The story of germ life

QR56
C76s

Southern Branch
of the

University of California

Los Angeles

Form L-l

This book is DUE on the last date stamded below

m-g

1 5 1933
APR 2 7 1934

J rjtfi,
MAY 1 9 193b

MAR 6 -1958

Form L-9-5m-7,'22

VARIOUS KINDS OF BACTERIA.

. To the left the common hay bacillus (Bacillus subtilis) • to the right a Spirit
lum. B. A Coccus form (Planococcus\ C, D, E. Species of Pseudomonas.
f, G. Species of Bacillus. F being that of typhoid fever. H. Microspira.
/, A", Z, M. Species of Spirillum.— (After Engler and Prantl.)

THE STORY OF
GERM LIFE

BY

H. W. CONN

PROFESSOR OF BIOLOGY AT WESLEYAN UNIVERSITY,

AUTHOR OF EVOLUTION OF TO-DAY,

THE LIVING WORLD, ETC.

WITH ILLUSTRATIONS

NEW YORK
MCMXII

COPYRIGHT, 1897,
Bv D. APPLETON AND COMPANY.

*•' '' ' Prihfecf ftf the "United States* o! America

PREFACE.

(P THE rapid progress of discovery in the last
few years has created a very general interest in

^~ bacteria. Few people who read could be found
to-day who have not some little idea of these
organisms and their relation to disease. It is,

\* however, unfortunately a fact that it is only their
relation to disease which has been impressed upon
O the public. The very word bacteria, or microbe,
- conveys to most people an idea of evil. The last
few years have above all things emphasized the
j importance of these organisms in many relations
( entirely independent of disease, but this side of
j the subject has not yet attracted very general
attention, nor does it yet appeal to the reader
with any special force. It is the purpose of the
following pages to give a brief outline of our

r\ knowledge of bacteria and their importance in

\ | the world, including not only their well-known
agency in causing disease, but their even greater
importance as agents in other natural phenomena,
It is hoped that the result may be to show that
these organisms are to be regarded not primarily
in the light of enemies, but as friends, and thus
to correct some of the very general but erroneous
ideas concerning their relation to our life.

MIDDLETOWN, April i, 1897.
3

CONTENTS.

CHAPTER PACK

I. — BACTERIA AS PLANTS 9

Historical.— Form of bacteria.— Multiplication of bac-
teria.—Spore formation. — Motion.— Internal structure. —
Animals or plants ?— Classification.— Variation.— Where
bacteria are found.

II. — MISCELLANEOUS USES OF BACTERIA IN THE ARTS. 41

Maceration industries. — Linen. — Jute. — Hemp. —
Sponges. — Leather. — Fermentative industries.— Vine-
gar.—Lactic acid. — Butyric acid.— Bacteria in tobacco
curing.— Troublesome fermentations.

III. — BACTERIA IN THE DAIRY 66

Sources of bacteria in milk.— Effect of bacteria on
milk. —Bacteria used in butter making. — Bacteria in
cheese making.

IV.— BACTERIA IN NATURAL PROCESSES . . .94

Bacteria as scavengers.— Bacteria as agents in Nature's
food cycle.— Relation of bacteria to agriculture.— Sprout-
ing of seeds.— The silo.— The fertility of the soil.— Bac-
teria as sources of trouble to the farmer.— Coal forma-
tion.

V.— PARASITIC BACTERIA AND THEIR RELATION TO

DISEASE 128

Method of producing disease.— Pathogenic germs not
strictly parasitic.— Pathogenic germs that are true para-
sites.—What diseases are due to bacteria. — Variability

6 THE STORY OF GERM LIFE.

CHAPTER PACK

of pathogenic powers.— Susceptibility of the individual.
— Recovery from bacteriological diseases. — Diseases
caused by organisms other than bacteria.

VI.— METHODS OF COMBATING PARASITIC BACTERIA . 165

Preventive medicine. — Bacteria in surgery. — Preven-
tion by inoculation.— Limits of preventive medicine.—
Curative medicine. — -Drugs.— Vis medicatrix naturae. —
Antitoxines and their use. — Conclusion.

LIST OF ILLUSTRATIONS.

FIGURE FACE

Various kinds of bacteria . . . Frontispiece

1. General shapes of bacteria 18

2. Method of multiplication of bacteria. ... 19

3. Micrococci 19

4. Streptococci 19

5. Sarcina 2O

6. Separate rods showing variations in size ... 20

7. Rod-forms united to form chains .... 20

8. Various types of spiral bacteria 21

9. Various shaped rods 23

10. Bacteria surrounded by capsules .... 23

11. Various types of bacteria "colonies" ... 24

12. Endogenous spores 26

13. So-called arthrogenous spores 27

14. Formation of spores in unusual forms (Crenothrix) . 28

15. Bacteria provided with flagella 29

16. Internal structure of bacteria 30

17. Threads of Oscillaria 32

1 8. Bacillus acetieum, of vinegar ..... 53

19. Bacillus acidi lactici, of sour milk . . . . 71

20. Dairy bacterium producing red milk .... 73

21. Dairy bacterium producing pleasant flavours in butter 80

22. Dairy bacterium producing pleasant aroma in butter 81

23. Dairy bacterium producing pleasant flavour in butter 83

24. Dairy bacterium producing " swelled " cheese . . 92

25. Diagram illustrating Nature's food cycle ... 99

7

8 LIST OF ILLUSTRATIONS.

FIGURE PAGE

26. Soil bacteria which produce nitrification . . . 103

27. Soil bacteria which produce tubercles on the toots of

legumes IO8

28. Diphtheria bacillus 134

29. Tetanus bacillus 135

30. Typhoid bacillus ....... 136

31. Tuberculosis bacillus 137

32. Anthrax bacillus 138

33. White blood corpuscles and other phagocytes . . 152

34. Malarial organism 161

THE STORY OF GERM LIFE.

CHAPTER I.

BACTERIA AS PLANTS.

DURING the last fifteen years the subject of
bacteriology* has developed with a marvellous
rapidity. At the beginning of the ninth decade
of the century bacteria were scarcely heard of
outside of scientific circles, and very little was
known about them even among scientists. To-
day they are almost household words, and every-
one who reads is beginning to recognise that
they have important relations to his everyday
life. The organisms called bacteria comprise
simply a small class of low plants, but this small
group has proved to be of such vast importance
in its relation to the world in general that its
study has little by little crystallized into a science
by itself. It is a somewhat anomalous fact that
a special branch of science, interesting such a
large number of people, should be developed
around a small group of low plants. The impor-
tance of bacteriology is not due to any importance
bacteria have as plants or as members of the
vegetable kingdom, but solely to their powers of

* The term microbe is simply a word which has been
coined to include all of the microscopic plants commonly in-
cluded under the terms bacteria and yeasts.
9

10 THE STORY OF GERM LIFE.

producing profound changes in Nature. There is
no one family of plants that begins to compare
with them in importance. It is the object of this
work to point out briefly how much both of good
and ill we owe to the life and growth of these
microscopic organisms. As we have learned
more and more of them during the last fifty years,
it has become more and more evident that this
one little class of microscopic plants fills a place
in Nature's processes which in some respects bal-
ances that filled by the whole of the green plants.
Minute as they are, their importance can hardly
be overrated, for upon their activities is founded
the continued life of the animal and vegetable
kingdom. For good and for ill they are agents
of neverceasing and almost unlimited powers.

HISTORICAL.

The study of bacteria practically began with
the use of the microscope. It was toward the
close of the seventeenth century that the Dutch
microscopist, Leeuwenhoek, working with his sim-
ple lenses, first saw the organisms which we now
know under this name, with sufficient clearness
to describe them. Beyond mentioning their ex-
istence, however, his observations told little or
nothing. Nor can much more be said of the stud-
ies which followed during the next one hundred
and fifty years. During this long period many a
microscope was turned to the observation of these
minute organisms, but the majority of observers
were contented with simply seeing them, marvel-
ling at their minuteness, and uttering many excla-
mations of astonishment at *he wonders of Nature.
A few men of more strictly scientific natures paid

BACTERIA AS PLANTS. II

some attention to these little organisms. Among
them we should perhaps mention Von Gleichen,
Miiller, Spallanzani, and Needham. Each of
these, as well as others, made some contributions
to our knowledge of microscopical life, and among
other organisms studied those which we now call
bacteria. Speculations were even made at these
early dates of the possible causal connection of
these organisms with diseases, and for a little the
medical profession was interested in the sugges-
tion. It was impossible then, however, to obtain
any evidence for the truth of this speculation, and
it was abandoned as unfounded, and even forgot-
ten completely, until revived again about the mid-
dle of the ipth century. During this century
of wonder a sufficiency of exactness was, how-
ever, introduced into the study of microscopic or-
ganisms to call for the use of names, and we find
Miiller using the names of Monas, Proteus, Vibrio,
Bacillus, and Spirillum, names which still continue
in use, although commonly with a different signifi-
cance from that given them by Miiller. Miiller
did indeed make a study sufficient to recognise
the several distinct types, and attempted to clas-
sify these bodies. They were not regarded as of
much importance, but simply as the most minute
organisms known.

Nothing of importance came from this work,
however, partly because of the inadequacy of the
microscopes of the day, and partly because of a
failure to understand the real problems at issue.
When we remember the minuteness of the bacteria,
the impossibility of studying any one of them for
more than a few moments at a time — only so long,
in fact, as it can be followed under a microscope;
when we remember, too, the imperfection of the

12 THE STORY OF GERM LIFE.

compound microscopes which made high powers
practical impossibilities ; and, above all, when we
appreciate the looseness of the ideas which per-
vaded all scientists as to the necessity of accurate
observation in distinction from inference, it is not
strange that the last century gave us no knowl-
edge of bacteria beyond the mere fact of the ex-
istence of some extremely minute organisms in
different decaying materials. Nor did the igth
century add much to this until toward its middle.
It is true that the microscope was vastly improved
early in the century, and since this improvement
served as a decided stimulus to the study of mi-
croscopic life, among other organisms studied,
bacteria received some attention. Ehrenberg,
Dujardin, Fuchs, Perty, and others left the im-
press of their work upon bacteriology even before
the middle of the century. It is true that Schwann
shrewdly drew conclusions as to the relation of
microscopic organisms to various processes of
fermentation and decay — conclusions which, al-
though not accepted at the time, have subse-
quently proved to be correct. It is true that
Fuchs made a careful study of the infection of
" blue milk," reaching the correct conclusion that
the infection was caused by a microscopic organ-
ism which he discovered and carefully studied.
It is true that Henle made a general theory as to
the relation of such organisms to diseases, and
pointed out the logically necessary steps in a dem-
onstration of the causal connection between any
organism and a disease. It is true also that a
general theory of the production of all kinds of
fermentation by living organisms had been ad-
vanced. But all these suggestions made little
impression. On the one hand, bacteria were not

BACTERIA AS PLANTS. 13

recognised as a class of organisms by themselves
— were not, indeed, distinguished from yeasts or
other minute animalculae. Their variety was not
mistrusted and their significance not conceived.
As microscopic organisms, there were no reasons
for considering them of any more importance
than any other small animals or plants, and their
extreme minuteness and simplicity made them of
little interest to the microscopist. On the other
hand, their causal connection with fermentative
and putrefactive processes was entirely obscured
by the overshadowing weight of the chemist Lie-
big, who believed that fermentations and putre-
factions were simply chemical processes. Liebig
insisted that all albuminoid bodies were in a
state of chemically unstable equilibrium, and if
left to themselves would fall to pieces without
any need of the action of microscopic organisms.
The force of Liebig's authority and the brilliancy
of his expositions led to the wide acceptance of
his views and the temporary obscurity of the re-
lation of microscopic organisms to fermentative
and putrefactive processes. The objections to
Liebig's views were hardly noticed, and the force
of the experiments of Schwann was silently ig-
nored. Until the sixth decade of the century,
therefore, these organisms, which have since be-
come the basis of a new branch of science, had
hardly emerged from obscurity. A few micros-
copists recognised their existence, just as they
did any other group of small animals or plants,
but even yet they failed to look upon them as
forming a distinct group. A growing number of
observations was accumulating, pointing toward
a probable causal connection between fermenta-
tive and putrefactive processes and the growth of
2

14 THE STORY OF GERM LIFE.

microscopic organisms; but these observations
were known only to a few, and were ignored by
the majority of scientists.

It was Louis Pasteur who brought bacteria to
the front, and it was by his labours that these or-
ganisms were rescued from the obscurity of scien-
tific publications and made objects of general and
crowning interest. It was Pasteur who first suc-
cessfully combated the chemical theory of fer-
mentation by showing that albuminous matter
had no inherent tendency to decomposition. It
was Pasteur who first clearly demonstrated that
these little bodies, like all larger animals and
plants, come into existence only by ordinary
methods of reproduction, and not by any sponta-
neous generation, as had been earlier claimed.
It was Pasteur who first proved that such a com-
mon phenomenon as. the souring of milk was pro-
duced by microscopic organisms growing in the
milk. It was Pasteur who first succeeded in dem-
onstrating that certain species of microscopic or-
ganisms are the cause of certain diseases, and in
suggesting successful methods of avoiding them.
All these discoveries were made in rapid succes-
sion. Within ten years of the time that his name
began to be heard in this connection by scien-
tists, the subject had advanced so rapidly that
it had become evident that here was a new
subject of importance to the scientific world, if
not to the public at large. The other important
discoveries which Pasteur made it is not our pur-
pose to mention here. His claim to be consid-
ered the founder of bacteriology will be recog-
nised from what has already been mentioned.
It was not that he first discovered the organisms,
or first studied them ; it was not that he first sug-

BACTERIA AS PLANTS. 15

gested their causal connection with fermentation
and disease, but it was because he for the first time
placed the subject upon a firm foundation by prov-
ing with rigid experiment some of the suggestions
made by others, and in this way turned the atten-
tion of science to the study of micro-organisms.

After the importance of the subject had been
demonstrated by Pasteur, others turned their at-
tention in the same direction, either for the pur-
pose of verification or refutation of Pasteur's
views. The advance was not very rapid, however,
since bacteriological experimentation proved to be
a subject of extraordinary difficulty. Bacteria
were not even yet recognised as a group of organ-
isms distinct enough to be grouped by themselves,
but were even by Pasteur at first confounded with
yeasts. As a distinct group of organisms they
were first distinguished by Hoffman in 1869, since
which date the term bacteria, as applying to this
special group of organisms, has been coming
more and more into use. So difficult were the
investigations, that for years there were hardly
any investigators besides Pasteur who could suc-
cessfully handle the subject and reach conclu-
sions which could stand the test of time. For the
next thirty, years, although investigators and in-
vestigations continued to increase, we can find
little besides dispute and confusion along this
line. The difficulty of obtaining for experiment
any one kind of bacteria by itself, unmixed with
others (pure cultures), rendered advance almost
impossible. So conflicting were the results that
the whole subject soon came into almost hopeless
confusion, and very few steps were taken upon
any sure basis. So difficult were the methods, so
contradictory and confusing the results, because

10 THE STORY OF GERM LIFE.

of impure cultures, that a student of to-day who
wishes to look up the previous discoveries in
almost any line of bacteriology need hardly go
back of 1880, since he can almost rest assured
that anything done earlier than that was more
likely to be erroneous than correct.

The last fifteen years have, however, seen a
wonderful change. The difficulties had been
mostly those of methods of work, and with the
ninth decade of the century these methods were
simplified by Robert Koch. This simplification
of method for the first time placed this line of
investigation within the reach of scientists who
did not have the genius of Pasteur. It was now
possible to get pure cultures easily, and to obtain
with such pure cultures results which were uni-
form and simple. It was now possible to take
steps which had the stamp of accuracy upon
them, and which further experiment did not dis-
prove. From the time when these methods were
thus made manageable the study of bacteria in-
creased with a rapidity which has been fairly
startling, and the information which has accumu-
lated is almost formidable. The very rapidity
with which the investigations have progressed
has brought considerable confusion, from the fact
that the new discoveries have not had time to
be properly assimilated into knowledge. To-
day many facts are known whose significance is
still uncertain, and a clear logical discussion of
the facts of modern bacteriology is not possible.
But sufficient knowledge has been accumulated and
digested to show us at least the direction along
which bacteriological advance is tending, and it
is to the pointing out of these directions that the
following pages will be devoted.

BACTERIA AS PLANTS. 1 7

WHAT ARE BACTERIA ?

The most interesting facts connected with the
subject of bacteriology concern the powers and
influence in Nature possessed by the bacteria.
The morphological side of the subject is interest-
ing enough to the scientist, but to him alone.
Still, it is impossible to attempt to study the
powers of bacteria without knowing something of
the organisms themselves. To understand how
they come to play an important part in Nature's
processes, we must know first how they look and
where they are found. A short consideration of
certain morphological facts will therefore be
necessary at the start.

FORM OF BACTERIA.

In shape bacteria are the simplest conceivable
structures. Although there are hundreds of dif-
ferent species, they have only three general forms,
which have been aptly compared to billiard balls,
lead pencils, and corkscrews. Spheres, rods, and
spirals represent all shapes. The spheres may be
large or small, and may group themselves in va-
rious ways; the rods may be long or short, thick
or slender; the spirals may be loosely or tightly
coiled, and may have only one or two or may
have many coils, and they may be flexible or
stiff ; but still rods, spheres, and spirals comprise
all types (Fig. i).

