contain more than one per cent. acid
and two per cent. alcohol. The specific gravity of koumiss is 1.008 to
1.020 at 60 deg. F. Appended is an analysis of two different samples of
koumiss:

  ---------------------------------------------------
                                 Prepared from
  ---------------------------------------------------
                          Mares' Milk.     Separated
                                          Cows' Milk.
  ---------------------------------------------------
                           Per Cent.       Per Cent.
  Water                     91.535          88.933
  Fat                        1.274           0.854
  Nitrogenous bodies         1.913           2.025
  Sugar                      1.253           3.108
  Ash                        0.293           0.444
  Carbon dioxide             0.876           1.027
  Alcohol                    1.850           2.647
  Lactic acid                1.006           0.796
  Glycerine                   ....           0.166
  ---------------------------------------------------

Fleischmann[63] gives a formula for preparing an artificial koumiss from
separated cows' milk, water, cane sugar, and milk sugar, with the
addition of distillery yeast. Needless to say, this product must possess
some of the characteristic by-flavour of the yeast employed, and is less
suitable than koumiss prepared by the aid of a lactic yeast. Schipin
investigated the fermentation of koumiss and found three distinct
organisms.

Rubinsky in a recent article threw much light on the phenomena of
koumiss fermentation. According to him, koumiss contains almost
invariably four different organisms, viz., koumiss yeast, koumiss
bacterium (_Lactobacillus_), _Streptococcus lactis_ (Lister), _Bacterium
aerogenes_, and occasionally _Bact. caucasicum_ (Nikolajewa). For the
preparation of normal koumiss only the two former organisms are
required; they exceed in number any of the other organisms whose
presence in the dairy is unavoidable. The presence of the two latter
organisms is favourable to the production of good koumiss, as, by
inducing a preliminary lactic fermentation, they tend to inhibit the
growth of undesirable extraneous bacteria, etc. In medium and strong
koumiss they die out on account of the amount of lactic acid formed
(1%).

Koumiss yeast possesses strongly differentiated protoplasm, but lacks
any cultural characteristics. Abundant growth occurs in milk, and lactic
acid (0.3%), alcohol, carbon dioxide, albumens and peptones, volatile
acids, and aromatic substances are formed.

Koumiss bacterium is related to the _Lactobacillus_ of various other
fermented milks, and is similar to _Bac. acidophilus_, and possesses
like these a distinct polymorphism (branched cells, long and short
bacilli, etc.). It is non-sporogenous, has an optimum temperature of 90
deg. to 97 deg. F., and possesses cultural characteristics similar to
those of the rest of the _Lactobacilli_.

The by-products of koumiss yeast appear to favour the growth of the
koumiss bacterium, as this organism, like the other _Lactobacilli_, is
favourably influenced by the presence of small quantities of peptone,
alcohol, and acid.

The organisms found by Schipin consisted of a species of _Saccharomyces_
and two bacilli, _Bacillus acidi lactici_ and a non-sporulating
bacillus. The latter organisms coagulate milk at 98 deg. F., but not at
room temperature, and although a minute description of cultural
characteristics is not given it would seem to be related to _Bacillus_
or _Lactobacillus caucasicus_.

_Leben Raib_ or _Leben_ (_Laban._)--This is a beverage prepared largely
by the Egyptians, and differs from keffir, as does matzoon, in
possessing a characteristic aroma and taste. It differs also from the
former by having only a very weak alcoholic fermentation, and by the
coagulum being coarse and lumpy instead of being extremely fine. It is
made from buffaloes', goats', or cows' milk by the addition of roba (or
old leben) to the previously boiled and cooled fresh milk. The use of
leben is many centuries old, and it is used in Egypt as in Arabia for
medicinal purposes, although that of the Syrians and Arabians is said to
differ from that of the Egyptians and Algerians. The fermentative
changes occurring in the formation of the Egyptian leben have been
investigated by Rist and Khoury,[64] and also by Guerbet,[65] who found
that five organisms were normally present. These comprised a
chain-forming bacillus (_Streptobacillus_), a second smaller bacillus
(_Bacillus lebenis_), a diplococcus, a saccharomyces, and a mycoderma.
Of these five organisms, it would appear that four live in metabiosis,
the streptobacilli and bacilli hydrolyse the milk sugar, the components
of which are split up by the yeast to alcohol and carbon-dioxide. The
alcohol thus formed, together with the glucose formed by hydrolysis, are
eventually converted to acid or combusted by the mycoderma species. The
leben thereby assumes the sharp, unpleasant flavour met with in old
samples. The diplococcus merely produces acidification and coagulation
of the milk. Rist and Khoury were able, by the use of these organisms,
to produce normal leben, especially when the true yeast was allowed to
grow in the milk for some time before inoculation with the other
organisms was made.

Some of the half-civilised tribes of Siberia, the Tartars and the
Burgaten, prepare a strong alcoholic beverage, araka or ojran, from
fermented milk. This is really a product of distillation, and contains
seven to eight per cent. of alcohol and volatile fatty acids.

  [Illustration: FIG. 13--Photo-micrograph of preparation
  from Armenian soured milk (Matzoon). This is related to
  Yoghourt, and contains, as will be seen from the above
  photo, yeasts, streptococci, diplococci, and a bacillus
  with the morphology of _Bacillus bulgaricus._ This, and
  similar foods, owe their peculiar properties primarily to
  the presence of _Bacillus bulgaricus_ (type A, White and
  Avery), and only in a lesser degree to the yeasts and
  lactic streptococci.]

_Matzoon._--This is a drink used largely in Western Asia, and is similar
in character to keffir, but has a peculiar taste which distinguishes it
from all other fermented milks. According to Weigmann,[66] it is
prepared from buffaloes', goats', or cows' milk, and is used partly as a
means of souring milk for butter-making and also as a lactic food, eaten
with spoons. In the same way buttermilk produced from milk which has
been previously ripened by matzoon is used as a beverage. Finally, the
coagulum (_than_) of such buttermilk is strained off, and, after being
pressed, is mixed with meal and dried by exposure to the sun's rays. The
preparation of matzoon is in many respects very similar to that of
keffir and koumiss, but differs by inducing a comparatively weak alcohol
fermentation. In common, too, with yoghourt, the prevailing temperature
is much higher than is required for keffir and koumiss.

In regard to the biology of matzoon, the occurrence of various organisms
has been recorded. Emmerling[67] isolated, in addition to a yellow
pigment-forming organism, _Bacillus subtilis_, _Bacillus lactis acidi_,
and several fungi, a small micrococcus capable of hydrolysing milk- and
cane-sugar. The organism produces and without gas formation, or
peptonisation of the medium. Of the nine yeasts isolated from matzoon by
Lindner[68] and Kalantharianz,[69] three were able to ferment milk sugar
without previous hydrolysis, while two others, by the simultaneous
production of lactic acid and fruit esters, gave to the matzoon its
characteristic taste and aroma.

_Yoghourt and Soured Milk._--Yoghourt is another fermented milk, and is
related to the matzoon of Armenia, the gioddu of Sardinia, and the leben
of Egypt. After a preceding boiling and reduction of the volume of the
milk, inoculation of the mass is made by the addition of a small
quantity of old culture, and it is then allowed to sour at a
comparatively high temperature. A moderately compact, jelly-like
coagulum is thus formed, while keffir and koumiss possess a liquid
consistency. The fermentation necessary for the two latter products only
proceeds, too, at a much lower temperature, at which yeasts play an
important part. According to Guerbet, yoghourt incubated for ten hours
at 113 deg. F. contained 0.34 per cent. lactic acid and 0.012 per cent.
alcohol. Luerssen and Kuehn[70] came to the conclusion that yoghourt
contained chiefly a mixture of _Bacillus bulgaricus_, diplostreptococci,
and a "granule" bacillus, so called on account of its granulated
appearance after treatment with methylene blue. According to these
authors, the first two organisms were found in each of eight samples of
maya (young yoghourt) and of yoghourt itself, but the occurrence of the
"granule" bacillus in plate cultures was by no means regular. In
addition, yeasts were found in almost every sample examined, but were
regarded more as accidental infections rather than as essential to the
formation of a typical product. The combined action of the three
organisms already mentioned gave rise to a product closely resembling
normal yoghourt. Piorkowski[71] subjected Bulgarian maya to examination
and associated himself with Metchnikoff[72] in finding three species, a
streptococcus, a diplococcus, and a specific organism to which he gave
the name _Yoghourt bacillus_. Similar results were also obtained by
Grigoroff.[73] Piorkowski's _Yoghourt bacillus_ is similar in form to
_Bacillus subtilis_, but does not sporulate, nor does it liquefy
gelatine. Young individuals are stained by Gram's method; older
individuals are, however, Gram negative. The optimum temperature is 112
deg. F. Kuntze attempted to isolate the organisms mentioned by Luerssen and
Kuehn, and by plate culture procured growth of a spore-forming bacillus
similar to Weigmann's _Bacillus matzoon_. To this organism is attributed
the power to impart a specific taste to the matzoon, but as growth is
comparatively slow, it can only be of significance in determining the
quality of the curd and cheese prepared from this product. Cultures were
also obtained which resembled in general character those of the organism
described by Luerssen and Kuehn as _Bacillus bulgaricus_ and named by
Kuntze _Bacterium W_. Granule formation was transient in this culture,
and the organisms eventually became inactive. Further analysis of maya
gave cultures of the "granule" bacillus, but these passed over from the
type forming irregular colonies (see Figs. 14, 15, 16) to that producing
smooth colonies. Further, although the granule formation persists
largely in milk, the organisms soon revert to the non-granular type if
cultivated on agar. By the use of the Gram-Weigert stain organisms from
a several-days-old culture on beer-wort-agar gave an interesting
reaction. The bacillar threads are in places Gram-negative, in others
Gram-positive, and bear small club-like swellings (see Fig. 14). Results
similar to these were also obtained with cultures of _Bacillus matzoon_
(Weigmann and Gruebner) and also with _Bacillus acidophilus_.

Neisser's method of staining failed to give such good effects by the
examination of fresh maya, as did an alcoholic aqueous solution of
methylene blue in showing up the granules of the organisms. Again,
Grixoni[74] found, but did not isolate, a similar granule-forming
organism (_Bacterium sardous_) in Sardinian gioddu. As already
mentioned in the description of leben, Rist and Khoury found a long
bacillar lactic ferment (_Streptobacillus lebenis_) which also exhibited
the irregular greyish white hairy colonies and high optimum temperature
characteristic of this group. On account of the similarity in form,
staining reactions, temperature requirements, and cultural growth of the
organisms described by Emmerling, Dueggeli, Weigmann, Grixoni, and Rist
and Khoury, Kuntze is inclined to regard them as belonging to one single
group of lactic ferments. According to him the granule formation is
rather variable, and may be induced or suppressed by cultural methods.
Not only do organisms of this group produce far more acid than the
normal lactic bacteria; they are also more resistant to acid, and are
able to develop in milk to which 0.5 per cent. hydrochloric acid has
been added. A comparatively high percentage of alcohol seems to
encourage growth, and this was obtained in milk containing 4 per cent.
alcohol. This would no doubt tend to explain the phenomenon observed by
Kuntze that milk is not so rapidly fermented by organisms of this group
as when cultures of diplococci and yeasts are added. Since organisms of
this group would seem to be widely distributed, the question of their
natural habitat arises. Luerssen and Kuehn were unsuccessful in their
search for such organisms in Koenigsberg milk, but Leichmann records the
occurrence of a long bacillus (_Bacillus lactis acidi_) in milk that had
spontaneously soured at 112 deg. to 120 deg. F. This organism, too, showed
characteristic growth on agar media, and produces laevo-rotatory lactic
acid. The examination of calves' stomachs showed, according to Kuntze,
only occasional long bacilli, but inoculation of sterile milk and
incubation at 100 deg. F. with repeated over-inoculation gave a culture
showing the characteristic granule reaction (see Figs. 18 and 20).
Although plate cultures made direct from calves' stomachs do not exhibit
the regular contours generally shown by the granule bacillus, yet this
growth may be induced by preceding cultivation in lactose bouillon to
which 0.5 per cent. acetic acid has been added. A similar organism,
_Bacillus acidophilus_, was isolated from calves' manure by means of
this acetic bouillon, as was also a diplostreptococcus which resembled
very closely the typical lactic acid streptococcus. This resemblance was
made all the more striking by the fact that they were capable of
coagulating milk at a temperature of 99 deg. to 104 deg. F. Since these
organisms are present in large numbers in manure and also in the
digestive tract of ruminants, it would seem probable that their
occurrence is not without significance for the operations of cheese
manufacture. According to Jensen, the practice of applying farmyard
manure to Swiss meadows has been regarded as absolutely essential to the
production of cheese of the best quality; while, on the other hand, the
application of artificial manures would seem to have been responsible
for an increase in abnormal cheese. Kuntze found further that by the
combined inoculation of sterile milk with the diplostreptococcus and the
"granule" bacillus from calves' stomachs, together with a yoghourt
yeast, he was able to obtain a product possessing a taste and aroma
little different from normal yoghourt. During their investigations upon
the ripening of Swiss hard cheese, Freudenreich and Jensen[75] isolated
five varieties of lactic acid bacilli, and were able to show that one of
these, especially _Bacillus casei [Greek: e]_, was of the greatest
importance for the production of good cheese. This organism has been
found by Thoeni to be present in rennet tablets, while a related
variety, _Bacillus casei [Greek: d]_, was found in fresh calves'
stomachs. Unfortunately, staining tests with these organisms were not
carried out, so that no data are available in regard to the presence of
granules. The photo-micrographs of these organisms show the small clubs
and true-branched forms. The presence of these diplococci and bacillar
lactic ferments in the intestinal tract of ruminants and horses might
possess some importance for the preparation of yoghourt in bags or tubes
made from the stomachs of these animals. Finally, Moro[76] has isolated
an acidophilic organism from the dejecta of infants which resembles
closely, both in manner of growth, resistance to acids, true branching,
and temperature optimum, the granule bacillus and related forms.

