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AGRICULTURAL BACTERIOLOGY

CONN

BY THE SAME AUTHOR

BACTERIA IN MILK

AND ITS PRODUCTS

12MO. 306 PAGES

CLOTH, SI. 25 net

AGRICULTURAL

BACTERIOLOGY

A STUDY OF THE

RELATION OF GERM LIFE TO THE FARM

WITH

. LABORATORY EXPERIMENTS FOR STUDENTS

Microorganisms of Soil, Fertilizers, Sewage, Water,
Dairy Products, Miscellaneous Farm Products

AND

OF Diseases of Animals and Plants

BY

H. W. CONN, Ph. D.

Professor of Biology at Wesley an University

AUTHOR OP ** THE STORY OF GBRM LIPB," " BACTERIA IN MILK AND ITS PRODUCTS," " PRACTICAL
DAIRY BACTERIOLOGY," " BACTERIA, YEASTS, AND MOLDS IN THE HOMB," ETC.

UWVEMITY OF CAUFORNIA

LIBfjARY

CX)LLEGE OF AGRICULTURE
DAVIS

SECOND EDITION^ RI^VISED ANX^eNLARGED

WITH 64 TLLUSTRATIpN§ ,

PHILADELPHIA

P. BLAKISTON'S SON & CO.

1012 WALNUT STREET
1909

'U^,<^, "llroJr^^ " ''^^

Copyright, 1909, by P. Blakiston's Son & Co

Printed by

The Maple Press

York, Pa.

PREFACE TO SECOND EDITION

Since the publication of the first edition of this work advance
along all lines of bacteriology has been very rapid. Scarcely a
phase of the relation of bacteria to agriculture has failed to receive
substantial contributions. Much new information has been
obtained, the relative importance of different subjects has been
changed, and in a few points our previous conclusions have been
corrected. These changes have been so considerable that in
preparing this second edition it has been found necessary to rewrite
the whole book in order to bring it up to the times. The subject has
grown so large that it is difficult to include within the limits of one
volume even the fundamental facts of the rapidly growing science,
and many subjects of importance have been treated very briefly.

The growing recognition of the importance of the subject to
students of agriculture has caused agricultural schools and col-
leges to give to it an increasing amount of attention. For this
reason this edition has been planned with special reference to its
use by classes; and some changes in method of presentation have
been adopted in order to make it more useful to students. For
the same reason there has been added a somewhat extended set of
experiments for elementary laboratory work. These laboratory
directions are far from exhaustive and are designed simply to intro-
duce the student to the methods of bacteriological work.

The close relation of the functions of the higher fungi to the
functions of bacteria has come to be fully realized to-day and has
made it necessary to include more extended references to the higher
fungi in this review. The only other important addition in this

035444-

42.744

VI PREFACE TO SECOND EDITION.

edition is a considerable extension of the treatment of bacterial
diseases of plants that have received so much investigation in the
last ten years. With these additions it is hoped that the present
edition will be a fair summary of our present information upon the
relation of germ life to agriculture.

H. W. C.

MiDDLETOWN, CONN.

June 15, 1909.

PREFACE TO FIRST EDITION

To set any exact limits to Agricultural Bacteriology is difficult.
Primarily the subject includes only phenomena produced by
bacteria, and phenomena that especially affect agriculture. But
some agricultural processes are so closely bound with other industrial
phenomena that they cannot be separated. Agriculture grades
by imperceptible degrees into numerous secondary industries.
Quite a number of the phenomena which will be considered in these
pages have a closer relation to these secondary industries than
they do to agriculture proper, but nevertheless they do have at
least an incidental relation to the farm and must, therefore, be
included in a discussion of Agricultural Bacteriology.

It has, moreover, in recent years, been a growing conviction that
a considerable number of phenomena, hitherto attributed to bacteria,
are directly due to a class of chemical ferments called enzymes.
These enzymes are sometimes produced by bacteria, but in other
cases by organisms totally unrelated to bacteria. When the latter
is the case the fermentations produced by them have, of course,
nothing to do with bacteriology proper. But we do not know
as yet how commonly these enzymes, or chemical ferments, are
concerned in agricultural processes, and even where they do occur
it is found that, in some cases, they are intimately associated with
true bacteriological action. It is impossible to separate chemical
from biological fermentations by a hard and sharp line, nor can we
tell to-day how far both of them may be concerned in any particular
type of fermentations. In the following pages, therefore, it will
be necessary to consider, to a certain extent, both types of fermenta-

vii

Vlll PREFACE TO FIRST EDITION.-

tion. While both must be described and discussed, the bacterio-
logical fermentations will demand most of our attention. For all of
these reasons the limits which we shall draw to the subject of
agricultural bacteriology are somewhat arbitrary, and some of the
topics here considered may not be regarded as belonging strictly
to the subject. All of them, however, have at least an incidental
relation to the farmer and his industry.

H. W. C.

MiDDLETOWN, CONN.

TABLE OF CONTENTS.

PART I.

General Nature of Microorganisms and Their Activities.

CHAPTER PAGE

I. — The General Characters of Microorganisms . ... i

II. — ^Fermentation, Putrefaction, and Decay 22

PART II.

Bacteria in Soil and Water.

III. — Nature's Food Supply. The Carbon Cycle . ... 37

IV. — Decomposition of Nitrogenous Compounds .... 47

V. — Nitrification and Denitrification 57

VI. — The Manure Heap and Sewage 69

VII. — Reclaiming Lost Nitrogen 90

VIII. — Bacteria and Soil Minerals in

IX. — Some Practical Lessons from Soil Bacteriology. . . 118

X. — Bacteria in Water 127

PART III.

Bacteria in Dairy Products.

XL — Bacteria in Milk 137

XIL— Control of the Milk Supply . . 165

XIII. — Bacteria in Butter-making 181

XIV. — Bacteria and other Microorganisms in Cheese-making 195

ix

X TABLE OF CONTENTS.

PART IV.

Relation of Microorganisms to Miscellaneous
Farm Products.

CHAPTER PAGE

XV. — Alcohol, Vinegar, Sauer Kraut, Tobacco, Silage,

Flax 211

XVI. — Preservation of Food Products 235

PART V.

Parasitic Bacteria.

XVII. — Resistance Against Parasitic Bacteria 251

XVIII.— Tuberculosis 261

XIX. — Other Germ Diseases 280

XX. — The Parasitic Diseases of Plants 293

PART VI.

Appendix.

XXI. — Laboratory Work and Disinfection 307

Index 327

PART I.

GENERAL NATURE OF MICROORGANISMS AND
THEIR ACTIVITIES. .

CHAPTER I.
THE GENERAL CHARACTERS OF MICROORGANISMS.

MICROORGANISMS AND FARM LIFE.

The successful farmer of to-morrow will be the one who most
skillfully regulates the growth of microorganisms. Though he
may not be conscious of it, much of the work that the farmer is
carrying on even now is, as we shall see, really directed toward the
control of germ life. In the consideration of the microorganisms
related to farm life we are concerned with three different types of
plants : Bacteria, Yeasts and Higher Fungi. Although the latter are
plants of considerable size, and hence hardly microorganisms, in many
respects they are related to the microscopic bacteria and yeasts,
and the functions of all three in farm life are so similar that all
must properly be considered together. The molds, being plants
of considerable size, have been known a long time, although only
recently has their relation to nature's processes been understood.
Yeasts were used, under the name of leaven, far back in history;
but it was not till 1680 that the Dutch microscopist, Leeuwenhoek,
showed with his microscope that yeast consists of minute globules;
and it was 150 years later when Schwann and Caignard-Latour
proved yeast to be a living plant. Leeuwenhoek was also first to
see bacteria, and studied them as early as 1695. His descriptions,

I

2 THE GENERAL CfiA.RACTERS OF MICROORGANISMS.

corisiSefing the fad f Rat Tie* had only simple lenses to work with,
were remarkably correct. Even his suggestions concerning their
nature sound quite modern and were certainly superior to much of
the speculation that followed. He intimated that they might be the
cause of disease. But for 150 years after Leeuwenhoek, although
the microscope became a familiar plaything, it was hardly thought
that these minute organisms offered a subject for serious study.
For a century they were simply objects of speculation, and many
were the exclamations which they excited as to the wonders of nature,
with here and there a suggestion as to their possible importance in
producing certain natural phenomena.

Relation to Disease. — Not until toward the middle of the
nineteenth century was it conceived that the microscopic organisms,
at first grouped together under the general head of animalculce,
could have more than scientific import. At that time there began
to appear suggestions as to their possible relations to certain diseases,
and almost simultaneously they were thought of as csiusmg fermen-
tations. Even before it was known what yeast was, it was recognized
as in some way associated with alcoholic fermentation; but not till
about 1838 was it clearly proved that yeast plants are the cause of
the fermentation of sugar. The development of a knowledge of
bacteria fallowed a little later. One of the first real contributions
to a knowledge of their significance was the demonstration in 1840,
of the fact that certain microscopic organisms cause blue milk.
Thus, at the very beginning of the modern study of bacteria, they
were associated with peculiar agricultural phenomena, an interesting
fact when we notice that, in the next quarter of a century or more,
the chief investigations, and all the interest in them, centered around
the question of their agency in producing disease. Bacteria are
still suffering in reputation from the fact that, for thirty years, they
were studied by microscopists chiefly from the standpoint of their
agency in the production of disease. It was quite early suggested,
and soon demonstrated, that these little plants have the power
of producing certain dreaded diseases, and the reputation which
they thus obtained still clings to them. The very word bacteria, or
germs, has become, in the minds of some, almost synonymous with

MICROORGANISMS AND FARM LIFE. 3

disease. Their relatiou to the medical profession was soon
recognized, and more or less extended courses in bacteriology have
rapidly made their appearance in medical schools. Health boards
and sanitary officers have recognized that their primary duty is
to deal with bacteria; and most of the regulations for the preserva-
tion of the public health have been directed toward the destruction
or control of these organisms.

As more information has accumulated during the last twenty
years or so, it has become evident that microorganisms, including
bacteria, do not deserve all the ill repute that they have acquired.
It has been learned that there are hundreds and even thousands of
kinds of bacteria, and that, while certain species are the cause of
disease, others are harmless, some are beneficial in the body, and
many perform functions of the highest significance and value.
Although the disease side of the bacteria story was the first to be
studied, it is only a small part of the subject. Among the many
hundred kinds of bacteria known, only a few, less than two score,
are as yet definitely known to have any power of causing disease
in man. As bacteriologists have widened their views and looked
outside of the human body, they have found that these organ-
isms are not only excessively abundant in nature, but have
relations to the phenomena of living things which were wholly
unsuspected. Within the last twenty years a larger and larger
amount of attention has been directed to the part played in nature
by microorganisms which are never parasitic and have no relations
to human disease. As a result there has developed a new branch of
bacteriology which deals with phenomena wholly separate from
disease.

Relation to Agriculture. — In particular it has been shown
that bacteria are related to agriculture. Not only is it true that
they are the cause of certain animal and plant diseases with which
the farmer has to contend, but it is becoming manifest that they are
intimately associated with many normal processes which are going
on in the soil, water, and elsewhere, and that they are fundamental
to the processes of agriculture.

The agricultural side of bacteriology is, if possible, more impor-

4 THE GENERAL CHARACTERS OF MICROORGANISMS.

tant than the pathological side. If the medical student needs to
know something of these organisms and their relations to disease,
even more does the agriculturist need to understand their relations
to his industry. These microorganisms play such a fundamental
part in the processes of nature that the life phenomena of animals
and plants are inextricably bound up in the functions of bacteria,
and without them life processes must soon cease. The physician,
in the curing of disease, gains a certain advantage from his knowl-
edge of bacteria; but the farmer is obliged to make use of these
agents in a large number of his farming processes; hence, it is a
matter of necessity that the agriculturist of the future should have
a practical knowledge of the general phases of bacteriology. The
solution of the most vital agricultural problems, like that of continued
soil fertility, involves bacteriology. From beginning to end the
occupations of the farmer are concerned in the attempt to obtain the
aid of these microorganisms where they may be of advantage, and
to prevent their action in places where they would be a detriment.
The farm cannot be properly tilled unless the farmer has, in addi-
tion to his seed crop and cattle, a stock of the proper kind of bacteria
to aid him in preparing the soil and in curing the crops. Farming
without the aid of bacteria would he an impossibility, for the soil would
yield no crops.

The relation of microorganisms to farm life is one of the most
recent branches of science. Scarce twenty years have elapsed since
the first steps in this direction were taken, and some of our scientists,
who are still young, have seen practically the whole development of
the subject from its starting-point in the early eighties. With a
science as young as this, it is inevitable that many questions remain
unsolved. Scientific discovery usually precedes any practical
application, and in these early years of the development of agricul-
tural bacteriology we must expect to find the theoretical side of the
subject proceeding rapidly, while the application of the facts to
farm methods lags behind and is, in many respects, hesitating,
tentative, or even unsatisfactory. Nevertheless, the discover-
ies made have already revolutionized agricultural processes.
Changes in agricultural methods, due to bacteriology, have been

WHAT ARE MICROORGANISMS.'' 5

largely adopted all over the world; but they have generally been
adopted by farmers in ignorance that they are benefiting from
bacteriological research. That these practical applications of
bacteriology to agricultural processes will increase with the next
few years is certain. Successful agriculture of the future is in-
dissolubly bound up in the problem of the proper handling of
microorganisms. We have reached a point where every advanced
farmer, who wishes to put himself into a proper condition to make
the best use of the means at his disposal and to profit by discoveries
as they are made, must at least have a general knowledge of the
fundamental factors of bacteriology as they are related to agriculture.

WHAT ARE MICROORGANISMS?

In studying the relation of germ life to the farm we are concerned
with a class of phenomena called fermentation, putrefaction, decay,
decomposition, and the like (see Chapter II). These phenomena
are all caused by living bodies that are frequently called microorgan-
isms. This term strictly means animals or plants of microscopic
size. But this conception of the term is at once too narrow and too
broad to cover the organisms we are to study. Some microscopic
organisms have no particular relation to the classes of phenomena
which we are considering. A great host of microscopic, green
water-plants and also many microscopic animals have nothing to do
with our subject, though they might properly be called micro-
organisms. On the other hand, some plants of large size, like molds
and toadstools, have a part to play in producing the decomposition
of organic structures very similar to that played by bacteria. These
cannot properly be called microorganisms, but nevertheless they
must be included with the study of bacteria and yeasts, since they
perform similar or closely allied functions in nature. A better term
to cover the organisms which we must study might be the rather
broad term of Fungi, for all of the organisms with which we are
concerned belong to this general class of plants. But this term is
also unsatisfactory, since it fails to convey the idea that the organisms
are largely microscopic. To most people the term fungus gives at

6 THE GENERAL CHARACTERS OF MICROORGANISMS.

once the impression of a large plant; and we are chiefly concerned
with microscopic forms. We shall, therefore, still use the term
microorganism, although some of the plants that we shall refer to
are not microscopic. In this discussion we are concerned chiefly
with Bacteria, secondarily with Yeasts, and to a less degree with
the Higher Fungi.

The Fungi. — All of the plants with which we are here concerned
belong to the class that botanists call Fungi. There is one charac-
teristic common to all Fungi — they all lack green coloring matter.
This green coloring material in ordinary plants makes it possible for
them to live upon the mineral ingredients in the soil; and green
plants only can be thus nourished. The colorless plants are
unable to obtain nourishment from the mineral world. The Fungi,
since they are all colorless, must live upon food furnished them by
other plants or animals. It is this fact that gives them their signifi-
cance in nature, and explains their important relations to farm life.
Fungi are very abundant everywhere, and there are thousands of
different kinds. For the purpose of our study, we may recognize
three groups:

I. Higher Fungi. — Under this general name we will include a
large number of colorless plants, mostly of large size. It includes
such plants as molds, mushrooms, toadstools, tree fungi, and hosts of
others less commonly known. Some of them are of great importance
in farm life, especially as agents in bringing about the decomposition
of vegetable matter, so that it may be incorporated into the soil to be
used again; here they play a part secondary only to bacteria. They
are of endless variety, and it would be manifestly impossible here to
attempt any consideration of their classification. One point con-
cerning them must be understood. In all the higher Fungi with
which we are concerned the body of the plant consists of a mass of
delicate threads which grow into a dense, usually white mass (Fig. i).
Sometimes the threads are large enough to be seen easily and some-
times they are so delicate that a microscope is required to see the
individual threads, though the mass of threads may be of consider-
able size. The mass of threads grows on the surface or in the
substance upon which the plant is feeding. This thread is able

WHAT ARE MICROORGANISMS? 7

in many cases, by growing, to force its way into the solid mass
of hard substances, like wood, and to push itself between the wood
fibers. Thus it is a primary agent in effecting the destruction of
wood. Such a mass of branching threads is called a mycelium, and

Fig, I, — One of the higher fungi, the common bread mold, Penicillium glaucum.
a, the whole plant; b, one of the spore-bearing branches more highly magnified.

is found in all the Fungi of this class. So far as the mycelium is
concerned, most of these plants are much alike. But the different
species have many different methods of reproduction, and it is
chiefly upon their reproductive bodies that botanists rely to distin-

FiG. 2. — Mucor, a common mold,
showing mycelium and spore for-
mation.

Fig. 3. — Aspergillus, a common mold, show-
ing mycelium and spore formation.

guish the different species. After the mycelium has grown for a little
time, it commonly sends up into the air small or large branches that
produce spores, or reproductive bodies. The method of spore
production differs sufficiently in the different fungi to make it

8 THE GENERAL CHARACTERS OF MICROORGANISMS.

possible to classify them. Frequently only the spore-producing part
of the plant is seen, and it may be the only part known, except
to botanists. For example, the toad stool is only the reproducing
portion of a fungus; it has a mycelium wholly under ground or
buried within the hard mass of the trunk of a tree. It is the myce
lium, however, that does the work for which these fungi are re
sponsible, and not the spore-producing part that we see. Figs, i to 3
show the general appearance of some of these fungi and their
methods of forming spores. With these methods of reproduction
and classification we are not concerned in this work, and only such
types as are related to our subject will be mentioned later in their
proper places.

2. Saccharomyces (Yeasts, Budding Fungi) . — These immensely
important plants are all microscopic in size. While varying
somewhat, an average size is, about i /4000 of an inch in diameter.
They are usually spherical or oval in shape, though sometimes
slightly elongated (Fig. 4, a). They form no mycelium and cannot
force their way into hard substances. Their
chief characteristic is their method of reproduc-
tion by a process called budding. There appears
on the side of the yeast cell a minute bud, which
continues to increase in size until it becomes as
large as the cell from which it has grown. Then
Fig. 4.— Yeast the two cells may break apart at once; or each
me^hVd'if'g^rowth by ^^Y ^^ ^^^^ producc buds before they separate,
budding, a, single In either casc, two or more cells are produced

cells; &, budding cells, r i 1 i 1 i i

from the one, and although they may remam
attached so as to form irregular masses of several cells, (Fig. 4, b),
each cell is really complete in itself. Eventually they break apart.
This budding takes place rapidly, though not so rapidly as the
division of bacteria, which will be mentioned later.

A second important character of yeasts is the nature of the
fermentation they produce. They have an action especially upon
sugars, which they break up into carbonic acid and alcohol. This
action makes them play a large part in nature's processes, quite
distinct from that of bacteria.

GENERAL CHARACTERS OF BACTERIA. 9

Any further classiiication of yeasts is quite unnecessary for our
purposes.

3. Schizomycetes {Fission Fungi, or Bacteria). — This group
comprises the bacteria proper; it is certainly the most abundant
of the three, and in some respects it is the most important. It
is with the bacteria that we are chiefly concerned in this work.
Bacteria have sometimes much the same shape as yeasts. The
chief distinction between them is their method of multiplication.
Instead of budding they multiply by fission. The bacterium
elongates a little, and then divides into two equal -<-\ ^ — n

halves at once (Fig. 5). Hence the name fission —

fungi. Bacteria are also, as a rule, smaller than . — . /"^^^
yeasts, frequently not more than 1/25000 of an ^^^ \.^
inch in diameter. The size would make it possible {"^^

for 8,000,000,000 to be crowded into a mass no ^-^V/

larger than a pinhead; and we can, therefore, easily si^wing~mrthod
understand that there may be 100,000,000 in a ofdivision by
drop of milk. Occasionally, however, there are
larger bacteria and smaller yeast cells. While the size is no sure
criterion between the two, when one finds, under the microscope,
rather large round or oval plants, he is pretty safe in calling them
yeasts, while the smaller ones he may call bacteria. But it is
necessary, in some cases, to study the method of reproduction before
one can with certainty distinguish yeasts from bacteria.

This group of bacteria is of such primary importance to our
study that we must learn further facts concerning their classifica-
tion and characters.

GENERAL CHARACTERS OF BACTERIA.

Colonies. — Bacteria are so minute that they cannot be handled
as individuals, but must be treated in masses. One of the primary
difficulties in the study of these organisms has been to get masses
of bacteria that would be large enough to handle, and yet would
contain only one kind of bacteria. Such masses are called pure
cultures, and it was this difficulty in procuring pure cultures that

lO THE GENERAL CHARACTERS OF MICROORGANISMS.

for a long time prevented the development of the. science. Bacterio-
logical study to-day commonly begins with cultivating the bacteria,
i.e., allowing them to grow in some medium adapted to them until
they become abundant enough to be handled in bulk. To prevent
the mixing of the different kinds that may be in the material we are
studying, they are usually grown in a solid or jelly-like medium,
which holds the individuals fast in one spot. As the individuals
multiply in this solid medium, they are unable to separate from each
other; so they remain in little clusters which in time become large

enough to be seen without a microscope.
Such clusters are called colonies, and
figures of some of them are shown in Fig. 6.
The shape and appearance of the colonies
produced by different kinds of bacteria are
often very different, showing, indeed, greater
Fig. 6.-Colonies of bacteria, varieties than can be seen in the bacteria
themselves with a microscope. As a result the shape and appear-
ance of these colonies are often used to separate the numerous
bacteria from each other and to classify them. A colony, when it
comes from the multiplication of a single individual bacterium, is
made of one kind of bacteria only. This colony may easily be
picked out with a sterile needle, and when properly placed in
another culture medium it becomes a pure culture. The starting-
point in practical bacteriological study is thus the colony rather
than the individual bacterium (see Laboratory Work).

Form of Bacteria. — Bacteria are of three quite different shapes,
but are all very simple, i. Simple spheres (see Fig. 7, a). Such
spherical forms are called Cocci. In common microscopical
preparations no internal structure can be seen, the bacteria appearing
as deeply stained balls. The Cocci, however, differ somewhat
in their method of growth, thus enabling the microscopist to distin-
guish different kinds, as will be mentioned presently. 2. The rod-
formed bacteria (Fig. 7, h). These organisms are longer than they
are broad, sometimes only slightly so, but at other times very much
longer, forming, indeed, long, slender threads. 3. The spiral-
formed bacteria. These are either long, coiled spirals, or very

GENERAL CHARACTERS OF BACTERIA.

II

short ones, with only a single turn (Fig. 7, c). This type is of less
importance than the others.

Motility of Bacteria. — The next point of distinction among
bacteria is based upon their motility. Some bacteria are capable
of an active swimming motion, others are stationary. The motion
is produced by minute, extremely delicate, vibrating hairs, called

Fig. 7. — General shape of bacteria, a, spheres; &, rods; c, spirals.

flagella (Fig. 8). The flagella are so delicate that they cannot often
be seen in the living bacteria, and they do not stain by the ordinary
method of staining. Therefore, they are never seen in the usual
microscopic preparations. They may be seen by special methods,
but these are so difficult that the beginner cannot use them satisfac-
torily. The question of their motility is, however, usually determ-

FiG. 8.— Showing bacteria with flagella; a, peritrichic; 6, lophotrichic; c, monotrichic.

ined without staining, by the study of the living bacteria (Experiment
No. 8). These flagella are differently distributed upon different
bacteria. Sometimes there is a single one on the end of a rod
(Fig. 8, c) — monotrichic; sometimes a small tuft at one or both ends
of a rod (Fig. 8, b) — lophotrichic; and sometimes there is a cover-
ing of flagella over the whole body of the bacterium (Fig. 4, a) —
peritrichic.

12 THE GENERAL CHARACTERS OF MICROORGANISMS.

Classification. — Based upon the distinctions thus mentioned,
the bacteria are divided into groups:

Spherical Bacteria:

Dividing in one plain, so as to form chains (Fig. 9, a), Strepto-
coccus.

Dividing in two plains, and not forming chains (Fig. 9, h),
Micrococcus.

Dividing in three plains, and forming
cubical masses (Fig. 9, c), Sarcina.

Rod-shaped Bacteria:

With flagella and consequently
motile (Fig. 8)*, Bacillus.
Without flagella and consequently
Fig. 9.— Showing different non-motile (Fig. 7, h) , Bacterium.

types of COCCI, a, &, and c, Micro- . \ o / ^ / :>

cocci; d, Streptococci; e, Sar- With a single flagellum, Pseudo-

cina. _„ _ _, ^ _

monas.
Spiral Bacteria (Fig. 3, a), Spirillum.

The genus Bacillus is further divided as follows:

Bacilli with only one flagellum (Fig. 8, c) are named Mono-

trichic Bacilli, or Pseudomonas.

Bacilli with one flagellum at each end, Microsporon.

Bacilli with a tuft of , flagella at one end (Fig. 8, b), are called

Lophotrichic Bacilli.

Bacilli with flagella over the whole body (Fig. 8, a) are called

Peritrichic Bacilli.

Higher Bacteria (Cladothrix, Leptothrix, Streptothrix, Actinomyces)
(Fig. 10).
Under this head are included a few forms of fungi which re-
semble other bacteria in some respects, but differ in others. They
are composed of threads which are commonly larger than the

*Unfortunately bacteriologists are not agreed to-day in regard to the
use of the terms above given. The names Bacillus and Bacterium are not
always used as here stated, and recent classification of the spherical forms
recognizes, in addition to the names given, three others, Diplococcus, Meta-
coccus, and Ascococcus. This variation in nomenclature results in great
confusion. In the absence of any well-accepted classification to-day, we
shall in this book use the names 'as above defined.

GENERAL CHARACTERS OF BACTERIA.

13

threads of bacteria, and .which may show frequent branching, a
characteristic not usual in bacteria. They also have a peculiar
method of forming reproducing bodies. The group is not one of
very great importance. One type of Streptothrix is extremely
abundant in soil and appears as round, white opaque colonies with
an extensive brown halo upon the plates described in Experiment
No. 24.

Thus it will be seen that the term bacteria applies to the whole
group of organisms that multiply by division, the study of which
constitutes the study of bacteriology, while
the term Bacterium refers to a single division
of the group, viz. : the non-motile, rod forms.
The term Bacillus should apply to motile
forms only. The names Bacillus and Bac-
terium are sometimes confused; for example,
the tubercle bacillus, according to the above
classifiication, is a Bacterium, since it is non-
motile; and indeed recent study indicates that
it belongs to the group of higher fungi; but the
name bacillus was given it years before the
above distinctions were recognized, and we
will still use the common name. Some other
bacteria, named twenty years ago, retain their
earlier names in some books, but they are
slowly having their names brought into
harmony with the above distinctions.

The term Coccus is applied to any spherical organism of the
group bacteria.

This classification gives only what are recognized as the genera
of bacteria. A further classification of the group into species is at
the present time in a condition of the greatest confusion. Many
hundred varieties have been described by different bacteriologists,
but there is great difficulty in giving any distinctive description of
such minute organisms, which have so few characters; and it is
quite uncertain whether these many hundred described species
represent distinct forms or whether they should be reduced to a

Fig. 10, — Actinomy-
ces, a, a small colony;
h, bingle rods {Bostrom).

14 THE GENERAL CHARACTERS OF MICROORGANISMS.

much smaller number of species. It is frequently uncertain whether
a species described by one bacteriologist is the same as that de-
scribed by another under the same name. The difficulties in the
way of a proper description and classification of the species of
bacteria have hitherto been insurmountable, and at the present
time the subject is in such extreme confusion that no one except an
expert can understand it. Fortunately this confusion of species
is of no importance for our purpose. Agricultural bacteriology is
not at present concerned with the problem of the species. All that
it is necessary for us to know in connection with our subject will be
referred to in the separate sections in the following pages, and the
subject of the classification of bacteria may be left without further
consideration.

Multiplication of Bacteria. — As already mentioned, the
primary method of the multiplication of bacteria is by simple
division. Bacteria are so minute that it seems strange to assign
to them much of a part to play in nature's processes. But their
extraordinary power of multiplication gives them unlimited possi-
bilities.

The elongation of a rod and its division into two parts, followed
by a repetition of the process, may be extremely rapid. Frequently
it does not take more than half an hour for the whole phenomenon
to take place, and sometimes even less time is required. Such
division, in geometrical ratio, results in an increase in numbers
that is almost inconceivably great. If a division once an hour
could be maintained for twenty-four hours, there would be pro-
duced, as the offspring of a single bacterium, some seventeen million
descendants, and in five days there would be a mass sufficient to fill
the oceans. This rate is, manifestly, iiot continued for any great
length of time, or the world would be full of them; their growth is
checked by lack of food, and still more by the substances they se-
crete, which act as poisons. But this possibility of reproduction
represents an almost unlimited power, constantly curbed by the
lack of proper conditions. Bacteria may thus be looked upon as
possessing a wonderful possibility of reproduction, a force of in-
conceivable magnitude, held more or less in check by adverse condi-

I

GENERAL CHARACTERS OF BACTERIA. 1 5

tions, but ever ready to exert their influence when the conditions are
favorable. Since they are feeding during their growth, they must
produce profound changes in the material upon which they feed.
It is this reserve force, possessed in greater or less degree by all
bacteria, which makes them such wonderful and powerful agents
in producing the great changes in nature which we are now forced to
attribute to them.

Production of Spores. — There is another method of produc-
ing new individuals, an understanding of which is necessary to a
knowledge of bacteria. This is the production of spores, and is
illustrated in Fig. ii, a-e. The bacterium there figured consists of
a rod. The contents of one of the rods ^^ ^^ ^...^
collects itself in a spherical or oval body in <^ 3 c cT V^
the center. This later breaks out of the V.^ ^

rod, the rest of the individual then dying 4^^J>o ¥

and disappearing. The oval body itself is ^T^ y^^^ /in ^
a spore, and is capable, when placed under ^ ff V^

proper conditions, of developing into a new "^ ^ ^^

rod, e. Inasmuch as only a sinde spore

- .11 . . . Fig. II. — Spore formation.

arises from a smgle bacterium, it is not a a to «, stages in spore for-
multiplication. Its purpose is not so much °^^t^°^ ^^^ germination.
to increase the number of individuals as to enable the bacteria to
endure adverse conditions without being killed. The ordinary bac-
teria are likely to be killed by being dried, and will readily succumb
to moderate heat, a temperature of 165° F.* being sufficient to kill
almost any of them. But these spores are covered with a hard case
which enables them to resist the conditions which the active, growing,
and multiplying forms cannot resist. They may be completely dried
for months, and even years, and still retain their vitality. They may
be heated very much hotter than the active forms without injury; in-
deed, some of these spores may be in boiling water for many minutes
— an hour or longer — without having their vitality destroyed, since,
if the spores are subsequently cooled, they are capable of germinating
and growing into new bacteria. As a result of this it will follow
that, while it is very easy to kill ordinary bacteria by heat, it is
* Temperatures used in this book always refer to the Fahrenheit scale.

l6 THE GENERAL CHARACTERS OF MICROORGANISMS.

far more difficult to destroy spores. Many species of bacteria
produce such spores (Fig. ii, /) ; others do not, and hence some are
much more easily killed by heat than others. Milk, for example,
contains many kinds of bacteria. By the simple boiling or, indeed,
the heating of the milk to a temperature of i6o° F., a vast majority
of the bacteria are killed; but the few spores that may chance to
be in the milk are not thus killed, and subsequently these will be
able to develop. If milk contains spore-bearing bacteria, it cannot
be sterilized by boiling; and, since it almost always does contain
them, boiling is not sufficient to sterilize it. This phenomenon of
the high resisting powers of spores must always be borne in mind
in all problems of sterilizing.

Relations to Conditions. — Temperature. — The rate of multipli-
cation of bacteria, yeasts, and molds depends upon the temperature.
At freezing they do not grow at all. As the temperature rises above
freezing they begin to multiply, and their rate of multiplication
increases as the temperature rises, up to a certain point which is
the optimum temperature. If the temperature rises still higher,
the rate declines and finally growth stops. If heated still more,
the organisms are killed. The lowest temperature at which they
will grow, the minimum temperature, varies with different species.
Some will grow at a temperature only just above freezing, at ^2>° F.,
while, at the other extreme, some will not grow at temperatures
lower than 120° to 140° F. The optimum temperature also varies.
Some species grow best at moderately low temperatures, 60° or
as low as 50° F., while others flourish best at a temperature from
90° to 100° F. When the temperature -is above 100°, most bacteria
grow less rapidly than when it is a little lower, while at a slightly
higher temperature they cease growing. A few species, however,
grow best at unexpectedly high temperatures, some having been
found flourishing at 140° or even higher. These peculiar bacteria
are called thermophiles. How they can find conditions in nature
warm enough for their growth is a question.

The death temperature is a factor of great importance, since it is
so closely associated with the matter of sterilization by heat. Most
bacteria, when in an active condition, are killed by a temperature

GENERAL CHARACTERS OF BACTERIA.

17

'^'^^Sw^issa*^*!!

^^K>f 140° if maintained for half an hour. At this temperature,
however, they die slowly; a temperature of 150° destroys them more
l^jrapidly still, while a temperature from 170° to 180° is proportionately
^^Bwiore effective. A total destruction of bacteria, including their
spores, can be brought about only by a temperature above that
of boiling water, and this is usually accomplished, in the case of
liquids, in a closed chamber where the
team can be generated under con-
siderable pressure. If the steam is
Illowxd to collect in such a chamber
t a pressure of 15 pounds, the tem-
erature, then, will be about 240°.
^his temperature, kept up for half or
three-quarters of an hour, destroys
even the most resisting spores. Lab-
oratories usually have a small appa-
ratus designed for this purpose, called
an autoclav (Fig. 12), and this is used
constantly for sterilizing liquids.

Sterilization. — This is a process
closely related to the question of death
temperatures. Sterilization is some-,
times, to be sure, brought about by
adding poisonous chemicals to the
material to be sterilized; but more
commonly, and almost universally,

when we are dealing with food products, sterilization is accomplished
by heat. If a material to be sterilized contains only active organisms,
it might be accomplished by subjecting it to a moderately low
heat, 140° to 150° F. But it is almost always a fact that anything
which we wish to sterilize is likely to contain spores, and, since
these withstand a higher temperature, no moderate heat will
accomplish the purpose. Even boiling is not sufficient to destroy
spores, so, to be sure of complete sterilization, a temperature above
boiling is necessary. If the object is a solid that can bear heat
it is simply heated at about 300° F. for an hour or so. If it is a

Fig, 12, — An autoclav used in
sterilization of liquids under pressure
{Eyr).

l8 THE GENERAL CHARACTERS OF MICROORGANISMS.

liquid it is placed in an autoclave (Fig. 12), and heat is applied until
there is a steam pressure from 10 to 15 pounds. This produces a
temperature sufl&cient to destroy spores.

Sometimes it is desirable to sterilize liquids that will not stand
these high temperatures, as, for instance, gelatin (Experiment No.
1 2) . This can be accomplished by discontinuous heat. The material
is heated to about 180° F., or more commonly to boiling. It is then
cooled and allowed to stand twenty-four hours in a warm place.
The heat has destroyed the active bacteria, but has not killed the
spores, which, during the twenty-four hours, will germinate and
grow into active bacteria. Heat is again applied as before, and this
time any active bacteria that may have come from the germination
of the spores are killed. The material is allowed to stand another
day so that any spores that may have failed to germinate the first
day may grow, then heat is applied again. Experience shows that
three heatings of this sort will destroy all the organisms and
sterilize the liquid. To be successful in this method it is necessary
that the interval between the heatings should be long enough for
the spores to germinate, but not long enough for the bacteria
arising from them to form any more spores. Twenty-four hour
intervals have been found to be the best.

Relation to Cold. — While heat will destroy all bacteria, cold will
not do so. It is practically impossible to destroy the life of bacteria
by freezing, at least with any certainty; for no matter how low the
degree of temperature used, the life of some of these organisms seems
to be totally resistant. Experiments have shown that bacteria
cooled to the temperature of liquid air, or even liquid hydrogen, are
not all killed, but after being warmed are still able to germinate.
Although these extremes of temperature, do not destroy all bacteria,
the simple matter of freezing and thawing will kill a great number
of them. If water containing a large number of bacteria is frozen
and subsequently thawed, the bacteria will be found much reduced
in numbers, although they are not by any means all killed. When,
therefore, water is contaminated by sewage containing typhoid
bacteria, and ice is collected from it for domestic purposes, the
typhoid bacteria may still be found alive in the ice. Such ice may

GENERAL CHARACTERS OF BACTERIA.

19

still be a source of danger. But it must also be remembered that
freezing destroys a very large proportion of these germs, so that the
danger from the ice is far less than from the water before it was
frozen.

Relation to Air. — Nearly all living organisms require air, and it
was formerly supposed that nothing could live without it. Certain
types of bacteria, however, are able to live without air. Indeed,
some species, while they grow readily if they have no contact with
air, fail to grow at all when the slightest amount of air is present,
growing only in the absence of oxygen. This type of bacteria is
spoken of as anaerobic. At the other extreme, there is a long list of
bacteria which can grow only in the presence of air', failing to grow
if they do not have oxygen at their command. This is the type of
aerobic bacteria. Between the two is an intermediate group
capable of growing either in the air or out of contact with it, and
these are spoken of as facultative anaerobic.

Relation to Moisture. — Bacteria will grow only in the presence of
considerable quantities of moisture; indeed, they demand more
moisture than most organisms. Some of them will hardly grow at
all unless there is 30 per cent, of moisture in the material in which
they are living, and even then the growth is slow. On the other
hand, they flourish most luxuriantly in localities where the water is
from 90 to 100 per cent. Hence, as materials dry, bacteria will
cease to grow in them, and any substance that can be dried can be
thoroughly protected from their action. This explains why dried
fish and dried meat, fruits, dried milk, etc., will keep indefinitely.
The drying, however, does not actually kill the bacteria, for al-
though they do not grow when the water is extracted from them,
they may remain alive for weeks, months, or even years. In other
words, it is impossible to depend upon drying as a means of de-
stroying bacteria, for, while many individuals will fail to live, many
others do not seem to be injured at all by the drying, and are capable
of resuming life again as soon as they find moisture.

Yeasts are much like bacteria in respect to need for water, and
will not grow unless the water content is high. But other fungi
with which we are concerned, the molds and mushrooms, can get

20 THE GENERAL CHARACTERS OF MICROORGANISMS.

along upon a smaller amount of water. Substances that are too
dry to putrefy may be spoiled by molding; hence it is much more
difficult to preserve certain kinds of partly dry food from moulding
than from decaying. Flour, in a flour barrel, may become musty
from the development of molds, but it will hardly show signs of
decay or putrefaction unless it becomes actually wet.

Relation to Food. — Bacteria and the other fungi feed upon an
immense variety of foods. A few of them are able to nourish
themselves upon mineral matter, and some can gain their necessary
carbon from the small amounts of carbon dioxide in the air, re-
sembling, in this respect, the green plants that are engaged in build-
ing up starch and other organic compounds. This class of bacteria
is of great theoretical interest and doubtless of much importance in
nature. But the vast majority of microorganisms are unable to use
mineral foods, requiring, like animals, to be fed with organic food.
In other words, they require for their life the same kind of foods
that the animal kingdom requires. They can consume proteids,
starches, sugars, fats, woody tissue, and, in short, almost anything
that is found in the bodies of animals and plants. The different
varieties of microorganisms do not all flourish upon the same kind of
food. Some seem to be able to live upon a large variety of sub-
stances, while others demand particular foods. While almost any
kind of proteids will serve for the sustenance of the common putre-
factive bacteria, the tubercle bacillus does not flourish well anywhere
outside the living body, and, if it is to be cultivated in the laboratory,
it demands a very special kind of culture medium. But speaking
in broad terms, the three classes of organisms with which we are
concerned in our subject, seem to be particularly adapted to different
kinds of food. Bacteria have special relations to proteid foods,
like lean meat, egg albumen, gluten of wheat, etc., and if substances
of this nature are consumed by microorganisms, it is commonly by
bacteria. Yeasts, on the other hand, have a special fondness for
sugars and, therefore, for starches, which are easily changed into
sugars. The larger fungi may feed upon either proteids or sugars,
but they have special relations to the woody tissues and celluloses of
vegetable structures. This classification of the foods upon which

GENERAL CHARACTERS OF BACTERIA. 21

these different forms subsist is by no means exact, for each group
may contain members that make use of all kinds of foods; but,
generally speaking, the higher molds and mushrooms attack the
, harder plant tissues, the yeasts attack sugars, while the bacteria are
especially concerned in the destruction of proteids.

The food which bacteria consume may be either living or dead
when they attack it. In the case of most bacteria the organisms
are unable to feed upon the material while it is alive. If bacteria,
for example, are placed upon living muscle, they are usually unable
to attack it and soon die; but if they are placed upon the same
muscle after it is dead, they feed upon it readily and cause it to
putrefy. Those organisms which feed upon lifeless bodies include
the vast majority of bacteria. There are, however, other species
that are capable of living upon the bodies of animals and plants
while these are still alive. Inasmuch as they can feed upon living
organisms they are liable to produce disease and constitute in general
the disease bacteria. Bacteria feeding upon living animals and
plants are called parasites. Bacteria feeding upon dead animals
and plants are called saprophytes. Both saprophytes and parasites
are of great importance.

CHAPTER II.

FERMENTATION, PUTREFACTION, AND DECAY.

THE NATURE OF THE ACTIVITIES OF MICRO-
ORGANISMS.

Everyone at all familiar with nature must realize that there is
constantly going on, in earth, water, and air, an uninterrupted series
of slow changes. Rocks disintegrate; fruits decay and their juices
ferment; vegetables rot; animal bodies putrefy; milk sours; cheese
ripens; the soil becomes contaminated by the decaying waste of
sewage and then purifies itself; streams become foul and grow clear
again; even tree trunks rot and disappear. These and hosts of
other kindred phenomena are matters of such every-day occurrence
that we scarcely ever stop to think what they mean or how they are
brought about. But it is with these phenomena that we are chiefly
concerned in the study of germ life on the farm. These changes
have one characteristic in common: they are all the result of chemical
decomposition. Until recently it has been supposed that they are
the result of purely chemical forces. The chemical agency of
oxidation, especially the so-called slow oxidation, has been supposed
to account for most of them.

But it has been proved by modern study that pure chemical
forces are not able to produce these phenomena, and that many a
process formerly called slow oxidation is not the result of chemical,
but rather of biological forces. If microorganisms can be kept from
them, fruits will not decay, vegetables will not rot, and many other
changes will fail to appear. Most of the slow changes referred to
are the result of the action of the great class of fungi, foremost
among which stand the bacteria and yeasts. The reason why these
organisms are so closely associated with phenomena is because they
are capable of bringing about profound chemical changes.

22

CHEMICAL CHANGES PRODUCED BY MICROORGANISMS. 23

From facts already considered it will be evident that micro-
organisms have properties that certainly fit them for this work.
They feed, not upon minerals, as a rule, but upon the organic
material in nature; and each kind of organic food, proteid, sugar,
starch, wood, etc., is especially subject to the attack of one of the
classes of fungi. We have seen also what inconceivable powers of
multiplication are possessed by^bacteria, and, while the other or-
ganisms do not grow so fast, they are all rapid growers. While they
are growing and multiplying with such vigor, they are producing
profound changes in the chemical nature of the food upon which
they are feeding.

CHEMICAL CHANGES PRODUCED BY MICRO-
ORGANISMS.

The chemical changes thus brought about are very numerous.
The chemist of to-day has hardly begun to study them, and his
knowledge is, as yet, very fragmentary. Only a very few of them
are understood, and in regard to the simplest of these our knowledge
of the phenomena is yet lacking in many important respects. A few
only, bearing directly upon the subject of agriculture, will be ex-
plained. They may be grouped under two quite distinct heads.

Synthetic Processes. Anabolism. — These consist in the
building of complex bodies out of simpler ones. The fundamental
importance of synthetical processes to the continuance of life is
evident enough. The animal kingdom, in general, demands complex
compounds as foods, and cannot live upon the simple compounds
found in the air and the soil, like carbonic dioxide, nitrogen, am-
monia, etc. (CO2, N, NH3). In order that animals may use the
elements existing in nature, some process must build them into
complex bodies. This is largely accomplished by the green plants
that furnish animals with food. But even these plants demand
some of their food in a complex form, not being able, for example, to
use nature's free nitrogen store in the atmosphere until it has been
built up into some compound like nitric acid. The constructive
or synthetic processes are thus of fundamental importance to the life

24 THE NATURE OF THE ACTIVITIES OF MICROORGANISMS.

processes of both animals and plants. Among the chemical changes
which are brought about by bacteria, some are of this synthetic
character.

Analytical Processes. Decomposition: Katabolism. — The
most noticeable action of bacteria is that of decomposition. The
great majority of them, just like animals, live upon complex chemical
foods, and these compounds are broken to pieces by their action and
reduced to simpler molecules. Acting in this way, the fungi are
the most important agents in nature for reducing to a simpler condi-
tion the great quantity of organic matter which would otherwise
accumulate upon and within the soil, or in bodies of water. The
chemistry of the decomposition of organic substances is still in its
infancy, and as yet only the general nature of the changes is under-
stood. The decomposition of these compounds in general brings
the elements back to simpler conditions and nearer to the form in
which they can serve as food for ordinary plants.

Both synthetical and analytical processes are carried on, to a
certain extent, by all bacteria. If they grow and multiply they
must be manufacturing proteid and protoplasm out of the food prod-
ucts, for each new bacterium is made of protoplasm. This build-
ing of protoplasm is a synthetic process, and is, of course, character-
istic of all growing bacteria. On the other hand, all bacteria like-
wise produce a certain amount of decomposition of the materials
which serve them as food, giving rise to simpler products as excre-
tions. But while all bacteria thus perform both types of chemical
change, the decomposition activity is, in general, much greater than
that of synthesis; they are destructive rather than constructive agents.

In still another respect the chemical changes produced by bacteria
are two-fold. In some cases the new products which arise are of
the nature of excretions. By this is meant that certain substances
are taken into the bacteria and then subjected to a series of changes
within their bodies. These changes are classed together under the
name of metabolism. As a result of the metabolic changes there
arise new chemical products which may be eventually eliminated
from the body of the bacteria as excretions. Some of the new
products arising in a mass of organic material undergoing decompo-

TYPES OF FERMENTATION AND DECAY. 25

sition by bacteria are ■ thus of the nature of excretions {e.g.,
ptomaines) . In other cases the new chemical bodies are apparently
produced entirely outside the body of the bacteria, and are not
in any sense excreted products. In such cases the microorganisms
excrete substances which act upon the outside substances, producing
chemical changes in them. The substances thus produced are not
excretions, but by-products.

TYPES OF FERMENTATION AND DECAY.

The various processes known as fermentation, decay, putre-
faction, etc., are all closely related, and, while an attempt has been
made to distinguish between them, no real logical distinctions can
be made. They are all progressive chemical changes taking place
under the influence of organic substances which are present in small
quantity in the fermenting mass. They are fundamentally of the
nature of chemical decompositions by means of which organic
substances are broken down and new substances are formed.
They may best be understood by the consideration of three examples
illustrating three different types:

Alcoholic Fermentation. — When yeast is added to a sugar
solution, it grows rapidly and soon changes the sugar into carbon
dioxide and alcohol. The sugar is probably taken into the body of
the yeast and decomposed into these two products, which are then
liberated from the yeast, the gas appearing as bubbles and the alcohol
remaining in the solution. The change is sometimes expressed by
the chemical equation, C6Hj2 06 = 2C2H60-|-2C02. But this
equation represents only the end-products and by no means correctly
expresses the changes that occur. This fermentation occurs in
malt to make beer, in apple juice to make cider, and is the basis
of alcoholic industries in general. It also occurs in the raising of
bread.

The Amyolytic Fermentation. — If a little saliva is mixed

with starch and water, there begins at once a conversion of the

starch into sugar, and it may continue until all the starch is thus

changed. This fermentation is also expressed by a chemical

3

26 THE NATURE OF THE ACTIVITIES OF MICROORGANISMS.

equation, C6Hjo05+H2 0 = C6Hj2 06, though the equation certainly
does not represent the change that goes on. Starch is known not
to be such a simple molecule as CaHjoO^, but some multiple of that
formula, and probably a very high one. Its decomposition into
sugar is really a long series of steps, only the final result being
partly represented in the equation. This fermentation occurs in
food after it is mixed with saliva in the mouth.

Putrefaction and Decay. — If any proteid body — meat, eggs,
or the like — be left for some time exposed to the air, it will give off
unpleasant odors, for it is undergoing putrefaction and decay.
These two processes, though frequently considered the same, are
slightly different. Both are the result of the chemical decomposition
of organic compounds, and the terms are commonly applied only
to the decomposition of material that contains proteids. Both
result in chemical decompositions which are very complete, and
more complex and indefinite than the other two types of fermenta-
tions. They are produced by microorganisms, chiefly bacteria,
which feed upon the putrefying mass, taking certain atoms out of
the organic molecules. These molecules, thus losing some of their
atoms, change their chemical nature. The remaining atoms
necessarily rearrange themselves to form new compounds which are
simpler in structure. The distinction between putrefaction and
decay consists in the fact that decay is the term applied to decompo-
sition in the presence of oxygen, while putrefaction takes place
in the absence of oxygen. The former is much more complete
than the latter, resulting in the more complete destruction of the
substance decomposed.

Organized and Unorganized Ferments.— These three ex-
amples of fermentation are very different from one another. One
seems to break the sugar molecule into two simple portions, carbonic
acid and alcohol; the second simply adds a molecule of water to one
of starch; while the third results in a complete decomposition of a
highly complex proteid into a large number of by-products, both
known and unknown. But in some important respects all three
agree. Each differs from ordinary chemical processes in several
respects and all agree in the following points:

TYPES OF FERMENTATION AND DECAY. 27

1. They are all cl6sely associated with life processes; i.e., are
brought about directly or indirectly by living agents.

2. They are all closely dependent upon temperature, ceasing
at low temperatures and also at high temperatures, and occurring
with vigor within limits of temperature not far apart. Most of
them occur most vigorously at temperatures between 80° and 100° F.

3. They are all produced by the stimulating action of some
special body, present in the fermenting material in a quantity
which is very small, considering the great changes produced.

4. These bodies (ferments) are all rendered inert or destroyed
by heat; a boiling temperature commonly destroys them so completely
that they are unable to renew their action even after cooling. Low
temperatures simply check their activity, which they are able to
renew if warmed again.

5. Their action is completely stopped by an accumulation of
the products of their own activity.

If we ask what is the body producing the action (the ferment),
we find that the first and last of the types described dififer from the
second in one radical point. Whereas the alcoholic fermentation
and putrefaction are directly produced by living germs, either yeasts
or bacteria, the amyolytic fermentation is not produced by a living
organism, but by some non-living substance secreted from a living
being. To explain this a brief account is required of the develop-
ment of our knowledge of fermentations in general.

Fermentations have been known for centuries. Even in ancient
Egypt the production of alcohol was familiar. Every savage tribe has
its own method of obtaining alcohol by the fermenting of fruit juices,
and the process is one of the most widely-known changes in nature.
For a time it was regarded as a putrefying process, the yeasts found
in the fermented material being looked upon as an impurity which
was separated from the rest. The chemical nature of alcoholic fer-
mentation was determined early in the nineteenth century, but its
relation to the yeasts was not determined until 1837, when Schwann
demonstrated that fermentation would not occur except under the
influence of yeasts. The conclusion that it was the result of the
growth of yeasts was vigorously combated for years by Liebig, who

28 THE NATURE OF THE ACTIVITIES OF MICROORGANISMS.

looked upon the process as a purely chemical change; but event-
ually Pasteur and others proved that fermentation is a physiological
process, brought about only by the growth of yeast.

For a long time there was no conception of more than one type of
fermentation. But even in the days of Schwann it was recognized
that there was another type of chemical changes which resembled
the yeast fermentation in some respects. This was the sort of
changes which occur in the digestion of food and which were known
even in those early days to be due to certain materials present in the
digestive fluids. As early as 1833 a substance called diastase was
known which could convert starch into sugar, and in 1836 pepsin,
causing the digestion of proteids in the stomach, was discovered.
Although these processes were realized to be different from the
fermentation produced by yeast, their general similarity led to their
being called fermentations, and the active substance in each case
was known as a ferment.

It very soon appeared that these two types of fermentation were
different in some fundamental respects. Whereas alcoholic fermen-
tations, produced by yeast, can be stopped by certain chemicals
like glycerine, the other type of fermentation, due to digestive fer-
ments, cannot be stopped by such materials. Moreover, the
microscope shows that the second type of ferments does not contain
any living bodies like yeast. Hence, while yeast is a living ferment,
the digestive ferment cannot be regarded as hving. But these latter
ferments contain some substances which are very peculiar in their
nature. Like living organisms, they are destroyed by high heat, and
they act only at a moderate temperature. Unlike most simple
chemical changes, these fermentations do not occur at high tempera-
tures, but become impaired and stopped when the temperature
rises slightly above 100° F. It has been found possible to isolate
from the fermenting material (saliva, gastric juice, etc.) the ferment-
ing body. From the digestive juices a substance can be obtained in
the form of a powder which can be preserved indefinitely. It con-
tains no living cells, is not alive, and clearly does not belong to the
same class of bodies with the yeast plant. But it will cause the
fermentation to take place when added to a fermentable substance.

IMPORTANCE OF FERMENTATION IN FARM LIFE. 29

These discoveries led to a sharp separation of ferments into two
different classes. On the one hand were those which, like yeast,
were produced by organisms and were called organized ferments,
and on the other were those which contained no organisms and
were called unorganized ferments. These latter ferments received
the name of enzymes, which name is now in most common use.

What are enzymes? Over this question there has been not a
little discussion. But in spite of it we know very little about them.
They seem to be chemical bodies, capable of producing chemical
changes in certain substances. But their action seems to differ
from chemical actions in general in that the ferment itself is ap-
parently not used up in the process. Whether this is strictly true
may, from theoretical reasons, be doubted; but at all events, no
direct evidence exists that they are used up, and everything indi-
cates that they can act indefinitely. A very small amount of an
enzyme may produce a very large amount of chemical change, and
the enzyme does not appear to enter into the new chemical bodies in
any degree whatever. In some respects the enzymes resemble
living bodies, especially in their relation to heat, and in the fact that
they are always produced by living organisms. But in other re-
spects they are sharply marked off from the organized ferments. A
long series of disinfectants like glycerine and alcohol, which kill
the organized ferments, have no influence upon the enzymes. The
latter do not increase by growth in the fermenting material, nor
does their continued action depend upon their nutrition. The
opposite is true of yeast and bacteria. The distinction between
these two classes of fermentations has been kept clearly in mind
in the development of our knowledge of fermentation in the last
half-century.

IMPORTANCE OF FERMENTATION IN FARM LIFE.

The value of all these types of fermentation in agriculture is
evident from the following list of the most important of them. In
the first class may be mentioned:

The alcoholic fermentation; the butyric fermentation, which pro-

30 THE NATURE OF THE ACTIVITIES OF MICROORGANISMS.

duces butyric acid in butter; the lactic fermentation, which often
causes the souring of milk and various other products, and which is
responsible for the ripening of cream; the acetic fermentation, which
produces acetic acid and forms vinegar; the proteolytic or peptonizing
fermentation, which renders soluble certain insoluble proteids, an
example of which is found in the ripening of cheese; the oxidizing
fermentation, which causes the oxidation of organic matter, as in
the fermentation of tobacco; the nitrifying fermentation, which con-
verts ammonia into nitrates or nitrites; the denitrifying fermentation,
which converts nitrates into nitrites or simpler compounds by
depriving them of oxygen. Then there are the phenomena of putre-
faction and decay, which are endless in variety and which lie at the
bottom of continued soil fertility.

There is a much longer list of the unorganized ferments, or
enzymes, derived from both plants and animals. Some of the
most important are the following :

Diastase, found in both plants and animals, which changes
starch to sugar; inulase, which has a similar action upon inulin;
invertase, trehalase, rafinase, melizitase, lactase, which act upon
sugars, changing their chemical formula?, or, as the chemist says,
inverting them. Emulsin, myrosin, erythrozym, tannase, lotase,
and some others, which act upon chemical substances called gluco-
sids; pepsin, trypsin, from animal digestive juices, and galactase
from milk, together with hromelin, papain, and vegetable trypsin,
from plants, which act upon proteids, causing them to change
into simpler compounds. These are called proteolytic enzymes.
Lipase acts upon fats, splitting their chemical molecules; rennet
acts upon milk, causing it to curdle; thromhase is in the blood and
is the immediate cause of blood clotting; cytase is an important
enzyme, acting upon several parts of a plant cell and causing the
cell structure to disintegrate; pectase causes the formation of
vegetables jellies from materials in vegetable cells; urase brings
about the ammoniacal fermentation of urea. All of' the actions
above mentioned are the result of chemical decomposition in the
fermenting body, generally accompanied by the absorption of water.
There is another class of enzymes, called oxidases, which cause

ORGANIZED AND UNORGANIZED FERMENTS. 31

the fermenting body to absorb oxygen. Among these are, laccase,
an enzyme concerned in the formation of lacquer varnish from sap;
tyrosinase, producing colors in fungi; and oenoxydase, an enzyme
that causes certain diseases in wine. This list could be largely in-
creased by adding other less important enzymes.

The simple enumeration of these lists is sufficient to emphasize
their variety, and only a brief examination is needed to show their
intimate relation to farm processes. Nearly all of those enumerated
have a more or less important relation to farm life, and not a few
farm products are quite dependent upon them, for example: vinegar-
making, due to the action of both yeasts and bacteria, and cheese
making, due to the enzyme, rennet, and likewise to bacteria.
When to this list we add the many serious animal and plant diseases
caused by germ life, with which the farmer is waging constant war-
fare, it becomes evident that agriculture and bacteriology must
hereafter be closely combined.

Recognizing the great variety of these allied phenomena, it
becomes a little uncertain to what the term fermentation should be
applied. It originally referred to the alcoholic fermentation, but
later it was applied to the changes due to enzymes, and enzymes as
well as yeasts were said to be ferments. Frequently it has been
applied to any type of sugar fermentation brought about by yeasts
or bacteria, by which gas is produced; and when bacteriologists
use the term they usually refer simply to this change in sugars.
A term with so varied a meaning is of little value, and to-day there
is a tendency to give up its use, except in a popular sense to cover
such a general list of phenomena.

IS THERE ANY DISTINCTION BETWEEN ORGAN-
IZED AND UNORGANIZED FERMENTS?

The confusion is rendered still greater by the discovery of a series
of facts that lead to the breaking down of the distinction between
the organized ferments and the enzymes. It will be noticed that
these enzymes all come from living organisms, being secreted by
them; pepsin is secreted by the gastric glands, diastase by cells of

32 THE NATURE OF THE ACTIVITIES OF MICROORGANISMS.

the grain, etc. The larger part of the enzymes listed above are
secreted by certain plants. The power to secrete enzymes is thus
quite a common property of plant cells. Indeed, it is becoming
evident that many so-called life processes are produced directly
by enzymes secreted by animals and plants. Now, the action
produced by the enzyme trypsin, secreted by the digestive glands of
animals, is very similar, if not identical, with the action produced
by certain of the bacteria when growing and acting upon proteid
food. It is a natural question to ask if it may not be true that
the bacteria secrete an enzyme similar to trypsin, and that their
action upon their food is really a digestion due to the enzyme which
they secrete. Are not both cases properly called digestion? If
we can find such an enzyme in a solution where these bacteria have
been growing for a time, it would follow that they must have secreted
it and that their action upon the proteid food is due directly to the
enzyme. This question will at once broaden into a second one,
and we shall be forced to ask whether the action on all organized
ferments may not be explained by supposing the living bacteria
or yeasts to secrete an enzyme whose direct action is responsible
for the fermentative change. If this be the case, the distinction
between the organized and unorganized ferments disappears.
The so-called organized ferments would then act in exactly the
same way as the unorganized, the difference being simply that
in the one case the enzyme is secreted by the active cells of larger
animals and plants, and in the other by the active cells of bacteria
and yeasts.

Now this conclusion is not simply a theoretical one, but it has
been demonstrated to be true for at least a considerable portion of
the organized fermentations. In the first place, it has been shown
that the power of secreting enzymes is a common one among fungi;
common molds are known to secrete enzymes of much the same
nature as digestive enzymes. They soften up proteid substances,
in order, apparently, that they may absorb them. In other words,
they "digest" them for their own use. When, in pursuance of this
idea, we study carefully the various fermentations at first regarded
as belonging to the class of organized ferments, we find, in some cases.

ORGANIZED AND UNORGANIZED FERMENTS. 33

that the living bacterial cells do secrete an enzyme that actually
produces the chemical change in the fermented body. For example;
there is a class of bacteria that has the power of curdling milk
without rendering it acid, an action very similar to that of the
enzyme rennin (rennet), secreted by the stomach glands of calves.
But since the curdling of milk by bacteria was produced by living
organisms that grow and multiply during the process, it was regarded
as one of the class of organized fermentations, and was so identified.
But it has been demonstrated that this curdling is due to an enzyme
secreted by the bacteria, and that this enzyme is quite similar to
rennet. It may be entirely separated from the bacteria cells and
preserved in the form of a powder, somewhat in the same way
that rennet can be separated from the stomach of a young calf. It
will curdle milk as quickly as the rennet. Further, these same
bacteria produce a second enzyme which has the power of digesting
the curdled milk, and this second ferment is similar to that secreted
by the pancreas of a mammal.

Many other examples of the same nature might be mentioned.
The general processes of putrefaction and decay are produced, it is
true, by the destructive agency of microorganisms, but directly, to a
great extent at least, by the enzymes secreted by the bacteria. But
while many of the organized fermentations are thus explained,
some have not been brought so easily into this category, since it has
been difficult to prove that they do really produce an enzyme. The
longest known fermentation of all, the alcoholic fermentation of
sugar by yeast, did not for a long time disclose any enzyme, even
though careful search was made for one. But, thinking that per-
haps in this case the yeast cell produced the enzyme but did
not excrete it, retaining it in its own body, Buchner devised a
method of crushing the yeast cell and squeezing out the inclosed
juice. Upon doing this he obtained a liquid containing no living
matter, but capable of producing the alcoholic fermentation in a
normal manner. The liquid evidently contained an enzyme which
had thus been pressed out of the yeast cell. This enzyme has been
named zymase. It would seem from this that the yeast cell is a
little chemical laboratory that manufactures an enzyme and then

34 THE NATURE OF THE ACTIVITIES OF MICROORGANISMS.

takes inside of itself the sugar which the enzyme ferments, after
which the cell ejects the products of fermentation, alcohol, and car-
bon dioxid.

There are still, however, some fermentations concerning which it
has been impossible as yet to prove the formation of an enzyme.
The lactic acid bacteria have the power of fermenting milk-sugar
and producing lactic acid from it. Careful search has been made,
for an enzyme with but partial success. It is very probable that here,
too, the enzyme may be produced and that it is not secreted from
the bacterial cell. Should this eventually prove to be true, it
would apparently reduce all types of fermentation to the one of
enzyme action. This would not reduce in the slightest degree the
importance of the microorganisms in the matter. It would still be
the fact that this large class of chemical changes is brought about by
the life activities of living organisms, but we would understand that
they perform their action by first secreting enzymes and that the
enzymes are the direct agents for bringing about the fermentative
changes.

It is desirable to notice also that even if we* accept the enzyme
conception of fermentations we are no nearer a satisfactory under-
standing of the real nature of the phenomenon. For over fifty
years science has been trying to explain these mysterious changes
in fermentable bodies. At one time it was thought that they were
purely chemical processes; but this has been disproved by showing
that living organisms are necessary to their production. Pasteur
thought they were due to "life without oxygen," claiming that the
living germ required oxygen for its life, that if it did not find plenty
of free oxygen, it would take atoms of this element out of the sugar
molecules or other fermentable body, and that the withdrawal of this
oxygen caused the molecule to fall to pieces. This theory has also
been abandoned. The theory that all living fermenting agents se-
crete a chemical enzyme appears to stand the test of experiment, but
it explains little, for we do not know what enzymes are and we have
absolutely no knowledge of how they act. Are they wholly lifeless
chemical bodies or are they semiliving, as some would say ? What-
ever they are, they are still as great mysteries as the fermentations

FERMENTATIONS NOT ALL DUE TO MICROORGANISMS. 35

they produce have always been. The real nature of the fermenting
processes is, in short, quite unknown.

FERMENTATIONS NOT ALL DUE TO MICRO-
ORGANISMS.

One final question needs to be raised. Are all of the many kinds
of slow progressive changes, resembling fermentations in a broad
sense, due to the action of microorganisms, either by direct action
or through the agency of the enzymes they produce ? After we have
recognized that higher plants may produce enzymes, we see at once
that there may be certain fermentative processes in the soil or else-
where, for which microorganisms are not directly responsible. If a
plant produces an enzyme, this body may remain ready for action
after the plant which produced it is dead, and fermentative changes
may go on in a mass of vegetable tissue for which microorganisms
are not responsible. It very commonly happens that after the
death of the plant it undergoes some kind of fermentative change.
When piled into a compost heap or stored in a silo, the plant tissues
certainly show unquestionable evidence of marked fermentative
changes. These phenomena are accompanied by a rise in tempera-
ture and have all the characteristics of true fermentation. In
such heaps bacteria are certainly present and the rapidly widening
conception of the agency of bacteria in producing fermentations
led to the conclusion that they cause all such fermentations. But
the growing knowledge of the nature and abundance of enzymes
is leading to the conclusion that some of these fermentations are not
due to bacterial action at all, but simply to the enzymes which were
excreted by the plants during their life and which get a chance to act
in the fermenting heap. If the corn during life produced enzymes,
these would find their way into the silo and inevitably start fer-
mentations which would, of course, have nothing to do with bacteria.

While, then, fermentations and putrefactions must, in general, be
attributed to germ life, we must ever bear in mind that similar or
identical phenomena may sometimes be caused by enzymes from a
different source.

36 THE NATURE OF THE ACTIVITIES OF MICROORGANISMS.

THE PURPOSE OF FERMENTATION.

All these types of fermentations, whether caused by the metabo-
lism of bacteria or yeasts, or by enzymes secreted by these organ-
isms or by higher plants, are of vital importance in agricultural
processes. Without their agency in breaking up organic com-
pounds, the soil would rapidly become unfit for supporting life.
The agricultural industry is not only dependent upon fermentations
for many minor processes, but it is fundamentally dependent upon
them for its continuance. While this is true, it must not be as-
sumed that the various bacteria produce their results for the benefit
of agriculture or for the benefit of the soil. There is no purpose
in the matter. Each species of animal and plant acts its own life
for its own good. If it secretes an enzyme that produces a fermenta-
tion, this is done for its own benefit and not for the farmer's. The
yeast ferments sugar, and bacteria putrefy proteids for uses of their
own. Incidentally it may result that the natural processes of life
phenomena are benefited thereby; but primarily all of the enzymes
secreted and all of the fermentations produced are for the benefit of
the organisms secreting them. If a bacterium or a mold secretes
an enzyme into a lot of milk which causes its digestion, its purpose is
to digest the milk for its own use and not for any incidental results
that may accrue to the cheese-maker.

PART II.

BACTERIA IN SOIL AND WATER.

CHAPTER III.
NATURE'S FOOD-SUPPLY. THE CARBON CYCLE.

THE CONTINUATION OF THE FOOD-SUPPLY.

The farmer's primary occupation consists in converting soil,
water, and air into human food. This he does through the agency
of plants that grow in the soil and furnish the food necessary for
his stock, in addition to a part of his own food. So long as plants
find in the soil proper conditions for growth, the food-supply will not
fail. The problem of keeping up the food-supply of plants thus
becomes the one problem of supreme importance.

By far the largest part of the plant food, in weight, comes from
the air in the form of carbonic dioxid and water, and these two
substances are practically inexhaustible. But, in addition, some
foods are obtained from the soil. These last are present in the soil
in limited quantities only, and some of tjiem are found only in the
upper layers. They are constantly being used by successive genera-
tions of plants. This constant use, in the course of centuries,
would have quite exhausted the soil were there not some means by
which these supplies were replaced. That there is some such means
is evident from the fact that plants have continued to grow on
the same soil for countless generations, the soil remaining as fertile
as ever. Clearly the problem for agriculturists is to find out the
factors that have kept up the fertility of virgin soil and to apply
them properly to cultivated soil. In this way only can the continued

37

38 nature's food-supply, the carbon cycle.

fertility of the soil be assured. While various agencies are concerned
in this matter of soil fertility, the agency of microorganisms is
certainly one of the largest.

PLANT FOODS.

The green plants live chiefly upon the following foods :

Water. — This material, coming from the rains, is unlimited in
amount and need not detain us.

Carbonic Dioxid. — This gas (CO^) furnishes the carbon
which is the basis of most plant structures, wood, cellulose, starch,
sugar, etc. It is present in the air in small percentage only, but
is kept fairly constant by processes which we shall consider.

Nitrates. — These, which are salts of nitric acid (HNO3),
constitute the chief form in which plants obtain their nitrogen.
Nitrogen in considerable amount is an absolute necessity for all
plant life, and while plants can probably assimilate some nitrogen
from ammonia, it is certain that ordinarily they do not obtain much
from this source. The higher compounds of nitrogen, like proteids,
ures, or other complex bodies, cannot furnish plants with nitrogen
directly, nor, on the other hand, can nitrites (salts of nitrous acids,
HNO2) or free nitrogen in the air supply any nitrogen directly to
plants. Practically all the nitrogen must be obtained by the plants
in the form of nitrates from the soil, and to keep a constant supply
of nitrates in the soil must be the first aim of the farmer.

Phosphates. — A small amount of phosphorus is needed by
plants and is obtained in the form of the soluble phosphates from
the soil. The mineral soil ingredients contain much phosphorus
in insoluble compounds, and agencies for rendering these soluble
are necessary to soil fertility.

Potash. — Some form of potassium salts is necessary. These
salts abound in soils, but some agency must be employed to dissolve
them.

Sulphates. — These salts are also needed in small amounts
only.

Iron Salts. — Needed in small quantities only.

MICROORGANISMS IN THE SOIL. 39

Lime and magnesiaf should also be in the soil for reasons that
will be given later, but they are only slightly used by most plants.

There are still other materials used by plants in very minute
quantities, but they hardly fall in the scope of our study. All
the foods above mentioned are commonly called inorganic foods,
since they come chiefly from the soil and the air. Organic foods
on the other hand refer to the more highly organized products, which
are the immediate remains of living things, like roots, starches,
fats, wood, cellulose and other similar bodies. ,Our problem, then,
is to explain nature's methods of keeping the soil supplies of these
various inorganic ingredients from diminishing.

MICROORGANISMS IN THE SOIL.

The upper layers of the soil are exceedingly rich in bacteria,
the number varying according to conditions, from a few thousands
to many millions per gram. In sandy soil there may be very few,
while in soil polluted with organic matter, as in the vicinity of
manure heaps, there may be as many as 100,000,000 per gram or
even more, 1,600,000,000 per gram having been found in some soils.
They rapidly diminish in numbers, as we pass to the lower layers,
and at a depth of from four to six feet, they have almost disappeared.
Below this they are rarely found, except in places where drainage
currents carry them downward. The microorganisms thus found
in the soil include bacteria in the greatest abundance, and also
quantities of the higher fungi and yeasts. Each of these classes is
represented by many varieties, and each has an important share in
the complex activities going on in the soil. These functions and
the relation of the soil microorganisms to them may best be under-
stood by noticing in succession their relation to the various soil
ingredients that constitute plant foods.

ORIGIN OF SOIL.

The ingredients in the soil may be divided into two classes: i.
The purely mineral matters. 2. The organic ingredients consti-
tuting the humus.

40 NATURE S FOOD-SUPPLY. THE CARBON CYCLE.

The Mineral Ingredients. — These come primarily from the
rocks that constitute the earth's surface, soil being sometimes de-
scribed as ground-up rock. The agents that cause the grinding of
the rocks are physical, chemical, and biological. The physical
agencies are chiefly those of freezing and thawing, together with the
solvent action of waters. The chief chemical agent is direct oxida-
tion by the oxygen of the atmosphere. The physical and chemical
agents together produce what has been called the "weathering"
of rocks, resulting in their crumbling into fine fragments With these
we are not particularly concerned. The biological agencies are those
of the soil microorganisms. We do not yet know very definitely how
great a part they play in this process, but that it is an important part
is surely proved. One of the results of their growth is the liberation
of carbonic dioxid from decomposing masses. This gas is readily
dissolved in the soil water, and water containing carbonic dioxid in
solution is able to dissolve a considerable quantity of carbonate of
lime. These carbonated waters, therefore, play a great part in the
disintegration of limestone, which is one of the prominent factors
concerned in the formation of soils. Again, the microorganisms
which decompose organic matters in the soil produce a variety of
organic acids. Among these are the lactic, butyric, and acetic acids,
as well as many others. These acids have a solvent action upon
various rock formations, and, by dissolving out certain parts of the
rocks, they slowly but surely cause them to crumble. Some of
these matters will be considered on later pages in other connections,
but we are interested in them here as showing that bacteria are
prominently concerned in the disintegrations of rocks which result
in the formation of soil.