In size there is some variation, though not
very great. All are extremely minute, and never
visible to the naked eye. The spheres vary from
0.25 /i to 1.5 /A (0.000012 to 0.00006 inches). The
rods may be no more than 0.3 p in diameter,
or may be as wide as 1.5 /* to 2.5 /*, and in length

i8

THE STORY OF GERM LIFE.

vary all the way from a length scarcely longer
than their diameter to long threads. About the
same may be said of the spi-
ral forms. They are decid-
edly the smallest living or-
ganisms which our micro-
scopes have revealed.

In their method of grcnvth
we find one of the most char-
acteristic features. They
universally have the power
of multiplication by simple
division or fission. Each in-
dividual elongates and then
divides in the middle into
FIG. i.-GeneraT shapes tw° similar halves, each of
of bacteria: a, Spheri- which then repeats the pro-
cai forms ; b, Rod- cess. This method of mul-
rKms?1™31 c' Sp" tiplication by simple division
is the distinguishing mark

which separates the bacteria from the yeasts, the
latter plants multiplying by a process known as
budding. Fig. 2 shows these two methods of
multiplication.

While all bacteria thus multiply by division,
certain differences in the details produce rather
striking differences in the results. Considering
first the spherical forms, we find that some species
divide, as described, into two, which separate at
once, and each of which in turn divides in the op-
posite direction, called Micrococcus, (Fig. 3). Other
species divide only in one direction. Frequently
they do not separate after dividing, but remain
attached. Each, however, again elongates and di-
vides again, but all still remain attached. There
are thus formed long chains of spheres like strings

BACTERIA AS PLANTS.

of beads, called Streptococci (Fig. 4). Other species
divide first in one direction, then at right angles
to the first division, and a third division follows at
right angles to
the plane of
the first two,
thus producing
solid groups of
fours, eights,
or sixteens
(Fig. 5), called
Sarcina. Each
different spe-
cies of bacteria
is uniform in
its method of

division, and HI

these differen-
ces are there-
fore indica-
tions of differ-
ences in spe-
cies, or, according to our present method of
classification, the different methods of division

FIG. 2.— Method of multiplication of bacte-
ria : a and b, Bacteria dividing by fis-
sion ; c, A yeast multiplying by budding.

FIG. 3. — Micrococci.

FIG. 4. — Streptococci.

represent different genera. All bacteria produ-
cing Streptococcus chains form a single genus Strep*

20 THE STORY OF GERM LIFE.

tococcus, and all which divide in three division
planes form another genus, Sarcina, etc.

FIG. 5.— Sarcina.

FIG. 6. — Separate rods
showing variations in
size, magnified about
looo diameters.

The rod-shaped bacteria also differ somewhat,
but to a less extent. They almost always divide
in a plane at right angles to their longest dimen-
sion. But here again we find some species sepa-
rating immediately after division, and thus always
appearing as short rods (Fig. 6), while others

remain attached
after division
and form long
chains. Some-
times they ap-
pear to continue
to increase in
length without
showing any
signs of divis-

FIG. 7.— Rod-forms united to form chains, ion, and in this

way long threads

are formed (Fig. 7). These threads are, however,
potentially at least, long chains of short rods, and
under proper conditions they will break up into
such short rods, as shown in Fig. 7 a. Occasion-
ally a rod species may divide lengthwise, but this
is rare. Exactly the same may be said of the

BACTERIA AS PLANTS.

spiral forms. Here, too, we find short rods and
long chains, or long spiral filaments in which can
be seen no division
into shorter elements,
but which, under cer-
tain conditions, break
up into short sections
(Fig. 8).

RAPIDITY OF
MULTIPLICATION.

It is this power of
multiplication by di-
vision that makes bac-
teria agents of such
significance. Their
minute size would
make them harmless
enough if it were not
for an extraordinary
power of multiplica-
tion. This power of
growth and division
is almost incredible.
Some of the species
which have been care-
fully watched under

the microscope have been found under favourable
conditions to grow so rapidly as to divide every
half hour, or even less. The number of offspring
that would result in the course of twenty-four
hours at this rate is of course easily computed.
In one day each bacterium would produce over
16,500,000 descendants, and in two days about
281,500,000,000. It has been further calculated

3. — Various types of spiral
bacteria.

22 THE STORY OF GERM LIFE.

that these 281,500,000,000 would form about a
solid pint of bacteria and weigh about a pound.
At the end of the third day the total descendants
would amount to 47,000,000,000,000, and would
weigh about 16,000,000 pounds. Of course these
numbers have no significance, for they are never
actual or even possible numbers. Long before
the offspring reach even into the millions their
rate of multiplication is checked either by lack of
food or by the accumulation of their own ex-
creted products, which are injurious to them. But
the figures do have interest since they show faint-
ly what an unlimited power of multiplication these
organisms have, and thus show us that in dealing
with bacteria we are dealing with forces of al-
most infinite extent.

This wonderful power of growth is chiefly due
to the fact that bacteria feed upon food which is
highly organized and already in condition for ab-
sorption. Most plants must manufacture their
own foods out of simpler substances, like carbonic
dioxide (CO2) and water, but bacteria, as a rule,
feed upon complex organic material already pre-
pared by the previous life of plants or animals.
For this reason they can grow faster than other
plants. Not being obliged to make their own
foods like most plants, nor to search for it like
animals, but living in its midst, their rapidity of
growth and multiplication is limited only by their
power to seize and assimilate this food. As they
grow in such masses of food, they cause certain
chemical changes to take place in it, changes
doubtless directly connected with their use of the
material as food. Recognising that they do
cause chemical changes in food material, and re-
membering this marvellous power of growth, we

BACTERIA AS PLANTS.

are prepared to believe them capable of producing
changes wherever they get a foothold and begin
to grow. Their power of feeding upon com-
plex organic food
and producing chemi-
cal changes therein,
together with their
marvellous power of
assimilating this ma-
terial as food, make
them agents in Na-

ture of extreme
portance.

FIG. 9. — Showing various shaped
rods.

DIFFERENCES BETWEEN DIFFERENT SPECIES OF
BACTERIA.

While bacteria are thus very simple in form,
there are a few
other slight varia-
tions in detail
which assist in dis-
a tinguishing them.
The rods are some-
times very blunt at
the ends, almost
as if cut square
across, while in
other species they
are more rounded
and occasionally
slightly tapering
(Fig. 9). Some-
times they are sur-

d, Bacteria showing the supposed rounded t)V a thin
structure in which x is the nucleus, ,

and v the protoplasm. layer of some gelat-

FIG. 10. — Bacteria surrounded by cap-
sules : a and b represent zoogloea ;
c, Chains of cocci with a capsule ;

THE STORY OF GERM LIFE.

inous substance, which forms what is called a
capsule (Fig. 10). This capsule may connect them
and serve as a cement, to prevent the separate
elements of a chain from falling apart (Fig. 10 c).

Sometimes such
a gelatinous se-
cretion will unite
great masses of
bacteria into
clusters, which
may float on the
surface of the
liquid in which
they grow or
may sink to the
bottom. Such
masses are called
zooglcea, and their
general appear-
ance serves as
one of the char-
acters for distin-
guishing differ-
ent species of
FIG. ii.— Various types of bacteria "colo- bacteria (Fig. IO,
nies " formed when growing in nutrient a and A). When
gelatine. Each different type of colony orowino-in cnliH
is produced by a different species of Sowing in SOlld

bacterium. media, such as a

nutritious liquid

made stiff with gelatine, the different species have
different methods of spreading from their central
point of origin. A single bacterium in the midst
of such a stiffened mass will feed upon it and pro-
duce descendants rapidly; but these descendants,
not being able to move through the gelatine, will
remain clustered together in a mass, which the

BACTERIA AS PLANTS. 25

bacteriologist calls a colony. But their method of
clustering, due to different methods of growth, is
by no means always alike, and these colonies
show great differences in general appearance.
The differences appear to be constant, however,
for the same species of bacteria, and hence the
shape and appearance of the colony enable bac-
teriologists to discern different species (Fig. n).
All these points of difference are of practical use
to the bacteriologist in distinguishing species.

SPORE FORMATION.

In addition to their power of reproduction by
simple division, many species of bacteria have a
second method by means of spores. Spores are
special rounded or oval bits of bacteria protoplasm
capable of resisting adverse conditions which
would destroy the ordinary bacteria. They arise
among bacteria in two different methods.

Endogenous spores. — These spores arise inside
of the rods or the spiral forms (Fig. 12). They
first appear as slight granular masses, or as dark
points which become gradually distinct from the
rest of the rod. Eventually there is thus formed
inside the rod a clear, highly refractive, spherical
or oval spore, which may even be of a greater
diameter than the rod producing it, thus causing
it to swell out and become spindle formed (Fig.
12 c]. These spores may form in the middle or at
the ends of the rods (Fig. 12). They may use up
all the protoplasm of the rod in their formation,
or they may use only a small part of it, the rod
which forms them continuing its activities in spite
of the formation of the spores within it. They are
always clear and highly refractive from contain-

THE STORY OF GERM LIFE.

ing little water, and they do not so readily absorb
staining material as the ordinary rods. They ap-
pear to be covered with a layer of some substance
which resists the stain, and which also enables
them to resist vari-
ous external agen-
cies. This protect-
ive covering, to-
gether with their
small amount of
water, enables them
to resist almost any
amount of drying,
a high degree of
heat, and many
other adverse con-
ditions. Common-
ly the spores break
out of the rod, and
the rod producing
them dies, although
sometimes the rod
may continue its
activity even after
the spores have
been produced.

A r t h r ogenous
spores (?). — Certain
species of bacteria
not produce spores as just described, but

FlG. 12.— Endogenous spores: a and
b, Spores forming at intervals in
the rods ; c, Spores forming in the
middle of the rods and causing the
middle to swell ; d, Spores form-
ing at the end of the rods and
causing the end to swell.

do

may give rise to bodies that are sometimes called
arthrospores. These bodies are formed as short
segments of rods (Fig. 130). A long rod may
sometimes break up into several short rounded
elements, which are clear and appear to have a
somewhat increased power of resisting adverse

BACTERIA AS PLANTS.

b

13. — So - called arthrogenous
spores : a, Forming as segments
of rods ; b, As segments of a chain
of cocci.

conditions. The same may happen among the
spherical forms, which only in rare instances form
endogenous spores.
Among the spheres
which .form a chain
of streptococci some
may occasionally be
slightly different
from the rest. They
are a little larger,
and have been
thought to have an
increased resisting
power like that of
true spores (Fig. 13 FIG.
b}. It isquite doubt-
ful, however, wheth-
er it is proper to re-
gard these bodies as spores. There is no good
evidence that they have any special resisting
power to heat like endogenous spores, and bac-
teriologists in general are inclined to regard them
simply as resting cells. The term arthrospores
has been given to them to indicate that they are
formed as joints or segments, and this term may
be a convenient one to retain although the bodies
in question are not true spores.

Still a different method of spore formation
occurs in a few peculiar bacteria. In this case
([Fig. 14) the protoplasm in the large thread breaks
into many minute spherical bodies, which finally
find exit. The spores thus formed may not be all
alike, differences in size being noticed. This
method of spore formation occurs only in a few
special forms of bacteria.

The matter of spore formation serves as one

THE STORY OF GERM LIFE.

of the points for distinguishing species. Some
species do not form spores, at least under any of
the conditions in which they have been studied.
Others form them readily in almost any condition,
and others again only under special conditions
which are adverse to their
life. The method of spore
formation is always uni-
form for any single species.
Whatever be the method
of the formation of the
spore, its purpose in the
life of the bacterium is al-
ways the same. It serves
as a means of keeping the
species alive under condi-
tions of adversity. Its
power of resisting heat or
drying enables it to live
where the ordinary active
forms would be speedily
killed. Some of these
spores are capable of re-
sisting a heat of 180° C. (360° F.) for a short time,
and boiling water they can resist for a long time.
Such spores when subsequently placed under fa-
vourable conditions will germinate and start bac-
terial activity anew.

FIG. 14. — Formation of
spores in unusual forms
(Crenothrix).

MOTION.

Some species of bacteria have the power of
active motion, and may be seen darting rapidly
to and fro in the liquid in which they are grow-
ing. This motion is produced by flagella which
protrude from the body. These flagella (Fig. 15)

BACTERIA AS PLANTS.

29

arise from a membrane surrounding the bacterium,
but have an intimate connection with the proto-

FlG. 15.— Bacteria provided with flagella : a, Single flagellum ; b,
Two flagella ; c, A tuft of flagella at one end ; d, Tufts of
flagella at both ends ; e, Uniform covering of flagella ; f,
Showing the origin of flagella from the outer layer of the body.

plasmic content. Their distribution is different
in different species of bacteria. Some species
3

30 THE STORY OF GERM LIFE.

have a single flagellum at one end (Fig. 150).
Others have one at each end (Fig. 15 b). Others,
again, have, at least just before dividing, a bunch
at one or both ends (Fig. 15 c and d), while others,
again, have many flagella distributed all over the
body in dense profusion (Fig. 15 <?). These flagella
keep up a lashing to and fro in the liquid, and the
lashing serves to propel the bacteria through the
liquid.

.INTERNAL STRUCTURE.

It is hardly possible to say much about the
structure of the bacteria beyond the description
of their external forms. With all the variations
in detail mentioned, they are
extraordinarily simple, and
about all that can be seen is
their external shape. Of
course, they have some in-
ternal structure, but we
know very little in regard to
it. Some microscopists have
described certain appearan-
ces which they think indi-
cate internal structure. Fig.
16 shows some of these ap-
pearances. The matter is as
yet very obscure, however.
The bacteria appear to have
a membranous covering
G' tunfrf tSria.Stn :" which sometimes is of a cel-
lulose nature. Within it is

protoplasm which shows various uncertain ap-
pearances. Some microscopists have thought
they could find a nucleus, and 'have regarded
bacteria as cells with inclosed nucleii (Figs. 10 a

BACTERIA AS PLANTS. 31

and is/). Others have regarded the whole bac-
terium as a nucleus without any protoplasm,
while others, again, have concluded that the dis-
cerned internal structure is nothing except an ap-
pearance presented by the physical arrangement of
the protoplasm. While we may believe that they
have some internal structure, we must recognise
that as yet microscopists have not been able to
make it out. In short, the bacteria after two
centuries of study appear to us about as they did
at first. They must still be described as minute
spheres, rods, or spirals, with no further discern-
ible structure, sometimes motile and sometimes
stationary, sometimes producing spores and some-
times not, and multiplying universally by binary
fission. With all the development of the modern
microscope we can hardly say more than this.
Our advance in knowledge of bacteria is con-
nected almost wholly with their methods of growth
and the effects they produce in Nature.

ANIMALS OR PLANTS?

There has been in the past not a little ques-
tion as to whether bacteria should be rightly
classed with plants or with animals. They cer-
tainly have characters which ally them with both.
Their very common power of active independent
motion and their common habit of living upon
complex bodies for foods are animal characters,
and have lent force to the suggestion that they
are true animals. But their general form, their
method of growth and formation of threads, and
their method of spore formation are quite plant-
like. Their general form is very similar to a
group of low green plants known as Oscillaria.

THE STORY OF GERM LIFE.

Fig. 17 shows a group of these Oscillarise, and
the similarity of this to some of the thread-like

bacteria is de-
cided. The Os-
cillari(z are, how-
ever, true plants,
and are of a
green colour.
Bacteria are
therefore to-day
looked upon as
a low type of
plant which has
no chlorophyll,*
but is related to
Oscillaria. The
absence of the
chlorophyll has
forced them to
adopt new rela-
tions to food,
and compels
them to feed
upon complex
foods instead of the simple ones, which form the
food of green plants. We may have no hesita-
tion, then, in calling them plants. It is interest-
ing to notice that with this idea their place in the
organic world is reduced to a small one systemat-
ically. They do not form a class by themselves,
but are simply a subclass, or even a family, and
a family closely related to several other common
plants. But the absence of chlorophyll and the
resulting peculiar life has brought about a curi-

FlG. 17. — Threads of Oscillaria, the nearest
allies of bacteria.

* Chlorophyll is the green colouring matter of plants.

BACTERIA AS PLANTS. 33

ous anomaly. Whereas their closest allies are
known only to botanists, and are of no interest
outside of their systematic relations, the bacteria
are familiar to every one, and are demanding the
life attention of hundreds of investigators. It is
their absence of chlorophyll and their consequent
dependence upon complex foods which has pro-
duced this anomaly.

CLASSIFICATION OF BACTERIA.