[This group of sixteen illustrations (Figs. 14 to 29), showing various
aspects of the Yoghourt bacillus and others of a cognate nature, is
taken from the _Centralblatt fuer Bakteriologie_ of Jena.--L. M. D.]

  [Illustration: FIG. 14.--Granule Bacillus from Yoghourt.
  Shredded preparation of a fresh skim-milk culture at 37 deg.
  C. for six hours. Stain: aqueous methylene blue. (Enlarged
  1:500.) In Figs. 15 and 17 will be noticed the chain
  arrangement of the bacillus, which, in spite of the
  supposed data of Luerssen and Kuhn, will be generally
  noticed in the granule bacillus.]

  [Illustration: FIG. 15.--Granule Bacillus from Yoghourt,
  cultivated after the usual Agar method, for twenty-four
  hours at 37 deg. C. Stain: aqueous methylene blue. (Enlarged
  1:500.)]

  [Illustration: FIG. 16.--Granule Bacillus from Yoghourt.
  Agar Milk Sugar Culture cultivated for forty-eight hours
  at 37 deg. C. Below is the true branching, above, the
  distorted involution form. This production of involution
  forms occurs chiefly in old cultures, and is an indication
  of degeneration. Stain: aqueous methylene blue. (Enlarged
  1:700.)]

  [Illustration: FIG. 17.--_Bacteria W._ from Milk,
  cultivated twenty-four hours at 37 deg. C. Methylene blue.
  (Enlarged 1:500.) The similarity in the pictures ought to
  serve as a proof of the near relation of the granule form
  and non-granule varieties.]

  [Illustration: FIG. 18.--Agar Milk Sugar Culture. From the
  original Bulgarian Yoghourt. In the centre, and beneath,
  the characteristic hairy irregular colonies of the granule
  bacillus (_Bacillus bulgaricus_ group), to the left, the
  smooth contoured yeast colonies. The colonies of the
  former organism always remain microscopic in size.
  (Incubated several days at 20 deg. to 25 deg. C. Magnified X 10.)]

  [Illustration: FIG. 19.--Agar Milk Sugar Culture. Surface
  colony of granule bacillus from calf's stomach. The great
  resemblance this colony bears to those formed by the
  granule bacillus from Yoghourt will be apparent. This
  fact, as well as close agreement in other cultured
  features, induced Kuntze to place these organisms in one
  group. (Incubated two days at 37 deg. C. Magnified X 100.)]

  [Illustration: FIG. 20.--Agar Milk Sugar Culture.
  Deep-lying colony of granule bacillus from calf's stomach.
  The form of the colony is often determined by the relative
  presence or absence of air. (Two days at 37 deg. C. Enlarged
  about 1:50.)]

  [Illustration: FIG. 21.--Agar Milk Sugar. Colony of
  _Bacterium W._ from Yoghourt (non-granular variety of the
  granule bacteria, as far as possible identical with
  Luersen and Kuehn's _Bacillus bulgaricus_), of a cubical
  branching-out form.

  According to Kuntze, the granule formation of this and
  related organisms is variable, while White and Avery
  regard it as a constant characteristic. (Incubated two
  days at 37 deg. C. Magnified x 50.)]

  [Illustration: FIG. 22.--Two colonies of _Bacillus
  acidophilus_ from calf's manure. Agar Milk Sugar Culture.
  With this organism, also, we have conformation to one type
  of colony, while, in other respects, temperature
  requirements and production, etc., we have close agreement
  with the granule bacillus (_Bacillus bulgaricus_). (Two
  days at 37 deg. C. Enlarged about 1:50.)]

  [Illustration: FIG. 23.--Beer-wort Gelatine.
  Fourteen-days-old colony of Yoghourt yeast. (Enlarged
  about 1:50.)]

  [Illustration: FIG. 24.--Shredded preparation of the
  Bulgarian original Yoghourt. Stain: aqueous methylene
  blue. Granule bacillus, diplostreptococci, and yeast. (See
  also other photo-micrographs of Yoghourt. Enlarged
  1:70.)]

  [Illustration: FIG. 25.--Granule Bacillus from Yoghourt.
  Cultivated in skim milk in twenty-four hours at 37 deg. C.
  Stain: aqueous methylene blue. (Enlarged 1:50.)

  By means of this staining treatment the presence of
  granules (not spores) can be easily detected. Treatment
  with fuchsine fails to bring out these formations.]

  [Illustration: FIG. 26.--_Bacteria W._, Agar Milk Sugar
  Culture. Cultivated twenty-four hours (knobs, clubs).
  Stain: Gram's method coloured with aqueous fuchsine
  afterwards. (Enlarged 1:600.)]

  [Illustration: FIG. 27.--_Bacteria acidophilus_ from
  calves' manure, isolated by means of bouillon as acid as
  vinegar. Shredded out of the usual Agar culture.
  Twenty-four hours at 37 deg. C. Stain: aqueous methylene blue.
  (Enlarged 1:700.)]

  [Illustration: FIG. 28.--Mucus from calf's stomach
  inoculated into milk after eight transferrings. Shredded
  preparation cultivated in milk for twenty-four hours at
  37 deg. C. Diplostreptococci and granule bacillus. Stain:
  aqueous methylene blue. (Enlarged 1:500.)]

  [Illustration: FIG. 29.--Diplostreptococcus from Yoghourt.
  Pure culture in skim milk. A comparison of the
  illustrations will show how close a resemblance exists
  between bacteria found in the mucous membrane of calf's
  stomach and those occurring in Yoghourt. In fact, by the
  combined action of granule bacilli, and of
  diplostreptococci from calf's stomach, together with a
  Yoghourt yeast, it is possible to prepare normal
  Yoghourt.]

In a review of the literature of the subject of soured milks, Makrinoff
suggests the adoption of the two names, _Streptobac. lebenis viscosus_
and _Streptobac. lebenis non-viscosus_, for the organisms of the
so-called Bulgaricus group, and known at present as
_Bacillus-bulgaricus_, _Streptobac. lebenis_, _Bacillus of Massol_,
_Granule bacillus_, _Bact. Mazun_, _Bac. lactis acidi_, etc.[77]

White and Avery[78] have made a comparative study of a large number of
varieties and species of lactic acid bacteria of the above type obtained
from various fermented milks and milk tabloids. Their descriptions are
so detailed and their conclusions are so important that we give them at
length. According to this work, the whole of the thermophilic lactic
acid bacilli of the so-called Bulgaricus type may be divided into two
sub-types, A and B.


_The Cultural Characteristics of the Bacillus Bulgaricus Group_

The cultural characteristics of all the strains of _Bacillus bulgaricus_
(granule bacillus) are as follows:

_In Whey Agar._--All strains exhibit wide variation in size, 2  mu to 50  mu
long and about 1  mu broad.

Almost all individuals are intensely Gram-positive, and show regularity
of outline. All strains show involution form, exhibiting vacuoles, and
often show empty cell membranes. The latter are Gram-negative, and vary
greatly in both dimensions as well as in form. All strains show tendency
to chain formation, some being arranged in chains of six to twenty-five
segments, which may contain both Gram-positive and Gram-negative
individuals. Type B exhibits Gram-negative spherical bodies varying from
0.25  mu to 1  mu in size, adhering to the sides of some of the
Gram-negative individuals.

_In Whey._--In this medium there is a marked tendency toward
degeneration and involution. In the early stages of incubation, at 100 deg.
to 112 deg. F., the bacilli are uniform in size and intensely Gram-positive;
in succeeding stages the irregular, vacuolated, inflated, and ruptured
forms predominate. Between the eighteenth and twenty-fourth hours of
incubation at 112 deg. F. the strains of type A develop oval to
kidney-shaped nodules attached to a stem extending from the cell
substance. As the incubation is prolonged these nodules increase in
size, often measuring 1  mu to 2  mu in length; this nodule formation occurs
at the expense of the cell protoplasm, and appears to be a marked
characteristic of growth in whey. Cultures of type B do not form nodules
or clubs, but small spherical bodies more or less securely attached to
the cell wall are seen. Again, type A assumes the form of small bacilli
in chains, while type B strains develop to a greater length and exist
almost exclusively as single isolated forms. True branching has been
observed in strains of type B.

_In Milk._--In milk there is a tendency to thread-formation consisting
of four to ten segments in the case of type A, while type B shows longer
and more curved forms. With increasing age of the culture there also
appears to be increase in the length of the organisms. All strains are
non-motile, non-sporogenous, and non-capsule-forming.

_Staining Reactions._--All strains are readily stained by the usual
aniline dyes.

_A. Gram's Method._--Young individuals give an intense reaction with
this stain; old bacilli are easily decolourised, and degenerate forms
are always Gram-negative, while single individuals have been observed
which showed gradation from one pole of the cell to the other.

_B. Loeffler's Methylene Blue._--According to the behaviour of the
organisms studied, a separation into two types appears possible, type A
being uniformly impregnated, while type B shows distinct
differentiation. The cell body is seen to contain a varying number of
round to oval bodies or granules. This is the appearance already
mentioned by Dueggeli, Luerssen and Kuehn, and Kuntze, and from which the
granule bacillus derives its name. In opposition to the observations of
Kuntze, the occurrence of granules was not found to be variable; it was,
indeed, so constant as to constitute a distinguishing characteristic
between the two types. The organisms of this group are difficult to
cultivate, and freshly isolated growth is obtainable only on media
containing whey, malt, or in milk. They grow equally well under aerobic
or anaerobic conditions. The optimum temperature for growth is 113 deg. to
115 deg. F.; growth is fair at 85 deg. F., slight at 75 deg. F., and does
not take place at 68 deg. F.

Colonies on whey agar are round to irregular, greyish white, curled and
filamentous, often streaming, and in a few cases smooth and even in
structure. Gelatine is not liquefied. There is no surface growth on
gelatine stab-cultures. Along the stab the growth is filiform, beaded,
with subsequent horizontally projecting ramifications. Milk is
coagulated in eight to eighteen hours at 112 deg. F., and is the most
favourable medium for growth.

[I am indebted for this group of illustrations (seventeen in number) to
the editor of _Bacteriotherapy,_ New York, U.S.A.--L.M.D.]

  [Illustration: FIG. 30--Photo micrograph of preparation
  made from Yoghourt, showing yeast cells, large lactic
  diplococci, small slender bacilli and many large bacilli
  possessing the morphology of _Bacillus bulgaricus_. Yeast
  cells are almost invariably found in native Yoghourt, but
  do not appear to be essential to the production of a
  tropical beverage. Indeed, they would seem to be
  responsible for the unpleasant astringent taste often met
  with in old samples of this product.]