The Humus. — There is a vast difference in the fertility of a
sand and a garden soil, Sandy soil may contain all the necessary
mineral matters, but it lacks the something needed for plant growth
which the garden soil contains. This something is called humus,
an element rather difficult to define and still more difficult to describe
in chemical terms. It is abundant in fertile soil, but scarce or
wanting in barren soil. Though its chemical value is too complex
to be stated or even known, its origin is easy to understand.

THE TRANSFORMATION OF CARBON. 41

Humus is the remains of life of previous generations. When
plants die, their roots, together with their leaves, branches, and
fruits, inevitably become incorporated into the soil. Animals, too,
leave upon the ground a quantity of excrement and other discharges ;
and plants likewise probably discharge excretions into the soil. When
animals die their bodies also may become mixed with the earth.
Thus, practically all kinds of organic matter from animals and
plants are being mixed continually with mineral ingredients in the
surface layers of the soil. The microorganisms in the soil feed
upon these dead materials, causing an extensive series of decomposi-
tions and recombinations. To this mass of complex organic bodies
undergoing decomposition in the soil has been given the name
humus. It will be evident from this explanation of its origin that
humus cannot have a definite composition, and that it will hardly be
alike in any two soils. It will be composed of different materials
to start with, and there will be a variety of different stages of decom-
position. W^e cannot hope to find any definite composition of
humus, but we can study the kinds of decomposition and recombina-
tions that are going on in it and that result in making it a suitable
food for plants. In this study we must ever keep in mind the fact
that dead bodies of animals and plants are not in condition to serve
another generation of plants as food. We cannot feed plants upon
eggs, or urine, or starches, or sugars. Though containing carbon
and nitrogen in abundance, these elements are locked up in them out
of the reach of the green plants, and before they can be utilized
again they must be freed from their combinations and brought into
simpler forms. This is accomplished by the microorganisms in the
soil. Our study of these changes may best be centered around the
two chemical elements, carbon and nitrogen.

THE TRANSFORMATION OF CARBON.

The green plants seize the carbon dioxid (COa) from the air by

means of their leaves and, utilizing the energy of sunlight, build this

carbon into higher compounds. Starch is formed first, and later other

substances — cellulose, wood, fats, sugar — are built from the elements

4

42 NATURE S FOOD-SUPPLY. THE CARBON CYCLE.

found in the starch alone; while, by combining them with some
nitrogen, various proteid bodies are produced. When once carbon
has assumed these forms it is no longer within the reach of another
generation of plants. It is locked up and cannot again be utilized
until it has once more been reduced to a condition of carbon dioxid.

The compounds thus built up have different destinies. Some of
these are eaten by the animal kindgom and, after serving the needs
of the animals, are exhaled as CO2 to join the atmosphere again. A
large part is not appropriated by animals, but begins at once to
undergo destructive changes which bring their ingredients back again
to their starting-point. Some of the processes of chemical destruction
are comparatively simple. The starches, sugars, and fats are sub-
ject to chemical changes which take place under the direct in-
fluence of chemical forces, since they may be directly oxidized. All
forms of active combustion in fires produce such oxidation, the result
of which is that the carbon in the compounds burned is united with
oxygen and liberated in the form of CO2, the hydrogen being
liberated in the form of water. These join the atmosphere, while
the minerals remain behind as ash. Thus, all forms of combustion
in carbonaceous material restore some of the carbon to the atmos-
phere in the form of CO2, and upon this the plants again feed.

But although direct oxidation may form a considerable part of
this process of food reduction, another very large factor is due to the
agency of microorganisms. Fires rarely occur in nature, unless
started by man, and there must be some other means of oxidation.
A slow oxidation of carbonaceous material occurs in nature at all
times, and ordinarily it has been attributed to direct chemical
processes. It is quite doubtful, however, if this slow oxidation
would occur were it not for the agency of microorganisms. At all
events a considerable part of the so-called slow oxidizing processes
is the direct result of their growth. The various kinds of organisms
bring about the gradual destruction of the different types of car-
bonaceous materials.

Sugars. — These are contained in fruits and some vegetables,
and as they decay, the sugar commonly undergoes an alcoholic
fermentation, produced by the action of yeasts and molds. The

THE TRANSFORMATION OF CARBON. 43

fermentation which goes on in a decaying apple is identical
with that which occurs in the brewer's vat. The result is the
formation of CO2 and alcohol, the carbon dioxid passing into
the atmosphere to contribute to the store of this important food.
The alcohol, under normal conditions, also passes into the air and
is eventually further oxidized into carbonic acid and water. Thus,
the carbon of the sugars, by the agency of yeasts and molds, is
restored to the air. Starches have nearly the same history, since
they are readily converted into sugars by enzymes secreted by the
plants, and are then fermented. To a certain extent bacteria
also ferment sugars, producing a series of acids.

Cellulose. — Cellulose is a material closely related to starch, and
is found in the cell walls of all plants. Wood and straw contain it
in considerable quantity, while cotton and wood fibers are almost
pure cellulose. Swedish filter-paper is one of the purest forms.
The material is quite resistant to ordinary forms of decay and is
seldom affected by common plant decay. But certain bacteria
are able to act upon it so as to ferment it and set free its carbon.
Several of these have been isolated and studied. Some of them act
in the absence of oxygen (anaerobic), while others act only in its
presence (aerobic). The former can carry on their activity in
the midst of a manure heap so tightly packed as to exclude air,
while the latter will occur in moistened masses of vegetable tissue
exposed to the air. These cellulose-fermenting bacteria are abun-
dant everywhere and are constantly at work in the soil, fermenting
the hard cellulose parts of the great variety of plant roots, stems, and
leaves that accumulate in the soil or in the waters of streams and
swamps. When the mass is alkaline in reaction the cellulose may be
fermented by bacteria; but when it is acid, as in sour soils, bacteria
cannot grow. Under these conditions certain of the molds in the
soil may ferment the cellulose. The chemical nature of the fermen-
tation need not concern us, only so far as to notice that, as a result,
the carbon is set free, either in the form of carbonic dioxid or
marsh gas (CHJ, the latter gas becoming readily converted later
into carbon dioxid. The total result is the restoration of the
carbon to its original condition in the air, where it can be utilized

44 nature's food-supply, the carbon cycle.

by the next generation of plants. Certain mineral matters are
also set free from the cellulose in the form of ash, which adds to the
fertility of the soil.

A fermentation of cellulose is believed to occur also in the intes-
tines of herbivorous animals. These animals utilize, to a certain
extent, cellulose materials as a food; these undergo a fermentation
in the intestines resulting in the formation of certain substances
that are assimilated by the animals as food. Cellulose-fermenting
bacteria are found in the intestines of such animals in considerable
abundance, and it is thought that they play an important part in
the ordinary digestion of celluloses. Whether the animal might
not be able to digest them without the aid of bacteria has not yet
been proved, but it is almost certain that the bacteria do, under
ordinary conditions, play an important part in the process. The
fermentation begun in the intestines is finally completed in the
manure heap, and thus, after a time, the cellulose is completely de-
composed and its carbon restored to the atmosphere.

Wood. — Another product of plant life somewhat closely
related to cellulose is woody tissue. The fermentation and destruc-
tion of wood is certainly a matter of necessity, if the carbon supply
is to be kept constant. That there is such a fermentation is evident
to anyone who has walked through a forest and noticed the
condition of the fallen trunks and branches. A fallen tree will
remain for a time upon the surface of the ground, apparently
unaltered. But presently it becomes softened by some agency, not
manifest at first, and the hard, woody mass is slowly but surely
converted into a soft friable substance, which eventually crumbles
into a brownish powder and is incorporated into the soil, contributing
to the formation of the humus. This destruction of woody tissue
is also brought about by microorganisms, but in this case it is not
bacteria that are at first concerned.

The first phenomenon that occurs in such a decaying tree trunk
is the growth of larger fungi. Various forms of mushrooms and
tree fungi start their growth on its surface and send delicate mycelium
threads into the substance of the wood. These threads grow first
underneath the bark and in the superficial layers of wood; but

THE TRANSFORMATION OF CARBON.

45

gradually they penetrate the hard wood and, by the chemical
excretions they produce, soften this hard, tough substance. With-
out the growth of such fungi in the wood there would seem to
be no way of softening the wood sufficiently for decay. After the
wood has been somewhat softened by the fungi, wood-eating in-
insects begin their work upon it, using the fungi largely as food.
It is probable that bacteria also may assist in this matter, but

BACTERIA

VARIOUS CARBON
COMPOUNDS BUT
EVENTyUALLY ALL
REDUCED TO CO2

vT /f

IN ATMOSPHERE

Fig. 13. — The carbon cycle.

the larger fungi are chiefly responsible for the destruction of the
woody tissue.* The final result is that the carbonaceous material
in the wood is liberated by being combined with oxygen, and passes
off into the air to join the atmospheric store of carbon. The
hydrogen and oxygen are converted into water, and in their turn
enter the atmosphere as water vapor. In this way, by a slow process

♦These same processes, so useful in the general changes in nature, are.
of decided disadvantage when they occur in timber that is desirable to
be preserve 1. The ordinary decay of timber is brought about by the
kind of fungi and bacteria above mentioned. Since none of these or-
ganisms can grow without water, it follows that well-dried wood will not
decay, from which is to be drawn the lesson that the best method of pre-
serving timber is by thorough drying.

46 nature's food-supply, the carbon cycle.

of decomposition, wood is converted into simple chemical com-
pounds which join nature's food-supply in the air.

By the means thus indicated the large part of the carbon ex-
tracted from the air by plants is restored again to the air in the form
in which it first existed. This carbon cycle is represented graphi-
cally in the accompanying diagram (Fig. 13).

CHAPTER IV.

NITROGEN. DECOMPOSITION OF NITROGENOUS
COMPOUNDS.

The nitrogenous foods of plants are next in importance to carbon
dioxid and water. Plants cannot grow without nitrogen, and they
need it in larger quantity than any other mineral foods. The ni-
trogenous fertilizers have commonly a more noticeable effect in
stimulating crops than other minerals. The amount of material
in the world that can serve directly as nitrogen food for plants is
decidedly limited, and therefore it is expensive. For these as well
as other reasons, the problem of continued soil fertility is more
closely bound up with the matter of nitrogen than any other chemical
element.

SOURCES OF NIROGENOUS FOOD.

Plants take their nitrogen from the soil, chiefly in the form
of nitrates. While it is true that they can utilize ammonium
salts also, under ordinary conditions ammonia furnishes little
food directly to the plant, the far larger part being furnished
by soil nitrates. The amount of nitrate in any soil is however,
very limited, there being only from o.i per cent, to 0.2 per cent,
in ordinary soils. As crop after crop is grown, the small amount in
the soil is gradually used up and must be replaced if the soil is to
continue yielding crops. The farmer buys nitrates in the form of
commercial fertilizers to replace the amount taken from his soils by
his crops. These commercial nitrates, however, are also limited
in amount. They are confined to a few deposits of nitrates, chiefly
in warm dry regions. The best known come from Chili, whose
nitrate mines to-day furnish the greater part of the nitrates for the

47

48 NITROGEN. DECOMPOSITION OF NITROGENOUS COMPOUNDS.

world. But these beds do not solve the question of continued soil
fertility, for they will soon be exhausted and some other source of
nitrates must be discovered. Fortunately, we have learned that
there are processes in nature by which the soil nitrates are replaced,
quite independently of the store of nitrates in Chili or elsewhere,
and this replacement is a phenomenon of the life activities of the
bacteria and other microorganisms of the soil.

If the nitrates absorbed from the soil are replaced, it must be
from one of two sources or from both.

1. From the Nitrogen in Organic Bodies. — After plants absorb
nitrates from the soil, they build them up into organic compounds,
chiefly proteids, which subsequently may or may not be utilized as
food by animals. Whatever be its history, whether in animals or
plants, this proteid material always contains nitrogen; and eventually,
by processes which we shall study, this nitrogen may again assume
the form of nitrates and restock the soil.

2. The Nitrogen of the Atmosphere. — This is an inexhaustible
source of supply, if it can be utilized. We shall learn that there
are means by which it becomes available for plants.

There seem to be no other possible sources for replacing soil
nitrates, and we will therefore consider these two in detail.

ORGANIC NITROGEN. ITS NATURE.

The nitrates are built up by the plants into a variety of com-
pounds, mostly of the nature of proteids, like gluten of wheat,
legumen of peas, and other similar bodies. All plants contain some
such compounds which serve a purpose in the life of the plant.
While the plant is still alive they remain as proteids without much
change. After the death of the plant that produced them the pro-
teids are at the disposal of nature's forces of destruction. Some of
the proteids are seized by animals and utilized for their life proc-
esses. They are slightly changed inside the animal's body, but are
not built into bodies more complex than proteids. The animal
forms animal proteids out of them, producing myosin, gelatin,
chrondin, and other compounds, none of which are likely to be more

ORGANIC NITROGEN. ITS NATURE. 49

complicated than the original proteid of the food. Thus, in the
bodies of plants and animals alike the nitrogen reaches a condition
allied to proteid. But, while proteids may serve as food for animals
and for the great class of colorless plants (fungi) they are quite out
of the reach of the green plants, which are the great food producers
of nature. Our next problem, then, must be to learn how. these
proteids are reduced to their original condition of nitrate.

Part of the proteid thus built up into the body of the plant or the
animal remains there until the animal or plant dies, and at death it
is still a proteid and as complex as ever. In this form it may be-
come incorporated into the soil when the animal or plant dies, or it
may become eaten as food and pass through the body of another
animal. But much of it will eventually reach the soil while still
in the form of proteid.

A second portion of the proteid is used up in the animal's
body to furnish energy and heat; it is metabolized, as we say.
When it is thus used its complex chemical molecule is broken to
pieces, and it is reduced to much simpler compounds. But it is not
decomposed sufi&ciently to bring the nitrogen back within the reach
of plant life. The carbon in this proteid is in part removed from it
and combined with oxygen, to be exhaled as CO2. The molecule
falls to pieces and various simpler by-products arise; but in the
animal's body, practically all of it eventually assumes the form of
urea (CONaHJ. Though this urea is a nitrogen molecule far
simpler than proteid, still it is not simple enough for a plant food.
Urea, or a closely allied compound, is the form in which nearly all of
the nitrogenous material resulting from proteid metabolism in the
animal body is excreted. Urea thus represents one stage in the
destruction of proteid compounds, and to this stage the proteids are
brought as the result of the metabolism in the life processes of
animals. In some animals this urea is secreted as urine by the
kidneys, but in others (birds) it is mixed with the feces; in all cases
it contains the nitrogen which is no longer of any use to the animal
world. It is estimated that some 38,000 tons of urea are excreted
daily by the human race. To this quantity must be added the far
greater amount excreted by other animals, for all animals, large

5

50 NITROGEN. DECOMPOSITION OF NITROGENOUS COMPOUNDS.

and small, secrete it or an allied substance, and the total is enor-
mous. What becomes of it all?

Thus the nitrogen of the nitrate absorbed by the plant has
reached two quite different conditions. Part of it is still in the
highly complex form of proteid, either in the dead body of the
animal or the plant. A second part has been partly broken down
in its passage through the animal's body, and has reached the con-
dition of urea or some allied body. But in neither condition is it
within reach of another generation of green plants. It must be
still further broken down before it is available for plants.

ORGANIC NITROGEN. ITS DECOMPOSITION.

Decomposition in General. — This means the breaking to
pieces of complex compounds so as to form simpler ones. The
term thus defined is a very broad one, and covers a long series of
changes, of a purely chemical nature. But more commonly the
term has a narrower meaning, and refers to the breaking down of
organic products under the influence of microorganisms. This is
one of the most important functions of soil bacteria. The destruc-
tion of nitrogenous compounds, urea proteids, gelatins, or other
bodies, is brought about by several agencies, but the chief one is
undoubtedly that of microorganisms. A small amount of the pro-
teid appears to be decomposed in plant tissue without the aid of
bacteria; another portion is broken down by yeasts; another by
molds and other fungi. But decomposition is chiefly due to a class
of bacteria called the decomposition bacteria.

But even as thus limited, this term is still a broad one including
different species of bacteria and various types of decomposition.
Two types are generally recognized, under the names of decay
and putrefaction. These two terms are frequently not very clearly
distinguished, being used indiscriminately to refer to the decomposi-
tion of organic substances under the influence of bacteria. There
is a distinction between them, however, which may be properly
drawn.

Putrefaction. — This is the name given to a partial decomposi-

ORGANIC NITROGEN. ITS DECOMPOSITION. 5 1

tion that is far from complete. It is generally produced by bacteria
growing in the absence of oxygen, and hence by the anaerobic or
facultative anaerobic bacteria. These break down the proteids,
but do not carry the decomposition to its final stages, the final pro-
duct, thus formed, being still quite complex. Many of them have
unpleasant odors and many of them are poisonous.

Decay. — This is the type of complete decomposition that takes
place in the presence of oxygen. It is produced by aerobic bacteria,
and results in a very complete disintegration of the decomposing
body. The end-products are much simpler than in the case of
putrefaction, and the gaseous products arising have little or no odor.
C02,N and H2O are among these final products, and are all odorless.
Putrefaction and decay cannot be sharply separated from each other,
the former being in many cases only a step toward the latter. The
bad-smelling or poisonous products of putrefaction will, if exposed
to the air, undergo further disintegration until the decay is complete.
But, though not sharply distinct, the difference above noted is a
convenient method of designating the complete decomposition,
in the presence of air, from the incomplete decomposition in the
absence of air.

Of the many species of bacteria associated with putrefaction
and decay, some are likely to be found under one set of conditions
and others under different conditions. Some are particularly
common in decaying vegetable substances and others in decaying
animal tissues, while some are most characteristic in fermenting
urea. No attempt need be made here to classify this miscellaneous
host of putrefactive organisms. They include cocci, bacilli, and spiral
forms as well as yeasts and higher fungi (Figs. 14, 15). Some
of them produce their fermentation only when oxygen is present,
while others do so in the absence of oxygen, and the by-products
produced in the absence of oxygen are different from those produced
in its presence, since the former are more likely to be of a poisonous
nature. These decomposition bacteria occur practically everywhere
in nature — in the air, in all bodies of water, and in extreme abund-
ance in the soil. They are so widely distributed and so abundant
that they are sure to seize hold of any bit of nitrogenous organic

52 NITROGEN. DECOMPOSITION OF NITROGENOUS COMPOUNDS.

matter, which, having become lifeless, can serve them as food.
Every bit of excreted urea, even that secreted by the smallest insects,
every dead animal body, every bit of vegetable matter whether it
be leaf, branch, or fruit, provided it contain proper moisture, is sure
to be appropriated as food by some of these ubiquitous putrefactive
bacteria. The material is used as food by the microorganisms, and,
as a consequence, they multiply rapidly within the decaying sub-
stances, developing vigorously for a time. After they have used
up the food, their growth is checked and some of them remain
ready to grow again when more organic matter comes within their

Fig. 14.— Proteus vul- Fig. 15.— Com-

garis, a common bacter- mon decomposition

ium of decomposition. bacteria. B. fluor-

escens and B. sub-
tilis.

reach. By their action, then, every bit of organic matter which
reaches the soil is seized and rapidly decomposed.

The chemical nature of these destructive changes is very
complicated and highly varied. It will be a long time before our
chemists understand them, for they involve problems in physiolog-
ical and organic chemistry yet unsolved. We know that many new
products are formed, and that these new products must be regarded
as belonging to at least two types, so far as concerns their relation
to the bacteria. Some of them must be regarded as secretions or
excretions from the bacteria and hence as the result of the active
metabolism of the microorganisms. These are probably rather
small in amount, but of great significance in some connections,
inasmuch as many of them are poisonous. Others must be looked
upon as by-products of decomposition. By this is meant that, as
the bacteria take certain atoms from the complex molecules for
their own use, the rest of the molecule can no longer retain its

ORGANIC NITROGEN. ITS DECOMPOSITION. 53

earlier form, and consequently its atoms must enter into new relations
to form new bodies. These by-products have not been actually in the
bacteria and are not the direct results of metabolism. The new
products formed in the decomposing mass are partly gaseous.
This is proved by the odor that commonly arises from putrefying
bodies which are indications of the exhalation of volatile products.
A chemical study has shown, in many cases, the actual nature of
these gaseous products, indicating that the end-products are
chiefly CO2, H, CH^, NH3, H^S, and N, in addition to others, present
in much smaller amount, producing the peculiar and characteristic
odors. Some of the new products are solids and may be either
soluble or insoluble. If soluble they are dissolved in the course
of time by the rain which falls upon the decaying mass and pass
into the soil, perhaps to be drained away in the drainage-water.
The insoluble bodies are also incorporated into the soil, becoming
eventually mixed with the solid masses of the earth.

The list of the by-products of such decompositions is a long one.
A few of these are as follows : Carbon 'dioxid, hydrogen sulphid,
marsh gas, hydrogen, nitrogen, calcium carbonate, propionic acid,
valerianic acid, acetic and lactic acids, alcohol, succinic acid,
phenol, indol, leucin, tyrosin, skatol, etc.

This list is far from complete. It includes only a few of the
products already known, and beyond question there are numerous
bodies, formed as by-products or excretions, which still remain
to be discovered. The actual products which appear will depend
upon three factors: (i) The substance which is decaying; (2)
the species of bacteria which produces the decay; (3) the conditions
under which the decay occurs.

The Ammoniacal Fermentation. — One phase of these decom-
position processes must be especially mentioned. After passing
through an unknown series of intermediate stages, the nitrogen
of the decaying mass assumes, in large part, the condition of
ammonia. One of the first and easiest substances to undergo
this ammoniacal fermentation is urea. Urine is always filled
with bacteria, even while in the ducts from the bladder, and among
them are several species that cause it to break down to form ammonia

54 NITROGEN. DECOMPOSITION OF NITROGENOUS COMPOUNDS.

(Fig. 1 6). Most of these bacteria produce this action through an
enzyme that they secrete, named urase. Under proper conditions,
as much as 97 per cent, of the nitrogen in the urea is converted into
ammonia in a space of four days. The ammonia is a volatile
product and has, consequently, a tendency to pass off into the air,
as may readily be recognized from the odor of ammonia that is
frequently perceived around a manure pile. This represents a per-
manent loss of nitrogen, and should be avoided as much as possible.

Fig. 16. — Various bacteria causing the ammoniacal fermentation of urea (Beijerinck).

The loss is greater when the liquid is concentrated, and consequently
less if the urine can be poured upon the soil at once, than if stored
in vats or even mixed with solid manure.

Although urea shows the ammoniacal fermentation most readily,
other nitrogenous bodies, like proteids, etc., also may give rise to
ammonia (Fig. 17), which is, indeed, one of the common end-products
of proteid decomposition. The chemical changes that occur in
proteid decomposition are complex and not wholly understood.
The first step seems to be quite like that taken when they are
digested in the digestive tract of animals, for, under the action of the

ORGANIC NITROGEN. ITS DECOMPOSITION. 55

peptonizing bacteria, they are converted into peptone-Wke bodies

which are simpler than ordinary proteids. These are further

reduced into amido acids, and the latter finally converted into

ammonia, which is quite likely to unite at once with carbonic

dioxid, that is also being liberated, to form carbonate of ammonia

((NH4)2C03). The condition in which the nitrogen actually exists

in the humus has been a matter of considerable dispute. Some

have thought that it remains in the form of proteid in large part,

others have concluded that the humus nitrogen

is chiefly in the form of amido acids. But it

is evident that there is long series of stages

between the proteid and the final ammonia

compound, and that the nitrogen in any lot

of soil may be in any one of these stages. In

whatever form it exists in the humus, a certain ^ -o . •

' Fig . 1 7 . — Bactena pro-

portion of it is being constantly reduced to the ducing ammoniacal fer-

form of ammonia. This portion alone is lead- ^^^^^^b'b- stutzerC^'
ing toward a condition where it can again be
utilized by plants. The rest, whether in the form of proteid or
otherwise, is, for the present, locked up out of the reach of plant
life. The humus may thus contain a large amount of nitrogen and
still have little of it available; i.e., within the reach of plants.

Self-purification of the Soil. — The universal occurrence of
such a decomposition of organic bodies is no new discovery. It
has long been known and its extreme significance is now recognized,
since it is the first step necessary to bring the nitrogen locked up
in the proteid back again within reach of plants. But its value
in producing what has been called the self-purification of the soil,
has been only recently appreciated. As we have seen, the final
end-products are largely gaseous (NH3,C02,N, etc.), and these
will tend to pass off from the soil into the air. A little thought will
show us that without the existence of some such process the soil
would rapidly become unfit for the support of life simply by becom-
ing clogged up with the remains of past animals and plants. If
all the bodies of animals remained on the soil after death and if
the roots and stems of plants were not disposed of by some such

56 NITROGEN. DECOMPOSITION OF NITROGENOUS COMPOUNDS.

process, it is evident enough, from simple mechanical reasons, that
vegetation would soon cease, since there would be no room left in
the soil for new plants. When we realize, in addition, that the
very processes which purify the soil of these cumbersome bodies are
bringing them toward a condition for further use, we can appre-
ciate the extreme significance of these decomposition bacteria in
agriculture.

All the types of decomposition which we have mentioned take
place in the humus of the soil; sugars, starches, cellulose, woody
tissues, proteids, and all other kinds of organic bodies are attacked
by microorganisms and eventually thoroughly decomposed. Since
this decomposition is the first step in the conversion of the products
of one generation of living things toward the condition in which they
can again be used, the conditions of the soil should be such as to
favor such decomposition. The thorough decay is possible only in
the presence of oxygen, and hence a cultivation of the soil facilitates
decomposition. Hard packed soils are inferior to looser soils
for this reason. The presence of large amounts of carbohydrates,
sugars, starches, straw, etc., is apt to give rise to acids, and soils
containing them may become sour. In such soil the nitrogenous
decomposition is checked, since decomposition bacteria cannot
stand much acid. It is evident, therefore, that in sour soils the
addition of lime to neutralize the acid will make it possible for
the bacteria to carry on an active decomposition that will soon place
its food materials once more within the reach of plant life. The
more vigorous the decomposition changes, roughly speaking,
the higher the fertility of the soil. Black marsh soil shows the highest
amount of decomposition; clay shows less, as a rule, and sandy
soil the least. The number of bacteria in any soil is directly
proportional to the activity of the decomposition changes going on
within it.

CHAPTER V.
NITRIFICATION AND DENITRIFICATION.

NITRIFICATION.

The pulling of the organic nitrogen compounds to pieces does
not in itself bring the nitrogen into the best available condition for
plants. It is in the form of nitrates that plants most readily absorb
nitrogen, and at the end of the decompositions noticed ammonia
compounds are formed, but no nitrates. Plants may be able to
absorb nitrogen in the form of ammonia salts, but this occurs only
to a slight extent, and by far the largest amount is assimilated in
the form of nitrates. Consequently, if these decomposition pro-
ducts are to be utilized by plants, they need to be changed from
ammonia salts into nitrates. This process has been called nitri-
fication.

Nitrification is a process of oxidation. In the oxidation of am-
monia compounds to form nitrates there are two separate stages.
The first is one by which the ammonia is oxidized into a nitrite.
A nitrite is a salt of nitrous acid (HNO2), and it contains less oxygen
than a nitrate. Nitrites are not plant foods, for, as far as known,
ordinary plants never absorb nitrogen in this form. The second
change is the addition of another atom of nitrogen to the nitrite,
giving a nitrate or salt of nitric acid (HNO3), the form in which the
nitrogen is most completely available for plants.

Nitrates are really of very great significance in nature. They
are readily soluble in water, so that they are easily taken up by the
soil and absorbed by the roots; thus nitrates feed the whole world of
green plants. In addition to this, nitrates form the basis of most
explosives. Gunpowder has saltpeter as its basis, and saltpeter is
nitrate of potash. Nitroglycerin, too, is made from nitric acid, and
practically all the other commonly used explosives are produced

57

58 NITRIFICATION AND DEN ITRIFI CATION.

from nitrates. Nitrate formation is, then, a matter of the greatest
significance. While there are, perhaps, some other methods by
which nitric acid can be formed, beyond doubt the nitrate store in
the soil has been formed chiefly through the process of nitrification.

Nitrification in the Soil. — It is very easy to demonstrate that
such nitrification actually takes place in ordinary soil. If we place
a quantity of soil in a proper vessel and subject it at intervals to a
chemical analysis, it will be found that there is an increase in the
amount of nitrates present, after it has remained undisturbed for a
few weeks. This fact has been known for nearly a century. The
next step in the discoveries was made in 1877, when it was demon-
strated that this nitrification is associated with the presence of living
matter in the soil. This can be proved by placing two lots of the
same soil under such conditions that in the one phenomena of life
may go on, while in the other they are stopped. If, for example, one
lot of soil is sterilized by heating it sufficiently to destroy the living
germs present, and then this soil is compared with another lot
treated in all respects the same, except that it is not sterilized, the
latter will be found to increase its nitrates, while the former will show
no such increase. The same results are obtained if the soil is mixed
with antiseptics which prevent bacteria growth. In short, any-
thing which prevent-s the occurrence of life phenomena in the soil,
prevents the nitrification.

Isolation of the Nitrifying Organisms. — Such experiments
repeated many times and verified by numerous observers demon-
strated that nitrification is the result of a living process. Inasmuch
as such soil contains no plants large enough to be seen, it follows that
the living agent of nitrification must be some form of microorganism.
It proved, however, to be a very dijficult matter to find the organisms
concerned in the process. The number of bacteria in the soil is large
and many different species are there found. But although many
of these bacteria were isolated and carefully tested, for a long time
none proved to have any power of nitrification. Most of them, indeed,
produced the reverse effect, that of deoxidizing nitrates, but none
of them raised the nitrites into a state of nitric acid. None of them
could oxidize ammonia so as to form nitric or even nitrous acid. If

NITRIFICATION.

59

a small quantity of soil is added to a solution of nitrite the nitrite soon
becomes converted into nitrate, under the influence of the fermenta-
tion started by the presence of the soil. This shows that the soil
must contain the nitrifying organisms. But the bacteria which
are isolated from such soil by ordinary methods showed no power
of nitrification. Evidently the nitrifying bacteria cannot be found
by the ordinary bacteriological methods.

The cause of the trouble as well as the secret of successful study
was soon learned. In bacteriological studies the common method of
isolating bacteria is to get them to grow in culture media made by
the bacteriologist. The media commonly used contain a certain
amount of organic compounds which serve as food for the bac-
teria. But experiment soon showed that the presence of the smallest
amount of organic matter is directly injurious to the nitrifying
bacteria, so that they will not grow at all in ordinary culture media.
It was necessary to devise some culture media that contained no
organic matter, and as soon as this was done it was possible to
isolate from the soil bacteria having the power, under proper con-
ditions, of oxidizing ammonium and nitrite compounds into ni-
trates. For a while the results of experiments were in some con-
fusion, since in some cases nitrates appeared to be formed, while in
others they did not. It became evident that nitrification was not a
simple phenomenon, and further study showed that the nitrification,
as occurring in ordinary soil, is a two-fold process. The first step in
the process oxidizes the ammonia into nitrites. In most of the ex-
periments the nitrogen was put into the culture fluids in the form of
sulphate or carbonate of ammonia and this was readily oxidized into
nitrite. The second step was the oxidation of the nitrites into
nitrates. The two steps are not only independent, but they are
brought about by two different species of bacteria. One organism
has the power of producing nitrite out of ammonia, but can carry
the oxidation no farther, failing to produce nitrates. The second
species can act upon the nitrites, carrying their oxidation up to the
form of nitrates, but it has no power to act upon ammonia. The
two together can produce the complete nitrification of both am-
monium and nitrite compounds.

60 NITRIFICATION AND DENITRIFICATION.

The Nitrifying Bacteria.— It thus appears that there are two
types of nitrifying bacteria. The first converts ammonium com-
pounds into nitrites, and, hence, are called the nitrite bacteria
(Fig. 18). They have been found in soils of very widely separate
localities, and probably live in all soils. Two slightly different
varieties have been recognized, both spherical bacteria, and named
Nitrosomonas and Nitrosococcus, names that will probably soon go
out of use. They appear to be able to form nitrites from almost any
kind of ammonium salt, and, since they are quite universally dis-
tributed in all decaying organic matter,

*4C» jl *^* #1 n ^^ ^^^^ ^^ ^^ ^^^ humus, they will evi-

dently seize the ammonium compounds
produced by ammoniacal decomposition,
• -^ / '^ and convert them into nitrites (Fig. 18, A).

•*• ^A c They are incapable, however, of forming

*'<>R nitrates from any nitrogen compound

^ S{ tJ* except ammonium salts, and hence the

Fig. iS—Nitrifying bacteria, proteid compounds of decaying bodies

^ IS a nitrous and B and C • .^ i .,, , ^ ^

nitric bacteria. cannot be nitrilied till they are reduced

to the form of ammonia. The second
type of nitrifying bacteria is called the nitrate bacteria, since they
oxidize the nitrites into nitrates. Only a single type of this class
has been found, and it was named Nitrobacter (Fig. 18, B and C).
It is smaller than most nitrite organisms and of a slightly elongated
shape. It is also widely distributed, probably in all soils, and is
able to convert any kind of nitrite into nitrate. It cannot, how-
ever, act upon any nitrogen compounds except nitrites, and hence
its action must be preceded by that of the nitrite bacteria.

In ordinary soil these two kinds of nitrifiers act together and
simultaneously. So closely connected is their action that it is
difficult to find any traces of nitiites in the soil, since they are
converted into nitrates as rapidly as they are formed. The whole
nitrification may be very rapid. If ammonium salts are added to
soil, they cannot commonly be found in the drainage- water from the
soil, since the nitrification progresses so rapidly that they become
completely converted into nitrates before draining away. But

CONDITIONS OF LIFE OF NITRIFYING ORGANISMS. 6l

though occurring simultaneously, the two steps in the nitrification
appear to be distinct and produced by distinct organisms. It
has been claimed recently that there are other classes of soil organisms
that take these two steps in one, converting ammonia and even
organic matter directly into nitrates. If this be true, they represent
distinct classes of nitrifiers, but the observations have not yet been
sufi&ciently verified.

CONDITIONS OF LIFE OF NITRIFYING
ORGANISMS.

The importance of the phenomenon of nitrification makes it
very desirable to understand thoroughly the conditions under which
it may best occur, and, consequently, the means for stimulating
or hindering it. The conditions regulating the life of these nitrifiers
are, in some respects, peculiar.

Organic Food. — In respect to food these nitrifiers are among
the most remarkable of all organisms. Not only do they need no
organic food, but the presence of organic matter in the solutions, even
in small quantity, is directly injurious. The bacteria will grow
readily in mineral solutions, but if a small quantity of organic
matter is added, the growth stops. In ordinary laboratory solutions
a very small amount of organic matter acts like an antiseptic. In
the soil, however, the nitrifiers behave differently, and are not
checked in their growth by such small quantities of organic matter
as serve to check them in laboratory solutions. This injurious
action of organic matter is a curious phenomenon. The more
highly organized the compound, the more decided its checking
action, and thus, the more valuable the material for ordinary kinds
of bacteria, the greater its injury upon the nitric bacteria. These
bacteria thus grow under conditions detrimental to other bacteria,
but will not grow under the conditions which other species find
most favorable. A more sharp contrast can hardly be conceived.
Not only bacteria, but all other colorless plants are obliged to depend
upon organic food as a source of energy, in this respect resembling
animals. But here is a group of organisms that not only does not

62 NITRIFICATION AND DENITRIFICATION.

need, but cannot grow in the presence of, organic matter. They do
not, therefore, need any other living organisms to interpose between
them and the mineral world, but may develop under conditions in
which they are supplied with mineral substances alone. It is
more surprising perhaps to find that they do not need light, but can
utilize the mineral substances while growing in perfect darkness.
This fact was at first conceived as quite contrary to our general
ideas of the relation of life to physical energy. We have supposed
that the only source of energy for living things is sunlight, and that
this energy is stored up by green plants in the form of chemical
compounds of high complexity. The animals and colorless plants
use these stores as food, breaking them up and using. the energy
liberated for their own use. But here we have organisms which do
not require organic material as a source of energy and are not able
to utilize sunlight itself directly. Evidently they must obtain their
energy from some other source than that which is commonly utilized
by animals and plants. That they have a source of energy at com-
mand is evident from the fact that they can assimilate CO2 and
build it into their own tissues, a process that requires energy. The
present belief is that they obtain their energy from the oxidation
of the ammonia compounds, a process that apparently can furnish
them with all they need. But whatever its source, these nitrifiers
are able to live under conditions in which other organisms cannot
exist.

Since the nitrifiers are injured by organic matter, it follows that
nitrification cannot be expected in highly concentrated decompos-
ing masses. Raw sewage contains so much high organic matter
that nitrification does not take place in it, and if it is applied directly
to the soil, in considerable quantity, it will effectually prevent the
nitrification necessary to render the nitrogen available to plants.
In the manure heap, too, nitrification cannot be expected so long as
the quantity of organic matter is high.

As the manure rots, however, the organic nitrogens are reduced,
until finally nitrification can begin. We have seen that decomposi-
tion gives rise to ammonia, usually combining with carbonic acid
to form ammonium carbonate. This compound is also injurious

CONDITIONS OF LIFE OF NITRIFYING ORGANISMS. 63

to the nitrifiers and, if it'becomes too abundant, will stop nitrification
until, either by vaporization or by denitrification, or otherwise,
it is reduced to an amount not deleterious to nitrification, when
the process begins. This checking of the action of nitrifiers by
organic matter or ammonia, certainly occurs in laboratory solutions
and concentrated compost heaps, but it does not appear to be of
much significance in ordinary soil. Nitrification takes place more
vigorously in soil than in solutions, and proper testing has shown
that the organic matter in ordinary soil does not prevent a vigorous
nitrification.

Moisture. — The nitrifiers require a moderate amount of moisture.
Too dry a soil will not allow of their growth. But, on the other hand,
too much moisture is equally detrimental. It has just been stated
that they do not grow so readily in laboratory solutions as in soil.
It is also a fact that in very wet soil, ''water-logged," nitrification
is greatly reduced or lacking.

Reaction. — The nitrifiers cannot develop in an acid medium
and are usually absent from acid soils. Soils may become acid
from various causes, one of the chief of which is the production of
certain organic acids {lactic, succinic, acetic, butyric, etc.), from the
bacterial decomposition of carbohydrate material. Large amounts
of sugar might give rise to an acid condition, but the more common
cause is the decomposition of cellulose and woody substances. In
forest land the decay of leaves and branches, as well as other vege-
table structures containing cellulose material, usually fills the soil
with these acids and, as a result, nitrification has practically ceased
in forest soils. The same is true in some open pastures and other
soils where such decay is extensive. The value of liming such soils
is evident. Lime neutralizes the acids and restores the alkaline
condition necessary for the nitrifiers, so that they may resume the
activity stopped by the acid. Too much lime, however, defeats its
end by making the soil too alkaline.

Humus. — That nitrification may take place, it is of course
necessary that there be plenty of nitrogenous material to be nitrified.
This must be in the form of an ammonium salt which, as we have
seen, is the condition reached by the organic nitrogen at the end of

64 NITRIFICATION AND DENITRIFICATION.

its decomposition. The ordinary humus will therefore furnish
plenty, but soil deficient in humus will show but little nitrification.

Temperature. — Nitrification occurs in the soil under a very
wide range of temperature. It goes on at temperatures fully as low
as 37° F.; it is most vigorous at about 99°, becomes manifestly
checked at 110°, and almost ceases at 122°. From these facts it will
be seen that it may continue in the fall until the appearance of
frosts and, in many localities where the winter is not too cold, will go
on all winter long. For this reason a cultivation of soil in the fall
is undesirable, since cultivation, by mixing air with soil, hastens
nitrification, and during the winter or late fall there is no growing
crop to utilize the nitrates as they are formed. These, therefore,
drain away from the soil during the spring and winter, leaving it
poorer in the spring than if the cultivation had not taken place.
Nitrification is the most vigorous in the summer months, during
which season the growing crops are in best condition for absorbing it.
This is one of the reasons why a wheat crop is so exhausting to the
soil. It grows during the fall and spring, but the ground lies idle
in the summer and hence during the season of greatest formation
of nitrate, there is no crop growing to prevent the loss by drainage.

Air. — Nitrification is a process of oxidation and therefore re-
quires oxygen. The more thoroughly the air is mixed with the soil
the more vigorous will be the nitrification. This process, therefore,
is more pronounced in sandy loams or mixtures of clay and sand
than it is in heavy clay soils. In heavy soils, where the earth
particles are very fine, the soils are too poorly aerated to enable the
nitrifiers to get a sufficiency of oxygen. From this we learn the
very practical lesson that cultivation of the soil stimulates nitrifica-
tion. Experience and theory both tell that the loosening up of soil
during the growth of plants greatly stimulates plant growth, and the
primary reason is evidently because this furnishes the necessary
oxygen for a vigorous nitrification, thus furnishing the crops with a
larger supply of the easily assimilated nitrates. In this fact, too, we
find an explanation of the fact that only the upper layers of the soil
are fertile since nitrification will go on only in the layers where
oxygen readily penetrates. About 65 per cent, of the total nitrifica-

EXTENT OF NITRIFICATION. 65

tion occurs in the upper twelve inches of soil, 30 per cent, more in the
layers from twelve to thirty-six inches lower, and little or none be-
low this. Surface soils alone are thus highly fertile.

EXTENT OF NITRIFICATION.

The production of nitrates in ordinary soil is very vigorous.
While in some soils it does not occur at all, from a lack of some of the
conditions already mentioned, in other soils nitrates are rapidly
formed. In fact, a much larger amount of nitrates is produced in a
cultivated soil, ordinarily, than is used by the crops. In some care-
ful tests it has been shown that twice as much nitrate is formed as is
used by the crop, the rest being lost to the soil by drainage. This is
particularly true when wheat is grown, wheat being an especially
exhausting crop. To furnish this amount of nitrate a proper amount
of organic nitrogen must be added in the form of manure or other-
wise. With plenty of such material as a source, nitrification is very
vigorous during all seasons, except when the soil is actually frozen.

The Unlocking of Soil Nitrogen. — It happens not infre-
quently that soil may contain large amounts of nitrogen and yet
fail to produce good crops, the plants seeming to be insufficiently
supplied with nitrogen in spite of its abundance. These barren
soils will not yield good crops unless supplied with a considerable
amount of nitrogen as a fertilizer. Upon an open hillside or a
meadow we may find the land very poor for supporting vegetation,
and yet its soil, when analyzed, may yield a considerable quantity
of nitrogen. In such a soil the nitrogen is simply locked up in the
humus in a form useless to plants. At the end of decomposition,
a large part of the nitrogen may be held in a form not available for
ordinary vegetation, so that plants growing in such soil will be
nitrogen-starved, although growing in the midst of plenty of nitrogen
compounds. Such soils might become highly fertile if some agency
for unlocking these nitrogenous compounds could free the nitrogen
from its stable relations, thus producing compounds of a nature to be
assimilated by plants. A nitrification is evidently what is needed to
make these soils productive. If a comparatively small amount of
6

66 NITRIFICATION AND DENITRIFI CATION.

manure is added to such soils the results are sometimes surprising
in causing an increased fertility far beyond that which might be
expected from the small amount of manure itself.

For example, one frequently sees that an open pasture or meadow
supports a somewhat limited crop of grass, although nitrogen com-
pounds may be abundant enough in the soil. If cows are pastured
there it is common to find plots of brilliant green, vigorously growing
vegetation, surrounding the droppings of the cow excrement. Now
this may be due in part to the food contained in the excrement
which is utilized by the plant, but it is not wholly thus explained.
The effect lasts for a long time, and months afterward the oasis of
green may be seen in the pasture, gradually increasing in size until
it reaches far beyond what must have been the limits of the direct
effect of the plant food in the excrement. The explanation seems
to be that by this excrement the nitrifying bacteria are stimulated,
and these in a short time begin the work of converting the soil
nitrogens into nitrates. Their influence continues to extend through
the soil as they multiply and act upon a wider and wider circle, so
that an increased vegetation may continue for a long time under
the influence of these nitrifying bacteria which are constantly con-
verting the soil nitrogens into nitrates. That this is the whole ex-
planation in these cases is by no means sure, but it is certain that the
nitrifiers do unlock much nitrogen previously not in an available
condition.

DENITRIFICATION.

There is another group of microorganisms in soil and other
decaying masses acting in exactly the reverse direction from the
nitrifiers. Whereas nitrification oxidizes ammonia compounds and
nitrites, to form nitrates, denitrification takes the oxygen out of
nitrates, reducing them to nitrites and ammonia, and may even
reduce these to free nitrogen. Nitrification prepares plant foods,
but denitrification destroys them. The one process is useful, the
the other detrimental, to soils

Three different types oi reduction of nitrogen compounds

DENITRinCATION. 67

are comprised under this head: i. The reduction of nitrates into
nitrites. 2. The reduction of nitrates to give ofiF free nitrogen. 3.
The reduction of nitrites into free nitrogen. The term denitrifica-
tion is sometimes used to cover all of these types of reduction, and
sometimes more particularly to refer only to the reduction of the
nitrates and nitrites, so as to liberate free nitrogen. In its strict
use it should be confined to the latter process.

It is evident that these different types of reduction will have
different effects upon soil fertility. Those portions of the nitrogen
that are reduced to nitrates or ammonia, under proper conditions
may be built up again into nitrates by the nitrifying bacteria. But
those that are reduced to a condition of free nitrogen pass off
into the air and out of the reach of plant life. This nitrogen,
therefore, represents an actual loss to the soil. Denitrification
is a process very different from the general type of decomposition
which we have described. Decomposition begins with proteids and
reduces them to ammonia compounds. Denitrification begins with
nitrates and nitrites, and liberates free nitrogen.

The Denitrifying Bacteria. — Denitrification is the result
of the action of a class of bacteria known as the denitrifiers. Very
many bacteria have the power of extracting the oxygen from nitrates,
reducing them to nitrites, but the list of those that can liberate free
nitrogen is shorter. Some of them act in aerobic conditions, and
others in anaerobic conditions. The names B. denitrificanss.
I and II have been given to two of them, but others have been found
with similar properties. They are very widely distributed; they
are found not only in soil and water, but in the air and all organic
decomposing refuse. They are very abundant in the manure heap,
especially if it contains much hay and straw, and they are likely
to cause a considerable loss of nitrogenous matter by liberating
the nitrogen as free nitrogen gas. Excrement always contains
them, but they are more abundant in the excrement of herbivorous
animals than of carnivorous animals. These bacteria, in order to
grow vigorously, require some carbon-holding food, and they cause
the largest amount of denitrification when abundantly supplied
with carbohydrates. Sugars, starches, glycerin, or organic acids

68 NITRIFICATION AND DENITRIFICATION.

may furnish this needed carbon, and the cellulose present in hay
or straw will also furnish it. Any form of decaying matter that
contains great amounts of hay or stubble is especially subject
to denitrification. Horse manure, containing as it does large
amounts of hay, shows greater losses of nitrogen than the manure
of cattle, which contains less carbonaceous material.

The extent of the actual losses caused by these denitrifiers in
ordinary farm processes is not fully known. It is certain that in
concentrated decomposing solutions the action is vigorous, but
it is not so great in less concentrated masses. In the manure heap
there is always some loss in this way, and when great quantities
of manure are spread over a plot of cultivated ground, denitrifica-
tion doubtless causes considerable loss. When, however, the manure
is applied in limited quantity, so that it is mixed with a considerable
amount of soil, the evidence seems to show that the losses are slight
if any. In ordinary soil, therefore, denitrification is not a phenome-
non of much significance. In concentrated manures, however,
especially if they contain much hay, it may be great. One very
impoitant lesson is to be drawn from these facts. Nitrates should
never be mixed with manure. The nitrates will simply be thrown
away, since the denitrification in the manure heap will surely
reduce most of the nitrate to free nitrogen, thus causing its complete
loss. Further, the denitrification is greatest in fresh, concentrated
manure, while it diminishes greatly in manure after it has partly
decayed. The denitrifiers do not find the partly decomposed
organic substance favorable to their life, and do not flourish. Hence,
the use of large amounts of partly rotted manure upon a soil is
possible without bringing about a nitrogenous loss, while the use
of the same amount of fresh manure would be undesirable.

CHAPTER VI.
THE MANURE HEAP AND SEWAGE.

CONTENTS OF THE MANURE HEAP.

The value of the manure heap is recognized by every farmer.
So thoroughly is this appreciated that, in some countries, the wealth
of the farmer is measured by the size of his manure heap, which
is commonly exposed prominently in front of his house. Every-
where one may measure quite accurately the thrift of a farmer by
an examination of this somewhat unsavory product of farm life,
and the extent of his intelligence may likewise be gauged by the
care he bestows upon it. We can readily understand its importance
when we remember that in this manure heap are going on, in a
condensed space, exactly the transformations of food material
which we have been considering.

The manure heap is always an extremely complex mixture
of organic substances, of nearly every conceivable kind. It contains
great quantities of partly broken-down vegetable tissues, which have
passed through the alimentary canal of the cattle, partly digested.
It will contain large or small amounts of hay or straw derived from
bedding and from the incompletely digested food, especially if
horses contribute to its formation. It may contain sawdust or
some other form of woody tissue. It will be likely to contain more
or less flesh and bone from dead animals, and will be sure to contain
proteids, albuminoids, gelatins, fats, sugars, starches, and, indeed,
nearly all types of organic matter produced by animals or plants,
all of which will be in various stages of digestion and decomposition.
Lastly, and perhaps most important, it will contain much nitrogen
in the form of urea, in the liquid manure, which represents the
result of the nitrogenous metabolism of animal life. This liquid
manure is by far the most valuable part of the manure, since it

69

70 THE MANURE HEAP AND SEWAGE.

contains the nitrogen which has been actually metabolized by ani-
mals, and which can now be brought back readily into a condition
available for plant life. The liquid manure contains three-fourths
of the total nitrogen of the whole heap, and four-fifths of the total
potash. But farmers frequently fail to realize this, and allow this
material to waste by soaking into the ground. In addition to these
ingredients manure always contains a large amount of water and
an unknown number of species and varieties of bacteria in very
great abundance.

In this manure the bacteria find plenty of food and moisture
and their growth is rapid. There is a great struggle for existence
among them and, in the weeks of fermentation, first one and then
another species may gain mastery. If the bacterial contents of
such a mass be studied at intervals, the number and variety of species
which are most abundant are found to be constantly changing.
At first the ordinary intestinal bacteria abound; later the putrefactive
bacteria become most abundant, and finally the denitrifying and
nitrifying bacteria are in the majority. All of this indicates faintly
the wonderful complexity of bacterial life and the intensity of the
struggle for existence among the numerous species originally present
in the manure.

Losses from the Manure Pile. — The result of this bacteria
growth is an extensive and profound series of chemical changes
by which the manure is profoundly modified. These are partly
useful and partly injurious, but, taken as a whole, they are neces-
sary. Most of the material in the manure is in a form not capable
of being used by plants, and must be greatly transformed before it is
available for vegetation. The transformations are much the same
as those we have already considered in the soil, but they take place
under different conditions, which somewhat modify them. In our
study of the subject it should be borne in mind that the most im-
portant feature of manuring is the furnishing of nitrogen to the crops,
and the first care should be to protect this material and avoid its
loss.

The losses from manure are due to two causes, i. Leaching. A
considerable portion of the nitrogen is in a soluble form, including

THE FERMENTATIONS OF MANURE. 7I

all of that in the liquid Inanure. From manure heaped upon soft
ground, large amounts of this are completely lost by draining away
or soaking into the ground. If the manure is left exposed to rains
this loss is greatly increased. As a result the ordinary manure heap
decreases very much in value during the weeks or months that it is
stored in the pile. This part of the loss can be entirely prevented
by storing the manure where the liquids will not leach into the
soil. 2. By fermentation. This subject requires a more extended
consideration.

THE FERMENTATIONS OF MANURE.

Destructive. — The first chemical changes which go on are
those of general decomposition. An ammoniacal fermentation is
universal. The liquid manure is most rapidly decomposed by this
fermentation, the substance undergoing in a very few days, sometimes
in a few hours, a reduction into ammonia compounds, as already
mentioned above. This is completed before the ammoniacal fer-
mentation of the other nitrogen bodies has fairly begun, and suggests
that the proper method of handling manure will be to treat the
liquid manure separately from the solid portion. Eventually the
nitrogenous compounds in the solid manure will also undergo am-
moniacal fermentation. The starches, sugars, cellulose and woody
tissue undergo a decomposition by which COj is set free and various
other substances are left. The fats and fatty acids are also decom-
posed, liberating CO2 with other less known bodies. The decom-
position of the proteids liberates sulphur, commonly as H^S, and this
may unite with water to form sulphuric acid. The sulphuric acid
may combine with the ammonia to form ammonium sulphate, or the
ammonia may combine with the carbon to form carbonates. A
large quantity of material is lost from the manure during these
changes. The loss includes carbon in large amount, a matter of no
significance, however, as it has simply gone into the air from which
it can readily be reclaimed by plants. But the loss includes much
nitrogen, and this is a misfortune, since it is the nitrogen that the
farmer desires to keep.

72 THE MANURE HEAP AND SEWAGE.

This loss occurs in several ways. i. Liberation of ammonia.
Since the ammonia resulting from decomposition is a gas, it will, to a
considerable extent, dissipate itself at once into the atmosphere.
Such portions of it as unite with carbon dioxid to form ammonium
carbonate are less volatile, but this, too, is partly volatilized. The
odor of ammonia common around a manure heap plainly demon-
strates this loss. 2. Denitrification. If by this term we refer only
to the reduction of nitrates so as to set nitrogen free, the process is
not very important in a manure heap, since there is present only a
little nitrate, none, indeed, at first, when the fermentations are
greatest. If nitrates are present, denitrification will cause a loss, and
in the later stages of the rotting of manure, after nitrates are formed,
this loss might be considerable. But it seems that loss from this
cause is not so great as was formerly supposed. 3. Destruction of
ammonia. There seems to be a direct "burning" of ammonia
compounds in the manure heap by which the nitrogen is set free
from it as free nitrogen. Little is known concerning this factor at
present.

The extent of the nitrogen losses from these sources may be
considerable. Various estimates of the amount have been made,
and it seems not beyond the mark to say that, in the ordinary condi-
tions on the farm, at least 50 per cent, of the nitrogen is lost to the
manure. It is sometimes considerably more than this, 50 per cent,
being a fair average. When the farmer remembers the high cost of
nitrogen fertilizers he may perhaps realize the very poor economy of
allowing this loss to continue. Not all the loss is avoidable, for
under the best conditions, perhaps 15 per cent, is lost; but even if this
is true, 35 per cent, may be saved by proper care. It is possible for
a farmer to know when this loss is becoming excessive by two means :
I. The appearance of a strong odor of ammonia tells its own story;
and while some such odor may always be expected, a strong odor
indicates a too rapid loss. 2. The heating of the manure indicates
rapid aerobic fermentations and this is always accompanied by a
large nitrogen loss. Properly kept manure will not show a great
rise in temperature and never a rapid one. The farmer may be
confident that a noticeable heating of his manure pile means a large

THE FERMENTATIONS OF MANURE. 73

loss. Some manure he^ts more rapidly than others, that from the
horse being especially subject to this destructive fermentation; a
fact due partly to the large amount of hay that it contains and partly
to its loose and porous nature, which allows a free access of air. It
suffers more loss for this reason than most other types of manure — a
loss that may be lessened by mixing with it some of the moister,
denser cow manure. Liquid manure also is subject to heavy losses,
because it so rapidly undergoes the ammonical fermentation.

There are two general methods of controling and reducing these
losses. The first is by chemical means. Since the ammonia is
volatile and a strong base, the addition to the manure of some
chemical to conbine with it will produce salts that will be more
likely to be retained in the manure. For this purpose quite a list
of substances has been recommended. Among them are, gypsum,
burned lime, shell lime, lime-stone, kainii, superphosphates and sul-
phuric acid. Each of these has a value when properly used, but
none of them will wholly prevent nitrogen loss and all are some-
what costly. The losses due to ammonia vaporization may be pre-
vented by these chemicals; but the losses caused by the liberation
of free nitrogen cannot be checked by any means short of stopping
bacterial growth, and this would check the beneficient as well as the
injurious fermentations. On the whole, the result of experience
seems at present to be against the use of chemical means of
preserving manure.

The second method is mechanical and is more efficient. It is
based upon the facts already emphasized, viz., that the destructive
fermentations take place most vigorously in the presence of a large
supply of oxygen and that the volitilization is much more rapid
from a partly dry than from a wet mass. Hence manure that is
loosely piled loses much more nitrogen than that which is firmly
compacted. The practice of firmly compacting manure into conical
heaps with smooth sides is best calculated to reduce the losses to a
minimum. Experiment has shown that a lot of manure firmly
compacted may lose 15 per cent, of its nitrogen during storage,
while a similar lot loosely stored loses 35 per cent.; a very striking
testimony to the value of compacting. If, further, the manure be
7

74 THE MANURE HEAP AND SEWAGE.

Stored in cemented pits, that will prevent loss by draining, and if
the excess of the liquid manure is caught in special tanks and
frequently spread upon the fields before fermentation has progressed
far enough to cause^much ammoniacal fermentation, the greater
part of the ordinary losses may be prevented. In thus storing the
manure it should be kept moist by the use of liquid manure, but
not allowed to become water soaked. It has recently been shown
that the losses from manure may be greatly reduced by spreading
fresh manure upon the older manure that has already begun to
undergo an active fermentation, probably because the carbonic
dioxid evolved in the fermentation of the older portions combines
with the ammonia developed from the newer portions, this checking
its dissipation. The presence of large amounts of hay in manure
makes it difficult to compact and, moreover, furnishes large amounts
of fermentable matter that increases nitrogen loss. It is therefore
usually unwise to allow much hay or straw to be mixed with solid
manure.

Thus the best methods of protecting manure from loss are: i.
The exclusion of air. 2. The regulation of the amount of moisture.
3. The separation of the excess of liquid manure from the solid and
its distribution upon the soil at frequent intervals. 4. Prevention
of loss in liquid manure by leaching. 5. The presence of some
already fermenting manure to furnish carbonic dioxid to combine
with the ammonia as it is produced. 6. The use of some kind of
^^ litter ^^ to absorb the liquid manure and prevent its loss.

Constructive Fermentations. — In order that the manure may
become plant food the end-products of decomposition must be built
up into the form of nitrates by nitrification. Nitrification, however,
cannot take place in the fresh manure since it contains too large
quantities of organic products, which, as we have seen, prevent the
growth of nitrifyers.

Exactly when it begins is a little uncertain, but it appears to
start only after the high organic compounds have been almost
wholly broken up into ammonia, and the ammonia formed has
either united with the acids to form salts or has been dissipated
into the air. The oxidation of the ammonia salts into nitrites is

THE FERMENTATIONS OF MANURE. 75

then brought about by the nitrous bacteria which are not prevented
from growing by the presence of free ammonia. The nitric bacteria
are, however, so extremely sensitive to ammonia that they cannot
begin the formation of nitric acid till ammonia gas has entirely
disappeared and therefore probably not until decomposition has
ceased. When the nitrifying processes do begin, they complete the
ripening of the manure. They oxidize the nitrogen compounds
which are left, the ammonia salts becoming first changed to nitrites
and then to nitrates. As this process continues the manure is
more and more filled with nitrates and therefore becomes a better
and better food for plants. At last when the process is ended and
the manure is fully ripened, enough of nitrogen is converted into
nitrates to furnish a most valuable supply of food for vegetation.

Fresh and Ripened Manure. — The transformations which
we have considered constitute what is called the ripenings rotting,
or composting of manure. They are clearly similar to those changes
already considered as taking place in the transformations in the
humus, but rendered more intense by the concentration of the
manure heap. It is evident that manure is of no value to plants
until it has undergone these transformations, and equally evident
that the transformations may, and some of them do, go on in the
soil after the manure is mixed with it as well as in the manure heap.
Indeed, they will probably go on better in the soil, and in some
important respects it is an advantage to incorporate the manure
with the soil while fresh rather than to wait for it to ripen. We have
noticed that the loss from decomposition and denitrification is
slight when these processes occur in the soil, while they are con-
siderably higher when the ripening occurs in the concentrated
manure heap. The loss is especially large from the liquid manure
in warm weather, which, if kept in tanks or allowed to accumulate
with the manure pile, will undergo a very rapid ammoniacal
fermentation resulting in large losses of nitrogen. If, however,
it is mixed at once with the soil the ammonia is fixed as fast as formed
by the soil ingredients, is soon nitrified, and the loss is largely
prevented. There has thus come to be recommended the practice
of spreading the manure upon the soil as quickly as convenient.

76 THE MANURE HEAP AND SEWAGE.

not allowing it to accumulate, and undergo the fermentation that
inevitable means loss of nitrogen. Whether this will always be
feasible will depend upon conditions on the individual farm; but
it is certainly to be highly recommended in all localities where
climatic conditions and the exigencies of farm occupations make it
possible.

It is to be borne in mind that in using manure as a fertilizer
the soil receives advantages that are not derived from mineral
fertilizers. Not only does the manure contain a considerable list
of substances of value to the crops, present in small quantities
only, and not present in mineral fertilizers, but manure contains
considerable organic material in a partly decomposed condition
that aids in forming a permanent humus. The texture of the soil
is improved by this so that the final result is a soil superior to that
containing only mineral fertilizers. The soil thus treated becomes
more tenacious, richer, washes less with rains and is generally to
be preferred. Mineral fertilizers, with the exception of nitrates
may be mixed with manure. The nitrates, if thus mixed, would
be lost by denitrification.

SALTPETER PLANTATIONS.

These nitrifying forces are not confined to the soil, but may
occur in other localities, always resulting in the production of nitrates.
Before the discovery of the nitrate beds of South America it was the
custom of agriculturists to prepare their own nitrates by a simple
process, not then understood, but now known to be due to nitrifying
bacteria. The places where nitrates were thus formed were called
saltpeter plantations, and the saltpeter was produced by exactly the
processes we have already considered. The method was as follows :

Masses of chalky soil were mixed with various organic bodies
and the whole heaped into a pyramidal pile, rendered somewhat
porous by the admixture of brushwood. The heap was still further
furnished with fermentable nitrogen by frequently watering it with
liquid manure. In this heap occurred the various kinds of nitrogen
decomposition already mentioned, and later the nitrification process

THE COMPOST HEAP.

77

began. The result was Ihat nitrates were formed in the interior of
the heap in large quantity. Eventually the nitrates were extracted
by water and converted into nitrate of potassium by the addition of
some potassium salt.

This method of making saltpeter was discovered before science
had any idea of the real nature of the process, and it was a practical
means of utilizing a part of the nitrogen in the organic substances
derived from animals and plants. Whether it was the most efficient
means or more useful than the simple compost heap and manure
pile can hardly be stated.

Saltpeter plantations have gone out of existence since the in-
troduction of Chilian saltpeter. It is probable that the nitrate beds
of Chili are the remains of some old inland arms of the sea where
great growths of seaweeds accumulated which, after the drying of
the inland sea, were converted into nitrates by the processes of
decomposition and nitrification due to bacterial action.

Nitrates are formed upon the walls of closets and stables where
ammonia fumes are abundant. On such walls may frequently be
seen a snow-white mass consisting of calcium nitrate. It is the result
of nitrification of the ammonia which unites with oxygen and pro-
duces nitric acid. The acid combines with the calcium present in
the brick- work to form calcium nitrate. The action is an undesirable
one from the standpoint of the persistence of the walls, since it pro-
duces a corroding action tending to weaken the structure. It may
be readily prevented by sprinkling the walls with a strong solution of
some powerful antiseptic, such as formalin or corrosive sublimate.

THE COMPOST HEAP.

It is evident that in a compost heap there must be going on a
series of similar bacterial transformations. By proper means the
farmer may make use in his soil of almost any organic material
which contains nitrogen or the minerals needed for his crops.
Vegetable tissues of all sorts contain more or less nitrogen and may
readily be brought under the influence of the bacteria which are
able to reduce them to plant foods. A valuable source of such

78 THE MANURE HEAP AND SEWAGE.

material may be obtained from seaweeds, if they are at hand. In-
deed, any abundant vegetable substances may thus be heaped into a
mass, and, if moistened sufficiently by rains, the bacteria will be
sure to work within it, gradually transforming the nitrogens, and
converting them finally into nitrates for plant food. Into his
garbage heap, then, the farmer may throw all sorts of organic
debris, animal or vegetable, with the confidence that his bacterial
aids will in time place the nitrogenous material at his service as a
fertilizer. Thus, by the aid of his invisible allies the agriculturist
will be able to make use of the wastes on his farm and in time return
to his soil a considerable portion of the nitrogen.

SEWAGE AND ITS TREATMENT.

Composition of Sewage. — By sewage we ordinarily understand
the material which collects in the sewerage system of our larger com-
munities and which has no exact counterpart on the farm. It al-
ways contains the products of the life of men and animals, which are
no longer useful; also large quantities of both animal and vegetable
foods which have passed through the alimentary canals of men and
animals unassimilated. It contains a large amount of urea which
has come from the animal metabolism; and also woody matter,
cellulose, fat, starch, and an indefinite series of other organic
bodies. Almost anything which enters the city may find its way
eventually into the sewers where, mixed with large quantities of
water, it contributes to the sewage. The sewage thus contains
exactly the same sort of material as that found in the manure heap
and the compost pile. Evidently the problem of the various steps
of decomposition of this material will be nearly identical with that
already considered.

TREATMENT OF CITY SEWAGE.

As cities have grown, the matter of disposing of their sewage be-
comes more and more difficult. In small communities the digging
of cess-pools is satisfactory; but as larger numbers of people con-

TREATMENT OF CITY SEWAGE. 79

gregate together, this method becomes objectionable, and finally
impossible. The treatment of city sewage has become a problem
involving the ingenuity of the expert sanitary engineer. It cannot
be said that any wholly satisfactory method has yet been devised
for handling this difficult problem.

In the first place it is evident that sewage contains material that
is very valuable if it can be used upon the soil. The large amounts
of nitrogen in the urea alone from a large city would be worth mil-
lions of dollars yearly if it could be utilized. The nitrogen was taken
originally from the soil by the crops, and the continued fjertility of
the soil is dependent upon its being in some way replaced. It re-
quires no argument to show the wastefulness of throwing this valu-
able material away without attempting to utilize it. In China
careful attention is paid to prevent the loss of such material, and as a
result the soil remains fertile; while in our country a constantly
decreasing fertility has followed the practice of wasting it. The only
methods yet devised of utilizing city sewage on a large scale is by
what is called sewage farming.

Sewage Farming. — This method of disposing of sewage has
been established in the last thirty years as a means of at once dis-
posing of and utilizing the sewage of large cities. These farms,
necessarily located as near as possible to the city, receive its sewage
and distribute it over the fields by conduits, thus furnishing the crops
at the same time with nourishment and water. Upon such soils
crops are raised, mostly garden crops, since these are sure of a ready
market in the city. This plan of utilizing sewage has been very
vigorously urged, and many such farms have been organized in
England, in continental Europe, and some in this country. Enor-
mous sewage farms are cultivated near the cities of Paris and Berlin,
the latter city having thousands of acres under cultivation. In some
of the arid western sections of United States, where water is es-
pecially valuable, sewage farming has also become very profitable.

There can be no doubt that this method of disposing of sewage is,
theoretically, the proper one. It has two distinct advantages:
I. Economic. It puts back into the soil the great quantities of
nitrogen and other materials taken from it by the crops. 2. Sani-

8o THE MANURE HEAP AND SEWAGE.

tary. The sewage ingredients, " after being incorporated into the
soil, undergo the various types of bacterial decompositions which
have been described in recent chapters. The organic compounds
are decomposed by bacterial action, a part of the resulting decom-
position products going into the air as gas, and a part being built up,
in the soil, into nitrates, to feed the growing crops. The offensive
waste material is thus disposed of by being converted into inoffen-
sive and useful products. Sewage farms thus prevent the sewage
contamination of streams, harbors, and seaside resorts. This in
itself is sufficient to make this method of disposal a desirable one.

But the appearance of certain practical difficulties has prevented
a wide development of this system. It is, of course, impossible to
expect farmers to adopt this system unless it is profitable, and, un-
fortunately, it frequently proves that such sewage farms are run at
a loss instead of a gain. To be sure, in some places very favorable
returns have been yielded, and largely increased crops have been
reported. But in other places unfavorable reports have been made,
and at the present time sewage farming is not increasing. Since
the objections to it are purely practical, they may in time be over-
come. The chief objections are as follows: i. It is unhealthful to ir-
rigate garden crops with a sewage that is sure to contain disease
germs. This objection applies chiefly to vegetable products which
are eaten without cooking, like lettuce, celery, etc. 2. Land near
the large cities is usually too valuable to be used for farming proc-
esses. If the farm is at some distance from the city the expense of
carrying the sewage to it becomes so great as to make the under-
taking a losing instead of a profitable one. 3. Only a fairly porous
and partly sandy soil can absorb the quantity of sewage necessary
for the disposal of the product. In order that the soil may absorb-
it, the sewage must be decomposed and nitrified by bacteria. If
this nitrification does not occur, the soil becomes clogged with the
sewage products. Hence, if the soil is heavy and contains much
clay it cannot be used for sewage farming. While sewage farms
are successful and profitable in the sandy soils around Berlin, they
are not possible in many another locality where the soil is of a dif-
ferent texture. 4. The extreme dilution of the sewage makes it

t

TREATMENT OF CITY SEWAGE. 8 1

mpractical, or even impossible, to use it in some localities. The
il can absorb only a certain amount of water without becoming
too wet for the raising of crops. In regions where rains are common,
all the water is furnished by rain that can be handled by the soil,
unless it is very sandy, so that the addition of much more water
would spoil the crops. In many localities, especially in the United
States, the sewage from a city is very dilute. We are very ex-
travagant in the use of water, and a given quantity of American
sewage contains much less fertilizing material than the same amount
of German sewage. American sewage cannot be valued at more
than one cent a ton, and it is impossible for any but tha most sandy
soils to absorb to advantage such great quantities of water, for the
minute quantity of nourishing matter it contains.

These are some of the reasons why sewage farming is not
generally successful, and there is little to hope for along these lines
until some new methods can be devised for making the fertilizing
ingredients of sewage more easily available and more profitable.
It must be recognized, however, that this end is to be desired, since
surely there ought to be some method of saving the enormous loss
that comes from waste sewage. It can at present be profitably
undertaken only in dry regions, or where a sandy soil can absorb
large amounts of water.

Sewage Disposed of as a Waste Product. — For the reasons
just given it will be understood why sewage has come to be regarded
as a waste product, to be disposed of as inexpensively, but as ef-
ficiently as possible, the desire being to destroy it and not utilize it.

Chemical Treatment. — The first method used was to treat the
sewage with chemicals that partly purify it. This is an expensive
method, troublesome and unsatisfactory, and although used for a
few years, it has been replaced quite generally by the bacterial
method of treatment, which is the one most commonly adopted
to-day by communities that need to find some method of sewage
disposal.

The Bacterial Treatment of Sewage. — This method is based
upon exactly the same bacterial activities that we have been con-
sidering in recent chapters, the sewage being treated in a manner

82 THE MANURE HEAP AND SEWAGE.

that hastens the decomposition power of the bacteria so that they
will rapidly destroy the organic products in the sewage. The
method has not been devised by any one person, but has been the
result of observations and experiments of several, extending over
many years, and finally crystallized into practical results.

The bacterial treatment of sewage depends upon the destructive
action of the decomposition and putrefactive bacteria. Putre-
factive bacteria decompose all kinds of organic bodies, both the
nitrogenous and those purely carbonaceous. Most of the solid
matter in the sewage is composed of these organic bodies, and it is
evident that if the sewage can be induced to undergo a thorough
decomposition under the action of microorganisms, this will produce
a great effect upon the composition of solid matters present.
Almost all of them will be reduced to simpler compounds. The
carbonaceous material will be reduced eventually, if the process
is complete, into CO2 and water, with the liberation of hydrogen
or perhaps marsh gas (CHJ. Such gases would leave the liquid
and join the atmosphere. The nitrogenous material would suffer
the decomposition, resulting in the production of ammonia; and
denitrification, which would be sure to occur, would still further
reduce this to free nitrogen. Such gases also would be sure to join
the atmosphere unless held in solution in the liquids. In short,
the putrefactive processes, which in the manure heap produce a
loss deprecated by the agriculturist, would produce here exactly
the result which the sanitary engineer desires to reach, a destruction
and dissipation of organic material.

Such changes will take place as readily in sewage as in manure
or in the soil. Indeed, observation and analysis show that they
commonly take place much more rapidly. In the first place,
the organic matter to be acted on is generally in a soluble or partly
dissolved condition, and very easily acted upon by bacteria.
Secondly, the great abundance of water facilitates the action, for
bacteria require an abundance of water for their best growth. Thirdly,
the bacteria are present in extreme abundance. All sewage con-
tains bacteria in large numbers, although naturally the number
varies. A common sewage contains from 7,000,000 to 10,000,000

TREATMENT OF CITY SEWAGE. 8^

bacteria per c.c. Among" these bacteria are always large numbers
of the various decomposition bacteria, ready to seize upon the
organic material and decompose it. Such sewage, if left to itself,
will undergo a rapid and quite complete decomposition, which
results in reducing large quantities of matter to a gaseous state.
Other parts are rendered perfectly soluble and are completely
dissolved in the water, so that the water of the sewage is left free
from putrescible matter.