While it has generally been recognised that
bacteria are plants, any further classification has
proved a matter of great difficulty, and bacteriolo-
gists find it extremely difficult to devise means of
distinguishing species. Their extreme simplicity
makes it no easy matter to find points by which
any species can be recognised. But in spite of
their similarity, there is no doubt that many
different species exist. Bacteria which appear to
be almost identical, under the microscope prove
to have entirely different properties, and must
therefore be regarded as distinct species. But
how to distinguish them has been a puzzle.
Microscopists have come to look upon the differ-
ences in shape, multiplication, and formation of
spores as furnishing data sufficient to enable
them to divide the bacteria into genera. The
genus Bacillus, for instance, is the name given to
all rod-shaped bacteria which form endogenous
spores, etc. But to distinguish smaller subdi-
visions it has been found necessary to fall back
upon other characters, such as the shape of the
colony produced in solid gelatine, the power to
produce disease, or to oxidize nitrites, etc. Thus
at present the different species are distinguished

34 THE STORY OF GERM LIFE.

rather by their physiological than their morpho-
logical characters. This is an unsatisfactory
basis of classification, and has produced much
confusion in the attempts to classify bacteria.
The problem of determining the species of bac-
teria is to-day a very difficult one, and with
our best methods is still unsatisfactorily solved.
A few species of marked character are well
known, and their powers of action so well under-
stood that they can be readily recognised ; but
of the great host of bacteria studied, the large
majority have been so slightly experimented upon
that their characters are not known, and it is im-
possible, therefore, to distinguish many of them
apart. We find that each bacteriologist working
in any special line commonly keeps a list of the
bacteria which he finds, with such data in re-
gard to them as he has collected. Such a list is
of value to him, but commonly of little value to
other bacteriologists from the insufficiency of the
data. Thus it happens that a large part of the
different species of bacteria described in literature
to-day have been found and studied by one in-
vestigator alone. By him they have been de-
scribed and perhaps named. Quite likely the
same species may have been found by two or
three other bacteriologists, but owing to the
difficulty of comparing results and the incom-
pleteness of the descriptions the identity of the
species is not discovered, and they are probably
described again under different names. The
same process may be repeated over and over
again, until the same species of bacterium will
come to be known by several different names, as
it has been studied by different observers.

BACTERIA AS PLANTS. 35

VARIATION OF BACTERIA.

This matter is made even more confusing by
the fact that any species of bacterium may show
more or less variation. At one time in the his-
tory of bacteriology, a period lasting for many
years, it was the prevalent opinion that there was
no constancy among bacteria, but that the same
species might assume almost any of the various
forms and shapes, and possess various properties.
Bacteria were regarded by some as stages in the
life history of higher plants. This question as
to whether bacteria remain constant in character
for any considerable length of time has ever been
a prominent one with bacteriologists, and even
to-day we hardly know what the final answer will
be. It has been demonstrated beyond perad-
venture that some species may change their
physiological characters. Disease bacteria, for
instance, under certain conditions lose their
powers of developing disease. Species which sour
milk, or others which turn gelatine green, may
lose their characters. Now, since it is upon just
such physiological characters as these that we
must depend in order to separate different species
of bacteria from each other, it will be seen that
great confusion and uncertainty will result in our
attempts to define species. Further, it has been
proved that there is sometimes more or less of a
metamorphosis in the life history of certain
species of bacteria. The same species may form
a short rod, or a long thread, or break up into
spherical spores, and thus either a short rod, or
a thread, or a spherical form may belong to the
same species. Other species may be motile at
one time and stationary at another, while at a

36 THE STORY OF GERM LIFE.

third period it is a simple mass of spherical
spores. A spherical form, when it lengthens
before dividing, appears as a short rod, and a
short rod form after dividing may be so short as
to appear like a spherical organism.

With all these reasons for confusion, it is not
to be wondered at that no satisfactory classifica-
tion of bacteria has been reached, or that differ-
ent bacteriologists do not agree as to what consti-
tutes a species, or whether two forms are identical
•or not. But with all the confusion there is slowly
being obtained something like system. In spite
of the fact that species may vary and show
different properties under different conditions,
the fundamental constancy of species is every-
where recognised to-day as a fact. The members
of the same species may show different properties
•under different conditions, but it is believed that
under identical conditions the properties will be
constant. It is no more possible to convert one
species into another than it is among the higher
orders of plants. It is believed that bacteria
do form a group of plants by themselves, and
are not to be regarded as stages in the history
of higher plants. It is believed that, together
with a considerable amount of variability and
an occasional somewhat long life history with
successive stages, there is also an essential con-
stancy. A systematic classification has been
made which is becoming more or less satisfactory.
We are constantly learning more and more of the
characters, so that they can be recognised in
different places by different observers. It is the
conviction of all who work with bacteria that, in
spite of the difficulties, it is only a matter of time
when we shall have a classification and descrip-

BACTERIA AS PLANTS. 37

tion of bacteria so complete as to characterize
the different species accurately.

Even with our present incomplete knowledge
of what characterizes a species, it is necessary to
use some names. Bacteria are commonly given a
generic name based upon their microscopic ap-
pearance. There are only a few of these names.
Micrococcus, Streptococcus, Staphylococcus, Sarcina,
Bacterium, Bacillus, Spirillum, are all the names in
common use applying to the ordinary bacteria.
There are a few others less commonly used. To
this generic name a specific name is commonly
added, based upon some physiological character.
For example, Bacillus typhosus is the name given
to the bacillus which causes typhoid fever. Such
names are of great use when the species is a com-
mon and well-known one, but of doubtful value
for less-known species. It frequently happens
that a bacteriologist makes a study of the bac-
teria found in a certain locality, and obtains thus
a long list of species hitherto unknown. In these
cases it is common simply to number these spe-
cies rather than name them. This method is fre-
quently advisable, since the bacteriologist can
seldom hunt up all bacteriological literature with
sufficient accuracy to determine whether some
other bacteriologist may not have found the
same species in an entirely different locality.
One bacteriologist, for example, finds some sev-
enty different species of bacteria in different
cheeses. He studies them enough for his own
purposes, but not sufficiently to determine whether
some other person may not have found the same
species perhaps in milk or water. He therefore sim-
ply numbers them — a method which conveys no
suggestion as to whether they may be new species

38 THE STORY OF GERM LIFE.

or not. This method avoids the giving of separate
names to the same species found by different
observers, and it is hoped that gradually accumu-
lating knowledge will in time group together the
forms which are really identical, but which have
been described by different observers.

WHERE BACTERIA ARE FOUND.

There are no other plants or animals so uni-
versally found in Nature as the bacteria. It is
this universal presence, together with their great
powers of multiplication, which renders them of
so much importance in Nature. They exist almost
everywhere on the surface of the earth. They
are in the soil, especially at its surface. They do
not extend to very great depths of soil, however,
few existing below four feet of soil. At the sur-
face they are very abundant, especially if the soil
is moist and full of organic material. The num-
ber may range from a few hundred to one hun-
dred millions per gramme.* The soil bacteria
vary also in species, some twoscore different spe-
cies having been described as common in soil.
They are in all bodies of water, both at the
surface and below it. They are found at con-
siderable depths in the ocean. All bodies of fresh
water contain them, and all sediments in such
bodies of water are filled with bacteria. They
are in streams of running water in even greater
quantity than in standing water. This is simply
because running streams are being constantly
supplied with water which has been washing the
surface of the country and thus carrying off all

* One gramme is fifteen grains.

BACTERIA AS PLANTS. 39

surface accumulations. Lakes or reservoirs, how-
ever, by standing quiet allow the bacteria to set-
tle to the bottom, and the water thus gets some-
what purified. They are in the air, especially in
regions of habitation. Their numbers are great-
est near the surface of the ground, and decrease
in the upper strata of air. Anything which
tends to raise dust increases the number of bac-
teria in the air greatly, and the dust and emana-
tions from the clothes of people crowded in a
close room fill the air with bacteria in very great
numbers. They are found in excessive abun-
dance in every bit of decaying matter wherever it
may be. Manure heaps, dead bodies of animals,
decaying trees, filth and slime and muck every-
where are filled with them, for it is in such places
that they find their best nourishment. The bod-
ies of animals contain them in the mouth, stom-
ach, and intestine in great numbers, and this is, of
course, equally true of man. On the surface of
the body they cling in great quantity ; attached
to the clothes, under the finger nails, among the
hairs, in every possible crevice or hiding place in
the skin, and in all secretions. They do not,
however, occur in the tissues of a healthy indi-
vidual, either in the blood, muscle, gland, or any
other organ. Secretions, such as milk, urine, etc.,
always contain them, however, since the bacteria
do exist in the ducts of the glands which conduct
the secretions to the exterior, and thus, while the
bacteria are never in the healthy gland itself,
they always succeed in contaminating the secre-
tion as it passes to the exterior. Not only higher
animals, but the lower animals also have their bod-
ies more or less covered with bacteria. Flies have
them on their feet, bees among their hairs, etc.

40 THE STORY OF GERM LIFE.

In short, wherever on the face of Nature there
is a lodging place for dust there will be found
bacteria. In most of these localities they are
dormant, or at least growing only a little. The
bacteria clinging to the dry hair can grow but lit-
tle, if at all, and those in pure water multiply very
little. When dried as dust they are entirely dor-
mant. But each individual bacterium or spore
has the potential power of multiplication already
noticed, and as soon as it by accident falls upon
a place where there is food and moisture it will
begin to multiply. Everywhere in Nature, then,
exists this group of organisms with its almost in-
conceivable power of multiplication, but a power
held in check by lack of food. Furnish them
with food and their potential powers become
actual. Such food is provided by the dead bod-
ies of animals or plants, or by animal secretions,
or from various other sources. The bacteria which
are fortunate enough to get furnished with such
food material continue to feed upon it until the
food supply is exhausted or their growth is
checked in some other way. They may be re-
garded, therefore, as a constant and universal
power usually held in check. With their uni-
versal presence and their powers of producing
chemical changes in food material, they are ever
ready to produce changes in the face of Nature,
and to these changes we will now turn.

USE OF BACTERIA IN THE ARTS. 41

CHAPTER II.

MISCELLANEOUS USE OF BACTERIA IN THE ARTS.

THE foods upon which bacteria live are in
endless variety, almost every product of animal
or vegetable life serving to supply their needs.
Some species appear to require somewhat definite
kinds of food, and have therefore rather narrow
conditions of life, but the majority may live upon
a great variety of organic compounds. As they
consume the material which serves them as food
they produce chemical changes therein. These
changes are largely of a nature that the chemist
knows as decomposition changes. By this is
meant that the bacteria, seizing hold of ingre-
dients which constitute their food, break them to
pieces chemically. The molecule of the original
food matter is split into simpler molecules, and
the food is thus changed in its chemical nature.
As a result, the compounds which appear in the
decomposing solution are commonly simpler than
the original food molecules. Such products are
in general called decomposition products, or some-
times cleavage products. Sometimes, however, the
bacteria have, in addition to their power of pull-
ing their food to pieces, a further power of build-
ing other compounds out of the fragments, thus
building up as well as pulling down. But, how-
ever they do it, bacteria when growing in any
food material have the power of giving rise to
numerous products which did not exist in the
food mass before. Because of their extraordi-
nary powers of reproduction they are capable of
producing these changes very rapidly and can

42 THE STORY OF GERM LIFE.

give rise in a short time to large amounts of the
peculiar products of their growth.

It is to these powers of producing chemical
changes in their food that bacteria owe all their
importance in the world. Their power of chem-
ically destroying the food products is in itself of
no little importance, but the products which arise
as the result of this series of chemical changes
are of an importance in the world which we are
only just beginning to appreciate. In our at-
tempt to outline the agency which bacteria play
in our industries and in natural processes as well,
we shall notice that they are sometimes of value
simply for their power of producing decomposi-
tion ; but their greatest value lies in the fact that
they are important agents because of the prod-
ucts of their life.

We may notice, in the first place, that in the
arts there are several industries which may prop-
erly be classed together as maceration industries,
all of which are based upon the decomposition
powers of bacteria. Hardly any animal or vege-
table substance is able to resist their softening
influence, and the artisan relies upon this power
in several different directions.

BENEFITS DERIVED FROM POWERS OF
DECOMPOSITION.

Linen. — Linen consists of certain woody fibres
of the stem of the flax. The flax stem is not
made up entirely of the valuable fibres, but
largely of more brittle wood fibres, which are of
no use. The valuable fibres are, however, close-
ly united with the wood and with each other in
such an intimate fashion that it is impossible to

USE OF BACTERIA IN THE ARTS. 43

separate them by any mechanical means. The
whole cellular substance of the stem is bound
together by some cementing materials which hold
it in a compact mass, probably a salt of calcium
and pectinic acid. The art of preparing flax is
a process of getting rid of the worthless wood
fibres and preserving the valuable, longer, tougher,
and more valuable fibres, which are then made
into linen. But to separate them it is necessary
first to soften the whole tissue. This is always
done through the aid of bacteria. The flax stems,
after proper preparation, are exposed to the ac-
tion of moisture and heat, which soon develops a
rapid bacterial growth. Sometimes this is done
by simply exposing the flax to the dew and rain
and allowing it to lie thus exposed for some time.
By another process the stems are completely im-
mersed in water and allowed to remain for ten to
fourteen days. By a third process the water in
which the flax is immersed is heated from 75° to
90° F., with the addition of certain chemicals, for
some fifty to sixty hours. In all cases the effect
is the same. The moisture and the heat cause a
growth of bacteria which proceeds with more or
less rapidity according to the temperature and
other conditions. A putrefactive fermentation is
thus set up which softens the gummy substance
holding the fibres together. The process is known
as "retting," and after it is completed the fibres
are easily isolated from each other. A purely
mechanical process now easily separates the valu-
able fibres from the wood fibres. The whole pro-
cess is a typical fermentation. A disagreeable
odour arises from the fermenting flax, and the
liquid after the fermentation is filled with prod-
ucts which make valuable manure. The process

44 THE STORY OF GERM LIFE.

has not been scientifically studied until very re-
cently. The bacillus which produces the " ret-
ting " is known now, however, and it has been
shown that the " retting " is a process of decom-
position of the pectin cement. No method of
separating the linen fibres in the flax from the
wood fibres has yet been devised which dispenses
with the aid of bacteria.

Jute and Hemp. — Almost exactly the same use
is made of bacterial action in the manufacture of
jute and hemp. The commercial aspect of the
jute industry has grown to be a large one, involv-
ing many millions of dollars. Like linen, jute is
a fibre of the inner bark of a plant, and is mixed
in the bark with a mass of other useless fibrous
material. As in the case of linen, a fermenta-
tion by bacteria is depended upon as a means of
softening the material so that the fibres can be
disassociated. The process is called " retting,"
as in the linen manufacture. The details of the
process are somewhat different. The jute is com-
monly fermented in tanks of stagnant water, al-
though sometimes it is allowed to soak in river
water for a sufficient length of time to produce
the softening. After the fermentation is thus
started the jute fibre is separated from the wood,
and is of a sufficient flexibility and toughness to
be woven into sacking, carpets, curtains, table
covers, and other coarse cloth.

Practically the same method is used in sepa-
rating the tough fibres of the hemp. The hemp
plant contains some long flexible fibres with others
of no value, and bacterial fermentation is relied
upon to soften the tissues so that they may be
separated.

Cocoanut fibre, a somewhat similar material, is

USE OF BACTERIA IN THE ARTS. 45

obtained from the husk of the cocoanut by the
same means. The unripened husk is allowed to
steep and ferment in water for a long time, six
months or a year being required. By this time
the husk has become so softened that it can be
beaten until the fibres separate and can be re-
moved. They are subsequently made into a num-
ber of coarse articles, especially valuable for their
toughness. Door mats, brushes, ships' fenders,
etc., are illustrations of the sort of articles made
from them.

In each of these processes the fermentation
must have a tendency to soften the desired fibres
as well as the connecting substance. Putrefac-
tion attacks all kinds of vegetable tissue, and if
this "retting" continues too long the desired
fibre is decidedly injured by the softening effect
of the fermentation. It is quite probable that,
even as commonly carried on, the fermentation
has some slight injurious effect upon the fibre,
and that if some purely mechanical means could
be devised for separating the fibre from the wood
it would produce a better material. But such
mechanical means has not been devised, and at
present a putrefactive fermentation appears to
be the only practical method of separating the
fibres.

Sponges. — A somewhat similar use is made
of bacteria in the commercial preparation of
sponges. The sponge of commerce is simply
the fibrous skeleton of a marine animal. When
it is alive this skeleton is completely filled with
the softer parts of the animal, and to fit the
sponge for use this softer organic material must
be got rid of. It is easily accomplished by rot-
ting. The fresh sponges are allowed to stand in
4

^6 THE STORY OF GERM LIFE.

the warm sun and very rapidly decay. Bacteria
make their way into the sponge and thoroughly
decompose the soft tissues. After a short putre-
faction of this sort the softened organic matter
can be easily washed out of the skeleton and
leave the clean fibre ready for market.

Leather preparation. — The tanning of leather
is a purely chemical process, and in some pro-
cesses the whole operation of preparing the
leather is a chemical one. In others, however,
especially in America, bacteria are brought into
action at one stage. The dried hide which comes
to the tannery must first have the hair removed
together with the outer skin. The hide for this
purpose must be moistened and softened. In
some tanneries this is done by steeping it in
chemicals. In others, however, it is put into
water and slightly heated until fermentation
arises. The fermentation softens it so that the
outer skin can be easily removed with a knife,
and the removal of hair is accomplished at the
same time. Bacterial putrefaction in the tannery
is thus an assistance in preparing the skin for
the tanning proper. Even in the subsequent
tanning a bacterial fermentation appears to
play a part, but little is yet known in regard
to it.

Maceration of skeletons. — The making of skele-
tons for museums and anatomical instruction in
general is no very great industry, and yet it is
one of importance. In the making of skeletons
the process of maceration is commonly used as
an aid. The maceration consists simply in allow-
ing the skeleton to soak in water for a day or
two after cleaning away the bulk of the muscles.
The putrefaction that arises softens the connect-

USE OF BACTERIA IN THE ARTS. 47

ive tissues so much that the bones may be readily
cleaned of flesh.