  [Illustration: FIG. 31--Photo micrograph of smear from
  Greek Curdled Milk called "Giaourti," and showing yeast
  cells, long bacilli and a mould (_Oidium lactis_),
  possessing very large elongate cells. The presence of the
  latter is very undesirable, as it rapidly combusts the
  lactic acid, digests the casein, and imparts a strong
  unpleasant cheesy flavour to the beverage.]

Type A produces 2.7 per cent. to 3.7 per cent. inactive lactic acid in
milk, while type B produces only 1.2 per cent. to 1.6 per cent.
laevo-rotatory lactic acid in milk. There is a small quantity of acetic,
formic, and succinic acids formed. The conclusions of White and Avery
are:

I. A review of the morphological culture and biochemical features of the
lactic acid producing bacilli from yoghourt, matzoon, and leben, appears
to justify their classification as a single group.

II. This group would seem to be identical with _Bacterium caucasicum_
(Kern).

III. The significant variations exhibited by these bacilli in regard to
the presence or absence of granules demonstrable by differential stains,
the degree of lactic acid production, and the nature of the acid
produced, suggest a division into two different types--the true type A,
and the paratype B.

Quite recently Hastings and Hammer[79] recorded the isolation from milk
of an organism producing more acid than either _Bacterium coli commune_
or _Bacillus lactis acidi_. It is characterised by possessing a high
optimum temperature, and by the limited conditions under which it grows
on nutrient media. On this account these investigators suppose it to be
related to those described in the paragraphs on fermented milks, leben,
matzoon, etc., and which are regarded by Kuntze as being identical.

Similarly Boutroux[80] found 1.5 per cent. acidity produced in a
solution containing albuminous matter and glucose; while Richet[81]
states that with the addition of gastric juice to milk as much as four
per cent. acidity may be formed. After storing samples of milk for eight
days at 100 deg. F., Koning[82] found 2.35 per cent. and 2.5 acid; while
similar samples stored at 60 deg. to 62 deg. F. for the same period only
developed 0.9 per cent. Heinemann[83] records the production of 3.0 per
cent. acid in milk incubated at 100 deg. F.; and Jensen states that
_Bacillus casei [Greek: e]_ is capable of developing 2.7 per cent.
lactic acid.

Dr. H. B. Hutchinson, bacteriologist at Rothamsted Experimental Station,
has also been successful in isolating a bacillus from English market
milk resembling in every particular those classified by White and Avery
as type A.

  [Illustration: FIG. 32 is a photo-micrograph of soured
  milk inoculated with a tablet containing viable and pure
  cultures of _Bacillus bulgaricus_, and incubated for
  seventy-two hours. These tablets constitute a valuable
  means of preparing soured milk for therapeutic purposes.]

  [Illustration: FIG. 33 is a photo-micrograph of milk
  inoculated with a ferment tablet in which _Bacillus
  bulgaricus_ is no longer viable, and the only growth
  obtained is that of an organism allied to the _Bacillus
  subtilis_ (Hay bacillus) group. Such milk would be
  absolutely without value.]

It will thus be seen that organisms related to those of Oriental and
Occidental milk beverages are present in conditions where it is
impossible for them to attain to any active growth. The same class of
organism has also been found in many cases in butter and cheese
throughout the United States.

Of recent years the consumption of milk fermented by these organisms has
been introduced more or less successfully into all European countries.
This custom is due, as we have seen,[84] to a very great extent to the
announcement of Metchnikoff[85] that the action of such organisms in the
alimentary tract conduce to a prolongation of life. Moro found that the
dejecta of children contain large numbers of _Bac. lacidophilus_ and
_Bac. bifidus_, but, as age advances, the bacterial flora of the
intestines tends to change. The number of acid-producing organisms
gradually becomes less, and other bacteria capable of producing
far-reaching decomposition of albuminoid matter tend to increase.

Working on the assumption that senility is partially due to the
absorption of by-products formed from albuminoid food by the
decomposing or putrefactive bacteria mentioned, Metchnikoff instituted a
search for organisms capable of suppressing the growth of the
putrefactive bacteria.

It has long been known that milk allowed to become sour will keep for a
considerably longer period in hot weather than if lactic bacteria had
not grown. This preservative action of lactic acid also comes into play
in the manufacture of sauerkraut and in the preservation of meat by
immersion in sour milk.

  [Illustration: FIG. 34.--Photo-micrograph of smear of
  culture of _Bacillus bulgaricus_, recommended by
  Metchnikoff for use in cases of intestinal
  auto-intoxication. Unlike the ferments of normally soured
  milk, which are sometimes indifferent, or even injurious,
  in their action, this bacillus is capable of growth at
  blood heat, and, by producing much larger quantities of
  lactic acid than such organisms as _Streptococcus
  lacticus_, _Bacillus coli commune_, or _Bacteria lacticus
  aerogenes_, inhibits the multiplication of bacteria
  responsible for the putrefaction of albuminoid food in the
  intestines.]

Bienstock has shown that the growth of _Bac. putrificus_ is inhibited by
the action of _Bact. coli commune_, which is capable of setting up a
slight lactic acid fermentation. _Bact. coli commune_, however, gives
rise to substances of an injurious character, and, although present very
abundantly in the intestinal tract, it may by reduced almost entirely by
the active growth of lactic acid bacteria. This fact is of great value
to the cheese-maker, since by the addition of a lactic acid culture
(starter) to milk before renneting, gas-producing bacteria such as
_Bact. coli_ may be checked in growth. Since the ordinary lactic acid
bacteria such as _Streptococcus lacticus_, _Bac. lactis acidi_, and
others, are incapable of growth at blood temperature, it appeared
necessary to procure cultures of lactic bacteria able to grow at
temperatures of 100 deg. F. to 112 deg. F. Such an organism was found in
Bulgarian soured milk (yoghourt), and was considered pre-eminently
adapted to this purpose. As has been shown in the preceding paragraphs,
this organism is merely one of a large group of bacteria found
distributed in the intestinal canal of many domestic animals, in manure,
and in ordinary market milk. It is then not surprising that the
introduction into the intestinal tract of bacteria of the type
_Bulgaricus_ in the form of tabloids has not met with any decided
success. Although it was considered to be merely necessary to introduce
the desired type of organism into the body, and the amount of lactic
acid taken into the system by the administration of soured milks was
looked upon as of secondary importance, yet, it would seem, in the light
of recent investigations, that benefits derived from a soured milk
regimen are attributable in part to a chemical as well as a purely
bacterial action. This receives support from the fact that soured milk
beverages prepared by the use of ordinary lactic bacteria, distinct from
those of the _Bulgaricus_ type, often exert a beneficial influence upon
human beings even although the organisms responsible for the
fermentation are incapable of growth at blood temperature.

It may be mentioned in conclusion that cultures prepared by the use of
organisms of the type _Streptococcus lacticus_ combined with _Bac.
bulgaricus_ possess a more agreeable flavour and aroma than those
prepared from a pure culture of _Bulgaricus_ alone.

  [Illustration: FIG. 35--_Bacillus bulgaricus_, showing the
  cultures in English cow's milk. (Magnified 450 diams.)]

  [Illustration: FIG. 36--Photo-micrograph of pure culture
  of _Bacillus bulgaricus_. The administration of cultures
  of this organism is indicated in all cases of intestinal
  ailments, caused by the excessive growth of proteolytic
  bacteria, and consequent putrefaction of foods in the
  alimentary tract. By the formation of large quantities of
  lactic acid, a state of asepsis is ensured, which is
  particularly valuable in cases of operations on the
  abdomen and intestines.]

  [Illustration: FIG. 37.--Photo-micrograph of smear of
  combined culture of _Bacillus bulgaricus_ and _Bacteria
  paralacticus_. This double culture possesses an advantage
  over single cultures in that, while the characteristic
  disinfecting action of the former is retained, any
  secondary action of the growth of this organism upon the
  milk-fat is checked by the growth of _Bacillus
  paralacticus_, thus ensuring the production of a more
  palatable product.]




CHAPTER VI

THE PREPARATION OF SOURED MILK IN THE HOUSE


There is no great difficulty in making soured milk at home: the
necessary operations are quite simple, but at the same time they must be
conducted with precision and care, otherwise the results may be
unsatisfactory and disagreeable; there may even sometimes be danger in
badly prepared sour milk. It is always an advantage in such matters to
understand the reason of things, and a few notes on the surrounding
conditions, and what has to be accomplished, may be of assistance to the
would-be experimenter.

The majority of intelligent people are now acquainted with the fact that
the germs of bacteria are to be found everywhere on the surface of the
earth, in air, and in water, and that they are the sole cause of the
decay of all manner of perishable articles.

The distribution is unequal--bacteria are much more plentiful where
there is decaying matter--in dirty houses, sewage, or other contaminated
water, etc. Milk is a splendid food for bacteria, and numerous varieties
multiply in it exceedingly, and many of these are injurious, producing
putrefactive changes which render the milk unwholesome, even poisonous
in some cases. Others are beneficial, and are absolutely necessary for
the souring of milk for making butter or cheese and for the ripening of
the latter. The soured milk which is the subject of this book is the
work of certain lactic-acid-producing bacteria, and the problem we have
before us is to encourage the growth of the latter to the uttermost and
to exclude the others.

As bacterial germs are present in the air and readily sow themselves
into any medium with which they come in contact, the first consideration
is to get good fresh milk which has been as little exposed to the air as
possible. The second is to conduct the experiment where the germs are
fewest, and in cleanly surroundings, far removed from decaying matter
and free from taints and smells.

  [Illustration: FIG. 38.--Photo-micrograph of smear of
  one-month culture of _Bacillus bulgaricus_. In spite of
  its age, the culture is perfectly free from any foreign
  organisms, which would otherwise lower its value for the
  preparation of soured milk, and might, indeed, make it
  directly injurious.]

  [Illustration: FIG. 39.--Photo-micrograph of culture of
  _Bacillus bulgaricus_ in malt. In cases of acute
  enteritis, where milk cannot be supported, the lactic
  bacilli may be cultivated in malt, and administered to the
  patient in this form, with occasional doses of syrup of
  malt, in order to induce a vigorous growth of the lactic
  ferments in the body.]

  [Illustration: FIG. 40.--Photo-micrograph of smear from
  milk that had been allowed to sour spontaneously. Ordinary
  market milk is always subject to infection from the air,
  milking vessels, manure, etc., and from these sources a
  mixed bacterial flora arises, with the result that the
  milk exhibits curdling, acidity, gaseous fermentation, or
  mould growth, after being stored for a short time. This is
  due to the action of sush bacilli, diplococci, yeasts, and
  moulds as are shown in this illustration.]

However fresh the milk may be, it will contain useless or injurious
bacteria, and we must get rid of these before attempting to introduce
those whose growth we wish to encourage. This is effected by heat. All
the living bacteria and most of the germs are killed at temperatures
somewhat under the boiling point. Having sterilised the milk in this
way, it is necessary, as far as possible, to prevent the entrance of
fresh germs from the atmosphere, and we therefore let the milk cool down
in covered dishes. When the temperature descends to about 100 deg. F. the
culture of the special bacteria is introduced, the covers are replaced,
and the milk vessels maintained at or near this temperature for twelve
hours, when the soured milk is ready for use. It is not necessary to use
fresh culture every time--a little of the soured milk will take its
place, and this may be repeated as many as fourteen times before it is
necessary to start off again with a fresh culture. A great deal depends
on the care exercised and the freedom of the surroundings from bacterial
germs. Under the best conditions wild germs will gradually accumulate in
the soured milk, but their increase may be greatly delayed by attention
to the precautions mentioned. The ordinary souring of milk for butter
and cheese making is conducted in cool surroundings, as already stated,
because in such conditions the lactic-acid-producing germs increase
relatively faster than the wild germs, and so gain the upper hand, but
in the case of our special soured milk we kill out, practically, all
wild bacteria and germs, and the pure culture having the field to
itself, we can conduct the operation at a higher temperature where the
action of the bacteria is at its maximum, and so obtain the necessary
lactification in the minimum of time.

The appliances for the souring of milk on the domestic scale require
some consideration. We propose to describe the principal forms of
apparatus which have been put on the market for the purpose, and then to
give such suggestions as may assist the ingenious in making apparatus
for themselves. Those who wish for information on the subject of larger
apparatus will find it in the following chapter.

  [Illustration: FIG. 41--Photograph of Agar Culture,
  inoculated with a lactic powder offered to consumers under
  a fancy name. Working on the assumption that the presence
  of lactic bacteria is inimical to the growth of septic
  organisms, this preparation has been placed on the market.