To bring about this result two different methods of treatment
have been adopted, sometimes used together and sometimes sepa-
rately, each of which has several modifications.

The Septic Tank. — This is a method of making use of the anaerobic
bacteria which decompose products rapidly, but incompletely. The
septic tank is a large closed chamber, perhaps below the surface of
the ground, and closed upon all sides and the top, with simply a vent
pipe extending from the top to allow the escape of gases. The
sewage is passed into one end of the tank in a somewhat slow but
constant stream, and the cavity of the tank is so divided by partitions
as to insure a slow uniform passage of the sewage through the tank,
and a final exit at the other end by an effluent pipe. The flow is
regulated so that each particle of sewage remains in the tank from
twenty-four to forty-eight hours.

During this slow flow through the tank bacterial action is
vigorous, and it is chiefly the anaerobic bacteria that develop,
since the closed tank allows little oxygen to enter. Furthermore,
a heavy scum usually grows on the surface that prevents the excess
of oxygen. In these anaerobic conditions, therefore, decomposition
proceeds rapidly, the organic bodies becoming partly broken down.
Gas is evolved in quantity and bubbles up through the liquid to
find exit from the tank by special vents. The gases represent the
partial destruction of the organic matters in the sewage, and as
fast as they are evolved the organic ingredients in the sewage
disappear and the sewage becomes clearer. When it leaves the
outlet, after flowing through the tank, it is much purer than when
it entered, and may then be discharged into streams without
greatly contaminating them, if the process has been efficient. The

84 THE MANURE HEAP AND SEWAGE.

evolved gases are only partly oxidized and are sometimes collected
and burned into the final condition or CO^, etc. The fermentation,
being of the nature of putrefaction, gives rise to unpleasant odors,
since the gases contain various compounds of sulphur and phosphorus
that are only partly oxidized.

The Filter Bed and Contact Bed. — These two methods, though
differing in detail, are identical in principle, and both are designed
to stimulate the activities of the aerobic bacteria. In the filter
beds the sewage is received upon great open beds, the bottoms of
which are made of masses of coke, broken stone, clinkers, sand,
etc., arranged in layers of different degrees of fineness, the finest at
the top. Through these the sewage filters and appears below,
greatly purified. It was at first supposed that the process was a
mechanical filtering through the sand, but it is now known that the
mechanical filtering has little to do with it. The contact beds are
similar, large, open beds, filled with coarse coke, clinkers, or other
material, but not arranged for filtering. The sewage is conducted
upon these beds, allowed to remain there for a few hours, and then
withdrawn to be replaced by more sewage. Although no filtering
takes place, this sewage is purified by its sojourn in the contact bed.

In both cases the primary action is that of aerobic bacteria,
aided, doubtless, by direct chemical activities of the oxygen of the
air. The bacteria rapidly cause the decomposition of the organic
products, and the decomposition is more complete than in the
septic tank, so that simple gases, like CO^ and N are evolved.
The gases are no longer oxidizable. The action on the sewage is
made more complete and efficient if the sewage be first passed through
the septic tank and then over a contact or filter bed.

Sprinkling, Trickling, or Percolating Filters. — This represents a
third slightly different method of bacterial purification of sewage. A
mass of stones or some other favorable material, broken into
fragments not less than half an inch in diameter, is spread in a
layer several feet thick. The sewage is then sprayed or sprinkled
upon this mass, and it slowly trickles through the rock layer. The
broken rock fragments are so coarse that there is no filtering action,
but, as the sewage slowly trickles downward, it is acted upon by

TREATMENT OF CITY SEWAGE. 85

chemical and bacterial kgents, so that it flows out below quite
changed in its nature. Sewage treated in this way does not look
clear after treatment, but the organic products in it have undergone
a change that makes them non-putrescible, and they will not undergo
any further putrefactive changes. This method of treating sewage
is recent and as yet not fully understood.

Effect on Organic Products. — As a result of these two types of
decomposition the various organic bodies in the sewage are very
largely destroyed by processes similar to those that occur in the
manure heap. Various gases are liberated (HN3, N, CO2, CH^,
H2S, etc.), and the total amount of solid matter is thus greatly re-
duced. Later in the process, especially in the contact beds where
oxygen is abundant, a vigorous oxidation of the nitrogen compounds
begins {nitrification) which results in the formation of nitrates.
These nitrates are, however, thoroughly soluble and become at once
dissolved in the water of the sewage, which consequently clears up.
In this way nearly all of the nitrogen which was held in high com-
pounds in the original sewage, has either become dissipated into the
air as ammonia or free nitrogen, or has become converted into
nitrates and has dissolved in the water to form a clear solution which
is not objectionable when discharged into streams.

This whole topic is only a part of the general subject of the
transformation of nitrogen. Whenever nitrogenous matter is
mixed with water and allowed to stand for a time, decomposition
changes begin which result in a more or less complete destruction of
the compounds. This occurs in the soil, in the manure heap, in the
privy vault, in the sink drain or in sewage, the phenomena being
fundamentally the same in all cases, although differing in details
with differences in the kind of compounds present, the amount of
water, the temperature, the access of oxygen, the species of bacteria
present, and, doubtless, other factors. It results in a purification of
the soil or a purification of sewage from similar reasons.

Effect on Bacteria. — It might be supposed that the bacterial
treatment would increase the number of bacteria in the sewage.
The rapid destruction of organic matter certainly points to active
bacterial growth and we should expect to find bacteria more abun-

86 THE MANURE HEAP AND SEWAGE.

dant at the end than at the beginning of the treatment. But for
reasons as yet little understood, the reverse is the case. The
number of bacteria in the treated sewage appears to be always less
than in the raw sewage. The amount of reduction in bacteria is by
no means constant. Sometimes it is comparatively small. In a
series of tests upon the sewage of London, treated in this way, a
reduction of only about 32 per cent, was found (7,000,000 to 5,000,-
000). In other cases the reduction is greater, and sometimes there
is found a number as high as 9,000,000 per c.c. in the raw sewage,
and only from 5,000 to 10,000 in the treated product. Something
evidently is at work destroying the bacteria, but its efficiency varies
widely in different instances.

Whether these methods of treating sewage destroy its dangerous
nature as well as its offensiveness is not easy to answer. The
danger in sewage comes primarily from the disease bacteria it may
contain, foremost among which is the typhoid bacillus. The
bacterial treatment greatly reduces the number of bacteria, but does
not by any means eliminate them. Does it eliminate the disease
germs? So far as evidence goes to-day it seems that the typhoid
bacillus is eliminated by the treatment, and the effluent from such
beds fails to show typhoid bacteria, even when they have been pur-
posely put in the sewage. Bacteriologists who have had confidence
in the efficacy of the purification have not hesitated to drink
freely of the water from such a sewage filter bed. It is certain,
therefore, that the treatment greatly improves the healthfulness
of the sewage. But that it removes all danger from it cannot be
positively stated.

Such a disposal of sewage means, of course, a complete loss of the
nitrogenous material, for no method is adopted for utilizing the
wasted nitrates. But this fact is no longer regarded so seriously as
it was a few years ago. We have learned that there are efficient
forces in nature for bringing back from the atmosphere the nitrogen
dissipated from the soil, and it is a matter of less significance to throw
away the sewage nitrogen than it appeared to be when the only
known source of nitrogen was supposed to be the fixed nitrogen of
the soil. Since the soil can readily replace its lost nitrogen through

TREATMENT OF FARM SEWAGE.

TREATMENT OF FARM SEWAGE. 87

the agency of certain species of bacteria (see Chapter VII), it is no
\^m serious matter if some of the nitrogen is thrown away.

L.

^^m Upon the ordinary farm the sewage problem is rarely of any im-
portance, because of the small amount of material. The wastes
which form the sewage in the city are kept separate on the farm and
are not all treated alike. Part goes to the manure or compost heap,
and later is returned to the soil with the manure. Part goes to the
privy vault and is handled like manure; while still another part
drains from the sink and is generally allowed to waste itself on the
ground. A considerable portion of city sewage, like the refuse
from factories, etc., has no counterpart on the farm.

Nothing further need be said concerning the first of these
portions. The contents of the privy vault have practically the
same relations to bacterial decomposition and denitrification as
manure, and should be handled in essentially the same manner.
It is always emphatically necessary, however, to remember that
the contents of the privy vault are far more likely to contain patho-
genic bacteria than is barnyard manure, and it should, consequently,
be much more carefully handled. That such material has been
the means of distributing typhoid fever in many cases is surely
demonstrated. The bacilli of this disease are voided by the patient
in the excreta, and are thus sure to find their way into the vault,
to be subsequently distributed over the fields, where they may
percolate through the soil and pollute streams and wells. The
contents of the privy vault should never be left in position where
it can possibly pollute the water of either brook or well. Precaution
ns should also be taken to prevent its distribution around the farm by
means of soiled boots or tools which have been used in handling
it. There is much more likelihood of finding pathogenic bacteria
in human excrement than in that of domestic cattle, and the
disease germs thus found are far more likely to be injurious to
human health. Evidently the farmer should exercise much more
care in disposing of the contents of his privy vault than in the use of

88

THE MANURE HEAP AND SEWAGE.

his barnyard manure, and the constant addition of lime thereto
is certainly to be most thoroughly recommended. In other respects
this material has exactly the same relations to decomposition and
reconstructive processes as barnyard manure.

The portion of sewage which comes from the wash-water of
the sink or the dairy on the ordinary farm is so small that it may
commonly be left to care for itself. The amount of solid material
in such water is slight, and it can be allowed to run out on the soil
where, generally, it is rapidly absorbed and decomposed without

SEPTIC TANK

Fig. 19. — Diagram showing the method of applying the septic tank to a farm house.

any undue pollution. The organic matter undergoes the same type
of decomposition as that to which all organic bodies are subjected
under the influence of bacteria, and becomes eventually converted
into plant food and incorporated into soil. The drainage which
comes from the large dairy or creamery may be too much to be
disposed of by such a simple manner. In this case some means
must be adopted for its disposal. The problem thus presenting
itself is precisely the same as that presented to the city for disposing
of its sewage, and the same means are to be used in each case.
The time is coming, and, in some places, has arrived, when
it is necessary to find a plan for disposing of the sewage on the ordi-
nary farm in some other way than by emptying it into a stream.

TREATMENT OF FARM SEWAGE.

89

It is very easy for the farm to make use of the principles of a septic
tank in caring for and even utilizing its sewage. Fig. 19 shows
diagrammatically a means of accomplishing it efficiently and at
comparatively small expense. The diluted sewage from the house
is conducted to a tank sunk in the ground at any convenient distance.
The tank should be of such a size that it will hold the entire sewage
for twenty-four hours. If each person uses twenty gallons of water

Profee'ii^ etc.

jprhteids

/reeMtpef^eir

Mtrcus
/tacter/a^ . . ^^

/ '>^

MtrlcMcterJa/
Mtrates f/nscllj

Fig. 20. — The nitrogen cycle.

-/i^u/n^s

per day, the tank for a household of ten should be three feet deep,
two feet wide and six feet long. It must be covered so as to exclude
air and light, and the sewage must flow slowly and quietly through
the tank, thus making it a septic tank. The discharge frcrm the
tank is best received into a second tank from which it can be
conducted to a stream or upon the garden for fertilizing and
irrigating it.

CHAPTER VII. .
RECLAIMING LOST NITROGEN.

THE LOSS OF NITROGEN.

In spite of these transformations of nitrogenous compounds,
and partly because of them, there is a constant loss of nitrates from
the soil. This loss is from the following sources:

1. Sewage. — Any animal or vegetable material that falls into
the streams will, unless dissipated into the air, be carried to the
ocean. Much nitrogen is brought to the city where it is used as
human food and, as sewage, carried to the river and perhaps to
the ocean, where it is lost.

2. Drainage. — The rains are constantly percolating through the
soil and carrying away dissolved material. Since nitrates are soluble,
large amounts are thus carried off to the rivers which drain the land.

3. Decomposition and Denitrification. — These processes, by
reducing organic nitrogen to ammonia and by reducing nitrates
to free nitrogen, cause large losses. These gases of course pass
from the soil to join the atmosphere. Such processes are going
on wherever organic matter is found — in the river, the soil, the
manure heap, sewage, and elsewhere.

4. Direct Chemical Decomposition. — A considerable portion
of the earth's fixed nitrogen is dissipated by direct chemical processes.
Explosions of gunpowder or other nitrate explosives liberate free
nitrogen, which goes at once to join the nitrogen of the atmosphere.

Through all these channels the soil is being constantly deprived
of its nitrogen. Eventually it all reaches the atmosphere, for
whether it enters the ocean or dissipates itself in the streams,
soil, or elsewhere, by means of decomposition it finally allows the
nitrogen to pass of as a free gas to join nature's inexhaustible supply

90

THE LOSS OF NITROGEN. 91

in the air. It is quite necessary for the continuance of soil fertility
that this lost material should be restored.

Our farm lands slowly become incapable of supporting the
crops demanded of them. This loss of fertility in worn-out farms
is due, doubtless, to a number of factors, but the loss of nitrogen
is certainly the most prominent one. All over the agricultural
world it has been found necessary to replace this lost nitrogen in
the soil. For this purpose we have depended mostly upon commer-
cial fertilizers, which commonly contain nitrogen in the form of
nitrates. Of such fertilizers there is . a small supply in the
world, chiefly in South America, and as they are brought from
long distances they are sold at high prices. But the few large
deposits of nitrates in the world are being rapidly exhausted.
The high prices of nitrates are necessary and are bound to increase
as the soil needs them more and more and as the supply diminishes.
Clearly enough, the supplying of the lost nitrogen will become
more and more expensive as the great nitrogen stores are used up.
The seriousness of this problem of a constant draining of nitrogen
from the soil has been quite prominent in the minds of chemists
and agriculturists, as they have learned in the last few years the
significance of nitrogen for agriculture.

The continuation of agriculture depends upon the existence
of some means of reclaiming the nitrogen from the atmosphere
for the use of plants. If there is no such means it is evident that
the nitrogen store of the soil will be used up and vegetation will
eventually, and, in highly cultivated lands, speedily die of nitrogen
starvation. If, on the other hand, there is a possibility of reclaiming
such lost nitrogen there is no need of nitrogen starvation, since there
is an absolutely unlimited store of this. element in the form of the free
nitrogen of the air. It is quite evident that there is some means
within the reach of organic nature for making usfe of this atmos-
pheric nitrogen. Vegetation has continued on the earth for an
unknown number of centuries without any apparent diminution of
the nitrogen supply. This would not have been possible unless
the soil could have obtained from the air a stock of nitrogen to
replace that lost by the processes already indicated.

92 RECLAIMING LOST NITROGEN.

Where did the nitrates come from that are now in the soil ? Soil is
made of crumbled rock which did not originally contain nitrates; it
certainly must have obtained them from some source. The various
bacteria we have been studying only transform nitrogen compounds;
they do not make a new supply. The nitrogen in the air would be an
inexhaustible source if it were only available; but the bacteria we
have considered have no power of obtaining this nitrogen. They
can transform nitrogen compounds, but they cannot fix or gather
nitrogen from the air. It might naturally be supposed that ordinary
plants could obtain nitrogen from the air as they do CO2. But the
most careful testing has shown that when such plants are growing
under ordinary conditions they cannot assimilate any nitrogen from
the air, but must depend upon the compounds in the soil. Free
nitrogen is of no use to them, only nitrogen compounds. Some
other source of soil nitrates must be sought.

The Ammonia Theory. — For a time it was held that the am-
monia in the air was the source from which plants obtained nitrogen,
and that it was carried into the soil by the rains. When this supply
was found to be insufficient to account for soil nitrates, it was
claimed that plants could absorb ammonia directly from the air
through their leaves. But this theory failed to stand the test of
experiment, and was finally abandoned.

Fixation of Nitrates in Soil. — It was next shown that, under
proper conditions, ordinary soil will increase its stock of nitrates,
independently of visible vegetation. A lot of earth placed in a
proper vessel and kept free from vegetation will, in time, be found to
contain more nitrates than at the outset. Part of these nitrates may
be due to the process of nitrification already mentioned, by which
the nitrogen compounds, which were in the soil, but not in the form
of nitrates, are converted into nitric acid by the nitrifying bacteria.
But this is not the whole explanation, because analysis of such soil
shows that at the end of several weeks there may actually be a
larger amount of total nitrogen in the soil than there was at the start.
If, then, this total nitrogen has been increased, it must have been
derived in some way from the atmosphere.

I

I

NITROGEN GATHERING OR NITROGEN-FIXING BACTERIA. 93

NITROGEN-GATltERING OR NITROGEN-FIXING
BACTERIA.

It was soon demonstrated that nitrogen fixation in the soil is not
due to purely chemical processes, but rather to the growth of micro-
organisms. That it is due to the action of living organisms is proved
by the effect of sterilizing such soil. Two vessels may be filled with
similar soil, one of which is sterilized by heating, while the other
serves as a control. The former fails to gain nitrogen, no matter
how long it is kept in contact with the air; the latter slowly but
surely increases its store of fixed nitrogen in the form of nitrates.
This proves that some living organisms are concerned, and the fact
that no visible plants are growing in the soil shows that the higher
plants do not produce the result. The only conclusion that can be
drawn, therefore, is that microorganisms are the agents for reclaim-
ing free nitrogen from the atmosphere and fixing it in the earth in
some form of nitrogen compounds, which eventually become nitrates
and, thus, plant foods.

Such facts plainly pointed toward bacteria or allied organisms as
the real agents for fixing nitrogen from the air, and this suggestion
once made was quickly followed by the isolation of the bacteria con-
cerned. It is now a demonstrated fact that the power of gathering
atmospheric nitrogen and fixing it in the soil belongs to bacteria, and
during the last fifteen years much study has been devoted to the
microorganisms concerned. It appears that there are two general
types of such nitrogen fixations associated with different classes of
bacteria: i. Nitrogen fixation by bacteria alone (non-symbiotic).
2. Nitrogen fixation by bacteria in connection with legumes
(symbiotic).

NON-SYMBIOTIC FIXTURES.

These are soil bacteria that are able to produce an increase of
nitrogen in ordinary soil without the aid of other organisms. Of
these there are two types, the first acting anaerobically, and the
second aerobically. i. The first one that was found with this
power was isolated from soil and named Clostridium pasteurianum
(Fig. 21). It is an anaerobic bacterium, and in culture media will not

94

RECLAIMING LOST NITROGEN.

grow in the presence of oxygen. In the soil, however, it is often
associated with a second bacterium that is aerobic, the latter
absorbing the oxygen so that the anaerobic form can grow. Or-
dinarily the nitrogen fixation in the soil is due to these two growing
together, but the Clostridium alone is able to assimilate nitrogen if
kept in an oxygen-free atmosphere. In its growth the bacterium
consumes some of the organic material in the humus, and from this
source obtains the necessary energy for its action. The organism
is widely distributed, having been isolated by several bacteriologists
from dififerent soils. Practically nothing is known as to its activity in
soil under ordinary conditions. 2. In 1901 it was proved that the
soil also contains bacteria of the aerobic type that can fix nitrogen.

Fig. 21. — Clos-
terium pasteuri-
anum; an anaero-
bic nitrogen fixer
{Winogradski).

Fig. 22. —
Azotobacter
agili s, an
aerobic n i -
trogen fixer
(Beyerinck.)

Fig. 23.-5.
d aniens, an
aerobic nitro-
gen fixer (Loh.
and West).

Two different varieties of these were first isolated, and to them was
given the general name of Azotobacter (Fig. 22). Several other
varieties have been found later (Fig. 23). They are considerably
more vigorous than the aerobic type, and fix a considerably larger
amount of nitrogen — two or three times as much. In order to de-
velop efficiently they must be supplied with a considerable quantity
of organic food, and in ordinary soil the humus furnishes this food.
By the energy they obtain from this source they gather from the air
an extra quantity of nitrogen. These nitrogen fixers are very
susceptible to the presence of the smallest amount of acid, and fail to
fix nitrogen entirely if the soil is even slightly acid. The use of a
little lime to neutralize the acidity may thus frequently start an
active nitrogen fixation in a soil in which it did not previously occur,
arid hence greatly increase its productiveness. It has been shown
also that this class of nitrogen fixers, though able to grow alone, will

SYMBIOTIC BACTERIA AND LEGUMINOUS PLANTS. 95

perform their functions best when growing with certain other soil
organisms. They grow well with other fungi and with some
algae, organisms generally found associated with them in the soil.

Other Nitrogen Fixers. — It has been claimed that other organ-
isms are capable of fixing atmospheric nitrogen. Some species
of molds have been placed in this class, and certain species of algcsy
as well as a considerable list of other kinds of bacteria. Indeed, the
power of fixing nitrogen has been said by some to be a fairly common
property of bacteria. Concerning this subject little is known at
present, but it is quite likely that the list of nitrogen-fixing organisms
will be considerably extended in the next few years.

Nitrogen Fixation in the Soil. — As yet little is known concern-
ing the actual efficiency of these bacteria in the soil, although they
are certainly very active. Soils do gain nitrogen and continue to
do so for periods of years. A long series of tests has shown that
crops can be removed from some soils year after year with
no diminution in the amount of nitrogen that may be found
there. In these soils no legumes have been grown, and hence it
would seem that the supply of nitrogen must have come from the
supply which the bacteria gather from the air. The general
belief to-day is that this method of fixation of nitrogen is of very
great significance in all soils, and plays a much larger part in the
maintenance of the soil nitrates than we formerly supposed. It
is probable that the bacteria do not fix the nitrogen in a form
immediately available to plants. They probably build it into some
more highly complex compound, very likely of a proteid nature,
which is incorporated in their own bodies. Later the processes
of decomposition and nitrification act upon these compounds and
eventually convert them into available nitrates. Of this series
of changes, however, little is yet known.

SYMBIOTIC BACTERIA AND LEGUMINOUS.
PLANTS.

The Value of Legumes. — It has been known for a long time
that leguminous plants in some way enrich the soil, even the Romans
having commented upon the fact. The idea was revived in the

96 RECLAIMING LOST NITROGEN.

eighteenth century and has been more or less fully realized by
farmers since that time. To what this soil-enriching function is
due has not been understood till within the last thirty years. It
is now known to be due to the fact that the legumes increase the
nitrogen present. As already noticed, experimental evidence
indicates that ordinary plants are unable to assimilate atmospheric
nitrogen. Long series of experiments were conducted to test the
matter and the more rigidly the experiments were performed,
the more evident did it become that such an assimilation does
not occur in ordinary green plants. It was, however, shown
in 1883-4 that this conclusion did not hold in regard to the
great family of legumes. It was demonstrated very conclusively
that peas and beans, growing in a soil free from nitrogen and fed
upon food containing no nitrogen, did, in the course of a few weeks'
growth, increase the amount of nitrogenous material present in
the plant, and, inasmuch as the only possible source of this nitrogen
was the atmosphere, the conclusion was unhesitatingly drawn
that peas can assimilate atmospheric nitrogen. This conclusion
was contradictory to the belief accepted at the time, and although
vigorously disputed, was soon found to be strictly correct. Mnay
of the plants of the great family of legumes certainly do have
the power, under certain circumstances, of fixing atmospheric nitro-
gen and absorbing it into their tissues.

Root Tubercles. — The next step was the observation that the
fixation of nitrogen by legumes is associated with the develop-
ment upon the roots of little nodules known as tubercles (Fig. 24) .
These tubercles are little swellings on the roots, sometimes very
numerous, and varying from the size of a pinhead to the size of a pea.
They can easily be found on nearly any legume growing luxuriantly
in the soil, if the roots are carefully dug from the soil in such
a way as to prevent the nodules from being destroyed, and if the
soil is carefully washed away. They were at first regarded as
galls upon the roots, similar to those that appear upon the leaves
and branches of trees, and, therefore, were looked upon as a type
of disease. It is, however, evident that if they are of the nature of
a disease, they do the plants no injury, for the plants developing

m

^K the

SYMBIOTIC BACTERIA AND LEGUMINOUS PLANTS.

97

no

these tubercles are as luxurious as those without them. Indeed,
as soon as the nitrogen-fixing power of legumes was demonstrated,
it became evident that the fixation of nitrogen was associated with
the formation of tubercles. Only such plants as develop tubercles
are able to increase the amount of nitrogen in their tissues, and
the amount of nitrogen fixation is roughly proportional to the
development of tubercles. Plants without tubercles show
increase; those with a moderate number, a
slight increase; and those with abundant
tubercles grow luxuriently and show a larger
increase in nitrogen.

These facts led to experiments inregard
to their formation of tubercles. The tuber-
cles will not form upon the roots of legumes
grown in sterilized soil. Under these cir-
cumstances the plants develop no tubercles,
fix no nitrogen and, unless fed with nitro-
genous food, make very little growth, being
stunted and small. It was next shown that
if the legumes were sown in sterilized sand,
without nitrogenous food, and were then
moistened by water which had been stand-
ing in contact with ordinary soil, results were quite different.
Such water, sometimes called a soil infusion, is made by'simply soak-
ing soil in water and then filtering off the solid particles, using the
filtrate for watering the growing legumes. Plants watered with such
infusions show two interesting stages of growth. They sprout
readily and for a short time grow vigorously; then the vigorous
growth ceases and the plant seems to be suffering for lack of food.
This has been called the nitrogen hunger stage, and represents a
period in which the plant has used up the nitrogen in the seed, and
consequently all that was within reach. Control plants, grown in
similar soil and watered with pure water, never recover from
this stage, but those that were watered with the soil infusions,
after a few days of such nitrogen hunger, recover, begin once
more a vigorous growth and eventually produce large-sized plants

Fig. 24.— Tubercles on the
roots of the Soy bean.

98 RECLAIMING LOST NITROGEN.

with a good yield. Upon examining the roots of the plants they are
found to have developed tubercles, while the control plants, watered
with sterilized pure water, do not develop tubercles. These facts
of course indicate that in the soil infusion some agencies are
present which stimulate the development of tubercles and the
consequent fixation of nitrogen, and that the power of absorbing
atmospheric nitrogen enables the plant to recover from the nitro-
gen-hunger stage.

The Tubercle Bacteria. — These facts naturally suggest that
bacteria, or other microorganisms, are the cause of the tubercles.
Microscopic study of the tubercles shows a
somewhat perplexing structure. The tubercle is
the result of the excessive growth of the cells of
the root, but they are filled with peculiar bodies.
During the early growth of the tubercle, long,
thread-like sacs appear, which force their way
through the cells (Fig. 25). These filaments seem

.^JJ^:1^'~^a''7^^^ to be hollow tubes which contain smaller bodies,
tibethread-Iike ^ '

pouches in the tuber- somewhat like bacteria. As the legume in-
represents ^wo^cells creases in size these bacteria-like bodies undergo
with the sacs pene- a transformation in shape, growing larger and

tratmgthem(5^e/aw). , , . , F j 8 & 6

branchmg somewhat, so as to form structures
like those shown in Fig. 26. These are called bacterioids, and they
are characteristic of the tubercles of legumes. The next step was,
naturally, to isolate these bodies and study them by bacteriological
methods. It is easy to isolate from the tubercles bacteria that will
grow in culture media, and these organisms were named B. radicicola.
Experiments with the bacteria thus isolated have been extensive
and, on the whole, satisfactory, though occasionally they have been
conflicting. It has been proved many times that tubercles can be
produced upon legumes by the cultures thus obtained. Legumes
have been grown in sterilized soil and watered with bacterial in-
fusion from these cultures: the usual result has been the growth of
abundant tubercles and the fixation of nitrogen. Some striking
experiments have been made with germinating peas. Such peas, if
kept moist and warm, will grow for several days, sending out their

I

SYMBIOTIC BACTERIA AND LEGUMINOUS PLANTS. 99

normal roots even without being planted in the soil. By dipping the
tip of a needle into cultures of the microorganisms and then pricking
the rootlets of young legumes at various points, the development of
tubercles will almost inevitably follow such slight wounds. In
favorable experiments the tubercles appear in six days after the
inoculation and always at the point of inoculation. These facts
proved that the cultures are concerned in the development of the
tubercles.

The study of the organisms themselves and of their relation to the
legume tubercle has proved somewhat puzzling. The organisms
isolated are ordinary bacteria, B. radicicola, and in laboratory

Fig. 26. — Showing the bacterioids found in root~tubercles.

culture media they resemble other bacteria, occasionally producing
the peculiar bacterioid forms. Usually there is nothing in their
growth in the laboratory culture media to suggest that they may pro-
duce the peculiar bodies found in the tubercles. When such cultures
are inoculated into the roots of legumes the results are not always
successful, sometimes no tubercles following. But, as a rule, the
inoculation is followed by the growth of the tubercle, the develop-
ment of the curious tube-like filaments growing among the cells, and
there is the subsequent appearance of the bacterioids in the fila-
ment. The appearance of the pouch-like threads and the bacteri-
oids has been a puzzle that has not yet been wholly explained.

It is evident that the tubercle bacteria must exist in the soil.
But in spite of careful search no bacteria have yet been isolated
from the soil which have the power of producing tubercles when
inoculated into legumes. This, together with the irregularity of

lOO RECLAIMING LOST NITROGEN.

results obtained in trying to use the cultures of B. radicicola, has led
to suspicions that the actual bacterium that produces the tubercle
may not be the B. radicicola which has been isolated, but some
other, which has escaped observation and which is frequently at-
tached to B. radicicola. Indeed, DeRossi recently claims to have
found the B. radicicola associated with what he thinks is a second
bacterium that has quite different properties. The latter is much
more like the bacteria forms that appear in the young tubercle, and
shows a tendency to form bacterioids in culture media. According
to DeRossi, it always produces the tubercles when inoculated into the
root tissue of legumes. These bacteria do not grow well in culture
media, not becoming visible for about two weeks, and have been
overlooked in previous experiments since they are hidden by the
vigorously growing B. radicicola with which they are closely as-
sociated. DeRossi thinks this a new organism and the cause of the
tubercle rather than the species ordinarily accepted as the cause.
It is doubtful whether this is anything different from B. radicicola.
But whichever result is reached, it remains equally true that the
tubercles are the result of the action of bacteria that enter the root
tissues, and stimulate the root cells to excessive growth, although,
perhaps, B. radicicola is not the real exciting cause. This conclu-
sion of DeRossi, if true, would in a measure explain the irregularity of
results obtained by the use of what were previously supposed to be
pure cultures of the tubercle organism (see page 107).

The Production of Tubercles by the Bacteria. — Just how the
bacteria produce the tubercle is not known. Tubercles, galls, or
tumors are not infrequently produced in plants by bacteria and molds,
these constituting one of the well-known types of plant diseases.
Apparently these legume tubercles are produced in somewhat the
same way, only instead of injuring the plant they benefit it. It
appears too that the plant offers some resistance to the entrance of
the bacteria into its root, and, when well nourished, is able to pre-
vent their entrance. When there is plenty of nitrogen food in the
soil, the plant grows vigorously, so that this resistance may be
sufficient to prevent the formation of tubercles. When, however,
the nitrogen food is scanty, the plant is weaker and cannot resist the

ARE THERE DIFFERENT SPECIES OF ttlBERCLE M^J&I^ '? lOI

entrance of the bacteria. The growing pea, when it enters the
nitrogen-starved stage (see page 97) becomes weakened and the
tubercle organism readily penetrates its roots. Thus it happens
that these tubercles form only upon plants that grow in soils some-
what deficient in nitrogen, and thus under exactly the conditions
where nitrogen assimilation is needed. Whenever the bacteria do
succeed in entering the root they stimulate the plant to excessive
growth which results in the formation of tubercles, and they them-
selves become transformed into the bacterioids.

Assimilation of Nitrogen. — Just how the nitrogen is assimi-
lated is also uncertain. It is possible that the legume thus stimu-
lated can absorb the nitrogen directly from the air. A second
possibility is that the bacteria assimilate the nitrogen, and that later
the legume utilizes this extra supply that has been absorbed. It is
impossible to decide between these views, at present, although, con-
sidering that some bacteria are known to possess this power of
nitrogen fixing while green plants do not have such power, the
probability is in favor of the latter view. However this may be, it
is certain that the legumes obtain from the growth of the tubercles
an extra supply of nitrogen which is derived from the air.

ARE THERE DIFFERENT SPECIES OF TUBERCLE
BACTERIA?

It is practically certain that nearly all soils contain bacteria
capable of living in symbiosis with leguminous plants. Nearly
all soils, except extremely sandy soils that support little or no
vegetation, will support leguminous plants and develop tubercles
on their roots. One can hardly examine the roots of legumes any-
where without finding tubercles, a fact which shows that the bacteria
in question are very widely distributed in nature. But are the
bacteria all of the same species? A very large number of species
of legumes with their tubercles can grow in most if not all soils.
Are the bacteria that form tubercles upon the clover the same as
those that form them upon the pea, or is there a different species
of bacteria for the different species of legume ? It would not seem

I02 . \ : ^^ ^ >r '^ ^^ Ki:iPMI»^^NG LOST NITROGEN.

probable that there could be in the soil a different variety of bacteria
for every variety of legume, but rather that one kind of bacteria can
grow in many legumes. But the facts are not quite so simple as this.
Not all species of legumes are capable of developing root tubercles
equally well in all soils. Some soils will luxuriantly support certain
species of beans, peas, or clovers, producing a large crop, developing
quantities of tubercles and fixing an abundance of nitrogen, while
the same soil will not support other species of legumes with equal
readiness. For example, the soil of Connecticut is not adapted
to the legume called the soy bean. When this bean is planted in the
ordinary Connecticut soil it does not flourish, but yields a small
crop unless heavily fertilized, and does not produce tubercles.
This species does, however, grow readily in Massachusetts. Some
years ago the experiment was tried of importing Massachusetts
soil, upon which this plant had produced abundant tubercles,
and mixing it with the Connecticut soil, subsequently planting the
soy bean. The result was an excellent growth of the soy bean
and the development of tubercles. Afterward these particular
plots of land were capable of producing large luxuriant crops of
the soy bean, with abundant root tubercles and a large fixation
of atmospheric nitrogen. Evidently Connecticut soil does not
contain the bacteria adapted for producing the tubercles in the soy
bean, although those which produce tubercles on the pea and the
clover are abundant enough.

Similar experiments have been repeated elsewhere until it has
become evident that the root tubercle bacteria are not all alike.
Varieties adapted to one species of legume may be unable to produce
tubercles upon a second species; in some cases one type of bacteria
may be able to grow in the roots of several allied legumes but not
in others. For example, the tubercle organism of sweet clover
will do well with alfalfa. All of these facts have suggested that
there are different types of leguminous bacteria, each adapted to
different species of legumes.

To what extent this conclusion is true it is by no means easy to
determine. It is certainly true that some varieties of legume^will
grow in soils with an abundant production of tubercles, while

ARE THERE DIFFERENT SPECIES OF TUBERCLE BACTERIA? IO3

Other varieties of closely related legumes are unable to produce
an abundant crop of tubercles in the same soil. This is evidently
due to the lack of microorganisms especially appropriate to the
legume in question, since inoculation with proper soil infusion pro-
duces tubercles at once. But just what this means is not so evident.
It certainly means that different legumes demand different varieties
of tubercle bacteria. Whether these different varieties are distinct
species is, of course, a fruitless question inasmuch as we do not
know what we mean by a species among bacteria. But it is of
importance to know whether these types are quite distinct or
whether they are simply physiological varieties of the same general
species. If the former is true we should expect them to remain
distinct, but if the latter is true we might expect the soil bacteria
to be capable of adaptation, by cultivation, to different legumes.
On the whole, the evidence is decidedly in favor of the latter view
and indicates that the different tubercle bacteria are probably all
one general species, but that under different conditions they assume
slightly different physiological relations. They can accommodate
themselves to growth in one or another legume, and having become
especially adapted to one species, they do not so readily develop in
the root of a second species, but, allowed to develop in the soil in
which the latter plants are growing, they adapt themselves in time
to the new plant. In other words, experiments indicate that there
is probably only one species of tubercle bacteria, and that this
species assumes different physiological characters under the influence
of the different conditions in which it grows. It may adapt itself
especially for growth in one leguminous plant and consequently
lose its ability to develop well in others; but if a new legume is
planted in the same soil, a slow change of physiological characters
takes place, and the soil organism becomes in time adapted to the
new leguminous plant. This conclusion is clearly in complete
harmony with the fact that the soil may at any time contain the
organisms which will support one species of legume luxuriantly,
while another species will have only a scanty growth. The matter
of practical importance is that a soil may support one species of
legume luxuriantly, with abundant tubercle production, while

I04 RECLAIMING LOST NITROGEN.

a second species will not flourish upon it because of lack of tubercle
bacteria properly adapted to the second species.

THE UTILIZATION OF THE NITROGEN-FIXING
POWERS OF LEGUMES.

Although there are still unsettled questions concerning the
nature of the tubercles, the power possessed by legumes of fixing
nitrogen through their aid is of the utmost importance. The
legumes are the most practical means within reach for restoring to
the soil the nitrogen dissipated into the air, and it becomes a
matter of great significance to agriculture to determine the best
practical method of making use of this power. It would seem that
we have here the factor needed for making possible a cultivation of
the soil without exhausting its nitrogen. Virgin soil has all its
factors of nitrogen loss and gain nearly balanced; cultivated soils
have a balance on the debit side. If we can discover a practical
method of applying these factors of nitrogen assimilation, one of the
great agricultural problems will be solved. Up to the present time
the matter has not been brought to a condition where we can feel
that we know how to handle these nitrogen-fixing forces to the
greatest advantage; but so much has been learned that already
our agriculturists are making use of the knowledge to a great extent,
and we may fairly expect that the next few years will see these
forces more thoroughly under the control of the farmer than to-day.

In making use of this means of gaining nitrogen the following
facts must be considered.

I. Selection of a Proper Legume. — The question of the proper
legume to grow in any soil, for the purpose of fixing its soil nitrogen,
is one that must be determined largely by experiment. In all cases
it should be the legume that grows most luxuriantly upon soils not
particularly well fertilized, and which, at the same time, produces
the most abundant crop of tubercles upon its roots. These factors
will depend upon climate, the chemical nature of the soil and the
variety of soil bacteria. In selecting the legume the individual
must take into consideration all the facts within his reach. Some

UTILIZATION OF NITROGEN-FIXING POWERS OF LEGUMES. IO5

species grow better in some climates than others, and certain soils
seem to be, for some reason, better adapted for particular species,
quite independent of the question of the presence of the proper soil
bacteria. By the proper consideration of the facts of his experience
the farmer can, without much difficulty, determine what species of
legume grows best in his soil. The most vigorously growing
legume is the best. In clay soils red and yellow clover, lupin, sera-
dilla, horse beans, and vetches are successfully grown. Which of the
varieties is to be selected must be determined by the conditions of
the soil and the needs of the farmer for the particular crop which he
raises. The essential feature must be that the species selected
should be one that will grow well in the soil in question, otherwise
the advantage of the nitrogen fixation will not be obtained.

2. Insuring Presence of Proper Bacteria. — In order that the soil
may increase its nitrogen store it is evidently necessary for tubercles
to develop in large numbers on the roots of the legumes. For this
purpose, of course, it is necessary that the proper variety of bacteria
shall be present in the soil, otherwise no tubercles will be formed, or
the tubercles formed will be few and small. To insure this result
may sometimes require a little experimenting and observation.
Some species of legume find in a certain soil the tubercle organism
adapted to them, while other species of legume may not find the
proper organisms in the same soil. The soy bean is a most excellent
crop for nitrogen gathering since it is an extremely luxurious grow-
ing legume, producing abundant tubercles and a large fixation of
nitrogen when supplied with the organisms which produce tubercles.
But in order to make use of this crop it may be necessary to import
the proper bacteria from other soils. On the other hand, there are
some species of legumes, like most kinds of peas, which are capable
of growing in most soils and producing an abundance of tubercles.

Further, a legume, which, during the first season produces only a
small number of tubercles, may succeed better the second year than
the first and may fix more nitrogen. The growth of the crop in the
soil during the first year apparently either increases the number of
soil organisms appropriate to this particular legume or produces
such changes in the physiological character of the bacteria present

I06 RECLAIMING LOST NITROGEN.

that they are better adapted to the legume. In either case, the
second season will show a more luxuriant growth and a more suc-
cessful nitrogen fixation.

Soil Inoculations. — Experience has shown that it is not always
possible to get a good growth of the desired legume, because of the
failure to obtain a proper quantity of tubercles. That this is due
to the lack of the right variety of bacteria in the soil seems certain,
and has led to the practice of inoculating the soil. The first method
of doing this is to obtain soil from some locality where the legume is
known to produce a goodly numbers of tubercles and then either to

Fig. 27. — Two snap-bean plants, growing in coal ashes, one with
and one without inoculation {Ferguson).

mix this soil with that of the field to be planted, or to make a soil infu-
sion to be used for soaking the seeds or for watering the young plants.
The results of this procedure are, in the main, satisfactory, for
generally the production of tubercles is thus stimulated, and much
increased crops produced (Fig. 27). In many instances of this
kind it has been found possible to cultivate a legume in soils in which
it would not previously grow, by simply inoculating the new soil
with soil where the legume has previously grown. Alfalfa, for ex-
ample, has been successfully started by this means in many
places in the eastern part of this country where it would not pre-

UTILIZATION OF NITROGEN-FIXING POWERS OF LEGUMES. I07

viously grow. There seems no doubt that the phenomenon is
simply one of inoculating the soil with the proper bacteria.

But soil inoculations with legume earth are troublesome. Soil is
bulky and a considerable quantity is needed. To obtain a sufficient
amount involves expensive freight charges and the carting of heavy
loads. Soil inoculations may also distribute plant diseases and
troublesome weeds. If tubercles are produced by bacteria it ought
to be possible to obtain the results by inoculating with pure cultures
of bacteria. It should be possible to cultivate the bacteria in a
laboratory and then to distribute to the farmers the cultures of the
organisms. If this could be done it would be a far simpler matter
than the use of soil itself. The first attempt to furnish such a culture
resulted in an article called Nitragin, which was brought out in
Germany. This product was eagerly tried by experimenters and
practical farmers; but, although in some cases it seemed to give
favorable. results, the success attending its use was so uncertain that
it fell into disrepute. Later, various improvements were introduced
into the methods of making and distributing the cultures, and a
new product, called New Nitragin, has been put forward which
gives somewhat better results. This has been tried quite exten-
sively in the last three years and the results have been much more
positive than in the earlier attempts. Meantime other attempts
toward the same end were made in this country. In the labora-
tories of the Department of Agriculture extensive experiments were
carried out, seeming to show the possibility of increasing the nitro-
gen-fixing powers of these bacteria by cultivating them in solutions
that are poor in nitrogen. After continued experiments in this line,
cultures of the tubercle-producing organisms were sent out for test-
ing from the department. These too proved unsatisfactory. They
were first sent out upon absorbent cotton, but the bacteria did not
live long on the cotton fibers and the farmers were likely to receive
cotton containing only dead bacteria. Then they were sent out in a
liquid or upon agar but their use has never been very great.

It thus appears that the use of pure cultures of tubercle organisms
for soil inoculation has hitherto not been very successful. But this
does not by any means indicate that the methods will not soon be so

Io8 RECLAIMING LOST NITROGEN.

improved that they will be practical. The plan is logically a proper
one, and if it be found possible to develop the tubercle bacteria in
sufl&cient quantity and to distribute them in a living condition,
these soil inoculations may become of great value to the agricultural
industry.

The reasons for failure thus far are varied. The difficulties of
keeping the cultures pure, of distributing them to the farmers in
a still vigorous condition, and of finding some device by which the
farmers can successfully inoculate legumes with cultures have
been regarded as the primary obstacles. Moreover, some soils
are already stocked with proper tubercle bacteria so that the addi-
tion of more would be superfluous. If, however, the claims of
DeRossi are correct and the tubercles are caused not by the
B. radicicola, but by another much more slowly growing organism,
the irregularities in these results are readily explained, and it will
be necessary to proceed along a different line in developing cultures
of the organism that really produces the tubercles. At the present
time, therefore, the pure cultures of the tubercle organisijis that
have been put on the market for soil inoculation are not reliable,
although we may confidently expect that the methods will be so
improved in the future as to make them of practical value. Mean-
time, soil inoculations continue to be made with legume earth
from lands where the desired legumes are growing vigorously; and
this method of soil inoculation has proved of much practical value
in developing a vigorous growth of legumes and a consequent in-
creased fixation of atmospheric nitrogen.

3. Utilization of the Nitrogen. — The next problem is how
such a store of nitrogen, fixed in the soil, may best be utilized for
the benefit of the next crop. There are two methods by which
this nitrogen may be made available for crops subsequently
growing in the same soil. The first, which is commonly called
green manuring, consists in allowing the legume to grow vigor-
ously for a time, and then in plowing the whole crop into the soil, with
the expectation that the nitrogen stored up in the plants will be
available in the soil for the next crop. The method by which the
nitrogen becomes available is based upon the facts already noticed.

UTILIZATION OF NITROGEN-FIXING POWERS OF LEGUMES. IO9

When these crops are thus plowed into the soil they are brought
at once within reach of the soil bacteria.

The bacteria seize hold of the proteid products in the plants, as
well as the cellulose and other organic substances, and cause their
rapid decomposition. After this process is finished the nitrifying
bacteria in the soil oxidize the ammonia left after the decomposition
ceases and convert it into nitrate. Thus, after a few weeks, a con-
siderable portion of the nitrogen material which was fixed in the
legume has been converted into nitrate, available for plant life.
These remain in the soil and may be used by the next crop of plants
sown on the same field, thus increasing its yield by means of the
nitrogen which has been fixed by the legume and the bacteria
together, and has been converted into an available form by the soil
bacteria.

A second method of utilizing the nitrogen is by converting it
into manure. The crop of legumes is reaped and fed to animals,
the roots and stubble only being plowed into the soil. The portion
fed to the animals is later returned to the soil as manure. Part
of the nitrogenous material is thus metabolized by the animal body
to urea, and part passes into the feces unassimilated, while part
remains in the roots and soil. But it is all eventually decomposed
by the putrefying bacteria, and goes through the same series of meta-
morphoses which we have already described in sufficient detail. The
result is that, in the end, most of it is returned to the soil in a form
available for plant life. This method of utilizing the nitrogen is
certainly the best economy, since it has a double advantage: The
nitrogen is used twice, once as a food for the stock and a second
time as a food for the crops in the form of manure.

It is of course manifest that under either of these methods of
treatment not all of the nitrogen fixed by the legume and the
bacteria is rendered available for the next series of crops. At
the very best, part of it will be lost to the soil by the process of
putrefaction which liberates free ammonia, and by denitrification
which liberates free nitrogen. It is impossible, by any means now
at our disposal, to prevent this loss, and thus a portion of the fixed
nitrogen is, even with the best treatment, dissipated again into

no RECLAIMING LOST NITROGEN.

the air. But by proper treatment this loss can be reduced to
a minimum and there may always be a surplus of gain. Even
taking into account all the nitrogen loss that comes from these
processes the use of a leguminous crop upon a soil poor in nitrogen
furnishes to that soil for the next crop a store of nitrogen considerably
in excess of that which it possessed before.

CHAPTER VIII.
BACTERIA AND SOIL MINERALS.

MINERALS NECESSARY FOR PLANTS.

Although the different minerals in the soil are needed by plants
in smaller quantities than the nitrogenous foods, still they are quite
as necessary, and vegetation cannot be supported without them.
They come primarily from the rocks that form the earth's crust.
In these rocks there is practically an unlimited supply of the neces-
sary minerals, but they must be rendered available as plant food.
Most of these rocks contain their minerals in an insoluble condition
and, in order to be absorbed by vegetation, they must be dissolved
in the soil waters. Although this subject has not been studied so
thoroughly as the transformation of nitrogen, still it is known that
chiefly through the agencies of the soil microorganisms the minerals
are brought into solution.

LIME AND MAGNESIA.

These two minerals may be considered together since they are
closely allied and their relations are the same. The importance of
lime to soil has long been recognized and our previous study has
shown one of its most important uses. We have learned how
necessary is the activity of the soil bacteria in the transformation of
plant foods, and how, as a rule, bacteria cannot grow in the presence
of the slightest acid reaction. But general processes of decomposi-
tion are constantly giving rise to acids, so that the soils tend to
become more and more acid. As the acidity increases the bacterial
action declines and fertility correspondingly diminishes. The
addition of lime to such soils is necessary, therefore, to reduce the
acidity. Other needs there may be for lime, but the primary one is
to keep the bacterial activities in the soil at a high state of activity.

Ill

112 BACTERIA AND SOIL MINERALS.

But there are also constant losses of lime from the soil. A small
quantity is carried away by the crops taken from the land, but a far
larger quantity is lost to the soil by drainage. The soluble lime
salts are dissolved by the soil waters and pass off with the drainage.
Very large amounts are thus removed so that a more or less frequent
liming is necessary to maintain in the soil a quantity sufficient to
keep the proper condition for bacterial action. Different soils show
wide differences in the amount of lime needed. Soils containing
limestone rock have an abundant natural supply, while soils without
limestone need to be furnished with it in varying amounts. The
lime thus drained away is a permanent loss, for it finds its way into
the ocean whence it is not easily returned to the soil. But this
loss is not serious, since limestone rocks are practically unlimited
and there need be no lack in the supply of available lime. Lime is
rendered available chiefly, if not wholly, through the action of bac-
teria. Limestone consists mainly of carbonate of lime which is
only very slightly soluble in water, and cannot be utilized directly,
for this reason. But water containing carbonic dioxid in solution
readily dissolves the carbonate of lime. We have seen that by the
constant decomposition processes going on in the soil, carbon
dioxid gas is being set free from the decomposing organic com-
pounds, such as proteids, sugar, cellulose, etc. This gas is taken up
by the water, which is then able to dissolve the limestone. The
greater the extent of the bacterial action, the greater will be the
amount of carbon dioxid eliminated, and the amount of lime
brought into solution; the more effectually also will the soil be main-
tained in proper condition for bacterial growth. Hence, as the
amount of lime in the soil increases, the bacterial action will become
greater, more lime will be dissolved, and consequently more will be
lost by drainage.

In this way the limestones on the earth's crust are being dis-
solved and carried away. The extent to which this is possible is
indicated by the huge limestone caves whose great spaces show how
the limestone has been dissolved by waters which held carbon di-
oxid in solution. All such dissolved lime finds its way to the ocean
where it supplies marine animals and plants with the lime for their

PHOSPHORUS.

113

shells, and where it is also laid down in the deposits of lime material
that may, in later ages, form new limestone rocks. But, aside from
this future possibility, the bacterial agencies of the earth's surface
are constantly dissolving the limestones and adding them to the
soil to be subsequently carried away by drainage.

In recent years calcium cyanid has become much used as a
fertilizer. It furnishes lime and results in distinct nitrogen gains
to the soil. In the utilization of this material bacteria are necessary
to convert it into ammonium salts before it can be assimilated by
plants.

PHOSPHORUS.

Vegetation needs only very small amounts of phosphorus, but
these small amounts are requisite to the production of good crops, as
has been many times appreciated by the farmer who finds decidedly
increased crops following the application of phosphate fertilizers to
the soil. There are many substances containing phosphorus which
may be used to supply the amount needed by the soil. They are:
I. Mineral compounds, of which the chief are ground phosphate rock
(floats), superphosphates and a by-product of steel manufacture
called Thomas slag. 2. Organic compounds. A considerable quan-
tity of phosphorus is contained in the humus, likewise in bone, which
is used as a fertilizer chiefly for its phosphorus. The solid part of
barnyard manure contains phosphorus, and a variety of other
sources, are also utilized — ground fish, tankage, castor pomace, and
the like. The phosphorus in some of these substances is readily
soluble in water, and this must always be the case before it can be
utilized by plants.

Apparently the solution of the phosphates is dependent upon
bacterial action. It is easy to understand how the phosphorus from
organic sources is rendered available through the agency of the soil
organisms. As these bacteria decompose the various organic prod-
ucts in the soil, the phosphorus contained in them is set free from
its combinations. Bone, for example, is vigorously attacked by the
bacteria, and is in time completely disintegrated, the phosphorus
being, of course, freed from its relations. The entire series of

114 BACTERIA AND SOIL MINERALS.

changes through which it passes is not yet known. Part of the
phosphorus finally assumes an insoluble condition, but a part is dis-
solved in the soil water and becomes available as plant food. This
solvent action of the bacteria is attributable to the acids that are
produced. As we have already seen, the decomposition of organic
products always gives rise to certain organic acids and these are
capable of dissolving phosphorous compounds that would be in-
soluble in water alone. The solvent action resulting from bacterial
decomposition is not wholly the result of the acids, for by some
means yet unknown the phosphorous compounds may be dis-
solved even when no acid is produced. They are not, however,
dissolved in sterile soil; therefore the availability of the phosphorus
is due to bacterial activities. Such a formation of soluble phos-
phorus from decaying organic compounds is going on constantly in
the humus, and in soils rich in humus the process furnishes phos-
phorus in sufficient quantity for vegetation.

Sometimes, however, more phosphorus is needed, and it may be
supplied by minerals. The rock phosphates are rendered available
in much the same manner as the organic phosphates. The phos-
phorous compounds in the rock are very slightly, if at all, soluble in
water. In ordinary soil small, but sufficient quantities are dis-
solved through the agency of the soil bacteria. Hence also the
acids produced by decomposition are important agents in dissolving
the rock which, though not soluble in water, is soluble in acids. It
is a well-known fact that these phosphates are made more available
as a fertilizer by being composted for a time in manure, a fact
clearly explained by the solvent action of the acids produced by
decomposition, as well as by other functions of the bacteria not yet
understood. They are also made more effective when plowed into
the ground with the plants used for green-manuring, this condition
giving rise to rapid bacterial action, resulting in a decomposition
which aids in rendering the phosphorous compounds available.
Thomas slag is also dissolved by similar activities. In short, while
bacteria do not furnish phosphorus, they are the active agents in
rendering available the phosphorus from both organic and mineral
sources.

POTASH — SULPHUR. H^

POTASH.

The relation of potash in the soil is almost exactly the same as
that of phosphorus. It comes primarily from the rocks where it
exists largely in the form of silicate of potassium. This is an insoluble
salt, and soils may contain it in large quantity and still suffer from
lack of available potash. It is rendered available in very much the
same way as in the case of phosphorus, largely through the action
of the decomposition produced by the soil bacteria.

SULPHUR.

Sulphur is one of the ingredients of protein, and, therefore,
is necessary to plant life. Ordinary plants obtain it only in the form
of sulphate, which they absorb from the soil. But microorganisms
are concerned in the transformations by which the soil is properly
stocked with the sulphates. The transformations show at least two
different steps:

I. Sulphur is set free from its combinations. 2. Sulphur is
reconibined into sulphuric acid that unites with mineral matter to
form sulphates.

Liberation of Sulphur as H^S. — All proteid matter contains
sulphur, and when its decomposition takes place through the agency
of bacteria the sulphur is liberated in the form of hydrogen bi-
sulphid (HjS) which vile-smelling gas may usually be detected
around decomposing proteid. This same gas is liberated from the
decomposition of sulphate of lime that is carried in drainage waters
to the ocean. Several kinds of bacteria have been found capable
of liberating HjS from such deposits. In certain parts of the world
large deposits of such sulphites (gypsum) have accumulated and
are constantly acted on by bacteria which liberate H^S, producing
the "curative muds" of the Black Sea and other localities. Such
muds are saturated with hydrogen bisulphid gas. This reduction
of sulphates is, in a way, comparable to denitrification since it is
the result of deoxidation and since it also destroys substances that are
already plant foods. Some species of bacteria appear able to attack
pure sulphur, causing it to combine with hydrogen as H^S. From

ii6

BACTERIA AND SOIL MINERALS.

these several sources much sulphur is liberated into the air in the
form of H2S, the liberation in all cases being due to the action of
bacteria, difiFerent classes acting on different compounds containing
sulphur.

Recombination of Sulphur Compounds. — The recombination
of the H2S to form sulphuric acid and then sulphates is brought about
in some cases apparently by purely chemical forces, since the gas
will easily combine with oxygen if the conditions aie right. But
a large part of it enters new combinations through the agency
of microorganisms. There is a group of bac-
teria that consume H^S, oxidising the gas within
their bodies and utilizing the energy thus liber-
ated for their own life energy. They are as
dependent upon the presence of H2S as ordinary
plants are dependent upon COj. In the pres-
ence of this gas they flourish, and as they oxidize
the gas the sulphur is set free from its combina-
tion with hydrogen and separated as pure sulphur.
The sulphur appears then within the bodies of
the bacteria as minute reddish dots (Fig. 28).
The bacteria that can perform this function seem
to be of two types, one type belonging to the higher fungi (see page
12) and the other being true bacteria. The latter are sometimes
called the "red bacteria" because of the color produced by the sul-
phur grains within them. These bacteria may continue thus to liber-
ate the sulphur and in waters where H2S is abundant large quantities
of pure sulphur may be deposited. These are the so-called sulphur
springs around which deposits of sulphur may be found. As long as
the gas is abundant the bacteria flourish; but if the gas disappears
they appear to use up the sulphur in their own bodies, after which
they die. In some way the sulphur in their bodies is in the end
converted into sulphuric acid, which then combines with any lime
that may be present to form sulphate of lime. Very little is known
as to when or how the sulphur in the cell walls of these sulphur
bacteria gets converted into sulphuric acid, or whether it is a purely
chemical or a biological phenomenon. But although the whole

Fig. 28.— Sulphur
bacteria. A, Beg-
giatoa; B, Ophido-
monas. Both show
sulphur masses in the
rods {Winogradsky).

IRON. 117

process is not fully understood, it is evident that microorganisms
have a close relationship to the transformations of sulphur in the
waters and soils. They liberate it from its combination in proteid,
they oxidize the liberated gas into sulphur and finally into the
form of sulphuric acid which soon forms a sulphate. It is also
claimed that some kinds of bacteria can oxidize sulphites into
sulphates. Microorganisms are thus responsible for the constant
metamorphosis of sulphur compounds that keeps the soil properly
supplied with this element. Of their activities in ordinary cultivated
soil we know little or nothing.

IRON.

A small quantity of iron is needed by plants, and a group of
bacteria, called iron bacteria, has been supposed to have some rela-
tion to a circulation of iron nature, somewhat similar to that of
sulphur. These bacteria are commonly seen covered with a deposit
of hydroxid of iron, giving them a reddish-brown color. It has
been thought that they used iron in their activities much as sulphur
uses iron. But the most recent work indicates that this is probably
an error, and makes the agency of bacteria doubtful. At all
events, nothing reliable is known to-day upon the subject, although
it is not impossible that here, too, the bacteria of the soil, and
especially of waters, may be of some significance.

CHAPTER IX.

SOME PRACTICAL LESSONS FROM SOIL BACTERIOLOGY.

The close dependence of soil fertility upon the action of micro-
organisms is manifest, and it is evident that farm processes should be
such as to stimulate desired bacterial action and check these activi-
ties that are detrimental. Practical methods of doing this have been
only partly devised and there are still many problems for the future
concerning the method of treating soil. Nevertheless, the knowl-
edge of bacterial action has already taught some definite and useful
lessons. The uncertainty still attached to certain phases of the
subject may be illustrated by a recently discovered fact that the
sterilizing of certain unfertile soils will decidedly increase their
fertility. This has been proved definitely, but the meaning of the
fact is still obscure. Bacterial action is positively needed in the soil,
and it is rather surprising that sterilizing soil will increase its fertility.
It has been suggested that the treatment kills injurious bacteria,
giving the beneficial species that subsequently get in a better op-
portunity for growth. It has been suggested likewise that the
sterilization kills all animals and plants that m.ay be in the soil, thus
giving the bacteria that subsequently get into the soil, or that may
have resisted the sterilization, an extra amount of organic matter to
decompose and to reconvert, by nitrification, to nitrate. The fact of
this beneficial influence of sterilization is undoubted, although its
explanation is uncertain; and the phenomenon is here mentioned as
an illustration of the gaps still existing in our knowledge of soil
bacteriology. But in spite of it all, some definite conclusion as well
as practical lessons can already be drawn.*

* Reference should be made here to the conception concerning soil fer-
tility held by some, notably those connected with the Bureau of Soils of
the Department of Agriculture, that the primary trouble in "worn-out
soils" is not lack of sufficient plant food, but the presence of poisonous
excretions that prevent the growth of plants. It is claimed that each crop

ii8

SOIL INOCULATIONS. II9

SOlL INOCULATIONS.

The need of bacterial action in the soil naturally suggests the
question whether the necessary activities may not be brought about
or increased by inoculating the soil with the desired bacteria, just as
a brewer inoculates his malt with yeasts. This plan has been tried
extensively by at least two different methods.

Nitrogen Fixers, Alinit, Nitrifying Bacteria. — Alinit is a
material placed on the market and widely used for a time. It was
said to be made from a pure culture of the bacteria that can fix free
nitrogen in the soil. Careful testing, however, failed to show any
favorable results from the use of alinit, and so it has been abandoned.
Other nitrogen fixers have also been tested as pure cultures inocu-
lated into soil, with like failure. The attempt to simulate nitrifica-
tion by the use of cultures of nitrifiers has likewise failed.

Tubercle Bacteria of Legumes. — Nitragin. — As already
noticed, this commercial product, supposed to contain the bacteria-
producing root tubercles, was found to be a failure, although claims
are still made of the success attending the use of the New Nitragin
and of some of the other cultures of similar organisms. While
these may be found practical and while it would seem as if this
method would be likely, in the future, to become successful, at the
present time the results are so uncertain that a decision as to the
value of such inoculation for the developing of legume tubercles must
be held in abeyance. Inoculations with legume earth, however, have
proved to be of great value, and whenever it is desired to cultivate
a legume in a soil where it does not readily grow, this inoculative

excretes into the soil certain substances that serve as poisons to another
similar crop on the same soil. It is said that practically all soils at all times
contain a sufficiency of food, but that the accumulation of these excre-
tions after a time renders the soil incapable of supporting a satisfactory
crop. The value of fertilizers is not to give food, but to neutralize these
excretions, and that a proper rotation of crops will serve just as well, since
the excretions from one kind of plant, while injurious to the same plant,
will not injure a different kind of plant. Such a conception would largely
revolutionize the methods of treating the soil, since, if accepted, it would
lead to the abandonment of any attempt to feed the crops and would re-
place such methods by those designed simply to remove the poisonous
excretions. This theory as to soil fertility would bring into greater
prominence the agencies of soil bacteria, but it is very vigorously disputed
and certainly has not reached a position where it warrants an acceptance.

I20 SOME PRACTICAL LESSONS FROM SOIL BACTERIOLOGY.

method should always be tried. Soil from some locality where the
legume grows luxuriantly should be imported and mixed with the
field which is to be planted with the legume. But one should be
careful that the inoculating soil does not bring troublesome weeds or
plant diseases. In using either the earth inoculations or pure
cultures, it must be borne in mind that if a soil is already well stocked
with the tubercle bacteria, inoculations are not likely to do any good;
but in soils where a new legume is to be grown or where the legume
to be planted does not flourish, soil inoculation may be of decided
advantage.

Soil Inoculation with Manure. — Manure is added to the soil
primarily as a means of furnishing plant food; but it has become
evident that the inoculation of the soil with the immense amount of
bacteria in the manure is in itself of extreme value, sometimes, as in
pasture soil, of more value than the actual food substances in the
manure. The use of manure upon the soil must, therefore, be
looked upon as one of the very useful methods of inoculating the
soil with the bacteria needed to carry out the soil transformations.

CONTROL AND STIMULATION OF SOIL BACTERIA.

It has become more and more evident, as information has ac-
cumulated, that a vigorous activity of the bacteria found in the soil
is needed to carry out the various transformations of plant foods.
These bacteria are commonly abundant enough; and sometimes
they find the conditions so favorable that they grow rapidly, pro-
ducing vigorous actions; but at other times the conditions in the
soil are unfavorable, and they are held in check. What is chiefly
needed, then, in the treatment of soil is, not the inoculation of more
bacteria, but a modification of the soil conditions so as to favor the
growth of those already there. While this is a complicated sub-
ject and one that will require different treatment in different cases,
a few general principles may be formulated.

Acidity. — Most bacteria, and practically all the useful bacteria,
are very sensitive to the presence of acid, failing to grow at all in
an acid medium. If the soil is but slightly acid, bacterial agencies

CONTROL AND STIMULATION OF SOIL BACTERLA. 121

are checked, while the activities of molds and larger fungi are
increased.

In the soils of forests, for example, the fungi and molds grow
luxuriantly, but bacterial action is comparatively slight. While the
higher fungi are valuable agents in bringing about the decomposi-
tion of certain organic bodies, and are therefore useful, they cannot
perform the final transformations by which the soil ingredients become
available as plant foods. These transformations, especially nitrifica-
tion, require bacterial growth. Hence, it follows that one of the first
necessities of proper bacterial activity is an alkaline reaction in the
soil. In some localities this matter cares for itself. If the soil
contains lime in any form, the solution of lime by the carbonated
water, resulting from the carbonic dioxid of decomposition, will
keep the soil properly alkaline. Decomposition in itself will also
produce an alkaline condition, since the ammonia resulting from
ammoniacal fermentation will neutralize the acids. If, therefore,
a vigoious decomposition of organic matter is going on, little
attention need be given to the matter of acidity. But some soils
are acid from one cause or another, and proper bacterial activities
cannot be expected here without the correction of this acidity.
This is most easily done by the addition of lime, either in the form
of limestone, plaster, ground shells, or some other common substance.
The restoration of alkaline reaction will be followed by a stimulation
of bacterial activities and an increased fertility.

Aeration. — The soil bacteria are aerobic and anaerobic, and both
types are sometimes useful and sometimes detrimental. Speaking
broadly, however, the aerobic processes in the soil are the more
desirable. Anaerobic decomposition is incomplete, and gives
rise to many undesirable products, while aerobic decomposition is
complete and hence a more useful process. Nitrification, too,
can go on only in the presence of oxygen, and is stimulated by a
quantity of this gas. The value of a frequent stirring or cultivating
of the soil, which introduces air into it, is, therefore, evident. The
simple stirring of the soil, to bring oxygen into close contact with its
bacteria, may be of as much value as an application of manure. In
some soils, indeed, it is more valuable than manure, since there

122 SOME PRACTICAL LESSONS FROM SOIL BACTERIOLOGY.

may be plenty of organic products in the soil which only need trans-
forming in order to be available for plants. All desirable processes
which are likely to occur in the soil are benefited by aeration. In
especially rich collections of organic refuse, however, like the manure
heap, aeration will cause large losses through denitrification, and
hence the manure should be closely packed to exclude air. This
may be true also in some instances of intensive gardening, where
large amounts of manure are applied to the soil as top dressing.
But in ordinary soil, aeration from frequent stirring stimulates
desirable bacterial activities.

Manures Better than Commercial Fertilizers. — This perfectly
evident conclusion is of so much importance as to deserve special
emphasis. The reasons for the conclusion are several. Manure
adds bacteria as well as chemical food. It helps to keep a proper
alkalinity in the soil. It adds various ingredients that help to form
humus in the soil, resulting in a better texture and more lasting
good. Manure adds to the soil in small amounts various useful
materials, which are not present in commercial fertilizers. For
these cogent reasons manure fertilizers are to be preferred, as a
rule, to chemical fertilizers. From all these facts may be drawn
the practical lesson that a properly kept farm should keep plenty of
live stock and, instead of selling its manure, should use it freely on
the soil.

FALLOWING.

It is an old idea that the soil, after yielding several crops, needs
a rest, an idea that goes back as far as the Romans. From this arose
the plan of occasionally allowing the soil to remain without a crop
for a season or for part of a season. This plan has practically
gone out of use in all ordinary soils, for careful study shows that
a detriment rather than a benefit results from such fallowing.
Under certain conditions fallowing may be an advantage. There
is a smaller loss of water from fallow land than from land with grow-
ing crops, due partly to the increased evaporation from the stirred
soil and partly to the fact that crops draw quantities of water from
the soil, to be evaporated from the growing leaves. In climates

GREEN MANURING.

123

where water is scarce and must be conserved, fallowing may result
in advantage. It is also claimed that fallowing may enable the
soil to dispose of the poisonous secretion from plants that would
injure a second crop growing on the same soil. But, apart from
these facts, fallowing results in a loss to the soil. In the first place,
fallowing adds nothing to the soil, while a crop, especially a legume,
may do so. Moreover, during the fallow season the bacterial activi-
ties in the soil continue, converting the material in the humus
into nitrates and other soluble substances, which are then available
plant foods. If a crop is growing in the soil these will be absorbed
by the crop and utilized. If, however, the land is fallow, there is
nothing to utilize these products as they are formed, and they will
be, in a measure, lost; for they will be dissolved in the soil waters
and drained away from the soil into the general system of brooks and
streams. If, in the meantime, nothing of any value is added to
the soil, at the end of the fallowing it will actually be poorer than at
the beginning, except in the matter of water. Its store of humus
will be partly converted into available plant food and lost, while
nothing takes its place. For these reasons the practice of fallowing
has been almost wholly given up, except for special soils. Indeed,
it is a growing custom not to allow the soil to remain fallow at all,
not even during the season of the year when the main crop is not
growing; but to sow it with a cover crop, which will catch and hold
the plant foods that are constantly being made available. Nitrifica-
tion, as we have seen, goes on at all seasons when the soil is not
actually frozen, and considerable losses of nitrogen will result from
the leaching of these nitrates away from the soil at the seasons
when it is not covered with a crop. The loss may be largely retained
by a quickly growing cover crop. Such cover crops plowed into
the soil will benefit it, and the next main crop will be improved;
but a fallow season leads to direct loss.

GREEN MANURING.

The use of cover crops, just mentioned, is closely related to the
practice of green manuring, but the latter has an additional purpose

124 SOME PRACTICAL LESSONS FROM SOIL BACTERIOLOGY.

besides all the advantages of a cover crop. It not only prevents
the loss of available plant foods by drainage, but it also adds a
considerable quantity of food to the soil. It not only serves as a
catch crop to hold the nitrates that may form during the season
when the main crop is not growing, but it may add to the total nitro-
gen of the soil. The general plan of green manuring is to grow upon
the soil some leguminous crop that increases the nitrogen content
of the soil, and, after proper growth, to plow the whole crop into the
soil. The addition of this large amount of organic matter to the soil
will stimulate the bacterial activities of decomposition. The roots,
stems, leaves, and fruits of the crop undergo a decomposition and
subsequent nitrification, resulting finally in the formation of nitrates
which can be utilized by the next crop grown on the same soil.

When adopting the plan of green manuring the first thing is to
select the crop that is to be so utilized. Manifestly, from what has
been learned, this should be some one of the legumes, since this family
of plants alone assimilates nitrogen from the air, at least in any con-
siderable quantity. Other plants have been used for the purpose,
but while they are valuable in supplying some organic material
which helps maintain the store of humus, they are far inferior to
legumes which, in addition to all the other advantages, add usable
nitrogen in quantity. Attention should be given to the nature of
the soil, and to the kind of legume that will best flourish in the soil ;
the legume must produce plenty of root tubercles, otherwise the
chief value of the green manuring is lost. Green manuring is of
particular value in sandy, loose soils, where the humus is scanty,
and where the texture of the soil facilitates losses by draining. In
such soils so rapid is the draining that it is sometimes difficult to get
fertilizers to remain in the soil long enough for their proper assimila-
tion by the plant. The use of legumes, plowed under to furnish a
mass of decaying vegetation, greatly improves the texture of the soil
and will, in time, give them a fair humus content. By this means
very unpromising sandy soils can be reclaimed to a fair condition of
fertility. The legumes found to be best adapted to such sandy soils
are the cow pea, the soy bean, the velvet bean and the crimson clover.

With clay soils, on the other hand, green manuring must be

GREEN MANURING. 1 25

handled somewhat differently. The density of the soil reduces the
ordinal y losses by drainage, so that there is less need of the green
manuring. The legumes found most useful on such lands are
lupins, seradellay yellow, red and crimson clover, field peas, horse
beans and vetches. Because of the density of the soil, decomposition
does not progress so freely; hence care must be taken not to overdo
the treatment by plowing in too much of the green plant.

The extent of the utilization of the legume after growing, depends
upon the completeness of the decomposition and the eventual nitrifi-
cation of the material that is plowed under. It is possible to plow
under such a large quantity of vegetable matter that it will not
properly decay, either because the density of the soil prevents suflBi-
cient aeration, or because too much acid forms, checking bacterial
activities. No value accrues from green manuring unless thorough
decomposition occurs. For this reason it is generally best to plow
in the leguminous crop before it has fully matured, for then it has
assimilated most of its nitrogen but has not become too bulky for
proper decay in the soil. Frequently it is best to reap the crop and
feed it to cattle, plowing in only the roots and stubble, this giving all
the organic matter that can be readily decomposed in the soil. If,
subsequently, the manure from the cattle that eat the crop is added
as a dressing, the greatest possible use will have been made of the
leguminous crop.

The actual value of such green manuring has been demonstrated
many times. Sandy soils have been brought under fair cultivation,
and depleted farms have been reclaimed to cultivation by the skill-
ful use of this nitrogen-fixing power of legumes, aided by the tubercle
bacteria. A constant increase in nitrogen can be brought about
thus till the quantity is sufficient for large crops. In one extended
series of experiments and observations it was found possible to in-
crease the amount of nitrogen in a soil from .02 per cent, at the start,
to .17 per cent, at the end of about twenty-five years, equivalent to
5,000 pounds of nitrogen per acre. In another test the plowing in of
a crop of the velvet beans stubble upon a soil subsequently planted
with oats, increased the yield of oats from seven to thirty-eight
bushels per acre; and in this case the velvet bean crop was reaped

126 SOME PRACTICAL LESSONS FROM SOIL BACTERIOLOGY.

and utilized, only the roots and stubble being necessary for the in-
creased yield.