Citric acid. — Bacterial fermentation is em-
ployed also in the ordinary preparation of citric
acid. The acid is made chiefly from the juice of
the lemon. The juice is pressed from the fruit
and then allowed to ferment. The fermentation
aids in separating a mucilaginous mass and mak-
ing it thus possible to obtain the citric acid in a
purer condition. The action is probably similar
to the maceration processes described above, al-
though it has not as yet been studied by bacteri-
ologists.

BENEFITS DERIVED FROM THE PRODUCTS OF
BACTERIAL LIFE.

While bacteria thus play a part in our indus-
tries simply from their power of producing de-
composition, it is primarily because of the prod-
ucts of their action that they are of value.
Wherever bacteria seize hold of organic matter
and feed upon it, there are certain to be devel-
oped new chemical compounds, resulting largely
from decomposition, but partly also from con-
structive processes. These new compounds are
of great variety. Different species of bacteria
do not by any means produce the same com-
pounds even when growing in and decomposing
the same food material. Moreover, the same
species of bacteria may give rise to different
products when growing in different food mate-
rials. Some of the compounds produced by such
processes are poisonous, others are harmless.
Some are gaseous, others are liquids. Some
have peculiar odours, as may be recognised from

48 THE STORY OF GERM LIFE.

the smell arising from a bit of decaying meat.
Others have peculiar tastes, as may be realized
in the gamy taste of meat which is in the incipi-
ent stages of putrefaction. By purely empirical
means mankind has learned methods of encourag-
ing the development of some of these products, and
is to-day making practical use of this power, pos-
sessed by bacteria, of furnishing desired chemical
compounds. Industries involving the investment
of hundreds of millions of dollars are founded
upon the products of bacterial life, and they have
a far more important relation to our everyday
life than is commonly imagined. In many cases
the artisan who is dependent upon this action of
microscopic life is unaware of the fact. His
processes are those which experience has taught
produce desired results, but, nevertheless, his
dependence upon bacteria is none the less funda-
mental.

BACTERIA IN THE FERMENTATIVE INDUSTRIES.

We may notice, first, several miscellaneous in-
stances of the application of bacteria to various
fermentative industries where their aid is of more
or less value to man. In some of the examples
to be mentioned the influence of bacteria is pro-
found and fundamental, while in others it is only
incidental. The fermentative industries of civili-
zation are gigantic in extent, and have come to
be an important factor in modern civilized life.
The large part of the fermentation is based upon
the growth of a class of microscopic plants which
we call yeasts. Bacteria and yeasts are both
microscopic plants, and perhaps somewhat close-
ly related to each other. The botanist finds a

USE OF BACTERIA IN THE ARTS. 49

difference between them, based upon their method
of multiplication, and therefore places them in
different classes (Fig. 2, page 19). In their gen-
eral power of producing chemical changes in their
food products, yeasts agree closely with bacteria,
though the kinds of chemical changes are differ-
ent. The whole of the great fermentative indus-
tries, in which are invested hundreds of millions
of dollars, is based upon chemical decompositions
produced by microscopic plants. In the great
part of commercial fermentations alcohol is the
product desired, and alcohol, though it is some-
times produced by bacteria, is in commercial
quantities produced only by yeasts. Hence it is
that, although the fermentations produced by
bacteria are more common in Nature than those
produced by yeasts and give rise to a much larger
number of decomposition products, still their com-
mercial aspect is decidedly less important than
that of yeasts. Nevertheless, bacteria are not
without their importance in the ordinary ferment-
ative processes. Although they are of no im-
portance as aids in the common fermentative
processes, they are not infrequently the cause of
much trouble. In the fermentation of malt to
produce beer, or grape juice to produce wine, it
is the desire of the brewer and vintner to have
this fermentation produced by pure yeasts, un-
mixed with bacteria. If the yeast is pure the
fermentation is uniform and successful. But the
brewer and vintner have long known that the
fermentation is frequently interfered with by ir-
regularities. The troubles which arise have long
been known, but the bacteriologist has finally
discovered their cause, and in general their rem-
edy. The cause of the chief troubles which arise

50 THE STORY OF GERM LIFE.

in the fermentation is the presence of contami-
nating bacteria among the yeasts. These bac-
teria have been more or less carefully studied by
bacteriologists, and their effect upon the beer or
wine determined. Some of them produce acid
and render the products sour; others make them
bitter ; others, again, produce a slimy material
which makes the wine or beer "ropy." Some-
thing like a score of bacteria species have been
found liable to occur in the fermenting mate-
rial and destroy the value of the product of both
the wine maker and the beer brewer. The spe-
cies of bacteria which infect and injure wine are
different from those which infect and injure beer.
They are ever present as possibilities in the great
alcoholic fermentations. They are dangers which
must be guarded against. In former years the
troubles from these sources were much greater
than they are at present. Since it has been dem-
onstrated that the different imperfections in the
fermentative process are due to bacterial impuri-
ties, commonly in the yeasts which are used to
produce the fermentation, methods of avoiding
them are readily devised. To-day the vintner
has ready command of processes for avoiding
the troubles which arise from bacteria, and the
brewer is always provided with a microscope to
show him the presence or absence of the con-
taminating bacteria. While, then, the alcoholic
fermentations are not dependent upon bacteria,
the proper management of these fermentations
requires a knowledge of their habits and char-
acters.

There are certain other fermentative processes
of more or less importance in their commercial as-
pects, which are directly dependent upon bacte-

USE OF BACTERIA IN THE ARTS. 5 1

riai action Some of them we should unhesitat-
ingly look upon as fermentations, while others
would hardly be thought of as belonging to the
fermentation industries.

The commercial importance of the manufac-
ture of vinegar, though large, does not, of course,
compare in extent with that of the alcoholic fer-
mentations. Vinegar is a weak solution of acetic
acid, together with various other ingredients
which have come from the materials furnishing
the acid. In the manufacture of vinegar, alcohol
is always used as the source of the acetic acid.
The production of acetic acid from alcohol is a
simple oxidation. The equation C2H6O -|- O2 =
C2H4O2+H8O shows the chemical change that
occurs. This oxidation can be brought about by
purely chemical means. While alcohol will not
readily unite with oxygen under common condi-
tions, if the alcohol is allowed to pass over a bit
of platinum sponge the union readily occurs and
acetic acid results. This method of acetic-acid
production is possible experimentally, but is im-
practicable on any large scale. In the ordinary
manufacture of vinegar the oxidation is a true
fermentation, and brought about by the growth of
bacteria.

In the commercial manufacture of vinegar
several different weak alcoholic solutions are
used. The most common of these are fermented
malt, weak wine, cider, and sometimes a weak so-
lution of spirit to which is added sugar and malt.
If these solutions are allowed to stand for a time
in contact with air, they slowly turn sour by the

52 THE STORY OF GERM LIFE.

gradual conversion of the alcohol into acetic acid.
At the close of the process practically all of the
alcohol has disappeared. Ordinarily, however,
not all of it has been converted into acetic acid,
for the oxidation does not all sf^p at this step.
As tffe oxidation goes on, some of the acid is
oxidized into carbonic dioxide, which is, of course,
dissipated at once into the airj and if the process
is allowed to continue unchecked for a long
enough period much of the acetic acid will be lost
in this way.

The oxidation of the alcohol in all commer-
cial production of vinegar is brought about by
the growth of bacteria fflvthe liquid. When the
vinegar production is going on properly, there is
formed on the top of the liquid a dense felted mass
known as the "mother of vinegar." This mass
proves to be made of bacteria which have the
power of absorbing oxygen from the air, or, at all
events, of causing the alcohol to unite with oxy-
gen. It was at first thought that a single species
of bacterium was thus the cause of the oxidation
of alcohol, and this was named Mycoderma aceti.
But further study has shown that several have
the power, and that even in the commercial man-
ufacture of vinegar several species play a part
(Fig. 18), although the different species are not yet
very thoroughly studied. Each appears to act
best under different conditions. Some of them
act slowly, and others rapidly, the slow-growing
species appearing to produce the larger amount
of acid in the end. After the amount of acetic
acid reaches a certain percentage, the bacteria are
unable to produce more, even though there be al-
cohol still left unoxidized. A percentage as high
as fourteen per cent, commonly destroys all their

USE OF BACTERIA IN THE ARTS.

53

power of growth. The production of the acid is
wholly dependent upon the growth of the bacteria,
and the secret of the successful vinegar manu-
facture is the skilful manipulation of these bac-

FlG. 18.— Bacillus aceticum, the bacterium which is the common
cause of the vinegar fermentation.

teria so as to keep them in the purest condition
and to give them the best opportunity for growth.
One method of vinegar manufacture which is
quite rapid is carried on in a slightly different
manner. A tall cylindrical chamber is filled with
wood shavings, and a weak solution of alcohol is
allowed to trickle slowly through it. The liquid
after passing over the shavings comes out after a
number of hours well charged with acetic acid.
This process at first sight appears to be a purely
chemical one, and reminds us of the oxidation
which occurs when alcohol is allowed to pass
over a platinum sponge. It has been claimed,
indeed, that this is a chemical oxidation in which
bacteria play no part. But this appears to be an

54 THE STORY OF GERM LIFE.

error. It is always found necessary in this method
to start the process by pouring upon the shavings
some warm vinegar. Unless in this way the shav-
ings become charged with the vinegar-holding
bacteria the alcohol will not undergo oxidation
during its passage over them, and after the bac-
teria thus introduced have grown enough to coat
the shavings thoroughly the acetic-acid produc-
tion is much more rapid than at first. If vinegar
is allowed to trickle slowly down a suspended
string, so that its bacteria may distribute them-
selves through the string, and then alcohol be al-
lowed to trickle over it in the same way, the oxida-
tion takes place and acetic acid is formed. From
the accumulation of such facts it has come to be
recognised that all processes for the commercial
manufacture of vinegar depend upon the action
of bacteria. While the oxidation of alcohol into
acetic acid may take place by purely chemical
means, these processes are not practical on a large
scale, and vinegar manufacturers everywhere de-
pend upon bacteria as their agents in producing
the oxidation. These bacteria, several species in
all, feed upon the nitrogenous matter in the fer-
menting mass and produce the desired change in
the alcohol.

This vinegar fermentation is subject to cer-
tain irregularities, and the vinegar manufacturers
can not always depend upon its occurring in a
satisfactory manner. Just as in brewing, so here,
contaminating bacteria sometimes find their way
into the fermenting mass and interfere with its
normal course. In particular, the flavour of the
vinegar is liable to suffer from such causes. As
yet our vinegar manufacturers have not applied
to acetic fermentation the same principle which

USE OF BACTERIA IN THE ARTS. 55

has been so successful in brewing — namely, the
use, as a starter of the fermentation, of a pure cul-
ture of the proper species of bacteria. This has
been done experimentally and proves to be feas-
ible. In practice, however, vinegar makers find
that simpler methods of obtaining a starter — by
means of which they procure a culture nearly
though not absolutely pure — are perfectly satis-
factory. It is uncertain whether really pure cul-
tures will ever be used in this industry.

LACTIC ACID.

The manufacture of lactic acid is an industry
of less extent than that of acetic acid, and yet it
is one which has some considerable commercial
importance. Lactic acid is used in no large quan-
tity, although it is of some value as a medicine
and in the arts. For its production we are wholly
dependent upon bacteria. It is this acid which,
as we shall see, is produced in the ordinary
souring of milk, and a large number of species
of bacteria are capable of producing the acid
from milk sugar. Any sample of sour milk may
therefore always be depended upon to contain
plenty of lactic organisms. In its manufacture
for commercial purposes milk is sometimes used
as a source, but more commonly other substances.
Sometimes a mixture of cane sugar and tartaric
acid is used. To start the fermentation the mix-
ture is inoculated with a mass of sour milk or de-
caying cheese, or both, such a mixture always con-
taining lactic organisms. To be sure, it also
contains many other bacteria which have differ-
ent effects, but the acid producers are always so
abundant and grow so vigorously that the lactic

56 THE STORY OF GERM LIFE.

fermentation occurs in spite of all other bacteria.
Here also there is a possibility of an improve-
ment in the process by the use of pure cultures of
lactic organisms. Up to the present, however,
there has been no application of such methods.
The commercial aspects of the industry are not
upon a sufficiently large scale to call for much in
this direction.

At the present time the only method we have
for the manufacture of lactic acid is dependent
upon bacteria. Chemical processes for its manu-
facture are known, but not employed commer-
cially. There are several different kinds of lac-
tic acid. They differ from each other in the
relations of the atoms within their molecule, and
in their relation to polarized light, some forms
rotating the plane of polarized light to the right,
others to the left, while others are inactive in this
respect. All the types are produced by fermenta-
tion processes, different species of bacteria hav-
ing powers of producing the different types.

BUTYRIC ACID.

Butyric acid is another acid for which we are
chiefly dependent upon bacteria. This acid is of
no very great importance, arid its manufacture
can hardly be called an industry ; still it is to a
certain extent made, and is an article of commerce.
It is an acid that can be manufactured by chemical
means, but, as in the case of the last two acids, its
commercial manufacture is based upon bacterial
action. Quite a number of species of bacteria
can produce butyric acid, and they produce it from
a variety of different sources. Butyric acid is a
common ingredient in old milk and in butter, and

THE USE OF BACTERIA IN THE ARTS. 57

its formation by bacteria was historically one of
the first bacterial fermentations to be clearly un-
derstood It can be produced also in various
sugar and starchy solutions. Glycerine may also
undergo a butyric fermentation. The presence
of this acid is occasionally troublesome, since it
is one of the factors in the rancidity of butter and
other similar materials.

INDIGO PREPARATION.

The preparation of indigo from the indigo plant
is a fermentative process brought about by a spe-
cific bacterium. The leaves of the plant are im-
mersed in water in a large vat, and a rapid fer-
mentation arises. As a result of the fermentation
the part of the plant which is the basis of the in-
digo is separated from the leaves and dissolved in
the water ; and as a second feature of the fer-
mentation the soluble material is changed in its
chemical nature into indigo proper. As this
change occurs the characteristic blue colour is de-
veloped, and the material is rendered insoluble in
water. It therefore makes its appearance as a
blue mass separated from the water, and is then
removed as indigo.

Of the nature of the process we as yet know
very little. That it is a fermentation is certain,
and it has been proved that it is produced by a
definite species of bacterium which occurs on the
indigo leaves. If the sterilized leaves are placed
in sterile water no fermentation occurs and no
indigo is formed. If, however, some of the spe-
cific bacteria are added to the mass the fermenta-
tion soon begins and the blue colour of the indigo
makes its appearance. It is plain, therefore, that

58 THE STORY OF GERM LIFE.

indigo is a product of bacterial fermentation, and
commonly due to a single definite species of bac-
terium. Of the details of the formation, however,
we as yet know little, and no practical applica-
tion of the facts have yet been made.

BACTERIA IN TOBACCO CURING.

A fermentative process of quite a different na-
ture, but of immense commercial value, is found
in the preparation of tobacco. The process by
which tobacco is prepared is a long and some-
what complicated one, consisting of a number of
different stages. The tobacco, after being first
dried in a careful manner, is subsequently allowed
to absorb moisture from the atmosphere, and is
then placed in large heaps to undergo a further
change. This process appears to be a fermenta-
tion, for the temperature of the mass rises rapidly,
and every indication of a fermentative action is
seen. The tobacco in these heaps is changed
occasionally, the heap being thrown down and
built up again in such a way that the portion
which was first at the bottom comes to the top,
and in this way all parts of the heap may be-
come equally affected by the process. After this
process the tobacco is sent to the different manu-
facturers, who finish the process of curing. The
further treatment it receives varies widely ac-
cording to the desired product, whether for smok-
ing or for snuff, etc. In all cases, however,
fermentations play a prominent part. Some-
times the leaves are directly inoculated with fer-
menting material. In the preparation of snuff
the details of the process are more complicated
than in the preparation of smoking tobacco. The

THE USE OF BACTERIA IN THE ARTS. 59

tobacco, after being ground and mixed with cer-
tain ingredients, is allowed to undergo a fermen-
tation which lasts for weeks, and indeed for
months. In the different methods of preparing
snuff the fermentations take place in different
ways, and sometimes the tobacco is subjected to
two or three different fermentative actions. The
result of the whole is the slow preparation of the
commercial product. It is during the final fer-
mentative processes that the peculiar colour and
flavour of the snuff are developed, and it is during
the fermentation of the leaves of the smoking to-
bacco— either the original fermentation or the
subsequent ones — that the special flavours and
aromas of tobacco are produced.

It can not be claimed for a moment that these
changes by which the tobacco is cured and finally
brought to a marketable condition are due wholly
to bacteria. There is no question that chemical
and physical phenomena play an important part
in them. Nevertheless, from the moment when
the tobacco is cut in the fields until the time it is
ready for market the curing is very intimately
associated with bacteria and fermentative organ-
isms in general. Some of these processes are
wholly brought about by bacterial life ; in others
the micro-organisms aid the process, though they
perhaps can not be regarded as the sole agents.