  The plate shows, however an abundance of colonies of
  foreign organisms--sporogenous bacilli, _Staphylococcus
  pyogenes albus_, and _Staphylococcus pyogenes aureus_.
  These organisms are shown in the appended
  photo-micrographs, and constitute impurities in the
  preparation.]

  [Illustration: Spore forming bacillus]

  [Illustration: _Staphylococcus pyogenes albus_]

  [Illustration: FIG. 42--Photograph of Test Tubes of Sterile
  Milk, inoculated with a tablet preparation said to contain
  pure cultures. The darker liquefied portion of the
  tube-contents is due to digestion of the curd by
  proteolytic bacteria, thus indicating impure culture. Pure
  cultures of lactic acid bacteria coagulate the milk
  uniformly, but do not produce any subsequent change in the
  appearance of the culture, even after several months.]

  [Illustration: FIG. 43--Photograph of Test Tubes of
  Sterile Milk, each tube having been inoculated with a
  tablet of a preparation said to contain pure cultures.
  Here, again, there is evident peptonisation of the curd,
  thus indicating infection by proteolytic ferments.
  Cultures from these tubes demonstrated the presence of a
  foreign organism. Microscopical examination failed to
  disclose the presence of _Bacillus Bulgaricus_.]

  [Illustration: FIG. 44--Photograph of Test Tubes of
  Sterile Milk, inoculated with a tablet of
  "Lactobacilline." In contra-distinction to those shown in
  Figs. 42 and 43, these tubes exhibit homogeneous curdling
  of the milk without any subsequent digestion or
  peptonisation of the coagulum. This is indicative of the
  purity of the culture.]

The Society "Le Ferment" of Paris, which has been authorised by
Professor Metchnikoff to prepare and supply to the public his sour milk
culture, provides an apparatus for the treatment of the milk. It is
shown in Fig. 45, which consists of a double box having the intervening
space packed with a non-conducting material. It is provided with a
tight lid. Inside, there is accommodation for two milk vessels, each
with a capacity of about two thirds of a pint. The most difficult thing
in the souring of milk is to maintain the temperature as nearly at 100 deg.
F. as possible while the culture is in action. This result is attained
by filling the vessel in the middle with boiling water. The insulated
walls hinder the escape of heat, and the quantity of boiling water used
is calculated to maintain the temperature steady for the twelve hours of
cultivation; but in cold, frosty weather it is necessary to refill the
central vessel with boiling water in the middle of the period.

  [Illustration: FIG. 45]

The milk jars are washed with hot boiled water and turned upside down to
dry. They should not be wiped with a cloth. Boil the milk to be treated
for ten minutes, stirring it to promote evaporation, as it is
advantageous to have it in concentrated form. Cool rapidly to 100 deg. F.
by placing the boiling vessel in cold water, add to each bowl one third of
a tube of the culture in powder form, fill up with the boiled and cooled
milk, stir well and cover. Place the jars in the box and fill the
central vessel with boiling water, shut the lid tight, and do not open
it (unless a fresh charge of boiling water is needed) for ten or twelve
hours, when it will be ready for use. If the liquid culture is used (one
small phial for each bowl) the milk should be cooled to 86 deg. F. instead
of 100 deg. F., as with the powder. The culture is also supplied in tabloid
form. The powder and tabloids keep well, but the liquid can only be
relied on for about two months. The milk prepared as above should be
stored in a cool place, the lids being kept on the bowls. It is good for
about two days, after which it becomes too sour. It can be eaten with
sugar, which not only sweetens it but is beneficial in affording
additional suitable food for the acid-producing bacilli. If fresh milk
cannot be had, condensed, sterilised, or pasteurised milk may be used,
but, of course, fresh milk is best. Condensed milk should be diluted
with two parts of boiling water and then treated like ordinary milk.

An apparatus on similar principles is sold by the Maya Bulgare Company,
Ltd., and is illustrated in Fig. 46.

  [Illustration: FIG. 46--Soured Milk Apparatus of the Maya
  Bulgare Company, Limited, consisting of an insulated box,
  hot-water vessel, and covered vessels containing the milk
  and culture. The apparatus consists of cabinet in deal,
  Maya Bulgare ferment in 20-dose bottles, Maya Bulgare
  ferment in 100-dose bottles, compressed Maya Bulgare
  tablets in boxes of 8 tubes, Maya Bulgare caramels in
  boxes of 40, reduced milk, china funnels, and
  thermometers.]

The box is insulated, but the door is on the side, the hot water vessel
is underneath, and the covered vessels containing the milk and culture
are placed on a shelf above. In the front of the illustration are shown
the various packages in which the liquid and powder cultures are put up.
The procedure is exactly the same as with "Le Ferment" apparatus.

Lactic Ferments, Limited, make use of a different principle to maintain
the temperature steady during the lactifying period. Their apparatus
(Fig. 47) consists of a water vessel mounted on a stand. The milk
vessels (tumblers) are placed in the water, and the temperature
maintained at the proper figure by a small night light burning
underneath. It is recommended that the milk should be placed in an
earthenware jar or jug, which is stood in a pot of water kept boiling
for an hour. After cooling add from three to six previously crushed
tabloids of culture, and stir well with a glass rod which has been
sterilised in boiling water. The milk is then transferred to three
tumblers, which it should fill, and these are put into the water vessel,
the water in which should be at about 100 deg. F., and the night light
started.

  [Illustration: FIG. 47]

Messrs. Allen & Hanbury, Limited, also make use of the night light to
maintain the proper temperature during incubation in their "Sauerin"
apparatus (Fig. 48).

No water, however, is placed in the metal container. The procedure is
the same as that already described, and both tablet and liquid pure
cultures are supplied. For children it is recommended that the
incubation should occupy from three to four hours only, in other cases
eight to ten hours. Grated nutmeg, ground cinnamon, or other flavouring,
and cream may be used with the soured milk.

The night light is also employed in the "Veronelle" apparatus of Messrs.
Clay, Paget and Company, Limited (Fig. 49).

  [Illustration: FIG. 48.--Messrs. Allen & Hanbury's Soured
  Milk Apparatus. They maintain the temperature by means of
  a night light, and the culture they use they call
  "Sauerin."]

  [Illustration: FIG. 49.--Vironelle Apparatus for souring
  milk, made by Messrs. Clay, Paget & Company, Limited. The
  milk in this case is placed in an earthenware jar, and is
  sterilised by placing in a saucepan of water and boiling
  it. The culture is added after cooling, the period of
  incubation being about six hours.]

The containing vessel is of tin or aluminium, and has two stands, the
high one for hot and the low one for cold weather, as in the latter
case greater heat is needed to maintain the incubating temperature. The
milk is placed in an earthenware jar and is sterilised by placing it in
a saucepan of water and boiling it; continuing the boiling for half an
hour. It is allowed to cool to about 98 deg. F., and placed in the
incubator, culture added, and the lamp lighted, the cover of the
incubator being kept on. The period of incubation is given as six hours.
To prepare the next day's supply a tablespoonful of the soured milk is
retained and used instead of the culture. This may be continued for
fourteen days, when a fresh start with culture is necessary. The soured
milk will keep for thirty-six hours. Capacity, one and one half and two
pints; also a large size for family use.

For the preparation of soured milk on a small scale, one of the various
forms of vacuum flasks now on the market may be used with satisfactory
results. A little cold water must be poured into the flasks, and warm
water added, until, by means of three to four changes, boiling water can
be safely poured in without cracking the flask.

This boiling water must be allowed to remain in for about twenty
minutes, and then replaced by freshly boiled milk that has been cooled,
so that its temperature in the flask is about 105 deg. F. The culture of
lactic organisms should then be added, the opening of the flask plugged
with clean cotton-wool, and the cap screwed on.

In an actual test, the temperature of the milk placed in such a flask
was 105 deg. F., at 7.30 P.M., and had dropped to 93 deg. F. by 9 A.M., the
following day. The milk was curdled, and possessed the normal acid taste
of such cultures.

The different types of apparatus are all quite simple, and it would be
easy to make something at home. Get two round tins, the one less in
diameter by from two to three inches than the other, put one or two
pieces of wood across the bottom inside the larger tin, and fill up the
space between with cotton-wool, which is an excellent non-conductor of
heat. Place the smaller tin centrally inside the larger one. Fix three
or four distance pieces of wood in the space between them, fill up with
cotton-wool, leaving a little space at the top to permit the lid of the
smaller tin to be fixed on. The boiling-water vessel may be a tin
saucepan with a lid, but no handle, and its proper place would be on the
bottom of the inner tin. A tripod stand made of three pieces of wire
bound together, and with legs reaching past the hot-water vessel to the
bottom of the tin, would support a false bottom of tin forming the shelf
on which the vessels of milk to be treated would rest. These might be
tumblers covered with tin lids. To prevent radiation through the lid of
the inner tin, a thick pad or hood of cotton-wool packed between cloth
would be placed over the top. A little experimenting would be necessary
to determine the quantity of boiling water required to maintain the
proper temperature.

The soured milk obtained in the above manner is of the consistency of
ordinary buttermilk; a separation of whey frequently takes place, and
this may be poured off if desired. The taste and flavour should be
pleasantly acid and agreeable, and both are distinctive enough to give a
good idea of the purity of the product. In many places a more
concentrated article is made by boiling down the milk to one half or one
third of its bulk, and then fermenting it in the ordinary way. A kind of
thick pudding is thus obtained, which is highly recommended both as an
agreeable article of food and as a stronger medium for the support of
the germs it is the purpose of the sour milk treatment to introduce
into the digestive system.

The cultures for making soured milk can now be had from all the leading
wholesale and retail chemists, with directions as to the quantities to
be used.

It is very necessary that the milk used should be not only fresh and
good, but also free from chemical preservatives. The effect of these is
to inhibit the growth and development of bacteria, and they have
therefore an injurious influence on the special lactifying germs it is
our object to cultivate. Preservatives are now not nearly so much used
as they were, a few years ago, and there should be no difficulty in
obtaining milk free from them.

For keeping both fresh and soured milk good a small ice-chest is an
excellent device. The germs which are continually dropping into milk
kept in open vessels in the air, even in cleanly surroundings, are
mostly kept out in the close ice-chest, and the low temperature prevents
in a natural way the development of the bacterial germs already in the
milk. For the preservation of all kinds of foods the ice-chest is a
capital investment, not to mention the benefit of having cooled drinks,
etc., as required. They manage things well in this respect in the United
States, where ice is regarded as a necessity in the summer time by even
the poorest people, and is delivered with the same regularity as the
milk.

It is necessary to utter a word of warning as to certain forms in which
the sour milk bacillus is being offered to the public. It is being
compounded with sugar, chocolate, and other articles, and sold in the
form of sweets, etc. There is no reliable proof that these preparations
are valuable. Certainly, sugar is a medium in which the lactifying germs
can live, but the quantity so introduced into the system must be very
small compared with what is obtained from properly fermented milk. It
takes some time, even with strong cultures, to fix the acid-producing
germs in the large bowel where they are wanted, and until proper
evidence is forthcoming that confectionery preparations are efficacious
we would recommend that only the regularly fermented milk be used. It
would save trouble, no doubt, to treat oneself with a few chocolate
creams containing the necessary germs daily, but if the matter is taken
up seriously it will be better to take some pains and stick to methods
the efficacy of which has been demonstrated, leaving the others until
their _bona fides_ has been proved. There are always enterprising firms
who are prepared to simplify things for us, but we must make sure that
their simplifications are warranted.




CHAPTER VII

THE PREPARATION OF SOURED MILK IN THE DAIRY


There is a tendency in certain medical quarters to discourage the use of
soured milk "made for profit." This view leaves out of account the fact
that besides being of value in medicine, the article in question is also
an excellent food, which, as we have seen, has been consumed by
multitudes of people for ages in many parts of the world. There seems
also to be satisfactory evidence that a larger percentage than usual of
the people who make soured milk a staple of diet attain to a ripe old
age. How does it become such a dangerous thing the moment the doctors
get it into their hands? Of course if a man has an acute disease he
places himself entirely in the hands of his medical man, and eats what
is prescribed for him, or at least he ought to do so, and if he makes
such a submission he is entitled at least to the comfort of being able
to feel that his doctor is free from unreasonable prejudices. For the
implication that an article "made for profit" is naturally suspect casts
an unwarranted stigma on a large number of honourable people. There are
dishonest tradesmen just as there are dishonest and careless doctors,
but to saddle a whole class with the offences of a few would not be a
justifiable proceeding in either case. Besides, it is not to the
interest of the manufacturing chemist or the dairyman to turn out
spurious cultures or bad soured milk, and on the whole we see no reason
why they should not engage in the business.