The great lesson to be drawn from this subject is that, by means
of the nitrogen-fixing power of the legumes, aided by bacteria in
their roots, the farmer has a practical means of maintaining the
nitrogen content of his soil at a proper degree for high fertility.
There is no need of purchasing nitrate fertilizers. The money may be
better spent on phosphorus and potash. The cultivation of legumes
seems to be the secret of the continuance of agriculture, and if the
farmer will only learn the principles and acquire the habit of alter-
nating legumes with his other crops, he may maintain indefinitely
a high fertility in his soil, in spite of long-continued cultivation.
When in addition to this we remember the fact that the soil minerals
are being constantly dissolved in the soil waters, it becomes evident
that the farmer is by no means as dependent upon artificial fertilizers
as has been supposed.

CHAPTER X.

BACTERIA IN WATER.

This subject is of great importance in the relation it bears to the
water supplies of cities, and most of its important phases concern
only the city water-supply. So far as relates to farm life the sub-
ject has interest in two directions: i. The purity of the drinking-
water. 2. The pollution of streams.

ABUNDANCE OF BACTERIA IN WATER.

All surface waters contain bacteria. We shall find them when-
ever we examine the water of the ocean, the brook, the pool or the
reservoir. Even rain water contains them, doubtless washed from
the air, and the same is true of snow and hail.

The number of bacteria in water is not exactly what would be
expected in accordance with our ideas of pure water. The water in
the running brook is commonly thought of as purer than that of the
stagnant pond. But this is certainly not true; the brook contains
more bacteria than the pond, and the supply streams always contain
more bacteria than the water of the lake or reservoir. The reason
for this is evident. The. brooks form the drainage system of the
country. The rains wash the whole surface of the land, and all the
dirt and dust is carried into the brooks. In this dust will always be
hosts of bacteria which are thus carried by the streams into the lake
in great numbers. In the lake many of them soon die; others
settle to the bottom; the water in the reservoir rapidly becomes
purified, and it always contains fewer bacteria than the water
brought into it by its supply streams.

The number of bacteria in a body of water will depend upon the
extent of the contamination which it receives from sources of active
bacterial growth. The actual number is quite variable, ranging

127

128 BACTERIA IN WATER.

from a score or more per c.c. in very pure waters to a few hundreds
in a moderately pure reservoir; and from this number to many
thousands in streams which are badly contaminated with sewage.

I. THE PURITY OF DRINKING-WATERS.

In determining the purity of drinking-water we are not so much
concerned with the number of bacteria it contains as with the kinds.
Very large numbers may be present and yet the water may be
perfectly wholesome, while, on the other hand, with only a small
number present the water may be deadly. As we shall see in a
later chapter, the bacteria in milk may be reckoned by the millions
per c.c, and yet the milk may be perfectly healthful; and at the same
time bacteriologists regard with suspicion water that contains them
only in thousands. The reason for this difference is simple. When
milk contains these large numbers they are almost sure to be harmless
types; but if water contains even a few thousands, the typhoid
bacillus is likely to be among them. It is impossible to condemn
any sample of water simply from the number of bacteria which
it contains; still the number serves as a useful measure of purity
for the following reason: Water that is fairly pure and contains
only the bacteria liable to come from ordinary sources seldom contains
more than a few hundreds of bacteria per c.c; it is only water
that is receiving contamination from sewage or some other source
of decaying filth that contains large numbers of bacteria. Hence,
the finding of large numbers of bacteria in a water-supply suggests
sewage contamination and the water at once becomes suspicious.

SEWAGE CONTAMINATION.

Water may receive hosts of bacteria from various sources, but
the one great and almost only source of real danger is from sewage
contamination. Most of the types of bacteria found in nature
and in natural water are perfectly harmless, so that it makes little
difference whether they are abundant or few in the water we drink.
But this is not true of the types likely to be found in sewage. Sew-

THE PURITY OF DRINKING-WATERS. I29

age contains every form of human excretions; and since it is by
means of the excretions that the pathogenic bacteria find exit
from the diseased patient, it will thus be easily understood that
sewage-contaminated water is likely to contain bacteria which are
pathogenic for man. Such water is therefore always dangerous,
a fact abundantly proved by the great prevalence of water-borne
diseases in cities whose water-supply is contaminated with sewage.
When the bacteria in water are in the thousands per c.c, they render
the water unsafe, not because this number of bacteria is injurious,
but because such water is commonly sewage-contaminated.

When we recognize the great chance which sewage-contaminated
water has of becoming impregnated with the germs of human
diseases, it is a little surprising to learn that the number of kinds of
disease actually distributed by water is very small. Only one of
our common diseases is known to be frequently distributed by
water. This is typhoid fever, in regard to which the evidence is
abundant and conclusive. This evidence need not be given here,
but it is sufficient to demonstrate that typhoid fever is very commonly
acquired from drinking-water, that the danger comes wholly from
water which has in some way become contaminated with human
excrement, usually through sewage, and that the drinking of sewage-
contaminated water is probably the most prolific source of this
dreaded and serious disease.

Other water-borne diseases are of less importance. Asiatic
cholera is distributed by water, but this is, at least in this country,
of no significance. Certain forms of dysentery are probably distrib-
uted by water, but little is known of this matter as yet. No'other
diseases are known to be thus distributed.

Detection of Sewage Contamination. — Sewage contamination
is a rapidly growing danger. As population increases, the amount
of sewage also increases, and it becomes more and more difficult
to dispose of it so as to prevent its contaminating the sources of
drinking-water. Many a stream formerly used for drinking purposes
has had to be abandoned because it has become so polluted with
sewage as to be no longer safe. It is thus a matter of prime necessity
to find some delicate means of determining whether water is sewage

130 BACTERIA IN WATER.

contaminated; for while sometimes the contamination is so great as to
be evident, in most cases, especially in wells, it cannot be detected
by ordinary examinations. The chemical analysis of water gives no
sure indication, and the determination of the number of bacteria
alone is only suggestive. It chances, however, that there is a
species of bacterium called B. coli, that is a common inhabitant of
the human intestine, but is rarely found free in nature or inhabiting
pure waters. This B. coli is so abundant in feces that it is practically
sure to be found in all sewage-contaminated waters, while it
is not found, at least to any great extent, in water free from sewage
contamination. Since this bacillus is fairly easy to recognize by
bacteriological methods, it is not difficult to determine whether
or not it is present in a sample of water. Hence this bacterium
becomes a test for sewage pollution. A sample of water showing
the presence of B. coli is almost surely contaminated by sewage,
while water free from it is not thus polluted. The report from a
bacteriologist that B. coli is found means, then, that the water is
unsafe, since sewage contamination may at any time infest it with
typhoid germs. While B. coli itself is harmless, its presence indi-
cates the certainty of danger.

PURITY OF DRINKING-WATER FROM DIFFERENT SOURCES.

Recognizing sewage contamination as the great source of danger
in drinking-water, we may classify waters as pure or safe in propor-
tion to their freedom from such contamination.

Water from Streams. — Ordinary streams are the most likely
to be sewage contaminated. They constitute the drainage system
of the land, receiving sewage from towns, villages, and cities. The
amount of sewage, and hence the extent of the danger, depends upon
the number of people contributing to produce it and upon the size
of the stream. The only safe position to hold, however, is that
all streams upon whose banks are human habitations are polluted
and unsafe for drinking. The question of the purification of such
water will be noticed later.

Wells. — Next to running streams, wells are the most dangerous
source of drinking-water. The extent of the danger depends upon

THE PURITY OF DRINKING-WATERS. I3I

the location of a well and its depth. In very deep wells bacteria
have a chance to be filtered out of the water as it passes through the
soil before it reaches the well, so that, if care be taken to prevent
contamination at the surface, the water is safe. This is always true
of artesian wells. But in the shallow well the chance of dangerous
contamination is great. The most common, as well as the most
dangerous contamination of well-water, comes from the privy vault.
Both vault and well are, for convenience, placed near the house and
frequently near each other. The well is sunken several feet below
the surface of the ground, while the vault is close to the suiface.
The contents of the vault inevitably soak into the ground and will be
surely distributed in every direction, taking naturally the course of
water currents under the surface. It is almost certain that, if the
well is close at hand, the water courses will lead to it and the con-
tents of the vault will thus find their way into the well. It requires
no argument to demonstrate the danger from such conditions. Nor
will anyone familiar with agricultural communities fail to recognize
that exactly such conditions frequently exist. Indeed, they are
sometimes even worse than this, for one may find the vault actually
upon an elevated mound and the well sunk into the soil at its foot
not twenty feet away.

Under such conditions one need not be surprised at the spread of
typhoid. A single case of the disease on the farm will contaminate
the vault, and may soon infect the well. The infection may be
from water percolating through the soil or from surface currents in
time of rains, washing the contaminated water into the mouth of the
well. The farmer rinses his milk pails in the water from the well
and subsequently puts his warm milk in the cans. The typhoid
bacilli which were in the well thus get into the milk, where they
find conditions for rapid growth, and the farmer, wholly unconscious
of having done anything out of the way, distributes the bacilli to the
neighboring community which he supplies with milk. A typhoid
fever epidemic breaks out which remains a mystery, unless some one
is sharp enough to trace it to its source in the farmer's well.

Such is not an imaginary instance, but represents a type of
typhoid epidemic many times repeated. It is simply illustrative of

132 BACTERIA IN WATER.

one of the sources of typhoid epidemics which has been found com-
mon, and many instances of almost exactly these conditions could
be given. Nearly three hundred typhoid epidemics have been
traced to milk, many of which are directly attributable to the well.
The trouble arises partly from carelessness, but chiefly from ignor-
ance. Certainly, for his own health and that of the community
which he supplies with milk, every farmer should be impressed
with the fact that the problem of his well is most critical. It should
be scrupulously guarded, and should be located in such a place as to
render drainage from the privy vault an impossibility. The safest
thing would be to give up the well entirely and depend upon some
spring or reservoir; but where this is impossible the well should be
on higher ground than the privy vault, or be removed from it not
less than one hundred feet.

Unfortunately, everyone who has been brought up on a farm is
likely to feel that this danger is imaginary, at least for his own
particular home. He has drunken water from the well all his life,
and so have his fathers before him, and he cannot be convinced of
any danger therein. But the fact remains that many a well of
exactly this sort has been the cause of typhoid. Though used for
years without suspicion it has, nevertheless, been a means of death.
The trouble gives no warning when it comes, and the well which has
been pure for years may suddenly begin to distribute typhoid fever
bacilli without the least suspicion on the part of those using it. In
ignorance the farmer not only drinks the water himself, but dis-
tributes the germs to the city, insisting all the while that his well has
"the finest water in the country." The only safeguard is either to
abandon the well entirely, or to have such an absolute isolation be-
tween his vault and his well as to make communication between
them by soil drainage an absolute impossibility.

Since the water in the well is likely to become contaminated with
typhoid bacteria, if excreta are thrown upon the ground or are
placed in a vault in the vicinity of the well which is used for drinking
or dairy purposes, especial care should be taken that no surface
rivulets in time of rain should run toward the well. If they do,
contamination of the water by surface drainage is almost certain.

THE PURITY OF DRINKING-WATERS. I33

Cisterns.— Cisterns, to hold rain-water caught from the roofs of
houses, have frequently been used as a source of water and are, to a
certain extent, so used to-day, particularly in localities where the
natural waters of the soil are very hard. These cisterns are just as
dangerous as wells; sometimes more so. They are generally
placed where it is almost sure that they will become contaminated in
some way, and actual examination of such cisterns usually shows
the B. coli present, indicating sewage contamination. Instances
are also known where they have been the means of distributing
typhoid fever.

Stored Water in Reservoirs or Lakes. — These constitute a
far better source for drinking-water, and under ordinary circum-
stances are perfectly safe. Even the water of a contaminated
stream will become free from dangerous disease germs when it has
been stored for a few weeks. This is partly because the bacteria
sink to the bottom, and are not likely to get into the water mains;
but it is chiefly because the disease germs cannot live very long in
water. Typhoid germs cannot live more than six weeks (usually
not so long) in ordinary water, and if it be stored so long before it is
used, it will be free from this danger, even though at first it was
sewage contaminated. The stored water of reservoirs thus con-
stitutes the best large supply of water. It may be something of a
surprise to be told that stored water is purer and safer than running
water, but study and experience have shown this to be positively the
case.

Springs. — These are thoroughly reliable sources of drinking-
water if they are properly guarded. The water comes from under-
ground and has filtered through the soil for unknown distances.
There may be cases, it is true, where the filtering is through only a
thin layer of soil, insufl&cient to purify. But if such cases exist,
they are very unusual, and examination shows spring-water to be
free from disease germs, unless carelessly contaminated after the
water leaves the soil. The spring should be classed with the artesian
well in this respect, and is the best source of water that can be
obtained.

Filtered Water. — The rapidly extending contamination of

134 BACTERIA IN WATER.

waters by sewage and the growing demand for water have led to
development of methods of filtering such contaminated water in
large quantities. This is done by passing it through layers of sand
which are constructed in such a way as to remove most of the
bacteria. These filters are in wide use to-day by cities that have
to depend upon a contaminated supply. The bacteria are not
wholly removed from the water, but so nearly that practically all
dangers disappear. Experience has shown that the use of filters
very greatly reduces the amount of typhoid fever in cities dependent
upon a contaminated water-supply. It is also found that the
purified water improves the general health of the community, quite
apart from the decrease in typhoid fever.

Ice. — Ice, though not thought of as water, in summer months
is put into drinking-water to cool it. The ice melts and whatever
bacteria are in it are liberated and swallowed with the water. It
has been a belief that free2;ing purifies water, so that many have
been perfectly willing to use ice from ponds whose water they would
not drink. It is a very wide practice to cut the year's ice supply
from sewage-contaminated streams, and from places where no one
would think of drinking the water: e.g., from the Hudson River,
below Albany. It has become a matter of great importance to
know whether freezing does purify such ice and render it safe.
The subject has been most carefully investigated, with the following
conclusion. Ice does in a measure purify itself in freezing, but not
wholly. If typhoid bacilli are in the water, they may be found in
the loose snow ice at the top of the frozen layer, but there are very
few, if any, in the clear ice below. After the ice has been stored
for a while the typhoid bacilli become less and less abundant, and
after a few weeks they practically disappear. Even after months
of freezing, however, a few may sometimes be found, so that no
ice from contaminated water can be guaranteed as absolutely free
from them even after six months' storage. But the number that
resists this storage is so extremely small that the ice is as pure as
filtered water. No cases of typhoid fever have been definitely
traced to such a source, though one or two doubtful cases have
been so attributed. In general, then, it appears that stored ice

THE CONTAMINATION AND PURIFICATION OF STREAMS. I35

is safe, provided it is free from snow ice and has been stored at least
two or three months.

II. THE CONTAMINATION AND PURIFICATION
OF STREAMS.

The sewage contamination of streams has been increasing year
by year, until many a stream that was clear and limpid thirty years
ago is now a vile collection of filth. Until some other means of
disposing of sewage is generally adopted, this pollution must continue
to increase. There has been a widely held belief that running water
purifies itself, and that these streams rapidly become free from
their pollution. This is partly correct and partly erroneous. A
stream does not purify itself by running, but there is always a
tendency for water to become pure, and in time sewage contamina-
tion quite disappears from water, whether running or stagnant.
The best studied example of this is in the Chicago Drainage Canal.
Recently the city of Chicago converted the Illinois River into a
drainage canal for the great amount of sewagfe of that city. This
river is a small one and flows very slowly. It finally empties into
the Mississippi River, after flowing some 300 miles. It empties
a few miles above the point where St. Louis takes its water-supply,
and naturally it excited considerable alarm in the latter city. A
careful examination of the bacteria in the river shows that there is
a constant decrease in numbers as the distance from Chicago is
increased, and when it finally empties into the Mississippi, all of
the bacterial contamination from Chicago has disappeared. In
this flow the river has purified itself of sewage bacteria. In other
examples when the polution is less a flow of even ten miles largely
purifies the water.

Evidently the phenomenon is practically identical with the
bacterial purification of sewage, modified by the different conditions.
The following factors have been advanced as explaining it:

The dilution of the water by tributary streams. This doubtless
accounts, in part, for the decrease in number of bacteria per c.c,
but it cannot be a very important factor in cases such as shown.

136 BACTERIA IN WATER.

where the number of bacteria in the river finally becomes no greater
than the number in the tributary streams.

The action of sunlight is known to be injurious to bacteria, and
it has been thought that this may be one of the factors destroying
the bacteria in streams. But its action in muddy streams must be
very slight.

Other living organisms in the water have a deleterious action.
Microscopic animals certainly destroy great quantities of bacteria,
actually feeding upon them, and they may be one of the efficient
means of the self-purification of streams.

It is well known that bacteria are generally heavier than water
and that they will slowly sink to the bottom. In slowly flowing
streams sedimentation probably plays an important part.

The food in the water is of course used up either by bacteria or
some other organisms, and finally becomes insufficient to support
bacteria life.

Although these factors do not wholly explain the purification
of streams, it is certain that sewage-polluted streams are in time
freed from most of their bacteria. Commonly, however, such streams
continue to receive contamination all the way to their mouth, and
never again become fit for drinking purposes, unless the water is
subsequently purified by filtering or otherwise.

PART III.

BACTERIA IN DAIRY PRODUCTS.

CHAPTER XI.

BACTERIA IN MILK.

In no phase of farm life has bacteriology made such profound
changes as in dairy methods, changes so great as to amount almost
to a revolution. Many dairy methods of twenty-five years ago
have been abandoned and many new ones adopted, chiefly through
the discoveries of bacteriologists.

BACTERIA IN MILK WHEN SECRETED.

Milk, when secreted from the mammary gland of a healthy cow,
is generally, if not always, free from bacteria. It has been no easy
matter to demonstrate this fact, since there are bacteria in the milk
before it leaves the udder. But a sufficient number of careful ex-
periments have shown that these really come from the outside,
entering the udder through the milk ducts, and that they do not
come from the milk glands.

If the cow is not in perfect health her milk may not be free from
bacteria. When a cow is suffering from generalized tuberculosis,
or when she has this disease localized in the udder, her milk, when
secreted, is sure to contain bacteria. Indeed, any udder infection
due to bacteria, even a simple inflammation of the mammary gland,
is likely to result in the contamination of the milk with the bacteria
which cause the trouble. Milk from a cow suffering from udder
trouble is no longer pure milk. It may contain tuberculosis bacilli,
12 137

138 BACTERIA IN MILK.

or, in cases of inflamed udders, it is likely to contain pus^ together
with considerable quantities of chain-forming streptococci. These
should not be present in good milk, and there is reason for believing
that they are the cause of certain illnesses in man.

Confining our attention for the present to milk from healthy
animals, we notice that, if we could keep bacteria out of the milk,
none of the ordinary changes, not even the souring which is so
nearly universal in normal milk, would take place. Indeed, milk
which is free from bacteria will remain visibly unchanged for an
indefinite time. It is not, however, absolutely free from subsequent
chemical changes, since there is present in the milk an enzyme which
produces slow changes. This enzyme, called galactase, is secreted
by the milk gland with the milk, and may thus be said to be part of
the milk. It can slowly convert the casein of the milk into soluble
proteids. Its action is very slow, however, and seemingly of no
significance, except in the ripening of cheese. At all events, none
of the ordinary fermentations appearing in milk are attributed to
this galactase or to any other part of the milk itself, but are all due
to microorganisms. We may, therefore, take as a starting-point
these two highly important facts: i. Milk from healthy cows will,
if it could be kept free from bacteria, show none of the ordinary
milk fermentations. 2. All of these fermentations are due to
microorganisms that get into the milk after the milk is secreted from
the mammary gland.

SOURCES OF MILK BACTERIA.

Recognizing that milk is germ free when secreted from the milk
gland, we are hardly prepared to learn that, by the time it has been
drawn from the cow, received in the milk-pail, and removed from the
cow stall, it may contain bacteria to the extent of many thousands
per c.c. But this is frequently and, indeed, commonly the case.
The number of bacteria in freshly drawn milk varies greatly with
the conditions existing in the dairy. There may be only a few
hundreds in each c.c, or, under exceptional conditions, a smaller
number still; but it is much more likely that the milk, by the time

SOURCES OF MILK BACTERIA. 139

it has been removed from the stall, contains many thousands of
bacteria.

Since all the troublesome changes which occur in milk and
make it such a difficult product to handle, are due to the action of
bacteria upon the milk, it is to the interest of the dairyman, the milk
distributor, and the consumer to have as few bacteria as possible.
Therefore, it is a matter of much importance to learn the sources
from which these milk bacteria are derived. Knowledge upon this
point will enable the dairyman to adopt precautions in the produc-
tion and caring for the milk that will materially reduce their number.
A slight attention given at the right point will produce better results
than a much greater attention unintelligently applied.

The Cow. — The first source of milk bacteria is the cow. Al-
though the healthy cow secretes milk in a sterile condition, it is by no
means sterile when it leaves the milk duct. There are always some
bacteria in the ducts ready to be washed into the milking pail with the
first jet of milk. At the close of the milking enough milk is left in
the ducts to furnish food for bacteria, which may get in through the
external opening ; and between the milkings, at the warm tempera-
ture of the cow's body, these bacteria multiply (Fig. 29). Bacteria
are thus always abundant near the opening of the teat, although
the inner parts of the duct contain smaller numbers. They are sure
to contaminate the first jets of milk drawn, so that this first lot,
called fore milk, always contains more bacteria than that drawn
later in the milking. Toward the close of the milking the bacteria
sometimes disappear, so that the last milk may be actually sterile
when it leaves the duct. While this is not always the case, the last
milk is always purer than the first.

From these facts it follows that milk is sure to contain bacteria
by the time it reaches the mouth of the milk duct. While, by the
use of special precautions, small amounts of milk can be drawn so
carefully as to avoid all bacteria, this is an impossible procedure in
dairying, and the dairyman must recognize that there is no practical
means by which he can obtain sterile miik. Indeed, it would avail
but little if he could, for it would be contaminated almost at once
from other sources.

I40

BACTERIA IN MILK.

The exterior of the cow is an even more prohfic source than the
milk ducts. Her skin, even when kept in fairly good condition, is
never very clean, and will always hold more or less dirt and dust
laden with bacteria. The cow in many poorly kept dairies is rarely,

Fig. 29, — A cow's udder cut across and showing the milk ducts.

if ever, cleaned; her flanks, tail, and skin become covered with a coat-
ing of manure, until the amount of filth thus attached to the animal is
surprisingly great. All of this filth is laden with bacteria, and
during the milking process numerous particles of it are constantly

SOURCES OF MILK BACTERIA. 14I

shed from her body by the movements of her flanks, by the switching
of her tail, and by the rubbing of her skin by the milker. Since the
milk-pails are generally widely opened, they receive a large amount
of this filth, which consists of almost every conceivable kind of
material. Besides excrement there are insect wings, grass, straws,
hairs, and many other small particles, all bacteria laden.

Milk-vessels. — The next prolific sources of bacteria are the milk-
pails and other dairy vessels, in which the bacteria remain alive
from one milking-time to the next. On an ordinary farm these
vessels are rarely, if ever, washed bacteriologically clean; for washing
in hot water with subsequent drying in the sun is wholly insufficient
to remove the bacteria. They are sure to remain in the vessels,
clinging in corners and cracks, partly dried perhaps, but alive and
ready to begin active life just as soon as they are supplied with the
food which comes to them in the next lot of milk drawn. The
ordinary farm has no really effective means of washing milk- vessels.
Even live steam, as ordinarilly used, a few seconds on each pail, will
not do it completely. Many a troublesome experience of the milk
dealer in warm weather is attributable directly to imperfectly
washed milk cans, and disappears at once when all the milk-vessels
are thoroughly sterilized by live steam. So far as numbers are con-
cerned, those in the milk- vessels probably form the largest source of
bacterial contamination.

The Air. — Other sources furnish bacteria to a less extent. Some
doubtless come from the air. In earlier years it was thought that
this was a great source of contamination, but now we know that
the air bacteria are ordinarily of little importance, although some-
times they may be a source of trouble. Fresh, out-of-door air does
not contain many bacteria, and if milking could take place in the open
air, this source of contamination would be almost excluded. In a
close barn, however, conditions are very different. The motions of
the crowded cattle dislodge bacteria from their skins. Hay, dirt,
cobwebs, soiled bedding and other dry dust-producing materials
are allowed to accumulate, and particles from any of these sources
are likely to be dislodged and float for a time in the air. The gen-
eral manner of feeding the animals is even a larger sourcTe of contam-

142 BACTERIA IN MILK.

ination. If dry hay or other dry food is thrown down in front of the
cattle, a large amount of dust will arise and spread through the air
of the stable. Such dust is crowded with bacteria, many of which
are alive and will settle into the milk-pail during milking. The
common practice of keeping cattle in the same room where they
are milked is thus very productive of a large source of bacterial
contamination.

The Milker. — Of late years it has become evident that the
bacteria coming from the milker or other persons in the dairy are
among the most serious. This is not so much because of the
number of bacteria that may enter the milk from this source, but
because of their types. In ordinary dairies the milker rarely makes
any special toilet before milking, but is liable to perform this task in
old, soiled clothing, with no attempt at cleaning his hands and face.
Under these circumstances, while, so far as concerns numbers, he is
not so great a source of bacteria as the cow, some of these organisms
are sure to fall from his hands or clothes into the milk-vessels,
especially if he adopts the filthy habit of wet milking. The number
of bacteria from such a source is, probably, not great, and does not
add materially to the bacterial content. But in one respect these
bacteria assume a more important significance. The bacteria
which produce diseases in one animal do not necessarily produce
diseases in other animals. Those which produce diseases in cattle,
with some exceptions (tuberculosis), do not usually have the same
effect on man. But it is evident that any disease germs that may be
present in one man are just the kind that can develop in any other
human being. Therefore, bacteria contamination from human
sources is more dangerous to other human beings than any infection
from animals. For this reason the bacteria which enter the milk
from the milker are liable to be more dangerous than those which
come from any other source.

TYPES OF BACTERIA FOUND IN MILK.

Many different types of bacteria get into milk from these various
sources. Some of them are useful, some are of no particular signifi-

TYPES OF BACTERIA FOUND IN MILK. 143

cance, some are troublesome to the dairyman though not distinctly
harmful, while some are decidedly injurious either to the dairy prod-
ucts or to man. A knowledge of these types is of primal impor-
tance to an understanding of their relations to dairying. The more
important types are given in the following pages. For clearness and
convenience we may divide them into three groups: i. Normal
milk bacteria. 2. Abnormal milk bacteria. 3. Disease bacteria. The
first two concern dairy problems only, while the last concerns the
relation of milk to the public health.

I. NORMAL MILK BACTERL\.

Under this head we refer to types of organisms that are practically
always present in milk and cannot be avoided by any ordinary
means. They do not, of course, belong to the milk, but they are so
widely distributed in barns and dairies that practically they cannot
be avoided. There are very many different kinds among them,
several scores at least having been described in milk from various
localities. But they may be conveniently grouped and studied
under three heads:

Lactic Acid Bacteria. — The most common fermentation of
milk is its souring, a phenomenon so universal that it has been sup-
posed to be a change belonging to milk itself. But it is now known
to be produced always by the growth of bacteria. These organisms
transform the milk sugar into lactic acid, a change that is sometimes
expressed by the formula CgHj^Og = 2031^603; but this equation

(Sugar) (Lactic acid)

fails to express the real nature of the change that occurs, which is
much more complex. The fundamental phenomenon, however, is
that the milk is made sour by the formation of lactic acid out of milk
sugar. This is first seen in the appearance of a sour taste and later
in the curdling. Milk contains its casein in a state of partial solu-
tion, but if the milk is made sufficiently acid the casein can no longer
remain in solution and is precipitated. The precipitation of casein
is the curdling of milk, and it occurs when we add to it any kind of
acid. In the normal souring of milk, when the acid reaches 0.7 per
cent, to 0.9 per cent, the milk curdles.

144 BACTERIA IN MILK.

The Souring of Milk during Thunder Storms. — The only natural
agent that causes souring is the growth of microorganisms. There
is, however, a wide-spread belief that thunder storms will sour and
curdle milk. This belief rests upon a mistaken interpretation of
observed facts. It is certainly true that milk is frequently found
sour after a thunder storm, and the natural interpretation is that
the electricity of the storm has produced the souring. A careful
study of the phenomenon has shown that this inference is incorrect.
Electricity, in the form of a current or electric sparks, has no power
to sour milk; and, further, if milk is kept properly cooled, the thunder
storm has no effect upon it. Moreover, if milk has been deprived
of bacteria, it will keep indefinitely, remaining sweet in spite of
thunder storms. In short, all evidence shows that the thunder
storm has no power of souring milk, unless bacteria are present to
produce the lactic acid, and that thunder and lightning have no
direct effect upon the souring of milk.

What, then, brings about the frequent souring of milk during
thunder storms and the wide-spread belief that thunder is the cause ?
The answer seems to be the simple one, that the same agencies
which produce the thunder storm cause a rapid growth of bacteria.
The thunder storm is brought on by climatic conditions, dependent
chiefly upon the temperature, and these same conditions are just
those that stimulate bacterial growth. It will thus happen that the
same sort of warm weather which produces the thunder storm also
hastens the growth of bacteria in milk if not kept artificially cooled
with ice. It will frequently happen, as a result, that the milk will
be ready to show signs of souring at the same time that the thunder
storm appears, frequently in the afternoon. The two phenomena
occur together, not because the one causes the other, but because
the same climatic conditions which produce the storm hasten the
growth of bacteria. A similar warm spell will sour the milk just
as quickly, even though no thunder storm appears. Whether this
is the whole explanation may be doubtful, but it is clearly demon-
strated that the thunder and lightning have nothing to do directly
with the phenomenon. The souring of milk is always produced by
bacteria.

TYPES OF BACTERIA FOUND IN MILK. 1 45

Varieties of Lactic Acid Bacteria. — A very large number of ap-
parently different kinds of acid-forming bacteria have been obtained
from milk. The different varieties all agree in producing lactic
acid, but differ in some other slight points, recognized by bacteri-
ologists. To what extent these many varieties should be combined
so as to make a small number of groups, and to what extent they
should be kept separate, is a matter over which there is as yet no
agreement. It is known that the same bacterium can show differ-
ences under different conditions. The power of a bacterium to
curdle milk may be increased by proper laboratory methods,
and when we find that, of these numerous described types, some
differ from others only in the rapidity with which they curdle milk,
we naturally infer that the different results are brought about by
the same bacterium growing under slightly different conditions.
Those who have given the most attention to the subject are convinced
that the lactic acid-forming bacteria that have been described must
be reduced to a few types, though no one yet ventures to say how
few.

Among them are three well-marked types, quite radically distinct
from each other, and each playing an important part in the dairy.
Two of them are the dairyman's friends, while the
other is always his foe.' 'S^g^<^

I. Bacterium acidi lactici, Streptococcus lacticus. — q^^^
These two names are applied to the same organism.
The first name was originally given to it when it was ^ ^^^/ ^o-—

o -^ o Bacterium

described as a short rod (Fig. 30). Recently it has acidi lac t id
been claimed that it is not a rod, but a coccus, and lactkts)!'^^^^
with this conception the second name has been given as
the only correct one. Which of these two names is more correctly
applied has not yet been settled. But whatever its name and
microscopic appearance, it is a quite well-known organism, with a
distinctive action on milk. This type of lactic acid bacterium
grows better when not in free contact with the air. It grows better
under the surfaces of media than on the surface, failing to make
any visible growth on the surface of potato and scarcely any on
agar culture slants (see page 313). In milk, however, it grows
13

146 BACTERIA IN MILK.

with great rapidity, soon turning it acid. The rapidity of the acid
production is variable with different cultures. It is so rapid in
some cases that, if the specimen be placed at body heat, it will
curdle in six hours. With other cultures, the curdling under similar
circumstances would not occur for three days; with some cultures
curdling never occurs. All specimens of milk, however, become
acid, although not always sufficiently to precipitate the casein.
Between these extremes every conceivable grade may be found in
cultures that are, in other respects, identical; and they represent,
doubtless, one type, differing in its power of producing acid.

To this type belongs the largest number of bacteria known to
cause the souring of milk. Most of the butter starters and cheese
starters (see page 189) belong to this general class. But the name
represents a type rather than any single organism. In other words,
B. acidi lactici represents a group of closely allied varieties. If we
are asked whether it represents a species or a collection of species,
we must answer that no one knows what is meant by the term
species among bacteria. The term species, whatever its significance
among higher animals and plants, seems to have no meaning among
bacteria. It is impossible, therefore, to say whether Bad. lactis
acidi is a single species or a group of species; and we may be content
simply to recognize under this name the group of lactic acid bacteria
which most commonly cause milk souring and which comprise
varieties that, while agreeing in most respects, have slightly differing
characters.

The type of milk curdling produced by this organism is quite
easily recognized. The milk becomes strongly acid, and turns
into a hard curd, without any trace of gas bubbles, and without the
separation of whey: it has a clean, sharp taste, and no odor (Fig.
31, h). This type of curdling has been recognized as a desirable
one by the dairyman, since it is most favorable for dairy processes
and is consistent with the production of the best grades of butter
and cheese. This organism grows readily at temperatures from
60° to 100° F., growing more rapidly at higher temperatures. At
a temperature of about 70° it grows with great rapidity, and at
this temperature it seems to be more vigorous than any other

TYPES OF BACTERIA FOUND IN MILK.

147

bacterium ordinarily found in milk. For this reason, as we shall
presently see, milk kept at 70° becomes, in a short time, almost
completely filled with this species of bacterium at the expense of
all the others that might originally have been there. This type of
organism is a friend to the dairyman, unless he be a milk man who
wants to deliver his milk sweet.

Fig. 31. — Showing the action of different types of bacteria upon milk, a, the
aerobic type {Bad. aerogenes); h, the anaerobic type {Bad. acidi lactici); c and d, the
peptonizing type, with the curd in different stages of digestion.

II. Bacterium aerogenes. — This type of lactic acid organism is not
so abundant in milk as the first, although it may be found more or
less abundant in most samples of milk. Microscopically, it is
practically indistinguishable from the first variety, but it differs in
two pronounced points (Fig. 32). The first is that it grows luxuri-
antly in contact with the air or oxygen, while the first variety does

148 BACTERIA IN MILK.

not. The aerogenes type, therefore, grows abundantly on the sur-
face of culture media, like potato or agar. The second and more
noticeable point is the fact that it produces a fermentation of milk-
sugar, giving rise to a quantity of gas. When inoculated into milk
it causes a souring which is rapidly followed by curdling, the rapidity
of the curdling varying in different specimens. The curd which is
produced differs very much from that of the first type
of lactic acid bacteria. It is always more or less filled
with gas bubbles, and when care is taken to obtain a
typical curd, it appears crowded with holes, which
Fig. 32.— represent the bubbles of gas formed by the organism
genes. * ^' (-^^S* 3^)' '^^^ whey commonly separates in a short
time from the curd, and the final appearance is strik-
ingly different from that of the curdled milk produced by the
first type.

The production of gas is the cause of the ruin of vast quantities
of cheese. If milk, when it is made into cheese, contains a consider-
able quantity of these bacteria, instead of the more common type,
the bacteria grow and develop gas, the cheese becomes filled with
the bubbles, swelling more and more, until it finally results in what
is known as swelled cheese (Fig. ^7,). At the same time that this
swelling occurs, the flavor of the cheese becomes unsatisfactory, so
that the swelled cheese may be practically worthless. These or-
ganisms have been the cause of the loss of enormous amounts of
money to cheese makers. In butter-making they are not so dis-
astrous, but here, too, their presence is undesirable, for they some-
times produce unpleasant flavors in the creams, resulting in an
inferior grade of butter. This type of organism, therefore, is
decidedly the dairyman's foe.

Several varieties of bacteria belong to this general type of gas-
producing organisms. Among them is B. coli, which is very
similar to B. aerogenes, except that it is motile. This, an inhabitant
of the intestine (see page 130)/ is very commonly found in milk.

III. Bacillus Bulgarious. — A third radically different type of acid
bacterium is one that has recently come into prominence in various
forms of beverages composed of soured milk. In certain parts of

TYPES OF BACTERIA FOUND IN MILK. 149

Europe sour milk is commonly used as a beverage, and has been
highly recommended as a healthful drink. It is claimed that the
lactic acid, present in abundance in these sour milks, has a very
beneficial action in the intestine, preventing the growth of the com-
mon putrefactive germs, and serving in general as a corrective for
various intestinal disturbances. It is not ordinary sour milk that is

Fig. 33. — Curds from two lots of milk soured by a gas-forming and a
non-gas-forming bacterium.

especially recommended for this purpose, but a special form, found
most common in Bulgaria, and used veiy widely as a drink in that
country. Such milk contains a variety of lactic acid bacterium
very different from the two above described, and deserving to be
called a distinct type. It is in the form of a long, large rod (Fig. 34) ,
which frequently forms long chains. It differs from the more com-
mon type in producing a much larger quantity of lactic acid. The

150 BACTERIA IN MILK.

ordinary sour milk organisms produce from 1.2 per cent, to 1.5 per
cent, of lactic acid, and then cease to grow; but this Bulgarian type
produces as much as 3.0 per cent, of acid, double the amount pro-
duced by the common type. This type is very vigorous and when
growing in milk will soon destroy other bacteria. Quite a number
of commercial products containing this organism are now on the
market, and are used somewhat widely in making a fermented milk.

Though originally found in Bulgaria, bacteria that

y^y^^^ agree with it in all essential respects have been

X /'—^\ found elsewhere. It has been found in this country

as well as in Europe, but thus far on grain rather
^garicus. " " than in milk. Several of the fermented milks found

in different countries appear to contain representa-
tions of this type of lactic acid organism.

Peptonizing and Rennet-forming Bacteria. — Occasionally
a dairyman is puzzled by a somewhat unusual phenomenon: his
milk curdles, but remains sweet. This is apt to occur in the fall or
spring when the food of the cattle is being changed, and is due to a
class of bacteria that secrete enzymes. The bacteria in question
really secrete two enzymes, one of which is similar to rennet^ secreted
by the stomach of a calf, and the other is similar to trypsin^ se-
creted by the pancreatic gland of man and other animals. Hence
these bacteria secrete two enzymes that have actions essentially
like those of digestvie fluids.

When this class of bacteria grow in milk, both of these enzymes
act. upon it. The rennet enzyme shows its effect first, and causes the
milk to curdle; but since no acid is produced by these organisms this
curd is not sour. The curd is also softer than that produced by
the lactic acid bacteria. The phenomenon is sometimes called
s^eet curdling. After a short time, usually two or more days, the
second enzyme begins to show its effects. This, acting like a
digestive fluid, changes the nature of the casein from an insoluble
to a soluble condition, and as fast as this occurs the curd is dis-
solved in the liquid of the milk. The curd thus disappears, as the
casein is dissolved, and, finally, the whole curd may be dissolved so
that the milk becomes liquid again (Fig. 31, c, (/). But it is a totally

TYPES OF BACTERIA FOUND IN MILK.

151

different product from the original milk, since it no longer contains
casein, but only the digested and dissolved products of casein^
This softening and dissolving of the curd is so much like the diges-
tion that goes on in the intestine of animals, that it has commonly
been called digestion. The bacteria that produce it are also some-
times called the peptonizing bacteria, since they produce peptones
among the soluble products that come from the digested casein.

Still another term is applied to these bacteria. One of the
common culture media used in bacteriological work is solidified

w \J

:f

-£^

F;f?

vJ v_y v_y v_y

Fig. 35. — Gelatin stab cultures. e,f, and g, show liquefaction; a, filiform; b, beaded;
c, villous; d, arborescent; e, napiform; /, infundibuliform; g, stratiform.

with gelatin. Now, many kinds of bacteria cause the solidified jelly
to become liquid (Fig. 35 E. F. G.). The liquefaction of the gelatin
is due to the same enzyme that causes the digestion of the milk curd.
Hence, we find that the bacteria that liquefy gelatin commonly
have the power of dissolving milk curd. The term liquefiers is
applied to them, since they liquefy both curdled milk and gelatin.
This type of bacteria is very abundant, and in the number of kinds
exceeds the number of lactic acid bacteria. They are found pro-
fusely in the dairy, especially in the filth that gets into the milk.
Practically every sample of fresh milk will contain them in greater
or less numbers. But it is very doubtful whether this type of bacteria
is of much or of any significance in ordinary daiiying. Although
the varieties may be numerous and their number may be great in

152 BACTERIA IN MILK.

fresh milk, they very rarely get an opportunity to have any consider-
. able effect upon the milk. The lactic bacteria grow so very much
more rapidly that they soon entirely outnumber the enzyme class,
and, indeed, in most cases stop their growth. As a result, whereas
the latter may be comparatively numerous in fresh milk, they become
less rather than more abundant as the lactic bacteria grow, and
finally disappear. Under such conditions their significance in the
milk is probably nothing. Occasionally, however, it may happen
that a sample of milk does not chance to have any lactic organisms
in it, or that they are so few as to fail to get the upper hand of the
others. If this occurs, the other species of bacteria may find the
conditions favorable to their growth, as in cases of sweet curdling.
This class of bacteria plays an important part in the changes which
may take place in so-called sterilized milk, which has been heated
to a temperature of boiling water. Such milk still contains a
considerable number of spore-bearing bacteria that resist this
temperature. The milk does not sour, inasmuch as all lactic acid
bacteria are killed, since they never produce spores. The class of
enzyme-forming bacteria, however, are very commonly spore
bearers, and resist the temperature of boiling water. Milk which
has been boiled, therefore, not infrequently undergoes changes
which affect its taste and its chemical nature, due to the class of
bacteria here considered. Occasionally they are of significance in
cheese-making. During the long ripening of cheese they have a
better chance to grow than in milk. Whether they have much
influence upon hard cheeses seems doubtful, but in the ripening of
soft cheeses they sometimes produce very bad results, causing much
loss to the cheese-makers. While, therefore, they are of little impor-
tance to the one who handles milk, they play a considerable part
in the making of cheese.

This class of liquefying bacteria usually produces no acid;
but there is a small group of the same class that differs from the
others in producing both a digesting enzyme and an acid. They
are sometimes called acid liquefiers. It has been thought that they
play a part in the ripening of cheese, but this is by no means
certain and in general they are of little significance.

TYPES OF BACTERIA FOUND IN MILK. 1 53

Neutral Types. — Among the normal milk bacteria there are
many that appear to have no noticeable action on milk. They
produce no acid and, apparently, no enzyme. When they grow
in milk they produce no noticeable effect upon it. So far as we
can see they are of no significance in dairying. Nor do we have
any reason for believing that they have any pathogenic effect upon
persons drinking the milk. They are, therefore, simply classed as
neutral types, and need not here be further considered.

ABNORMAL MILK BACTERIA.

The types of milk bacteria included under this head differ
from those already considered merely in the fact that they are
comparatively rare. Whereas milk will practically always sour
through the agency of the lactic bacteria and will nearly always
contain bacteria of the peptonizing class, the following kinds of
bacteria are not commonly found. Most of them are occasionally
the cause of troublesome dairy infections. When they occur in
milk, in numbers sufficient to cause troublesome changes, they
may always be regarded as coming from some unusual source of
contamination, one which may be prevented. While souring of
milk cannot be prevented by any practical means, because of the
universal distribution of lactic acid bacteria, these types of
troublesome infections may be prevented if sufficient care is taken
in regard to cleanliness, and they may be checked if the dairy-
man simply learns whence the contamination arises. For these
reasons, in practical dairying, it is a matter of special importance
to understand their sources.

Slimy Milk. — Slimy milk is not an uncommon trouble in the
dairy. It is sometimes produced by a diseased condition of the
cow, slimy milk being a common characteristic of garget. In
such cases the milk is slimy when drawn. Such milk is certainly
not fit to drink.

In other cases the milk is not slimy when drawn, but appears
like normal milk. * After a few hours, at about the time when
milk would usually sour, instead of becoming acid in the normal

154 BACTERIA IN MILK.

way, it becomes viscid, and finally it may be so slimy that it can

be drawn out into long threads. At the same time it has a sweetish

taste. Such milk is practically worthless. It cannot be used for

butter-making, for the cream will not separate. It will not be used

for drinking oi cooking purposes, although there seems to be no

reason for believing that it is not perfectly wholesome. In some

countries, indeed, such slimy milk is a favorite beverage; but in this

^^ country most people, not wishing to drink slime, will

.-^?# throw it away. Sometimes such an infection proves

'K% very troublesome. It may spread through a whole

^#1 farming district, affecting many dairies and continuing

^OV \ *# fo^ ^ lo^g time. Although not always easy to follow,

• ft* such infections may generally be traced to some com-

F1G.36.— s. mon source of distribution. For example, a central

lactisvisCOSUs; . . it" ^^^ c

the common Creamery, receivmg such slimy milk from some patron,
^^Mrrw/'^'Jf may distribute the trouble over the whole patronizing
district by returning to the farmers the milk vessels
not properly sterilized.

The cause of this sliminess is the growth of bacteria. Several
different kinds of bacteria have been discovered with this property.
The best known of them, and probably the most common, is one that
has been named B. lactis viscosus (Fig. 36). This has been found
to be the cause of the trouble in Europe, and a similar if not the
identical organism has been found in America. It appears to be
a very vigorous organism, and, when once present, will grow so
rapidly as to make the milk slimy in spite of the action of the ordinary
acid-forming bacteria that may be present.

To understand the sources from which this troublesome organism
is derived may be a matter of great importance to a dairyman.
Three sources have thus far been detected: i. Sometimes it may
come from water used in washing the milk cans or, more likely,
from the water in which the cans have been standing to cool the
milk. 2. It may come from the udder of the cow; perhaps a single
cow in a herd being thus infected and her milk contaminating that
of the whole dairy. 3. Slimy milk bacteria have been found in the
dust of the air in dairies. If, therefore, a dairy is troubled with

TYPES OF BACTERIA FOUND IN MILK. 1 55

slimy milk, the dairyman should look first to his water-supply, es-
pecially if the milk has been cooled by standing in cans in the water.
Then he may turn his attention to the food of the cows to see if he
has any special lot of hay or other food that holds the troublesome
organisms. This may be tested by changing the food for a time.
Lastly, he will do well to keep the milk of the different cows separate
for a few days, to see if the trouble can be traced to any particular
cow. Having once found the source, the remedy is simple: either
by applying some method of disinfection at the source of infection,
or seeing that infected water does not come in contact with the milk
cans, or removing the milk of the cow that is at fault, or changing
the food.

Bitter Milk. — Next to slimy milk, perhaps bitter milk offers the
most trouble to the dairyman. Three quite different sources of
bitter milk can be distinguished: i. The cow. She may give
bitter milk because of improper food, such as lupines, which will
impart a bitter taste. Bitter milk is also quite common in a late
stage of lactation. These types may be recognized by the fact that
the milk is bitter as soon as it is drawn from the cow, and the bitter-
ness does not increase later. 2. Microorganisms. ' ^
In such cases the bitterness is a matter of slow •^ A^Vx
development. The milk, when drawn, tastes as Hff ^ (S
usual, and the bitterness appears after standing a ^ (J ^
few hours, increasing in intensity untiL, in a short Fig. 37.— Organ-
time, it is at its maximum. In these instances |sms producing bitter

' milk, a, A coccus;

the bitterness is produced by microorganisms b, a yeast Toruia
which grow in the milk. Two or three varieties of ^ amson .

bacteria have been described that have this power, and have been
the cause of a troublesome bitter fermentation in milk (Fig. 37, a).
The source of the trouble has been traced, in one case, to organisms
in the udders of a single cow in a herd. Bitter milk is not of very
common occurrence. In cheeses the development of a bitter taste
is much more common, doubtless because, during the ripening, the
bacteria have a longer time to develop their bitter products. A
bitter taste in cheese has been in some cases traced to bacteria, and
in one extended series of troubles, which affected the cheese-making

156 BACTERIA IN MILK.

over an extensive territory, the cause was found to be due to a yeast
that infected the factory and the utensils used in cheese-making
(Fig. 37, 6). The remedy in such cases lies in a thorough disinfec-
tion of the cans, vats, etc. 3. Microorganisms in boiled milk. It
may frequently happen that boiled milk will become bitter. The
boiling destroys the acid-forming bacteria, but leaves alive some of
the spore-producing organisms. These may subsequently develop
and produce bitter products. This type of bitter milk is of little
significance, however, since the practice of keeping milk after it is
boiled has almost disappeaied.

Fermentations Changing the Color of Milk. — The first

bacterial fermentation of milk clearly described was that of blue

J milk, noticed and studied over sixty years ago. This

/% trouble has, therefore, an historic interest because of

x^t ^^^ connection with the early development of bacteri-

^' o\ogy. It has little practical interest, however, since

Fig. 38.— j^ jg q£ ygj-y j.g^j.g occurrence. It is caused by a well-

1 he organism •' -^

producing known bacterium named B. cyanogenes (Fig. 38) that
cyanogenes. ^^^ been found in this country as well as in Europe.
When the organism is inoculated into milk it produces
no visible effect until the milk is two or three days old. Then blue
patches appear in it that extend as the milk sours, until the whole
becomes of a sky-blue color. As a dairy infection it is very unusual,
and no well-marked case of such blue milk infecting a dairy has
apparently been reported from this country.

Other fermentations producing pigments are also reported by
bacteriologists. Red milk has occasionally been mentioned. Milk
may sometimes be red when it is drawn from the cow because of the
presence of blood, due to some trouble in the udder. But there are
also types of red milk developing slowly, and due to the growth of
bacteria. B. prodigiosus, B. erylhrogenes, and B. lacto rubifaciens
are three species that have been described as having this power.
None of them is of practical importance in the dairy. Red spots
in cheeses do sometimes result from the growth of bacteria, but red
milk is the rarest of occurrences. In addition to these we some-
times hear of yellow milk, orange milk, green milk, amber-colored

TYPES OF BACTERIA FOUND IN MILK. 157

milk, and black milk. I3y carefully selecting the varieties of bacteria,
and inoculating them into tubes of sterile milk there may be produced
samples of milk, each showing different colors, all the colors of the
rainbow being thus obtained. All of these phenomena do certainly
occur in the bacteriological laboratory, and all are produced by the
growth of different species of microorganisms. But they are usually
procured by inoculating sterile milk with particular kinds of bacteria
and allowing them to act on the milk for many days. They are not
ordinarily dairy phenomena, and will hardly ever be likely to ap-
pear as dairy infections. They are of scientific rather than of
practical interest.

Miscellaneous Faults. — There is a considerable list of troubles
appearing occasionally in milk that are due to the growth of unusual
bacteria. Some of these are the following: Premature curdling^ the
milk curdling too quickly and without souring; failure to curdle at
all, even after several days; had tastes such as turnip taste, rancid
taste, putrid taste; difficulty in churning; had tasting sour milk; yeasty
smell; soapy consistency. These faults are all unusual and in all cases
the growth of unusual bacteria is the cause. The remedy is al-
ways the same, more care in cleanliness and more thorough steriliza-
tion of the milk-vessels. Any sample of milk in which lactic acid
bacteria fail to develop normally will be sure to show some trouble
due to the growth of bacteria that happen to be present and whose
rapid growth is not prevented by the acid-foiming bacteria. Some-
times such troubles may be remedied by the addition to the milk of
a culture of ordinary lactic acid bacteria.

Alcoholic Fermentation of Milk. — Most sugar solutions will
readily undergo an alcoholic fermentation, but milk sugar does not
easily make this change. It may be converted into lactic acid,
but not readily into carbon dioxid and alcohol. Hence an alcoholic
fermentation of milk is not a normal phenomenon, although it may
be pioduced by the addition of a little cane-sugar to the milk. The
possibility of making milk undergo an alcoholic fermentation by the
addition of yeasts is made use of in the manufacture of kummys.
This beverage was originally prepared by the Arabs from mare's
milk, which will normally undergo an alcoholic fermentation; but

158 BACTERIA IN MILK.

now an imitation product is widely made and used, prepared from
cow's milk. A small quantity of sugar is added to milk and some
common baker's yeast. An alcoholic fermentation soon begins,
and the fermented product is kummys. Various modifications of
this general process are adopted by different makers, for kummys
has become a commercial article.

In addition to these there are several other types of beverages
made from milk in common use among different nations, in the
production of which alcohol is formed. One, known as kefir,
has long been used in the Caucasus mountains. The fermentation

Fig. 39. — A large-sized kefir grain and the three species of bacteria of
which it is composed (Freudenreich).

is brought about by adding to the milk what are known as kefir
grains (Fig. 39). These are hard nodules of various sizes which
have the power of starting an alcoholic fermentation in ordinary
cow's milk. The origin of these kefir grains is unknown. To-
day they are handed from person to person, taken from the fer-
mented milk and dried to be used again. During the fermentation
in the milk they increase in size and new grains may be obtained
from fragments of the old ones. In Egypt the people use a fermented
milk called leben. Another, called mazoon, is common in Armenia.
The Turks have one they call yoghourt, and in Sardinia still another
is found with the name of goiddu. In all these cases the beverage
is prepared by the use of ferments that the people keep on hand,
whose original sources are unknown. These ferments, so far as

GROWTH OF BACTERIA IN MILK. 1 59

they have been stud fed, prove to be based upon the combined
action of yeasts and bacteria. Very h'kely the bacteria change
the milk-sugar into a fermentable form and at the same time sour the
product. The yeast is probably responsible in all cases for the
alcoholic fermentation proper, although in some the milk souring
by the bacteria is the primary feature, while the action of the yeasts
is secondary and is not regarded by some as at all essential to the
product. In several of these products the type of lactic acid
organism mentioned under the name of B. bulgaricus is present.
The beverages are generally regarded as more digestible than
ordinary milk.,

GROWTH OF BACTERIA IN MILK.

The number of bacteria that may be in any sample of milk is,
in the first place, dependent upon the number and variety that get
into the milk during and aftei the milking. But the original
contamination is only a small factor in determining their number
at any subsequent time. Milk furnishes excellent food focJoacteria,
and when drawn from the cow it is warm. Hence a rapid multi-
plication of bacteria begins; but although the milk furnishes such
an excellent medium for them, they do not begin to multiply
at once. For a few hours their number remains the same or even
decreases. There seems to be something in fresh milk that injures
them. Whatever this may be, its influence ceases after a few hours.
This power of checking bacteria growth is sometimes called the
germicidal power of milk, and it lasts from three to twenty-four
hours, 'according to temperature, being less at higher temperatures.
After it. has passed, the bacteria begin to increase rapidly and
the number present at any later period is more dependent upon the
extent of their multiplication than upon the original contamination.
The rate of multiplication of all bacteria depends upon temperature.
The majority of milk bacteria grow best at temperatures between
60° and 100° F., and, generally speaking, they grow more rapidly
at the higher temperatures. The effect of temperature is showni
by the following example:

l6o BACTERIA IN MILK.

Fresh milk contained 6,525 bacteria per c.c.

After 25 hours at 50° the same milk contained, 6,425 bacteria "
After 25 hours at 70° the same milk contained, 6,275,000 bacteria "

In this example it is seen that for twenty-five hours the bacteria
in milk kept at 50° did not multiply at all, while in that kept at 70°
they multiplied one thousand fold. It is not common to find such
a striking difference, but in all cases there is a very marked contrast.

PROTECTIVE ACTION OF LACTIC ACID
BACTERIA.

If ordinary proteids, like eggs or meat, are left undisturbed to
the action of bacteria, they will putrefy. Milk also contains a
ptoteid, casein, which is just as liable to putrefaction as other
proteids. But under ordinary conditions it does not undergo this
unpleasant change. Milk sours, but rarely putrefies. The reason
for this is found in the power of the lactic acid bacteria to restrain
the growth of other species. Almost from the start, the lactic acid
bacteria in milk grow more rapidly than the other types, and as
they become more abundant, they prevent the other kinds from
growing; they thus efcctually restrain the growth of the putrefactive
bacteria, so that milk that has begun to sour will not putrefy. This
is really a very useful function, for, whereas soured, milk is wholesome,
putrefied milk is not wholesome, and the lactic acid bacteria thus
protect the milk from a decomposition which would be far worse
than souring. It has also come to be a recognized fact that many
of the troublesome faults in milk may be remedied by using a culture
of lactic acid bacteria. In cases of bitter milk, of premature curd-
ling, and of other miscellaneous troubles, due to undesired bacteria,
a remedy is found by putting into the milk a culture of a vigorous
lactic acid bacterium that will grow rapidly and prevent the
undesirable bacteria from developing sufficiently to cause trouble.
The use of this principle in butter- and cheese-making has become
very widely extended.

It is this restraining action of the lactic acid bacteria that explains
the generally recognized fact that sour milk, or butter-milk, is not
only a wholesome, but a very useful beverage. It seems a little

DISEASE GERMS IN MILK. l6l

strange that these products, containing as they do, bacteria reckoned
by the hundreds of millions per c.c, should be recommended as
beverages for infants and invalids. A glassful of well soured
milk will certainly contain 100,000,000,000 bacteria, and yet it
is a wholesome as well as a refreshing beverage. The explanation
however, is simple enough. These myriads of bacteria are practically
all of the type of lactic acid bacteria, which are not only harmless
in themselves, but which prevent the growth of various kinds
of putrefactive germs that might produce trouble in the intestine.
The presence of a goodly number of lactic acid bacteria, therefore,
may prevent the growth of certain types of intestinal putrefaction
that would otherwise cause trouble. The farmer's belief that
butter-milk and sour milk are healthful drinks, which seemed hardly
credible for a while when the immense numbers of bacteria contained
in them were first recognized, appears, after all, to be well founded
on scientific fact. The use of such milk is becoming recommended
very widely, and already there are on the market commercial prepa-
rations of lactic bacteria to be used in preparing such milks. These
preparations, as a rule, contain the particular form of lactic bacteria
mentioned on page 148 which has the characteristic of being more
vigorous, and making milk more acid than the ordinary lactic acid
bacteria, and, therefore, having in even greater degree this power of
preventing the growth of other more mischievous organisms. The
healthful properties ascribed to the alcoholic beverages mentioned
on page 158 are probably due to the presence of the beneficent
lactic acid bacteria.

DISEASE GERMS IN MILK.

It has long been recognized that milk may be a distributer of
disease. This general statement is disquieting, but the knowledge
is of little use unless it can be made more definite. The subject
can be made more intelligible if we notice what kind of diseases
are thus distributed and how the dangers arise. There are four defi-
nite diseases known to be distributed in this way, and, in addition,
a less definite type of intestinal trouble.
14

1 62 BACTERIA IN MILK.

Tuberculosis. — This subject will be considered in a separate
chapter.

Typhoid Fever. — Typhoid fever is produced by a well-known
bacterium primarily inhabiting the human intestine (Fig. 40).
Inasmuch as the cow is not subject to typhoid fever, milk, when
freshly drawn, will never contain typhoid bacilli. This disease,
therefore, bears quite a different relation to dairy matters from
tuberculosis. Milk, if infected with tuberculosis bacilli, contains
them when freshly drawn, and secondary infection is
a matter of no significance. But fresh milk never
contains typhoid bacilli, and if they are present in the
milk, they come wholly from secondary contamination.
Fig. 40.— The chief sources of these secondary contaminations
bacillul^ °^ ^^^- ^' Direct contact with persons who have or are
recovering from the disease. It is well known that
patients may, after recovery from this disease, carry around the living
bacilli for a long time; ^'bacillus carriers" they are called. In other
cases the patient may be so slightly sick with the disease as to keep
about his work, having what is called "walking typhoid." If people
from either of these classes are employed in the dairy, they will be
pretty sure to infect with typhoid fever germs whatever dairy utensils
they handle. 2. Patients who are sick enough to be confined in
bed eliminate large numbers of bacilli in their excretion, and this,
together with clothing soiled by it, may be carelessly handled by
some one who is employed in the dairy. The chance of milk infec-
tion from such persons is, then, very great, and no one who has
anything to do with the care of a typhoid fever patient should be
allowed to have any contact with the dairy. 3. Infected water is
a common source of contamination. This does not mean that
the milk is necessarily watered; but milk may become infected
by simply allowing the cans to stand in impure water while they are
cooling or by rinsing the cans in such water after they have been
washed. There are also other secondary sources. That the danger
from these sources is real and not imaginary, may be judged from
the fact that already at least three hundred typhoid epidemics have
been traced to milk.

DISEASE GERMS IN MILK.

163

Scarlet Fever and Diphtheria. — There is positive evidence that
these two diseases may be distributed by milk and that some
epidemics are attributable to the milk-supply. The cause of scarlet
fever is yet uncertain, and it is not known whether cows can contract
the disease and then produce milk already contaminated, or whether,
as in typhoid fever, the contamination of the milk is wholly secondary.
A few epidemics of scarlet fever have been traced to the cow with more
or less certainty, and it is beyond doubt also that the milk may
become infected with the cause of this disease by secondary
contamination. The farmer should, therefore, take
precautions to prevent any person from working in*
the dairy who is recovering from scarlet fever.

Diphtheria is produced by a well-known bacillus
(Fig. 41). Here again there seems some doubt whether _ _,

° ° Fig. 41.— The

cows have the disease. It is certain, however, that the diphtheria bac-
milk may become secondarily infected through con- t^"""^-
valesccnt diphtheria patients working in the dairy and handling the
milk. Some instances of diphtheria have been traced to such a cause.
Diarrheal Diseases. — Besides the diseases mentioned, milk
is responsible for a portion of those obscure diseases characterized
by diarrheal troubles, which are especially prevalent in warm
weather. Among these are cholera infantum, which is responsible
for the death of so many children, and summer complaint, which is
less serious. These troubles are not yet so well understood as the
others we have mentioned. They do not appear to be caused by
any single specific bacterium, but are probably due to the excessive
multiplication of a number of certain kinds of bacteria in the milk.
That they are due to milk bacteria is proved by the facts that (i)
they occur most frequently at the seasons of the year when milk
bacteria are most numerous; (2) they are more prevalent among in-
fants fed upon cow's milk than among breast-fed children. What
kinds of bacteria are at fault in the production of these diseases
we do not know. Quite a number of bacteria are found in milk
which produce poisonous secretions and which may be agents in
the production of these obscure diseases. For the purpose of
our discussion it is sufficient to state that they are probably due

164 BACTERIA IN MILK.

to putrefactive bacteria, which are the bacteria of filth. Anything
which increases the amount of filth in the milk will have a tendency
to increase the amount of such troubles, and any advance in clean-
liness will have an influence in the opposite direction.

\

CHAPTER XII.

CONTROL OF THE MILK-SUPPLY.

A better regulation of the milk-supply is emphatically needed, and
this need has become more and more evident as the facts enumerated
in the last chapter have been gradually disclosed. It would enable
the dairyman to avoid the many troubles due to undesirable organ-
isms and would be to the public at large a means of protection
from the illnesses due to milk. In consequence of this need, a
series of regulations and suggestions have arisen looking toward
the improvement in the quality of milk We may best consider
these under three heads: i. Dairy pro' lems. 2. Transportation
problems. 3. Public control.

L DAIRY PROBLEMS.

Manifestly the first place demanding attention in the attempt
to reduce the possible evils resulting from undue bacterial contamina-
tion is the dairy. The primary lesson to be learned here is the
need of cleanliness. But there are several subordinate divisions
of this general subject.

The Cow. — The health of the cow is a matter of such great
importance that it hardly needs to be said that no sickly cow should
be allowed to contribute to the milk-supply. All tuberculous cows,
in particular, should be excluded, or their milk used only after
pasteurization. Every dairyman should be .on the watch for udder
troubles, and if any signs of hardness, of inflammation, or of running
sores appear on the udders, or if the animal gives bloody milk,
she should at once be excluded from the milk-produ'cing herd until
completely recovered. The cow should also be kept clean. For-
tunately, there has been a decided change in this respect, and at
the present time cattle in dairies are not infrequently groomed and

165

l66 CONTROL OF THE MILK-SUPPLY.

brushed, and are sometimes kept in as cleanly a condition as
ordinary horses. The habits of the cow, especially when closely
confined in the stall, inevitably result in a large amount of manure
adhering to the animal's flanks, tail, and udders, and unless this
is removed by curry comb and brush, and by washing if necessary,
the character of the milk is sure to suffer.

The Stables. — It is much better to have stables on high giound,
where there is ready drainage, than on low ground. Both air and
light are necessary in stables, for the best results. Each cow
should have three to four square feet of window surface, and 400
to 450 cubic feet of air space. While the animals are in the yard,
as they should be daily, the stables should be thoroughly aired.

The cleanliness of the stable is a matter of utmost importance.
The habits of the cow and the nature of the manure are such as
render a high state of cleanliness very difficult. But the dairyman
should understand that all accumulation of manure or other filth is a
direct detriment to the quality of the milk. The removal of the
manure from the stalls should be as frequent as possible, never less
than twice a day. The manure, when removed, should be taken as
far as possible from the barn, and should never be heaped outside,
close by the barn nor be allowed to accumulate in the cellar. By
far the best method is to distribute it daily upon the fields, where it
may serve as a fertilizer. Attention should be given to the dust,
cobwebs and hay that may be clinging to the ceiling of the barn, for
all such are traps for accumulating dirt, as well as sources of bacteria,
thus aiding in the contaminating of the milk. Plastered or sheathed
walls and ceilings are very much to be preferred to a rough finish.
The bedding of the cattle is a matter of some importance also; and
clean shavings appear, on the whole, the best for this purpose. A
coat of whitewash should be applied with a spray pump at least once
a year.

Personnel. — Special attention should be given the persons em-
ployed on a dairy farm. The milking clothes should be made of
washable materials. Some dairies insist that this clothing must be
sterilized each day. A thorough washing and drying of the hands
should precede the milking. All these me.asures are necessary,

DAIRY PROBLEMS. 167

since the persons employed in the dairy are more likely to be a
source of danger than anything else. No one should he allowed to
handle any milk, to wash the milk cans, or to have anything whatsoever
to do with the milking utensils if he is suffering from or recovering
from any contagious disease. Nor, indeed, should any farm furnish
milk to the public if there is a case of typhoid, scarlet fever, or
diphtheria among its employees, unless a health inspector pro-
nounces the sanitary conditions satisfactory.

The Milking-room. — It is quite customary to milk cows in the
ordinary cow stalls. Some of the better dairies have adopted the
plan of having a separate milking-room, and find beneficial results in
the character of the milk. It is certainly preferable to using the
ordinary cow barn as a milking-room.

The Milk-vessels. — Perhaps the most important factor for
reducing bacterial contamination is the proper cleaning of all milk-
vessels. This refers to milk pails, strainers, coolers, separators,
milk cans, glass bottles, etc., used in the dairy. The cleaning
of such utensils is no easy task, and after the most thorough
washing and scrubbing many bacteria will still be left in the
cracks and clinging to the milk-vessels, ready to feed and multiply
in the next lot of milk. All milk-vessels should be of metal, and
if the coating of tin is worn off they should be discarded, for they
cannot be kept clean. They should not be allowed to dry before
washing, for dried milk is difficult to remove. They should first be
soaked in warm water to loosen the milk; then washed thoroughly
in hot water, containing, preferably, soap or sal-soda, and thor-
oughly scrubbed; after this they should receive a second rinsing in
hot water. Such a cleaning is not, however, sufficient to sterilize
them. Hence, no creamery should depend upon the farmer to wash
milk cans. Where a supply of steam is to be had a sterilization
should follow the washing. Washing with hot water is better than
with cold, washing with sal-soda is better than simple washing, but
sterilizing is best of all. Each dairyman should adopt as thorough a
cleaning as parcticable.

The Milking. — Moistening the udder with a damp cloth or
sponge just before milking prevents the fall of much of the dirt into

1 68

CONTROL OF THE MILK-SUPPLY.

the milking pail. The precaution is a simple one, costs nothing and
really has a surprising result in decreasing the number of bacteria
that get into the pail.

Covered Milk-pail. — The old fashioned pail had a flaring top,
the purpose of which was to make the milking as easy as possible;
but, incidentally, it resulted in exposing the milk to much contami-
nation by dirt and bacteria. Various devices for protecting the
milk from such exposure by the use of covered milk-pails are now
used. There is quite a variety among them, but they all have the
general plan of decreasing the size of the
^"j^w^oB^^^^ opening of the milk- vessels, so as to expose
Wt^ j^m ^/Bf ^^^^ surface for the entrance of dirt, and
V ■^- — ^'^^^^B they also have in the opening some kind of

' '^^ a cloth strainer for catching the larger

particles of dirt, thus keeping them from
the milk (Fig. 42). This is one of the
easiest, cheapest and most efficient means
for improving the character of the milk.

Milking Machines. — A still more recent
means of reducing contamination is by
milking machines. These consist of rubber
tubes ending in special cups for attachment
to the teats of the cow, and connected at
the other end with large cans that can be sterilized. The cans
are connected with a system of vacuum tubes, and at the
point where the rubber tubes are attached to the can there is a
mechanical device by which the vacuum is made to draw the milk
through the tubes intermittently, thus imitating natural milking.
It would seem that such a plan, which carries milk directly from
the teat to the sterilized can, would be almost ideal, and would
practically remove all dirt contamination. Where these machines
have been intelligently used they have been found efficient in pro-
ducing a very clean quality of milk. But the long rubber tubes are
by no means easy to keep clean, and when they are used by careless
employees, the bacteria become very abundant inside the tubes and
the other parts of the somewhat complicated machine. In other

Fig. 42. — A milk pail
with a special cover designed
to keep out the dust which
falls into the pail durinj
milking.

DAIRY PROBLEMS. 1 69

words, it requires very great care to clean and sterilize these milking
machines in order to produce even as good results as are obtained
by hand milking. But if care be taken to sterilize thoroughly all of
the apparatus, better and more reliable milk can be obtained by the
use of the milking machine.

Rejecting Fore Milk. — ^For reasons already indicated, the first milk
drawn at each milking will contain more bacteria than the rest.
The practice of rejecting the fore milk, either allowing it to waste
upon the floor, or collecting it in a separate dish, is, no doubt, an
advantage, but the extent of the advantage has been overdrawn.
The extra number of bacteria obtained in a pail of milk from the
entrance of the fore milk, is very small compared with the larger
number that enter the milk from other sources.

Value of Trained Dairymen. — Apparatus without a proper man
to use it is valueless. It makes no difference how many rules may
be drawn concerning the dairy, how complicated the apparatus
becomes, or how careful may be the directions given to the em-
ployees, it is quite impossible to expect satisfactory results without
properly educated and trained assistants. An untrained man will
succeed in getting only bad results, even with the best of apparatus.
The employees in our dairies at present are, in many cases, without
any proper training. They do not know the character of the prod-
uct they are producing; they do not know the dangers to which it
is subject; they do not understand the universal presence of bacteria;
they do not understand, in general, the pi:oblems that are concerned
with their business. They are quite likely to believe the whole
subject of bacteria in milk to be foolishness and not worth their
attention. Under these circumstances, no matter how many
directions are given or how much instruction there may be, satis-
factory results will never be obtained.

Cooling. — The importance of cooling the milk, and cooling it
immediately, cannot be overstated. When milk is drawn from the
animal, it is at a temperature to stimulate the growth of bacteria to
their utmost. It is true that, for a while, because of the germicidal
property of milk (see page 159), the bacteria do not grow; but this
condition lasts only a short time, after which, if the milk is warm,
IS

170 CONTROL OF THE MILK-SUPPLY.

they begin to develop with great rapidity. But if the milk is at once
reduced to a low temperature, the bacteria that have found their
way into the milk will not grow very rapidly. These facts are so
simple as hardly to require statement; but, unfortunately, many a
dairyman, although he may theoretically understand them, fails to
appreciate their importance. The essential point to be emphasized
is the necessity of immediately cooling the milk to a temperature as
low as 40° F. if possible. It is just as necessary to cool clean milk
as it is to cool dirty milk. Unless it is done, the cleanest milk will
soon contain as many bacteria as the dirtiest milk.

Straining and Filtering. — The long-continued practice of
straining the milk through a metal strainer or through cloth has in
its favor the fact that it will remove the larger particles of dirt; but
it does not remove the bacteria, for they will pass through any
strainer. Sand filters have also been used by some dairy com-
panies, and these are more efficient than simple straining. But
these filters are not of very much value and they are not widely
used. Centrifugal force is sometimes used for cleaning the milk,
and is fully as efficient as sand filtering. All of these means, while
effective in removing the large particles of dirt, are. practically of
no value in removing the bacteria, which show as high numbers
after such treatment as before.

II. TRANSPORTATION PROBLEMS.

Under this head will be included not only methods of treating
milk during transportation, but also of preparing it for preservation
during the transportation or until it is consumed. Milk, as a rule,
receives no preparation for transportation, except that of cooling and
placing in clean cans. Then, if rapidly shipped and kept cool, it
should remain good until some time after it has reached the con-
sumer. But the rapidity of bacteria growth, especially in hot
weather, makes it difficult to transport milk, in good condition, for
very long distances. Consequently, careful search has been made
for some method* of treating milk so as to preserve it.

TRANSPORTATION PROBLEMS. 171

The Use of Preservatives. — It is easy to add to the milk
various chemicals which will prevent the growth of bacteria, and
consequently preserve the milk. Many such substances have
been used. There are quite a number of preservatives on the
market which are sold to the farmer to assist him in preserving his
milk. The basis of most of these is either horacic acid, salicylic acid,
or formalin. All of these substances are injurious to man, and
their use should not be allowed in preserving an article so freely
used as milk. Such methods are illegal, and are unhesitatingly to
be condemned.