At the outset the tobacco producer has to
contend with a number of micro-organisms which
may produce diseases in his tobacco. During the
drying process, if the temperature or the amount
of moisture or the access of air is not kept in a
proper condition, various troubles arise and va-
rious diseases make their appearance, which either
injure or ruin the value of the product. These

60 THE STORY OF GERM LIFE.

appear to be produced by micro-organisms of
different sorts. During the fermentation which
follows the drying the producer has to contend
with micro-organisms that are troublesome to him ;
for unless the phenomena are properly regulated
the fermentation that occurs produces effects
upon the tobacco which ruin its character. From
the time the tobacco is cut until the final stage
in the curing the persons engaged in preparing
it for market must be on a constant watch to
prevent the growth within it of undesirable or-
ganisms. The preparation of tobacco is for this
reason a delicate operation, and one that will be
very likely to fail unless the greatest care is taken.
In the several fermentative processes which
occur in the preparation there is no question that
micro-organisms aid the tobacco producer and
manufacturer. Bacteria produce the first fermen-
tation that follows the drying, and it is these or-
ganisms too, in large measure, that give rise to
all the subsequent fermentations, although seem-
ingly in some cases purely chemical processes
materially aid. Now the special quality of the
tobacco is in part dependent upon the peculiar
type of fermentation which occurs in one or an-
other of these fermenting actions. It is the fer-
mentation that gives rise to the peculiar flavour
and to the aroma of the different grades of tobacco.
Inasmuch as the various flavours which charac-
terize tobacco of different grades are developed,
at least to a large extent, during the fermentation
processes, it is a natural supposition that the dif-
ferent qualities of the tobacco, so far as concerns
flavour, are due to the different types of fermen-
tation. The number of species of bacteria which
are found upon the tobacco leaves in the various

THE USE OF BACTERIA IN THE ARTS. 6 1

stages of its preparation is quite large, and from
what we have already learned it is inevitable that
the different kinds of bacteria will produce dif-
ferent results in the fermenting process. It
would seem natural, therefore, to assume that the
different flavours of different grades may not un-
likely be due to the fact that the tobacco in the
different cases has been fermented under the in-
fluence of different kinds of bacteria.

Nor is this simply a matter of inference. To a
certain extent experimental evidence has borne out
the conclusion, and has given at least a slight in-
dication of practical results in the future. Acting
upon the suggestion that the difference between
the high grades of tobacco and the poorer grades
is due to the character of the bacteria that pro-
duce the fermentation, certain bacteriologists
have attempted to obtain from a high quality of
tobacco the species of bacteria which are infesting
it. These bacteria have then been cultivated by
bacteriological methods and used in experiments
for the fermentation of tobacco. If it is true that
the flavour of high grade tobacco is in large meas-
ure, or even in part, due to the action of the pe-
culiar microbes from the soil where it grows, it
ought to be possible to produce similar flavours
in the leaves of tobacco grown in other localities,
if the fermentation of the leaves is carried on by
means of the pure cultures of bacteria obtained
from the high grade tobacco. Not very much has
been done or is known in this connection as yet.
Two bacteriologists have experimented independ-
ently in fermenting tobacco leaves by the action
of pure cultures of bacteria obtained from such
sources. Each of them reports successful experi-
ments. Each claims that they have been able to

62 THE STORY OF GERM LIFE.

improve the quality of tobacco by inoculating the
leaves with a pure culture of bacteria obtained
from tobacco having high quality in flavour. In
addition to this, several other bacteriologists have
carried on experiments sufficient to indicate that
the flavours of the tobacco and the character of
the ripening may be decidedly changed by the use
of different species of micro-organisms in the fer-
mentations that go on during the curing processes.

In regard to the whole matter, however, we
must recognise that as yet we have very little
knowledge. The subject has been under investi-
gation for only a short time; and, while consid-
erable information has been derived, this infor-
mation is not thoroughly understood, and our
knowledge in regard to the matter is as yet in
rather a chaotic condition. It seems certain,
however, that the quality of tobacco is in large
measure dependent upon the character of the fer-
mentations that occur at different stages of the
curing. It seems certain also that these fermen-
tations are wholly or chiefly produced by micro-
organisms, and that the character of the fermen-
tation is in large measure dependent upon the
species of micro-organisms that produce it. If
these are facts, it would seem not improbable
that a further study may produce practical re-
sults for this great industry. The study of yeasts
and the methods of keeping yeast from contami-
nations has revolutionised the brewing industry.
Perhaps in this other fermentative industry, which
is of such great commercial extent, the use of
pure cultures of bacteria may in the future pro-
duce as great revolutions in methods as it has in
the industry of the alcoholic fermentation.

It must not, however, be inferred that the dif-

THE USE OF BACTERIA IN THE ARTS. 63

ferences in grades of tobacco grown in different
parts of the world are due solely to variations in
the curing processes and to the types of fermen-
tation. There are differences in the texture of
the leaves, differences in the chemical composi-
tion of the tobaccoes, which are due undoubtedly
to the soils and the climatic conditions in which
they grow, and these, of course, will never be af-
fected by changing the character of the ferment-
ative processes. It is, however, probable that in
so far as the flavours that distinguish the high and
low grades of tobacco are due to the character of
the fermentative processes, they may be in the fu-
ture, at least to a large extent, controlled by the
use of pure cultures in curing processes. Seem-
ingly, then, there is as great a future in the de-
velopment of this fermentative industry as there
has been in the past in the development of the
fermentative industry associated with brewing
and vinting.

OPIUM.

Opium for smoking purposes is commonly
allowed to undergo a curing process which lasts
several months. This appears to be somewhat
similar to the curing of tobacco. Apparently it
is a fermentation due to the growth of micro-
organisms. The organisms in question are not,
however, bacteria in this case, but a species of
allied fungus. The plant is a mould, and it is
claimed that inoculation of the opium with cul-
tures of this mould hastens the curing.

TROUBLESOME FERMENTATIONS.

Before leaving this branch of the subject it is
necessary to notice some of the troublesome fer-

64 THE STORY OF GERM LIFE.

mentations which are ever interfering with our
industries, requiring special methods, or, indeed,
sometimes developing special industries to meet
them. As agents of decomposition, bacteria will
of course be a trouble whenever they get into
material which it is desired to preserve. Since
they are abundant everywhere, it is necessary to
count upon their attacking with certainty any
fermentable substance which is exposed to air
and water. Hence they are frequently the cause
of much trouble. In the fermentative industries
they occasionally cause an improper sort of fer-
mentation to occur unless care is taken to pre-
vent undesired species of bacteria from being
present. In vinegar making, improper species of
bacteria obtaining access to the solution give
rise to undesirable flavours, greatly injuring the
product. In tobacco curing it is very common
for the wrong species of bacteria to gain access
to the tobacco at some stage of the curing and
by their growth give rise to various troubles.
It is the ubiquitous presence of bacteria which
makes it impossible to preserve fruits, meats, or
vegetables for any length of time without special
methods. This fact in itself has caused the de-
velopment of one of our most important indus-
tries. Canning meats or fruits consists in noth-
ing more than bringing them into a condition in
which they will be preserved from attack of these
micro-organisms. The method is extremely sim-
ple in theory. It is nothing more than heating
the material to be preserved to a high tempera-
ture and then sealing it hermetically while it is
still hot. The heat kills all the bacteria which
may chance to be lodged in it, and the hermetical
sealing prevents other bacteria from obtaining

THE USE OF BACTERIA IN THE ARTS. 65

access. Inasmuch as all organic decomposition
is produced by bacterial growth, such sterilized
and sealed material will be preserved indefinitely
when the operation is performed carefully enough.
The methods of accomplishing this with sufficient
care are somewhat varied in different industries,
but they are all fundamentally the same. It is
an interesting fact that this method of preserving
meats was devised in the last century, before the
relation of micro-organisms to fermentation and
putrefaction was really suspected. For a long
time it had been in practical use while scientists
were still disputing whether putrefaction could be
avoided by preventing the access of bacteria. The
industry has, however, developed wonderfully
within the last few years, since the principles
underlying it have been understood. This un-
derstanding has led to better methods of destroy-
ing bacterial life and to proper sealing, and these
have of course led to greater success in the pres-
ervation, until to-day the canning industries are
among those which involve capital reckoned in
the millions.

Occasionally bacteria are of some value in
food products. The gamy flavour of meats is
nothing more than incipient decomposition.
Sauer Kraut is a food mass intentionally allowed
to ferment and sour. The value of bacteria in
producing butter and cheese flavours is noticed
elsewhere. But commonly our aim must be to
prevent the growth of bacteria in foods. Foods
must be dried or cooked or kept on ice, or some
other means adopted for preventing bacterial
growth in them. It is their presence that forces
us to keep our ice box, thus founding the ice
business, as well as that of the manufacture of

66 THE STORY OF GERM LIFE.

refrigerators. It is their presence, again, that
forces us to smoke hams, to salt mackerel, to dry
fish or other meats, to keep pork in brine, and to
introduce numerous other details in the methods
of food preparation and preservation.

CHAPTER III.

RELATION OF BACTERIA TO THE DAIRY
INDUSTRY.

DAIRYING is one of the most primitive of our
industries. From the very earliest period, ever
since man began to keep domestic cattle, he has
been familiar with dairying. During these many
centuries certain methods of procedure have
been developed which produce desired results.
These methods, however, have been devised sim-
ply from the accumulation of experience, with
very little knowledge as to the 'reasons underly-
ing them. The methods of past centuries are,
however, ceasing to be satisfactory. The ad-
vance of our civilization during the last half
century has seen a marked expansion in the ex-
tent of the dairy industry. With this expansion
has appeared the necessity for new methods, and
dairymen have for years been looking for them.
The last few years have been teaching us that
the new methods are to be found along the line
of the application of the discoveries of modern
bacteriology. We have been learning that the
dairyman is more closely related to bacteria and
their activities than almost any other class of
persons. Modern dairying, apart from the mat-

RELATION OF BACTERIA TO DAIRY INDUSTRY. 67

ter of keeping the cow, consists largely in trying
to prevent bacteria from growing in milk or in
stimulating their growth in cream, butter, and
cheese. These chief products of the dairy will be
considered separately.

SOURCES OF BACTERIA IN MILK.

The first fact that claims our attention is, that
milk at the time it is secreted from the udder of
the healthy cow contains no bacteria. Although
bacteria are almost ubiquitous, they are not found
in the circulating fluids of healthy animals, and
are not secreted by their glands. Milk when
first secreted by the milk gland is therefore free
from bacteria. It has taken a long time to
demonstrate this fact, but it has been finally satis-
factorily proved. Secondly, it has been demon-
strated that practically all of the normal changes
which occur in milk after its secretion are caused
by the growth of bacteria. This, too, was long
denied, and for quite a number of years after
putrefactions and fermentations were generally
acknowledged to be caused by the growth of
micro-organisms, the changes which occurred in
milk were excepted from the rule. The uni-
formity with which milk will sour, and the diffi-
culty, or seeming impossibility, of preventing this
change, led to the belief that the souring of milk
was a normal change characteristic of milk,
just as clotting is characteristic of blood. This
was, however, eventually disproved, and it was
finally demonstrated that, beyond a few physi-
cal changes connected with evaporation and a
slight oxidation of the fat, milk, if kept free
from bacteria, will undergo no change. If bac-

68 THE STORY OF GERM LIFE.

teria are not present, it will remain sweet indefi-
nitely.

But it is impossible to draw milk from the
cow in such a manner that it will be free from
bacteria except by the use of precautions abso-
lutely impracticable in ordinary dairying. As
milk is commonly drawn, it is sure to be contami-
nated by bacteria, and by the time it has entered
the milk pail it contains frequently as many as
half a million, or even a million, bacteria in every
cubic inch of the milk. This seems almost in-
credible, but it has been demonstrated in many
cases and is beyond question. Since these bac-
teria are not in the secreted milk, they must
come from some external sources, and these
sources are the following:

The first in importance is the cow herself;
for while her milk when secreted is sterile, and
while there are no bacteria in her blood, neverthe-
less the cow is the most prolific source of bacte-
rial contamination. In the first place, the milk
ducts are full of them. After each milking a lit-
tle milk is always left in the duct, and this fur-
nishes an ideal place for bacteria to grow. Some
bacteria from the air or elsewhere are sure to
get into these ducts after the milking, and
they begin at once to multiply rapidly. By the
next milking they become very abundant in the
ducts, and the first milk drawn washes most of
them at once into the milk pail, where they can
continue their growth in the milk. Again, the
exterior of the cow's body contains them in
abundance. Every hair, every particle of dirt,
every bit of dried manure, is a lurking place for
millions of bacteria. The hind quarters of a
cow are commonly in a condition of much filth,

RELATION OF BACTERIA TO DAIRY INDUSTRY. 69

for the farmer rarely grooms his cow, and during
the milking, by her movements, by the switching
of her tail, and by the rubbing she gets from the
milker, no inconsiderable amount of this dirt and
filth is brushed off and falls into the milk pail.
The farmer understands this source of dirt and
usually feels it necessary to strain the milk after
the milking. But the straining it receives through
a coarse cloth, while it will remove the coarser
particles of dirt, has no effect upon the bacteria,
for these pass through any strainer unimpeded.
Again, the milk vessels themselves contain bac-
teria, for they are never washed absolutely clean.
After the most thorough washing which the milk
pail receives from the kitchen, there will always
be left many bacteria clinging in the cracks of the
tin or in the wood, ready to begin to grow as
soon as the milk once more fills the pail. The
milker himself contributes to the supply, for he
goes to the milking with unclean hands, unclean
clothes, and not a few bacteria get from him to
his milk pail. Lastly, we find the air of the milk-
iig stall furnishing its quota of milk bacteria.
This source of bacteria is, however, not so great
liS was formerly believed. That the air may con-
'.ain many bacteria in its dust is certain, and
doubtless these fall in some quantity into the
milk, especially if the cattle are allowed to feed
upon dusty hay before and during the milking.
But unless the air is thus full of dust this source
of bacteria is not very great, and compared with
the bacteria from the other sources the air bac-
teria are unimportant.

The milk thus gets filled with bacteria, and
since it furnishes an excellent food these bacteria
begin at once to grow. The milk when drawn is

70 THE STORY OF GERM LIFE.

warm and at a temperature which especially
stimulates bacterial growth. They multiply with
great rapidity, and in the course of a few hours
increase perhaps a thousandfold. The numbers
which may be found after twenty-four hours are
sometimes inconceivable ; market milk may con-
tain as many as five hundred millions per cubic
inch ; and while this is a decidedly extreme num-
ber, milk that is a day old will almost always
contain many millions in each cubic inch, the
number depending upon the age of the milk and
its temperature. During this growth the bacteria
have, of course, not been without their effect.
Recognising as we do that bacteria are agents for
chemical change, we are prepared to see the milk
undergoing some modifications during this rapid
multiplication of bacteria. The changes which
these bacteria produce in the milk and its prod-
ucts are numerous, and decidedly affect its value.
They are both advantageous and disadvantageous
to the dairyman. They are nuisances so far as
concerns the milk producer, but allies of the but-
ter and cheese maker.

THE EFFECT OF BACTERIA ON MILK.

The first and most universal change effected
in milk is its souring. So universal is this phe-
nomenon that it is generally regarded as an in-
evitable change which can not be avoided, and, as
already pointed out, has in the past been regarded
as a normal .property of milk. To-day, however,
the phenomenon is well understood. It is due to
the action of certain of the milk bacteria upon
the milk sugar which converts it into lactic acid,
and this acid gives the sour taste and curdles

RELATION OF BACTERIA TO DAIRY INDUSTRY. 71

the milk. After this acid is produced in small
quantity its presence proves deleterious to the
growth of the bacteria, and further bacterial
growth is checked. After souring, therefore, the
milk for some time does not ordinarily undergo
any further changes.

Milk souring has been commonly regarded as
a single phenomenon, alike in all cases. When it
was first studied by bacteriologists it was thought
to be due in all cases to a single species of micro-
organism which was discovered to
be commonly present and named
Bacillus acidi lactici (Fig. 19). This |
bacterium has certainly the power jji

Bacillus acidi lactici (Fig. 19). This

found to be very common in dai-
ries in Europe. As soon as bacte- FlG
riologists turned their attention acidi lactici, tt&
more closely to the subject it was ofT^miLk"156
found that the spontaneous sour-
ing of milk was not always caused by the same
species of bacterium. Instead of finding this Ba-
cillus acidi lactici always present, they found that
quite a number of different species of bacteria
have the power of souring milk, and are found in
different specimens of soured milk. The number
of species of bacteria which have been found to
sour milk has increased until something over a
hundred are known to have this power. These
different species do not affect the milk in the
same way. All produce some acid, but they
differ in the kind and the amount of acid, and
especially in the other changes which are effected
at the same time that the milk is soured, so that
the resulting soured milk is quite variable. In
spite of this variety, however, the most recent

72 THE STORY OF GERM LIFE.

work tends to show that the majority of cases of
spontaneous souring of milk are produced by
bacteria which, though somewhat variable, prob-
ably constitute a single species, and are identical
with the Bacillus acidi lactici (Fig. 19). This spe-
cies, found common in the dairies of Europe, ac-
cording to recent investigations occurs in this
country as well. We may say, then, that while
there are many species of bacteria infesting the
dairy which can sour the milk, there is one which
is more common and more universally found than
others, and this is the ordinary cause of milk
souring.

When we study more carefully the effect upon
the milk of the different species of bacteria found
in the dairy, we find that there is a great variety
of changes which they produce when they are al-
lowed to grow in milk. The dairyman expe-
riences many troubles with his milk. It sometimes
curdles without becoming acid. Sometimes it
becomes bitter •, or acquires an unpleasant " tainted"
taste, or, again, a "soapy" taste. Occasionally a
dairyman finds his milk becoming slimy, instead of
souring and curdling in the normal fashion. At
such times, after a number of hours, the milk be-
comes so slimy that it can be drawn into long
threads. Such an infection proves very trouble-
some, for many a time it persists in spite of all
attempts made to remedy it. Again, in other
cases the milk will turn blue, acquiring about the
time it becomes sour a beautiful sky-blue colour.
Or it may become red, or occasionally yellow. All
of these troubles the dairyman owes to the pres-
ence in his milk of unusual species of bacteria
which grow there abundantly.