The widespread use of soured milk in other countries as a regular
article of diet seems to indicate that all manner of people, except
those suffering from diseases which necessitate medical regulation of
diet, might with probable benefit to themselves add this article to
their food list; and it looks as if a good many of them intend doing so,
even if scandalised doctors threaten "to abandon the cure."

The dairyman who knows his business does not need to be told of the care
which is necessary to keep milk in good condition. The merely commercial
consideration of avoiding loss has made him ready to inquire into the
best means of prolonging the life of milk as a merchantable article.
For a time he relied on chemical preservatives, but their day is now
almost over, and filtration, pasteurisation, and cold storage have taken
their place. Any one conversant with the trade knows how widely these
methods have been adopted of late years; we may, therefore, assume that
the average dairyman has at his command milk suitable for the incubation
process.

The demand for soured milk is not as yet a very large one, and the
apparatus so far developed for its production is meant for the treatment
of small quantities. After describing the principal appliances at
present in the market we propose to make some suggestions as to the
construction of larger apparatus.

A firm which has given great attention to the question of maintaining
fixed temperatures is that of Messrs. Charles Hearson & Co., Ltd. Their
incubators for chicken hatching are known all over the world; and their
appliances for biological incubation are very generally used in
bacteriological laboratories. With such experience it was natural that
they should turn their attention to soured milk apparatus, and the
result is the "Lactobator" (Figs. 50 and 51).

  [Illustration: FIG. 50.--"Lactobator" made by Messrs.
  Charles Hearson & Co., Limited, which is used for the
  incubation of pure culture in milk in a fairly large way.
  The illustration shows the "Lactobator" closed.]

  [Illustration: FIG. 51.--Messrs. Hearson & Company's
  "Lactobator," showing the internal arrangements.]

A copper vessel made to contain water has placed in it a stoneware jar
which holds two gallons of milk; on the top is a lid which carries a
thermometer for indicating the temperature of the milk. Heat is supplied
by a gas ring under the copper vessel; and in the gas supply is the
patent thermostat made use of by Messrs. Hearson also in their
biological and poultry incubators, in which a capsule containing a
liquid arranged to boil at a certain predetermined temperature is the
regulating factor. When the liquid boils, the capsule expands, and by
certain mechanical devices regulates the gas supply so as to produce
exactly the temperature required.

The procedure is as follows: The jar is filled with milk, and water is
run into the copper vessel by the funnel until it runs over at the
overflow pipe. The thermostat is lifted off and the full gas supply
allowed to pass to the burner, the temperature of the milk brought up to
180 deg. F. and maintained for half an hour at this figure. The gas is then
turned off, and cold water run through the funnel until the temperature
of the milk registers 95 deg. F. The culture is added, the lid replaced,
and the thermostat put into the pocket at the side of the vessel; the gas
relighted, and when the temperature reaches 100 deg. to 106 deg. F. the
capsule of the thermostat will expand and close the gas to a peep, which
is just sufficient to maintain the temperature within the above limits.
After eight hours the incubation is completed.

Edgar's patent apparatus, the "Lactogenerator," as provided by the Dairy
Supply Co., Ltd., is shown in Fig. 52.

  [Illustration: FIG. 52. Edgar's "Lactogenerator"]

The milk is placed in a tinned copper-jacketed vessel and water run in
through a vertical pipe until it runs off at the overflow. Two gas
connections are required with cocks on each, the one to heat up the milk
to the boiling point and maintain it at this for thirty minutes. A
skimmer which has been placed in the milk lifts out the coagulated
protein and albumen which rise to the top. The cock is then shut and
cold water run through the jacket till the thermometer shows 90 deg. F.,
when the culture is added, and the other gas supply with the regulator
turned on, and the temperature is automatically maintained at about 90 deg.
F. Time of incubation eight to nine hours. It is recommended to turn
cold water into the jacket at the end of the period to prevent
overincubation.

A somewhat similar apparatus is that of the Willows Refrigerating Co.,
Ltd. (Fig. 53), with the exception that it has no automatic heat
regulator. It is made of tinned steel, and the operations are the same,
but the sterilising temperature (obtained by a gas ring or hot plate) is
given as 180 deg., and the incubating temperature 100 deg. to 104 deg. F.
for a period of twelve hours. Presumably this temperature is maintained
by a small gas jet or other similar source of heat. The capacity is two
gallons.

  [Illustration: FIG. 53

  Apparatus of the Willows Refrigerating Co., Ltd.]

In the apparatus hitherto described the milk is sterilised in bulk, and
is filled into bottles or jars after incubation, which is not a
desirable thing to do, unless the soured milk is for immediate
consumption, as there is likely to be contamination with injurious germs
from the atmosphere. In the domestic apparatus the milk is usually
incubated in covered jars in which it can be kept until required for
use, and the practice on the larger scale should be the same.

The Dairy Outfit Co., Ltd., have recognised this in their "Lacto"
apparatus (Fig. 54).

  [Illustration: FIG. 54

  "Lacto" Apparatus of the Dairy
  Outfit Co., Ltd.]

A cylindrical vessel is set loosely on a stand, beneath which is a lamp
calculated to maintain the incubating temperature. The milk is placed in
bottles with metal screw tops, and these are put into the cylindrical
vessel; water is run in round them through the side funnel, the vessel
lifted off the stand, and heated to sterilising point on a stove. Cold
water is then run in through the funnel until the temperature is low
enough for incubation. Culture is added to each bottle and the lids
screwed on, the vessel lifted on to its stand, and the lamp lighted. The
cover of the apparatus has a thermometer fixed on it.

On the large scale the treatment of the milk would take place entirely
in the jars in which it would be sent out, and the sterilisation and
incubation would be conducted in different pieces of apparatus. The
sterilisation would be effected either (1) by direct steaming, or (2) by
hot water heated by steam. Fig. 55 shows the first type of
sterilisation. The tank is of wrought iron or steel with strengthening
pieces of angle iron. The door, with pulleys and counterweight for easy
handling, is fastened steam-tight by hinged bolts. The apparatus is
mounted on a stand at a convenient height for handling the bottles; and
in front is another stand with channel iron rails to take the waggon in
which the bottles or jars to be sterilised are packed. When the door is
fast, steam is turned on, and regulated to produce the proper
temperature by the thermometer fixed in the shell, in which a pressure
gauge is also secured. After sterilising, the door is opened and the
waggon drawn forward to the outside, allowed to cool, or removed
elsewhere to cool, and allow space for a new charge.

  [Illustration: FIG. 55.--Sterilising Apparatus for
  sterilising milk on the large scale. The bottles of milk
  are sterilised, and the culture can then be added, and the
  incubation allowed to proceed in an insulated chamber.]

The second method of sterilising is by hot water, as in Fig. 56. The
bottles or jars are placed on a perforated false bottom in the
rectangular tank, water run in up to the necks, and steam turned on; the
lid is fastened with hinged and hooked bolts; a thermometer fastened in
the lid, and with a long stem enclosed in metal, indicates the
temperature. At the end of the sterilising process cold water is turned
on, and at the same time the overflow water cock is opened; the cold
water gradually reduces the temperature, and the incubating point is
quickly reached.

  [Illustration: FIG. 56 Another Method of Sterilising
  (Dairy Supply Co., Ltd.).]

Incubation in bottles or jars, sterilised in these ways, can best be
conducted in an insulated room, with say, six inches of silicate cotton,
granulated cork, or washed cow hair packed between two-inch by six-inch
battens, covered with matching on either side, and lined with sheet
zinc. It would be an advantage to have an air-lock or anteroom into
which the waggons or trays of sterilised jars could be run, and the door
of the anteroom closed before the door of the insulated room is opened.
This would tend to prevent variations of temperature in the room, and
also, by checking free communication with the outside air, decrease
contamination. The waggons of jars would be run in, and culture added to
each jar by a sterilised pipette. The atmosphere of the room would be
kept pure by running in air frequently through a filter of moist
cotton-wool by means of an electric fan, and at intervals the interior
would be sterilised by the use of formalin vapour.


  [Illustration: _Details of an American Apparatus for
  Preparing Soured Milk_

  FIG. 57

  The figures give diagrams A, B, C, and D of an apparatus
  useful for the preparation of lactic foods. The incubating
  can A, is made of block tin, and is intended to contain
  the milk. B, the warm water container, should be a stout
  walled vessel with a circular aperture in the lid, through
  which the incubating can may be passed, and clamped down
  as in C.

  B is fitted with three stout iron legs, which should be
  sufficiently long to allow of a small lamp or gas-jet
  being placed beneath the container to maintain a uniform
  temperature.

  D gives an external view of the apparatus.

  For the preparation of soured milk, separated milk is
  placed in the incubating can, and heated up to 100 deg. C.
  (212 deg. F.) for thirty minutes. It is then allowed to cool
  to room temperature, and the culture, or tablet containing
  the lactic acid bacteria, is then added, and thoroughly
  stirred for a minute or so. The can is then immersed in
  the warm water container and kept at a temperature of 86 deg.
  F. to 104 deg. F., according to the organisms used, for ten to
  twelve hours. By the end of this time the milk ought to be
  converted to a jelly-like mass, and after being stirred
  vigorously for a short time, may be cooled on ice, and is
  then ready for consumption.]

The incubating temperature could very conveniently be maintained by an
electric radiator, and as the insulation would largely prevent leakage,
the amount of electric current used would not be large. The regulating
apparatus might consist of a thermometer with platinum wires fused
through the stem at the proper temperature, say 100 deg. F. When the
mercury rises to this figure it will complete the circuit of a battery
which will actuate certain well-known devices for turning off the current
which actuates the radiator. In this way a very fine automatic
arrangement would be achieved. Steam pipes might be used instead of the
radiator, and the thermometer above described could be used in this case
also, with appliances to cut off the steam.

On the large scale, labour-saving appliances, such as the mechanical
brush jar and bottle washer, and the automatic filler for jars or
bottles, would be employed, and an overhead trackway for carrying the
trays of jars from the steriliser to the incubator would be a great
convenience. A further adjunct of considerable importance would be a
cold room, worked either by ice or a refrigerating machine, in which the
jars could be stored after incubation, so as to arrest the process of
lactification, and maintain the soured milk in good condition until
required for use.




CHAPTER VIII

SOURED MILK IN HEALTH AND DISEASE


When people are ill the best thing they can do is to place themselves in
the hands of the doctor, who will try to regulate their lives, including
their diet, in accordance with the conditions which science suggests as
the most likely to lead to their recovery.

It is not the aim of this book to teach persons who should be under
medical treatment to doctor themselves; soured milk may or may not be
beneficial in their case--that is for the medical man to say; and
further, if it should be beneficial the doctor ought to have its
preparation under his control. Slight differences in quality and purity
may count for much in cases of acute disease, differences which might
not matter to the person who requires no medical attention, and who
consumes the article as a health-giving food. A considerable body of
evidence is already on record as to the potency in certain cases of
soured milk as a curative agent, and it seems to have taken its place in
medicine as a recognised remedy.

There is a wide field of usefulness, however, outside of the strictly
medical one. Professor Metchnikoff has collected many striking examples
of individuals and peoples inhabiting different parts of the world, who
thrive, and in many cases attain to a great age, and whose diet consists
largely of soured milk. He has made a wide and general inquiry into the
causes which tend to shorten life, and makes out a strong case in
support of the view that in many cases this is the result of what is
called auto-intoxication or self-poisoning. In man and in the mammalia
generally, the colon or large intestine is very largely developed; this
organ is not of much value in the digestion of food, and seems to be
chiefly a receptacle for waste material; it is, as a rule, extremely
rich in bacterial flora, which produce putrefactive changes in the waste
material. As a result various poisonous principles are evolved, and
these find their way into the blood, accompanied frequently, there is
every reason to believe, by the injurious bacteria themselves. In this
way many diseases and ailments are produced which shorten life. The
inquiry then naturally turns to what is the best way of dealing with
this state of matters. It is known that the bacteria referred to
flourish best in alkaline or at least non-acid surroundings, and it is
known that these conditions very frequently exist in the large
intestine. Acids are the best antiseptics; they have been used from time
immemorial as preservatives; pickles are preserved in vinegar or acetic
acid, and when milk is allowed to sour under proper conditions, the
germs of putrefaction are destroyed or their activity inhibited, and it
keeps a considerable time. Doubtless, in hot countries, it was this
property of lactic acid which first led to milk being artificially
soured with a view to its preservation as an article of food. So
powerful is lactic acid in this respect that it is a custom in some
countries to preserve meat by placing it in soured milk.