The Use of Heat. — A more legitimate method of obtaining the
same result is by the use of heat. All bacteria are destroyed by heat
and therefore, by this simple means, it is, possible, to kill the living
organisms in milk, and thus preserve the milk from their subsequent
action. This has given rise to two chief methods of treating milk —
sterilization and pasteurization.

I. Sterilization. — This means the use of heat sufficient to de-
troy all bacteria at once. It is perfectly possible to do this, but since
milk always contains spore-bearing bacteria, sterilization requires a
high temperature for the purpose. A temperature of boiling will
not destroy the spores, so it is necessary to heat the milk to several
degrees above boiling. This involves the use of special apparatus,
in which bottles of milk can be inclosed in special vessels, sub-
jected to steam under pressure, and subsequently hermetically
sealed while still within the closed vessels. Such a procedure
inevitably makes the milk rather expensive. But milk thus pre-
pared is supposed to be germ-free, and, consequently, should keep
indefinitely. Unfortunately, even these temperatures do not al-
ways destroy all the spores, for some samples of milk thus treated
have subsequently undergone fermentative changes, due to the
germination of the spores that are left alive. Further, it has ap-
peared that these later changes, due to the resisting spores, are
frequently such as do not change the appearance of the milk to the
eye, so that such milk, though containing bacteria in quantity, will
be drunken as pure milk. The fermentation has, moreover, filled
the milk with bacterial products of more or less injurious nature,

172 CONTROL OF THE MILK-SUPPLY.

and consequently the drinking of such milk is far worse than drinking
fresh milk which is, most likely, supplied chiefly with lactic bacteria.
Sterilized milk, if it does retain a single spore, will be in time, more
dangerous than ordinary fresh milk. For this reason, among
others, this practice of treating milk to superheated steam for the
purpose of absolute sterilization has disappeared.

The term sterilization is sometimes applied to the simple boiling
of milk. This was recommended by physicians long before its
real significance was understood and has been very widely used in all
civilized countries. Its ease of application explains the reason for
its popularity. It is only necessary to place the milk upon the
stove and allow it to come to a boil, and the end is reached. In
some countries very little milk is used without such previous boiling,
and even the children are taught in school that it is dangerous to
drink milk without such treatment. The purpose aimed at in this
wide use of boiling, which is commonly, though not properly,
called "sterilization," is simply to destroy the danger of distributing
diseases by the destruction of pathogenic bacteria. This purpose
is certainly achieved, for the boiling temperature does destroy all the
pathogenic bacteria which are likely to be in milk, since none of
these are spore producers.

But several practical objections have arisen:

1. The bacteria spores are not destroyed, and such milk, if kept,
will surely undergo a fermentation. But this is of little importance
if the boiled milk is to be used at once.

2. The milk acquires the well-known taste of boiled milk which
is, to most people, unpleasant. People are willing to take boiled
milk upon an emergency as an ivalid diet, but few will continue its
use. The taste is not enjoyed, and, rather than drink boiled milk,
the majority of people will give up drinking milk altogether. This
is certainly not desirable, since milk forms one of the best and
cheapest foods. Any treatment which greatly reduces the amount
used is, in itself, undesirable; and the practice of boiling milk
certainly does reduce the amount used.

3. Milk treated to a temperature as high as boiling becomes
somewhat less easy of digestion and assimilation. The heat pro-

TRANSPORTATION PROBLEMS. 1 73

duces several important changes which result in its being less easily
handled by the digestive organs. The difference is not very great,
and a healthy individual is able to digest such milk well enough;
but delicate children and invalids are not so well nourished upon
boiled milk as upon raw milk.

4. Boiling the milk is a treatment which has not proved practical
to adopt on a large scale at a central source of supply. It offers,
therefore, no assistance either to the producer or to the distributer
in enabling him to furnish milk which, since it keeps longer, gives
greater satisfaction.

The practice of boiling milk in order to "sterilize" it is widely
adopted in private families, but the objections urged against it
have led to its being less and less recomm^ended. In its place has
come an extended use of the second method of treating milk by
heat.

2. Pasteurization. — This method, originally devised by Pasteur
for treating wine, consists in heating the milk to a moderate tempera-
ture only, and then rapidly cooling it. The temperatures chosen
have varied. Sometimes a temperature as low as 140° F. is adopted,
and continued for from twenty minutes to half an hour or more;
sometimes 150° to 160° is used for about ten minutes, and some-
times as high a temperature as 180° is used, the milk being just
brought to this point and then cooled at once. Any of these
methods is called pasteurization.

Such temperatures are manifestly not sufficient to sterilize the
milk, since they are even less efficient than boiling. But in pasteuri-
zation no attempt is made to sterilize it, but simply (i) to destroy the
large majority of bacteria and (2) to destroy the disease germs
that are liable to be in the milk, and therefore to render it safe for
drinking. A low temperature is chosen in order to avoid the chemi-
cal changes that are pioduced by boiling and that show themselves
in the boiled taste. These changes begin to appear at about 156°,
and any temperature below this scarcely changes the milk at all,
while higher temperatures will bring them about. For this reason
the lower temperatures are better. But will these moderate
temperatures accomplish the desired ends ?

174 CONTROL OF THE MILK-SUPPLY.

Such moderate temperatures certainly do increase the keeping
quality of the milk. While a temperature of 156° F. does not
destroy spores, it does very largely destroy the active, non-spore-
bearing bacteria. Now the lactic acid bacteria, which are the cause
of the souring of milk, produce no spores, and consequently they are
largely killed by such moderate heat. Hence the total number of
bacteria in milk is immensely reduced, and the milk has its keeping
quality much increased. Milk thus treated will frequently remain
good two days longer than similar milk not pasteurized.

Will such temperatures destroy disease bacteria? Of the
diseases mentioned above as liable to distribution by means of milk,
there is only one in regard to which there has been any disagreement.
It is admitted on all sides that typhoid and diphtheria bacteria
are killed by the low heat (140° F. for one-half hour); the same
is probably true of scarlet fever. The tuberculosis bacillus, how-
ever, will withstand higher heat without injury, and hence, in order
to be sure of destroying these organisms, it has been thought neces-
sary to heat the milk to temperature of 185° F. At this temperature
the cooked taste and the chemical changes begin to appear. The
piesent conclusion, the result of the most recent and careful experi-
menting, is happily a satisfactory one. If milk is heated in such
a manner as to avoid the formation of a scum on its surface, at a
temperature no higher than 140° F., but continued for half
an hour, the virulence of the tubercle bacillus will be so much
reduced that milk containing these bacilli will be rendered harmless.
This temperature is considerably below that at which the chem-
ical changes in -the milk take place. Milk may thus be deprived
of its danger of distributing disease germs without having its
physical or chemical nature noticeably changed. Such milk,
when cooled, cannot be distinguished from fresh milk.

The value of pasteurization is becoming rapidly recognized, and
this method of treatment is being widely adopted. The advantages
lie in the following facts:

1. It produces milk which cannot be distinguished from fresh
milk and will be used as freely.

2. It increases the keeping propeity of the milk, but not to the

TRANSPORTATION PROBLEMS. 1 75

extent of leading the consumer to believe he can keep it indefinitely.
The consumer is thus forced to use it up before the spore-bearing
bacteria get an opportunity of multiplying sufficiently to produce
the injurious secretions which occasionally render sterilized milk
dangerous. The very fact that the method does not destroy all
bacteria is a safeguard.

3. It removes the danger of distributing pathogenic bacteria.
This is certainly quite true of the typical diseases mentioned.
Whether it similarly removes the danger of diarrheal diseases,
not dependent upon any known specific bacteria, is not yet positively
known by experiment, inasmuch as we do not know the actual
cause of the diseases. But the practical experience of physicians
tells us that pasteurized milk acts as efficiently as sterilized milk
in reducing these diseases.

4. This method of treatment is perfectly applicable upon a
large scale. Several forms of apparatus have been devised that
accomplish the end rapidly and upon large quantities of milk.
Of these, there are two general types. In one a large quantity of
milk is heated to the desired temperature and maintained at this
temperature as long as desired, after which it is cooled. These
are called discontinuous pasteurizers. In the other type the milk
is passed through the apparatus in a constant stream, being heated
and cooled while it passes through. In these machines the milk
is sometimes only just brought to the desired temperature, and
cooled at once; and in all cases the extent of the heating is dependent
upon the rapidity of the stream flowing through. These are called
continuous pasteurizers. Generally speaking, this type is apt to
be less efficient than the discontinuous pasteurizers, and are more
subject to irregularity. Either type is efficient if properly managed,
but carelessness and haste on the part of the employees may render
either kind unreliable and inefficient.

In the last few years the plan of pasteurizing the milk on a large
scale has come to be frequently adopted. It is done in creameries
in connection with butter-making, and in some of our large cities
for the treatment of the general milk-supply. In the pasteuriza-
tion of the public milk-supply the purpose has not been, primarily, to

176 CONTROL OF THE MILK-SUPPLY.

protect the public, but to keep the milk from souring. Milk
distributers have found it difficult to furnish milk that will keep
without preservatives, but have learned that the application of heat
enables them to do so. For this reason pasteurization has become
adopted by some large milk companies.

Pasteurization is sometimes applied to cream, to enhance its
keeping and enable it to find a market. The cream keeps well,
but loses some of its consistency. It appears thinner than before
treatment, and will not whip so well as ordinary cream. Its consist-
ency may be restored by adding a little of a material called viscogen.
This is made by adding a strong solution of cane-sugar to freshly
slacked lime, and allowing the mixture to stand until the upper part
of the mixture is clear. This clear liquid is poured off and added
to the cream in the proportion of one part to one hundred or one
hundred and fifty parts of cream. This restores the consistency to
the cream, but, since it is an addition of a foreign substance, its
use is illegal.

In our larger cities a considerable part of the milk on the market
is pasteurized; sometimes it is sold as pasteurized milk and some-
times it is not so labeled.

Preparations of Milk. — The microorganisms that spoil milk
will not grow in it if the water is removed, and several methods have
been devised for producing a form of milk that will keep, all of which
are based upon the removal of the water. Condensed milk is the
oldest and has a wide use. It consists of ordinary milk evapo-
rated to about one-third of its original bulk, to which is com-
monly added a large amount of sugar. The sugar prevents the
growth of bacteria, and this condensed milk, put up in cans, keeps
well. In some forms of condensed milk the sugar is not added, but
the product is preserved by sterilizing by heat. When subsequently
diluted with water, condensed milk does not exactly replace the
fresh article, because of the added sugar in the one type and the
effect of sterilization in the other. A product known as concen-
trated milk has recently been placed on the market. In this case
the milk is first skimmed and then subjected -to a heat of 140° F.
till enough water is evaporated to bring the milk to about one-fifth

TRANSPORTATION PROBLEMS. 1 77

of its original bulk. Then the cream, which has also been sub-
jected to the same heat, is replaced, making a product one-fourth its
former weight. This milk has been pasteurized by the heat used in
evaporation and is consequently free from disease bacteria. When
the original amount of water is replaced it is indistinguishable from
fresh milk. Concentrated milk will keep for several days without
spoiling, and can be much more easily handled than ordinary milk.
In still other preparations the water is almost wholly removed, pro-
ducing milk powders, several different brands being on the market.
They are prepared by various means, but in all the water is dried
away from the milk, leaving a form that can be converted into a
powder. Since they contain little water they will keep almost in-
definitely. They have great use for special purposes, but are not
a satisfactory substitute for fresh milk since they do not readily dis-
solve again when water is added to them.

Transportation. — In the transportation of milk to market
three factors are to be borne in mind: i. Cleanliness. This means
that only thoroughly sterilized cans should be used to hold the milk,
and that they should be completely closed, so as to avoid contamina-
tion from without. The necessity for a complete sterilization of the
milk cans cannot be exaggerated. 2. Temperature. If the milk is
to be delivered in a good condition, it must be kept cold during
transportation. This is accomplished fairly well by the ice car.
3. Rapidity. The more quickly milk can be delivered to the cus-
tomer, the better the result. But milk kept cold, below 45° F., may
be delivered from 24 to 36 hours old and be in better condition
than milk fresh from the farm, only five or six hours old, which has
not been properly cooled. For this reason it not infrequently
happens that milk brought in a milk cart, directly from the farm
only a few miles distant from the consumer, is of poorer quality, so
far as numbers of bacteria are concerned, than milk that has been
brought long distances in a well iced milk car, though it may be
36 or even 48 hours old. As an actual fact, milk furnished small
communities near the source of the supply is frequently of poorer
quality and, on the whole, less reliable than that furnished the
larger cities.

178 CONTROL OF THE MILK-SUPPLY.

III. PUBLIC PROBLEMS.

Although this subject primarily concerns the regulation of the
milk-supply after it reaches the city, certain aspects of it are inti-
mately associated with farm life. City authorities are every year
extending their control more and more directly to the farm. The
public is making certain demands regarding the milk-supply that
must be acceded to by the milk producer.

Freedom from Disease Germs. — This demand needs no argu-
ment. To meet it the only plan within sight at present is the in-
sistence that only healthy cows shall be used in the production of
milk; that no milk shall be distributed for drinking purposes from
cows having any kind of udder disease; that no person suffering
from or recovering from a contagious disease, or having direct con-
tact with others thus suffering shall be employed in the dairy or
handle the milk in any way; that the milk shall not be watered, and
that in washing the milk- vessels no water shall be used that is in the
slightest degree open to suspicion of sewage contamination. In
addition to these demands it must be insisted that precautions be
taken for excluding stable filth from the milk, and that the milk be
cooled at once to prevent undue growth of bacteria.

Milk Standards. — A legal standard set for the chemical com-
position of market milk is nearly everywhere adopted and does not
concern our immediate subject. A few cities have set a standard
as to the number of bacteria that will be allowed in milk offered for
sale. Boston has a standard of 500,000 per c.c. This has as yet
been done in only a few places and it is still uncertain whether such
standards can be enforced or are of much value. The milk pro-
ducer needs only to remember that, to reach these standards, he
must use care in the dairy to insure cleanliness along lines already
pointed out. Special grades of milk are becoming more or less
common in various localities. Sanitary dairies of exceptionally
high character have been conducted with more or less success. In
these every possible precaution is adopted to produce milk under
ideal conditions. Only tested and inspected cows are used, and
numerous devices are carried on to protect the milk from all possible

PUBLIC PROBLEMS.

179

suspicion of. filth contamination. The milk from these dairies is
certainly superior to the ordinary milk, but the production is so
expensive that it must be sold at a high price, and this has interfered
with the commercial success of some of these enterprises. What is
known as certified milk has, in recent years, come into some promi-
nence. This is milk produced in dairies that are under the inspec-
tion of a certifying board. This board, usually composed, in part at
least, of physicians, keeps a constant oversight of the milk from cer-
tain dairies and over the methods of its production. If they find that
the milk comes up to the somewhat high standard that they set, and
if they are convinced that proper methods are used in its production,
this board gives to that dairy the right to use its certificates. It is
not so expensive to produce milk under these conditions as to carry
out the many precautions adopted by the sanitary dairies. Some
extra care is needed, but it is within the reach of almost any well
kept farm to produce certified milk. This milk brings a higher
price than ordinary milk, but it is more reliable because more care
has been required- to produce it. Neither sanitary milk nor certi-
fied milk forms anything more than a very small portion of the milk-
supply of our cities.

Dairy Inspection. — During recent years the practice of inspect-
ing dairies has sprung up. This was started first by some of the
milk-supply companies of the large cities, because they wished to
protect their supply for commercial purposes. Some of them began,
at least a dozen years ago, to send inspectors periodically among the
dairies which furnished them with milk. Within a few years it
has been realized that a public dairy inspection of this sort would
be of great value in improving the general milk-supply and in
furnishing the public with better milk. Such a public dairy inspec-
tion has been begun in some sections around the larger cities.
The inspectors visit the farms, note all methods employed, condemn
the faulty ones and make suggestions as to improvement. The
inspection is for the advantage of the consumer and producer,
and the dairyman should welcome rather than resent such visits
and helpful suggestions.

The inspectors give attention to the following points: i.

l8o CONTROL OF THE MILK-SUPPLY.

General cleanliness in the dairy. 2. The condition of the cows.
3. The source of the dairy water. 4. The condition of the barn.
5. The method of disposing of the manure. 6. The method of
milking. 7. The condition of the milkers. 8. The treatment of
the milk after milking. 9. The method of washing and sterilizing
all dairy utensils. 10. The botthng of the milk. 11. The method
and care of transportation. The farmer should be prepared to
meet the inspector upon all these points.

While it is expensive to produce sanitary milk, and while the
same is true, though to a less extent, of the production of certified
milk, it is possible greatly to improve the character of the milk
without any material increase in expense. The purpose of dairy
inspectors is to show how the milk may be improved; and the dairy-
man should remember that by the use of such simple precautions
as cleaning the cow, moistening the udder before milking, using
a covered milking pail, and more thoroughly sterilized milk-vessels,
the character of the milk will be.greatly improved. It is gratifying
to know that there has been a decided improvenlent in the quality
of milk furnished our cities in recent years.

CHAPTER XIII.
BACTERIA IN BUTTER AND OLEOMARGARINE.

BACTERIA IN BUTTER-MAKING.

In the making of butter, bacteria are the dairyman's allies. The
butter-maker always, even though unconsciously, makes direct use
of bacteria when he subjects his cream to a process almost univer-
sally adopted in butter-making, called ripening, or, in Europe,
more commonly called souring. In butter-making, the cream is
not usually churned immediately after it is separated from the milk,
but it is allowed to lie in a moderately warm vat for a period of twelve
to twenty-four hours or even longer, that it may ripen. In some
places there is a demand for what is known as sweet cream butter,
which is simply butter made from fresh cream without ripening;
but such a demand is very limited, and most butter is made from
ripened cream.

CREAM-RIPENING.

The custom of ripening cream is an old one, doubtless as old
as the process of butter-making. Upon a farm where the amount
of cream is small, it is always necessary to allow it to accumulate
for some days till there is sufficient for a proper churning. During
this period it is sure to undergo ripening without any intention on
the part of the farmer. On ordinary farms, the cream is left to take
care of itself, and is thus sure to be ripened by the time there is
enough to churn. But the centralization of butter-making into
creameries, where large quantities of cream are handled daily, has
put a new aspect upon the problem. The ripening will no longer
care for itself, but must be carefully attended to by the butter-maker.
The necessity for some accurate means of controlling the ripening

i8i

l82 BACTERIA IN BUTTER AND OLEOMARGARINE.

has become more and more apparent with each step toward the
concentration of butter-making. The farmer may, perhaps,
allow his cream to care for itself, since his product is so small.
But such a plan would ruin a creamery where there are thousands
of pounds of butter made each day. Only as the ripening can be
controlled, is concentration of butter-making successful.

The Purposes of Cream-ripening. — These are as follows:

1. Ripening the cream makes it churn more easily and increases
the yield of butter. This is true, at all events, for gravity cream;
it is less significant, and perhaps not true, for separator cream.

2. Butter made from properly ripened cream is thought to keep
better. 3. By far the most important purpose in cream-ripening
is the production in the butter of a desirable flavor and aroma.
Butter made from unripened cream lacks the peculiar flavor of
high-grade butter, since this is the result of the ripening. If the
ripening is not satisfactory, the flavor and aroma of the butter are
sure to be inferior.

The importance of this factor in butter-making for our creameries
is very great. The market price of butter depends largely upon the
flavor. Butter without flavor or with bad flavor brings a price
in the market which hardly pays for the making, while a product
with a good flavor and aroma will sell for at least three or four cents
more a pound; and the exceptionally fine-flavored product of special
creameries brings a fancy price — two or three times that of poor butter.
The flavor will frequently add one-third or one-half to the price
which could be obtained for poorly flavored butter or for butter
without flavor. Hence, the success or failure of a creamery business
depends, in large measure, upon the ripening. A creamery
which fails to ripen its cream properly fails to obtain a desirable
flavor. Hence, it obtains a lower price for its butter and may
hardly meet expenses; while a neighboring creamery, that is more
successful in its cream-ripening, obtains a good product and,
consequently, a price for its butter which makes the business a
financial success. This matter is of more significance to-day than
in earlier years, because our butter-making is coming to be concen-
trated in large creameries.

BACTERIA IN BUTTER -MAKING. 1 83

The Cause of Cream-ripening. — The ripening of cream is a
phenomenon of bacteria growth. The many bacteria in the cream
find it an excellent medium for food, and if kept at a fairly
warm temperature during the ripening period, their development
is rapid. For the twelve to twenty-four hours of ripening, the
bacteria multiply, and, by the time the cream is ripened and ready
to be churned, they are present in prodigious numbers. Analyses
of ripened cream have disclosed the fact that, whereas in the sweet
cream bacteria may be from 2,000,000 to 3,000,000 per c.c, in
the same cream when ready to churn there may be about 500,000,000
per c.c. The numbers at the time of ripening, however, vary widely,
being sometimes as low as 200,000,000, or even lower, and sometimes
as high as 2,000,000,000 per c.c.

The growth of bacteria in the cream produces chemical changes
which considerably modify its nature. The lactic acid bacteria
always develop lactic acid, and the cream becomes sour; but there
are other changes as well. We do not yet know what all these
changes are or to what extent they contribute to the ripening
phenomenon. That the other changes have something to do with
the production of the flavor in butter is evident from the fact that
a butter flavor cannot be produced in the cream by adding lactic
acid to it, and if the ripening were wholly the result of souring,
the addition of lactic acid should produce the same results as normal
ripening.

Growth of Bacteria During the Ripening. — At the outset
cream contains many kinds of bacteria, and the composite cream
of a creamery has more kinds than that of a private dairy. The cream
is commonly kept between 60° and 70°, at which temperature
many bacteria develop rapidly, but not all kinds with equal vigor.
During the first few hours there is a general increase in the number
of nearly all the kinds of bacteria originally present in the cream,
so that, after six or eight hours, there are higher numbers of all
species of bacteria than were found at first. During this time,
however, the lactic acid bacteria, especially of the Bad. acidi lactici
type, increase more rapidly than the others. In the very fresh
cream this species may have been comparatively small in numbers,

184 BACTERIA IN BUTTER AND OLEOMARGARINE.

forming not more than i or 2 per cent, of the whole, but the per-
centage rises rapidly. After several hours, the time varying with
different specimens, the acid bacteria constitute a large proportion
of the whole. From this time, after they form perhaps 50 per cent,
of all the bacteria present, the other species begin to be seriously
affected by the acid produced. The acid-forming germs still con-
tinue to increase in numbers, while the others cease to grow so
rapidly, soon begin to diminish, and finally may largely or
wholly disappear. The result of this is that, during the last stages
of the ripening, there may be present in the cream nothing but acid
bacteria, which sour the cream and produce the final changes in the
ripening.

Thus it will be seen that the ripening of cream may be divided
into two stages. In the first the growth of the miscellaneous
species of bacteria continues, and all types may become more or less
abundant. In the second the acid-forming germs gradually force
the others into the background and finally crowd them out entirely.
Both of these stages doubtless contribute to the final product.
Without the proper lactic organisms it is impossible to get the
proper flavored butter. But butter made from pasteurized cream
and ripened by pure cultures of lactic acid bacteria does not develop
so much flavor as that in which the original bacteria are allowed
to grow with the acid germs. Hence, it is probable that the develop-
ment of the miscellaneous bacteria in the first phase of the ripening
has not a little to do with the final butter flavors.

The Effect of Different Species of Bacteria. — The butter-
maker thus needs bacteria, but he must have the right kind. When
cream is collected for a large creamery from many sources there
are sure to be in it quantities of different varieties of bacteria, each
patron contributing his quota. Each species may be expected to
have its effect upon the cream during the ripening, and the resulting
butter will show this effect. Actual study has proved that different
species of bacteria, when allowed to grow in the ripening cream,
produce very different types of butter. Some produce hitter butter,
others tainted butter, others insipid butter, and others a strong odor,
almost like that of putrefaction. Some species produce a tallowy

BACTERIA IN BUTTER-MAKING. 1 85

butter, others a turnip-tasting, or putrid butter. In general, it is the
lactic bacteria which produce the desired results, while other types,
if excessively abundant, give rise to the abnormal flavors.

Since the bacteria are so varied in their action, it may be a matter
of surprise that cream-ripening, if left to itself, so commonly results
favorably. The primary reason for this is the superior vigor of the
lactic acid bacteria. Since, in the ordinary bacterial growth in
cream, the lactic bacteria finally get the upper hand and grow at the
expense of all the others, it ordinarily happens that the ripening
produces a good flavor, and a satisfactory butter is obtained. Un-
fortunately, however, the favorable species of lactic bacteria do not
always get the upper hand in the cream-ripening. Sometimes large
numbers of other bacteria are present in the cream, just as vigorous
and just as capable of rapid growth as the desirable lactic acid
germs. In such cases the unusual bacteria may develop abundantly
and produce a variety of uncommon changes in the cream, with the
result of giving an undesirable flavor to the butter. Such a phe-
nomenon explains the occasional appearance of bad-tasting butter.
The fact that such improper ripening does sometimes occur clearly
points to the need of some control over the ripening, especially in
creameries where a uniformly good product is necessary for financial
success.

CONTROL OF CREAM-RIPENING.

The butter-maker has no control over the kinds of bacteria that
get into his cream, and a creamery must take cream filled with
whatever bacteria chance to be most common in the dairy furnishing
it. But though he cannot control this factor, he can, more or less
satisfactorily, regulate the growth of the bacteria.

Temperature of Ripening. — At a temperature of from 65° to
70° the favorable lactic acid bacteria get the upper hand of other
species more readily than at either a higher or a lower temperature.
At temperatures above or below this, different species, mostly un-
favorable, are more likely to gain the upper hand. Hence, by
keeping the temperature at about 65°, the undue development of
mischievious bacteria is more likely to be prevented.
16

1 86 BACTERIA IN BUTTER AND OLEOMARGARINE.

Duration of Ripening.— The butter-maker can stop the
ripening at any point, for, after the cream is churned into butter,
the bacteria growth ce^-ses. The necessary duration of the ripen-
ing will vary, however, with the conditions. Sometimes cream,
when brought to a creamery, is already sour and has, therefore,
become ripened even before the butter-maker receives it. In other
cases, especially in winter, it will not only be sweet, but will contain
small numbers of bacteria and require a much longer ripening.
Moreover, milk produced under good dairy conditions, clean and
fairly free from bacteria, will ordinarily require longer ripening than
milk produced under less favoiable conditions and containing al-
ready great numbers of bacteria. The length of time will vary
also with the temperature, being, of course, longer at lower tempera-
tures. To determine when the cream is sufficiently ripened, the
butter-maker has two methods. One is the general appearance to
his eye and taste, and the other is the degree of acidity. The latter
factor is determined by the methods described on page 309, and
the ripening is generally continued until the acidity is 0.5 to 0.65
per cent.

THE USE OF STARTERS.

By far the most important change in the methods of cream-
ripening is in the wide and almost universal introduction of starters.
Twenty-five years ago it was sometimes customary to add a starter
to cream in cold weather simply for the purpose of starting the
ripening; but to-day almost all good creameries use starters, not so
much for starting, as for regulating the ripening.

Prof. Storch, of Copenhagen, first conceived the possibility
of furnishing to butter-makers cultures of the proper species of
bacteria, which they might add to' their cream for the purpose of
ripening, somewhat as yeast is used in brewing. This experimenter
not only conceived the method, but put it into practical operation
in Denmark. His method consisted i. in pasteurizing the cream
at about 165° F., for the purpose of destroying most of the bacteria
that might be present, and 2. in adding to it a pure culture of
bacteria, whose value in producing a good flavor had been deter-

BACTERIA IN BUTTER-MAKING. 187

mined by experiment. This method is, of course, logically
satisfactory, for, since pasteurization^destroys most of the bacteria
present in the cream, it follows that the ripening will be produced
by the species of bacteria introduced by the adding of the pure
culture. Professor Storch was soon followed by other experimenters
and the method adopted in Copenhagen was extended more or less
widely in north Germany and Denmark. In Denmark it is now
used almost universally, and in north Germany quite widely, in
general dairying.

In the United States the use of pure cultures for cream-ripening
has had a somewhat different history. It was introduced to dairy-
men shortly after its development in Copenhagen, but for some
time little attention was paid to it, so that it was hardly brought to
the notice of the ordinary butter-maker. Our butter-makers were
not in condition to pasteurize their cream. In 1895 a slight change
was made in the process. In order to bring the subject more
widely to the attention of dairymen, a method was suggested of
using the cultures without previously pasteurizing the cream.
This seemed illogical, since the cream is already filled with bacteria,
and the addition of a new culture could hardly be supposed to give
entirely satisfactory results. But when we remember how a vigorous
lot of lactic acid bacteria can overcome other species,- the method
does not appear so illogical after all. With this change our butter-
makers were willing to try pure cultures and in a short time American
butter-makers learned of their meaning and began to experiment
with them widely. The result of the dozen or so years of experience
has been to show the extreme value of starters as a means of controll-
ing the ripening, until to-day starters of some kind are almost univer-
sally used in all good creameries and dairies.

Preparation of Starters.— While starters are very widely
used to-day, they are not always pure cultures. Two quite different
methods of preparing them are in use.

Natural Starters. — A natural starter is nothing more than some
normally soured milk. In order to obtain it it is only necessary
to select several quarts of good milk and place it in a clean, sterilized
pail or can, covered to keep out the dust, and keep it in a temperature

1 88 BACTERIA IN BUTTER AND OLEOMARGARINE.

of from 65° to 70°. After one or two days the milk should show
signs of souring; when it has become decidedly sour, but not yet
curdled, it is to be used as a starter. It requires some skill on the
part of the butter-maker to know whether the starter thus obtained
is of the best character and whether it should be used or thrown
away and another obtained. Starters made in this way are not
sure to be uniform, inasmuch as the different samples of milk may
contain different types of bacteria, and experience is needed on the
part of the butter-maker to know whether the starter is satisfactory.

Starters from Commercial Cultures. — Commercial starters are
now a well-known article, and several different brands may be pur-
chased. In all cases they are prepared by bacteriologists and
consist of a culture of bacteria — usually a pure culture, though not
always — that have been found by experiment to produce favorable
results in the ripening. These starters as purchased are sometimes
in the form of a powder, sometimes in the form of a liquid, but in
all cases contain too small a quantity to add directly to the cream
that is to be ripened. The quantity of bacteria must, therefore,
be increased before using by a process called building up. The
procedure is as follows:

A quart of skim milk, whole milk, or cream is placed in a glass
jar and sterilized, either by boiling or, better, by pasteurizing at
180° for half an hour, stirring frequently to insure uniform heating.
The milk is then cooled, and when it has reached a temperature of
80° the commercial culture, from Si freshly opened package, is thor-
oughly stirred in; the whole is covered to keep out the dust and
placed at a temperature of about 65°. When the milk has become
quite sour, but before it is curdled, it is ready to use as a starter.
If a larger amount of starter is needed, this first starter is placed in
a large can of pasteurized milk and allowed to grow in it at 65°
until the whole becomes soured. By this means any desired amount
can be prepared.

The starter thus prepared is added to the cream in varying
proportions, the larger the amount the quicker the ripening. Some-
times one part of the starter to ten parts of cream is used; in other
cases a smaller amount is used and sometimes more. After the

BACTERIA IN BUTTER-MAKING. 1 89

ripened cream is ready tb churn, a certain quantity of it is removed,
placed in a clean can, and set aside to serve as a starter for the next
day's churning. In this way some starter is reserved each day,
to be used in the cream collected that day; and thus the original
starter is carried on from churning to churning. After some days,
however, it is necessary to resort once more to a pure culture, built
up in the same way.

There is not very much to choose between natural starters and
commercial cultures. Natural starters cost nothing except the
trouble of making them, but, on the other hand, they are not
uniform, and not always to be depended upon. Commercial cultures
cost a small sum, but they are rather more uniform than natural
starters. It has been claimed that the flavor of butter from cream
ripened with a natural starter is higher than that ripened with a pure
culture. This is easy to understand. A good starter should sour
cream promptly; should thrive at 60° to 72°; should coagulate
milk and cream into a homogeneous mixture, and should produce
an agreeable aromatic taste. No single bacterium known has all
these characteristics, but a mixture, such as a natural starter, may
have them. On the other hand, if a creamery notices the develop-
ment of "off tastes" in the butter, the best method of removing them
is by the use of a commercial pure culture. Both kinds of starters
thus have their advantages.

THE USE OF STARTERS.

In Pasteurized Cream. — If the cream is first pasteurized so as
to destroy most of the bacteria present, the added starter will have a
free chance to grow. The pasteurizing of cream is simple and not
very expensive, and it produces a medium largely free from bacteria.
The use of starters in pasteurized cream has become practically
universal in Denmark and some of the other countries of Northern
Europe. There are two reasons for this: i. A higher and more
uniform grade of butter can be obtained in this way. 2. The
prevalence of tuberculosis has brought about the enactment of a law
requiring all milk that goes through the creamery to be pasteurized
in order to destroy the tuberculosis germs. For this reason Den-

IQO BACTERIA IN BUTTER AND OLEOMARGARINE.

mark butter is always made from pasteurized cream, and this
makes it necessary to use an artificial starter, since pasteurized
cream will not ripen of itself. The pasteurization destroys practi-
cally all of the acid bacteria, and, as we have learned, when the acid
bacteria are absent the putrefying bacteria are quite sure to develop.
Hence, pasteurized milk requires an acid starter to insure a proper
ripening.

In Unpasteurized Cream.— By this method the starter is
simply added to the ordinary cream. The use of starteis in this
way is open to a theoretical objection. The cream already con-
tains bacteria in large numbers and, ordinarily, in considerable
variety. These would themselves produce the ripening of cream,
even without any starter. The effect of the starter added to the
cream already filled with bacteria will, evidently, not always be
uniform. It might produce little or no effect, or, if the starter is
added in considerable quantity, it might overcome the effect of the
smaller number of bacteria originally in the cream. In practice it is
found that the use of starters does have this latter effect, and in most
cases, there is a noticeable improvement in butter made from cream
thus ripened. The results, however, are not absolutely uniform,
and even with the use of a large amount of starter it will sometimes
happen that the bacteria present in the cream will have more in-
fluence than those of the starter, and the butter will suffer.

The use of cultures in unpasteurized cream was first begun in the
United States and has been more widely adopted here than any-
where else. Butter made from unpasteurized cream is not so
uniform as that made from pasteurized cream, but the butter made
in this way is, at least to the American taste, superior to butter made
with pasteurization, due probably to the fact that pasteurization
prevents the growth of miscellaneous bacteria that ordinarily
occurs before the lactic bacteria develop. Pasteurized cream butter
is somewhat milder in flavor than that made from unpasteurized
cream, and the American market demands a flavor somewhat
stronger than that which is popular in Europe. Hence, to the
American taste, up to the present time, the butter from pasteurized
cream is not superior to that made from unpasteurized cream.

BACTERIA IN BUTTER-MAKING. 19I

»« .
THE GENERAL VALUE OF STARTERS.

The fact that starters, with or without pasteurization, have
become almost universally used among the better class of cream-
eries is in itself sufficient proof that they are of practical value.
Their advantage lies in four directions: 1. They enable the butter-
maker to handle his cream more easily and uniformly. He can
regulate the ripening in such a way that his cream will always be of
a certain grade of ripeness at a certain time of day; for a little
experience tells him how much of his culture, under proper condi-
tions, should be added to the cream to produce the proper grade of
ripening at the particular time when he desires to churn. 2. The
use of starters has produced a greater uniformity in the grade of
butter. The butter-maker can depend more certainly upon pro-
ducing butter of a high grade, month after month, than he can with-
out starters. There is a general belief also among those who have
tested the butter in countries where starters are widely used, that
there is an improvement in the average quality of the butter, as well
as in its uniformity. 3. It has become pretty definitely agreed that
the flavor of butter is improved by the use of such cultures. It is
somewhat difficult to obtain definite proof of this, owing to the un-
certainty of scores in butter tests. But the fact that all good dairies
now use them is sufficient testimony to their value in improving the
general quality of the butter. 4. They are the best means of
remedying butter "faults." Every creamery has experiences of
deterioration in the flavor of the butter without any visible cause.
Such troubles are known to be due commonly to the growth of
unusual and undesirable bacteria in the cream. When they are
discovered, the sterilizing of the dairy utensils and the use of a large
quantity of a vigorous starter will generally remedy the trouble at
once. Moreover, the constant use of a starter goes a long way
toward preventing these "faults."

It is doubtful whether the use of starters produces butter of a
character superior to the best butter made without them. Indeed,
some think that it is not quite equal to the best butter made without
starters. But the uniformly high grade of culture butter is admitted,

192 BACTERIA IN BUTTER AND OLEOMARGARINE.

and the greater satisfaction in being able to control the process has
caused the wide adoption of starters among butter-makers.

BACTERIA IN BUTTER.

Although bacteria continue to grow during the ripening period,
their growth is practically stopped by churning and butter-making.
Many of them are removed with the butter-milk; others are washed
away during the washing and working of the butter. Large
numbers are still left in the butter. Ordinarily these bacteria do not
grow in the butter, though, if it is not salted, some of them may
grow and hasten its spoiling. Unsalted butter does not keep long,
and its destruction is largely due to bacteria. But if the butter is
salted, as is the rule in most countries, the salt checks the growth of
bacteria. As a result of this and the compact condition of the
butter, together with its small amount of water, the bacteria do not
find butter a favorable medium for growth, and they begin to diminish
in numbers. A very few hours' time shows a great reduction in
numbers, and this continues until, after a few weeks, the butter con-
tains comparatively few. They do not entirely disappear, for some
are found even in very old butter. The ordinary species of organ-
isms, which have been active agents in the cream-ripening, play no
further part in the changes which may occur in the butter. The
following figures of the number of bacteria in butter will illustrate
the facts.

No. of Bacteria per Gram of Butter.
Two hours old. One day old. Four days old. Thirty days old.
■ 54,000,000 26,006,000 2,000,000 300,000.

It is well known that, if butter is not used immediately, certain
changes occur in it which continue slowly for many weeks. The
butter retains its fresh, delicate flavor and aroma for only a few
days; but if it is kept cool and away from the light, it may remain
sweet and good for many months. If, however, it is not kept very
cold, further changes soon begin to appear which slowly progress
and eventually ruin the butter. The most noticeable feature
is the appearance of rancidity. This change is accompanied by the

BACTERIA IN OLEOMARGINE PRODUCTS. 1 93

development of butyric acid and frequently by a considerable
change in the C(^nsistency of the butter. It finally becomes strongly
rancid and tallowy, totally ruined for use. The cause of this
rancidity has been difficult to determine, apparently because a
variety of factors contribute to it. It is probably due, in part, to
chemical fermentation, produced by enzymes in the milk, and in
part to the growth of bacteria. The rancidity is much more likely
to occur if the butter is exposed to the light, and it develops more
readily in warm than in cold temperatures. At temperatures below
freezing rancidity does not occur. If butter is, therefore, kept
cool and in large masses, it may be held for a long time without
the appearance of any very noticeably strong flavor. In the end,
however, the rancidity is sure to appear. To what extent bacteria
are concerned in this change we do not yet know, although most
investigators have concluded that they are prominently concerned
in the phenomenon. Rancidity may certainly be looked upon as
a fermentation change, and the only method the dairyman has of
controlling it is by cool temperatures, by packing the butter in large
masses, by paraffining the butter tubs, and by keeping it from the
light. It may be delayed by pasteurizing the cream and by using
pasteurized water for washing, facts that show its close relation to
bacteria. Fortunately, it is a matter of no very great importance,
because butter can be kept without difficulty for some months, and
it is almost always possible to market it before it has spoiled.

BACTERIA IN OLEOMARGARINE PRODUCTS.

The materials out of which oleomargarine is m^de are chiefly
stearin, lard, cottonseed oil, and other oils. These are warmed to
the melting-point, are thoroughly mixed, and then drawn off into
cold brine, which chills the oils into a hard mass. The process
is certainly a useful method of utilizing quantities of oils which
would otherwise be waste products. It makes a -wholesome,
digestible food, which could have no objection raised against it
if it could only be sold upon its own merits, instead of under the
false guise of butter. In order to make the product the more
resemble butter, it has been customary to color it; but this practice
17

194 BACTERIA IN BUTTER AND OLEOMARGARINE.

is now largely prevented by a prohibitive tax on colored oleomarga-
rine. The bacteria normally present in oleo products are commonly
much less numerous than in butter, and the oleomargarine is, on
the whole, less likely to distribute infectious diseases than ordinary
butter, inasmuch as the chance for contamination is less.

But, although the oleo products thus made resemble butter in
appearance, they do not resemble it in taste, and the factories are
therefore forced to use some special method of imparting to their
product a flavor as closely as possible like the butter which they are
trying to imitate. To do this they depend upon the very same flavors
as those found in butter and obtain them from a similar source.
A certain amount of whole milk, skim milk, or cream (varying
according to the quality desired in the product) is placed in a large
vat, or in cans, and allowed to sour. After the milk has properly
soured, or ripened, it is placed in the mixing vat with a quantity of
melted oils, generally in the proportion of about one part of milk to
four parts of the oils. When this mixture is hardened by the cold
brine, the milk is held with fats, and thus becomes a part of the
final product. Inasmuch as the milk has developed a flavor in its
souring, just as cream does during its ripening, this flavor is imparted
to the oleo product, and the final result is a mass of fats with the
flavor of butter more or less prominently developed.

It is clear that this flavor is due to exactly the same factors as
those which produce the butter flavor. The oleo-maker fully
understands that his flavors are due to the action of bacteria, and
he uses the best means at his disposal to favor their growth. Ordi-
narily he aUows his milk to sour by normal lactic fermentation.
In some factories, in recent years, he has not been satisfied to depend
upon such a method, but has come to use, more and more largely,
pure cultures of bacteria in order to introduce greater regularity in
the process. In some oleo factories, indeed, so fully aware have the
makers been of the extreme significance of this matter of proper
bacteria to the successful manufacture of oleo products, that they
have actually built and furnished bacteriological laboratories and
employed bacteriologists to keep constant guard over these factors
in the oleo-making.

CHAPTER XIV.

BACTERIA AND OTHER MICROORGANISMS IN
CHEESE.

CHEESE-RIPENING.

Cheese consists primarily of the casein and fat of milk, collected
first as a curd and then allowed to undergo a series of chemical
changes called ripening. Ordinarily the casein is precipitated
from the milk by rennet, although it is done in some types of cheese
by simple souring. Then the curd is separated more or less from
the whey, and pressed into definite shape. The whey removes
most of the milk-sugar, and the cheese retains about two-thirds
of the food material in the milk, and since it is in a very dense form,
it is one of the most nutritious of our foods. The popularity of
cheese as a food depends rather upon its flavor than its food value
and the flavor develops during the ripening. Cheese-ripening
is a very complex phenomenon and one as yet only partly understood.
This is due partly to the intricacy of the subject and partly also to
the fact that there are very many different kinds of cheeses, and the
ripening of the different types is not by any means the same. Al-
though there are some hundred varieties of cheese, they may be ar-
ranged fairly well into two groups: i. The hard cheeses, and
2. The soft cheeses. The ripening of the hard cheeses is very dif-
ferent from that of the soft, and the ripening of the different types
of soft cheese varies greatly one from the other. Each kind of
cheese must, therefore, be studied as a special problem.

Chemical and Physical Changes. — During the ripening,
the cheese, which is at first rather hard, tough and elastic, gradually
becomes softer. The extent of this softening depends largely
upon the amount of water present, and, in the soft cheese, with their
large amount of water, a slimy and almost liquid consistency may

195

196 BACTERIA AND OTHER MICROORGANISMS IN CHEESE.

finally be reached. This softening is due to a change in the chemical
nature of the casein by which it changes from an insoluble into more
or less soluble products. The changes in the casein during the
ripening are, in general, similar to those that occur when the casein
is digested under the action of digestive juices, so that they are
frequently spoken of as a digestion of the curd. During the ripening
the insoluble casein is converted into a series of simpler chemical
bodies, peptones, proteoses , etc., and as these become partly dissolved
the hard texture of the cheese becomes softer. Not only are the
changes similar to those of digestion, but they are produced by
enzymes similar to, though probably not identical with, the enzymes
in the digestive juices. The ripening of a cheese is thus a prediges-
tion which renders the cheese more easily digested when eaten. ^'

The enzymes that produce this ripening of the cheese come froAi
three quite different sources. One enzyme with this power of
digesting curd is in the original milk itself. This is the galactas'e
already mentioned. Another is added to the milk with the rennet',
for rennet is made from the stomach of a mammal, and will always
contain some of the pepsin from the stomach. The latter is an
enzyme with strong digestive power and is sure to be present in
some quantity in the rennet, and hence in the cheese after the addition
of rennet. These two enzymes doubtless continue to act upon the
casein during the ripening, and are responsible for a certain portion
of the digestive changes that are taking place. But there is also a
third source of enzyme that, in some cheeses, is more important than
the others. As already noticed, certain microorganisms have the
power of secreting enzymes, and some of them, growing in or on the
ripening cheese, develop enzymes which contribute largely to the
ripening. In some of the soft cheeses this is certainly the chief
source of the enzymes.

Flavors. — The production of flavors is of no less importance
than the chemical digestion of the cheese. At the present time,
however, there is a very profound ignorance concerning the real
source and cause of cheese flavors. They are without doubt the
products of decomposition. They appear in the cheese only
toward the end of the ripening process, and are regarded generally

THE HARD CHEESES. I97

as due to the end-products of decomposition. The peptones and
proteoses that result from the digestion of the caseins do not them-
selves have any of these peculiar cheese flavors; but toward the end
of the ripening some of the material seems to be still further broken
down into the simpler end-products which show the flavors charac-
teristic of cheese.

The relation of microorganisms to the ripening of hard and soft
cheeses is so different that they must be considered separately.

THE HARD CHEESES.

These include many varieties, the best known of which are the
Cheddar cheeses (the most common in America), the Swiss
cheeses, and the Edam cheeses of Holland. In all these cheeses the
water is pressed out of the curd as completely as possible so that the
resulting cheese is very dense. In spite of its dense consistency, a
development of bacteria goes on for many days during the ripening.
Since cheese is made from milk, it must necessarily contain from
the outset many kinds of bacteria, and among them there is a con-
siderable percentage of lactic acid organisms. For a number of
days, sometimes for several weeks, these bacteria increase in number.
After this they decrease until, when fully ripened, they are very few,
compared to their numbers at certain stages of the ripening. A
single example will illustrate. Fresh cheese contained 6,600,000
per gram, when four days old, 51,000,000 per gram, and when four
months old, 1,000,000 per gram.

It is the lactic acid bacteria that are most persistent, and while
in the early stages of the ripening other types are abundant, in the
fully ripened cheese, or even the half ripened cheese, there are usually
none left except the lactic acid bacteria. While there are variations
in the bacteria in different kinds of cheese and in different specimens
of the same variety, the above represents the general history of their
growth, and in all cases it appears that the lactic acid organisms are
finally found alone.

It must be confessed that we do not yet know very much about
the part bacteria play in the ripening of the hard cheeses. That

198 BACTERIA AND OTHER MICROORGANISMS IN CHEESE.

they are necessary to the ripening is proved by the fact that cheeses
do not ripen normally when they are ripened in chloroform vapor,
which prevents bacteria growth, but allows the enzyme action to
continue as usual. Although some of the digestive changes go on as
usual in these cheeses, the ripening does not become complete,
and the cheeses never develop either the same final chemical char-
acter or the flavors of cheeses in which the bacteria have had an
opportunity for growth.

Chemical Action of Bacteria. — When cheese-ripening was
first studied, it was believed to be primarily due to the action of
bacteria. We have already seen that certain kinds of bacteria have
the power of changing casein to peptone — the liquefying type — and
this change in the cheese-ripening was at first supposed to be due to
the growth of these peptonizing bacteria. But later it became evi-
dent that the liquefying bacteria are not common in cheeses, espe-
cially in the better grades. If present at the beginning they rapidly
decrease in numbers, until they almost or entirely disappear, a fact
which forced the conclusion that they cannot contribute materially
to the ripening of cheeses. More recently, it has been claimed that
certain "acid liquefiers" — i.e., peptonizing bacteria that at the same
time produce acid — are intimately connected with the ripening.
But there does not yet appear to be much evidence for this.

These facts led to a suggestion that the ripening is due really to
the lactic acid bacteria. These do not liquefy gelatin and do not
ordinarily have any power of changing casein to peptone. They
produce lactic acid which curdles the milk, after which they ap-
parently cease to act upon it at all. Hence, it would not seem that
they could digest cheese. But if the acid which they produce is
neutralized by the presence of some alkaline, like carbonate of soda,
the bacteria continue to grow, and eventually produce the peptoniza-
tion of the casein. Moreover, the grade of the cheeses is very
closely dependent upon the growth of lactic bacteria, and cheese
from which lactic acid bacteria are excluded by aseptic milking will
not ripen normally, while they would do so if the acid germs were
present. All of these facts together led to the conclusion that it is
this peptonizing power of the lactic acid bacteria, under certain con-

THE HARD CHEESES.

199

ditions, which is responsible for the chemical changes that take
place in the ripening cheese. This conclusion, however, has not
been very generally accepted; for while the lactic acid bacteria,
under these conditions, do produce a certain amount of peptoniza-
tion of the casein, the action is extremely slow and not very complete;
and it has not seemed to most students that the phenomenon in
question is sufficiently explained by this slow action of the lactic acid
bacteria.

Flavor Production by Bacteria. — Apparently the jlavors must
be due to bacterial action. Cheeses ripened in chloroform vapof,
whicih allows the enzymes to act, but prevents bacteria from growing,
though they ripen, do not develop flavors and these must be due to
some other cause than enzyme action. That they are the end-
product of chemical decomposition seems to be extremely probable.
In many cases they are associated with ammonia; and ammonia, as
is well known, is one of the final products of proteid destruction.
The only known agency that commonly produces the complete
destruction of proteids is bacterial, and, while the matter has never
been put to any satisfactory test, the most probable explanation
seems to be that these cheese flavors are the result of bacterial
decomposition.

Against this view, however, has been urged the fact that in the
well ripened cheeses hardly any bacteria, except lactic acid organisms,
are present, and that this class of bacteria does not, so far as is
known, have any power of producing cheese flavors. Some
bacteria, if they grow in proper abundance in milk, will in time
develop well-known cheese flavors; but these organisms have not
been found in old, strongly flavored cheeses. Whether they have
anything to do with the production of cheese flavors is, therefore,
uncertain. It has been suggested that the flavor of cheeses may be
due to the bacteria which grow in them during the first few days.
Liquefying bacteria are found during this early period, and before
the miscellaneous bacteria disappear, as they do later, some of these
liquefiers may secrete from their bodies substances, possibly enzymes,
that continue their action in the cheese, slowly, but for a long time.
Although the bacteria that produce them soon die, the chemical

200 BACTERIA AND OTHER MICROORGANISMS IN CHEESE.

ferments which they have produced may continue their activity until
they finally produce the new products that give the flavor.

One fact appears to be certain amid much that is still unsettled.
The lactic acid organisms certainly play an important part in the
process; at least in the ripening of the Cheddar cheeses and probably
the other hard cheeses as well. The lactic acid developed in the
early ripening cheese is necessary to the digestive changes that occur,
for the acid combines with the casein, a preliminary step in the
ripening. While their total action is not yet understood, it is
certain that they have a necessary part in the cheese-ripening.

As a result of these facts, cheese-makers have, in recent years,
learned that the use of lactic acid starters is decidedly advantageous.
This practice enables the cheese-maker to control much more
accurately the ripening, and to reduce the number of failures. The
reason why the inoculation of a lactic starter tends to reduce the
failures in cheese-making can easily be understood from the facts
already presented. The lactic acid bacteria have the power of
checking the growth of other germs, and even of destroying them
altogether. When, therefore, the milk has a large quantity of
lactic bacteria developing rapidly in the curd, the other bacteria,
which might under different circumstances produce putrefaction,
are prevented from increasing. In the making of cheeses this
protecting action of the lactic bacteria becomes very important,
and is, indeed, the secret of good cheese. The cheese remains for
weeks, or even months, in a moist condition, and there is opportunity
all this time for the growth of bacteria. If a proper lactic organism
is present at the outset, the cheese will be protected from the various
putrefactive types that would otherwise surely injure it. Their
presence in sufficient quantity is responsible for many of the defects
to be noticed later.

For these reasons, then, the cheese industry is learning the
prime importance of a strong lactic fermentation in milk that is to
be converted into cheese, and in order to bring this about it is
rapidly adopting the method of using starters. Cheese starters are
essentially identical with those used in butter-making, and they are
used in much the same way. Home starters are frequently made

THE HARD CHEESES. 20I

and inoculated into the milk, and the use of commercial starters is
also rapidly growing. It is interesting to find that the types of lactic
bacteria that are useful in butter-making are not always satisfactory
in cheese-making. Bacteria that give a fine flavor and aroma to
butter may produce a bitter taste with ruinous results when used
in cheese-making. The use of starters in the cheese industry seems
to be firmly established at the present time and is practically sure
to extend, for it is one of the methods of safe-guarding the cheese
against undesirable fermentations.

"Faults" in Hard Cheese. — The value of a cheese is wholly
dependent upon the success of the ripening. A great loss is entailed
upon cheese-makers by an imperfect ripening, resulting from a
variety of defects called faults. These are commonly due to the
growth of certain kinds of microorganisms which do not grow in
normal cheeses. The injury resulting to the cheese may be only
sufficient to make the cheese a little "off" in flavor but still passable,
or it may be so great as utterly to ruin the cheese and make it a total
loss. Some of these faults have been traced to their sources and
will be considered under the following heads:

Swelled Cheese. — This is, perhaps, the most common fault.
It is due to the development of a considerable quantity of gas which
fills the curd full of holes and causes it to swell and
lose its shape. Sometimes the holes are extremely O /? O \{
numerous and small, and sometimes they are fewer ^^ ^^^

but of larger size. In any case they are undesir- 0
able. Even good cheeses are apt to show some gas
holes, but so few as to do no special injury. Some- bacillus causing
times the gas is so abundant as to cause the /^^J/^i^ cheese

° {B. ShaTJert).

cheese to burst, in which case it is completely
ruined. Between these extremes are all kinds of intermediate
grades. The development of the gas is accompanied by an unusual
fermentation and an unpleasant taste and smell. The cause
of the trouble is the development of gas-producing bacteria. Several
different species are known which have this power of developing
gas in great quantities in the ripening cheese (Fig. 43). Most of
them, perhaps all, belong to the type which has been referred to

202 BACTERIA AND OTHER MICROORGANISMS IN CHEESE.

in Chapter XI as Bad. aerogenes type. As pointed out in that
chapter, the different varieties of this type vary much in the amount
of gas they produce; sometimes the quantity is very slight, sometimes
it is extraordinarily large; and it is easy to understand how different
strains and different quantities of bacteria will produce-grades
of gasiness in cheeses.

Bitter Cheese. — The development of a bitter taste is one of
the common troubles of cheese-makers. Sometimes this defect will
involve the whole output of a cheese factory and cause heavy losses
for a considerable period. Two different causes have been deter-
mined upon as responsible for the trouble. In one extended series
of losses thus resulting, the cause was found to be a yeast (Torula
amari Fig. 37) that obtained access to the cans and vats and con-
tinued for a long time to make trouble. The difficulty disappeared
with the thorough cleaning and sterilizing of all articles in the dairies
and factories. In another series of bitter cheeses the trouble was
found to be in one of the liquefying bacteria. This class of organisms
is nearly always present in milk, and though the growth of the lactic
bacteria usually crowds them out, sometimes, either because of
their extra abundance and vigor or because of lack of sufficiently
vigorous acid organisms, they are not overgrown by the lactic acid
bacteria, but continue to multiply until they develop bitter flavors
that injure or spoil the cheese. This cause of bitterness has been
detected in both the hard and the soft cheeses.

Putrid Cheese. — Sometimes soft spots appear upon the surface
of a cheese. They may become larger, eating their way into the
cheese, and producing a more or less slimy appearance. The
trouble is undoubtedly due to the growth of putrefying bacteria,
but not much is known about the matter at present.

Fruity or Sweet Cheese. — This is a phenomenon which occurs
sometimes over widely extended .districts and detracts from the
character of the cheese without always ruining it. It is character-
ized by a peculiar sweet taste, which, although not unpleasant,
spoils the flavor of the cheese and thus injures the sale of the prod-
uct. This trouble has been found to be due to a yeast which gets
into the milk.

SOFT CHEESES. 203

Rusty spot. — This is characterized by rusty, red spots on the
outside and, indeed, not infrequently throughout the whole cheese.
The cheese loses its value and may in the end become quite ruined
if the trouble develops sufficiently. The cause is a bacterium, B.
rudensis.

Many other "faults" may be recognized as interfering with the
normal ripening. Black spots and blue spots are sometimes noticed
and a variety of "off" flavors that cannot be described. In regard
to all of these troubles the cheese-maker has the serious disad-
vantage that they cannot be discovered until the ripening has be-
come partially completed, and then it is too late to apply any
remedy. The method of meeting them must be by prevention
rather than cure^ and after an improper ripening has begun, practi-
cally nothing can be done to stop it. By cleanliness, by frequent
sterilization of vats, and by the use of vigorous lactic acid starters
much can be done to prevent these troubles, but there seems to be
no remedy after the improper ripening has begun. A vigorous
lactic acid starter will go far toward preventing gassy cheese, and
the slimy whey used in the Edam cheese prevents it in that particular
brand. A regulation of temperature during ripening will also aid,
since the gassy organisms grow best at higher temperatures, while at
a lower, about 60°, the common lactic acid bacteria are the more
vigorous. When to these two suggestions of vigorous starters and
cool temperatures we add great care in keeping all milk-vessels clean,
and in sterilizing frequently by steam, we have. included practically
the only methods in use of much significance in guarding against
the various cheese faults.

SOFT CHEESES.

The essential difference between a hard cheese and a soft cheese
is that the latter has a very much higher percentage of moisture.
To bring about this condition, the method of manufacture is de-
signed to retain the whey in the curd. After the milk is curdled the
curd is sometimes dipped out directly into forms provided with
holes in their sides, through which the whey drains naturally

204 BACTERIA AND OTHER MICROORGANISMS IN CHEESE.

without the application of any pressure. In other cases the curd is
cut in the vat, but the curd and whey together are dipped into forms
for draining. As a resuh, there is produced a cheese which con-
tains a much greater amount of water than is allowed to remain in
the hard cheeses.

This large amount of water produces a ripening of a totally
dififerent character from that which occurs in the hard cheeses. The
process of ripening is different, the agents that bring it about are
different, and the final results are very different from those in the
hard cheeses. Moreover, the ripening is liable to greater variations
in the soft cheeses than in the hard cheeses, and it is more difficult to
control, because of the presence of so much moisture. Bacteria,
yeasts, and molds all find a suitable medium for growth in the wet
curd of the soft green cheese, and unless the progress of the ripening
is exactly right, the cheese-maker may expect the development of
kinds of microorganisms that are unfavorable to his product and
that will spoil his cheeses. Soft cheeses are much less uniform in
character than hard cheeses. They differ very greatly in texture
and flavor, and are subject to various defects that injure or ruin
them. They are, in short, more difficult to make with success than
the hard cheeses, largely, if not wholly, because the water they con-
tain offers such a favorable medium for the growth of bacteria and
other microorganisms.

The ripening of several of these cheeses has been carefully
studied by bacteriologists. A brief description of the phenomena
in three of these will illustrate the principles concerned The three
described represent three types of soft cheeses.

Camemhert Cheese. — This, together with Brie cheese and some
others, represents a type in which the ripening is due partly to
bacteria in the curd and partly to molds growing on the surface of
the cheese, but not penetrating below the surface. The cheeses are
small, about four inches in diameter and one inch thick. The
soft curd is dipped out with the whey into forms and allowed to
drain by its own weight. The cheese, with its large moisture con-
tent, is then allowed to ripen in a damp room where the temperature
is low. Sometimes two rooms of different temperatures are used.

SOFT CHEESES.

205

The ripening occupies from five to eight weeks, and a series of
changes takes place in the cheese, of which the following is a
summary:

The first phenomenon that occurs is the souring of the curd,
which is brought about by the Bad. lactic acid type of organism.
These bacteria grow in the milk previous to the addition of the
rennet, although the milk is not allowed to become very sour before
curdling. But they continue to grow during the curdling and for a
day or two after the cheese is made. If by
any chance the lactic bacteria fail to develop
vigorously, a ruined cheese is sure to result.

The second step" in the ripening is the ap-
pearance on the surface of the cheese of a
species of mold, which has been named
Penicillium camemberti (Fig. 44). This mold
appears in from two to four days and is at first
of a pure white color; later, when it begins to
produce spores, it becomes a steel gray, but
never a deep blue like the common mold. It
is a species of mold that apparently does not
occur in America, but is very common in
Europe in those sections where Camembert
cheese is made. Its absence from America is
the chief reason why this country has been unable to make
Camembert cheese. Where successful cheese of this type has been
produced, it has been by importing and inoculating this type of
mold into the American cheese factories. This white mold grows on
the surface of the cheese, but does not penetrate below the surface.
After about two weeks it reaches its limit of growth, forms spores,
and dries down to a somewhat thin crust. The growth of this mold,
together with other organisms, neutralizes the acid of the curd at
the surface of the cheese and renders it slightly alkaline.

In the meantime the mold has secreted an enzyme which has
the power of digesting the curd. As fast as the acidity of the curd
is reduced and the enzyme secreted, the latter acts upon the curd,
changing it from a hard consistency to a soft texture. At first the

Fig. 44. — Penicillium
camemhertii, the mold
ripening camembert
cheese {Thorn).

2o6 BACTERIA AND OTHER MICROORGANISMS IN CHEESE.

cheese is a hard, solid curd from surface to center; but as this enzyme
acts beneath the mold there is formed a thin layer of soft material.
This layer grows deeper and deeper as it encroaches upon the curd.
The enzyme produces a profound change in the casein, converting
it first into peptones and similar bodies; later these break down
into simpler bodies, or end-products, among which ammonia may
always be detected. These latter end-products give the flavor,
and appear to be produced by bacteria rather than by the action of
the enzymes secreted by the mold. During the ripening the cheese
will be found to have a core of a sour, acid curd in the center,
surrounded by a layer of soft, digested material. The cheese ripens
thus, from the surface inward, and is not completely ripened until
the soft layer reaches the center.

The flavors are not due to the enzyme diges-
tion,'but to the end-products of decomposition.
In the case of this cheese, as in the hard cheeses,
no positive knowledge is at hand as .to the exact
source of the flavor. That it is not due to the
mold alone is certain, from the fact that the
softened cheese may be nearly tasteless, if a pure
culture of mold has completed the ripening. The
peculiar Camembert flavor is, beyond doubt, as-
sociated with some of the microorganisms grow-
ing in or on the cheese, but at present no more
is known about the matter.

Roquefort Cheese. — This represents a type of
cheese that, like Camembert, is ripened by both
bacteria and molds. Closely allied to it are the
Stilton and Gorgonzola cheeses. The mold is a
blue instead of a white one, and it grows through the cheese and not
alone on its surface. To bring about the growth in the center of
the cheese special means are devised in its manufacture. The
cheese-maker begins by cultivating the necessary mold on bread.
After the mold on the bread has produced a great quantity of spores,
the mass is dried and ground into powder (Fig. 45). After curdling
the milk with rennet in the usual way and draining the curd, it

Fig. 45. — PenicU-
lium roquefortii, the
mold ripening Roque-
fort cheese {Thorn).

SOFT CHEESES. 207

is placed in a form in a thin layer, and over the top of the layer is
strewn a quantity of powdered, moldy bread with its thousands of
spores. Over this is placed another layer of curd with more
mold spores; then a third layer of curd over all. The mold is thus
planted within the cheese. The whole is then pressed bymoderate
pressure in a form. After a few days the cheese becomes hard
enough to be removed from the form and is next placed upon a
machine which punches it full of holes by means of small needles.
The purpose of this is to allow air to enter into the center of the
cheese, thus furnishing the molds in the center with the air they need
for growth. The cheese is then put into the ripening room, where
the molds develop, growing primarily within the cheese. As
the molds grow they develop a peculiarly peppery, piquant taste,
which is characteristic of the Roquefort cheese. Just before the
cheese is fully ripe it tastes bitter; but this taste disappears as the
final flavor develops. A good Roquefort cheese is only possible
when there is a luxuriant growth of these molds within the cheese,
no surface growth being allowed.

The successful manufacture of the Roquefort cheese in the
United States is yet to come. There seems to be no reason why
a cheese cannot be made in this country which, if ripened by the
Roquefort mold, will have the Roquefort flavor; but it is not likely
that a real Roquefoit can ever be made in America because, the
typical Roquefort is made of sheep's milk, and it is doubtful if
Americans will ever be content to raise sheep and milk them. Stilton
and Gorgonzola cheeses are, however, made from cow's milk and
ripened by the same mold that is found in the Roquefort. These
cheeses can certainly be made in this country. Stilton has already
been made in Canada, and there is no reason why its manufacture
cannot be undertaken and developed in the United States.

The Limhurger Cheese. — This represents a type of cheese in
which molds play no part in the ripening, but bacteria are the
primary and perhaps the sole agents.

After being drained in a mold, until firm enough to be handled
the cheeses are placed in a ripening cellar. Every few days they
are removed from the shelves and rubbed over with some liquid.

2o8 BACTERIA AND OTHER MICROORGANISMS IN CHEESE.

water being commonly used, although vinegar is sometimes put into
the water. The surface is thus kept constantly moist. Because
of this constant moisture on the surface of the cheese, molds cannot
grow upon it, for they need a damp, not a wet surface; but a quantity
of bacteria grow instead. These ripen the cheese, doubtless by
the secretion of chemical ferments, although the process has not
as yet been fully studied. The resulting cheese develops very
high flavors, closely resembling those of decay, and the cheeses
rapidly putrefy when they become old. If they are marketed
at the right stage the flavors are not strong enough to be disagreeable,
and many persons are very fond of them. The Limburger type
of cheese includes Backstein and some others.

PRACTICAL RESULTS.

The practical application of bacteriology to cheese-making is
just in its infancy, and it is quite impossible to determine the extent
of its development in the future. As already pointed out, cheese-
makers, in the last few years, have been using pure cultures of lactic
acid bacteria as starters to insure a more complete and more uniform
souring of the curd. This practice is rapidly growing. The lactic
starters have two purposes. First, the growth of the acid organisms
checks the growth of other bacteria that would be likely to spoil
the cheese, and this check seems to be quite necessary for the proper
ripening and for the preventing of faults. Second, the formation
of lactic acid appears to be a needed step in the chemical changes
that constitute the ripening. Hence, the use of a good starter of
acid organisms has a reasonable foundation, and we may confidently
assume that the practice of using starters will increase. In the
making of the Edam cheese of Holland, the practice of using slimy
whey to aid the ripening of the cheese has become very extended.
The slimy whey is a culture of bacteria in whey, and is, therefore,
simply another method of using a bacterial starter to control the
cheese-ripening. It hastens the ripening and makes it more uniform,
but it does not improve the cheese. In the manufacture of Roque-
fort cheese, mold cultures are intentionally added to bring about

PRACTICAL RESULTS. 209

the proper ripening, and in recent years pure cultures of molds have
been applied in the manufacture of cheeses of the Camembert
type. In these cheeses, too, lactic acid starters are very commonly
used. From these few instances it is evident that the practical
application of bacteriology to cheese-making has already begun,
and it is almost certain that a large field is open for the future in this
direction.

18

PART IV.

RELATION OF MICROORGANISMS TO MISCELLA-
NEOUS FARM PRODUCTS.

CHAPTER XV.

ALCOHOL, VINEGAR, SAUER KRAUT, TOBACCO, SILAGE,

FLAX.

Although the problems of. soil fertility and dairying offer the
largest field for the application of bacteriology to farm life, there are
many other problems of minor importance where microorganisms
play a part. Most of these concern food products, either their
preparation or preservation, although some have no relation to
foods.

In all temperate and cold climates it is necessary to preserve food
for the winter season. This applies equally to the farmer's own
food and to that of his cattle.
There is a difficulty in preserving
some kinds of food because of the
readiness with which putrefactive
bacteria cause their disintegration
and decay. Bacteria will feed upon
almost any kind of organic matter,
provided there is plenty of moisture
at hand; but some of the foods, like
most grains, have such a small
amount of water in them that bacteria are unable to grow, and
thei;e . is little difficulty in preserving these for an indefinite
length of time. Nature herself, at the end of the growing season,
extracts the water from the seeds, leaving the comparatively dry

211

Fig. 46. — Showing nature's method
of preserving seeds by drying. The
lower figures are dried and the upper
are fresh seeds.

212 ALCOHOL, VINEGAR, SAUER KRAUT, TOBACCO, SILAGE, FLAX.

mass to remain over the period of rest until the growing time comes
again (Fig. 47). Other kinds of food contain a large amount of
water, and the farmer must find some means of protecting such food
from bacterial action. This is accomplished in a variety of ways,
but may best be considered under two heads: i. The agency of
microorganisms in preparing the crop. 2. The methods of pro-
tecting the crop from the attack of mischievous organisms. To a
certain extent the two subjects overlap, since in several cases the
methods adopted for preserving the material furnish it with flavors
or other characters which distinctly add to its value.

THE ALCOHOLIC FERMENTATION.

The fermentation of sugar into alcohol and carbonic acid is due
to yeast. Among the various aspects of farm life there are quite a
number based upon this type of fermentation. We have seen that
yeasts are especially related to sugars, and that any product which
contains much sugar is more likely to undergo alcoholic fermenta-
tion than putrefaction. Yeasts, when dry, may remain alive for a
long time and float around in the air. The air at all times and in
almost all places is, therefore, sure to contain these living yeast
plants, ready to begin to grow and produce a fermentation whenever
they fall into a sugar solution. These air yeasts are sometimes
called wild yeasts in distinction from the cultivated yeasts that are
now articles of commerce. But whether from the air or from a
package of commercial yeast, the organisms are essentially the same
and their action the same.

The chief products of our farms which are liable to direct alcoholic
fermentation are the fruit juices. Alcoholic fermentation is also
the foundation of the gigantic distillery and brewery industries, which
make use of grains and other farm products. But these hardly
belong to our immediate subject. There are, however, a few forms
of fruit-juice fermentations more or less common on our farms.

Wines. — The name wine is given to the fermented juice of
fruits. The most common fruit used for this is the grape, whose
juice is rich in sugar and easily pressed from a mass of the fruit, as a

THE ALCOHOLIC FERMENTATION. 213

clear liquid. Upon the skin of the grape there are sure to collect,
during its growth, a variety of microorganisms, mostly from the air,
and among them will be enough yeasts to start a fermentation of the
sugars as soon as the juice is extracted from the grape. The grape
juice, therefore, needs no yeast added to it to start a fermentation,
since the wild yeasts are sufficient to give all the inoculation neces-
sary. In the making of wines the usual method is simply to press
out the juice from the grape and then to allow a spontaneous fermen-
tation to occur. Occasionally the practice of adding yeast to the
juices, in order to hasten or control the fermentation, has been
recommended. This method, which has made a complete revolu-
tion in the brewery industries, has not, as yet, been very extensively
applied to wine-making. The knowledge that there are many
kinds of yeasts with different values in fermenting, certainly suggests
that, in wine-making, an improvement may be anticipated by this
use of pure cultures. The use of pure cultures in wine-making is
becoming more common, and where they have been used an im-
proved product or a better control has been claimed.

Some farms, where grapes are raised in abundance, prepare for
market an unfermented grape juice which is essentially wine that
has not been allowed to ferment. The expressed juice is sterilized
by a temperature of about 170°, which is sufficient to destroy the
yeast cells and to prevent fermentation, if the juice be subsequently
kept from further contamination by being bottled. The principle
concerned is simple, but there are various practical difl&culties in the
way that make it difficult to produce a good quality of grape
juice.

The term wine usually refers to the fermented juice of the
grape. But in sections of the country where grapes are not exten-
sively grown other fruit juices are used. Wines are made from the
juice of blackberries, currants, raspberries, ^elder berries, etc. In the
making of wine from these fruits, since the juice is not very sweet,
sugar is commonly added in amounts varying with the sweetness of
the fruit and depending also on whether a sweet or sour wine is
desired. The mixture is then generally left to ferment spontaneously
under the influence of the wild yeasts that are abundant enough to

214 ALCOHOL, VINEGAR, SAUER KRAUT, TOBACCO, SILAGE, FLAX.

produce a vigorous action. Yeast is sometimes added. As a rule,
the fermentation is allowed to continue as long as it will, after which
the wine is bottled and thus preserved for use.

Cider. — This is nothing but apple wine, and is made in large
quantities in sections of the country where apples are abundant.
The expressed apple juice is seldom treated at all, but left to ferment
spontaneously. The amount of sugar in apple juice is small, and
the completely fermented product contains a proportionately small
amount of alcohol. Sweet cider is a name given to the product
while it is still fermenting; it contains but a small amount of alcohol,
but is filled with the carbon dioxid gas that is produced by the
fermentation. Hard cider is the name applied after the fermenta-
tion is nearly or quite over, when the evolution of CO2 has ceased
and the alcohol is at its maximum. In the making of cider, as in
most other fermentations, great improvements have been made in
recent years by the application of the discoveries of bacteriologists.
The use of pure cultures of yeasts, in the place of spontaneous
fermentation, makes the product of a better character and the fer-
mentation more uniform. Numerous other improvements have
been made in the details, so that this product, formerly made on the
farm in a haphazard fashion, without care and with little or no
knowledge of the processes, is now made on a larger scale in special
cider factories, resulting in a cider of a much higher quality.