Bacteriologists have been able to make out

RELATION OF BACTERIA TO DAIRY INDUSTRY. 73

satisfactorily the connection of all these infec-
tions with different species of the bacteria. A
large number of species have been found to cur-
dle milk without rendering it acid, several render
it bitter, and a number produce a
" tainted " and one a " soapy "
taste. A score or more have been
found which have the power of
rendering the milk slimy. Two
different species at least have the
power of turning the milk to sky- FIG. 20.— Dairybac-
blue colour; two or three pro- redTiikr0dUdng
duce red pigments (Fig. 20), and
one or two have been found which produce a yel-
low colour. In short, it has been determined be-
yond question that all these infections, which are
more or less troublesome to dairymen, are due
to the growth of unusual bacteria in the milk.

These various infections are all troublesome,
and indeed it may be said that, so far as concerns
the milk producer and the milk consumer, bac-
teria are from beginning to end a source of trou-
ble. It is the desire of the milk producer to
avoid them as far as possible — a desire which is
shared also by everyone who has anything to do
with milk as milk. Having recognised that the
various troubles, which occasionally occur even
in the better class of dairies, are due to bacteria,
the dairyman is, at least in a measure, prepared
to avoid them. The avoiding of these troubles
is moderately easy as soon as dairymen recog-
nise the source from which the infectious or-
ganisms come, and also the fact that low tem-
peratures will in all cases remedy the evil to a
large extent. With this knowledge in hand the
avoidance of all these troubles is only a question

74 THE STORY OF GERM LIFE.

of care in handling the dairy. It must be recog-
nised that most of these troublesome bacteria
come from some unusual sources of infection.
By unusual sources are meant those which the ex-
ercise of care will avoid. It is true that the sour-
ing bacteria appear to be so universally distrib-
uted that they can not be avoided by any ordinary
means. But all other troublesome bacteria ap-
pear to be within control. The milkman must
remember that the sources of the troubles which
are liable to arise in his milk are in some form of
filth : either filth on the cow, or dust in the hay
which is scattered through the barn, or dirt on
cows' udders, or some other unusual and avoid-
able source. These sources, from what we have
already noticed, will always furnish the milk with
bacteria; but under common conditions, and when
the cow is kept in conditions of ordinary cleanli-
ness, and frequently even when not cleanly, will
only furnish bacteria that produce the universal
souring. Recognising this, the dairyman at once
learns that his remedies for the troublesome in-
fections are cleanliness and low temperatures.
If he is careful to keep his milk vessels scrupu-
lously clean ; if he will keep his cow as cleanly as
he does his horse; and if he will use care in and
around the barn and dairy, and then apply low
temperatures to the milk, he need never be dis-
turbed by slimy or tainted milk, or any of these
other troubles; or he can remove such infections
speedily should they once appear. Pure sweet
milk is only a question of sufficient care. But
care means labour and expense. As long as we
demand cheap milk, so long will we be supplied
with milk procured under conditions of filth. But
when we learn that cheap milk is poor milk, and

RELATION OF BACTERIA TO DAIRY INDUSTRY. 75

when we are willing to pay a little more for it,
then only may we expect the use of greater care
in the handling of the milk, resulting in a purer
product.

Bacteriology has therefore taught us that the
whole question of the milk supply in our com-
munities is one of avoiding the too rapid growth
of bacteria. These organisms are uniformly a
nuisance to the milkman. To avoid their evil
influence have been designed all the methods of
caring for the dairy and the barn, all the methods
of distributing milk in ice cars. Moreover, all the
special devices connected with the great industry
of milk supply have for their foundation the at-
tempt to avoid, in the first place, the presence of
too great a number of bacteria, and, in the second
place, the growth of these bacteria.

BACTERIA IN BUTTER MAKING.

Cream ripening. — Passing from milk to butter,
we find a somewhat different story, inasmuch as
here bacteria are direct allies to the dairyman
rather than his enemies. Without being aware of
it, butter makers have for years been making use
of bacteria in their butter making and have been
profiting by the products which the bacteria have
furnished them. Cream, as it is obtained from
milk, will always contain bacteria in large quan-
tity, and these bacteria will grow as readily in
the cream as they will in the milk. The butter
maker seldom churns his cream when it is freshly
obtained from the milk. There are, it is true,
some places where sweet cream butter is made
and is in demand, but in the majority of butter-
consuming countries a different quality of butter

76 THE STORY OF GERM LIFE.

is desired, and the cream is subjected to a process,
known as "ripening" or "souring" before it is
churned. In ripening, the cream is simply al-
lowed to stand in a vat for a period varying
from twelve hours to two or three days, accord-
ing to circumstances. During this period certain
changes take place therein. The bacteria which
were in the cream originally, get an opportunity
to grow, and by the time the ripening is complete
they become extremely numerous. As a result,
the character of the cream changes just as the
milk is changed under similar circumstances. It
becomes somewhat soured; it becomes slightly
curdled, and acquires a peculiarly pleasant taste
and an aroma which was not present in the origi-
nal fresh cream. After this ripening the cream
is churned. It is during the ripening that the
bacteria produce their effect, for after the churn-
ing they are of less importance. Part of them
collect in the butter, part of them are washed off
from the butter in the buttermilk and the subse-
quent processes. Most of the bacteria that are
left ifi the butter soon die, not finding there a
favourable condition for growth ; some of them,
however, live and grow for some time and are
prominent agents in the changes by which butter
becomes rancid. The butter maker is concerned
with the ripening rather than with later processes.
The object of the ripening of cream is to render
it in a better condition for butter making. The
butter maker has learned by long experience that
ripened cream churns more rapidly than sweet
cream, and that he obtains a larger yield of butter
therefrom. The great object of the ripening,
however, is to develop in the butter the peculiar
flavour and aroma which is characteristic of the

RELATION OF BACTERIA TO DAIRY INDUSTRY. 77

highest product. Sweet cream butter lacks fla-
vour and aroma, having indeed a taste almost
identically the same as cream. Butter, however,
that is made from ripened cream has a peculiar
delicate flavour and aroma which is well known to
lovers of butter, and which is developed during
the ripening process.

Bacteriologists have been able to explain with
a considerable degree of accuracy the object of
this ripening. The process is really a fermenta-
tion comparable to the fermentation that takes
place in a brewer's malt. The growth of bacteria
during the ripening produces chemical changes
of a somewhat complicated character, and con-
cerns each of the ingredients of the milk. The
lactic-acid organisms affect the milk sugar and
produce lactic acid ; others act upon the fat, pro-
ducing slight changes therein; while others act
upon the casein and the albumens of the milk.
As a result, various biproducts of decomposition
arise, and it is these biproducts of decomposition
that make the difference between the ripened and
the unripened cream. They render it sour and
curdle it, and they also produce the flavours and
aromas that characterize it. Products of decom-
position are generally looked upon as undesirable
for food, and this is equally true of these products
that arise in cream if the decomposition is allowed
to continue long enough. If the ripening, instead
of being stopped at the end of a day or two, is
allowed to continue several days, the cream be-
comes decayed and the butter made therefrom is
decidedly offensive. But under the conditions of
ordinary ripening,, when the process is stopped at
the right moment, the decomposition products
are pleasant rather than unpleasant, and the fla/-
G

7 8 THE STORY OF GERM LIFE.

vours and aromas which they impart to the cream
and to the subsequent butter are those that are
desired. It is these decomposition products that
give the peculiar character to a high quality of
butter, and this peculiar quality is a matter that
determines the price which the butter maker can
obtain for his product.

But, unfortunately, the butter maker is not al-
ways able to depend upon the ripening. While
commonly it progresses in a satisfactory manner,
sometimes, for no reason that he can assign, the
ripening does not progress normally. Instead of
developing the pleasant aroma and flavour of the
properly ripened cream, the cream develops un-
pleasant tastes. It may be bitter or somewhat
tainted, and just as sure as these flavours develop
in the cream, so sure does the quality of the but-
ter suffer. Moreover, it has been learned by ex-
perience that some creameries are incapable of
obtaining an equally good ripening of their cream.
While some of them will obtain favourable results,
others, with equal care, will obtain a far less favour-
able flavour and aroma in their butter. The rea-
son for all this has been explained by modern bacte-
riology. In the milk, and consequently in the
cream, there are always found many bacteria, but
these are not always of the same kinds. There
are scores, and probably hundreds, of species of
bacteria common in and around our barns and
dairies, and the bacteria that are abundant and
that grow in different lots of cream will not be
always the same. It makes a decided difference
in the character of the ripening, and in the conse-
quent flavours and aromas, whether one or another
species of bacteria has been growing in the cream.
Some species are found to produce good results

RELATION OF BACTERIA TO DAIRY INDUSTRY. 79

with desired flavours, while others, under identical
conditions, produce decidedly poor results with
undesired flavours (Figs. 21-23). If tne butter
maker obtains cream which is filled with a large
number of bacteria capable of producing good
flavours, then the ripening of his cream will be
satisfactory and his butter will be of high quality.
If, however, it chances that his cream contains
only the species which produce unpleasant fla-
vours, then the character of the ripening will be
decidedly inferior and the butter will be of a
poorer grade. Fortunately the majority of the
kinds of bacteria liable to get into the cream
from ordinary sources are such as produce either
good effects upon the cream or do not materially
influence the flavour or aroma. Hence it is that
the ripening of cream will commonly produce
good results. Bacteriologists have learned that
there are some species of bacteria more or less
common around our barns which produce unde-
sirable effects upon flavour, and should these be-
come especially abundant in the cream, then the
character of the ripening and the quality of the
subsequent butter will suffer. These malign spe-
cies of bacteria, however, are not very common in
properly kept barns and dairies. Hence the pro-
cess that is so widely used, of simply allowing
cream to ripen under the influence of any bacte-
ria that happen to be in it, ordinarily produces
good results. But our butter makers sometimes
find, at the times when the cattle change from
winter to summer or from summer to winter feed,
that the ripening is abnormal. The reason ap-
pears to be that the cream has become infested
with an abundance of malign species. The ripen-
ing that they produce is therefore an undesirable

8o THE STORY OF GERM LIFE.

one, and the quality of the butter is sure to

surfer.

So long as butter was made only in private

dairies it was a matter of comparatively little

importance if there was an occasional falling off
in quality of this sort. When
it was made a few pounds
at a time, and only once or
twice a week, it was not a
very serious matter if a few
churnings of butter did suf-
fer in quality. But to-day
the butter-making industries

FIG. 2i.— Dairy bacterium are becoming more and more
^r^b^eT^s concentrated into large

species has been used creameries, and It IS a mat-
commercially for the rip- ter of a good deal more jm_
ening of cream. , .

portance to discover some

means by which a uniformly high quality can be
insured. If a creamery which makes five hun-
dred pounds of butter per day surfers from such
an injurious ripening, the quality of its but-
ter will fall off to such an extent as to command
a lower price, and the creamery suffers material-
ly. Perhaps the continuation of such a trouble
for two or three weeks would make a difference
between financial success and failure in the cream-
ery. With our concentration of the butter-mak-
ing industries it is becoming thus desirable to
discover some means of regulating this process
more accurately.

The remedy of these occasional ill effects in
cream ripening has not been within the reach of
the butter maker. The butter maker must make
butter with the cream that is furnished him, and
if that cream is already impregnated with malign

RELATION OF BACTERIA TO DAIRY INDUSTRY. 8 1

species of bacteria he is helpless. It is true that
much can be done to remedy these difficulties by
the exercise of especial care in the barns of the
patrons of the creamery. If the barns, the cows,
the dairies, the milk vessels, etc., are all kept in
condition of strict cleanliness, if especial care is
taken particularly at the seasons
of the year when trouble is likely
to arise, and if some attention is
paid to the kind of food which the &
cattle eat, as a rule the cream will
not become infected with injurious FIG. 22. — Dairy
bacteria. It may be taken as a JSj^JS
demonstrated fact that these ma- aroma in butter,
lign bacteria come from sources of
filth, and the careful avoidance of all such sources
of filth will in a very large measure prevent their
occurrence in the cream. Such measures as these
have been found to be practicable in many cream-
eries. Creameries which make the highest priced
and the most uniform quality of butter are those
in which the greatest care is taken in the barns
and dairies to insure cleanliness and in the han-
dling of the milk and cream. With such attention
a large portion of the trouble which arises in the
creameries from malign bacteria may be avoided.
But these methods furnish no sure remedy
against evils of improper species of bacteria in
cream ripening, and do not furnish any sure
means of obtaining uniform flavour in butter.
Even under the very best conditions the flavour
of the butter will vary with the season of the
year. Butter made in the winter is inferior to
that made in the summer months ; and while this
is doubtless due in part to the different food
which the cattle have and to the character of the

82 THE STORY OF GERM LIFE.

cream resulting therefrom, these differences in
the flavour of the butter are also in part depend-
ent upon the different species of bacteria which
are present in the ripening of cream at different
seasons. The species of bacteria in June cream
are different from those that are commonly pres-
ent in January cream, and this is certainly a fac-
tor in determining the difference between winter
and summer butter.

USE OF ARTIFICIAL BACTERIA CULTURES FOR
CREAM RIPENING.

Bacteriologists have been for some time en-
deavouring to aid butter makers in this direction
by furnishing them with the bacteria needful for
the best results in cream ripening. The method
of doing this is extremely simple in principle, but
proves to be somewhat difficult in practice. It is
only necessary to obtain the species of bacteria
that produce the highest results, and then to fur-
nish these in pure culture and in large quantity
to the butter makers, to enable them to inocu-
late their cream with the species of bacteria
which will produce the results that they desire.
For this purpose bacteriologists have been for
several years searching for the proper species of
bacteria to produce the best results, and there
have been put upon the market for sale several
distinct " pure cultures " for this purpose. These
have been obtained by different bacteriologists
and dairymen in the northern European countries
and also in the United States. These pure cul-
tures are furnished to the dairymen in various
forms, but they always consist of great quanti-
ties of certain kinds of bacteria which experience

RELATION OF BACTERIA TO DAIRY INDUSTRY. 83

has found to be advantageous for the purpose of
cream ripening (Figs. 21-23).

There have hitherto appeared a number of
difficulties in the way of reaching complete suc-
cess in these directions. The most prominent
arises in devising a method of
using pure cultures in the
creamery. The cream which
the butter makers desire to
ripen is, as we have seen, al-
ready impregnated with bac-
teria, and would ripen in a
fashion of its own even if no
pure culture of bacteria were FlG- 23.— Dairy bacteri-
added thereto. Pure cultures SfiStStfi?
can not therefore be used as
simply as can yeast in bread dough. It is plain
that the simple addition of a pure culture to a mass
of cream would not produce the desired effects,
because the cream would be ripened then, not by
the pure culture alone, but by the pure culture
plus all of the bacteria that were originally pres-
ent. It would, of course, be something of a ques-
tion as to whether under these conditions the
results would be favourable, and it would seem
that this method would not furnish any means of
getting rid of bad tastes and flavours which have
come from the presence of malign species of bac-
teria. It is plainly desirable to get rid of the
cream bacteria before the pure culture is added.
This can be readily done by heating it to a tem-
perature of 69° C. (155° F.) for a short time, this
temperature being sufficient to destroy most of
the bacteria. The subsequent addition of the
pure culture of cream-ripening bacteria will cause
the cream to ripen under the influence of the add-

84 THE STORY OF GERM LIFE.

ed culture alone. This method proves to be suc-
cessful, and in the butter-making countries in
Europe it is becoming rapidly adopted.

In this country, however, this process has
not as yet become very popular, inasmuch as the
heating of the cream is a matter of considerable
expense and trouble, and our butter makers have
not been very ready to adopt it. For this reason,
and also for the purpose of familiarizing butter
makers with the use of pure cultures, it has been
attempted to produce somewhat similar though
less uniform results by the use of pure cultures
in cream without previous healing. In the use
of pure cultures in this way, the butter maker is
directed to add to his cream a large amount of
a prepared culture of certain species of bacteria,
upon the principle that the addition of such a
large number of bacteria to the cream, even
though the cream is already inoculated with
certain bacteria, will produce a ripening of the
cream chiefly influenced by the artificially added
culture. The culture thus added, being present
in very much greater quantity than the other
"wild" species, will have a much greater effect
than any of them. This method, of course, can-
not insure uniformity. While it may work satis-
factorily in many cases, it is very evident that in
others, when the cream is already filled with a
large number of malign species of bacteria, such
an artificial culture would not produce the desired
results. This appears to be not only the theo-
retical but the actual experience, The addition
of such pure cultures in many cases produces
favourable results, but it does not always do so,
and the result is not uniform. While the use of
pure cultures in this way is an advantage over

RELATION OF BACTERIA TO DAIRY INDUSTRY. 85

the method of simply allowing the cream to ripen
normally without such additions, it is a method
that is decidedly inferior to that which first
pasteurizes the cream and subsequently adds a
starter.