How can acids be applied so as to control the bacterial flora of the
large intestine? Not in the ordinary way, because, when administered
through the mouth, they are used up long before they can penetrate to
the colon. The brilliant idea occurred to Professor Metchnikoff, of
administering acid-producing germs which might work their way through
the digestive system, and, reaching the large intestine, produce the
acid required. After much experimenting the bacillus of Massol,
_Bacillus bulgaricus_, was adopted as the most suitable. The Bulgarian
bacillus is an extremely vigorous one, multiplying with great rapidity,
and persisting in conditions that would be inimical to other microbes.
The growth and development of bacteria is interfered with by the
products of their own activity; thus, ordinary lactic-acid-producing
organisms die when a certain amount of lactic acid has been developed;
the same fate overtakes the Bulgarian bacillus, but it survives longer
and is able to produce as much as two and one half per cent. of lactic
acid in milk before it ceases operations. It seemed therefore the most
likely to be able to survive the journey through the digestive system.
Experiments fully bore out this supposition, as no great difficulty was
encountered in naturalising the Bulgarian bacillus in the large
intestine, not only in milk cultures, but grown in solution of malt,
bouillon, etc. It thrives in all kinds of sugar, and therefore can be
administered in a variety of media, very beneficial results following in
many cases. Direct tests showed a large reduction of the injurious
intestinal flora when the Bulgarian bacillus had been naturalised in
the colon, and the bacillus persisted long after it had ceased to be
administered. Specialists who have taken up the subject report the cure
of many ailments through the agency of soured milk, and it seems to have
entered upon a lengthening career of medical usefulness.

The fact of so many old people being found in countries where soured
milk is a staple of diet naturally raises the question as to whether its
general use in other countries might not have a beneficial effect on
health and longevity. Its usefulness as a remedial agent in certain
diseases is already demonstrated; is there not a strong probability,
amounting almost to a certainty, that its consumption by people in
health would tend to ward off many ailments and prolong life? Of course
there will be some for whom it is not suitable; there are people who
cannot eat strawberries without discomfort, but no one thinks of
prohibiting the general use of the fruit on that account. In the matter
of diet the person in health, if he exercises ordinary care, may be left
to find out for himself what suits him. The soured milk remedy is not a
disagreeable one, as, when properly prepared, the article forms both a
pleasant and refreshing article of diet. The question of getting the
right article, however, is a very important one. Milk is a splendid
rearing ground for many bacteria, some of which are very injurious;
among these may be pathological germs, the seeds of tuberculosis,
enteritis, etc. The danger with soured milk is, that in the process of
culture we develop the best condition for the increase of these when
they preponderate, or when, through the use of bad cultures, the
lactic-acid-producing bacteria are absent, or present only in small
numbers. By the thorough boiling of the milk, we get rid of all living
bacteria and nearly all spores or germs, and by scrupulous cleanliness
in the vessels used--scalding or even boiling them, and allowing them to
dry naturally in an inverted position--we greatly diminish the
probability of infection with fresh injurious germs from the atmosphere.
All depends on the purity of the culture employed; this can now be
obtained, prepared in the most careful manner, from wholesale chemists
making a speciality of its manufacture.

As we have seen, even the Bulgarian bacillus is ultimately killed by the
products of its own activity, and the natural corollary is, that the
life of cultures cannot be a long one. Only those cultures should be
bought which are labelled with the date to which they are guaranteed to
maintain their efficiency. With fresh good milk, careful boiling,
scalding, and cleanliness with regard to the containing vessels, and the
means of maintaining the incubating temperature for ten or twelve hours,
there is not the slightest difficulty in preparing perfectly reliable
soured milk. There are simple tests which will sufficiently guide the
experimenter; the soured milk should not be too acid to the taste, and
it has a flavour of its own by which its quality can be recognised. The
litmus test-papers mentioned in the chapter on the chemistry of milk are
very useful; both the red and the blue papers should be obtained and
used first of all in testing the quality of the fresh milk. After
incubation the soured milk should turn the blue paper decidedly red; if
this does not occur, test it with the red paper; if the latter turns
blue it is proof that the wrong fermentation has taken place--that
putrefactive germs have gained the upper hand. The most probable
explanation is, that the culture is bad, the Bulgarian bacillus is not
present, or if so, only in small numbers. With these simple tests,
combined with proper care, one cannot go far wrong. The Eastern nations
who prepare soured milk in various forms do not exercise the care we
have predicated, but they seem to make the article of fairly constant
and good quality. It has been suggested in explanation that, as the
ordinary flora differs in different countries, the bacterial flora
varies in a similar manner, and that in these Eastern countries
injurious bacteria are not so prevalent in the atmosphere as they are
with us.

It is also said that the flavour of the soured milk prepared in Bulgaria
is quite different from that prepared in Paris, London, or New York; one
reason probably is that the "maya" or ferment used in Bulgaria contains
several other organisms besides the Bulgarian bacillus, which raises the
question whether a pure culture of one bacillus is the best to use.

Professor Metchnikoff found that this bacillus alone had certain
defects; it attacks fat and is apt to give a tallowy taste when cream is
present in the milk. He therefore associated with it another
lactic-acid-producing organism, and this combination is the basis of his
culture called "lactobacilline." The presence of yeasts, which occur in
the Eastern ferments, has been advocated by some; the yeast in
association with the lactic organisms produces a small amount of
alcohol. The question of the composition of the culture will have to be
fought out by the experts, but meantime, if we go to the right source,
we have good enough cultures to go on with.

A good deal can be said for the use of skimmed or separated milk instead
of whole milk. Cream as a rule contains far more bacteria than the rest
of the milk, and we therefore start from a surer foundation when it is
removed; besides, the mechanical separator, now so largely used, removes
slime and other impurities from the milk, and these also are hotbeds of
bacteria.

Soured milk may be taken at any time, the first thing in the morning,
before or after meals, or the last thing at night. The quantity will
vary with the individual, but from half a pint to a pint is a fair
amount for daily use. If one wishes to have the maximum effect it is
necessary for the time being to curtail the use of butcher's meat and
substitute fish, yolk of eggs, and other similar foods; not much alcohol
should be taken, and smoking might be reduced to a minimum. Those who
cannot take even skimmed milk may use whey in which to cultivate the
bacillus; it is not desirable to employ the whey which has been
separated by the use of rennet, as in cheese- or junket-making. A better
article is obtained by adding a very small quantity of pure hydrochloric
acid to milk which has been boiled, and then filtering through a sieve,
which retains the curd while the liquid whey passes through; a pinch of
soda is added to neutralise the excess of acid, and, after boiling, the
liquid should turn red litmus paper blue; it is then ready for the
addition of the culture and incubation in the same manner as with milk.
A solution of malt--the extract dissolved in hot water is
convenient--may also be used instead of milk, and strongly malted bread
or biscuits are excellent to take with the soured milk or cultures in
other mediums, to supply food for the bacillus in the form of malt
sugar. Other sugars, cane or grape, are also very useful, and may be
taken in the form of fruit juices, syrups, confections, jams, sweet
puddings, etc.

We lay stress on the use of soured milk or other cultures of the
Bulgarian bacillus by people in health as a probable preventive of
disease and a possible agent in the lengthening of life, but it may be
of interest to give a short account of its use by medical men in the
treatment of various ailments. An English authority on the subject, Dr.
Herschell, states that the symptoms of the poisoning of the system by
the toxic substances produced by injurious bacteria in the large
intestine may include headaches, misery and depression of spirits,
drowsiness and stupor, giddiness, dimness of sight and dizziness,
fatigue without obvious cause, both of the muscles and brain, fear,
panic, and nervousness, disagreeable sensations in the limbs or face,
such as numbness, tingling, or prickling, crawling sensation of weight
or of heat or cold, dyspepsia of the sort where there is a deficiency of
hydrochloric acid and pepsin in the gastric juice, accompanied by
flabbiness and loss of power in the muscles of the stomach, and
characterised by flatulence, nausea, loss of appetite, with discomfort
and weight after food, furred tongue, emaciation, earthy colour of the
skin, offensive perspiration and the other signs of biliousness,
enlargement of the liver, and anaemia. These symptoms may have other
causes, and when one or several of them are present a chemical and
physical examination of the urine and faeces is necessary to prove that
they have resulted from auto-intoxication. When this is shown the
soured milk treatment is indicated, and many striking cures are detailed
as witnesses to its efficacy. The liver and kidneys are the natural
guardians of the body against the toxines we are speaking of, and
frequently they are over-strained; the soured milk treatment greatly
lightens their load. In malignant disease of the stomach, soured milk
will frequently be retained when all other foods are rejected. In cases
of neurasthenia and gout it has also proved of value, and in the
"run-down" condition which is so common in middle life. Chronic
diarrhoea and certain forms of constipation have in numerous instances
yielded to the treatment, the whey culture being usually found the most
suitable. Then, in some forms of anaemia, the lactic acid cultures have
proved most successful, and, as a means of rendering the
gastro-intestinal track aseptic previous to operations, they have proved
of considerable value.

If all this has been accomplished in a year or two, what may not we look
forward to in the future when more extended use and experiment shall
have more fully exhausted the possibilities of the cure? But if we
follow the example of the different nations who have so long used
soured milk as a regular article of diet, does it not seem probable that
we may eliminate some, at least, of the causes of ill-health that call
for the intervention of the doctor?

The human organism is by no means perfect; we have within us many
defective parts, and some organs whose working seems to be against the
welfare of the economy. It has now been clearly shown that one of the
chief of these is the large intestine, as to the use of which only vague
and unsatisfactory theories have been formed. There can be no doubt as
to the damage which it frequently inflicts on the system, and, thanks to
the researches of Professor Metchnikoff and other investigators, we seem
to be in possession of a natural remedy which is sufficient to deal with
the evils it produces.


  FOOTNOTES:

  [1] _Discoveries in Nineveh and Babylon_, by Layard, chap.
  xiii.

  [2] Ex. xviii. and xxiii.; Lev. ii. and xi.

  [3] _Encyclo. Biblica._

  [4] Burckhardt and Doughty.

  [5] _Annals of Dairying in Europe_, by Loudon M. Douglas.

  [6] Burckhardt, _Bedouins_.

  [7] This word is spelt in a great many ways by different
  writers: _Yoghourt_ would seem to be the one most
  favoured.--AUTHOR.

  [8] _Damascus and Palmyra_, by Chas. G. Addison, 1838.

  [9] _Travels in Syria and the Holy Land_, by Burckhardt,
  1822.

  [10] _Lands of the Saracens_, by B. Taylor.

  [11] _Travels through Sweden, Finland, and Lapland and to
  the North Cape in the years 1798 and 1799_, by Joseph
  Acerbi, 1802.

  [12] Letter to the author, from Mr. H. Cavendish Venables,
  British Vice-Consul at Varna.

  [13] _One Hundred and Twenty Years of Life_, by Reinhardt;
  _The Secret of Longevity_, by an F.R.M.S.

  [14] _Foods, their Composition and Analysis_, by A. W.
  Blyth.

  [15] _Dictionary of Applied Chemistry_, by T. E. Thorpe,
  C.B.

  [16] _Koumiss or Fermented Mares' Milk and its Uses, and
  the Treatment and Cure of Pulmonary Consumption and Other
  Diseases_, by L. Carrick, M.D., 1881.

  [17] _Transactions of the Royal Society of Edinburgh_,
  vol. i.

  [18] Clarke's _Travels_, 1810.

  [19] 1845.

  [20] _Dictionary of Applied Chemistry_, by Thorpe.

  [21] A leathern bottle.