Yeasts in Bread Raising. — The most common use of yeast
is in the raising of bread. All nations and all peoples have been
accustomed to make bread from the flour of different grains. The
earliest method was simply to stir the flour in water and bake
the mixture into a hard, unleavened bread. The next step was
to allow the dough to stand for a number of hours in a warm place
until it became somewhat swollen by the gas formed within it,
and then. to bake it. The gas made the dough porous and resulted
in a bread filled with holes, easier to masticate, of better flavor, and
more easily digested. This was leavened bread. The next step
was to take a little of the leavened dough and mix it with the next
lot of fresh dough, to hastenen the leavening, a process that was
simply inoculating the dough with the yeast organisms in the

THE ALCOHOLIC FERMENTATION. 21$

leaven. The next step, taken a long time afterward, was to discover
that it is the yeast in the leaven which produces the raising of
the bread, and then to separate the yeast from other undesired
materials in the leaven, and use it in pure cultures. This finally
gave the yeast that has been used for half a century or more. The
use of leaven has not altogether disappeared, but yeast is quicker
and more reliable.

The action of the yeast in bread-raising is very simple. The
dough contains a considerable quantity of starch and also a small
quantity of diastase, an enzyme capable of converting starch into
sugar. The yeast acts upon the sugar thus produced and forms
from it alcohol and carbon dioxid. The latter, being a gas,
forms bubbles in the dough, causing it to swell and become lighter.
When subsequently baked, these gas bubbles leave their traces in
the numerous holes that one finds in raised bread.

In the raising of bread the practice of depending on the wild
yeasts of the air has long since disappeared and yeast cultures are
now almost universally used. These commercial yeasts have been
chosen from the considerable variety of yeasts known, and are,
of course, the ones that have been found to produce the best results
in bread-raising. They are not the same varieties as those found
best for brewing. The yeast is cultivated in large quantity and
then put up in a convenient form for distribution, sometimes dried,
in which condition it will keep alive for weeks, and sometimes
compressed into a moist cake, compressed yeast, in which condition
it will keep only a few days.

Bacterial Impurities in Bread-raising. — The yeast cakes are
never pure yeast, but may contain undesired bacteria, which then
get into the dough and sometimes produce trouble. Occasion-
ally, too, such bacteria may get into the dough from other sources
than yeast, such as dirty water or dirty utensils in the kitchen.
During the raising, lactic acid bacteria always grow, and they
seem to be necessary in order to prevent the growth of other species
of more troublesome organisms. Sometimes such bacteria grow
too vigorously and may cause trouble. At least two different
faults in bread-making are known to be caused by undue growth

2X6 ALCOHOL, VINEGAR, SAUER KRAUT, TOBACCO, SILAGE, FLAX.

of bacteria. The first of these is sour bread, due to the growth in
the dough of acid-forming bacteria. This occurs most commonly
when the raising is allowed to continue too long or at too high a
temperature. The bacteria in question will not produce trouble
if fresh yeast be used and the raising be completed in less than
eight hours' time. A second fault, due to bacteria, is slimy bread.
This is of rare occurrence, though sometimes it will infect a bakery
and continue day after day. This bread, when fresh, appears normal ;

ybut after a few hours it becomes slimy, so that,
when broken, it appears as if filled with cobwebs.
^\ The trouble is due to bacteria, the source of which
t may be either the utensils, the flour, or the yeast
Fig. 47— The (Fig- 47). The remedy is in cleaning and steriliz-
bacteria that cause j^g all baking dishes. If this does not remove the

shmy bread. , , . • 1, , , , 1 <• n

trouble it is well to change the brand of flour or
get a fresh supply of yeast. The trouble may also be relieved by
keeping the bread cold so as to prevent bacteria growth. The
addition of a little lactic acid to the dough, or the use of equal
parts of sour whey and water in mixing the dough, is also recom-
mended as a remedy, based upon the fact that lactic acid bacteria
will check the growth of other organisms.

VINEGAR-MAKING.

Vinegar is used both as a direct condiment to give relish to foods
and as a preservative, as in the manufacture of pickles. It is made
on a large scale in vinegar factories and on a small scale on farms.
It is always made from some weak alcoholic solution, like cider,
weak wine, or beer, each locality using as a source the alcoholic
solution most easily obtained. The essential part of the process
is the chemical union of the alcohol with oxygen from the air, by
which it is converted into acetic acid. Such a simple oxidation can
be brought about by a purely chemical process. As long ago as
1 72 1, Davy discovered that platinum-black, or finely divided plati-
num, when mixed with alcohol, causes an active union with oxygen
to take place, which results in the production of acetic acid.

VINEGAR-MAKING. 21 7

When vinegar is formed in the usual way, a brownish gelatinous
mass, called "mother of vinegar" is formed, and for a time it was
believed that this mother of vinegar acted like the platinum-black,
"condensing" the oxygen, and thus causing a chemical union.
But the error of this conclusion was later shown, i. The ordinary
vinegar fermentation is stopped by the accumulation of acid, and
it will not occur at all if the amount of acetic acid in the solution be
more than 14 per cent. The formation of acid by platinum-black is
entirely uninfluenced by such an accumulation. 2. The formation
of the acid in vinegar is most abundant at about 95° F., diminishing
rapidly at higher temperatures, and may in itself produce so much
heat as actually to ignite the alcohol. 3. Later the production
of acetic acid by the growth of pure cultures of certain bacteria
showed vinegar-making to be a true fermentation.

The Vinegar Organism. — The mother of vinegar is a soft,
semi-solid mass, commonly forming a scum on the surface of the
fermenting alcohol. Vinegar is not forrned if this material be lack-
ing, and a very small bit placed on the surface of an alcoholic solution
soon extends itself and covers the whole surface, inducing an active
acetic acid formation. This mother of vinegar proves to be a mass
of microorganisms. It was first named Mycoderma by Persoon,
who studied it in 181 2, without having any suspicion that the skin
was the cause of the acetic acid. Later, Kiitzing, showed that this
skin was made of numerous minute, living organisms, and positively
asserted that they were the cause of the acetic fermentation.
But the chemist Liebig checked the advance of discovery by his own
theories of fermentation, which regarded the whole class of phe-
nomena as chemical processes.

It was eventually Pasteur who demonstrated that the process is
really a fermentation due to the activity of the microorganisms in the
mother of vinegar. An examination of this material shows it to be
made of a mass of bacteria. Pasteur used for them the name
Mycoderma aceti, but he did not study them sufficiently to show
what they were, although he demonstrated their relations to vinegar-
making. Hansen later proved they were bacteria, and showed
that in the different samples of "mother" there are several varieties.
19

2l8 ALCOHOL, VINEGAR, SAUER KRAUT, TOBACCO, SILAGE, FLAX.

Henneberg still later increased our knowledge of the bacteria, so
that we now know that there are at least fifteen varieties of these
vinegar organisms, differing from each other in various respects,
such as their optimum temperatures, the amount of acid they will
produce, etc. Bact. aceti, Bad. pasteurianum, Bad. kiltzingianum,
Bad. xylinoides, Bad. orleanense, and Bad. xylinum are names
applied to the most important types.

All of these acetic bacteria have certain very characteristic
points which they share in common, thus forming a group by them-
selves. They all exist in three different forms, shown in Fig. 48.

Fig. 48. — Acetic acid bacteria, showing long rods and rounded swollen centers.

They may form chains of short rods, looking like ordinary bacilli.
At high temperatures they grow out in long slender threads, some-
times very long, without any traces of divisions. These threads
may subsequently break up into short elements. At low tempera-
tures they have a peculiar habit of forming long threads with rounded
swollen centers. When these threads break up into short forms
only the thick, swollen centers remain undivided. This character
is such a peculiar one that it places these acetic bacteria in a class by
themselves. These different varieties are distinguished not only by
slight differences in structure, but also by some important dif-
ferences in relation to condition, and in their power of forming
acetic acid. They vary in the amount of acetic acid they will pro-
duce under similar conditions. For example, B. aceti produces

VINEGAR-MAKING. 219

1.27 per cent, of acid at 59° F., while under the same conditions
B. pasteurianum will produce 0.08 per cent. But, more important
still, is the fact that the temperatures which favor the different
varieties are not the same. B. aceti, for example, produces a good
fermentation at a temperature as high as42°F., whereas B. pasteuri-
anum at the same temperature will hardly multiply, and produces
no fermentation. Some of the species produce the maximum
effect more quickly than others, and some may begin to destroy the
acid produced under conditions of temperature and time in which
other varieties are still active.

Methods of Vinegar-making. — The farmer's method of vinegar-
making is simply to allow cider to remain in barrels for a sufficient
number of months to turn into vinegar. The result of this method
is variable, sometimes very good and sometimes very poor vinegar
resulting. Chance is relied upon to insure the presence of the
proper vinegar organisms, although to make more sure of a good
result, barrels are sometimes taken that have previously been used
for the same purpose, and that are, therefore, more likely to contain
the desired bacteria.

But vinegar- making, like other farm processes formerly carried
out by each farm independently, is becoming largely locahzed in
factories, where it can be conducted on a large scale and can be
more carefully watched. In these factories two methods are used,
differing radically from each other, and while different factories
have varying details in the process, the methods employed are
modifications of these two.

The Orleans Process. — Oaken casks are used, each new cask
being first steamed and then impregnated with hot vinegar, to "sour"
the cask. After this it is filled partly full of good clear vinegar and
about half a gallon of wine is added. This mixture is kept at about
70° F. for a week or so, when a little more wine is added, supple-
mented in another week by another lot. This is continued until
the cask contains about forty gallons (two-thirds full). Then about
half of the material is withdrawn, as vinegar; and from this time
on some two gallons of vinegar may be withdrawn at a time, its
place being made good by the addition of wine. The cask, when

220 ALCOHOL, VINEGAR, SAUER KRAUT, TOBACCO, SILAGE, FLAX.

once started, may continue in operation some six or eight years con-
tinuously, but eventually it becomes so filled with tartar and mother
of vinegar that it must be cleansed.

Shortly after the process of vinegar-making is started a skin of
the vinegar organisms grows on the surface, soon covering the
whole. Its action causes the alcohol to unite with oxygen from the
air, thus producing acetic acid. The bacteria in this method grow
chiefly on the surface of the liquid, and they develop luxuriantly
during the process. The oxidation does not always stop at the
formation of acetic acid, but is sometimes carried further so as to
split up the alcohol into simpler molecules. This results in a loss,
and is one of the difficulties to be met with in the manufacture of vin-
egar. This loss, though sometimes considerable, is generally not
great, for the accumulation of acetic acid will soon stop the growth
of the organisms. Different species of the organisms can endure
different amounts, but when the acetic acid has reached 14 per cent,
the bacteria are never able to produce any more.

The Quick Process. — A second process of vinegar-making, known
as the "quick process," does not, at first sight, appear to be caused
by microorganisms. This process consists simply in an intimate
mixture of alcohol with air by means of shavings. A mass of
shavings is placed in tall vessels and thoroughly moistened with an
alcoholic solution. Then the whole is inoculated with a little warm
vinegar followed by alcohol. The vinegar thus added starts the
process, and in a few hours new vinegar is produced. Alcohol is
now added at the top, slowly but continuously, and it percolates
through the shavings and appears at the bottom as vinegar. Such
a process seems at first to be more like a chemical phenomenon than
a fermentation induced by microorganisms. But it does not start
until a little warm vinegar has been added to the mixture, and such
vinegar will be sure to contain bacteria. This, of course, suggests
that the microorganisms, thus added, spread through the shavings,
grow rapidly, and soon induce the oxidation. Indeed, it has been
proved that, if the growth of the fungi is prevented in such a mixture,
no vinegar is formed. The shavings simply furnish a large surface
for the spreading out of the organisms. Hence, the quick vinegar

VINEGAR-MAKING. 221

process is also dependent upon the presence and active growth of the
vinegar plants.

Use of Pure Cultures in Vinegar-making. — The different
types of vinegar-making organisms vary much, requiring quite
different conditions of temperature for their best work. In the
processes of manufacture hitherto used considerable losses have
resulted from the fact that the acetic acid formed is destroyed by
the further action of the bacteria. The fermentation is apt to be
irregular and, even under the same conditions, does not always
produce equally desirable results. The reasons for the irregularities
are to be found in the fact that, in different factories, sometimes
even in the same factory at different times, many varieties of the
vinegar organisms are found. Moreover, several of these organisms
are almost sure to be found together in any mass of natural " mother."
It is impossible to devise conditions that will be most favorable for
all of the organisms, and hence, with a "mother" composed of
many varieties, there is sure to be some loss. Theoretically, it
would seem that vinegar-making could be improved by the use
of pure cultures of these organisms. With a pure culture it would
be possible to make the conditions such as to produce the best
results with the variety in question, and thus prevent the losses
that come from one variety destroying the product of another
variety. The use of pure cultures has revolutionized brewing,
has greatly improved the methods of butter-making, and is rapidly
changing the process of cheese-making. Bacteriologists feel
confident that the same principal can be apphed to vinegar-making.

Hitherto there has been but little application of pure cultures
to vinegar-making. To obtain absolutely pure cultures is difficult,
and to keep them pure from subsequent contamination is more
difficult still. Vinegar-makers have not thought the advantages
derived from such methods sufficient to pay for the labor and trouble
of applying them. They have, to a considerable extent, adopted
rougher methods of obtaining the vinegar organism in quantity
and in a comparatively pure condition. A little white spirit vinegar
is filtered through fine bolting cloth to remove the vinegar eels.
This is mixed with a little alcohol of 90 per cent, volume, and some

222 ALCOHOL, VINEGAR, SAUER KRAUT, TOBACCO, SILAGE, FLAX.

white wine which has been previously boiled, filtered and cooled.
This mixture is placed in shallow dishes and covered with glass
plates. The vinegar organism appears in a few hours as a thin scum
which ordinarily will be pure, or nearly so. If the scum does not
show any white spots (molds) it is gently lowered upon the surface
of the vat containing the alcoholic solution which is to be made
into vinegar. The result is a comparatively pure culture of vinegar
organisms, and a satisfactory fermentation. When used in making
vinegar from cider, this process gives a vinegar quite superior
to the ordinary type, having a finer flavor and better keeping
properties.

The farmer who simply lays aside his few barrels of cider or
other alcoholic 'solution that it may be converted into vinegar
will not be troubled or especially interested in the matter of pure
cultures. A little loss is nothing to him, while the preparing and
preserving of pure cultures is an impossibility. He feels tolerably
confident that the cider which he sets aside for the purpose will
contain some of the acetic acid bacteria and that in course of time
he will obtain vinegar. Whether he gets the advantage of all the
alcohol or loses half of it does not matter much to him. Even
if several barrels should not produce a proper quality of vinegar,
it would not be of much importance. Sometimes he finds that his
vinegar is stronger than at other times, and sometimes he finds
that its taste is much inferior to the ordinary grade of vinegar.
Perhaps this raises in his mind a temporary question as to the
reason for the differences. But he never pursues the subject further.

The Preservation of Vinegar. — Vinegar is apt to deteriorate
by standing. It loses some of its acidity, falls off in flavor, and
may become muddy and slimy. All these various troubles are
caused by the continued growth of the microorganisms in the
vinegar. In such vinegar may be found various growing bacteria,
and very commonly, especially in cider vinegar, may be found
vinegar eels in abundance. These latter are little worms that get
into the vinegar from some source and find it a favorable locality
for growth and multiplication, They probably injure the quality
of the vinegar, although, so far as is known, they are harmless

SAUER KRAUT. 223

to one who may consume the vinegar. Their presence is, however,
undesirable. All these troubles increase as the amount of acid
decreases, for the miscellaneous bacteria and the vinegar eels cannot
grow if the acidity is high, but they will grow when this acidity
decreases. The reduction in acidity is commonly due to the
action of bacteria and usually to the very kind of bacteria that
originally produced it; for these organisms, after producing the acid,
may cause a further oxidation which destroys it. Hence, it has
been suggested that pasteurization of the vinegar for the purpose
of destroying the bacteria and vinegar eels will enhance its keeping
property. Whether there is any practical value in this procedure
has not yet been determined by experience.

SAUER KRAUT.

This is a food used so widely in Europe and coming to be so
popular in this country that it may well be regarded as one of the
most important of the minor farm products. It is made of cabbage,
slightly fermented and prevented from decay by lactic acid bacteria
(Fig. 49). The cabbage leaves, after being washed, are shredded
and packed in casks under pressure, to remove most of the moisture.
In these casks a fermentation soon starts, ^

which is two-fold. Yeasts that are present ^ ^^0

produce an alcoholic fermentation, evolving ^ §8

gas that causes the v/hole mass to foam and _ ^ 9n

froth. At the same time, the lactic acid bac- qX Q© ^^3^
teria, the same species apparently that sour Fig. 49.— The bacteria
milk, develop rapidly and cause the mass to and "yeasts that ferment

, sauer kraut.

sour. The bacteria growth is primarily in
the juice squeezed out of the cabbage tissue, and not in the
solid matter. As the mass becomes sour from the acid, the
growth of all bacteria is checked. By this means the ordinary
putrefactive organisms are prevented from producing the decay
of the vegetable mass, as they would otherwise do. When properly
soured, sauer kraut has a flavor that makes it a relish. It may be
ready for consumption in two weeks, but it is usually kept much

224 ALCOHOL, VINEGAR, SAUER KRAUT, TOBACCO, SILAGE, FLAX.

longer than this. So long as it remains properly acid it will keep,
and if kept cold will remain in this condition for many months.
Eventually a scum appears on its surface. This scum proves to
be made of microorganisms, chiefly a species called Oidium lactis,
a very common species around farms. These organisms, growing
in the scum, gradually absorb and destroy the lactic acid and, as
they do so, the sauer kraut becomes less acid and is finally alkaline.
After this has occurred the putrefactive bacteria that are sure to
be present have an opportunity to grow, and the sauer kraut begins
to decay, so that it rapidly spoils. This product is, thus, one that
is at first prepared and preserved by certain kinds of microorganisms,
but is eventually ruined by the growth of other species.

Certain other vegetables are prepared in a similar way. Soured
beans are prepared in certain countries, and the souring of cucum-
bers to make dill-pickles is, apparently, an identical process. Soured
beets and asparagus are also articles of diet. Bacteria similar to
those found in sauer kraut are concerned both in the souring of
these products and in the subsequent neutralization of the acid
preparatory to the final spoiling of the product.

THE CURING OF TOBACCO.

Tobacco is a product whose value is almost wholly dependent
upon the success of its curing and its final preparation for market.
The green plant, as taken from the field, is in itself valueless, and
many a crop is injured or perhaps ruined in the curing. The
relation of the curing to microorganisms is not yet settled, but
since the curing is undoubtedly a fermentation, it properly belongs
to our subject.

When the leaves are fully grown the crop is reaped and hung up
in a shed or barn to undergo a partial drying. After the drying
process has reached a desired stage the leaves are ready for the
fermentation proper, the process upon which the value of the
product largely depends. There are two quite different methods
of bringing about this fermentation. In the first method the leaves
are left hanging a long time, and are eventually packed closely in

THE CURING OF TOBACCO. 225

boxes weighing several hundreds of pounds each. These boxes are
then left to take care of themselves. They are generally packed in
the cool weather of fall and remain undisturbed several months.
When the warmer weather comes, in the spring, a fermentation is set
up in the cases, which progresses without any attention from the
owner; but after a number of months the boxes are opened to de-
termine the success of the fermentation, and the crop is sold at a
price depending upon the character of the product.

The second method of fermentation, adopted chiefly in warmer
climates, keeps the whole process under close observation and is, in
this respect, undoubtedly superior. The leaves, after drying, are
piled upon each other, not too tightly, and a great heap is made,
sometimes three feet high, sometimes more. For the proper fer-
mentation of this heap there should be a warm, moist atmosphere,
such as is found in tropical and semi-tropical climates. Within a
short time the temperature of these masses begins to rise, sometimes
as high as ten degrees in a day. When the temperature reaches a
point between 125° and 130° F., the piles are opened and the leaves
are heaped up again in other similar piles, care being taken to put
on the inside those leaves which were before on the outside.
Another rise in temperature follows and again, after reaching i25°F.,
the heaps are thrown down and remade. This is repeated from
five to eight times, several days elapsing between the successive
heapings. At the end the tobacco is in the proper condition for
market. This second method is quicker and, in some respects,
better than the first method. The fermentations do not always end
here, however. The manufacturer commonly allows the tobacco
to undergo a second fermentation, called "sweating," which brings
the leaf into a better condition for use.

The primary fermentation is clearly the essential process of
tobacco-curing. During the fermentation some very essential
changes in the tobacco take place. The chief of these changes are
the following: A decrease in nicotin, an increase in alkaline reaction,
an increase in ammonia, the disappearance of sugar, an increase in
the amount of nitrate, a loss of water, a change in the texture of
the leaf, a change in color (the final color brown) and a change in

226 ALCOHOL, VINEGAR, SAUER KRAUT, TOBACCO, SILAGE, FLAX.

flavor. These numerous changes, while quite varied in nature, are
mainly due to oxidation.

The Cause of Tobacco Fermentation. — Three different
theories have been held and, to a certain extent, are still held, con-
cerning the cause of the fermentation. While not one of them
explains all the facts, all three may, in a measure, be correct.

The Chemical Theory. — This assumes that the free oxygen of
the air acts directly upon the cells of the tobacco leaves, although it
is admitted that microorganisms are necessary to raise the tem-
perature sufficiently to make the oxidation possible.

The Bacterial Theory. — This assumes that the fermentation is
the result of bacterial growth. Bacteria are found upon the leaves
of fermenting tobacco, and several distinct species have been
isolated and carefully studied. Some of them are well-known
species, but others are peculiar to tobacco. Some have been
named B. tohacci /, //, III, IV, and V. It has been claimed that
these have a causal relation to the fermentation of the tobacco, and
experiments have been carried out to test it. Tobacco leaves have
been sterilized and it is found that they will not undergo fermenta-
tion. If, however, they are inoculated with some of these bacteria,
they will undergo a fermentation, although the result does not show a
good flavor or aroma, which fact suggests that, though bacteria are
concerned in the process, there are other factors.

The Enzyme Theory. — The recognized importance of enzymes
in fermentation in general, has naturally raised the question of
their relation to tobacco-curing. Enzymes are known to be pro-
duced by plants, and would be expected in the tobacco leaves.
Indeed, they are found there readily enough, and among them are
certain enzymes called ozydases, peroxydases, and catalases, which
have the power, under different conditions, of producing an oxida-
tion of other substances. Are not these, rather than bacteria, the
cause of tobacco fermentation, which is chemically an oxidation?
Arguments for this view are found in the following facts:

I. The extremely rapid rise in temperature is too high to be
accounted for by ordinary bacterial action. Fermentation due to
bacteria may certainly produce a rise in temperature, but a rise as

THE CURING OF TOBACCO. 227

high as 130° F. is entirely beyond anything that could be expected
of living microorganisms. 2. The fermentation will go on in the
presence of corrosive sublimate that prevents bacteria growth.
3. While bacteria may be found upon the leaves of the fermenting
tobacco they are generally found only in small quantities, too few
to account for the fermentation which is producing a rise in
temperature of io° per day. Moreover, the amount of moisture in
the tobacco leaves is low, not over 25 per cent., and in such a condi-
tion bacteria do not readily grow. Lastly, nicotine is generally
looked upon as a means of checking bacteria, and hence the ferment-
ing tobacco cannot be regarded as a favorable place for bacteria
growth.

On the other hand, these enzymes are found in abundance on the
leaves, and they are capable of producing an oxidation, such as
occurs during the fermentation. The conclusion that the enzymes
from the tobacco leaves are active agents in the curing seems
indisputable.

But while these facts suggest that enzymes may play the chief
part in the fermentation, they by no means exclude the action of
bacteria. Tobacco lovers know that the tobacco of Cuba develops
in its fermentation a flavor which is not found in tobacco prepared
elsewhere. The same species of tobacco raised in other countries,
although it will undergo a fermentation of a normal character,
acquiring the chemical and physical properties which it develops
in Cuba, does not acquire the flavor that it has in its own home.
Cuban tobacco is now raised in the United States, but its flavor
is inferior to that raised in Cuba.

We have already noticed that in the ripening of cheese, though
the enzymes are extremely important agents in the chemical changes
going on, the bacteria are of chief importance in the production of
the flavors. The fermentation of the tobacco by the oxydases does
not satisfactorily explain the flavors. When Havana tobacco
is fermented in the United States, it ferments normally, but does
not develop the typical Cuban flavor. It is quite possible that
this flavor is, after all, a matter of bacterial action. When the
Cuban planter ferments his tobacco, he commonly sprinkles it

228 ALCOHOL, VINEGAR, SAUER KRAUT, TOBACCO, SILAGE, FLAX.

with special preparations, a process called "petuning." These
preparations are usually secrets, and each plantation is likely to
have its own. They consist of mixtures of various chemicals, of
which organic fluids containing ammonium carbonate frequently
form a part. The action of this petuning is problematical, but it
is believed by the planters to contribute to the production of the
peculiar flavors of Cuban tobacco.

Now these mixtures are good culture media for bacteria, and
when they are sprinkled upon the tobacco the leaves are, in a way,
inoculated with bacteria. On such petuned leaves bacteria are
abundant. But there is no evidence at hand to indicate whether
these bacteria have anything to do with the production of flavor.
It is certainly not impossible nor improbable that the flavor
production, which does not seem to appear typically outside of
Cuba, may be due in part to bacterial action, possibly to the action
of the very bacteria that the planter unconsciously sprinkles over his
leaves in the petuning which occurs before the fermentation begins.

Of course the suggestion that the flavor of tobacco may be
improved by the use of artificial pure cultures in the fermentation
is a natural one. The acknowledged relations of bacteria to the
flavors of butter, cheese, and other products naturally suggest an
attempt to improve the flavors of tobacco by bacterial inoculation.
Several experimenters have been trying this plan for years, with
what success it is hardly possible to say. The manifest financial
importance of such a process, could it be made successful, has
inclined experimenters to keep their work secret. While it has
several times been claimed that by the use of proper bacterial
cultures Havana flavors can be obtained in tobacco fermented
elsewhere, these claims have not yet been substantiated by any
public demonstration. They are still made by some who insist
that they have actually been successful in this line of experimenting
and that they have made Havana flavors from common tobacco
by bacterial inoculations.

Diseases of Tobacco. — Whether or not microorganisms play
a part in the normal ripening, it is certain that they sometimes injure
the crop and produce abnormal fermentation. The presence of

SILAGE.

229

too much moisture on the leaves is likely to be followed by the growth
of mischievous microorganisms. Molds are the most common
injurious organisms to appear under these conditions, but bacteria
may also develop and produce disastrous results. From the time
the tobacco begins to grow in the field until it has reached its final
state as a completed product, it is subject to a considerable number
of diseases. It is a very delicate plant, and slight changes in
moisture or temperature are almost sure to bring about troubles of
some kind that injure or ruin the crop. Of these troubles some are
produced by molds or special fungi, and some by bacteria. The
consideration of these various troubles, whether bacteiial or of a
different nature, concerns only the person interested in raising tobacco
and is of no special interest to the agriculturist in general. We
shall not, therefore, further consider them in this work.

SILAGE.

In the silo the agriculturist has devised a method of utilizing
certain food products of which the soil yields large crops, but which
contain so much water that they lose their value in great measure
when dried. The silo not only enables him to preserve such food,
but it impregnates it with new flavors which, in some respects, en-
hance its value, for it makes a product especially relished by cattle.

Preparation. — In the preparation of silage the material to be
used, most commonly corn not fully ripe, is cut into moderately
small pieces and packed away firmly as a solid mass, in a tall, air-
tight compartment. Sometimes the silo is filled quickly, and some-
times more slowly, and the rapidity should depend upon the rapidity
of fermentation. After the silo is filled it is closed at the top, and
frequently subjected to considerable pressure. The contents are,
thus, largely deprived of air. Air, of course, gets in around the
top, but there is little or none around the sides or bottom, so that
only the superficial layers are affected by it.

Fermentation. — After the packing important and profound
changes take place in the silage. The first phenomenon to be
noticed is a rapid rise in temperature, the primary fermentation.

230 ALCOHOL, VINEGAR, SAUER KRAUT, TOBACCO, SILAGE, FLAX.

The extent of this rise is dependent upon the amount of oxygen
present and the readiness with which the heat is radiated. The
temperature should not rise above 150° F., and, to give the best
result, it should be much lower. The proper production of silage,
however, does not appear to be dependent upon this rise in tempera-
ture, inasmuch as perfectly normal silage may be made in small
vessels where hardly any rise in temperature is noticeable.

This high temperature lasts a few days and then the mass slowly
cools. The production of heat appears to be very rapid for a few
days, and then somewhat quickly declines; but a less rapid evolution
of heat continues for a long time, perhaps several weeks. After
the reduction in temperature other changes begin, which are much
slower, and after several weeks the character of the material is
found to be greatly changed. This is a secondary fermentation.
of a different type. It develops a certain amount of acid, its chemical
nature is altered, and it develops a new flavor and aroma which should
be distinctly aromatic, without any signs of putrefaction or mustiness.
There is found to be a considerable loss of material, a loss ranging
from 4 per cent: to 40 per cent. This is a very wide range, and
shows that the method of ensilage has an extraordinary effect upon
the product obtained. The loss is chiefly a loss of carbohydrates,
although there is also an appreciable loss of albuminoids. The
loss is largely parallel to the amount of oxygen that finds its way
into the silo, being very slight if the oxygen of the air be thoroughly
excluded. Perfect exclusion of air is, then, the best means of
preventing the loss.

In a properly prepared silo the fermentative changes do not ex-
tend beyond this, and the material will now remain sweet for
months. The superficial layers may become decayed and ruined,
but the central mass itself is not affected. After the feeding from a
silo is commenced its contents must be used up somewhat rapidly,
for various undesirable fermentative changes may set up in the
superficial layers as they are successively exposed to the air.

The Causes of Ensilage Fermentation. — Three different
factors have been suggested as causes for the fermentations inside
the silo. These are: i. The action of bacteria. 2. Respiratory

SILAGE. 231

changes in the plant tissues, and 3. The action of enzymes. The
probabihty is that, as in the other cases where there has been a
similar dispute, all three processes are concerned.

Respiratory Changes. — The living plant cell is always carrying
on the physiological process of respiration, a process quite similar
to respiration in animals, and resulting in the use of oxygen and the
evolution of carbon dioxid. In this respiration carbohydrate
bodies are used, with some albuminoids as well, and heat is evolved.
Now, the plant cells do not die when the plant is cut down, but con-
tinue for some considerable time to carry on this process of respira-
tion. Cutting the plant to pieces appears, indeed, to increase
temporarily rather than to decrease the respiratory changes.
These may go on for several days, until, indeed, the plant cells are
fully dead. These are well-known facts, and recognized by botanists
for a long time. To these respiratory changes is due part of the
fermentation in silage. After the material is packed in the silo the
plant cells remain alive for several days and carry on these respira-
tory changes as long as they are alive and have oxygen at their com-
mand. This results in the gradual oxidation of the carbohydrate
material and the evolution of carbon dioxid. These changes are
thought to be fully sufl&cient to explain the first changes in the
silage, with the initial heating and evolution of gas.

Fermentations Due to Enzymes. — As already noticed, living plant
tissues secrete a variety of enzymes with varying powers of acting
upon carbohydrates and albuminoids. Such enzymes are present
in the corn stalks and fruit, and when these are packed in the silo,
the enzymes are of course stowed away with them. As the mass is
warmed up under the action of the respiratory process it is inevitable
that the enzymes will begin their action, and that the fermentations
occurring during the next few weeks will be affected by these
enzyme activities. It has as yet been impossible to say to what
extent the enzyme action is concerned in the phenomenon. Certainly
they must have much to do with the result.

The respiratory processes and the action of the enzymes to-
gether are capable of producing silage of ordinary type without the
aid of bacteria or other living agencies. Silage can be made in

232 ALCOHOL, VINEGAR, SAUER KRAUT, TOBACCO, SILAGE, FLAX.

experimental jars in which chloroform vapor prevents the growth of
bacteria, although it allows the enzyme action to continue as usual.
It goes through a fermentation that is fairly typical, a fact that shows
that the essential phenomena of ensiling may be wholly the result of
these two sets of activities.

The Action of Microorganisms. — It was first thought that the
fermentation of silage was a bacterial action wholly, but further
study showed the fallacy of this conception. The original fer-
mentation, by which there is a rapid rise in temperature, cannot
be the result of bacterial growth, since it is too rapid and the
temperature rises too high. There is no evidence to suggest that
any bacteria can produce a rise as high as 150°, a temperature that
destroys the life of most organisms. If the rise were due to bacteria
it would be rather slow, rising only as the bacteria had the oppor-
tunity to develop, while on the contrary it is very rapid. Finally
the possibility of making silage in a jar filled with chloroform vapor
shows that bacteria are not necessary for the phenomenon.

But this does not by any means exclude the agency of micro-
organisms in the ordinary formation of silage. Bacteria are cer-
tainly present and, in some cases, they are present in great numbers.
Some bacteriologists have not been able to find them so very abun-
dantly, but this seems to be due to the fact that they did not use
favorable media in studying them, for when a medium is used
that is adapted to the silage bacteria, they are found in abundance.
Certainly, if they are present and develop during the fermentation,
they must have some effect upon the silage. One effect they cer-
tainly seem to have. The silage turns acid during the ensiling, and
this acidity appears here, as in other cases which we have noticed, to be
a means of preventing subsequent putrefactive changes. Without
doubt this acidity may be attributed in part, if not wholly, to acid-
forming bacteria growing in the silo.

Further, there develop in the silage certain prominent flavors
which contribute largely to its value, and the source of these flavors
is as yet unknown. Aromatic flavors such as are found in silage do
not come from respiratory processes, nor do enzymes develop such
flavors, so far as is known. There are, some who think, however,

SOUR FODDER. 233

that silage flavors are really due to enzyme action. But considering
the fact that enzymes do not commonly produce any such flavors
while bacteria do, and also that bacteria certainly grow in the silage
after the first fermentation is over, it seems on the whole more
likely that the flavors must be attributed to bacterial action.

As a summary, then, it appears that silage involves three distinct
processes, each of which is capable of producing a profound modifi-
cation of the material in the silo. Probably all three may be con-
cerned, in different degrees^ at different times. The various lots
of silage do not always ferment alike, even under seemingly identical
conditions; and very possibly these three different processes are con-
cerned, in varying degrees, in the different lots of silage. The sub-
ject is complicated and probably so variable that we cannot at
present say, with any degree of accuracy, just what is the usual
course of events in this fermentation. A large amount of study
remains to be done on this subject, and doubtless, when the matter
is properly studied, so that it is better understood, great improve-
ments can be made in the process.

It is perhaps fitting to say that silage forms a good food for
cattle, although some dairy companies refuse to accept milk from
silage-fed cows. The reason that this kind of fodder has an effect
on the milk is probably due to the dirt and filth that get into the
milk from the silage food after milking, rather than to the silage
that the animals have actually eaten. If the milk were kept clean
and all the dairy processes carried out in a proper manner, it is
doubtful whether any trace of silage feeding would show in the milk.
But considering the carelessness in the ordinary dairy and the dirt
that commonly gets into milk, it may follow that the effect of silage
in the stable will show in the milk.

SOUR FODDER.

This is a food for cattle made out of the waste from beet sugar
manufactories, and other waste material. Slices of beet roots, after
the sugar is extracted, steamed potatoes, corn stalks, and various
other vegetable substances, may serve, as its basis. This material

234 ALCOHOL, VINEGAR, siuER KRAUT, TOBACCO, SILAGE, FLAX.

is packed in trenches in the ground, pressed by heavy weights,
and left to ferment. It undergoes a fermentation that converts
it into an acceptable food for cattle. Its value lies in the fact that
it is a means of utilizing what would otherwise be a waste product.
It is of little significance in this country.

THE RETTING OF FLAX AND HEMP.

Linen is made from the long tough fibers that are found beneath
the bark of the flax plant. In the plant they are firmly bound
together, and with the wood and bark make a solid mass, glued
together by a substance called pectin. To remove these fibers so
that they may be woven into hnen, this pectin must be disposed of
in some way. The method by which this has been accomplished
from time immemorial is by "retting." The flax is tied up in
bundles and immersed in the water of a stream or in vats. Here
it remains until the water bacteria have pretty thoroughly rotted
or "retted" it. By the decomposing action of these bacteria,
the pectin is dissolved and the fibers in the flax stem are loosened
from their connection with the other parts of the plant. A little
combing over properly constructed teeth separates the fibers from
each other, and gives the desired product for spinning and weaving.
The separation of the flax fibers has practically always been done
in this way. The bacteria concerned have been isolated from the
retting flax and obtained in pure cultures, and it is found that they
are able to produce the result when inoculated upon flax in pure
culture. Hitherto no substitute for this bacterial action has been
found that will satisfactorily replace the natural retting. It is
quite possible that some chemical means may be found that
will replace the bacterial process. Indeed, certain secret processes
are now in use that are based upon chemical methods and are
claimed to give uniform results in a much shorter time than the
ordinary retting. How soon these may replace the agency of bacteria
in the linen industries cannot be predicted.

Hemp is prepared from the hemp plant by a means essentially
similar to the retting of flax.

CHAPTER XVI.
THE PRESERVATION OF FOOD PRODUCTS.

THE SPOILING OF FOOD.

Practically all the materials raised on the farm as food for
man or animals may serve also as food for microorganisms. If
any of the various fungi attack foods, their presence is shortly
made manifest by signs of decomposition. The food, we say,
begins to spoil. Any one of our food products that contains sufficient
water is sure to be attacked sooner or later by some of the various
types of microorganisms, especially by the three classes we have
recognized.

By Bacteria. — These are particularly adapted for feeding upon
proteid matter, but they are not fond of sugar. Hence we find
them especially concerned in the spoiling of proteid foods. Meats,
milk, eggs, wheat, and other cereals, all contain unusually large
quantities of proteids and are liable to putrefaction, whenever
they are moist enough; and their putrefaction will practically
always be found to be due to bacteria. In all attempts to preserve
these substances it is to be remembered that we are dealing with
bacteria, some of which are liable to form spores and for that reason
are difficult to destroy. Pure sugar solutions, on the other hand,
will not undergo a bacterial fermentation, although impure sugars
may do so.

By Yeasts. — Although sugars are not attacked by bacteria,
they are the favorite food of yeasts, which destroy them by setting
up an alcoholic fermentation. If the sugar is in considerable
abundance, it serves as a partial protection against bacterial growth^
although it favors yeast activities. From this it follows that fruit
juices in particular are subject to yeast fermentation, but are not
specially liable to bacterial action. All such substances as fruit

235

236 THE PRESERVATION OF FOOD PRODUCTS.

juices, jellies, jams, in short, anything preserved by sugar, are
liable to yeast action. Therefore, in their preservation, it is
to be borne in mind that we are dealing chiefly with yeasts which
are much more easily killed than bacteria. Sterilization of these
products is much easier than sterilization of proteid foods.

By Molds and Higher Fungi. — Although these are less impor-
tant agents in the spoiling of foods than bacteria, they are important
in several directions. Many kinds of food — bread, cheese, etc. —
will support a mold growth if kept rather moist. Molds grow
chiefly on the surface, but when they become luxuriant they cause
the material to become "musty" and to develop unusual as well
as unpleasant flavors. Almost any food might in time be completely
spoiled by molds, but usually the bacteria and yeasts act more
rapidly than the molds, so that mold action is secondary. In the
decay of wood and timber it is the higher fungi that play the chief
part (bracket fungi and other tree fungi) . They force their mycelia
into the trunk of the solid tree, softening it and beginning the
process of decay. The common molds are the primary cause of
the decay of fruit, for they force their mycelia through breaks
in the skin of the fruit and then through the whole fruit. While
yeasts and bacteria may sometimes be concerned in the rotting of
fruit the molds are almost universally the cause of this phenomenon.

PRESERVATION OF FOODS.

The extremely varied nature of farm products has made it
necessary to find many different methods of preservation, since
what is well adapted for one may be useless for another. The
method of preserving wheat, for example, is not adapted for pre-
serving milk or fruit. There are several fundamental methods in
use, each of which has numerous modifications.

Protection from Microorganisms. — If it were possible to pre-
vent bacteria, yeasts, and molds from gaining access to food materials,
^e food could be preserved indefinitely. But these organisms or
their spores are so abundant everywhere that this is impossible,
except by hermetical sealing. Some foods, however, are thus pro-
tected. Fruits have a certain amount of protection against the

PRESERVATION BY DRYING. 237

molds that cause their decay, since their uninjured skins resist their
entrance. The smooth hard skin of many fruits is impervious to
the mycelium of the mold, though it can readily force its way in
through a bruise or crack into the softer substance within. Hence
the bruised apple decays quickly. Wiping the skin of fruit clean
and dry will protect it for a long time from decay. The wiping
cleans off most of the mold spores that may be on the skin, and the
drying of the skin leaves no moisture in which the few spores left
can germinate. If moisture condenses on the skin, as when the
fruit is taken from a cold room into a warm one, decay is sure to
follow, since this moisture starts the germination of the spores into a
mycelium and the latter is pretty sure to find some place in the skin
through which it can pass. Once inside the skin, it grows rapidly
through the soft pulp and the fruit is soon spoiled. The preserva-
tion of fruit is, thus, a matter of keeping it dry, at a low temperature,
and with an unbroken skin. Even the wrapping of fruit in paper
materially aids in its keeping, since the paper absorbs the moisture
that collects on the skin.

PRESERVATION BY DRYING.

The simplest means of preventing the growth of bacteria in food
products is by drying. Anything that can be dried without destroy-
ing its value as a food can in this way be effectually protected
against bacterial action. No method of preserving food products is
so universally used as this, and none other is so effective.

Grains. — In the preservation of the valuable cereal products
nature herself adopts this plan and, when the grain is ripening, the
large amount of water which was present in the green seed disap-
pears, leaving the ripened grain, somewhat shriveled, perhaps, but
with a very small water content. Such dried grains not only refuse
to germinate unless moistened with water, but bacteria are utterly
unable to grow within them. Nature wishes to preserve the grain
through the season of rest (winter), and in order to protect it from
bacteria she takes most of the water out, thus preventing the putre-
faction which would otherwise surely take place. In harvesting

238 THE PRESERVATION OF FOOD PRODUCTS.

the grain, therefore, all that is necessary for the farmer to do is to
collect the product after it is fully ripened, confident that it will not
contain enough water to make bacterial growth possible.

Flesh. — With other foods the task is more difficult. The flesh
of animals contains so much water that it undergoes decay at very
short notice. So abundant are the bacteria on every side that the
drying of flesh by simple means is practically impossible. We
sometimes read of hunters in the wilds of nature, or of savages in
cooler climates where the air is clear and dry, preserving flesh by the
simple process of cutting it into thin strips and hanging it up in the
sun to dry. Such a process would hardly suffice upon an ordinary
farm, for the flesh would be sure to decay before it was dry enough to
resist the action of bacteria. Whether this is due to the greater
amount of moisture in the air, or to the fact that there is a larger
number of bacteria in the air, around civilized communities, cannot
be stated. But it is certain that such a simple method of drying
flesh cannot be adopted by farms in general. This method of pre-
serving is, however, still used in hot climates, commonly with the
addition of salting, and produces a form of food known as pemmican,
charque, and tassajo. The flesh thus prepared loses considerable
of its flavor, but methods of using artificial heat have been devised
which, in a measure, remedy this defect. After it is once dried, flesh
may be preserved in this form almost indefinitely. The drying of
flesh is a process which hardly concerns agriculture in this
country.

The same end is very commonly reached on the farm by artificial
drying, accompanied by salting and smoking. In the preparation of
smoked hams, bacon, or other flesh, bacterial growth is prevented,
partly by the drying and partly by the actual germicidal action of the
smoke. When the smoke is produced from certain woods — beech
wood is especially favorable — various volatile products arise, such as
phenol and creasote, and these act as germicides. The bacteria on
the surface of the meat are destroyed, and the surface is dried and
affected by the volatile products in such a way that bacteria will not
readily start to grow upon the flesh. Smoked meats are thus pre-
served, in part by the drying, and in part by the action of the smoke.

PRESERVATION BY DRYING. 239

It is well to remember that drying and smoking do not kill the animal
parasites that may be in the meat, like trichina or tape- worms.

Fruit. — The drying of apples, squashes, pumpkins, and other
vegetables is a common process of farm life. In warmer regions of
the earth the sun's rays are sufficient to dry many fruits for preserva-
tion. Raisins and figs are thus prepared. In colder regions arti-
ficial heat must be employed. By the use of artificial heat it has
been found possible to preserve, by drying, a large number of fruits.
Pears, prunes, plums, raspberries, blackberries, blueberries, and straw-
berries represent some of the farm products which readily yield to
this method of treatment. In fruit prepared in this way the water
is not all removed, sometimes as much as 30 per cent, being left.
In most cases there is considerable sugar in the dried product which
aids in the preservation. In pears there is some 30 per cent, of
sugar, while in raisins there is about 60 per cent. It must always
be remembered that drying does not destroy the bacteria, but only
checks their growth, and if the fruit has been exposed to a possible
contamination of pathogenic bacteria, the drying does not remove
the danger. This method of preserving fruits naturally affects their
flavor and is frequently quite unsatisfactory for this reason, although
it does not materially affect their nutritive value. In recent years
hydraulic pressure has been used to extract the water with results,
on the whole, superior to the extraction by simple drying.

Hay. — One of the most important applications of the drying
process is in the preparation of hay. The fresh grass contains
so much moisture that it could not be preserved in masses without
undergoing extensive decomposition, and to obviate this the farmer
resorts to the simple plan of drying out some of the water. But
thisnphenomenon of drying is not always as simple as it looks, and
sometimes a fermentation is certainly involved. Where the climate
is moderately dry and the sun hot, the simple method of exposing
th.^. grass to the sun ^or a few hours is. most widely adopted. But
such a, method is not possible in regions where there is likely to
b^ia grfjat deal of rain.

:^:Cmmg of Hay. by Self -fermentation. — In countries where rains
are frequent and sunshine rare, the sun's rays cannot be depended

240 THE PRESERVATION OF FOOD PRODUCTS.

upon for the curing of hay, so a different principle is used. If the
moist grass is heaped in piles and allowed to stand for a few days,
there appears a marked rise in temperature. This continues rapidly,
the rate and the temperature reached depending upon the conditions:
the denser the packing, the higher the temperature. Commonly
the rise is not above 160°, although under some conditions it goes
above this, even to the point of spontaneous combustion. This latter
phenomenon is of rare occurrence, however, although probably it
is the cause of the spontaneous combustion that occurs occasionally
in a barn when the hay is packed away in too moist a condition.

The cause of such self-heating has not been definitely settled.
It is evident that the phenomenon has a decided resemblance
to the fermentation of tobacco and also to that of silage.
Three possible causes may be concerned: i. The respiratory
changes in the still living cells of the grass. 2. The action of
enzymes from the grass. 3. The growth of microorganisms.
Experimental tests have not yet settled positively the relation
between these possibilities. Sterilized hay will not undergo this
heating, while the same sterilized hay, if inoculated with certain
species of microorganisms (Oidium), will show a rise in temperature
apparently identical with the self-heating. This would clearly
indicate that microorganisms may be prominently concerned
in the process. But the sterilizing kills the plant cells so that the
respiratory changes are stopped, and also destroys most of the
enzymes present. Hence the fact that sterilized hay will not thus
heat is no proof that microorganisms alone are concerned in the
phenomenon. Further, it is extremely improbable that bacteria
or molds could develop heat sufficient to kill themselves, still less
sufficient to cause a spontaneous combustion. No experiment with
organisms has given a heat higher than 160° as the result of their
action. Hence, the extreme heat must be due to other causes.
Probably this fermentation, like many another, is of a mixed nature.
T^he moist grass still contains some living cells that for a time
remain alive and carry on respiratory processes; the enzymes in
the grass probably also start some chemical action and, lastly, the
microorganisms on the grass, by their growth, add to the fermenta-

PRESERVATION BY DRYING. 24I

tive changes going on in the hay. As a result of all three, the
temperature rises.

This self-heating is utilized in some countries to cure the hay.
The grass is built up into a stack or rick 13 to 16 feet high, and
16 to 24 feet in diameter. It is well trodden down, but not firmly
packed, and the whole stack is thatched so as to shed the rain.
In such ricks a spontaneous fermentation sets up and the mass
becomes heated. The temperature frequently rises as high as
160° F., but not much higher, and there is no danger of spontaneous
combustion. The rick is not opened, but the hay remains in the
mass until the farmer wishes to use it. It is immaterial whether
the hay is rained on or not, and this makes the process especially
adapted to rainy districts.

The fermentation which takes place in these ricks produces a
great change in the nature of the product. It becomes a firm,
dry mass, of a pale or dark brown color or, if the heating is too great,
it may be almost black. It has developed at the same time an
aromatic odor which resembles freshly baked bread. There
develops also a large amount of lactic and butyric acids, the amount
of lactic acid being as high as 7 per cent, and the butyric acid over 2
per cent. These acids are derived chiefly from the carbohydrates,
as is shown by the great reduction in the amount of these bodies in
the drying hay. A considerable part of the nitrogen material is also
lost, the total loss in the hay being about 14 per cent. This loss of
material is one of the objections to this method of curing hay.
It is known as brown hay.

Sometimes a slightly different method is used. The freshly
mown grass is piled in heaps from 10 to 13 feet high, the mass being
trodden down as tightly as possible to prevent the admission of
air. The temperature in these heaps rises rapidly, and is tested
by a thermometer. When it rises to about 158° F., which occurs
generally in from 48 to 60 hours, the heaps are opened and spread
out in thin layers to the air. The heat in the hay now rapidly dries
the product and, with a single turning, it is ready for storing. Hay
thus prepared is called burnt hay, and develops an aromatic odor
which ordinary sun-dried hay does not possess.

242 THE PRESERVATION OF FOOD PRODUCTS.

Lastly, it should be noticed that ordinary sun-dried hay will
sometimes, especially if stored in too moist a condition, undergo
a similar heating in the mow. The hay may be considerably
injured by such heating, so that it will lose some of its nutriment.
Sometimes the heat is sufficient to cause an actual igAition of the
hay.

Certain phenomena sometimes seen in cotton are clearly closely
akin to the fermentation just described, for cotton may undergo a
spontaneous heating sufficient to render it in danger of combustion,
and this must be due to processes similar to those just mentioned.
The same thing is true of hops which occasionally develop a like
spontaneous heating during the curing.

PRESERVATION BY COLD.

All the common species of bacteria grow more slowly as the
temperature is lowered, and cease growing entirely when it reaches
freezing. The nearer to freezing a fermentable substance is kept,
the greater the delay of the bacterial growth. In the large cold-
storage houses the food which is to be preserved may be cooled
to a temperature below freezing, and is, consequently, actually
frozen. At this temperature the bacteria never act and the material
may be kept indefinitely, although it is claimed that some molds
can grow at temperatures below freezing. It must be remembered,
however, that the low temperatures do not kill the bacteria, but
simply delay their action, and as soon as such food products are
warmed, the bacteria immediately begin to grow. Indeed, food
spoils very rapidly when taken from cold storage.

Where such low temperatures are not feasible, a moderate de-
gree of cold may check bacterial growth and delay putrefaction.
An ice chest usually maintains a temperature below 50°, and this is
very efficient in helping preserve food. A cool cellar answers the
same purpose, as well as the common plan of placing milk and other
foods in cold water to delay the spoiling. Fruits are particularly
benefited by these cool dry temperatures, and a cellar which has a
fairly uniform and low temperature is of great value on the farm in

PRESERVATION BY THE USE OF CHEMICALS. 243

helping to preserve fruits and vegetables that would otherwise soon
spoil. The value of ice as an aid in keeping all sorts of perishable
material is too fully understood to require further notice.

PRESERVATION BY THE USE OF CHEMICALS.

Many chemical substances are destructive to bacteria, and foods
may frequently be protected from bacterial action by the addition of
small quantities of some material, harmless in itself, yet having
a checking action upon bacteria. Such agents are called preserva-
tives. If they are to be used in the preservation of food products, it
is of course necessary that they should not be deleterious to health
and also that they should not impart disagreeable flavors to the food.
The number of substances that can be used without hesitation is not
very great.

The more powerful antiseptics, like carbolic acid and corrosive
sublimate, are, of course, out of the question. Certain milder ones,
borax J boracic acid, salicylic acid, formalin and benzoic acid, are more
or less extensively used. There are on the market various com-
mercial preservatives, Preservaline, Anti-fermentine, Freezine, etc.
These several articles have different compositions, but all are wholly
or in part made up of the substances named, most of them being
either borax or formalin. They are undoubtedly efficient in pre-
venting putrefaction and decay, for they are antiseptics, and if used
in sufficient quantity will stop bacteria growth. They have been
widely used in meats and in milk.

But the question arises whether they are not injurious to health.
Each is injurious to man if taken in sufficient quantity. Are they,
then, objectionable in the small quantities used in preserving food ?
This question has led to much experimenting, especially by the
U. S. Department of Agriculture. The general result of these exten-
sive experiments is to show that these preservatives, when used in
small amounts day after day, are injurious, although this conclusion
is still disputed. Hence, the general conclusion is that the pre-
servatives in question are to be condemned. They are certainly
illegitimate, and, since the same results can be reached in another

244 THE PRESERVATION OF FOOD PRODUCTS.

way, there is no excuse for their use in any ordinary food products.
They are especially to be condemned in milk.

NON-POISONOUS PRESERVATIVES.

Salt. — Salt is not an antiseptic in any proper sense and it does
not destroy bacteria. But it may be a preservative and when much
of it is present in a solution, it has a decidedly repressing action upon
bacterial growth, and may stop the ordinary putrefactive changes.
When used in the preservation of butter and fish, it also has the
advantage of imparting a relish to the product. It is in general use
for the preservation of flesh of various kinds. Flesh which is to be
smoked is commonly first salted, the salt adding to the efficacy of
this method of preservation. Salt pork is pork preserved in strong
salt brine, and corned heef and corned bacon are preserved in much
the same way. Ham is partly preserved by salt, and fish wholly
so. Butter and cheese both have their keeping qualities increased by
salt. But salt used in this way does not kill the bacteria, and any
flesh that contains injurious organisms, bacteria or others, is not
rendered wholesome by salting.

Sugar. — A moderate amount of sugar checks most bacterial
growth, and a large amount even stops yeast growth. Sugar, there-
fore, is widely used as a preservative. Since it is in itself a good
food there can be no objection to its use as a preservative, although
it always changes the taste and nature of the product. Condensed
milk may contain 30 to 40 per cent, of sugar. Jellies, preserves, jams,
marmalades are all fruits prepared in various ways and mixed with
more or less sugar as a preservative. Raisins, figs, and prunes are
whole fruits partly dried and preserved by the drying and the
large percentage of sugar contained in them. There are practical
difficulties in the way of using sugar with some foods, but with
others it has its value.

Vinegar. — Acetic acid is another legitimate food preservative,
and is extensively used in the manufacture of pickles. The acid
gives a sharp taste to the pickles and also largely prevents the growth
of the common putrefying organisms. The vinegar is frequently

PRESERVATION BY CANNING. 245

mixed with spices, both for the purpose of adding flavor and of aid-
ing in the preservation. Vinegar pickles will not keep indefinitely, for
after a time a scum grows over the surface. This is made of micro-
organisms which gradually weaken the strength of the vinegar until
the final decay of the pickles is only a matter of time, unless precau-
tion is taken to prevent the deterioration of the vinegar.

Spices. — Many common household spices are more or less
efficient as antiseptics and tend to delay putrefaction. In some
kinds of pickles spices are used, and mince meat, sausages, and
highly spiced fruit cakes are preserved chiefly by the spices they
contain.

PRESERVATION BY CANNING.

One of the most important methods of preserving perishable
food products was invented a century ago, long before the signifi-
cance of bacteria was known and long before the meaning of the
process was understood. It was invented by Appert, a Paris con-
fectioner in 1810, and consisted first in boiling the material to be
preserved and subsequently sealing it hermetically. It was at first
supposed that the significance of the sealing was to prevent the access
of air, but it is now known that its purpose is simply to prevent the
entrance of bacteria; for if these can be kept out, the presence of air
does not interfere with the preservation. It is interesting to note
that this method of preservation of food products was invented and
put to a wide practical use while scientists were disputing and labori-
ously experimenting over the problem of spontaneous generation.
The experiments by which scientists tried to settle this question con-
sisted in exactly the same devices as just mentioned, viz., the heating
of various organic materials to a high temperature in order to kill all
living organisms and then, after hermetically sealing, watching to
see if life developed in the sterilizing mass. While the scientists
were disputing as to the results, the method of canning was put into
practical use, and every can of preserved fruit was evidence against
spontaneous generation.

The general method adopted in canning is well known. Micro-

246 THE PRESERVATION OF FOOD PRODUCTS.

organisms are so abundant everywhere that every bit of food is
certain to be infested with them. The first step taken must be
the killing of all the organisms that may be adhering to the food to
be preserved. This is done by heat, the material being commonly
placed first in the receptacles in which it is to be finally sealed. The
amount of heat necessary varies much with the nature of the
material. If it is of a proteid nature, like meat, beans, peas, or
corn, it is likely to contain spore-forming bacteria, and will require
high and prolonged heating. This is especially true of corn,
peas, and beans, since these materials contain such resisting spores
that it was once thought that they could not be successfully canned.
But modern methods of applying heat above the boiling tempera-
ture have made it possible to sterilize thoroughly even these resisting
substances, and their canning is now perfectly feasible. To-day
temperatures of 230° to 250° are commonly used for such materials.
In canning fruit, as a rule, such high heat is not needed, since
fruits are more often spoiled by yeasts and molds than by spore-
bearing bacteria, and these organisms are easily killed by simple
boiling, or by even less heat.

The second step is the sealing. This consists simply in closing
the vessel containing the sterilized mass in such a way as absolutely
to exclude the air and with it all microorganisms. It is sometimes
done in tin cans, when a small hole is left in each can so that the
air and steam may escape during the sterilizing, after which process
the hole is sealed by a drop of solder. Sometimes glass jars are
used, and these are sealed by covers pressed forcibly down upon
a soft rubber ring. The principle is the same in either case. The
sterilized food thus removed from any possible means of contamina-
tion will keep indefinitely.

The development of the canning industry does not belong to
our immediate subject, but certain facts connected with the matter
have produced great changes in the possibilities of agriculture.
It has made possible the utilization of a great quantity of food
products which otherwise could not be used. Certain of our fruits
are extremely palatable but very perishable, and if it were necessary
to use them fresh or in a dry condition, only comparatively small

■ PRESERVATION BY CANNING. 247

quantities could be raised. For example: before the beginning of
tomato canning, only a very small crop could be utilized; but the
opening of this canning industry has entirely changed the conditions,
and now great tracts of land can be devoted to raising this delicacy,
thus opening to the farmer an entirely new outlet for his crop. The
same is true of many another farm product. It is no longer neces-
sary for the farmer to depend upon his own market, but, by the aid
of canning, his market may be the world, open to him the whole
twelve months of the year. The canning industry makes it possible
for the farmer to become a specialist, where it was impossible a
few years ago. He may raise green corn, or tomatoes, or straw-

A/ / O.°°'o°»

i»

.-•-^

Fig, 50. — Three species of bacteria causing the spoiling of canned corn
{Prescott and Underwood).

berries as abundantly as he pleases, and whatever he cannot find
an immediate market for may be preserved for a later season by the
process of canning. It is well for the agriculturist to learn that
in farming, as in all other industries, it is the specialist who succeeds,
and that the proper utilization of the process of canning is one of
the means of making a special product upon a farm yield proper
returns. Canning makes possible an intensive farming, undreamed
of a few years ago.

The present condition of the canning industry has been reached
only after years of experience, accompanied with many failures and
losses. Whole shipments have sometimes been ruined by " swelling,"
which means that the cans swell out from the force of the putrefying
gases forming within. The failure to appreciate the difl&culty of

248 THE PRESERVATION OF FOOD PRODUCTS.

killing bacteria spores has caused great losses of canned corn, peas,
and beans, as well as tomatoes. It must be recognized that, for
successful canning, every spore must be killed; for if a single one
be left alive in the middle of the can, the product is sure to spoil
(Fig. 50). The slowness with which heat will pass to the middle of
the can was not recognized until many losses had resulted from
insufficient heating. But the failures proved instructive, and after
bacteriologists studied the different problems presented by the
attempts to can food stuffs, the questions were answered one by
one, and successful rules were devised for the canning of any food
products subject to such methods. To-day failures are rare and
are all attributable to carelessness in the process. So thoroughly
has this subject been mastered that to-day any food that can stand
heat may be perfectly preserved by boiling and canning. Of course
the flavors are commonly changed by the process, and few of them
appear like the fresh material. But usually the flavors are less
changed than by any other method of preservation, and canned
goods are vastly superior to the dried foods with which our grand-
fathers were forced to be content in winter. Canning is especially
adapted to foods containing a good deal of water, and hence is
of especial use among foods that cannot be well preserved by drying.
Fruits are well adapted to canning, but ill adapted to drying, and
are ruined by salting.

BACTERIA IN EGGS.

The presence of bacteria in eggs results in trouble experienced
by every farmer, and one which it seems impossible to avoid.
It might be supposed that eggs, when freshly laid, would be free
from bacteria and hence not liable to decay. But this is certainly
not the case. Bacteria are known to enter the oviduct and contami-
nate the mass of the egg even before its shell is deposited. Hence
when the egg is laid it will commonly contain bacteria in greater or
less numbers. These bacteria can obtain plenty of oxygen from
the air that enters through the porous shell, and are thus able to
grow readily within the egg, where they soon cause its decay. A

BACTERIA IN EGGS. 249

bacteriological study of eggs has shown quite a number of different
bacteria in perfectly whole eggs, freshly laid, and there seems
to be no possible means of avoiding them completely. Even
after the shell is deposited and the egg laid, bacteria are capable
of entering it. The shell is somewhat porous and it has been
proved by experiment that bacteria can pass through the pores.
In short, the egg must be looked upon as a highly nutritious food
product, in most cases already inoculated with bacteria, and a
body which is practically suie to undergo decay in the course of
time. There are fewer bacteria in winter eggs than in those laid in
summer, and the cleaner the nest the less the bacterial contam-
ination.

It is, however, possible, by certain devices, to delay or prevent the
growth of bacteria in the egg. The bacteria found in eggs do not de-
velop at low temperatures and the eggs may be kept almost indefi-
nitely at a temperature of 34°. But since cold storage is not always
available, other methods must usually be adopted. One of the
simplest and best is by the use of water glass, a material made of
sodium and potassium silicate. This may be purchased cheaply
in the form of a thick syrup. It is then mixed with nine parts
of water and placed in clean stone jars. The eggs are placed in
the mixture and the whole set aside in a cool place. If the tem-
perature is not allowed to rise above 60° the eggs may be kept from
decay for a long time by this method, many weeks and even months
elapsing before they will decay. In preserving eggs in this way it is
important to know that April eggs will keep better than May eggs
and these better than June eggs, while eggs laid in the hot months
of the summer are less easily preserved, a fact probably due to a
greater bacterial contamination during the warmer months. From
this it will follow that the June storage eggs should be used first
and the April preserved eggs last.

Eggs thus preserved will keep from decay, but they will lose their
fresh taste. Indeed, this fresh flavor disappears in a very few days
and there is no way known by which it can be retained for very long.
But after the fresh taste is gone the eggs will remain without further
change for a long time and be usable.

250 THE PRESERVATION OF FOOD PRODUCTS.

BACTERIA IN THE SUGAR INDUSTRY.

A brief mention should be made of the relation of bacteria to the
sugar industry, which is an important phase of agriculture. The
relation of microorganisms to this industry is, according to our
present knowledge, only one of injury. After the product has been
harvested, bacteria may produce subsequent injury within it, giving
rise to well-known troubles. One source of trouble experienced in
sugar-making consists in the appearance, at various stages of manu-
facture, of jelly-like masses which may become very abundant and
troublesome. This has long been known and has been studied by
bacteriologists for many years, with the result of proving that it is
caused by the appearance and development of certain species of bac-
teria. ■ Several species are known and have been carefully studied,
al 1 of which have the power of producing a slimy section which gives
rise to the jelly-like masses in the sugar product. The slimy secre-
tion appears to be developed from the sugar, a conclusion proved
by the fact that the same microorganism, when growing out of con-
tact with sugar, develops no slime. A second trouble is in the loss
of sugar by inversion. This occurs in unrefined sugar during stor-
age or transportation, and is due to a bacterium that has been
isolated and tested.

PART V.

CHAPTER XVII.
PARASITIC BACTERIA.

RESISTANCE AGAINST PARASITIC BACTERIA.

We have learned that microorganisms may be both useful and
harmful. If they grow where they are wanted, they are useful;
but if they grow where they are not wanted, they produce many
undesirable effects. They spoil foods by causing their putrefaction,
they destroy vinegar by consuming the acetic acid. In wines the
growth of mischievous microorganisms causes a variety of bad
results that are sometimes spoken of as "diseases of wine," and we
also hear of " diseases of beer." But there is no good reason for the
use of the term here any more than in speaking of the diseases of
butter and cheese, when unusual bacteria cause them to ripen
abnormally.

In most of the examples thus far studied the material upon which
the microorganisms grow has been supposed to be lifeless, the
bacteria existing as saprophytes. There remains the study of these
organisms when growing upon the living tissues of animals, thus
living the life of parasites. In the latter case they may do injury to
the animal or plant upon which they live, thus becoming pathogenic,
or disease germs.

HOW MICROORGANISMS PRODUCE DISEASE.

When they multiply inside the body, microorganisms show very
different habits. Sometimes they become distributed over the
whole body, located at no particular spot (blood poisoning), while in
other cases they may be definitely localized at some one place

251

252 PARASITIC BACTERIA.

{diphtheria). Between such extremes there are many intermediate
types. Whenever the microorganisms muhiply in the body they
produce chemical changes, just as they do elsewhere. New chemi-
cal bodies are secreted by them and among these, in the case of
disease germs, there are some that are poisonous in their nature.
Such substances are called toxins. Wherever they are produced
they are liable to be absorbed by the blood, and the body may thus
be directly poisoned by them. If the bacteria are in the blood it-
self, this poisoning is easy to understand, but localized diseases are
similarly explained. Diphtheria, for example, is produced by
bacteria growing on the inside surface in the throat. The bacteria
themselves do not enter the body, but, growing in the throat, they
develop very powerful toxins, and these are absorbed into the blood,
producing a general poisoning of the whole body. All disease
germs produce poisonous materials which are absorbed by the
body, and these cause the direct injury characteristic of the various
diseases.

RESISTANCE AGAINST MICROORGANISMS.

A very large majority of microorganisms are quite unable to live
within the bodies of living animals or plants, and therefore are not
parasitic. If common putrefactive bacteria be inoculated into the
blood of a living cow or into her flesh, they will speedily die without
multiplying, disappearing in a very short time. If these same
bacteria are inoculated into the same animal after it is dead, they
will grow with rapidity, quickly causing the flesh to putrefy. Why
is there this difference ? The complete answer to this question is one
for which bacteriologists have long been searching, but have as
yet only partly found. A partial answer is that the living tissues
contain substances that are injurious to the bacteria. What these
substances are, how they act, why they disappear after death, and
numerous other questions concerning them are among the most
important of the problems before bacteriologists to-day. With these
complicated questions, however, we are not concerned in this work.

It is evident enough that some kinds of microorganisms can

RESISTANCE AGAINST MICROORGANISMS. 253

overcome this resistance, otherwise there would be no parasites.
These, capable of living and multiplying in the body, may produce
injury and are the disease germs. Fortunately, the number that
can thus live is small. Many hundred kinds of bacteria have
been discovered, carefully studied, and described in bacteriological
literature. We have no idea how many varieties exist in nature,
but there are certainly hundreds, and perhaps thousands. Of
these only little more than a score are known that can produce disease
in man and animals, and a somewhat larger number that can produce
disease in plants. A few yeasts occasionally produce similar troubles.
Quite a large number of molds, as parasites, give rise to disease in
plants, and a very few cause trouble in animals. The great host
of bacteria and other fungi live upon dead matter, and cannot
live as parasites. They may spoil foods, and destroy wines, beer,
butter, cheese, and other valuable substances, but they cannot
produce disease, since they are not able to overcome the resistance
offered by the living tissue.

The body has a resisting power against all kinds of micro-
organisms, disease germs as well as the non-parasitic species,
although, in the case of the former, it is insufficient to prevent their
invasion. Against the common saprophytes it is perfectly efficient;
against some parasitic bacteria it is moderately efficient and will,
in many cases, prevent the development of the disease, even after
the parasitic bacteria have entered (tuberculosis); against other
bacteria the resisting power is extremely slight (anthrax). The
resisting power varies with different species of animals, some
having the power of absolutely resisting certain bacteria, when we
call them immune. Man is immune against hog cholera, while
the hog is not. It also varies with the individual, some members
of a species having the resisting power highly developed, while
others yield easily to invasion. This we speak of as individual
resistance. The resistance varies also with the vigor of the germs.
Some epidemics of measles, for example, are mild and some severe,
and a person's resistance against an attack is partly dependent upon
the vigor of the germs.

Now, this resisting power is clearly located in the living cells of

254 PARASITIC BACTERIA.

the body and is dependent upon their normal functions. It is only
the living cell which can resist the invasion of microorganisms,
either wholly or partially. From this it follows that the resistance
will be greatest when the body cells are in the highest state of
physical activity, and will diminish when they become somewhat
impaired in vitality. Anything which tends to reduce the physical
health of the individual tends to reduce his power of resistance.
For example: sometimes an individual shows a great tendency
to develop boils or abscesses, and but little power of resisting them.
We say his "blood is in a bad condition." By this is really meant
that his body activities are so repressed that he is unable to resist
the invasion of some of the common bacteria which are present on
every hand and which an individual in healthy condition easily
repels. If his physical vigor can be restored, the troubles will
disappear, although the bacteria which produce the boils and
abscesses are just as abundant around him as before. Physical
vigor is the best protection against the invasion of parasitic bacteria,
and a weakened physical condition invites attack.

This matter is emphasized here because it is too generally lost
sight of in the combat against infectious diseases. During the first
years of the study of bacteriology there was a very general tendency,
in the attempt to avoid diseases, to place the whole emphasis
upon the methods of avoiding bacteria. If a disease is caused by a
bacterium, what more natural method could be suggested for
avoiding it than to avoid the bacterium? In accordance with this
idea there developed a long series of rules and regulations suggested
by bacteriologists and adopted by health boards, all designed for
the prevention of the distribution of disease germs. This is,
indeed, the foundation of modern sanitation.

Increasing of Individual Riesistance. — Recently there has
been a manifest reaction against this one-sided attitude. While
the importance of preventing the distribution of bacteria is still
acknowledged, there is to-day a growing recognition of another
side to the question. The strengthening of personal vigor is of no
less importance — many believe it is of more importance — than
the preventing of the distribution of bacteria. The weakening of

RESISTANCE AGAINST MICROORGANISMS. 255

personal vigor will do tnore toward increasing germ diseases than
a relaxing of the rules which try to prevent the distribution of
bacteria. Personal resistance of the individual will enable him to
repel many an attack of disease bacteria, even if he has been directly
exposed to them, while a weakened resisting power may result in
his yielding to the first attack of an invading bacterium. For some
of the less violent diseases (tuberculosis) this is much more emphatic-
ally true than for other diseases (anthrax). Now, it is not possible
to hope that we shall ever be able to exterminate all pathogenic
bacteria; even if we did, other forms would doubtless take their
places. Since we cannot exterminate them, it follows that all
individuals will, at some time, be exposed to the attacks of some
of the disease germs. Manifestly, then, the best means of elevating
the healthfulness of the race is to raise the resisting power, at the
same time doing our utmost to destroy pathogenic bacteria.

These facts are equally true, whether we are dealing with animals
or with man. It is of more importance for the farmer to understand
them when he endeavors to make a fight against the diseases
of domestic animals than it is for the physician or the veterinarian
who tries to cure the disease. With animals, as with man, the
individual resisting power is variable. When a lot of pigs are
attacked by that very fatal disease, hog cholera, some of them
escape with no signs of the disease, showing a superior resisting
power. Undoubtedly the resisting power of animals is due to a
proper physical vigor, little understood, but plainly dependent
upon proper conditions of life. Let the conditions be normal,
and the animal may resist the attack of parasitic bacteria; but let
them become abnormal, so as to reduce vitality, and the animal
is much more likely to succumb.