There is still another method of adding bac-
teria to cream to insure a more advantageous
ripening, which is frequently used, and, being
simpler, is in many cases a decided advantage.
This method is by the use of what is called a
natural starter. A natural starter consists simply
of a lot of cream which has been taken from the
most favourable source possible — that is, from
the cleanest and best dairy, or from the herd
producing the best quality of cream — and allow-
ing this cream to stand in a warm place for a
couple of days until it becomes sour. The cream
will by that time be filled with large numbers of
bacteria, and this is then put as a starter into the
vat of cream to be ripened. Of course, in the use
of this method the butter maker has no control
over the kinds of bacteria that will grow in the
starter, but it is found, practically, that if the
cream is taken from a good source the results
are extremely favourable, and there is produced
in this way almost always an improvement in the
butter.

The use of pure cultures is still quite new,
particularly in this country. In the European
butter-making countries they have been used for
a longer period and have become very much bet-
ter known. What the future may develop along
this line it is difficult to say ; but it seems at
least probable that as the difficulties in the de-
tails are mastered the time will come when start-
ers will be used by our butter makers for theif

86 THE STORY OF GERM LIFE.

cream ripening, just as yeast is used by house-
wives for raising bread, or by brewers for fer-
menting malt. These starters will probably in
time be furnished by bacteriologists. Bacteriol-
ogy, in other words, is offering in the near future
to our butter makers a method of controlling the
ripening of the cream in such a way as to insure
the obtaining of a high and uniform quality of
butter, so far, at least, as concerns flavour and
aroma.

BACTERIA IN CHEESE.

Cheese ripening. — The third great product of
the dairy industry is cheese, and in connection
with this product the dairyman is even more de-
pendent upon bacteria than he is in the produc-
tion of butter. In the manufacture of cheese the
casein of the milk is separated from the other
products by the use of rennet, and is collected
in large masses and pressed, forming the fresh
cheese. This cheese is then set aside for sev-
eral weeks, and sometimes for months, to under-
go a process that is known as ripening. During
the ripening there are developed in the cheese the
peculiar flavours which are characteristic of the
completed product. The taste of freshly made
cheese is extremely unlike that of the ripened
product. While butter made from unripened
cream has a pleasant flavour, and one which is
in many places particularly enjoyed, there is no-
where a demand for unripened cheese, for the
freshly made cheese has a taste that scarce any
one regards as pleasant. Indeed, the whole value
of the cheese is dependent upon the flavour of
the product, and this flavour is developed during
the ripening.

RELATION OF BACTERIA TO DAIRY INDUSTRY. 87

The cheese maker finds in the ripening of his
cheese the most difficult part of his manufacture.
It is indeed a process over which he has very
little control. Even when all conditions seem to
be correct, when cheese is made in the most care-
ful manner, it not infrequently occurs that the
ripening takes place in a manner that is entire-
ly abnormal, and the resulting cheese becomes
worthless. The cheese maker has been at an en-
tire loss to understand these irregularities, nor
has he possessed any means of removing them
The abnormal ripening that occurs takes on vari-
ous types. Sometimes the cheese will become
extraordinarily porous, filled with large holes
which cause the cheese to swell out of proper
shape and become worthless. At other times,
various spots of red or blue appear in the manu-
factured cheese; while again unpleasant tastes
and flavours develop which render the product of
no value. Sometimes a considerable portion of
the product of the cheese factory undergoes such
irregular ripening, and the product for a long
time will thus be worthless. If some means
could be discovered of removing these irregu-
larities it would be a great boon to the cheese
manufacturer; and very many attempts have
been made in one way or another to furnish the
cheese maker with some details in the manufac-
ture which will enable him in a measure to con-
trol the ripening.

The ripening of the cheese has been subjected
to a large amount of study on the part of bac-
teriologists who have been interested in dairy
products. That the ripening of cheese is the
result of bacterial growth therein appears to be
probable from a priori grounds. Like the ripen-

88 THE STORY OF GERM LIFE.

ing of cream, it is a process that occurs some-
what slowly. It is a chemical change which is
accompanied by the destruction of proteid mat-
ter; it takes place best at certain temperatures,
and temperatures which we know are favourable
to the growth of micro-organisms, all of which
phenomena suggest to us the action of bacteria.
Moreover, the flavours and the tastes that arise
have a decided resemblance in many cases to the
decomposition products of bacteria, strikingly so
in Limburger cheese. When we come to study
the matter of cheese ripening carefully we learn
beyond question that this a priori conclusion is
correct. The ripening of any cheese is depend-
ent upon several different factors. The method
of preparation, the amount of water left in the
curd, the temperature of ripening, and other mis-
cellaneous factors connected with the mechanical
process of cheese manufacture, affect its charac-
ter. But, in addition to all these factors, there is
undoubtedly another one, and that is the number
and the character of the bacteria that chance to
be in the curd when the cheese is made. While it
is found that cheeses which are treated by different
processes will ripen in a different manner, it is also
found that two cheeses which have been made
under similar conditions and treated in identically
the same way may also ripen in a different manner,
so that the resulting flavour will vary. The varia-
tions between cheeses thus made may be slight
or they may be considerable, but variations cer-
tainly do occur. Every one knows the great dif-
ference in flavours of different cheeses, and these
flavours are due in considerable measure to fac-
tors other than the simple mechanical process of
making the cheese. The general similarity of

RELATION OF BACTERIA TO DAIRY INDUSTRY. 89

the whole process to a bacterial fermentation
leads us to believe at the outset that some of
the differences in character are due to different
kinds of bacteria that multiply in the cheese and
produce decomposition therein.

When the matter comes to be studied by bac-
teriology, the demonstration of this position be-
comes easy. That the ripening of cheese is due
to growth of bacteria is very easily proved by
manufacturing cheeses from milk which is de-
prived of bacteria. For instance, cheeses have
been made from milk that has been either ster-
ilized or pasteurized — which processes destroy
most of the bacteria therein — and, treated other-
wise in a normal manner, are set aside to ripen.
These cheeses do not ripen, but remain for months
with practically the same taste that they had
originally. In other experiments the cheese has
been treated with a small amount of disinfective,
which is sufficient to prevent bacteria from grow-
ing, and again ripening is found to be absolutely
prevented. Furthermore, if the cheese under or-
dinary conditions is studied during the ripening
process, it is found that bacteria are growing dur-
ing the whole time. These facts all taken to-
gether plainly prove that the ripening of cheese
is a fermentation due to bacteria. It will be
noticed, however, that the conditions in the
cheese are not favourable for very rapid bac-
terial growth. It is true that there is plenty
of food in the cheese for bacterial life, but the
cheese is not very moist; it is extremely dense,
being subjected in all cases to more or less pres-
sure. The penetration of oxygen into the centre
of the mass must be extremely slight. The dens-
ity, the lack of a great amount of moisture, and

po THE STORY OF GERM LIFE.

the lack of oxygen furnish conditions in which
bacteria will not grow very rapidly. The condi-
tions are far less favourable than those of ripen-
ing cream, and the bacteria do not grow with
anything like the rapidity that they grow in
cream. Indeed, the growth of these organisms
during the ripening is extremely slow compared
to the possibilities of bacterial growth that we
have already noticed. Nevertheless, the bacteria
do multiply in the cheese, and as the ripening
goes on they become more and more abundant,
although the number fluctuates, rising and falling
under different conditions.

When the attempt is made to determine the
relation of the different kinds of ripening to dif-
ferent kinds of bacteria, it has thus far met with
extremely little success. That different flavours
are due to the ripening produced by different
kinds of bacteria would appear to be almost cer-
tain when we remember, as we have already no-
ticed, the different kinds of decomposition pro-
duced by different species of bacteria. It would
seem, moreover, that it ought not to be very diffi-
cult 'to separate from the ripened cheese the bac-
teria which are present, and thus obtain the kind
of bacteria necessary to produce the desired ripen-
ing. But for some reason this does not prove to
be so easy in practice as it seems to be in theory.
Many different species of bacteria have been sep-
arated from cheeses. One bacteriologist, studying
several cheeses, separated about eighty different
species therefrom, and others have found perhaps
as many more from different sources. More-
over, experiments have been made with a consid-
erable number of these different kinds of bacteria
to determine whether they are capable of produc-

RELATION OF BACTERIA TO DAIRY INDUSTRY. 91

ing normal ripening. These experiments consist
of making cheese out of milk that has been de-
prived of its bacteria, and which has been inocu-
lated with large quantities of the species in ques-
tion. Hitherto these experiments have not been
very satisfactory. In some cases the cheese ap-
pears to ripen scarcely at all ; in other cases the
ripening occurs, but the resulting cheese is of a
peculiar character, entirely unlike the cheese that
it is desired to imitate. There have been one or
two experiments in recent times that give a little
more promise of success than the earlier ones, for
a few species of bacteria have been used in ripen-
ing with what the authors have thought to be
promising success. The cheese made from the
milk artificially inoculated with these species
ripens in a satisfactory manner and gives some
of the character desired, though up to the pres-
ent time in no case has the typical normal ripen-
ing been produced in any of these experiments.

But these experiments have demonstrated be-
yond question that the abnormal ripening which
is common in cheese factories is due to the pres-
ence of undesirable species of bacteria in the milk.
Many of the experiments in making cheeses by
means of artificial cultures of bacteria have re-
sulted in decidedly abnormal cheeses. Many of
the cheeses thus manufactured have shown imper-
fections in ripening which are identical with those
actually occurring in the cheese factory. Sev-
eral different species of bacteria have been found
which, when artificially used thus for ripening
cheese, will give rise to the porosity and the ab-
normal swelling of the cheese already referred to
(Fig. 24). Others produced bad tastes and fla-
vours, and enough has been done in this line to

92 THE STORY OF GERM LIFE.

demonstrate beyond peradventure that the ab-
normal ripening of cheese is due primarily to the
growth of improper species therein. Quite a long
list of species of bacteria which produce abnormal
ripening have been isolated
from cheeses, and have
been studied and experi-
mented with by bacteriolo-
gists. As a result of this
study of abnormal ripening,
there has been suggested a
method of partially con-

FIG. *4.— Dairy bacterium trolling these — remedying
'swelled" them. The method con-
sists simply in testing the
fermenting qualities of the milk used. A small
sample of milk from different dairies is allowed to
stand in the cheese factory by itself until it un-
dergoes its normal souring. If the fermentation
or souring that thus occurs is of a normal charac-
ter, the milk is regarded as proper for cheese
making. But if the fermentation that occurs in
any particular sample of milk is unusual; if an
extraordinary amount of gas bubbles are pro-
duced, or if unpleasant smells and tastes arise,
the sample is regarded as unfavourable for cheese
making, and as likely to produce abnormal ripen-
ing in the cheeses. Milk from this source would
therefore be excluded from the milk that is to be
used in cheese making. This, of course, is a ten-
tative and an unsatisfactory method of control-
ling the ripening, and yet it is one of some prac-
tical value to cheese makers. It is the only
method that has yet been suggested of control-
ling the ripening.

Our bacteriologists, of course, are quite con-

RELATION OF BACTERIA TO DAIRY INDUSTRY. 93

fident that in the future more practical results
will be obtained along this line than in the past.
If it is true that cheeses are ripened by bacteria;
if it is true that different qualities in the cheese
are due to the growth of different species of bac-
teria during the ripening, it would seem to be
possible to obtain the proper kind of bacteria
and to furnish them to the cheese maker for arti-
ficially inoculating his cheese, just as it has been
possible to furnish artificially cultivated yeasts to
the brewer, and as it has become possible to fur-
nish artificially cultivated bacteria to the butter
maker. We must, however, recognise this to be
a matter for the future. Up to the present time
no practical results along the lines of bacteria
have been obtained which our cheese manufac-
turers can make use of in the way of controlling
with any accuracy this process of cheese ripening.
Thus it will be seen that in this last dairy
product bacteria play even a more important part
than in any of the others. The food value of
cheese is dependent upon the casein which is pres-
ent. The market price, however, is controlled
entirely by the flavour, and this flavour is a prod-
uct of bacterial growth. Upon the action of
bacteria, then, the cheese maker is absolutely de-
pendent ; and when our bacteriologists are able in
the future to investigate this matter further, it
seems to be at least possible that they may obtain
some means of enabling the cheese maker to con-
trol the ripening accurately. Not only so, but
recognising the great variety in the flavours of
cheese, and recognising that different kinds of
bacteria undoubtedly produce different kinds of
decomposition products, it seems to be at least
possible that a time will come when the cheese
7

94 THE STORY OF GERM LIFE.

maker will be able to produce at will any particu-
larly desired flavour in his cheese by the addition
to it of particular species of bacteria, or particular
mixtures of species of bacteria which have been
discovered to produce the desired effects.

CHAPTER IV.

BACTERIA IN NATURAL PROCESSES.

AGRICULTURE.

THUS far, in considering the relations of bac-
teria to mankind, we have taken into account only
the arts and manufactures, and have found bac-
teria playing no unimportant part in many of the
industries of our modern civilized life. So im-
portant are they that there is no one who is not
directly affected by them. There is hardly a mo-
ment in our life when we are not using some of
the direct or indirect products of bacterial action.
We turn now, however, to the consideration of a
matter of even more fundamental importance ;
for when we come to study bacteria in Nature,
we find that there are certain natural processes
connected with the life of animals and plants that
are fundamentally based upon their powers. Liv-
ing Nature appears limitless, for life processes
have been going on in the world through count-
less centuries with seemingly unimpaired vigour.
At the very bottom we find this never-ending ex-
hibition of vital power dependent upon certain
activities of micro-organisms. So thoroughly is
this true that, as we shall find after a short con-
sideration, the continuance of life upon the surface

BACTERIA IN NATURAL PROCESSES. 95

of the world would be impossible if bacterial
action were checked for any considerable length
of time. The life of the globe is, in short, de-
pendent upon these micro-organisms.

BACTERIA AS SCAVENGERS.

In the first place, we may notice the value of
these organisms simply as scavengers, keeping
the surface of the earth in the proper condition
for the growth of animals and plants. A large
tree in the forest dies and falls to the ground.
For a while the tree trunk lies there a massive
structure, but in the course of months a slow
change takes place in it. The bark becomes sof-
tened and falls from the wood. The wood also
becomes more or less softened; it is preyed upon
then by insect life ; its density decreases more
and more, until finally it crumbles into a soft,
brownish, powdery mass, and eventually the
whole sinks into the soil, is overgrown by mosses
and other vegetation, and the tree trunk has dis-
appeared from view. In the same way the body
of the dead animal undergoes the process of the
softening of its tissues by decay. The softer
parts of the body rapidly dissipate, and even the
bones themselves eventually are covered with the
soil and disintegrated, until in time they, too, dis-
appear from any visible existence. This whole
process is one of decay, and the result is that
the solid mass of the body of the tree or of the
animal has been decomposed. What has become
of it ? The answer holds the secret of Nature's
eternal freshness. Part of it has dissipated into
the air in the form of gases and water vapour ;
part of it has changed its composition and has

96 THE STORY OF GERM LIFE.

become incorporated into the soil, the final result
being that the body of the plant or animal disap-
pears as such, and its substance is converted into
gaseous form, which is dissipated in the air or into
simple compounds which sink into the earth.

This whole process of decay of organic life is
one in which bacteria play the most important
part. In the case of the decomposition of the
woody matter of the tree trunk, the process is be-
gun by the agency of moulds, for this group of
organisms alone appears to be capable of attack-
ing such hard woody structure. The later part
of the decay, however, is largely carried on bv
bacterial life. In the decomposition of the ani-
mal tissues, bacteria alone are the agents. Thus
the process by which organic matter is dissipated
into the air or incorporated into the soil is one
which is primarily presided over by bacterial
life.

Viewing this matter in a purely mechanical
light, the importance of bacteria in thus acting as
scavengers can hardly be overestimated. If we
think for a moment of the condition of the world
were there no such decomposing agents to rid the
earth's surface of the dead bodies of animals and
plants, we shall see that long since the earth
would have been uninhabitable. If the dead
bodies of plants and animals of past ages simply
accumulated on the surface of the ground with-
out any forces to reduce them into simple com-
pounds for dissipation, by their very bulk they
would have long since completely covered the
surface of the earth so as to afford no possible
room for further growth of plants and animals.
In a purely mechanical way, then, bacteria as de-
composition agents are necessary to keep the sur-

BACTERIA IN NATURAL PROCESSES. 97

face of the earth fresh and unencumbered so that
life can continue.

BACTERIA AS AGENTS IN NATURE'S FOOD
CYCLE.

But the matter by no means ends here. When
we come to think of it, it is a matter of consider-
able surprise that the surface of the earth has
been able to continue producing animals and
plants for the many millions of years during
which life has been in existence. Plants and ani-
mals both require food, animals depending wholly
upon plants therefor. Plants, however, equally
with animals, require food, and although they ob-
tain a considerable portion of their food from the
air, yet no inconsiderable part of it is obtained
from the soil. The question is forced upon us,
therefore, as to why the soil has not long since
become exhausted of food. How could the soil
continue to support plants year after year for
millions of years, and yet remain as fertile as
ever?

The explanation of this phenomenon is in the
simple fact that the processes of Nature are such
that the same food is used over and over again,
first by the plant, then by the animal, and then
again by the plant, and there is no necessity for
any end of the process so long as the sun fur-
nishes energy to keep the circulation continuous.
One phase of this transference of food from
animal to plant and from plant to animal is
familiar to nearly every one. It is a well-known
fact that animals in their respiration consume
oxygen, but exhale it again in combination with
carbon as carbonic dioxide. On the other hand,

98 THE STORY OF GERM LIFE.

plants in their life consume the carbonic dioxide
and exhale the oxygen again as free oxygen.
Thus each of these kingdoms makes use of the
excreted product of the other, and this process
can go on indefinitely, the animals furnishing our
atmosphere with plenty of carbonic acid for plant
life, and the plants excreting into the atmosphere
at the same time an abundant sufficiency of oxy-
gen for animal life. The oxygen thus passes in
an endless round from animal to plant and from
plant to animal.