  [22] "I have brought forward Tchembulatof's receipt, which
  differs from Bogoyavlensky's in the use of a larger
  quantity of millet-flour, and in the boiling of the latter
  apart from the milk. Dr. Postnikof's plan is the
  following: Half a pound of millet-flour and a quarter of a
  pound of malt are mixed with a sufficient quantity of
  honey to form a paste, which is put into a clean jar,
  covered with a linen cloth, and placed on a warm stove.
  The mass soon begins to rise, and is then taken out,
  wrapped in a piece of muslin, and dropped into a clean
  earthenware vessel, containing about a quart of new mares'
  milk, which is placed in the same temperature that the
  paste was kept in. As soon as signs of fermentation begin
  to show themselves in the fluid, the paste must be
  removed, while the milk, after being stirred, should be
  left in the same temperature till bubbles appear (only in
  very small quantities) on its surface. The ferment is then
  ready."

  [23] _Food and the Principles of Dietetics._

  [24] _Food and the Principles of Dietetics_, by Robert
  Hutchison, M.D.

  [25] _Bacteria in Milk and its Products_, by Conn.

  [26] _Dict. App. Chem._, Thorpe.

  [27] _Nature_, July 23, 1884.

  [28] _The Exploration of the Caucasus_, by Duncan W.
  Freshfield, 1896.

  [29] Quoted by George M. Sternberg, M.D., LL.D.,
  _Text-Book of Bacteriology_, 1898.

  [30] _Encyclo. Biblica._

  [31] Conn.

  [32] _Cyclo. of Biblical Lit._, M'Clintock and Strong, and
  Burckhardt's _Arabia_.

  [33] _The Indian Medical Gazette_, Sept., 1909, "A New
  Lactic Acid producing Streptothrix," by Gopal Ch.
  Chatterjee, M.B.

  [34] In their studies on Leben in the _Annales de
  l'Institut Pasteur_ of 1899, Rist and Khoury, in speaking
  of the amount of lactic acid produced by _Streptobacillus
  lebenis_ in milk, say "Nous avons mesure cette acidite
  dans une culture sur petit lait de vingt-quatre heures;
  elle etait .261 grms. per cent. exprimee en acide
  lactique," which will make the amount of lactic acid
  produced in one litre of milk 2.61 grms. The production of
  this small amount of lactic acid does not tally with the
  ordinary view of the vigorous lactic-acid-producing power
  of the bacillus.

  [35] _Prolongation of Life._

  [36] _Prolongation of Life._

  [37] An accurate census of Bulgaria is being prepared and
  will exhibit the cases of long life in that country.

  [38] See A. Rosam, _Oesterreichische Molkerei Zeitung_, 15,
  p. 31.

  [39] _Revue generale du Lait_, vii., pp. 8 and 9 (letter
  from Dr. Otakar Laxa of Prague, Bohemia, to the author).

  [40] _On the Prolongation of Human Life_, by Elie
  Metchnikoff; also _The Century Magazine_, Nov., 1909, "The
  Utility of Lactic Microbes," by the same author.

  [41] _Century Magazine_, Nov., 1909.

  [42] See _Annals of Dairying in Europe_, by Loudon M.
  Douglas.

  [43] Adapted from a report by Robert E. Turnbull, in _Live
  Stock Journal_.

  [44] _Facts about Milk_, by R. A. Pearson, B.S.,
  Washington.

  [45] _Care and Handling of Milk_, Marshall and Wright,
  Bulletin 221, Michigan, 1904.

  [46] _Journal of the Royal Society of Arts_, March 6,
  1908--"Modern Dairy Practice," by Loudon M. Douglas.

  [47] Skolotowski, _Wratsch_, 1883 (Russian), from
  Codwyssozki.

  [48] Podowyssozki, _Zeitschr. f. diat. u. physik.
  Therapie_ vol. v., 1901, p. 570.

  [49] Hammersten, _Jahresb. u. d. Fortsch. d. Tierchem_,
  1886, Bd. 16, p. 163.

  [50] Essaulow, _Dissert. Moscow_, 1895, _Abstr., Koch's
  Jahresb._, 1895, Bd. 6, p. 222.

  [51] Kern, _Bulletin Soc. des Naturalistes de Moscow_,
  1881, 3, p. 141.

  [52] Krannhals, _Deutsch. Arch. f. Klin. Med._, 1884, Bd.
  35, p. 18.

  [53] Beijerinck, _Centralbl. Bakt. Par._, 1889, Bd. 6, p.
  44.

  [54] Scholl, _Die Milch_, Wiesbaden, 1891, p. 38.

  [55] Adametz, _Centralbl. Bakt. Par._, 1889, Bd. 5, p.
  116.

  [56] Freudenreich, _Landw. Jahrb. d. Schweiz._, 1896, vol.
  x., p. 1.

  [57] Nikolaiewa, _Annals of the Botan. Lab. of the Med.
  Inst. for Women_, No. 10. St. Petersburg, 1907.

  [58] Kuntze, _Centralbl. Bakt. Par._, 1909, 24, p. 101.

  [59] See Chap. II.

  [60] Rubinsky, _Centralbl. Bakt. Par. II._, 1910, vol.
  xxviii., p. 161.

  [61] Biel, _Jahresb. ue. d. Fortschr. d. Tierchem_, 1886,
  16, p. 159.

  [62] Allik, _Dissertat. Dorpat._, 1896, 19, p. 303.

  [63] Fleischmann, _Lehrb. d. Milchwirtschaft_, 2d edition.
  Bremen, 1898.

  [64] Rist and Khoury, _Annal. Pasteur_, 1902, 16, p. 65.

  [65] Guerbet, _Comptes Rendus_, 1906.

  [66] Weigmann, _Lafar's Handb. d. Techn. Mykol._, 2d
  edit., 1905, vol. ii., p. 134.

  [67] Emmerling, _Cent. Bakt. Par._ 1898, vol. iv., p. 418.

  [68] Lindner, _Mikroscop. Betriebscontrolle, i. d.
  Gaerungsgew_, 3d edit., Berlin, 1901.

  [69] Kalantharianz, _Dissert. Berlin_, Abs. in _Koch's
  Jahresb._, 1898, Bd. 9.

  [70] Luerssen and Kuehn, _Centralbl. Bakt._

  [71] Piorkowski, _Sitzungsber. der Berl. med. Ges._, Nov.,
  1907.

  [72] Metchnikoff, _The Prolongation of Life._

  [73] Grigoroff, _Revue Medicale de la Suisse Romande_,
  1905, p. 10.

  [74] Grixoni, _Abstr. Cent. Bakt. Par._ 11, 15, p. 750.

  [75] Freudenreich and Jensen, _Cent. Bakt. Par._ 11, 1897,
  3, 545.

  [76] Moro, _Wien. klin. Wochenschr._, 5, 1900.

  [77] Makrinoff, _Cent. Bakt. Par._ 11, 1910, vol. xxvi.,
  p. 374.

  [78] White and Avery, _Cent. Bakt. Par._ II, 1909, vol.
  xxv., p. 161.

  [79] Hastings and Hammer, _Research Bull., Wisconsin
  Experimental Station_, 6, 1909.

  [80] Boutroux, _Comp. Rend._, 86, 1905, 605.

  [81] Richet, _Comp. Rend._, 86, 1905, 550.

  [82] Koning, _Milchw. Zentralbl._, 1905, 1, 280.

  [83] Heinemann, _Centralbl. Bakt. Par._ 1908, 21, 57.

  [84] Chap. I.

  [85] Metchnikoff, _The Prolongation of Life_, 1908, p.
  161.


  INDEX


  A

  Acerbi, 8

  Acidity of milk, 64

  Adametz on keffir, 92

  Albumen, 52

  Alcoholic fermentation, 17, 84

  Allen & Hanbury's apparatus, 132

  American incubating apparatus, 149

  Analysis of milk, 48, 61

  Aneyza Bedouins, 2

  Arabs, 2

  Araka, 106

  Ash of milk, 56


  B

  _Bacillus acidi lactici_, 107, 112

  _Bacillus acidophilus_, 110, 112

  _Bacillus bulgaricus_, 39, 46, 82, 108, 110, 123, 154

  _Bacillus casei_, 113

  _Bacillus caucasicus_, 92, 94, 95, 119

  _Bacillus caucasina_, 39

  _Bacillus coli_, 45

  _Bacillus esterificans_, 96

  _Bacillus keffir_, 96, 97

  _Bacillus lebenis_, 105

  _Bacillus matzoon_, 109, 110

  Bacillus of long life, 46

  _Bacillus putrificus_, 122

  _Bacillus subtilis_, 90, 92, 107

  Bacteria in milk, 76

  Bacteriology of fermented milks, 84

  _Bacterium acidi lactici_, 92, 96

  _Bacterium aerogenes_, 92, 96

  _Bacterium coli commune_, 119, 122

  _Bacterium sardous_, 110, 111

  Balkan Peninsula, 4

  Bedouins, 2

  Beijerinck on keffir, 91

  Biestings, 63

  Biology of the keffir grain, 90

  Blood, water contents of, 50

  Bourgoul, 6

  Bulgarian maya, 10, 109

  Bulgaricus group, cultural characteristics of, 115

  Burckhardt, 6

  Butin, 51

  Butyric acid fermentation, 16

  Butyrin, 51


  C

  Camels' milk, 2

  Caprinin, 51

  Capronin, 51

  Caprylin, 51

  Carrick on koumiss, 18

  Casein, 52, 53

  Centenarians in Servia, Bulgaria, and Roumania, 41

  Chatterjee on Dadhi, 38

  Chemistry of milk, 47

  Chocolate preparations and the soured-milk bacillus, 137

  Citrates in milk, 57

  Clay, Paget & Company's apparatus, 132

  Coagulation of casein, 59

  _Colitis_, 45

  Colostrum, 63

  Constituents of milk, 48

  Continuous apparatus for producing soured milk, 81

  Creamometer, 62


  D

  Dadhi, 15, 38

  Dairy Machinery & Construction Company's apparatus, 80, 82

  Dairy Outfit Company's apparatus, 145

  Dairy Supply Company's apparatus, 143;
    steriliser, 148

  Dirt in milk, 63

  Diseases of keffir grains, 97

  _Dispora caucasia_, 34, 90

  Dried sour milk, 5

  Duclaux, 51


  E

  Edgar's "Lactogenerator," 143

  Eggs, yolk of, 52

  _Enteritis_, 45

  Enzymes in milk, 57

  Equipment for town's dairy, 80

  Essaulow on keffir, 89, 92


  F

  Fat of milk, 50

  Ferments at the altar, 3

  Fluegge, 35

  Freshfield on keffir, 33

  Freudenreich, 92


  G

  Gaseous fermentation, 84

  Gay-Lussac, 17

  Gioddu, 107

  Globulin, 54

  Grieve, Dr. John, on koumiss, 19


  H

  Hammerstein on keffir, 89

  Handling of milk, 68

  Health and disease, 151

  Hearson & Company's "Lactobator," 141

  Hebrews, 3

  Houran, inhabitants of, 6

  Hueppe, 16

  Hutchinson, Dr. H. B., bacillus from English market milk, 120

  Hutchison on koumiss, 30


  I

  Ice chest, 136

  Impure cultures, 158

  Incubators, 141

  India, 1

  International Dairy Federation, 68


  J

  Jebours, 3


  K

  Kalmucks, 20

  Keffir, 15, 32, 85;
    old, 88

  Keffir grain, biology of, 90

  Kephir, 34, 85.
    _See also_ Keffir.