Tuberculosis, for example, is much more prevalent among
cattle that are kept stabled most of the time, than among those that
spend a considerable portion of the time in the open air. This may
be due, in part, to the fact that stabled cattle have a greater chance
of acquiring the contagion, since they are kept so close together.
But this is certainly not the whole reason. Young cattle that are
kept in the open for a year or two are less liable to take the disease

256 PARASITIC BACTERIA.

than those kept in the stable, even though subsequently they are
put under similar conditions. In localities where the animals run
out of doors all the time the disease is rare. The more closely they
are housed the greater the tendency to this disease, and it is practi-
cally certain that this greater tendency is not because they are so
much more likely to be infected, but because of the depressing in-
fluence which such a restricted life has upon the vitality of the
animals, reducing their resisting powers. It is also a general be-
lief that highly bred cattle have a greater tendency to this disease
than less highly bred stock. Stated in this way the conception may
not be correct; but it is practically certain that animals which have
been bred for the purpose of producing great quantities of milk are
rather more likely to yield to the disease than those not so highly
specialized. Such a specialization of the vitality in the direction of
an abnormally high action of the milk glands cannot fail to be at the
expense of other vital functions. These breeds have been developed
in one direction until they have become abnormal. It is not to be
wondered at if such an abnormal development should have resulted
in the reduction of their general vitality, and of their resisting power
against disease. It is the active, vigorous cow, which produces,
perhaps, but little milk and is not carefully housed by the farmer
that has the power of resisting disease. In short, the prevalence and
the increase of some of the diseases of domestic animals must be
attributed, in no inconsiderable measure, to the introduction into
our herds of conditions of life which lessen their resisting power,
and not wholly to the increasing chances of contagion due to close
contact of animal with animal. That the latter phenomenon is
also a factor is, of course, evident.

The conditions of life among domestic animals are, to a very
large degree, under immediate and perfect control. We can regu-
late the amount of outdoor life they have, their activity, their food,
their drink, and many other factors upon which their physical
vigor depends. We may keep the cow housed so that she has
little air; we may give her highly stimulating food with practically no
chance to use her muscles; or we can make quite a different animal
of her by changing her life and food. We can control the conditions

ACQUIRED RESISTANCE. 257

of life among animals far better than we can, or will, those of our
own life. In the conditions of civilized life each individual de-
mands his personal freedom in regard to matters regulating his own
affairs, and he absolutely refuses to be guided by rules and regula-
tions, even though he may know them to be for his best physical
good. No matter how good rules for living our physiologists may
make, they cannot force people to adopt them. But the farmer has
absolute control over the life conditions of his stock. He can
regulate their life as suits him, and he can, if he will, work out among
cattle the problem of health and disease as it cannot be worked out
among men. He may, by breeding, produce animals with some
valuable feature most extremely developed, but in so doing he
must remember that he is producing abnormal animals that are
likely to have little resisting power against disease. He may feed
them with stimulating food and force them in lines which suit him;
but he must bear in mind that there is a limit to the possibilities,
since all of these methods of treatment lead to abnormal conditions
and to greater liability to disease.

The adoption of precautions for preventing the distribution of
disease germs is doubtless a matter of very great significance; but of
more significance still is the endeavor so to modify the conditions of
life as to increase their resisting power against these bacteria. In
every case, doubtless, the plan adopted will be by the way of. com-
promise, and will be such as to give the greatest amount of physi-
cal vigor consistent with the ends which the farmer has in view in
his use of the animals. To turn them out into the fields with no
attempt to produce special types, and with no high feeding, would
doubtless produce a vigorous breed, but it would not produce milk.

ACQUIRED RESISTANCE.

Some species have a perfect resistance to the diseases that other
species will take, a condition called race immunity. Some individuals
will resist a disease that others of the same species cannot resist, and
this is individual immunity. An individual may also develop a
resistance to a disease which he did not at first possess. This is

258 PARASITIC BACTERIA.

acquired immunity. It has long been known that if a person has one
attack of certain diseases and recovers, he is, for a time at least,
protected from a second attack of the same disease. It is not common,
for example, to have scarlet fever twice, and the same is true of a
number of other diseases. This acquired immunity is, however,
quite variable. In some cases it is almost a perfect protection for
life, or at least for many years. With other diseases it is weaker,
affording only a partial protection and lasting only a few months or
perhaps only a few weeks. The question of what causes this ac-
quired immunity is closely akin to what causes race or individual
resistance. Doubtless the two are closely related and are probably
attributable to the same general cause. For our purpose it is only
necessary to know that recovery from one of these diseases leaves
the individual with his body filled with substances capable of re-
sisting the kind of bacteria that produced the disease. As long
as these resisting substances are present the individual will have
immunity.

It is somewhat surprising that recovery from a mild attack of one
of these diseases gives as much immunity as recovery from a severe
attack. Hence, with this principle in mind, the question has arisen
whether it may not be possible to give an individual a mild case of
some of the more dangerous diseases in order to give him power to
resist the more severe and perhaps fatal types. This was first done
in the case of smallpox, which has for a century been fought upon
this principle, since the vaccination pustule seems to be essentially a
mild type of smallpox. Hence, when a person is vaccinated, he is
given a mild form of smallpox, and this guards him from a more
severe attack. That vaccination is a protection against smallpox
is pretty generally admitted to-day, although some deny its power.

But whatever be the facts in regard to smallpox, there is no
doubt at all in regard to the successful application of this principle
to other diseases. Pasteur was the first to attempt an application
of this principle to a disease other than smallpox. He was at the
time working upon a serious disease of cattle — anthrax; one that
is practically always fatal. He argued that if he could find
means for producing a mild type of the disease, he might protect

ACQUIRED RESISTANCE. 259

the herds from the severe and fatal infection. But to induce a
mild attack was not easy. It would do no good to inoculate an
animal with a small number of the bacilli which produce the disease,
for these, by multiplying, would soon become so numerous as to
bring about a severe attack of the disease. It was evident that
this end could be reached only by weakening the power of the dis-
ease-producing bacilli. After continued experimenting he finally
accomplished his purpose by cultivating the bacilli at a temperature
somewhat above that at which they make their best growth. By
the use of a temperature of io8° F. he obtained cultures that were
so weak as to be unable to produce a fatal disease, even in suscep-
tible animals.

After reaching this result Pasteur, by an ever memorable
experiment, demonstrated to the world the possibility of combating
infectious diseases by the use of what are now known as weakened
cultures. He inoculated half of a lot of fifty susceptible animals,
including cattle and sheep, with his weakened virus. The animals
were slightly indisposed, but suffered no evil consequences. In a
few days he inoculated them with a second, stronger culture, with
a like harmless result. Having thus prepared these test animals,
he summoned to a public experiment an assemblage of noted men
in Paris, and, in the presence of them all, inoculated the entire
fifty animals with the strong infectious material taken from an
animal dead from the disease. Two days later the company
assembled again to find all of the unprotected animals either dead or
dying from a violent case of anthrax, while of the protected animals
not a single one showed the slightest evil result from the inoculation.

A more beneficial discovery has hardly ever been made. From
the date of Pasteur's experiment a constant succession of bacteri-
ologists has been trying to apply the same principle elsewhere.
We cannot here attempt to follow the development of the work,
but can only state that practical results of the utmost value have
been obtained. It has not been found possible to use just the same
method in other diseases that Pasteur used, but by a modification
of it, or by others that have come from it, it has been found possible
to withdraw the terrors from some of the most dreaded diseases.

26o PARASITIC BACTERIA.

The human diseases diphtheria, lock-jaw, bubonic plague, cholera,
and hydrophobia have either been mastered or at least mitigated
by discoveries that have come from the study which Pasteur started ;
while among animals at least two diseases are controlled by prevent-
ive inoculation — anthrax and black leg. Some success also has
attended similar methods with tuberculosis.

MICROORGANISMS THE CAUSE OF DISEASES.

The studies of the last twenty-five years have demonstrated that
the majority of diseases in animals and plants are produced by the
growth of parasites of some kind, and mostly by what may be called
microorganisms. Bacteria, yeasts, and molds are all concerned and,
in addition, some diseases are produced by microscopic animals.
The subject of germ diseases has become one of very wide range
and cannot be considered to any great length in this work. The
discussion of such diseases among animals belongs to veterinary
medicine, and of those among plants to botany. In our general
consideration of microorganisms as related to agriculture, we can
review only the important principles involved, and give a brief
survey of the more important diseases.

CHAPTER XVIII.
TUBERCULOSIS.

Of all germ diseases there is none so widely distributed as
tuberculosis. Not only is it of great significance from the stand-
point of human health, but it is the one disease of domestic animals
which demands almost universal attention and interest. Tubercu-
losis among cattle forms one of the most serious problems of
agriculture.

Cause of the Disease. — The organism which produces this
disease was first described by Koch in an epoch-making monograph
published in 1882. Koch first
isolated the bacterium from the
sputum of consumptive patients,
and subsequently found it in
abundance in animals suffering
from certain diseases now known
to be forms of tuberculosis. The
organism itself appears com-
monly in the form of a short,
slender rod (Fig. 51). Although
commonly called Bacillus tuber-
culosis, it cannot properly be
called a Bacillus, since it pos-
sesses no flagella.* (see page
12). Although this organism
does not form spores, it has a

considerable resistance against heating and even drying. It may be
dried, and yet remain alive for months, without losing its power of

* Recent studies have shown that the organism may show blanching
which is not the case with any true bacteria. It has been suggested that
it should be placed in a special family named Myxobacteriae, It will
doubtless retain the name B. tuberculosis.

261

Fig. 51. — Tuberculosis bacillus, a, in a
bit of animal tissue; b, showing irregu-
larities resembling spores; c, typical ap-
pearance of the bacilli from ordinary cul-
tures.

262 TUBERCULOSIS.

growth. It will withstand the heat of 140° for fifteen minutes or
more, and under some conditions a considerable higher heat. A few
minutes' heating at 1 75° will, however, kill it. Unlike many bacteria
the tuberculosis organism is quite limited as to the conditions under
which it can grow, and an understanding of these conditions is of
the greatest importance in comprehending the problems of its
distribution. The temperature limits within which its develop-
ment is possible are quite narrow. It grows best at a temperature
between 96° and 105° F., but it will grow more slowly at a tempera-
ture as low as 84° F. Below this it will not multiply at all. At
first it was supposed that it would not grow in any artificial medium
which could be prepared in the laboratory. In his original experi-
ments Koch was obliged to use coagulated blood serum as a culture
medium. It is now found that it can live and flourish in a variety
of culture media, provided a certain amount of glycerin be added.
It was at first said to be a perfect parasite, by which term is meant
that it would not live under any conditions except those of a warm-
blooded animal, demanding both a temperature and a medium
equivalent to the blood of such an anmial. But here, too, bacteriolo-
gists have changed their views, for the tubercle bacillus will grow
in many laboratory media and under conditions very different
from those of the living body.

The facts just enumerated are of the greatest significance as
indicating the possibilities of distribution of this disease. If the
bacillus can live outside the bodies of animals, we may look to
various places in nature as a source of infection, but if it demands
for its existence conditions of the living body, we may look to
animals alone for its source. Now, although it can grow under con-
ditions quite different from those of the living body, nevertheless, so
far as our present knowledge goes, the tubercle organism does not
grow outside the bodies of animals under any normal conditions. It
does not grow in water or in milk, two facts of the utmost im-
portance in understanding its distribution. It is true that the
bacillu^may frequently be found alive outside the bodies of animals.
It occurs in sputum, in milk, in water, in dust, etc., but in these
media it does not multiply, at least under any conditions to which

TUBERCULOSIS. 263

they are normally subjected, and we must therefore conclude that
its multiplication is confined to the bodies of animals. While it can
flourish in the artificial media of the laboratory, when kept at
special temperatures, it does not flourish in nature, outside the
bodies of animals upon which it lives as a parasite.

Animals Subject to the Disease. — Besides living in man the
organism can flourish in the bodies of cattle, hogs, dogs, cats, monkeys,
rabbits, guinea-pigs, and some other animals. In all these it pro-
duces very similar symptoms, differing slightly, of course, in the
different animals. The characteristic feature of the disease is the
production of tubercles — swollen masses of tissue — which eventually
break down into a cheesy mass. These tubercles may appear at
almost any part of the body. Of all the animals the guinea-pig is
the most delicately susceptible to the bacillus. An extremely small
infection will produce the disease in the guinea-pig, and for this
reason these animals are used in experiments to test the presence of
the bacillus. A little suspected milk inoculated under the skin of
the guinea-pig will produce the disease inevitably, if only the smallest
number of virulent germs are present. Besides these mammals a
number of birds show a similar disease, with a similar bacillus
present in the infected organs. The bacillus in birds is, however,
in some respects, slightly different from that in men and cattle, and
is frequently regarded as a different type of the organism.

Most parasitic bacteria are able to grow only on certain parts of
the body, diphtheria commonly in the throat, cholera in the intestine,
etc. But the tubercle bacillus can live in almost any part. It is
found in the intestinal organs, in the lymphatic glands, in the lungs, in
the bones, in the joints, in the kidneys, in the skin, and, in short,
almost anywhere. When occurring in the different organs in man
it receives different names; consumption, scrofula, lupus, hip disease,
nephritis are some of its common names.

Resistance Against Tuberculosis. — Although this organism
can attack almost any part of the body, it is also certain that the
body has a strong resisting power against it. It by no means follows
that a person will take the disease because some of the bacilli find
entrance into his body. On the contrary, as a general rule^ they

264 TUBERCULOSIS.

are soon overcome by the body resistance. Careful study has shown
that most people, by the time they have reached twenty-five years of
age, have not only been exposed to the disease, but have had mild
attacks, from which they have completely recovered. By building
up a proper physical vigor, an individual may successfully combat
these parasites. Plenty of wholesome, but not too rich food,
exercise, life out of doors as much as possible, sleeping in rooms
with windows open in winter as well as in summer, and deep breath-
ing exercises, by means of which the lungs are filled with fresh air,
are the means by which such resistance can be developed and main-
tained. All of these conditions are usually within the reach of
everyone, so that there is no reason why a person who will, cannot
develop a high resistance against this dreaded disease.

ARE BOVINE AND HUMAN TUBERCULOSIS THE

SAME?

Apart from its relation to the human being, the farmer is most
naturally interested in this disease, since it attacks his cattle.
Bovine tuberculosis is one of the most serious dangers, and threatens
the continuance of dairying.

The significance of the question whether human and bovine
tuberculosis are identical is self-evident. If the two are the same, it
will follow that the disease may pass from animals to man; if they
are not identical such transmission is impossible. For some fifteen
years after the cause of the disease was discovered, no question was
raised as to their identity. Both diseases are produced by bacteria
that appear identical, and that they were the same was taken for
granted. In 1900, however. Prof. Koch raised the question whether
they were not distinct, and gave experiments to show that the
human bacillus does not produce the severe bovine tuberculosis
when inoculated into cattle. The question caused intense interest
and much discussion, and in spite of many experiments designed to
settle the matter, there is still some dispute. A fair summary of the
facts as they appear to the majority of bacteriologists to-day is as
follows :

BOVINE TUBERCULOSIS. 265

Both bovine and human tuberculosis are caused by a bacterium
that has great similarity in the two animals. But there are slight
differences between them, both in microscopic appearance and in
methods of growth, sufficient to make it necessary to recognize them
as somewhat different types. When inoculated into animals, the
organism from the bovine source proves to be more virulent than
the one from the human source. The human bacillus, when
inoculated into cattle, generally produces only a slight trouble,
while the bovine bacillus is apt to bring about a progressive case of
the disease of very serious character. What effect the bovine
bacillus has when inoculated into man cannot yet be told from
direct experiment, but there appear to be a number of tolerably
sure cases of accidental inoculation of human beings with the bovine
bacillus that have been followed by a development of the disease.
The general conclusion is that, although the two are slightly different,
each may produce the disease in the other animal, and that the
disease is, therefore, transmissible from animals to man. While the
conclusion is still doubted by Prof. Koch, it is accepted by most
other bacteriologists. Whether the bovine bacillus is more virulent
for man than is the human bacillus, as it is for other animals, is by no
means settled. Furthermore, it is pretty generally agreed that
human tuberculosis comes more often from human sources than
from cattle.

BOVINE TUBERCULOSIS.

In recent years, owing largely to the feeding of swine with
creamery refuse, the disease is coming to be somewhat common
among swine. But it is among cattle that the trouble is most
widely distributed and of the most serious import. In cattle it
attacks chiefly the glands of the neck, the glands of the intestinal
tract, and the lungs. It may be located in the udder; and in these
cases the milk of the animal becomes a source of danger. For-
tunately, the percentage of cases of udderdisease is comparatively
small. In cattle it rarely attacks the bones, joints, or muscles.
23

266 TUBERCULOSIS.

METHODS OF DISTRIBUTION.

Tuberculosis is contagious. By this is meant that the relation
of the bacillus to the animal is such that there is an easy means
of communication between one animal and another under the
ordinary conditions of life. The knowledge of this fact in regard
to human consumption has been of great value, since it has been
followed by a steady decline in the amount of the disease. Such
knowledge has not yet reduced the amount of bovine tuberculosis.

We can easily understand the methods of contagion when we
remember that the bacilli are discharged from any of the open
tubercles. If the disease is located only in an internal lymphatic
gland it may not result in breaking down the gland, and there may
be no discharge. Under this condition there is no contagion from
one animal to another. But if it be located in the lungs the bacilli
will be discharged into the air passages and pass through the trachea
into the mouth. They will then infect all the discharges from the
mouth and nose. It is true that the cow does not expectorate, but
by putting her nose in the drinking trough she will be sure to con-
taminate the drinking-water, and when she licks another animal, as
she will be sure to do if she stands near others, she will leave some of
the bacilli clinging to the second individual, ready to begin their mis-
chief if they chance to get carried to a susceptible part, as they are
very likely to do by being swallowed. Moreover, since the cow does
not expectorate, she does swallow the secretions from her mouth.
The tubercle bacilli will thus be carried to the stomach, and through
the intestine, from whence they will be voided with the excrement.
If the disease is located in the intestine the bacilli will be sure to be
discharged with the excrement. In these ways the excrement of
tuberculous cattle is sure to be impregnated with the bacilli. Now
the conditions of the ordinary cow stall, even in the best cow barn,
are such as to make it almost inevitable that the infectious material
will soon be distributed through the whole barn. The excrement
may be carried over the floor, perhaps, for some distance to the
opening used for its exit, and the farmer's boots will always collect
more or less and carry it through the barn. The particles adhering

METHODS OF DISTRIBUTION. 267

to his boots will be sufe to be knocked off when dry, and will thus
be carried everywhere that the farmer goes. They will be certain
to be dislodged near a healthy cow and may become mixed with
her food which is commonly thrown on the floor in front of her; or the
particles may become dry and be distributed through the barn as
dust. In short it is inevitable that the bacilli voided with the
excrement will in time come in contact with every healthy animal
kept in the same barn.

Once distributed from infected animals, the bacilli may find
entrance into the healthy animals, by a variety of channels. Some
find entrance to the lungs, either by the dust particles or by the
bacilli-laden moisture drops from coughing animals, which are
breathed by healthy animals. The bacilli which find their way
into the watering trough will be swallowed, and the same will be
true of those which the animal takes into its mouth by licking its
infected neighbor. These two means of entrance are doubtless
responsible for most cases of bovine tuberculosis, and it is very
easy to understand how a single diseased animal in a barn may,
in time, infect most of the herd.

Abundance of Bovine Tuberculosis. — Tuberculosis is widely
distributed among cattle, although it is by no means universally
found in countries where cattle are kept. It is said not to occur
in Africa, and until recently it has been absent from China and
Japan, having lately been introduced with imported cattle. In
the western part of the United States, among the cattle living out
of doors most of the time, it is rare or absent. In general it is most
abundant in localities where the cattle are housed for a considerable
part of the year. It is consequently most abundant in northern
countries, and appears to be most widely distributed in northern
Europe.

It is practically impossible to state the percentage of cattle
suffering from tuberculosis. Among the animals examined in the
slaughter houses of Denmark it has sometimes appeared that more
than half of the cows are tuberculous. From these high figures
the percentage has ranged down to lo per cent, or even lower in
some places, and, in fact, is so variable that no general averages

268 TUBERCULOSIS.

are of any significance. In the United States the results differ
so widely that figures have, as yet, little value. Sometimes every
animal in a herd is found to be tuberculous, while other whole
herds are entirely exempt. In the eastern States the percent-
age is large, and in some localities it appears to approach the
figures given for Denmark. When the numbers of infected animals
in a herd range from o to loo per cent, it is evident that no resulting
average would be of any significance.

Increase of the Disease. — Is bovine tuberculosis on the
increase ? Statistics are so uncertain as to make any conclusion
difficult. Certainly we hear much more of the disease than we
did a few years ago, and the percentages reported to-day are much
higher. The knowledge of the disease is, however, of very recent
date, and the increasing interest in the subject has caused a more
and more careful inspection of slaughtered animals, which has
resulted in a constant increase in the number of reported cases.
Even in the same slaughter houses and under the same management,
the percentage of tuberculous animals reported has been increasing
year by year in such a way as to seem to indicate an alarming
increase in the last fifteen years. But a considerable part of this
increase is clearly due to increased experience and carefulness in
inspection. To what extent this factor explains it, and to what
extent there is an actual increase in the disease, no one can pretend
to say. It is, therefore, impossible to state whether bovine tubercu-
losis is rapidly or slowly increasing or remaining stationary.
But taking all facts together, the practical uniformity with which
the percentage of reported cases has increased in the last years,
has led to the general belief that the disease is actually and some-
what rapidly increasing among our herds.

But although no definite statistics can be given, either as to
the prevalence of the disease or its increase, bovine tuberculosis
is abundant enough. It presents a very serious problem to the
farmer. Entirely independent of the question of its relation to
human tuberculosis, the disease, as it exists among cattle, is a
menace to the dairy industry. The amount of financial injury
that it does to the farmer each year is very great — far in advance of

THE COMBAT AGAINST BOVINE TUBERCULOSIS. 269

any other disease. The insidiousness with which it finds its way
into and spreads through the whole herd, even before the farmer is
aware of its presence, the large number of cattle rendered worthless
through its agency, especially among high-bred and valuable ani-
mals, the suspicion which it throws upon the milk-supply, the
injury that it does to the animal which is to be used as food, the
great cost of tuberculosis legislation by the different States, all
these serve to emphasize the seriousness of the problem. Nothing
can be of more importance to the farmer than the discovery of some
means of controlling this disease. Legislation designed to control
it has been adopted by most states in Europe and America, but
such legislation has usually had in mind the protection of the public
rather than the assistance of the farmer.

THE COMBAT AGAINST BOVINE TUBERCULOSIS.

Resistance of Cattle. — The foundation of a successful contest
against the disease is a herd of animals in a proper condition to
resist it. This side of the question is too commonly neglected,
and nearly all of the attempts made to combat the disease have
been directed solely toward devising measures for preventing the
distribution of the bacillus. It is, however, impossible absolutely
to prevent the bacillus from being distributed by diseased ani-
mals, and occasional infection will occur in spite of all preventive
measures. Without some efforts directed toward producing a
healthy herd of resisting animals, it is quite certain that the endeavor
to prevent the distribution of the disease will be unsatisfactory.

It is doubtless much more easy to give the farmer directions
looking toward the prevention of the spread of the bacillus, than
it is to instruct him how he may increase the resisting power of
his animals. But nevertheless some suggestions may be made
which, if carried out, will certainly improve the conditions and
induce better health and, hence, greater resisting powers. There
is little doubt that in a majority of cases the cattle need more air.
Too many are crowded together in a small space in the winter season
and there is too little ventilation of the cow stalls. In the attempt

270 TUBERCULOSIS.

to keep animals warm, they have been too closely shut up in badly
ventilated rooms, and they breathe the warm air over and over again.
Such a condition, wholly independent of the tubercle bacilli which
might be present, has a debilitating effect upon cattle, just as it
does on men. Too frequently, even on the better farms, the cattle
are shut up in the stalls early in the fall, are not allowed to go out
during the long months of the winter, and never get a breath of
fresh air. Sometimes the case is even worse than this, for many cows
are thus shut up as soon as they begin to produce milk, and, winter
and summer alike, remain in close, poorly ventilated rooms. To
protect his cattle from cold the farmer makes his cow barn too warm
and allows it too little air. To save trouble he keeps the cows housed
all the time, with no out-of-door air; and to save expense he crowds
them together in the smallest amount of space. These facts
show why so many animals yield to tuberculosis in the colder coun-
tries. Warm rooms and a close crowding of the animals may
result in a saving of food, but it invites the spread of tuberculosis
if it once gains access to a single animal. In the human race it is
well known that the best protection against the disease, and the
best remedy for it after it has once started, is out-of-door life.
Doubtless the same is true of cattle, but this fact has been almost
forgotten in the attempt to produce the most milk possible at the
smallest expense. The farmer may perhaps insist that such crowded
conditions are necessary and unavoidable in the modern farm, but
he must also remember that, whether necessary or not, they are
certainly inviting tuberculosis and bringing his animals into a
condition where they are sure to yield to the infection the first time
that chance brings the bacillus in their vicinity. More outdoor
life and more air are the prerequisites for a healthy herd.

Anything which will induce a vigorous life will decrease the
tendency to the disease. Proper food is an important factor in
determining health. It may be difficult under the conditions of
modern farming to allow the cattle to have proper exercise in the
winter, but the lack of it is certainly one of the factors tending to
increase the liability to tuberculosis. Too great attention paid
to the increase in the yield of milk lessens the resisting power of

THE PROTECTION OF THE HERD. 27 1

cattle. Our agriculturists, by overfeeding with certain kinds of
food, and by special high breeding for the purpose of increasing the
yield of milk, are trying to turn an animal into a milking machine.
The highly bred animals are, of course, useful for the purpose for
which they are bred; but the agriculturist must remember that he
cannot turn his cow into a simple milking machine without suffering
some evil results from the change in her nature. In short, if the
cattle owner will learn that cattle are animals and not machines
and that they need something besides food and water to keep them
active, he will probably soon find the tendency to tuberculosis
becoming less.

THE PROTECTION OF THE HERD.

While the treatment of the cow as an animal and not a milking
machine must be the foundation of a healthy herd, the care of the
farmer most not stop there. The animals must be guarded against
infection and to this end much attention has been given in recent
years.

The Tuberculin Test. — Any method of protecting a herd against
tuberculosis must start with some method of detecting the disease
in animals. Certain forms of the disease, especially when in an
advanced stage, are easily discovered by clinical means, the
veterinarian being able to detect them by the examination of the
cattle. But there are other cases where no visible signs appear,
and these cannot be found by clinical means. The tuberculin
test has been devised to meet this difficulty and to dectect even the
mildest cases. Tuberculin was first prepared by Koch. It is
made by causing the tubercle bacilli to grow in a broth containing
glycerin. While growing in such a broth, the bacilli produce certain
toxic products which are soluble and which dissolve in the broth.
The material is then treated in such a way as to remove the bacilli,
and the clear, toxic-holding solution is tuberculin. Inasmuch
as it does not contain any living bacilli, it cannot possibly cause the
disease, and its use among animals cannot incite tuberculosis, as
has sometimes ignorantly been claimed.

272 TUBERCULOSIS.

Although containing no bacilli, tuberculin does contain the
toxins which the bacilli produce, and these toxins, if inoculated
into an animal in sufficient quantity, would poison it. When
injected in small quantity, the material has no effect upon the
healthy individual; but if the individual is already affected with the
disease, this inoculation produces a marked rise in temperature,
which soon disappears.

The fact that the injection is followed by a rise in temperature
makes it possible for this material to be used among cattle in detect-
ing tuberculosis. Healthy animals fail to respond to this inocula-
tion and are wholly uninjured by it. The farmer may, therefore,
have his herd tested with the confidence that his healthy animals will
not suffer by the test. On the other hand, the animals that have
become infected with the disease will show a rise in temperature,
and the test will thus make it possible to separate the affected
animals from those that are yet in health.

The accuracy of the test has been the subject of much dispute.
It has been found subject to some error. If animals are tested
under abnormal conditions, as, for example, when in new barns, or if
taken from a cattle car and tested at once, even healthy animals may
respond. But when the animals are in normal conditions the
healthy animals probably never respond, or at all events so rarely
as not to interfere with the accuracy of the test. Secondly, some
animals very far advanced in the disease fail to respond. These
cases are of little importance since they are commonly detected
readily by clinical symptoms. Thirdly, all animals which are
moderately attacked, and all of the very incipient cases of tuberculo-
sis, are detected by the tuberculin. Even a single minute tubercu-
lous gland is sufficient to cause a positive reaction to the test.

This last fact forms at once the strength and the weakness of the
tuberculin test. Tuberculin does pick out with great accuracy all
mild cases, and clinical symptoms will pick out the rest. But this
test fails to distinguish between severe and mild forms, putting in
one class the animal that may have a small tuberculous gland,
which may heal in a short time, and the animal with a severe case of
intestinal tuberculosis which is scattering bacilli to the great danger

THE PROTECTION OF THE HERD. 273

of the rest of the herd. Experience has shown that, of the animals
responding to the test, some run down rapidly and require slaughter-
ing in a few weeks, while others wholly recover, live several years
of useful life, and after death show, by postmortem examinations,
that the original tubercle has been healed and the animals have
come again into normal condition. There is thus a great difference
between clinical tuberculosis and tuberculin tuberculosis. The former
results practically always in the death of the animal, the latter may
be temporary and insignificant. The former certainly is, and the
latter may or may not be, a source of danger to the herd.

In the enthusiasm which followed this easy means of detection,
it was claimed that it might be possible to eradicate tuberculosis
completely from our herds, and some States started upon a sweeping
plan of testing all cattle and slaughtering immediately all animals
that responded to the test. But this entirely too radical plan
proved quite impracticable. Nevertheless, the use of tuberculin has
become of great value to the farmer in his attempts to get rid of this
disease among his cattle.

The Preservation of a Healthy Herd. — If a farmer has a herd
in which the disease has not appeared, it is of especial interest to him
to keep his herd in this condition; for, once the disease has entered
the herd, it is very difficult and expensive to stamp it out. Tuber-
culosis does not develop spontaneously in a herd of animals, but
is always introduced from the outside. A farmer who can raise his
own cattle and can properly protect them from contact with out-
siders need have no tuberculosis among them. But to protect the
herd requires some knowledge and great vigilance. To prevent
the entrance of the disease into his herd from without, the farmer
must exercise care in several directions.

First: In buying stock he must be sure not to purchase in-
fected animals. This is perhaps the greatest difficulty, for it is most
commonly by purchase that the disease is introduced into a herd.
There is only one way by which he may be sure that he is not
purchasing infected cattle, and this is by a proper tuberculin test,
under the guidance of a reliable veterinarian. The matter is made
more difficult by the fact that after an animal has been tested and

2 74 TUBERCULOSIS.

responded, she is for some time protected from a second test. A
dishonest dealer, therefore, may inoculate his cows privately and
then put upon the market all those that respond to the test, knowing
that for some time they will not again respond. One thing is
certain. No farmer can be confident of keeping his herd free from
thisxiisease unless he can be assured by the tuberculin test that he is
purchasing animals freed from every suspicion of the disease.

Second: He must prevent his cattle from associating with
strange cattle. If put out to pasture they must be kept by
themselves and guarded against chance contact with strangers.
Common watering troughs, in which miscellaneous cattle are
watered, must be shunned.

Third: He must not feed his calves upon milk from other
herds. The way in which this is most commonly done is by the use
of skim milk returned from a creamery or a separating station.
From such a creamery the farmer does not get back his own milk,
but always milk from another source, and, if there be a few cases
of bovine tuberculosis of the udder in the neighborhood, the bacilli
from these animals will soon be distributed through the separating
station over the entire region contributing to the station. This is
not mere theory, but positively ascertained fact. To such milk is to
be attributed the large amount of tuberculosis among swine in
recent years. The only safe procedure is for the farmer either to
bring up his calves on the milk from his own healthy herd or to
insist that all milk fed to them shall first be subjected to the process
of pasteurizing or boiling. So convinced are the agriculturists in
Denmark that this mixed milk is the cause of much of the bovine
tuberculosis, that a law has been passed forcing the pasteurization
of all milk which is thus brought to creameries for separation of the
cream. The farmer is thus protected from the tuberculosis of his
neighbors' herds.

Treatment of a Tuberculous Herd. — There appear to be four
general methods of treating a herd after this disease breaks out in it:

I. All advanced cases which are recognized as dangerous to
the public, including all cases of udder tuberculosis, may be removed
and the animals destroyed, the others being left undisturbed.

I

THE PROTECTION OF THE HERD. 275

This does away with most of the danger to the public consuming the
milk, but does nothing toward eradicating the disease from the herd.

2. All animals that have the disease as shown by clinical or
tuberculin test may be slaughtered. The attempt to enforce by
law such a treatment of the disease has failed wherever tried. It
involves too great a loss and dooms to slaughter many animals in the
incipient stages of the disease that might recover and are still
useful animals. It is sometimes done voluntarily by private owners
in their determination to keep a herd free from the disease. It
protects the herd and the public at the same time.

3. The great losses that are frequently involved in the slaughter
of all reacting animals have led to the adoption of other plans for
freeing the herd of the disease without such sacrifices. A plan
was devised some fifteen years ago by Bang, consisting of separating
the reacting animals from the others. The first step is to detect by
tuberculin all tuberculous animals. The advanced cases are slaugh-
tered. The other reacting animals are separated from the others
and placed by themselves, removed from every possible contact
with the rest of the animals in the herd. This is not because all
reacting animals are necessarily sources of danger, but simply
because there is no means of determining when any one of them
may become a source of danger to the animals about it. The healthy
(non-reacting) animals are then placed by themselves, either in a
new barn or the old one after it is thoroughly disinfected. By
this means a practical isolation is accomplished.

If the farmer wishes to preserve the healthy herd from future
attack, he must take precautions to have the isolation thorough.
It may be effected by simply building a partition in his cattle shed;
but in this case there should be no door in the partition, for that
would surely result in a carrying of bacilli from one compartment
to the other. The farmer should remember the facts already
pointed out as to the methods of distributing bacilli. If possible,
he should have separate attendants for the two herds, and at all
events, the boots worn in attendance on the infected herd should
not be worn in the shed occupied by the healthy animals. He
must remove all calves from the infected herd a few days after birth

276 TUBERCULOSIS.

and bring them up on the milk of the healthy herd alone. The
healthy herd must be tested every six months or so, and if any
show reaction they must at once be removed from the rest. The
tuberculous herd may be kept and milked, but the milk should be
sterihzed. By keeping up this procedure for a few years, it is possible
to eliminate the infected animals and have left a herd of healthy
animals.

4. A still more recent plan has been widely adopted in Germany
and seems at present to oflfer the simplest and most hopeful solution.
It consists in separating all calves, as soon as born, from their
mothers, and rearing them separately from the rest of the herd.
Tuberculosis is not hereditary, and the calves of tuberculous mothers
are, when born, free from the disease (except in rare instances).
If, therefore, they are at once separated from their mothers, brought
up on pasteurized milk, and not allowed any possible contact with
the other animals, they may be reared free from the disease, becoming
in a few years a herd of healthy cattle, and if they are guarded from
outside sources of contamination they will continue to be free from
the disease. Meantime the animals in the infected herd, whose
milk may be used if throughly pasteurized, may be slowly disposed of,
while the healthy, growing herd gradually replaces them with the
smallest possible loss to their owner. Of course the healthy
animals must not be allowed to enter the quarters formerly occupied
by the diseased herd until there has been a thorough disinfection
of the premises.

Which of these methods of procedure it is best to adopt depends
upon circumstances. If a man has only a small number of animals
and only one or two of them are tuberculous, his simplest plan
will be to slaughter the reacting animals at once. If his herd is a
large one, it is best to build up a healthy herd by one of the methods
outlined. He must remember that a single tuberculous animal
is a menace to his entire herd and he should begin his fight against
the disease at the very first discovery of an affected animal. Neglect
in using the tuberculin for fear that some reacting animals be found
in the herd is the height of folly. Half-way measures in handling
this subject are no better than none.

FLESH AND MILK FROM TUBERCULOUS ANIMALS. 277

Preventive Inoculation. — In recent years claims have been
made that a method of preventive inoculation against this disease
has been found by using dried human tubercle bacilli for rendering
cattle immune. Considerable data have been collected as to the
success of this method, and it seems pretty certain that a considerable
degree of immunity can thus be given to cattle. It is yet too early
to say, however, whether this procedure will ever be a practical
method of handling the tuberculosis problem.

THE USE OF FLESH AND MILK FROM
TUBERCULOUS ANIMALS.

The practical question of the disposal of milk and flesh from
tuberculous animals is constantly arising. The answer is clearly
dependent upon whether the disease in men and animals is the
same. Since it is generally agreed that, if not the same, the two are so
nearly alike that they may be transmitted from one to the other, it
is the concensus of all that the possibility of transference through
flesh or milk should be guarded against.

Flesh. — Tubercular matter when fed to susceptible animals
may produce the disease in the animal experimented upon. From
this it follows that, if the human and bovine tuberculosis are the
same disease, mankind may be exposed to danger from eating the
flesh of tuberculous cattle. But there is no danger unless there
are tubercle bacilli in the part eaten. The tuberculous infection
of cattle is commonly in the lungs, intestines or lymphatic glands,
and only rarely are the muscles affected.

If an animal has simply a tuberculous lymphatic gland, its
muscles are perfectly safe eating, unless they may have become
infected by the knife of the butcher which has previously cut
through some tuberculous mass in the animal. The danger to
man from eating tuberculous flesh is therefore slight. Further,
flesh is commonly cooked before it is eaten. Thorough cooking
will destroy the bacteria, but even the moderate cooking which
meat commonly receives is sufficient to destroy the bacteria upon
its surface, although the heat does not extend to the interior.

278 TUBERCULOSIS.

Inasmuch as flesh is rarely the seat of the tubercular infection, and
accidental contamination with the butcher's knife will be on its
surface, cooking will almost always render it harmless, unless the
infection is deep-seated. For these reasons the flesh of animals
slightly infected with this disease need not be condemned as food.
It is universally admitted that the actual danger from this source is
very small and perhaps does not exist at all.

Milk. — The problem of the use of milk from tuberculous
animals is a more difficult one to settle. The milk of tuberculous
cattle does not always contain the bacilli and it is an unsettled question
whether it will ever contain them unless the disease be located in the
udder. At all events, cows having tuberculous udders (some-
where about I per cent.) will produce milk infected with tubercu-
losis bacilli. That these bacilli are active and vigorous is proved
by thousands of experiments which have shown that such milk
is capable of producing tuberculosis in guinea-pigs. It is true
that the bacilli do not multiply in milk, but milk from one cow
can, by being mixed with other milk, infect a large amount. It
is possible that such milk may be a danger to the public health.
It has been abundantly shown that market milk frequently contains
tubercle bacilli in sufficient quantity to produce an infection in
guinea-pigs, and the same is true of market butter. All of these
facts certainly indicate a possible danger to the public from this
source.

In regard to the extent of this danger there has been a wide
difference of opinion. It has certainly been magnified by some.
The danger is, beyond question, frequently overdrawn. It is
sometimes doubted that mankind can ever acquire tuberculosis
from this source. Experiment has shown that large numbers of
the bacilli must be swallowed at once to produce infection even in
susceptible animals. The number of bacilli which a person will
swallow with a drink of milk will commonly be rather small, and
the human individual has a considerable power of resistance
against the disease. It is a further fact that, although bovine
tuberculosis has been increasing, human tuberculosis has been con-
stantly declining in recent years, and the decline has been equally

I

FLESH AND MILK FROM TUBERCULOUS ANIMALS. 279

great in those countries that use milk raw and in those countries
that sterilize the milk before drinking it. This decrease in tuber-
culosis does not apply to intestinal tuberculosis among young
children, indicating, possibly, that milk is a more common source
of infection for children than for adults. For these various reasons
it is a fair inference that the danger of tuberculosis from milk is
not very great for adults, though it may be considerable for young
children. It is quite certain that for young children it is unsafe to
resort to the use of milk from miscellaneous cows without the pre-
caution of pasteurization.

Certainly the logical method of dealing with milk would be
to exclude from the milk-supply all milk from tuberculous animals
or to allow it to be used only after pasteurization. Only thus
could absolute safety be assured. But this is quite impractical,
if, indeed, possible. A farmer who takes pride in his dairy and in
furnishing a special quality of milk will protect his cutomers by
periodic testing of his cattle and by the exclusion of all reacting
animals. But to enforce any regulations looking in this direction in
regard to the public milk-supply is simply impossible at the present
time and will remain so for some time to come. The end could
be reached through the milk supply companies, by the adoption of
the simple and inexpensive process of pasteurizing all milk before
distribution, and quite possibly such may be the ultimate solution
of the problem. Meantime the only feasible method of treating
the matter is to insist that the farmer shall rigidly exclude from the
animals furnishing the milk-supply all cows with diseased udders,
and to suggest to all who have a fear of using the milk because of
the slight danger existing in this food-supply, that the danger may
be wholly avoided by pasteurization.

CHAPTER XIX.
OTHER GERM DISEASES.

ANTHRAX OR SPLENIC FEVER.

Anthrax is a disease of domestic animals which has been known
for centuries. It is mentioned in the writings of Moses, and Homer
refers to it in the Ihad. It occurs practically all over the globe, in
all latitudes where cattle are kept, and seems to be entirely independ-
ent of climate. Every country of Europe suffers from it. Germany
has lost some 4,000 cattle from this disease in some years and
England nearly a thousand. In the United States the disease
is also frequent, though generally regarded as less common than
in Europe. Although widespread, it does not occur in great numbers
of cattle as do some of the other bacterial diseases. It may attack
the animals of a single herd and produce much destruction, but it is
not very contagious and does not readily spread from herd to herd.

Cattle and sheep are the only animals in which it normally
occurs as a spontaneous infection. Many other animals are,
however, capable of infection with it. Horses, goats, deer and mice
are very subject to the disease, while dogs, cats and white rats are not
susceptible. The disease is also found in man, and is then known
by various names, the most common being malignant pustule.
Mankind is, howeVer, not one of the very susceptible animals and,
when infected by a skin inoculation, the disease is quite apt to ^0
local, while in sheep and cattle it is almost sure to run a fat- . course.

Cause. — The discovery of the cause of this disease was one of
the first triumphs of bacteriology. Its exciting cause is a bacterium,
Bad. anthracis, which, though first seen in 1849, ^^^ ^^^ really
demonstrated as the cause of the disease until 1875, by the work of
Koch, and shortly afterward by Pasteur (Fig. 52). After some
twenty-four years of dispute the final demonstration was due to

280

ANTHRAX OR SPLENIC FEVER. 28 1

such experiments as the following. It was easy to show by the
microscope that this organism is present in the blood of the animals
suffering from the disease, and that a drop of such blood, containing
the organism, when injected into healthy animals would inevitably
produce the disease in the inoculated animals. But this did not
necessarily prove their causal agency, for it was possible to claim
that there were some other poisons in such blood. For final proof
it was necessary to separate the bacteria from the drop of blood,
cultivate them, and inoculate animals with the pure cultures. At
the time that this disease was first being studied no methods were
known of obtaining isolated bacteria in pure cultures, and hence

Fig. 52. — B. anthracis, the cause of splenic fever.

the long dispute. Pasteur finally procured his results as follows.
Finding that the bacterium would grow in a solution made by steeping
yeast in water, Pasteur inoculated a sterile flask of such yeast-water
with a drop of anthrax blood. In a day or two his flask was filled
with bacteria which had arisen from the first by division. The
inoculation of a second flask from the first showed like results, and
by continuing such inoculations from flask to flask he rapidly got
rid of all parts of the original drop of blood, except such parts as had
been multiplying in the flasks. His microscope showed him that the
only thing that multiplied and remained in his later flasks were the
bacteria present in the original drop of blood. Nevertheless, he
found that though he continued these inoculations indefinitely,
every flask was equally virulent, and a small drop of the culture
would inevitably produce anthrax in a susceptible animal in a very
few hours, the development of the.disease being always accompanied
by the growth in its blood of the bacilli in countless myriads. These
24

282 OTHER GERM DISEASES.

results left no loophole for criticism, proving that this bacterium was
the cause of anthrax, and thus for the first time demonstrating that
an infectious disease was produced by a bacterium multiplying
within the body of the animal in which it grows as a parasite.

The bacterium in question, Bad. anthracis, is a rod of moderate
size (Fig. 52). It multiplies by repeated division, the elements re-
maining attached to form long chains. Sometimes these long
threads show no signs of the divisions, and in certain media they
form marvelously twisted and contorted masses. When in an
active growing condition, this bacterium is readily killed by ordinary
disinfecting agents and by a moderate heat, a temperature of about
160° F. easily destroying the rods. But it produces resisting spores
which can easily be distinguished inside the rods as clear, ghstening
bodies. It is their resistance to ordinary agents that makes anthrax
so persistent, and this high resistance must be borne in mind when
the attempt is made to disinfect a stable which has been occupied by
an animal having this disease. These spores will resist the action of
5 per cent, carbolic acid solution for half an hour, or a i per cent,
solution of corrosive sublimate for about the same length of time.
Few other living bodies can resist such treatment. The spores will
also resist a temperature of about 280° F. for two or three hours.
When immersed in liquid they are much more easily killed, since the
temperature of boiling, if maintained for a few minutes, is com-
monly sufficient to destroy them. When dried the spores may
remain alive for a long time, many years at least, and yet all the time
retain their power of developing when placed under proper condi-
tions. All of these facts evidently make the disinfecting of an
infested locality a matter of very great difficulty.

Method of Infection. — Although this disease is extremely fatal,
animals affected rarely recovering, it is not particularly contagious,
and is rarely commuilicated directly from animal to animal. One
common method by which cattle are infected appears to be through
the food which they crop in the fields. It has often been noticed
that the disease breaks out in a herd shortly after it has been turned
out into a new pasture. In some of these cases which have been
investigated the explanation is simple. In such pastures bodies of

ANTHRAX OR SPLENIC FEVER. 283

animals dead from anthrax have been buried, and the spores have
remained alive for many years. Now, although these spores may
have been buried some distance below the surface, they are event-
ually brought to the surface. One of the means by which they are
brought up from under ground is through the agency of earth-
worms, and the spores are later taken into the stomachs of cattle
feeding on the grass. These spores resist the action of the di-
gestive juices and of the other bacteria present in the intestine, and
make their way through the intestinal walls into the body, producing
the disease. These facts readily explain many of the phenomena
connected with the outbreaks of epidemics.

In other cases the germs may find entrance through abrasions of
the skin. When thus introduced the bacteria first produce a simple
abscess in the skin, which soon turns into a gelatinous pustule.
This pustule does not heal, and from it as a center the bacilli spread
rapidly through the body, producing a general disease which may
terminate fatally. The name malignant pustule is appropriately
applied to this form of disease. In susceptible animals such re-
covery is very rare. In the case of animals which, like man, are
less susceptible to the disease, these abscesses may remain simple
localized infections, eventually healing without spreading through the
body. There are other modes of infection, but among animals the
disease is most usually acquired through the intestine or through
skin abrasions.

In the body of the infected animals the bacilli grow with great
rapidity. An extremely small number of them inoculated into the
body of a sheep may produce its death in about two days, and after
death the whole body is found to be filled with the bacilli in incal-
culable numbers. The disease is marked by a high fever and much
discomfort, and after death the most characteristic symptom is a
greatly swollen spleen, whence the name splenic fever. The spleen
is large, hard, and brittle, and contains enormous numbers of the
bacilli. The blood-vessels are also found to be full of them, and the
capillaries may literally be crammed with bacteria.

This bacillus is extremely virulent in its action upon susceptible
animals, so virulent, indeed, that a single bacillus, inoculated

284 OTHER GERM DISEASES.

under the skin, may be sufficient to cause the disease and death.
In the less susceptible animals it requires a larger dose to produce
similar results. The lesser susceptibihty of such animals as the
dog, the horse, the bird, etc., renders them practically immune
against spontaneous infection, and the disease occurs among them
only as the result of artificial experiments. In man the disease is
of rare occurrence, being practically confined to people dealing in
or handling hides or wool, and is acquired by them either through
abrasions in the skin, when it produces malignant pustule, or by
breathing the spores into the lungs, when it is called wool-sorter^ s
disease.

Preventive Inoculation. — Although anthrax is an extremely
fatal disease to animals and has, in the past, caused heavy losses
to agriculturists, it is a source of less loss to-day than in former
years, since it can be fairly well controlled by preventive inoculation.
We have noticed in the last chapter that Pasteur demonstrated the
important principle of preventive inoculation by his experiments
upon anthrax; the discovery has been of great practical value.
Cattle can be protected from anthrax by inoculation, and from
the time that Pasteur pointed out the method, hundreds of thousands
of animals have been thus inoculated and protected. But the
protection is not found to be very lasting, and animals must be
inoculated about once a year to be thoroughly safe from the disease.
This, of course; reduces the value of the inoculation, and confines
it to localities where, for special reasons, the disease is quite common.
It also explains why the method is not so widely in use now as at
first; but, nevertheless, large amounts of the inoculating material
have been used in this country as well as elsewhere, and it is thought
that immense losses have been prevented by this means since its
discovery by Pasteur.

OTHER GERM DISEASES AMONG ANIMALS.

No other diseases among animals have acquired so much interest
as tuberculosis and anthrax, although several others are known to
be produced by microorganisms and are of considerable importance

OTHER GERM DISEASES AMONG ANIMALS. 285

to agriculture. Only a brief mention of these is possible, but the
following list includes all of the important diseases of domesticated
animals, that have been proved to be caused by microscopic
parasites.

Swine Plague, Fowl Cholera, Rabbit Septicemia, Rinder-
seuche, Wildseuche {B. pleurosepticus). — These names are ap-
plied to a variety of affections of animals, but they all appear
to be essentially the same thing. The cause is a bacterium which
was first identified by Pasteur as the cause of fowl cholera and
later identified as the inciting agent in all these diseases. They
are all contagious and often produce considerable havoc among
domestic animals. The names given indicate the variety of animals
attacked. Rinderseuche is the name given when it attacks cattle,
and Wildseuche when it attacks deer; septic pleuropneumonia and
pneumoenteritis are also names applied to it.

The bacterium causing all these diseases is a short rod, so short
as sometimes to be called a Micrococcus. The cultures obtained
from different animals have been given different names, B. bovi-
septicus, B. suisepticus, etc., but the most careful study fails to
show differences sufficient to warrant their separation, and the
name B. pleurisepticus has been suggested as indicating its relation
to its many hosts. While it attacks many animals it is, so far as
known, harmless to man. It produces a type of disease quite similar
to the forms of blood-poisoning which have been, in medical practice,
called septicemia. It is extremely fatal to some animals, fowls
and rabbits succumbing to its action with extreme rapidity and
with almost absolute certainty. Among the larger animals its
course is not necessarily so fatal, but in all those referred to above
the disease is a serious one and almost always fatal. When
attacking the hog it produces one form of swine plague, this being
the type of the disease most commonly found among domestic
animals, and the one which will usually be most interesting to the
agriculturist.

Hog Cholera. {B. suipestifer.) — The hog cholera is a disease
related to the last, although clearly distinct from it, and is one
which develops spontaneously in swine only. It is quite common

286 OTHER GERM DISEASES.

to have swine plague and the hog cholera together in the same
animal. The disease sometimes results in very serious losses.
A herd of swine may be attacked by such a violent epidemic that
90 per cent, of the animals succumb to the infection. After the
death of the animals the bacilli which produced the disease are
found in all of the organs, but especially in the spleen. The disease
occurs in an acute form, which runs its course with excessive rapidity,
producing death in twenty-four hours, and in chronic form, which
has a slower course, lasting from two to four weeks before finally
resulting in the death of the animal. The organism which produces
the disease is named B. suipestifer (or B. cholerce suis), and is very
easily cultivated by ordinary methods in the laboratory. It is
capable of producing the disease, not only in the swine, but in
rabbits, guinea-pigs, mice, and some other animals; but as a spon-
taneous affection it is found in the hog only.

Glanders. Farcy. Rotzbacillus {B. mallei). — This disease,
well known among agriculturists, occurs not infrequently as a
normal infection in the horse and in the ass. It is characterized
by the appearance of ulcers in the nasal membranes, by enlarged
submaxillary lymphatics, which may turn into open discharging
ulcers. Later the lymphatics of the whole body may become
tumor-like swellings. Other parts of the body may eventually
be affected. The secretions from the various ulcers are found to be
decidedly infectious, and it is through these ulcers that the disease
is commonly distributed. It occurs in an acute form and in a
chronic form; the latter, chiefly in the skin, receiving the name
oi farcy, the former, chiefly in the lungs and nasal passages, more
commonly known as glanders. It occurs spontaneously only in
horses and asses, and causes great losses in nearly all localities. It
may occur by accidental or artificial infection in many other animals.
It occurs occasionally in men who have become accidentally inoc-
ulated in the treatment of horses suffering from the disease, and
when it does occur in man it is an extremely fatal disease, almost
always resulting in death.

The bacillus which produces the disease is named B. mallei.
It is a short stationary rod which lends itself readily to bacteriological

OTHER GERM DISEASES AMONG ANIMALS. 287

experiments. It is found to be capable of producing the disease
in cats, dogs, rats, field mice, and quite a variety of animals. It is
only slightly pathogenic for the sheep and the mice. The pig and
the cow seem to be immune from its action.

Symptomatic Anthrax. Black-leg. Quarter-evil. Rausch-
brand {B, anthracis symptomatici) . — This disease, with its variety
of names, is extremely common in Europe. It has been rare in the
United States, but in recent years is becoming more abundant,
being found as an epidemic in certain herds. It is a disease that
occurs chiefly among cattle, and is characterized by certain irregular
swellings in the subcutaneous tissues and muscles. The swellings
are seen especially over the quarters of the animal, and hence the
name quarter-evil. The muscles become dark colored and bloody
(hence the name black-leg), and contain large numbers of the
bacilli known to cause the disease. It is the cause of considerable
trouble to raisers of cattle, being almost universally fatal, although
it is not a disease that can be regarded as extremely common.

The organism which produces the disease is well known and is
named B. anthracis symptomatici. It is pathogenic for a large
number of animals when artificially inoculated. Swine, dogs,
rabbits, fowls, pigeons, guinea-pigs, and horses succumb to the
disease by inoculation, in addition to cattle, sheep, and goats, in
which the disease occurs spontaneously. It is most common
among cattle as a spontaneous affection, and quite rarely occurs in
sheep and goats. In the horse it is never known to occur spon-
taneously. So far as known, the bacillus is not pathogenic for man,
although this has never been demonstrated; but no instance has ever
been known of man suffering from the infection, even though every
opportunity for such infection has been offered. The disease is,
therefore, not regarded as injurious to man. The practice of in-
oculating animals against the disease by a "preventive culture" is
widely and successfully adopted in the United States.

Tetanus or Lockjaw {B. tetanus). — This is a disease of rather
rare occurrence among domestic animals, but it may sometimes
occur if an animal receive a wound by means of some object that has
been lying for a long time in the soil. The cause of tetanus is a

288 OTHER GERM DISEASES.

bacillus (B. tetanus), which lives normally in the earth and may get
into a wound and produce the well-known and commonly fatal
disease.

Abortion. — This troublesome disease sometimes appears in
a herd and produces great loss, and endless trouble to the dairyman.
Cows attacked by the disease do not carry their calves the full time,
but drop them early and become useless for the time as milk-cows.
If the animal is once affected she is likely to have the same trouble
the next time she is in calf, and perhaps her usefulness is ended.
This trouble has for some time been recognized as contagious and
has in recent years been demonstrated to be produced by a definite
species of bacterium. The bacterium may infect cow after cow, and
even the bull may distribute it through a herd of cattle. The best
remedy has been found to be thorough disinfection. The calf must
be destroyed, the stable disinfected, genital parts of the cow thor-
oughly washed with disinfecting solutions and the animal kept from
the rest of the herd. A thorough disinfection of this sort will com-
monly allay the trouble.

Takosis of Goats. — This is a disease of goats only recently
studied and found to be caused by a bacterium. It brings on a
general weakness and wasting away, which finally results in death.
It has caused great loss among the Angora goats in the northern
states. It is always fatal.

Lumpy Jaw, Malignant Tumor, Wooden Tongue. — These
three names are applied to the same disease, located, however, in
different places. The cause of the trouble is one of the higher
types of fungi rather than a bacterium. The name of the organism
is Actinomycosis and it differs from bacteria in forming longer
threads and in branching (see page 12). When it finds entrance
into cattle, generally through the mouth, it may invade the tissues
and produce the diseases named above. Sometimes it is found
in the throat, lungs, and skin. It is most common in cattle, but it
also occurs in swine, and may be given to other animals by inocula-
tion. It occasionally occurs in man. The disease is not common,
though it causes considerable loss at times, since it is serious and apt
to be fatal. It produces hard tumors that invade the bones or other

OTHER GERM DISEASES AMONG ANIMALS. 289

tissues, causing great distortion. The disease is not contagious and
its source is as yet unknown.

General Inflammatory Troubles. — Inflammatory, suppura-
tive, and tumor-forming troubles are liable to occur in almost any
part of the body of man or animal. These are commonly caused by
bacteria, particularly by the class called Streptococci. The affections
do not form any specific disease, but receive a variety of names
according to the location of the trouble. For example, when the
streptococcus produces inflammation of the udder it is called
garget, mammitis, or mastitis, while hoof rot and navel ill represent
other types of inflammation located elsewhere. The streptococci
that cause garget have been found abundantly in the milk of cows
and are believed to be the reason for some of the illnesses in man-
kind that follow the drinking of raw milk. Various forms of sores,
boils, abscesses, and the inflammations following wounds are also
caused, largely or wholly by streptococci, and most types of inflamed
tissue in an animal may be rightly attributed to the action of this
class of bacteria.

Another bacillus associated with a variety of troubles among
animals is named B. necrophorus. This organism produces more
than an inflammation; it gives rise to a general decay of the tissues
attacked (called necrosis) and, since it attacks many parts, it has a
variety of effects. In the skin it causes numerous inflammatory
diseases. It produces the foot rot of sheep and also of cattle. It
attacks the bones in the nose, causing their destruction; it may bring
about troubles in the alimentary canal, and it is the source of some
of the cases of hog cholera, as well as several other affections.

Foul Brood of Bees (B. alvei and B. larvce). — Foul brood is
a disease attacking the larvae of bees while still within their cells
causing them to become sickly and eventually killing them and pro-
ducing a decomposition of the body. The hive becomes vile-
smelling from the decomposition and the whole economy of the hive
is interrupted. The bees fail to collect honey and the hive may be
ruined. There are really two different diseases going by this name,
the American and the European foul brood, resembling each other
and yet being easily distinguished. Both are produced by bacteria,
25

290 OTHER GERM DISEASES.

the European by B. alvei and the American by B. larvce. In this
country the latter is the more common, though both are found.
Both diseases are readily carried from hive to hive. Sometimes this
is done by robber bees that steal honey from hives, and sometimes it
is carried by the bee-keeper who handles a diseased colony and then
a clean colony, or who places in a clean hive honey or combs from an
infested hive. Its very infectious nature should be thoroughly ap-
preciated by the bee-keeper and great care should be taken in
handling bees. It is also doubtless carried from locality to locality
by the custom of selling bees. The two diseases are widespread
over America, Europe, Africa, and Australia. It spreads rapidly,
sometimes infesting a whole district in the course of a single season
so as nearly to ruin the industry of the bee-keeper.

DISEASE CAUSED BY UNKNOWN PARASITES.

The causes of several well-known diseases have not yet been dis-
covered; nevertheless it must be recognized that they are caused by
microorganisms too small to be seen by our microscopes. That they
are caused by living agents of extremely minute size is shown by two
series of facts : i . Material may be obtained from animals suffering
from the disease which will produce the disease in others, but its power
is destroyed by the same disinfectants as those used to kill bacteria.
2. The infectious agent will pass through porcelain filters, whose
pores are too small to permit even the smallest bacteria to pass,
while it will not pass through some of the very fine porcelain filters
with pores still smaller, but large enough to allow liquid to pass
through them. There are other reasons for the conclusion, but
they cannot be given here. Although these organisms have never
been seen, quite a little is known of their general nature. The
animal diseases produced by invisible organisms are the following.

Foot-and-mouth Disease. — This disease, manifesting itself
chiefly in the mouth and feet of cattle, varies much in its severity.
Although not often causing death, it does result in great financial
losses to dairymen. It is readily transferred to other animals,
most kinds being susceptible to it. It occurs rarely in man, being

DISEASES CAUSED BY UNKNOWN PARASITES. 29 1

transported through the milk of diseased animals, but it is not a
very serious matter, being a mild infection only. For many years
it has caused heavy losses in the cattle-raising communities of
Europe. It has not been common in the United States, though a
few cases have occurred at intervals, and there have been two
rather severe epidemics within the last ten years. These epidemics
have been vigorously handled by the agricultural department
and have been speedily stamped out. It is hoped that by the vigor-
ous measures taken in killing all cattle attacked, the disease may
be prevented from gaining a foothold in the country, and that our
dairymen may thus be protected from the troubles and losses experi-
enced elsewhere. Hitherto the efforts have been successful. No
other remedy is known save that of isolation or slaughter.

Rinderpest. Cattle Plague. — This is a very serious disease,
originally found in Asia, but for centuries periodically invading
Europe, and recently very rife in Africa. It attacks cattle chiefly,
and its death rate is very high. Man is immune against it.

Rabies, or hydrophobia, is also produced by some agent not
yet surely known. It attacks dogs chiefly, although occasionally
it is found in horses, cattle, and man. So far as known the only
source of the disease is the bite of infected animals, and the great
majority of cases come from the bite of dogs. The name hydro-
phobia applies to the disease in man only, where a dread of water is
one of the symptoms. Since this dread of water does not appear
in dogs suffering from the disease, the name rabies is best applied.

Other diseases of the same category are: pleuropneumonia,
a serious disease of cattle; horse sickness, a destructive disease of
horses in South Africa; bird pest (Vogelpest) a highly infectious
and fatal disease of chickens; sheep-pox, a disease of sheep in the
Mediterranean countries. In all of these the exciting agent is
unknown and is probably too minute to be seen with the microscope

ANIMAL PARASITES.

There are some diseases of animals caused by microscopic animal
parasites. Of these the only well-known example in this country

292 OTHER GERM DISEASES.

is Texas fever or, as it is frequently called, the tick fever. This
latter name is given to it from the fact that the disease is dis-
tributed by means of the cattle tick. Other diseases caused by
animal parasites are surra and the tsetse fly disease or nagana,
neither of which is found in this country.

Diseases of Other Animals. — ^Parasitic diseases are found in
all animals bred upon the farm, each animal having its own peculiar
types. Ordinary fowls have fowl cholera, roup, diarrheal diseases,
etc., and turkeys, geese, and ducks have diseases of their own.
Even fishes are subject to diseases produced by bacteria of other
fungi. It is impossible in this work to consider this subject further,
but it is well to bear in mind that the list of parasitic diseases is a
long one and is being increased constantly as investigation is being
extended.

CHAPTER XX.
THE PARASITIC DISEASES OF PLANTS.

It is by no means easy to draw a sharp line between plant disease
and the phenomenon of decay. If the tissues of a living plant show
signs of decay it is called a disease; if the decay occurs in fruit or
vegetables after they are harvested we speak of it as decay. But
there are some parasitic organisms that may grow in the living plant
and thus find access to the fruit so that the fruit will decay after
harvesting. Should this be called a disease? In some cases the
parasites seem to do no injury to the living plant, but live in its tissues
to injure the stored fruit or vegetable later. In such cases it is
manifestly difficult to say whether the phenomenon should be
called a disease. In the types given in the following pages the
parasites in most cases do injury to the living tissues, although one
or two are exceptions.

While most parasitic diseases of animals are due to bacteria,
with a considerable number caused by animal parasites and
almost none by the higher fungi, a different condition of things
is found among plants. The larger majority of plant diseases are
caused by the higher fungi, a considerable number by bacteria,
while, so far as known, none are caused by microscopic animal
life. In our brief survey of this important field we may best divide
the subject into two divisions: i. The Fungoid Diseases. 2.
The Bacterial Diseases.

THE FUNGOID DISEASES OF PLANTS.

This is by far the largest class of plant diseases, but they can only
be touched upon in this work. The Fungi that cause this class of
diseases are mostly of some size and can hardly be called micro-
organisms. They do not therefore strictly belong to a discussion of

293

294 THE PARASITIC DISEASES OF PLANTS.

bacteriology, but their very close relation to germ life makes it
necessary to consider them briefly.

As stated on an earlier page, the higher fungi are characterized
by developing a mycelium. This delicate branching, usually color-
less thread, grows in profusion in or upon the substance that furnishes
the fungus with its nourishment. It is this mycelium that makes
these plants especially adapted to live as parasites upon plants. A
spore of some fungus falls upon the surface of a leaf and germinates,
sending out its tiny thread. This finds some opening into which it
can thrust its way. Sometimes the opening is a wound in the
cuticle, but in other cases it is the breathing pore of the plant, the
stomata. Once it has entered through this cuticle it finds the
tissues soft and moist and there is nothing to prevent its growing
through the plant. The mycelium can readily grow among the
plant cells, winding its way in all directions and may in time pene-
trate to all parts of the plant. Living thus as a parasite and drawing
its sustenence from its host it naturally produces more or less effect
upon the plant life, resulting in what are called plant diseases.

The mycelium is the growing part of the plant, but not its repro-
ducing part. These plants are reproduced by spores. Although
differing in their method of origin, the spores are always minute,
microscopic bodies, produced in immense numbers by the fungus.
Generally, though the fungus grows below the surface of its host,
the spores are produced on its surface. The mycelium is usually
out of sight, while at certain spots the parasite breaks through the
cuticle of its host in order to produce spores and discharge them into
the air. The mycelium is white or colorless, but the spores show a
variety of colors. It is evidently by these superficial spores chiefly
that the fungus is spread from plant to plant.

When one of these spores gets carried to the surface of another
plant it must first germinate before it can do any injury. In order
to germinate it must absorb moisture, a fact that explains the great
influence of the weather upon the fungoid diseases. In moist
weather the spores find plenty of moisture upon the surface of the
leaves, while in dry weather the necessary moisture is lacking. Once
it has germinated and its mycelium has entered the plant, it finds

THE FUNGOID DISEASES OF PLANTS. 295

plenty of moisture within so that it is no longer dependent upon the
weather.

The effects produced by these fungi growing in the plant tissues
are extremely varied. Any part of the plant may be affected, some
diseases showing in one place and others elsewhere. The leaf may
become covered with spots of various colors, or it may wilt, or
roll up or drop off. Scabs may grow on the plant or its fruit, or the
whole may show signs of rotting. Plant diseases have received
various popular names that are loosely applied and not very clear
in their meaning. The more common descriptive names are the
following :

Wilts are characterized by the wilting and withering of the plant.

Rots are characterized by a tendency of the plant tissue to
soften and decay.

Smuts show a mass of black or blackish spores.

Mildews show a whitish, powdery growth over the surface of the
host.

Rusts show spots of a reddish color, due to reddish-yellow
spores.

Anthracnose is a name frequently applied to diseases causing
spots on the leaves or elsewhere.

Blight is a term with no definite meaning, but is generally ap-
plied to almost anything that causes a general wilting and destruc-
tion of the plant.

These terms are all in a measure descriptive terms of the effects
produced by the parasites on the host. None of them are specific
diseases, but all are produced by many different parasites on many
different hosts, and in some cases the same parasite may produce
different types of disease at different stages of its life.

Methods of Combating Fungoid Diseases. — There are
several general methods by which these diseases may be kept in
check: i. By the selection of resistant varieties of the ycultivated
plants. Experience has shown that some varieties yield readily to
the parasites while others are highly resistant. A careful selection
of the varieties, guided by experience, is sometimes of value in
checking disease. 2. By regulating the conditions of the cultivated

296 THE PARASITIC DISEASES OF PLANTS.

plant in such a way as to render it best able to resist the disease.
This involves the matter of cultivation, fertilizing, controlling weeds
that serve as hosts of the parasite, etc., and demands a knowledge
of the methods and seasons for the spore distribution of the fungi,
and each disease has to be studied as a separate problem. 3. By
the use oi fungicides. These are properly selected chemicals that
act as powerful germicides upon the fungi, but do not injure the host-
plant. They are mostly applied by spraying, and the spray reaches
the surface of the plants only, being, therefore, of little or no value
after the mycelium has actually entered the plant tissue. Hence
to be useful they must be applied at just the right time, and each
disease must be carefully studied as to its time of sporing in order
that spraying may be a success. A majority of the successful
fungicides contain copper that seems to be especially efficient upon
this class of fungi. 4. With some of these diseases a rotation of
crops is efficient, since a fungus that attacks one host may be without
influence upon another species of plant. 5. Clean seed selection; i.e.,
selection of seed free from disease.

To describe the various fungoid diseases is impossible in this
work. A list of the more important ones is given below, classified
according to their host plant, with the popular name and the name
of the fungoid parasite.

Alfalfa. Leaf spot, Pseudopeziza Medicaginis (Lib.) Sacc.

Apple. Bitter rot, Glomerella rufomaculans (Berk.) Sp. and
von Schr. Black rot, Sphceropsis malorum Pk. Canker, Nectria
ditissima Tul. Leaf spots, Phyllosticta. Powdery mildew, Podo-
sphcera leucotricha (Ell. and Ev.) Salm. Rust, Gymnosporangium
macropus Lk. Scab, Venturia incequalis (Cke.) Aderh. Sooty
blotch, Phyllachora pomigena (Schw.) Sacc.

Asparagus. Anthracnose. Fusarium, Rust, Puccinia asparagi
DC. Rust, Cladosporium herbarium Link.

Beans. Anthracnose, Colletotrichum lindemuthianum (Sacc, and
Magn.) Bri. and Cav. Downy mildew, Phytophthora Phaseoli
Thax. Leaf blotch, Isariopsis griseola Sacc. Rust, Uromyces
appendiculatus (Pers.) Lk.

Beet, Leaf blight, Cercospora heticola Sacc.

THE FUNGOID DISEASES OF PLANTS. 297

Cabbage. Club root, Plasmodiophora Brassicce Wor. Leaf
molds, AUernaria BrassiccB and A. macrospora Sacc.

Celery. Leaf blight, Cercospora Apii Fr.

Corn. Leaf blight, Helminthosporium turcicum Pass. Rust,
Puccinia Sorghi Schw. Smut, Ustilago ZecB (Beckm.) Ung.

Cucumber. Downy mildew, Plasmopara cuhensis (B. and C).
Anthracnose, Colletotrichum lagenarium (Pass) . Scab, Cladosporium
cucumerinum (Ell. and Arth.).

Grape. Anthracnose, Sphaceloma ampelium DeBy. Black
rot, Guignardia hidwellii (Via. and Rav.). Downy mildew,
Plasniopora viticola (Ber. and De Ton.) Gray mold, Botrytis.
Powdery mildew, Uncinula necator Bur.

Muskmelon. Anthracnose, Collototrichium lagenarium Ell.
and Hals. Downy mildew, Plasmopora cuhensis Humph.

Oat. Black-stem rust, Puccinia graminis. Smut, Ustilago
Avence Jens.

Onion. Black mold, Macrosporium Porri Ell. Black spot,
Vermicularia circinans Berk. Downy mildew, Peronospora schlei-
deni Ung. Smut, Urocystis Cepulce.

Peach. Brown rot, Sclerotina frutigena Schrt. Leaf blight,
Cercosporella Persica Sacc. Leaf curl, Exoascus deformans Fckl.
Scab, Cladosporium carpophilum Thm.

Pear. Black mold, Fumago vagans Pers. Leaf spot, Spetoria
piricola Desm. Rust, Gymnosporangium globosum Farl.

Plumb. Black knot, Plowrightia morhosa Sacc. Brown rot,
Sclerotina frutigena Schrt. Powdery mildew, Podosphcera oxya-
canthcB DeBy.

Potato. Blight, Phytpphora infestans (one of the most destruct-
ive of our plant diseases). Dry rot, Fusarium oxysporum Schl.
Scab, Oospora scabies Thaxt.

Squash. Anthracnose, Colletotrichum lagenarium (Pass.) Ell.
and Hals. Black mold, Rhizorpus nigricans Ehr. Metallic mold,
Choanephora cucurhitarim Tha.

Strawberry. Fruit rot, Botrytis vulgaris Fr. Leaf blotch,
Ascochyta Fragarice Sacc. Leaf spot, Sphearella Fragarice Sacc.

Tobacco. Frost fungus, Botryosporium pulchrum Cda.

298 THE PARASITIC DISEASES OF PLANTS.

The above list contains only a few of the very large number of
known fungoid diseases of plants, but will serve the purpose of
showing their variety. The fungi that produce these diseases are
by no means closely related to each other. The higher fungi are
divided into many classes and the disease-producing parasites are
distributed among them all. For these distinctions, however, the
student must be referred to books upon botany.

THE BACTERIAL DISEASES OF PLANTS.

Only within recent years has it been appreciated that bacteria
are important agents in producing plant diseases. Even after
their agency in causing diseases in animals had been fully recog-
nized it was denied that they could produce troubles of this sort
in plants. Up to very recent date, it was claimed that it was an
impossibility for bacteria to penetrate plant tissue so as to produce
trouble. Plant cells are provided with hard cell walls of cellulose
and wood, which protect the living protoplasm within; and, since
these cells form the bulk of the plant and are adherent to each
other, it was difficult to see how bacteria could penetrate into the
plant at all. The mycelium of the higher fungi can do this readily
since it can thrust itself between the cells, and thus grow easily
within the solid tissues; but it seemed impossible to believe that
bacteria could penetrate the hard tissues. Within recent years,
however, it has been demonstrated that this is possible and the
last ten years have disclosed many bacterial diseases of plants,
until to-day we know of more bacterial diseases of plants than of
animals.

The Black Rot of Cabbage (Pseudomonas campestris). — An
illustration will best show the general course of such a disease and at
the same time indicate how conclusive is the proof of the agency of
bacteria. For this purpose will be chosen the black rot of the
cabbage, cauliflower, turnip, and several other members of the family
CrucifercB. The disease appears first, as a rule, upon the edges of
the leaves, as brown spots, that spread down the leaves following the
veins to the midrib and petiole and finally into the main stem of the

THE BACTERIAL DISEASES OF PLANTS.

299

plant. It then travels rapidly through the whole plant causing the
leaves to wilt, turn yellow, dry up and become thin and parchment like.
The veins in the leaves and stem are particularly affected and turn
black, this being the characteristic feature of the .disease and the
source of the name black rot (Fig. 53). Sometimes the veins alone
are affected. Sometimes the trouble does not appear in the grow-
ing plant, but only in the cabbage after storing, extending through
them rapidly and ruining them.

When these black veins are
studied with the microscope they
are found to be filled with bacteria
and it is easy by proper methods to
remove them and cultivate them in
the laboratory. Pure cultures of an
organism are thus obtained, Pseud,
campestris (Fig. 53). It is easy to
keep this growing in the laboratory
for months under strict observation.
Having thus obtained a pure culture
it can be demonstrated at any time
that it will produce the disease. It
is only necessary to dip the tip of
a needle into the pure culture and
then prick the leaf of a healthy plant
with it. This inoculation is followed

in a few days by the appearance of the characteristic symptoms of
the disease, starting at the point of the needle and travelling down
the plant in the usual way. By proper study it is possible to show
that the bacteria multiply in the plant following, the vascular bun-
dles which they first turn black and then destroy. Since these
bundles convey the water to the plant their destruction shuts off the
usual water-supply, and the plant wilts. It is possible at any time to
isolate the bacterium from these diseased plants and obtain it again
in pure culture. Cabbage plants pricked with sterilized needles
show no evil result, proving that it is the inoculated bacteria that
produce the disease. Such experiments as these, repeated many

Fig. 53.— The black rot of cabbage.
a, a bit of the stem showing^the
blackened fibrovascular bundles; 6,
cells, highly magnified, showing some
filled with bacteria; c, the bacteria.

300 THE PARASITIC DISEASES OF PLANTS.

times by different experimenters, leave no room to dou5t that the
bacteria are the cause of the disease in question.

The method by which the bacteria make their way into the plant
is interesting. We have learned in an earlier chapter that bacteria
frequently secrete enzymes. This Pseud, campestris secretes such an
enzyme and one that has the power of softening and dissolving cellu-
lose. As the bacteria multiply at the inoculated point they secrete
this enzyme, called cytase, which at once softens and disintegrates the
walls of the adjacent plant cells. The contents of the cells thus
exposed are quickly killed by the action of the bacteria, a toxin being
probably secreted by them for the purpose, and the bacterium, feed-
ing upon the food thus furnished, multiplies further. More cytase
is produced, dissolving more cell walls, and the disease progresses
as the bacteria thus enter the plants. In this way they travel
through the plant, chiefly in the vascular bundles, and finally may
affect the plant throughout. The cellulose-dissolving enzyme has
been found to be secreted not only when the bacterium is growing
in the host, but also in the laboratory in the bacteriologist's
test-tubes.

The bacteria have apparently three methods of entering the plant.
Through the uninjured cuticle they are unable to enter, nor can they
enter through the stomata of the plant. But if the cuticle be broken
by a wound or scratch, no matter how tiny, the broken cuticle will
offer an entrance to the germs. Further, there are on the edges of
the leaves minute openings called water pores. Through these pores
the bacteria also can enter. Seemingly they can also enter through
the roots, especially through the tips of the rootlets which are likely
to be exposed and broken during transplanting.

No effectual remedy against this disease has yet been found.
Its method of distribution from field to field is not well known, and
hitherto no means of checking it after it has made its appearance in
a field has been discovered. Wet weather, which is best for the
growth of the cabbages is, unfortunately, also best for the growth of
this parasite. That it lives in the soil from year to year seems
proved, and hence after it makes its appearance in a field it is likely
to recur year after year. Since it is confined to members of the

OTHER BACTERIAL DISEASES OF PLANTS. 3OI

Cruciferae, it is a natural 'suggestion that a change of crop to some
kind of plant not in this family should be made when any particular
plot of ground becomes infested with the disease. The destruction of
all weeds of the mustard family in the vacinity of cabbage plots is
also to be recommended..

OTHER BACTERIAL DISEASES OF PLANTS.

The illustration given will serve to show the kind of evidence
that is sought for in the study of plant diseases. In the list that
follows, demonstrative evidence has been obtained in practically all
cases, so that all of the diseases in this list may be accepted as caused
by bacteria. The list given is a long one, and if it be compared wi' h
the list of animal diseases given in the last chapter it will be seen to
surpass that list. These plant diseases have not the importance nor
have they developed the interest that attains to some of the animal
diseases, but nevertheless they are of great significance in farming
operations, sometimes causing very large losses. As in the case of
animal diseases the bacteria causing them are not confined to one
plant host. The black rot, for example, attacks the cabbage, the
cauliflower, the turnip, kale, Brussels sprouts, collards, rutabagas,
radish, as well as some other plants, all of the family Cruciferce. So,
as with the other diseases, the same parasite may attack several
hosts.

Classification of Bacterial Diseases. — ^Plant diseases are less
clearly defined and classified than animal diseases. Popular names
have been applied to them without careful discrimination till the
popular names have ceased to have any sharp meaning. The
bacterial diseases may, however, be fairly well divided into three
types, distinguished by the kind of effect they have upon the host.
These are: i. The Wilts. In these the bacteria attack chiefly the
vascular bundles, either destroying their cells or clogging them.
This shuts off the ordinary water-supply to the plants and causes
them to wilt and wither. 2. The Bacterioses and Rots. In these
diseases the bacteria invade the tissues generally, not being confined to
the bundles, and destroy the plant cells at once. They may cause the

302 THE PARASITIC DISEASES OF PLANTS.

tissues to become much softened, thus producing the soft rots, or they
may fail to cause this softening but injure them in other ways, so that
the plant does not rot but becomes filled with bacteria and the tissues
are much injured. These are sometimes called Bacterioses. 3,
The Tumor Diseases. In these cases the bacteria cause the forma-
tion of unusual growths, tubercles, or tumors, on the various parts of
the plants.

The Wilts. — The black rot of cabbage belongs to this class and
is really not a "rot," but a wilt. In addition, three others will be
briefly described.

Brown Rot of Potato, Egg Plant and Tomato {B. solanacearum) . —
Although frequently called a rot, this disease is really a wilt. It is a
widely distributed disease of the potato, especially in the northern
part of United States and Canada. The leaves of the attacked plant
first wilt and shrivel and then the stem turns brown or black. The
affection extends down the vascular bundles and may reach the
tuber. In this it spreads through the vascular bundles, causing in
time a destruction of the potato that has given to it the name of
brown rot. The bundles are found to be filled with bacteria in
great numbers, that destroy the cell walls, finally causing the com-
plete disintegration of these tissues. The isolation of the bacterium
is easy and inoculation experiments show that it is capable of pro-
ducing the same disease in various members of the potato family.
The bacterium appears to be carried from plant to plant by insects,
and the potato beetle is an important agent in its distribution.

The term potato rot is applied to any form of disease that is
followed by the rotting of the potato. There are several different
parasites that produce this phenomenon, some of them belonging
to the higher fungoid types. It is thought that this bacterial disease
is the cause of the larger part of the rots in our Northern States. A
second bacterial rot of the potato is caused by a bacterium named
B. solanisaprus (Har.). It is also a wilt rather than a rot, as we
have used the terms, although after it affects the tuber itself it pro-
duces a general decay of the tissues. It is common in Canada,
where it was first described. A third bacterial potato rot is caused
by B. atrosepticus (VanHall).

OTHER BACTERIAL DISEASES OF PLANTS. 303

It is important to not€ that the bacterium that causes the brown
rot of the potato can also live as a parasite in the tobacco plant where
it produces what is known as the Granville wilt.

The Wilt Disease of the Gourd Family (B. tracheiphiluSy Sm.). —
This bacterium attacks various members of the gourd family, being
best known in the cucumbers, muskmelons, pumpkins, and squashes.
The bacterium that produces it will grow readily in laboratory
media and invariably produces the disease when it is inoculated into
healthy plants. It causes the wilting of the plant by clogging up
its vascular ducts. The bacteria appear to be distributed by in-
sects which inoculate the plant, chiefly on the leaves, by puncturing
or by eating holes in them. The cucumber beetle and the squash
bug are especial offenders in this respect, and anything that will
keep these insects in check will help to reduce the troubles from the
disease.

The Corn. Wilt (Pseudomonas stewarti). — This disease affects
sweet corn in the early summer. The leaves wilt without apparent
cause and the plant gradually withers and dies, at times in four
days and at others as much as a month is required. Sometimes
the attacked plants will recover. Usually the leaves are affected one
after another, but sometimes the whole field seems to be attacked at
once. If the stem is cut lengthwise the vascular bundles will appear
as yellow streaks, which become black in the dead stems. If cut
across, these bundles exude a yellow viscid substance that is com-
posed mostly of bacteria that are the agents that produce the
disease. The germs are thought to be distributed by the seeds of
diseased plants, and no remedy has been suggested except to select
resistant varieties of corn, and to use care not to plant seed from
infected plants.

While this bacterium attacks only sweet corn, there is another
species that injures field corn. This has been variously named
{B. ZecB, B. cloacce). It causes quite a different type of trouble,
producing dark purplish discolorations on the leaf sheath, giving a
yellow coloration to the plant and causing the ears to undergo a
moist rot. It also attacks the broom corn.

A wilt of the sugar-cane is produced by Pseud, vasculans.

304 THE PARASITIC DISEASES OF PLANTS.

The Bacterioses and Rots. — A single illustration of this
type must suffice.

The Fire Blight of the pear, quince, apple, etc., (B. amylovorus.) —
This bacterium attacks various members of the apple family and
a number of other plants as well. The disease has been known
for over a century and almost every conceivable explanation has
been given for it. That it is caused by a bacterium has been finally
demonstrated by the isolation of the organism and the reproduction
of the disease by inoculation experiments. In the form known as
the twig gall, the first indication of the disease is commonly seen in a
browning or blackening of the leaves of the young shoots, which soon
die. It then extends into the stem by the way of the inner bark, causmg
it to become blackened. The whole of this tissue is destroyed by the
bacterium, causing a girdling of the tree. Then it extends down the
stem, sometimes going at the rate of an inch a day, and eventually
causing great injury or complete destruction. It- particularly
attacks the stored starch, converting it into a gummy substance.
The diseased area may extend for a distance down the stem causing
a patch of "canker", and if checked in its growth by the onset of
winter, it remains alive in the stem till warm weather, when it once
more begins its work of destruction. In moist weather a viscid
mass extends from the canker spots, containing bacteria. .Little
is known of its means of distribution, although it is thought that
it may find entrance through the flowers and be carried to them by
bees. It may, however, enter through wounds in the bark elsewhere.
The only feasible method of fighting it of any value is to cut away the
diseased parts as soon as the trouble appears, great care being taken
to be thorough in the pruning and to cut away every bit of diseased
wood.

Other examples of this type of bacterial diseases are the following.

Bean blight, produced by Bact. Phaseoli.

Cotton bacteriosis, produced by Bact. malveacarum.

Walnut bacteriosis, produced by Pseud, juglandis.

Mulberry blight, produced by B. cubonianus.

Black spot of plum, produced by Pseud. Pruni.

Wakker^s disease of hyacinth, produced by Bact. Hyacinthi.

OTHER BACTERIAL DISEASES OF PLANTS.

305

Soft rot of turnips, etc., produced by B. oleracecB.

Soft rot of carrots, produced by B. caratovorus.

Soft rot of sugar beet, produced by B. tenthium.

Soft rot of stored celery, caused by Pseud, fluorescens.

Rot of iris, produced by Pseud, iridis.

White rot of turnip, produced by Pseud, destructans.

Gummosis of beet, produced by B. Beta.

Soft rot of onions is also caused by bacteria, and there are some
other diseases less well known.

The Tubercular or Tumor Diseases. The Olive Knot {B.
savastanoi) . This disease, first studied in 1886, and attributed
upon insufficient proof to a bacterial origin,
has recently been demonstrated to be a
bacterial disease. The bacillus is a motile
one with several flagella at one end and
grows in ordinary culture media in the
laboratory. Several different bacteria have
been found associated with this disease, but
the one to which the above name has been
given is its cause, as shown by the fact
that the inoculation of olive trees with
cultures of the organism is invariably
followed by the appearance of the charac-
teristic symptoms of the disease at the point
inoculated. The effect of the bacillus is to
stimulate the plants to unusual growth. The various tissues of the
stem multiply more profusely than common, producing a swollen
growth on the stem which is called the olive knot (Fig. 54). This
injures the trees and sometimes kills them. The organism, so far
as known, enters- the plant exclusively through wounds. It occurs
in the various olive-raising countries of Europe and Africa, and also
in California.

The Crown Gall of the Peach and Other Plants (B. tumifaciens.) —

This disease, until recently attributed to a different class of

fungi, has now been proved to be caused by a bacterium. In][the

peach it commonly produces an enlarged growth at the crown of

26

Fig. 54.— The black knot
of the olive.

3o6

THE PARASITIC DISEASES Of PLANTS.

the plant, between the stem and the root. The parasite that
causes it has the power of growing upon a large series of plants,
producing tumors in various parts of the plant which injure it
more or less, according to the extent of the infection. Among the
plants that may be infected with it are the raspberry (Fig. 55), the
daisy, the hop, the radish, the cabbage, the tobacco, the sugar beet,
the grape, the tomato, the oleander, the apple, and some others.
It is unusual for a parasite to have such a long list of possible hosts,

but in all these plants it has been demon-
strated by Smith that tubercles will be
produced by the inoculation of pure
cultures of the organism. It is the cause
of considerable losses to horticulturalists.
Root Tubercles of Legumes. — These
have been considered in a different con-
nection (Chapter VII), but they are
properly classed here. They are cer-
tainly caused by parasitic bacteria,
although in this case apparently both the
parasite and the host are benefited by the
association, a condition sometimes called
symbiosis rather than parasitism.

Remedies. — Remedies for the bacterial
diseases are not as yet very satisfactory.
Spraying, so frequently efficient against
fungoid diseases, is of no value here, be-
cause the bacteria are always within the tissues of the plant where
the spray cannot touch them. Hence in dealing with plant diseases
in general it is always desirable to know whether they are fungoid
or bacterial, since in the latter case spraying is always useless.
Each disease has to be met by devices adapted to the peculiar
nature of the disease, and no general principles can be given beyond
that already pointed out on page 295.

Fig. 55. — The crown gall on the
loot of the raspberry.

PART VI.

APPENDIX.
CHAPTER XXI.

LABORATORY WORK.

Laboratory work should, so far as possible, accompany the study
of the text. It is impossible to make a series of experiments that will
closely follow the order of topics in the text, since a large amount of pre-
liminary work has to be done in making media before actual study of
bacteria begins. The order of experiments below given will be found a con-
venient one to follow, but may be modified to suit convenience.

APPARATUS NEEDED.

Steam sterilizer.

Autoclave.

Hot air sterilizer — A common gas oven used for cooking will do.

Stew-pan for cooking media.

Flasks. — Liter and half-liter.

Test-tubes, heavy — Board of Health pattern.

Petri dishes — four inches in diameter.

Pipettes — I c.c. and 2 c.c. Some larger ones are also convenient.
Each of the smaller ones should have a glass tube holder (Fig. 56) or there
should be a metal box with cover to hold fifty or more pipettes at once.

Wire baskets to hold test-tubes.

Test-tube racks, or common tumblers with a little cotton in the bottom
to hold test-tubes.

Beakers.

Evaporating dishes.

Fermentation tubes.

Burette holder with four burettes.

Evaporating dishes.

Measuring cylinders — i liter and 100 c.c.

Counting plate or counting card.

Platinum wire to be fused into glass rods.
. Culture oven with constant temperature of 98°.

Bunsen burners.

3o8

LABORATORY WORK.

Fig 56.—
1 c.c. pipettes
inclosed in
glass tubes for
sterilizing.

Forceps — Common and Cornet forceps.
Microscope with i /12 immersion lens and plenty of slides
and cover-glasses.

MATERIALS.

Peptone (Witte)
Salt

Beef extract
Gelatin— Gold label
Agar-agar

Litmus, dry in cubes
Absorbent cotton
Fuchsin

Dextrose, lactose, and
saccharose

Normal NaOH and Normal

HCl.
Phenolphthalein
Alcohol

Corrosive sublimate
NaOH
HCI

Azolitmin
Methylene blue
Common cotton, good quality

No. I. Washing and Sterilizing Glassware. — All glass-
ware must be thoroughly washed in hot water and soap.
New glassware should first be treated with i per cent. HCl.
Used glassware, containing remains of gelatin or agar, should
first be boiled in water containing powdered soap or sal soda.
Follow this with thorough washing in hot water, rinsing in
cold water and draining.

To begin with, the student may wash 50 test-tubes, 2 one-
liter flasks, one dozen Petri dishes and several i c.c. pipettes.
After drying, place the pipettes in glass holders or a metal
box, plug the test-tubes and flasks tightly with cotton and
place these -with the Petri dishes in the sterilizing oven.
Heat for one hour at 310° F. (155° C.) for one hour. All
glassware should be subsequently sterilized in the same
way before using.

No. 2. Preparation of Agar Culture Medium and Bouillon.
— Measure out the following:

Water i liter

Liebig's extract of beef 3 grams

Common salt 5 grams

Peptone 10 grams

a. Divide in two lots, set one-half aside (see below);
place the other half in a stew-pan and carefully weigh the
dish and its contents, noting the combined weight for future
use. Dissolve the mixture at about i 50° F. (6o°C.). Add
6 grams of agar-agar (1.2 percent.), cut into small pieces, and
dissolve by heat. It takes considerable heat to dissolve the
agar and may require boiling. Boil till the agar is com-
pletely dissolved and then replace the water that has evaporated by adding
cold water till the original weight has been restored.

MATERIALS.

309

If CI

y/oNormal
NaON

h. Adjust the acidity to 1.5 per cent, as follows:

Measure out 10 c.c. of the mixture, placing it in an evaporating dish
with ten times its bulk of water. Bring to a boil and add a few drops of
phenolphthalein solution.* This solution is colorless so long as it is acid,
but turns red when alkahne. The agar medium remains red after the
addition of phenolphthalein, showing it to be acid.

Place the evaporating dish under a
burette containing i/io normal NaOH
(one part normal NaOH diluted with
nine parts of distilled water) (Fig. 57).
Take the reading on the burette. Allow
the solution to fall drop by drop into the
evaporating dish, stirring between each
drop. As long as the material remains
acid no color will appear. Continue
adding the NaOH until a faint red color
appears and does not disappear upon
stirring. When this point is reached
the contents of the evaporating dish
are neutral.

Take the reading upon the burette
and determine the difference between
the first and second reading. The
difference gives the number of cubic
centimeters of i/io normal NaOH
needed to neutralize 10 c.c. of the cul-
ture medium. Divide by 10 to de-
termine the amount necessary to neu-
tralize one CO., and multiply by 990 to
determine the amount necessary to
neutralize the rest of the agar medium.

Add to the agar medium sufficient
NaOH to neutralize it. Instead of
adding i /lo normal, add normal NaOH,
using of course only i/io as many •
cubic centimeters as the above calcula-
tion shows would be needed of i/io
normal NaOH. This will bring the
whole to the neutral point.

Add normal HCl to the amount of
15 c.c. per liter. In this case, there being only 990 c.c. left, the amount
added should be 14.9 c.c. This makes an acidity of 1.5 per cent., the best
reaction for most bacteria.

c. Boil vigorously for fifteen minutes and then restore the original
weight by adding water. Test the reaction again as before to see if it is

♦ Eight per cent, phenolphthalein in 50 per cent, alcohol.

\

Fig. 57 — Two burettes arranged for
neutralizing culture media.

3IO

LABORATORY WORK.

correct. It should require 1.5 c.c. of i/io normal NaOH to neutralize
the acidity in 10 c.c. If the reaction is right, cool to about 60° F. and add
the white of an egg which has been mixed with a little water, adding slowly
with stirring. Heat slowly and allow to simmer until the egg has co-
agulated and the liquid is clear. This may take half an hour or more.
Add water to bring to the original weight again, plus the weight of the
added egg, and then filter as follows:

d. Place a considerable quantity of absorbent cotton in a large funnel
(Fig. 58). Over the top of a second funnel above the first, place some cheese-
cloth. Pour the hot agar medium into the cheese-cloth. It will run through

Fig. 58. — Showing method of filtering culture media.

rapidly ; then filter through the cotton to be caught below in a beaker or
flask. It should be transparent, clear, and of a yellowish-brown color. If
it is not clear a second boiling with a second egg will usually clear it.

Place 10 c.c. of this agar medium into each of 25 test-tubes, replacing
the cotton plug. In filling these tubes use either a 10 c.c. pipette or a
funnel, taking care not to allow the agar to touch the sides of the tubes
where the cotton is to be inserted.

e. Place the test-tubes, together with the flask containing the remain-
der of the medium (tightly plugged with cotton) in the autoclave and steril-
ize at I 5 lbs. for 30 minutes. Cool, and after the pressure is down to zero,
remove from the autoclave. While still hot lay the test-tubes down on a
table with their mouths slightly raised, so that the agar will form a slanting

MATERIALS.

311

surface (Fig. 59). Allow them to harden in this position and set aside for
future use. Keep this and all other culture media in a cool dark place until
used.

Bouillon. — To make bouillon the procedure is as above, except that agar
is not added. The other half of the dissolved mixture of water, peptone.

Fig. 59. — Showing method of hardening agar slants.

salt, and beef extract, in a, is brought to the acidity of 1.5 per cent, in
exactly the same way as above described, and, after a boiling (the egg
white is not necessary here) the bouillon is filtered through filter-paper,
placed in tubes, and sterilized in exactly the same manner as agar medium.

P'iG. 60. — A steam sterilizer (Fowler).

If it is not convenient to use the autoclave, either of these may be
sterilized by discontinouus heating as follows: Place the tubes and flask
in a steam sterilizer and steam for one-half hour (Fig. 60). Set aside for
twenty-four hours and then steam for another half-hour. Set aside once

312

LABORATORY WORK.

more for twenty-four hours and then steam a third time. If properly-
sterilized these media will keep indefinitely.

No. 2. Determination of the Number of Bacteria in Water. — Melt three
tubes of agar as above made in hot water and cool to about 125° (500C.)
With a sterilized pipette place a cubic centimeter of water from any source
in each of three Petri dishes (Fig. 61.), and pour the agar from one of the
melted tubes into the Petri dish. Replace the cover again at once and by
gentle agitation, thoroughly mix the agar in the dish with the water first
added. Do not do this violently enough to spill or throw the agar up on
the sides of the plate. After mixing set on a level table to harden and
then place in the culture oven. These preparations are called agar plates.
After twenty-four hours the plates will be seen to be dotted over with
colonies, each supposed to come from a single bacterium. Count the
number of colonies; this will give the number of bacteria in the original
c.c. of water that have been able to grow in the medium.

Fig. 61. — A petri dish for making "plates."

No. 3. Water Blanks. — Place in a considerable number of test-tubes
9 c.c. of water. In a series of small flasks or bottles place 99 c.c. of water
(i.e., add 100 c.c. and then remove i c.c.) After plugging tightly with
cotton, place in the autoclave and sterilize at 1 5 pounds for one hour. It is
very desirable to have test-tubes and bottles used for these water blanks
with a mark etched upon them at the 9 c.c. and 99 c.c. level. When they
are to be subsequently used for dilution care should be taken to see that
they are filled, exactly to the mark, since evaporation frequently with-
draws some of the water, and unless they contain the exact quantity, errors
will be introduced.

No. 4. Determination of the Bacteria in Milk. — Milk commonly contains
so many bacteria that it must be diluted before the bacteria are determined.
The amount of dilution needed will vary widely with the age of the milk.
For most market milk a dilution of 1,000 will serve. Proceed as follows:
Into a 99 c.c. water blank place i c.c. of the milk to be tested. Shake
vigorously so as to distribute the bacteria uniformly. With a second pipette
transfer i c.c. of this mixture to a 9 c.c. water blank and again thoroughly
mix. With a third pipette place i c.c. of this in a Petri dish and then pour
upon it the contents of an agar tube. Agitate as in the last experiment,
allow to harden and incubate in the oven for twenty-four hours. Use a
counting plate in counting the colonies. If they are too numerous to

)

MATERIALS.

313

count directly, count the number in one of the areas in the counting plate
and multiply by the number of such areas covered by the whole plate.
This will give the number of colonies on the plate, and this multiplied by
1000, will give the number in the original milk. There may be any where
from a few thousand to several millions. It frequently happens that the
dilution of 1000 is insufficient, giving too many colonies on a plate. Higher
dilutions are needed in such instances, but whether to make a higher dilu-
tion can only be determined by a knowledge of the age and
temperature of the milk and by experience.

From these and from the plates of the following two ex-
periments isolate and purify cultures as directed in No. 7.

No. 5. Bacteria in the Air. — Pour the contents of several
tubes of agar into Petri dishes, replace the cover and allow
to harden. Remove the cover from one of them and allow
it to remain open in the laboratory for two minutes. Then
replace the cover and place in the incubating oven. Expose
a second in the same way in a barn; a third out of doors; a
fourth in a barn after hay has been thrown down in front of
cattle. Other Petri dishes may be exposed in other localf-
ties. After twenty-four hours' incubation count the num-
ber of colonies and compare the relative number of bacteria
in the air at the different places.

No. 6. Bacteria on the Fingers. — Pour a Petri dish as
above directed and allow to harden. Remove the cover of
one and touch it gently with the fingers in several places.
The hands may then be thoroughly washed, and a second
Petri dish treated in the same way. Incubate for twenty-
four hours and see if bacteria colonies have grown where the
fingers touched the agar.

No. 7. Isolation and Purification of Bacteria. — Any of
the plates above prepared will show after proper incubation
a number of colonies. Comparing the different colonies
noticeable differences will be seen between them. These
differences in the colonies commonly indicate different kinds
of bacteria, for the same kind of bacteria produce, com-
monly, the same kinds of colonies.

Isolation. — Sterilize a platinum needle (Fig. 62), in a flame until red-hot
and after allowing it a few seconds to cool, dip the tip of it into one of the
colonies. Transfer the bacteria adherent to the needle to one of the agar
slant tubes by removing the plug and drawing the tip of the wire over
the surface of the agar. Sterilize the needle again before laying it down.
Label the tube with a gum label telling its source. In a note-book make a
brief record of the kind of colony from which it was obtained. Allow the
inoculated tube to grow, either in the incubating oven or in the room, until
a growth appears on the surface of the agar. This is an agar slant.

Purification. — If the colony thus isolated has grown from a single bac-
terium this growth on the agar will be a pure culture. But this is not
27

Fig. 62.—

P latinum

needle and

platinum loop.

314 LABORATORY WORK.

always the case and therefore the culture must be purified. With the tip
of a platinum needle remove a minute quantity of the growth on the agar
and place it in a 9 c.c. water blank. Thoroughly shake and transfer two
platinum loopfuls of the water to a melted agar tube. Shake gently so
as to mix, but not to produce bubbles, and then transfer two loopfuls of
this agar to a second agar tube, mixing as before. Pour the contents of
each agar tube into a Petri dish, harden and incubate as usual. If the cul-
ture was pure the colonies should be all alike. Pick out one of them with
the platinum needle, inoculate it upon another agar slant and label it a
pure culture from milk or whatever may have been its source. In this
condition it may be set aside and preserved for a long time. As long as the
agar remains moist the bacteria will usually be alive.

In the above manner isolate and purify a considerable number of cul-
tures of bacteria from the plates made in Nos. 4-6, and keep these in a cool,
aark place for use in various experiments given below.

No. 8. Microscopic Study of Bacteria. — Prepare one or both of the
following staining solutions:

Methylene Blue.

Saturated alcoholic solution of methylene blue, 1 5 cm.
Potassium hydrate (1:10,000),* 50 c.c.

Fuchsin Solution.

Saturated alcoholic solution of fuchsin, 5 c.c.

Five per cent, solution of carbolic acid, 45 c.c.

In the middle of a clean microscopic slide place a drop of water (steril-
ized). With a platinum needle remove a very small quantity of the bac-
teria growth from the surface of one of the slant cultures prepared in No. 7
and place in the drop of water. Stir this drop with the needle, to distribute
the bacteria and then (a) spread it over the slide. Allow it to dry in the air,
and then pass the slide three times slowly through a gas flame. The pur-
pose of this is to (6) fix the bacteria firmly to the slide so that they will
not be washed away. It is necessary not to use too much heat. This may
also be done by leaving the slide for a few minutes on a water-bath. After
fixing, cover the bacteria completely with several drops of one of the stain-
ing solutions and allow to (c) stain for several minutes. The length of time
necessary for this varies with conditions, one to five minutes being usually
sufficient. Wash off the stain in running water and then dry the slide by
gentle heat. Place a drop of immersion oil upon the stained bacteria and
place the slide under the microscope. Use a i /12 inch immersion, lowering
the objective into the immersion oil and focusing very carefully. If the
microscope has an Abbe condenser or a diaphragm it is best to have this
widely open. The bacteria are so minute that it is hardly possible to study
them with a lower magnifying power than a 1/12, although they can be

* To make this solution add i c.c. of a 10 per cent. KOH solution to 99 c.c. of water, and then
add 5 c.c. of this to 45 c.c. of water.

MATERIALS. 315

seen with a i /6 inch. Examine the bacteria and sketch. In this way
make a microscopic examination of all of the cultures isolated and puri-
fied, and compare with Figs. 7 and 9. If it is desired to preserve the speci-
men place a drop of Canada balsam on the bacteria after drying, and
then cover with a cover-glass.

Motility. — To determine the motility of bacteria transfer a small quan-
tity from an agar slant to a bouillon tube, and allow to grow for 24 hours.
Place a drop of the 24-hour-old bouillon culture on a slide and put upon it
a cover-glass. Examine this with a i /6 inch objective and with the dia-
phragm nearly closed. The best light for the purpose is artificial light (elec-
tric) placed near the microscope and reflected through by the plain surface
of the mirror. It will be very difficult at first to see the bacteria, but with
careful focusing they will appear as transparent dots or rods. Examine
carefully to determine whether they are stationary or motile, calling
only those motile that move back and forth across the stage and not those
that simply dance back and forth without locomotion (the Brownian
motion). It is sometimes desirable to keep the specimen under observa-
tion for some time in which case a hanging-drop method may be used.
A concave slide is to be used and a ring of vaseline painted around the
depression. The drop containing the living bacteria is placed in the
middle of a large cover-glass and inverted over the concavity of the slide.
By pressing it firmly into the vaseline ring it will be sealed so as to prevent
evaporation and may be kept under observation for hours.

No. 9. Bacteria in the Mouth. — With a clean knife scrape a little of
the material attached to the teeth and spread it in a very thin layer over a
slide. Dry, fix and stain, and with a microscope note the large numbers
of bacteria present. Sketch the varieties seen.

No 10. Gram Stain. — Prepare the following:

Anilin Oil Gentian Violet.

Saturated alcoholic solution of gentian violet, 6 c.c.
Absolute alcohol, 5 c.c.

Anilin water,* 50 c.c.

Grams lodin Solution.

lodin, I gm.

Potassium iodid, 2 gm.

Distilled water, 300 c.c.

Spread and fix on a slide, a little of one of the cultures of bacteria,
and stain for one and one-half minutes in the gentian violet solution. Pour
off stain, without washing, and place in the iodine solution for one and one-
half minutes. Apply 95 per cent, alcohol until the drippings do not stain
white filter-paper. This will take about three minutes and the specimen
will be largely decolorized. Wash in water and study with microscope to

♦Made by adding 2 to 3 c.c. anilin oil to 50 c.c. of water and shaking thoroughly, with subse-
quent filtering.

3l6 LABOEATORY WORK.

see if the bacteria are still stained blue or have been decolorized. Differ-
ent species differ in this respect. If they are still stained they are Gram-
positive; if decolorized, they are Gram-negative.

No. II. Microscopic Study of Yeast. — Rub up a bit of an ordinary yeast
cake in a little water. Place a dilute drop on a slide and proceed to stain
exactly as above described for bacteria. Study with 1/12 immersion lens
and compare with yeast as to size and shape. Look over the specimen and
find some cells that show buds.

No. 12. Gelatin Culture Medium. — a. Weigh out the same ingredients as
directed in No. 2, omitting the agar. After the mixture has dissolved add 1 2
per cent, of first-grade gelatin. Allow to soak till soft and almost melted.
Weigh the dish with its contents. Bring to a boil slowly and boil for five
minutes and add water to restore original weight.

b. Determine the acidity and bring the reaction to 1.5 as described in
No. 2.

c. Boil 1 5 minutes. Cool and add the white of an egg dissolved in a
little water. Heat slowly to boiling and allow to boil gently till the egg
is coagulated and the liquid clear ; usually about 1 5 minutes. Replace the
evaporated water.

Heat once more to boiling and filter through absorbent cotton. Place
10 c.c. in each of about fifty tubes and the rest in a flask, plugging both
with cotton. Sterilize in the steam sterilizer for twenty minutes. Set
aside for twenty-four hours and steam a second time; this time allow
half an hour steaming. Set aside for another twenty-four hours and steam
again. Gelatin cannot be sterilized in the autoclave satisfactorily, since
too high a heat will prevent its subsequently hardening when cooled.
Too long boiling will in the same way ruin the gelatin.

No. 13. Litmus Gelatin and Litmus Agar. — These are used chiefly to
detect acid-producing bacteria. Make agar or gelatin in the manner al-
ready described, except that i per cent.' lactose is added, and 1.5 per cent,
agar instead of 1.2 per cent., or 15 per cent, gelatin instead of 12 per cent.
These are to be filtered in the usual way, and are known as lactose agar
and lactose gelatin.

Prepare a litmus solution by soaking 50 grams of dry litmus cubes with
250 c.c. water. Soak for twenty-four hours and filter through filter-paper.
Add enough of this to the agar or the gelatin to give it a blue color. Tube
the medium as usual and sterilize.

Instead of using the litmus solution azolitmin may be used. This
is a powder that may be dissolved in a little alcohol and sufficient added to
the lactose agar or lactose gelatin to give a blue color. Its use is simpler
and in some jespects better than litmus solution.

No. 14. Gelatin Plates from Milk. — Procure some milk that is not more
than six hours old. Dilute 1000 times, as directed in No. 4. Place i /2 c.c.
of the dilution in two Petri dishes and i c.c. in two others. Pour into each
the melted gelatin from one of the gelatin tubes prepared in No. 12.
Thoroughly mix by gentle agitation and place in a cool place to harden.
Set aside at a temperature of about 70° for the bacteria to grow. If

MATERIALS.

317

the temperature rises above 80° the gelatin is likely to melt and spoil the
plate. It takes about two days for the colonies to appear. After two or
three days carefully study the plate, noting the liquefying colonies and the
non-liquefying colonies. Note also other differences. Isolate and inocu-
late upon agar slants several of the different colonies, including both
liquefiers and non-liquefiers.

Litmus gelatin or litmus agar plates should be made in the same way, and
the appearance of a red color around some of the colonies will make it pos-
sible to detect the acid-forming bacteria.

No. 15. Potato Tubes. — Select a large fair potato, care- , ^ ^

fully wash and peal. With a special cutter or with a broken
test-tube with sharp edges, bore out some cylindrical plugs
of potato. Cut them obliquely so as to make two wedge-
shaped pieces of each plug, and soak in running water
overnight. In the bottom of some large test-tubes place
a little cotton and enough water to cover it (Fig. 63). Place
a single potato slant in each tube and sterilize by one-half ||

hour steaming upon three successive days.

No. 16. Milk Tubes. — Place about 10 c.c. of skim milk in
test-tubes and sterilize for one-half hour on three successive ||||||l

days. The milk should be first tested with litmus-paper,
and if acid, should be made neutral by adding NaOH. ||{|

Litmus Milk. — This is made as above, except that enough
litmus solution is added before sterilizing to give a moder-
ately blue color.

No. 17. Fermentation Tubes. — Prepare 200 c.c. of
bouillon as described in No. 2, adding to it 2 grams lactose
and adjust the reaction to the neutral point. To a second
lot of bouillon add the same amount of dextrose and to a
third lot the same amount of saccharose. After dissolving
and filtering pour into fermentation tubes, enough to fill the
closed arm and half the bulb (Fig. 64). A dozen or more
tubes of each of these bouillons should be prepared and Fig. 63. —

labeled. Sterilize by steaming on three days. If gas col- Potato tube,
lects in the closed arm remove by tilting the tube.

No. 18. Testing Characters of Bacteria. — Several isolated and purified
cultures of bacteria have been prepared in No. 7. After having prepared
the several culture media above described, use them as follows : Make a
fresh agaT slant from each purified bacteria culture and allow to grow
about 24 hours. If possible use a culture of B. coli for one of the series of
tests. Then inoculate with a small quantity of the growth the following.

a. Two agar slants, h. One gelatin stab. This is made by dipping a
straight platinum needle into the bacteria and then thrusting it straight
into the gelatin of a gelatin tube, in the middle of the tube, and forcing the
needle to the bottom, carefully withdrawing without disturbing the gelatin.
c. A fermentation tube of each of the three sugars, d. Two milk tubes.
/. Two litmus milk tubes, g. Two potato tubes, inoculating the potato'on

3i8

LABORATORY WORK.

its surface only. Place one of the agar tubes, one of the milk tubes, litmus
milk tubes, and potato tubes in the incubating oven at 98°. Place all others
at room temperature. Allow to grow several days, examining each day,
For each species of bacterium note the following points:

Agar Slants; Color. Is growth thick or thin, moist or dry; does it
spread ?

Morphology. — With the microscope study stained specimens; note
shape — formation of chains — spores. Determine motihty.

Gelatin Stab. — Note liquefaction, needle growth, surface growth.
Compare growth with Fig. 35.

Bouillon. — Note turbidity, scum, sedi-
ment.

Milk Tubes. — Note at 98° and 70° the
development of acid as shown by its action
on litmus, curdling, separation of whey,
appearance of gas bubbles, subsequent
softening and solution of the curd, called
digestion.

Potatoes. — At 98° and 70°, note color,
abundance of growth, texture of growth,
discoloration of potato.

Fermentation Tubes. — After several
days note whether gas has collected in the
closed arm. If not, record the bacterium
as forming no gas. Test the liquid in the
bulb with litmus-paper to see if acid. If
gas is formed in any tube place a mark
on the tube at the top of the liquid to
mark the amount of gas. Then fill the
bulb completely with a 2 per cent. NaOH
solution. Place the thumb over the open-
ing of the bulb so that there will be no gas
bubble between the thumb and the surface of the liquid. Invert the
tube, allowing the gas to flow into the bulb, and by turning back and
forth mix the gas with the NaOH solution, keeping the thumb in position
all the time. After mixing turn the tube once more so that all the gas
will be in the closed arm. Remove the thumb and it will usually be found
that the level of the liquid in the closed arm rises, because some of the gas
has been dissolved in the NaOH. This dissolved gas is CO2. By deter-
mining the level of the gas before and after the treatment the proportion
of CO2 to the undissolved gas may be determined. This is called the gas
ratio.

Tabulate the characters of the different species of bacteria tested,
determining whether any two of them are alike in all respects. It is
by such characters that bacteria are described. To determine species is
too difficult for a beginner.

No. 20. Test for Indol. — Make the following :

Fig. 64. — ^Fermentation tube with
closed arm containing gas.

MATERIALS. • 319

Dunham's Solution.

Peptone, i gm.

Sodium chlorid, o . 5 gm.

Distilled water, 100 c.c.

Dissolve, place in test-tubes and sterilize as usual. After sterilization
uioculate tubes with several different pure cultures of bacteria and allow
to- grow for 10 days. Add i c.c. of a 0.0 1 per cent, solution (fresh) of
potassium nitrite and a few drops of concentrated sulphuric acid. Heat
gently. If a pink color appears it indicates the formation of indol, a charac-
ter used to distinguish certain species of bacteria {e.g., B. coli).

No. 21. Putrefa(;tion. — Place in a series of test-tubes with a little cold
water the following: a. A bit of raw meat; b. some white of egg; c.
some flour; d. some crushed beans; e. sugar;/, starch; g. a bit of melted
butter. Set in a warm place for two or three days and determine which
will putrefy and which will not.

From the tube containing the meat and the egg, remove a bit of the liq-
uid as soon as putrefaction begins and examine under a miscrocope (both
stained and unstained). Examine the liquid in the other tubes in the same
way. Remove a little of the putrefying mass from one tube and dilute by
placing it in a water blank. Transfer a platinum loopful of this dilution
to a melted gelatin tube and another to a melted agar tube. Mix by gentle
agitation and pour into Petri dishes. Allow to grow for two days and ex-
amine the colonies. Are both liquefiers and non-liquefiers present?

No. 22. Ammoniacal Fermentation of Urea. — Fill a test-tube or a flask
half-full of urine and allow to stand for a day or two in a warm place.
Note the odor of ammonia. Suspend a bit of red litmus-paper* in the
mouth of the tube and note that it turns blue from the ammonia fumes.
Remove a bit of the liquid with a platinum loop and examine (stained)
under microscope. Note the immense number of bacteria.

No. 23. Manure and Sewage. — Place a small drop of sewage and a small
bit of manure in separate water blanks. After thorough mixing remove a
loopful in each case and transfer to a second water blank for further dilu-
tion. After again mixing transfer a loopful of this second dilution to melted
agar or melted gelatin, gently agitate and then pour into Petri dishes.
Allow to grow for two or three days and note the number of colonies, in-
dicating the great numbers of bacteria in the original materials. A
quantitative determination can be made if desired by using i c.c. of the
sewage or i gram of manure, and diluting 100,000 times.

No. 24. Soil Bacteria. — For general study use standard media as already
described, adjusting the reaction to 0.5 per cent, acid instead of 1.5 per cent,
and using 1.2 per cent, agar and 12 per cent, gelatin. Plates made with
these media inoculated with soil will not fail to show numerous soil organisms,
bacteria and molds being very abundant. To obtain proper samples of

* Filter-paper moistened with Nessler's solution (used by chemists) is better, which should
turn yellow to reddish-brown if ammonia fumes arise.

320 LABORATORY WORK.

soil for the study of various soil problems requires special methods and spe-
cial care too difficult for elementary work. The relative number of bac-
teria in different soils may be determined as follows: Select two soils for
study, preferably one rather sandy and the other filled with humus. Ob-
tain a sample by mixing the soil well with a spade and take to the labo-
ratory about loo grams. Mix thoroughly the sample and weigh out one
gram. It is best to do this after passing the soil through a sieve. Place
in a 99 c.c. water blank and shake vigorously for two minutes. Transfer
I c.c. of this to a second 99 c.c. water blank and mix well. Transfer i c.c.
to a 9 c.c. water blank and mix again. From this transfer i c.c. to a Petri
dish and then pour upon it the contents of a melted agar or gelatin tube.
Mix in the usual way, harden, and after two to four days count the number
of colonies in the two soils. This will give the relative numbers approxi-
mately only. To obtain them exactly allowance must be made for the
water in the two soils.

No. 25. Denitrifying Bacteria. — Make a broth containing 1000 c.c.
water, i gm. peptone and 2 gm. potassium nitrate. Fill a few fermentation
tubes and sterilize by steam. Inoculate several with a little soil from differ-
ent localities. Incubate at ordinary room temperature for several days.
Gas will appear in the closed arm if denitrifiers are present. This gas is
mostly nitrogen and represents so much loss to the soil. The bacteria can
be isolated by the plate method if desired.

No. 26. Nitrogen Fixers. — Their action may be shown as follows:
Make a solution containing: MgSO^ 2 gm., KjHPO^ 2 gm., CaCl 0.2 gm.,
dextrose 2 gm., citric acid 5 gm., FeC\^ traces, water, (distilled), 1000 c.c.
Make the reaction neutral, taking great care not to pass beyond the neu-
tral point. Place some of this in a flask, sterilize by steam, and inoculate
with a little soil. Incubate at ordinary room temperature. After two or
three weeks, growth will be evident and usually a membrane appears on
the surface. This membrane contains nitrogenous matter and since there
is no nitrogen in the culture medium as above made, the nitrogen must
have been assimilated from the air. The isolation of these bacteria is
very difficult.

The study of the nitrifiers is too difficult to be undertaken by elemen-
tary students.

No. 27. The Presumptive Test for Bacillus coli. — This test is frequently
made to determine whether water is suspicious. Fill fermentation tubes
with lactose bouillon and inoculate five tubes with i /2 c.c. and five more
with I /lo c.c. of the water to be tested. Place in the incubating oven for
twenty-four hours. If gas appears in the closed arm sufficient to fill it
from I /id to 1/4 full, the test is positive and the water probably contains
B. coli. To determine this absolutely requires further tests that cannot
be given here. The purpose of using the different amounts of water is to
give a rough idea of numbers. If gas appears in all of the i /lo c.c. tubes
it will indicate that there are probably more than 10 of the gas-producing
organisms per c.c. of the water. If it appears in the 1 1 2 c.c. tubes but not
in the i/io it indicates that there are less than 10 per c.c. This pre-

MATERIALS. 32 1

sumptive test is only of value in suggesting suspicion, but insufficient to
state the presence of sewage contamination.

No. 28. Bacteria from the Root Tubercles of Legumes. — -The bacteria
that have been commonly supposed to cause root tubercles may be obtained
as follows:

Add 5 gm. of wood ashes to 1,000 c.c. water, heat in steam, boil for
one minute and filter. To the filtrate add 10 agar and 4 grm. maltose
(or some other sugar) ; heat in steam till dissolved, boil one minute and
filter. Place in test-tubes and sterilize by steaming on three successive
days, or in an autoclave for one hour at 10 pounds pressure.

Select some vigorously growing legume, not too large, and with a
spade dig up its mass of roots still embedded in soil. Wash away the soil
from the roots and probably plenty of tubercles will be found attached.
Remove a small tubercle with forceps, wash in tap water and then immerse
in a solution containing 500 c.c. water, i gram corrosive sublimate, and 2.5
c.c. HCl. It should be immersed in this for two to three minutes to steril-
ize the surface. Then the tubercle is held between folds of filter-paper that
has been moistened in the sublimate solution and a gash is cut in it with a
hot knife. A platinum needle is then sterilized and some of the central
mass of the tubercle removed and placed in a drop of sterile water on a slide.
Place a drop of sterile water in each of several Petri dishes and transfer a
small loopful of the drop on the slide containing the tubercle contents, into
the water drop in each of the Petri dishes. Pour into each a tube of the
maltose agar, allow to harden and incubate at 70°. The colonies will appear
in three to four days and may be isolated and studied in the usual manner.

No. 29. Bacteriological Analysis of Market Milk. — Collect in sterile
bottles a number of samples of market milk from different milkmen.
Keep cool with ice until they are brought to the laboratory and then plate
at once. Dilute 1,000, place i c.c. in each of two or three Petri dishes and
add a tube of ordinary agar. Incubate at 98° for twenty-four hours,
count the bacteria in each plate and determine the average. This is
the procedure commonly used in making bacteriological analyses of mis-
cellaneous samples of market milk. If there is any reason for thinking
the milk is very old a higher dilution is necessary. If, on the other hand, the
examination is to be made of milk known to be good and in cool weather,
a dilution of 100 is better.

No. 30. Bacteria in Sour Milk. — Allow some milk to stand till sour, but
not curdled. Dilute it 100,000 times (two 99 c.c. and one 9 c.c. water
blanks) and make plates in litmus gelatin or litmus agar. Incubate at
70° for two or three days and count the number of bacteria. Count the
number of acid colonies.

No. 31. Bacteria in Cream. — Make plates as in No. 30 frora fresh cream,
diluting 1,000 times and using litmus gelatin and litmus agar. Make other
plates from some ripened cream in gelatin and in agar and diluting 100,000
times. Incubate at 70° for three days and compare the plates from the
two lots of cream as to number of bacteria and relative proportion of
acid bacteria.

322 LABORATORY WORK.

No. 32. Eflaciency of Pasteurization. — Obtain some milk ten to fifteen
hours old. Make three plates as described in No. 30. Place the milk in
a jar, and heat in water to 140°, keeping it at that temperature for one-
half hour. Make from it a second series of plates. Incubate plates at 98° for
twenty-four hours. Count the number of colonies in the two sets of plates.

No. 33. Bacteria on Hay. — Place a handful of hay in water and warm
slightly for ten minutes. The water should be hardly more than luke
warm. This is called a hay infusion. Put a platinum loop of the infusion
into a water blank and inoculate a loopful of this dilution into an agar
plate. Incubate at 98° for one day and count the bacteria.

No. 34. Study of Common Molds. — Place under a bell glass, or in some
other closed box which will prevent evaporation, some pieces of bread,
slightly moistened, two or three pieces of cheese, and some slices of a lemon.
Keep these in a warm place for a few days until molds make their appear-
ance. Examine day by day until they become covered with spore masses.
Note the mycelium, its fineness of texture and the color of the spore masses.
Determine, if possible, whether the mold masses on the different objects
are the same or different species. Remove a bit of the mycelium, place
in a drop of water on a slide under a cover-glass and examine under the
microscope. Sketch the threads and their method of branching. Place
some of the spores under the microscope. Sketch. How do they com-
pare in size with bacteria and yeasts?

No. 3 5. Germination of Mold Spoxes. — Melt two or three agar tubes and
two gelatin tubes and add a few drops of HCl, just sufficient to make the
medium slightly acid. Pour out in Petri dishes and allow to harden.
With a platinum needle transfer the smallest possible quantity of spores
from one of the molds and touch the surface of the agar and gelatin in
several places with the tip of the needle. Examine with low-power micro-
scope and note that spores have been planted on the surface. Set in a warm
place and examine in twenty-four hours to see if the spores are germi-
nating. Sketch a germinating spore. Allow to grow till spores are formed,
studying daily with microscope.

No. 36. Yeast and Fermentation. — Grind up a few apples in a meat-
cutter squeeze the juice through cheese-cloth and then filter through filter-
paper. Fill six fermentation tubes with the juice, filling the closed arm
full and the bulb half -full ; plug with cotton. Set two of them in a warm
place. Sterilize the other four by steaming for half an hour. After steril-
izing inoculate, two with a little yeast (from a yeast cake) and set in a
warm place. Examine in eight to twelve hours. Note the gas bubbles
rising in the closed arm. Remove a little of the sediment and examine
under the microscope (both stained and unstained). Note the clusters of
budding yeast cells. How do they compare with the cells in the yeast
cake? After the arm is about half-full of gas, test with NaOH as described
in No. 18. By the amount of gas dissolved by the NaOH determine how
much of the gas is COj Does any fermentation occur in the sterilized
tubes? In the original unsterilized and uninoculated tubes? If fermenta-
tion occurs in the latter examine with a microscope to see if yeast is present.

DISINFECTION. 323

No. 37. Decay of Fruit. — Select some sound apples and inoculate them
with mold spores by dipping the tip of a knife-blade into a mass of mold
spores of the growths in No. 34 and thrusting the tip through the skin of
the apple. It will be best to inoculate different apples with each of the
kinds of mold that have grown on the objects in No. 34, some of which
will probably be the species to produce decay. Place the apples in a fruit
jar, close the mouth, not too tightly, and set aside in a warm place. Ex-
amine day by day and note that decay soon begins, starting at the inocu-
lated points. Allow the decay to continue till the mold breaks through
the surface and produces spores. If decay does not occur, it means that
the species of mold used were not those that produce decay, and the
experiment should be repeated with molds from other sources.

DISINFECTION.

No. 38. Disinfectants. — Of the many disinfectants in use three are of
particular practical value. These, in the strength commonly used, are the
following :

Carbolic Acid Solution, 1-20.

Carbolic acid crystals, 2 5 grams

Water, 500 c.c.

In weighing the crystals of carbolic care should be taken not to touch
them with the fingers since they will burn the skin.

Corrosive Sublimate Solution, i-iooo.

Corrosive sublimate, i gram

Water, 1000 c.c.

In making and handling these solutions it should be borne in mind that
they are very poisonous.

Chlorid of Lime.

Fresh chlorid of lime,

2 5 grams

Water,

500 c.c.

This disinfectant is cheap and effective if fresh, but it will not keep,
and should be made up at the time of using. One pound of the chlorid
of lime in six gallons of water will make up an efficient, cheap disinfectant
for disinfecting walls and floors of rooms and has the advantage of being
non-poisonous.

No. 39. Testing Disinfectants. — Mix the white of an egg with ten times
its bulk of water, and place the material in a series of test-tubes filling each
about one-third full. To the different tubes add the following: a. no
addition; b. 1/4 gram salt; c. i gram salt; d. 2 grams sugar; e. 5 grams
sugar;/, one drop of corrosive sublimate solution (i-iooo); g. six drops
of corrosive sublimate solution; h. one drop of formalin; i. three drops

324 LABORATORY WORK.

of formalin; ;. one drop of carbolic acid solution (1-20); k. four drops of
carbolic solution; /. ten drops of carbolic solution; m. 1/8 gram of borax ;
n. 1/4 gram of borax. Place all test-tubes in the incubating oven and ex-
amine at intervals to see which of them undergo putrefaction and which are
thoroughly disinfected. Note how very much more efficient some disin-
fectants are than others. Which proves to be the most efficient? It is
well in this experiment to close the tubes loosely with a cork to prevent
evaporation of the volatile disinfectants.

The Use of Disinfectants. — The ordinary use of disinfectants is in con-
nection with disease, their purpose being to destroy disease germs and
thus to prevent the spreading of disease. They are sometimes used for
other purposes, such as reducing offensive odors, etc., but primarily they
are for the checking of infection. There are various methods of killing bac-
teria which may be applied under different conditions. Heat, sunlight,
drying, chemicals, and disinfecting gases are all of use in certain connections.
The determination of which is to be used will depend upon conditions.
The first problem to be settled in all cases of disinfection is when and
where the disinfecting agent should be applied to produce the desired re-
sults. A few practical suggestions as to methods may be of value.

The Person. — Of all sources of danger the one of greatest importance is
the person ; first the patient, especially after recovery, when he is to mingle
with other people, and secondly the attendants on the patient. Disin-
fection of the patient during the di'sease is rarely possible, though his skin
should be kept clean by bathing in water to which a little glycerin is added.
The nurse, however, should keep scrupulously clean. Her hands should
be carefully washed in soap and water followed by strong alcohol, or the
corrosive sublimate solution above described. Such cleaning should follow
every time that the nurse handles the patient or any article of clothing or
eating utensils touched by the patient. Other parts of the body also need
attention, but not so frequently. The hair should be kept in a cap to pre-
vent its getting contaminated, for it is difficult to clean and almost impos-
sible to sterilize it. When the patient has recovered so as to leave quaran-
tine he should receive the same treatment.

Carbolic acid solution is especially' useful as a skin wash, and is extremely
valuable in cases of cuts or skin abrasions. If all cuts and bruises be
washed at once in the carbolic solution (1/20), many a serious sore and
many a case of blood poisoning will be prevented. Every household
should have a carbolic acid solution on hand for such purposes.

Clothing, Bedding, Etc. — These articles offer a difficult problem. The
following general directions may be given.

Burn everything which is of no great value.

Boil in water all articles that can be so treated. The boiling should
continue for half an hour and will be sufficient for complete disinfection.
Steaming is sometimes employed for articles too heavy for boiling, such as
mattresses and carpets. This requires special apparatus and can rarely be
performed at home. Any article that can be soaked in water may be dis-
infected by soaking it three or four hours in water containing one part for-

DISINFECTION. 325

malin to 5,000 parts of water. Exposure to air and sunlight are good dis-
infectants for light clothing, but not for heavy articles like mattresses.
There is no good method for their disinfection. Where the infection of
such articles is considerable the only safe thing to do is to destroy them.
Excreta. — The feces, the urine, and all discharges from patients are
most likely to contain infectious organisms and must be handled and
treated with great care. One of the best methods of treating is to place"
the excreta in a vessel and cover completely with a chlorid of lime solu-
tion prepared as above described. This should be allowed to act at least
an hour before the mixture is thrown into the sewer or otherwise disposed
of. Ordinary milk of lime or dry slacked lime is useful in earth closets
or privies.

The Sick Room. — While a room is bccupied by a patient little can be
done to disinfect it. In case of a contagious disease it is desirable that cur-
tains, hangings and carpets should be dispensed with, since these catch
and hold dust. Little else can be done beyond care in keeping the room
clean. After the room is vacated it is frequently desirable to disinfect it be-
fore it is again occupied. Carpets, curtains, and bedding should be removed
and disinfected as above suggested. All surfaces in the room, including
walls, ceilings, floors, tables, chairs, and especially cracks around mop-
boards and the floor should be washed freely with a disinfectant. Corrosive
sublimate solution is frequently used, or the chlorid of lime solution. If
care is taken to wash all surfaces thoroughly, putting plenty of the disin-
fectant into the cracks, the disinfection is complete and satisfactory.
Since this plan of washing is rather long and troublesome, a simpler plan
has been widely adopted in recent years of using a gaseous disinfectant.
The gas most commonly used is formaldehyd gas. This is applied in
various ways, but the simplest is as follows: All cracks in the room are
first sealed by pasting gummed paper over them, this including cracks
around mop boards, chimneys, as well as fire-places and key-holes.
Then a pailful of steaming water is placed in the room to give moist-
ure. Lastly, one or more "formalin candles" are lighted. These are
mixtures of solidified formalin which give off the desired gas when heated
and in the candles there is added a certain amount of paraffin that will
burn. These candles can be obtained from any drug store and upon
the wrapper there is always stated the number of cubic feet that the
candle is supposed to disinfect. The number of these candles to be burned
must therefore be determined by estimating the space in the room and
using candles accordingly. It as best to use about half as much again of
the formalin candles as recommended on the wrapper, since they will
rarely be as efficient as is claimed for them. After lighting the candles leave
the room quickly and seal the door on the outside with gummed paper.
Leave closed for about twelve hours and then open windows and doors so as
to allow the gas to pass from the room. If a sufficient amount of formalin
is used this disinfection is thorough.

The Stable. — The disinfection of the stable is difficult because of the
roughness of the lumber with which the stable is made. A satisfactory

326 LABORATORY WORK.

method of disinfection is as follows: Remove all dirt from all surfaces in
the stable. This must be done thoroughly or the disinfection will not be
complete. Water must be used freely to moisten up the dry filth that
has accumulated in various parts of the stable. The removal of the dirt
is thus facilitated, and the cleansing must be thorough. After such
cleaning, the whole stable should be washed with a solution of corrosive
'sublimate, above given (i-iooo). This may be done by simply washing
with a broom, or better, by spraying, provided a proper spraying apparatus
be at hand. It must be remembered, however, that corrosive sublimate
corrodes metals badly, and no metal spraying apparatus can be. used.
After the thorough wetting down of all surfaces of the stable by the disin-
fectant the stable must again be washed with water to remove the disin-
fectant. Instead of corrosive sublimate, a solution of chlorid of lime may
be used in the same way in washing the walls and floors. A disinfection
of a stable with formaldehyd or any other gaseous disinfectant is impos-
sible, since the stables are never tight enough to prevent the gas from escap-
ing rapidly.

The Dairy. — The disinfection of the dairy must follow along essentially
the same lines as the stable. Everything must first be cleaned as thoroughly
as possible, and then all woodwork may be washed with corrosive sub-
limate, or better, with a 3 to 5 per cent, solution of carbolic acid.
These solutions must not be used for washing the vessels which contain
milk. For cleaning these vessels nothing but boiling hot water and steam
are legitimate. After the disinfection of all parts, the whole must be
washed with water.

Other localities inhabited by animals. To disinfect the barn-yard
in which cattle are allowed to roam is practically an impossibility, and the
same thing is true of the pig pen. The amount of moist material accumu-
lated in these localities is so great as to make disinfection impractical by
any means yet devised. We must make the same statement in regard to
pastures where infected cattle are allowed to roam. To disinfect a pas-
ture is an impossibility; it must be left to the action of sunlight and rains,
and these will, in the course of time, commonly produce the disinfection.

INDEX

Abortion, 288

Abscesses, 289

Acetic fermentation, 30

Acidity, determination of, 309

Acidity of soil, 120

Acid liquefiers, 152, 198

Acquired resistance, 257

Actinomyces, 12, 13

Aerobic bacteria, 19

Agar culture medium, preparation
of, 308

Air, bacteria in, 313

Air, relation to, 19

Alcoholic fermentation, 2, 25, 42,
212, 322
of milk, 157

Alinit, 119

Ammoniacal fermentation, 53, 319

Amyolytic fermentation, 25, 27

Anabolism, 23

Anaerobic bacteria, 19

Analytical processes, 24

Animalculae, 2

Anthracnose, 295

Anthrax, 258, 280

method of infection, 282
preventive inoculation, 284

Antiseptics, 243

Ascococcus, 12

Aspergillus, 7

Autoclav, 18

Azolitmin, 316

Azotobacter agilis, 94

Bacillus, 12, 13
alvei, 289

anthracis symptomatici, 287
atrosepticus, 302
betae, 305

Bulgaricus, 148, 159
carotivorus, 305
choleras suis, 286
cloacae, 303
coli, 130, 148, 320
cubonianus, 304
cyanogenes, 1 56
danicus, 94
denitrificans, 67
erythrogenes, 156

Bacilus, fluorescens, 52

lacto rubifaciens, 156

lactis viscosus, 1 54

larvae, 289

mallei, 286

mycoides, 55

necrophorus, 289

olericeae, 305

pleurosepticus, 285

prodigiosus, 156

radicicola, 98, 99, 100

solanacearum, 302

savastanoi, 305

solanisaprus, 302

stutzeri, 55

subtilis, 52

suipestifer, 285

tetanus, 287

tobacci, 226

tracheiphilus, 303

tuberculosis, 261

tumifaciens, 305

Zeae, 303
Bacillus carriers, 162
Bacteria, meaning of term, 9
Bacterial treatment of sewage, 81
Bacterioses, 301, 304
Bacterium, 12, 13
Bact. aceti, 218

acidi lactici, 145, 183

aerogenes, 147, 202

anthracis, 280

hyacinthi, 304

malveacarum, 304

phaseoli, 304
Bedding, disinfection of, 324
Beggiatoa, 116
Bird pest, 291
Bitter butter, 184

cheese, 202

milk, 155
Black leg, 287

rot, 298

spot in cheese, 203
Blight, 295
Brie cheese, 204
Blue milk, i 56
Blue spot in cheese, 203
Boiling of milk, 172

327

328

INDEX

Bouillon, preparation of, 311

Bread raising, 214

Brown hay, 241

Budding, 8

Burnt hay, 241

Butter, bacteria in, 192

By-products, 25

Camembert cheese, 204
Canning, 245

Carbolic acid, solution, 323
Carbon cycle, 45

transformation of, 41
Cattle plague, 291
Cellulose, 43
Cheddar cheese, 197
Cheese ripening, 195
Chlorid of lime, 323
Cholera, Asiatic, 129
Cider, 214
Cisterns, 133
Cladothrix, 12

Clostridium Pasteurianum, 93
Clothing, disinfection of, 324.
Cocci, 10
Coccus, 13
Cold as a preservative, 242

relation to, 18
Colonies, 9
Combustion, 42
Commercial fertilizers, 122
Compost heap, 35, 77
Concentrated milk, 176
Condensed milk, 176
Contact bed, 84
Cooling of milk, 169
Corn wilt, 303

Corrosive sublimate solution, 323
Cow, care of, 165
Cream, bacteria in, 321
Cream ripening, 181

control of, 185
Crown gall, 305

Dairy, disinfection of, 326

inspection, 179
Decay, 26, 33, 50, 51
Decomposition, 24, 50
Denitrification, 30-36
Denitrifying bacteria, 67, 320
Diarrheal diseases, 163
Digestion by bacteria, 151
Digestion of curd, 151, 196
Dill pickles, 224
Diastase, 28, 215
Diphtheria in milk, 163
Diplococcus, 12
Discontinuous heat, 18

Disease germs in milk, 161
Diseases of plants, 293
Disease, relation of bacteria to, 2
Disinfectants, 323
use of, 324
Drinking water, sources of, 130
Drying, 237

Edam cheese, 197, 203
Eggplant rot, 302
Eggs, preservation of, 248
Excreta, disinfection of, 325
Excretions of bacteria, 24
Enzymes, 29, 30, 226, 231

list of, 30

secreted by bacteria, 33

Fallowing, 122

Farcy, 286

Farm Sewage, 87

Faults in cheese, 201, 208

Fermentation, 2, 25, 29, 35, 36

tubes, 317
Filter bed, 84
Filtered water, 133
Filtering milk, 170
Fire blight, 304
Fission fungi, 9
Flagella, 11

Flavors in cheese, 196, 199
Flesh, preservation of, 238
Food of bacteria, 20

supply, 37
Foods of plants, 38
Foot and mouth disease, 290
Food rot, 289
Fore milk, 139, 169
Form of bacteria, 10
Foul brodd, 289
Fowl cholera, 285
Fruit, decay of, 323

preservation of, 239
Fruity cheese, 202
Fuchsin solution, 314
Fungi, 5, 6
Fungoid diseases of plants, 293

list of, 296

methods of combating, 295

Galactase, 138, 196
Garget, 153, 289

Gelatin culture medium, prepara-
tion, 316
plates, 316
Germicidal power, 1 59
Glanders, 286
Goiddu, 158
Gorgonzola cheese, 206

INDEX

329

Gram stain, 315
Granville wilt, 303
Green manuring, 108, 123

Hard cheese, 197
Hay, bacteria in, 322
curing of, 239
Hemp, 234
Higher fungi, 6
Hoof rot, 289
Hog cholera, 285
Horse sickness, 291
Humus, 40

Ice, 134
Indol, test, 318
Inflammation, 289
Inoculation, protective, 258

diseases controlled by, 260
Inorganic foods, 39
Iron, 117

salts, 38
Immunity, 253, 257
Isolation of bacteria, 313

Katabolism, 24
Kefir, 158
Kummys, 157

Lactic acid bacteria, 143

protective action of, 160

Lactic fermentation, 30, 34

Leben, i 58

Leeuwenhoek, i

Legumes, use of, 104
value of, 95

Leptothrix, 12

Limburger cheese, 207

Lime, 39, 1 1 1

Liming of soil, 56, 94, 121

Linen, 234

Liquefaction of gelatin, 151

Lockjaw, 287

Lophotrichic bacilli, 11-12

Lumpy jaw, 288

Magnesia, 39
Malignant tumor, 288
Manure, 120, 122

bacteria in, 319
fresh and ripened, 75
heap, bacteria in, 70
composition of, 69
fermentation of, 71, 74
losses from, 70
protection of, 73
Mastitis, 289
Mazoon, 158

Metabolism, 24

Metacoccus, 12

Methylene blue, solution, 314

Micrococcus, 12

Microorganisms, meaning of term, 5

Microscopic study of bacteria, 314

of yeast, 316
Microsporon, 12
Mildews, 295
Milk, bacteria in, 137

bacteriological analysis of,
321
Milk bacteria, growth of, 1 59

sources of, 138
Milker, 42, 166

Milk faults, miscellaneous, 1 57
Milking machines, 168

room, 167
Milk pail, 168

standard, 178

vessels, 141, 167
Mineral ingredients in soil, 40
Moisture, relation to, 19
Molds, 6

study of, 322
Monotrichic bacilli, 11, 12
Motility, II, 315
Mucor, 7

Multiplication of bacteria, 14
Mushrooms, 6, 44
Mycoderma, 217
Navel ill, 289
Neutral types, 1 53
Nitragin, 107, 119
Nitrates, 38, 47, 57, 59, 77
Nitrification, 30, 57, 63, 64, 65
Nitrifying organisms, 58, 60, 61
Nitrites, 57, 59
Nitrobacter, 60
Nitrogen cycle, 89

fixation, 92, loi, 320

fixing bacteria, 93, 95
Nitrogenous food, 47
Nitrogen, loss of, 90
Nitrosococcus, 60
Nitrosomonas, 60

Number of bacteria, determination
of, 312

Oidium lactis, 224, 240
Oleomargarine, bacteria in, 193
Olive knot, 305
Ophidimonas, 116
Organic foods, 39
Organized ferments, 26, 31
Oxidizing fermentation, 30

Parasites,

21, 251

28

330

INDEX

Pasteurization, 173

efficiency of, 322
Penicillium, 7

Camembertii, 205

Roquefortii, 206
Pepsin, 28

Peptonizing bacteria, 55, 150
Percolating filter, 84
Peritrichic bacilli, 1 1
Phosphates, 38
Phosphorus, 113
Pleuropneumonia, 291
Potash, 38, 115
Potato rot, 302

tubes, 317
Powdered milk, 177
Preservatives, chemical, 243

in milk, 171
Preservation of food, 236
Presumptive test for B. coli, 320
Proteids, 48

Proteolytic fermentation, 30
Proteus vulgaris, 52
Pseudomonas, 12

campestris, 298

destructans, 305

fluorescens, 305

iridis, 305

prunii, 304

Stewarti, 303

vascularis, 303
Ptomaines, 25
Pure cultures, 9

in butter-making, 187

tobarco curing, 228

vinegar-making, 221
Purification of cultures, 313
Pus in milk, 138
Putrefaction, 26, 33, 50, 319
Putrid butter, 185

cheese, 202

Quarter-evil, 287

Rabies, 291

Rancidity of butter, 192
Rauschbrand, 287
Red milk, 156

Rennet-forming bacteria, i 50
Rennin, 33
Reservoir, 133

Resistance against microorganisms,
252-257
method of increasing, 2 54
Rinderpest, 291
Rinderseuche, 285
Root tubercles, 96, 100, 306

Root tubercle bacteria, 98-101, 119,

321
Roquefort cheese, 206
Rots, 295, 301, 304
Rotz bacillus, 286
Rusts, 295
Rusty spot, 203

Saccharomyges, 8
Salt as a preservative, 244
Saltpeter plantations, 76
Saprophytes, 21
Sarcina, 12
Sauer kraut, 223
Scarlet fever in milk, 1 63
Self -purification of soil, 55
Septic tank, 83
Sewage, bacteria in, 319

composition of, 78

farming, 79

treatment of, 78, 81
Sheep-pox, 291

Sick-room, disinfection of, 325
Silage, 229
Silo, 35
Slimy bread, 216

milk, 153

whey in Edam cheese, 203
Smuts, 295
Soft cheeses, 203
Soil, acidity of, 120

aeration of, 121

bacteria, 319

infusion, 97

inoculation, 106, 119

microorganisms in, 39

nitrogen in, 65

origin of, 39
Sour bread, 216

fodder, 233

milk, bacteria in, 321
Soured beans, 224
Spices as a preservative, 245
Spirillum, 12
Spoiling of food, 235
Spores, 7, I 5
Springs, 133
Sprinkling filter, 84
Stables, care of, 166.

disinfection of, 325
Staining of bacteria, 314
Starches, 43
Starters in butter-making, 186

in cheese-making, 200

preparation of, 187

use of, 189

value of, 191
Sterilization, 17

INDEX

33^

Sterilization, of milk, i 7 1
Sterilizing, 311

soil, 118
Stilton cheese, 206
Streams, contamination of, 135
Streptococci, 138, 289
Streptococcus, 12

bacteria in, 145
Streptothrix, 12, 13
Sugar, 42

as a preservative, 244

bacteria in, 250
Sulphates, 38
Sulphur, 115
Sweet cheese, 202

curdling, i 50
Swelled cheese, 148, 201
Swine plague, 285
Swiss cheese, 197
Symptomatic anthrax, 287
Synthetic processes, 23

Tainted butter, 184

Takosis, 288

Tallowy butter, 184

Temperature, relation to, 16

Tetanus, 287

Texas fever, 291

Thermophiles, 16

Thunder storms and sour milk, 144

Toad stools, 6

Tobacco-curing, 224

Tobacco, diseases of, 228

Tomato rot, 302

Torula amari, 155, 202

Toxins, 252

Transportation of milk, 177

Trickling filter, 84

Tuberculin test, 271

Tuberculosis, 261

animals subject to, 263
bovine and human, 264
combat against, 269

Tuberculosis, distribution of, 266
preventive inoculation, 277
resistance against, 263
treatment of in a herd, 273
use of flesh, 277
milk, 278

Tumor diseases, 302, 305

Turnip-tasting butter, 185

Turnip taste in milk, i 57

Typhoid in milk, 131, 162
fever in water, 129

Udder, 140

Unfermented grape juice, 213

Urase, 54

Urea, 49

Vaccination, 258

Vinegar as a preservative, 244

eels, 222

making, methods, 216, 219

organisms, 218

preservation of, 222
Viscogen, 176

Washing glassware, 308

Water, bacteria in, 127

Water blanks, 312

Water-bone diseases, 129

Water, sewage contamination of,

128
Wells, 130
Wildseuche, 285
Wilts, 29s, 301, 302
Wines, 212
Wood, 44
Wooden tongue, 288

Yeasts, 8, 27, 212, 316
Yoghourt, 158

Zymase, 33

UNIVERSITY OF CALIFORNIA
BRANCH OF THE COLLEGE OF AGRICULTURE

THIS BOOK IS DUE ON THE LAST BATE
STAMPED BELOW

OCT 2 3 1930

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5m-8,'26

ffciiY^fc*

Qorm , H. V

C6

Agricultiral bacteri-

ology,

OCT a 3 isso

mr

APR 17

MAY 1 i^^

? . (5 ^ ^ '41

42744

LIBRARY, BRANCH OF THE COLLEGE OF AGRICULTURE