  Keshk, 6

  Keshk-leben, 6

  Koumiss, 15, 18;
    Bogoyavlensky's method of preparation, 28, 98;
    analysis, 102;
    artificial, 102

  Krannhals on keffir, 91

  Kuntze, 95


  L

  Lactic acid, bacillus, 16;
    cultures, 55;
    fermentation, 16, 84;
    Ferments apparatus, 131

  "Lacto" apparatus, 145

  "Lactobacilline," 158

  _Lactobac. caucasicus_, 91

  _Lactobacillus keffir_, 94

  Lactometer, 64

  Lapland, 8

  Laurin, 51

  Layard, 2

  Leben, 15, 37, 104

  Leben Raib, 104

  Lecithin, 52

  "Le Ferment" apparatus, 128

  Liebig, 17

  Longevity, 155


  M

  Mares' milk, 24

  Matzoon, 15, 38, 106

  Maya, 42;
    Bulgarian, 10

  Maya Bulgare Company's apparatus, 131

  Meeresy, 5

  Metchnikoff, 34, 40, 44, 121, 158, 163

  Micro-organisms, discovery of, 13

  Middle Ages, 13

  Milk-filling apparatus for bottles, 82

  Milk, general properties of, 57;
    of different animals, 60;
    supply of the United Kingdom, 69;
    industry in the United States, 71;
    management, 74

  Mitscherlich, 17

  Myristin, 51


  N

  Neolithic times, 1

  Nikolaiewa, 95

  Nitrogenous constituents of milk, 52


  O

  Ojran, 106

  Olein, 51

  Oxygala of Pliny, 4


  P

  Paleolithic times, 1

  Palmitin, 51

  Pasteur, 14, 78

  Pasteurisation, 78

  Pelouze, 17

  Pilaff of rice, 5

  Pina, 21

  Podowyssowski on keffir, 87

  Preparation, of soured milk, 81;
    in the house, 125;
    in the dairy, 139

  Primary cooler, 78

  Proteids, 53

  Pyrenees, 4


  R

  Reindeer's milk as soured milk, 8

  Rubruquis, William de, 19


  S

  _Saccharomyces cerevisseae_, 90

  _Saccharomyces keffir_, 32, 33, 91, 93, 94

  Sakwaska, 88

  Sale of Food and Drugs Act, 1899, 49

  Scheele, 17

  Scholl on keffir, 91

  Scythians, 18

  Secondary cooler, 79

  Shammar Bedouins, 2

  Sheneena, 2

  Skolotowski on keffir, 86

  Smith, Professor Robertson, 3

  Soured milk, in the house, 125;
    in the dairy, 139;
    in health and disease, 151;
    from impure cultures, 158;
    use of, 159

  Souring of milk, 47, 54

  Specific gravity of milk, 65

  Stearin, 51

  Steriliser, 148

  _Streptobacilli lebeni_, 39

  _Streptobacillus lebenis_, 111

  _Streptococcus a_, 93, 94

  _Streptococcus acidi lactici_, 95, 96

  _Streptococcus b_, 93, 94

  _Streptococcus lacticus_, 92, 93, 122, 124

  Sugar of milk, 54

  Sugar preparations and the soured-milk bacillus, 137

  Suter-Naef on Swiss koumiss, 26

  Swedish whey cheese, 60

  Swiss hard cheese, 113

  Symptoms of disease, 161


  T

  Temperature allowances when testing milk, tables of, 66

  Town's dairy equipment, 80

  Transmission of disease by milk, 72


  U

  United Kingdom, milk supply of, 69

  United States, milk industry of, 71

  Urgoutnik, 43


  V

  Van Leeuwenhoek, 13

  Variation limits of milk, 49

  Vedas, 1

  "Veronelle" apparatus, 132

  Vina, 21

  Vinous fermentation, 17


  W

  Willows Refrigerating Company's apparatus, 144, 145

  Wilson on koumiss, 23


  Y

  Yoghourt, 9, 42, 46, 107

  Yoghourt bacillus, 109


  Z

  Zakvaska, 42

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  +17.--The Prolongation of Life.+ Optimistic Essays. By ELIE
        METCHNIKOFF, Sub-Director of the Pasteur Institute. Author of
        "The Nature of Man." etc. 8o., Illustrated Net, $2.50.
        (By mail, $2.70.) Popular Edition. With an introduction by
        Prof. CHARLES S. MINOT. Net, $1.75.

  In his new work Professor Metchnikoff expounds at greater length, in
  the light of additional knowledge gained in the last few years, his
  main thesis that human life is not only unnaturally short but
  unnaturally burdened with physical and mental disabilities. He
  analyzes the causes of these disharmonies and explains his reasons for
  hoping that they may be counteracted by a rational hygiene.


  +18.--The Solar System.+ A Study of Recent Observations. By Prof.
        CHARLES LANE POOR, Professor of Astronomy in Columbia
        University. 8o. Illustrated. Net, $2.00.

  The subject is presented in untechnical language and without the use
  of mathematics. Professor Poor shows by what steps the precise
  knowledge of to day has been reached and explains the marvellous
  results of modern methods and modern observations.


  +19.--Climate--Considered Especially in Relation to Man.+ By ROBERT
        DECOURCY WARD, Assistant Professor of Climatology in Harvard
        University. 8o. Illustrated. Net, $2.00.

  This volume is intended for persons who have not had special training
  in the technicalities of climatology. Climate covers a wholly
  different field from that included in the meteorological text-books It
  handles broad questions of climate in a way which has not been
  attempted in a single volume The needs of the teacher and student have
  been kept constantly in mind.


  +20.--Heredity.+ By J. ARTHUR THOMSON, M.A., Professor of Natural
        History in the University of Aberdeen; Author of "The Science of
        Life," etc. 8o. Illustrated. Net, $3.50.

  The aim of this work is to expound, in a simple manner, the facts of
  heredity and inheritance as at present known, the general conclusions
  which have been securely established, and the more important theories
  which have been formulated.


  +21.--Age, Growth, and Death.+ By CHARLES S. MINOT, James Stillman
        Professor of Comparative Anatomy in Harvard University,
        President of the Boston Society of Natural History, and Author
        of "Human Embryology," "A Laboratory Text-book of Embryology,"
        etc. 8o. Illustrated.

  This volume deals with some of the fundamental problems of biology,
  and presents series of views (the results of nearly thirty years of
  study), which the author has correlated for the first time in
  systematic form.


  +22.--The Interpretation of Nature.+ By C. LLOYD MORGAN, LL.D.,
        F.R.S. Crown 8vo. Net, $1.25.

  Dr Morgan seeks to prove that a belief in purpose as the causal
  reality of which nature is an expression is not inconsistent with a
  full and whole-hearted acceptance of the explanations of naturalism.


  +23.--Mosquito Life.+ The Habits and Life Cycles of the Known
        Mosquitoes   of the United States; Methods for their Control;
        and Keys for Easy Identification of the Species in their Various
        Stages. An account based on the investigation of the late James
        William Dupree, Surgeon-General of Louisiana, and upon the
        original observations by the Writer. By EVELYN GROESBEECK
        MITCHELL, A.B., M.S. With 64 Illustrations. Crown 8vo.
        Net, $2.00.

  This volume has been designed to meet the demand of the constantly
  increasing number of students for a work presenting in compact form
  the essential facts so far made known by scientific investigation in
  regard to the different phases of this, as is now conceded, important
  and highly interesting subject. While aiming to keep within reasonable
  bounds, that it may be used for work in the field and in the
  laboratory, no portion of the work has been slighted, or fundamental
  information omitted, in the endeavor to carry this plan into effect.


  +24.--Thinking, Feeling, Doing.+ An Introduction to Mental Science.
        By E. W. SCRIPTURE, Ph.D., M.D., Assistant Neurologist Columbia
        University, formerly Director of the Psychological Laboratory at
        Yale University. 189 Illustrations. 2d Edition, Revised and
        Enlarged. Crown 8vo. Net, $1.75.

  "The chapters on Time and Action, Reaction Time, Thinking Time,
  Rhythmic Action, and Power and Will are most interesting. This book
  should be carefully read by every one who desires to be familiar with
  the advances made in the study of the mind, which advances, in the
  last twenty-five years, have been quite as striking and epoch-making
  as the strides made in the more material lines of knowledge."--_Jour.
  Amer. Med. Ass'n._, Feb. 22, 1908.


  +25.--The World's Gold.+ By L. DE LAUNAY, Professor at the Ecole
        Superieure des Mines. Translated by Orlando Cyprian Williams.
        With an Introduction by Charles A. Conant, author of "History of
        Modern Banks of Issue," etc. Crown 8vo. Net, $1.75.

  M. de Launay is a professor of considerable repute not only in France,
  but among scientists throughout the world. In this work he traces the
  various uses and phases of gold; first, its geology; secondly, its
  extraction; thirdly, its economic value.


  +26.--The Interpretation of Radium.+ By FREDERICK SODDY, Lecturer
        in Physical Chemistry in the University of Glasgow. Crown 8vo.
        With Diagrams. Net, $1.75.

  As the application of the present day interpretation of Radium (that
  it is an element undergoing spontaneous disintegration) is not
  confined to the physical sciences, but has a wide and general bearing
  upon our whole outlook on Nature, Mr. Soddy has presented the subject
  in non-technical language, so that the ideas involved are within reach
  of the lay reader. No effort has been spared to get to the root of the
  matter and to secure accuracy, so that the book should prove
  serviceable to other fields of science and investigation, as well as
  to the general public.


  +27.--Criminal Man.+ According to the Classification of CESARE
        LOMBROSO. Briefly Summarized by his Daughter, Gina Lombroso
        Ferrero. With 36 Illustrations and a Bibliography of Lombroso's
        Publications on the Subject. Crown 8vo. Net, $2.00.

  Signora Guglielmo Ferrero's resume of her father's work on criminal
  anthropology is specially dedicated to all those whose office it is to
  correct, reform, and punish the criminal, with a view to diminishing
  the injury caused to society by his anti-social acts; also to
  superintendents, teachers, and those engaged in rescuing orphans and
  children of vicious habits, as a guide in checking the development of
  evil germs and eliminating incorrigible subjects whose example is a
  source of corruption to others.

       *       *       *       *       *

  The most valuable production since Darwin's "Origin of Species."

  The Nature of Man

  _Studies in Optimistic Philosophy_

  By Elie Metchnikoff

  Sub-Director of the Pasteur Institute, Paris

  Translated with an Introduction by

  P. Chambers Mitchell

  Secretary of the Zoological Society

  Octavo. Illustrated. Popular Edition. $1.50 net. By mail, $1.65

  It is not often that a scientific book may be read with ease, profit,
  and pleasure by the general reader, so that M. Metchnikoff's book
  comes in the nature of an agreeable surprise. It is marked by a
  refreshing _naivete_ and a large simplicity which are
  characteristically Russian. The scientific importance of this work is
  so great that it is spoken of in England as the most valuable
  production since Darwin's _Origin of Species_.

  Opinions of the Press

  "An extremely interesting and typical book.... With a distinguished
  frankness, M. Metchnikoff defines his attitude to our universal
  prepossessions. It is his theory that the infirmities of age are to be
  overcome. If there be ground for this conception, humanity is to be
  profoundly changed and what we call life now, will be the childhood
  and youth of that longer and larger life."--H. G. WELLS, in _London
  Speaker_.

  "Undoubtedly a great book (in some quarters it has been hailed as the
  greatest since Darwin's famous message to the world) and should be
  read by all intelligent men and women."--_The Nation._

  "A book to be set side by side with Huxley's Essays, whose spirit it
  carries a step further on the long road towards its goal."--_Mail and
  Express._

  New York--G. P. Putnam's Sons--London

       *       *       *       *       *

  "_Remarkable for its simple language and clear
  style.... Bears the stamp of a production of
  an erudite scientist and a deep thinker._"--Science.


  The Prolongation of Life

  Optimistic Essays

  _By_ Elie Metchnikoff

  _Author of "The Nature of Man," etc._

  _8vo. Illustrated Popular Edition. $1.75 net By mail, $1.90_

  M. Elie Metchnikoff is one of those rare scientists who have found a
  way to lay hold of and present to the world in untechnical
  phraseology, intelligible to the lay mind, such results of his
  researches as are of universal interest and go straight home to the
  bosoms and business of intelligent men. _The Nature of Man_, by the
  same author, was one of the most fascinating books, at once popular,
  and scientific, which have appeared for decades. The book here in
  question will stand beside it as a worthy companion volume. It is
  satisfactory to report that, absorbed as Metchnikoff is in "material"
  problems, and deep as he is in the mysteries of the physical universe,
  these essays show him to be an optimist who speaks with no uncertain
  voice.

  A great deal of attention is given in _The Prolongation of Human Life_
  to the subject of old age and its causes, with scientific observations
  of special cases among human beings and the lower animals. The author
  suggests means of prolonging life and health, while contemplating
  natural death with serenity, and finding that agreeable sensations
  accompany its approach. Beyond a certain point it seems to him a
  disadvantage to prolong life. Passing on from these mortuary
  lucubrations, the essays concern themselves with psychological
  matters, with optimism and pessimism and in general with questions of
  science and morals. The temperaments of certain great men are analyzed
  in studies that have for their subjects respectively Byron, Leopardi,
  Schopenhauer, and Goethe. In the preface the author says that he has
  avoided, as far as possible, repeating points which have been
  sufficiently treated in _The Nature of Man_.


  G. P. PUTNAM'S SONS

  NEW YORK     LONDON





End of Project Gutenberg's The Bacillus of Long Life, by Loudon Douglas

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