A similar cycle is true of all the other foods
of animal and plant life, though in regard to the
others the operation is more complex and more
members are required to complete the chain.
The transference of matter through a series of
changes by which it is brought from a condition
in which it is proper food for plants back again
into a condition when it is once more a proper
food for plants, is one of the interesting dis-
coveries of modern science, and one in which, as
we shall see, bacteria play a most important part.
This food cycle is illustrated roughly by the
accompanying diagram ; but in order to under-
stand it, an explanation of the various steps in
this cycle is necessary.

It will be noticed that at the bottom of the
circle represented in Fig. 25, at A, are given
various ingredients which are found in the soil
and which form plant foods. Plant foods, as
may be seen there, are obtained partly from the
air as carbonic dioxide and water; but another
portion comes from the soil. Among the soil
ingredients the most prominent are nitrates,
which are the forms of nitrogen compounds
most easily made use of by plants as a source of

BACTERIA IN NATURAL PROCESSES.

99

this important element. It should be stated also
that there are other compounds in the soil which

PRODUCTS OF ANIMAL LIFE

fRODUC

E'RCLE BACTERIA.

AND LEGUMES

SOIL - NITRATE

Flo. 25. — Diagram illustrating Nature's food cycle.
Explained in the text.

furnish plants with part of their food — com-
pounds containing potassium, phosphorus, and
some other elements. For simplicity's sake,
however, these will be left out of consideration.
Beginning at the bottom of the cycle (Fig. 25 A),
plant life seizes the gases from the air and these
foods from the soil, and by means of the energy
furnished it by the sun's rays builds these simple
chemical compounds into more complex ones.
This gives us the second step, as shown in Fig.
25 B, the products of plant life. These products

100 THE STORY OF GERM LIFE.

of plant life consist of such materials as sugar,
starches, fats, and proteids, all of which have
been manufactured by the plant from the ingre-
dients furnished it from the soil and air, and
through the agency of the sun's rays. These
products of plant life now form foods for the
animal kingdom. Starches, fats, and proteids are
animal foods, and upon such complex bodies
alone can the animal kingdom be fed. Animal
life, standing high up in the circle, is not capable
of extracting its nutriment from the soil, but must
take the more complex foods which have been
manufactured by plant life. These complex
foods enter now into the animal and take their
place in the animal body. By the animal activi-
ties, some of the foods are at once decomposed
into carbonic acid and water, which, being dis-
sipated into the air, are brought back at once
into the condition in which they can serve again
as plant food. This part of the food is thus
brought back again to the bottom of the circle
(Fig. 25, dotted lines). But while it is true that
animals do thus reduce some of their foods to
the simple condition of carbonic acid and water,
this is not true of most of the foods which con-
tain nitrogen. The nitrogenous foods are as
necessary for the life as the carbon foods, and
animals do not reduce their nitrogenous foods
to the condition in which plants can prey upon
them. While plants furnish them with nitroge-
nous food, they can not give it back to the plants.
Part of the nitrogenous foods animals build into
new albumins (Fig. 25 C); but a part of them they
reduce at once into a somewhat simpler condition
known as urea. Urea is the form in which the
nitrogen is commonly excreted from the animal

BACTERIA IN NATURAL PROCESSES. IOI

body. But urea is not a plant food; for ordinary
plants are entirely unable to make use of it.
Part of the nitrogen eaten by the animal is stored
up in its body, and thus the body of the animal,
after it has died, contains these nitrogen com-
pounds of high complexity. But plants are not
able to use these compounds. A plant can not be
fed upon muscle tissue, nor upon fats, nor bones,
for these are compounds so complex that the sim-
ple plant is unable to use them at all. So far,
then, in the food cycle the compounds taken from
the soil have been built up into compounds of
greater and greater complexity ; they have reached
the top of this circle, and no part of them, except
part of the carbon and oxygen, has become re-
duced again to plant food. In order that this
material should again become capable of enter-
ing into the life of plants so as to go over the
circle again, it is necessary for it to be once
more reduced from its highly complex condition
into a simpler one.

Now come into play these decomposition
agencies which we have been studying under the
head of scavengers. It will be noticed that the
next step in the food cycle is taken by the de-
composition bacteria. These organisms, exist-
ing, as we have already seen, in the air, in the
soil, in the water, and always ready to seize hold
of any organic substance that may furnish them
with food, feed upon the products of animal life,
whether they are such products as muscle tissue,
or fat, or sugar, or whether they are the excreted
products of animal life, such as urea, and produce
therein the chemical decomposition changes al-
ready noticed. As a result of this chemical
decomposition, the complex bodies are broken

102 THE STORY OF GERM LIFE.

into simpler and simpler compounds, and the
final result is a very thorough destruction of the
animal body or the material excreted by animal
life, and its reduction into forms simple enough
for plants to use again as foods. Thus the bac-
teria come in as a necessary link to connect the
animal body, or the excretion from the animal
body, with the soil again, and therefore with that
part of the circle in which the material can once
more serve as plant food.

But in the decomposition that thus occurs
through the agency of the putrefactive bacteria
it very commonly happens that some of the food
material is broken down into compounds too sim-
ple for use as plant food. As will be seen by a
glance at the diagram (Fig. 25 D), a portion of the
cleavage products resulting from the destruction
of these animal foods takes the form of carbonic-
acid gas and water. These ingredients are at
once in condition for plant life, as shown by the
dotted lines. They pass off into the air, and the
green leaves of vegetation everywhere again
seize them, assimilate them, and use them as
food. Thus it is that the carbon and the oxygen
have completed the cycle, and have come back
again to the position in the circle where they
started. In regard to the nitrogen portion of the
food, however, it very commonly happens that the
products which arise as the result of the decom-
position processes are not yet in proper condition
for plant food. They are reduced into a condition
actually too simple for the use of plants. As a
result of these putrefactive changes, the nitrogen
products of animal life are broken frequently
into compounds as simple as ammonia (NH3), or
into compounds which the chemists speak of as

BACTERIA IN NATURAL PROCESSES. 103

nitrites (Fig. 25 at D). Now these compounds are
not ordinarily within the reach of plant life. The
luxuriant vegetation of the globe extracts its ni-
trogen from the soil in a form more complex than
either of the compounds here mentioned ; for, as
we have seen, it is nitrates chiefly that furnish
plants with their nitrogen food factor. But ni-
trates contain considerable oxygen. Ammonia,
which is one of the products of putrefactive de-
composition, contains no oxygen, and nitrites, an-
other factor, contains less oxygen than nitrates.
These bodies are thus too simple for plants to
make use of as a source of nitrogen. The chem-
ical destruction of the food material which results
from the action of the putrefactive bacteria is too
thorough, and the nitrogen foods are not yet in
condition to be used by plants.

Now comes in the agency of still another class
of micro-organisms, the existence of which has
been demonstrated to us during the last few years.
In the soil everywhere, espe-
cially in fertile soil, is a class
of bacteria which has received
the name of nitrifying bacteria
(Fig. 26). These organisms
grow in the soil and feed upon
the soil ingredients. In the FIG. 26.— Soil bacteria
course of their life they have Trification? "
somewhat the same action upon
the simple nitrogen cleavage products just men-
tioned as we have already noticed the vinegar-
producing species have upon alcohol, viz., the
bringing about a union with oxygen. There are
apparently several different kinds of nitrifying
bacteria with different powers. Some of them
cause an oxidation of the nitrogen products by

104 THE STORY OF GERM LIFE.

means of which the ammonia is united with oxy.
gen and built up into a series of products finally
resulting in nitrates (Fig. 26). By the action of
other species still higher nitrogen compounds, in-
cluding the nitrites, are further oxidized and built
up into the form of nitrates. Thus these nitrify-
ing organisms form the last link in the chain that
binds the animal kingdom to the vegetable king-
dom (Fig. 25 at 4). For after the nitrifying or-
ganisms have oxidized nitrogen cleavage products,
the results of the oxidation in the form of nitrates
or nitric acid are left in the soil, and may now be
seized upon by the roots of plants, and begin once
more their journey around the food cycle. In this
way it will be seen that while plants, by building
up compounds, form the connecting link between
the soil and animal life, bacteria in the other half
of the cycle, by reducing them again, give us the
connecting link between animal life and the soil.
The food cycle would be as incomplete without
the agency of bacterial life as it would be with-
out the agency of plant life.

But even yet the food cycle is not complete.
Some of the processes of decomposition appear
to cause a portion of the nitrogen to fly out of
the circle at a tangent. In the process of de-
composition which is going on through the
agency of micro-organisms, a considerable part
of the nitrogen is dissipated into the air in the
form of free nitrogen. When a bit of meat de-
cays, part of the meat is, indeed, converted into
ammonia or other nitrogen compounds, but if the
putrefaction is allowed to go on, in the end a
considerable portion of it will be broken into
still simpler forms, and the nitrogen will finally be
dissipated into the air in the form of free nitro-

BACTERIA IN NATURAL PROCESSES. 105

gen. This dissipation of free nitrogen into the
air is going on in the world wherever putrefaction
takes place. Wherever decomposition of nitrogen
products occurs some free nitrogen is eliminated.
Now, this part of the nitrogen has passed beyond
the reach of plants, for plants can not extract
free nitrogen from the air. In the diagram this is
represented as a portion of the material which,
through the agency of the decomposition bacte-
ria, has been thrown out of the cycle at a tan-
gent (Fig. 25 E). It will, of course, be plain
from this that the store of nitrogen food must be
constantly diminishing. The soil may have been
originally supplied with a given quantity of nitro-
gen compound, but if the decomposition products
are causing considerable quantities of this nitro-
gen to be dissipated in the air, it plainly follows
that the total amount of nitrogen food upon
which the animal and vegetable kingdoms can
depend is becoming constantly reduced by such
dissipation.

There are still other methods by which nitro-
gen is being lost from the food cycle. First, we
may notice that the ordinary processes of vegeta-
tion result in a gradual draining of the soil and
a throwing of its nitrogen into the ocean. The
body of any animal or any plant that chances to
fall into a brook or river is eventually carried to
the sea, and the products of its decomposition
pass into the ocean and are, of course, lost to the
soil. Now, while this gradual extraction of ni-
trogen from the soil by drainage is a slow one, it
is nevertheless a sure one. It is far more rapid
in these years of civilized life than in former
times, since the products of the soil are given to
the city, and then are thrown into its sewage.

to6 THE STORY OF GERM LIFE.

Our cities, then, with our present system of dis-
posing of sewage, are draining from the soil the
nitrogen compounds and throwing them away.

In yet another direction must it be noticed
that our nitrogen compounds are being lost to
plant life — viz., by the use of various nitrogen
compounds to form explosives. Gunpowder, ni-
tro-glycerine, dynamite, in fact, nearly all the ex-
plosives that are used the world over for all sorts
of purposes, are nitrogen compounds. When they
are exploded the nitrogen of the compound is
dissipated into the air in the form of gas, much
of it in the form of free nitrogen. The basis
from which explosive compounds are made con-
tains nitrogen in the form in which it can be used
by plants. Saltpetre, for example, is equally
good as a fertilizer and as a basis for gunpowder.
The products of the explosion are gases no
longer capable of use by plants, and thus every
explosion of nitrogen compounds aids in this
gradual dissipation of nitrogen products, taking
them from the store of plant foods and throwing
them away.

All of these agencies contribute to reduce the
amount of material circulating in the food cycle
of Nature, and thus seem to tend inevitably in
the end toward a termination of the processes of
life; for as soon as the soil becomes exhausted of
its nitrogen compounds, so soon will plant life
cease .from lack of nutrition, and the disappear-
ance of animal life will follow rapidly. It is this
loss of nitrogen in large measure that is forcing
our agriculturists to purchase fertilizers. The
last fifteen years have shown us, however, that
here again we may look upon our friends, the
bacteria, as agents for counteracting this dissi-

BACTERIA IN NATURAL PROCESSES. 107

paring tendency in the general processes of Na-
ture. Bacterial life in at least two different ways
appears to have the function of reclaiming from
the atmosphere more or less of this dissipated
free nitrogen.

In the first place, it has been found in the
last few years that soil entirely free from all
common plants, but containing certain kinds of
bacteria, if allowed to stand in contact with the
air, will slowly but surely gain in the amount of
nitrogen compounds that it contains. These
nitrogen compounds are plainly manufactured by
the bacteria in the soil ; for unless the bacteria are
present they do not accumulate, and they do ac-
cumulate inevitably if the bacteria are present in
the proper quantity and the proper species. It
appears that, as a rule, this fixation of nitrogen
is not performed by any one species of micro-
organisms, but by two or three of them acting
together. Certain combinations of bacteria have
been found which, when inoculated in the soil,
will bring about this fixation of nitrogen, but no
one of the species is capable of producing this
result alone. We do not know to what extent
these organisms are distributed in the soil, nor
how widely this nitrogen fixation through bacte-
rial life is going on. It is only within a short
time that it has been demonstrated to exist, but
we must look upon bacteria in the soil as one of
the factors in reclaiming from the atmosphere the
dissipated free nitrogen.

The second method by which bacteria aid in
the reclaiming of this lost nitrogen is by a com-
bined action of certain species of bacteria and
some of the higher plants. Ordinary green
plants, as already noted, are unable to make use

I08 THE STORY OF GERM LIFE.

of the free nitrogen of the atmosphere. It was
found, however, some fifteen years ago that some
species of plants, chiefly the great family of
legumes, which contains the pea plant, the bean,
the clover, etc., are able, when growing in soil
that is poor in nitrogen, to obtain nitrogen from
some source other than the soil in which they
grow. A pea plant in soil that contains no nitro-
gen products and watered with water that con-
tains no nitrogen, will, after sprouting and growing
for a length of time, be found to have accumu-
lated a considerable quantity of fixed nitrogen in
its tissues. The only source of this nitrogen has
been evidently from the air which bathes the
leaves of the plant or permeates the soil and
bathes its roots. This fact
was at first disputed, but sub-
sequently demonstrated to be
true, and was found later to
be associated with the com-
bined action of these legumes
and certain soil bacteria.
When a legume thus gains
FIG. 27.-Soii bacteria nitrogen from the air, it de-
which produce tu- velops upon its roots little
bercies on the roots bunches known as root nod-
ules or root tubercles. The
nodules are sometimes the size of the head of a
pin, and sometimes much larger than this, occa-
sionally reaching the size of a large pea, or even
larger. Upon microscopic examination they
are found to be little nests of bacteria. In some
way the soil organisms (Fig. 27) make their way
into the roots of the sprouting plant, and find-
ing there congenial environment, develop in con-
siderable quantities and produce root tubercles

BACTERIA IN NATURAL PROCESSES. 109

in the root. Now, by some entirely unknown
process, the legume and the bacteria growing to-
gether succeed in extracting the nitrogen from
the atmosphere which permeates the soil, and fix-
ing this nitrogen in the tubercles and the roots in
the form of nitrogen compounds. The result is
that, after a proper period of growth, the amount
of fixed nitrogen in the plant is found to have
very decidedly increased (Fig. 25 E.).

This, of course, furnishes a starting point for
the reclaiming of the lost atmospheric nitrogen.
The legume continues to live its usual life, per-
haps increasing the store of nitrogen in its roots
and stems and leaves during the whole of its
normal growth. Subsequently, after having fin-
ished its ordinary life, the plant will die, and then
the roots and stems and leaves, falling upon the
ground and becoming buried, will be seized upon
by the decomposition bacteria already men-
tioned. The nitrogen which has thus become
fixed in their tissues will undergo the destructive
changes already described. This will result
eventually in the production of nitrates. Thus
some of the lost nitrogen is restored again to the
soil in the form of nitrates, and may now start
on its route once more around the cycle of food.

It will be seen, then, that the food cycle is a
complete one. Beginning with the mineral in-
gredients in the soil, the food matter may start
on its circulation from the soil to the plant, from
the plant to the animal, from the animal to the
bacterium, and from the bacterium through a
series of other bacteria back again to the soil in
the condition in which it started. If, perchance,
in this progress around the circle some of the
nitrogen is thrown off at a tangent, this, too,

110 THE STORY OF GERM LIFE.

is brought back again to the circle through
the agency of bacterial life. And so the food
material of animals and plants continues in this
never-ceasing circulation. It is the sunlight that
furnishes the energy for the motion. It is the
sunlight that forces the food around the circle
and keeps up the endless change; and so long as
the sun continues to shine upon the earth there
seems to be no reason why the process should
ever cease. It is this repeated circulation that
has made the continuation of life possible for the
millions and millions of years of the earth's his-
tory. It is this continued circulation that makes
life possible still, and it is only this fact that the
food is thus capable of ever circulating from ani-
mal to plant and from plant to animal that makes
it possible for the living world to continue its
existence. But, as we have seen, one half of this
great circle of food change is dependent upon
bacterial life. Without the bacterial life the ani-
mal body and the animal excretion could never
be brought back again within the reach of the
plant; and thus, were it not for the action of
these micro-organisms the food cycle would be
incomplete and life could not continue indefi-
nitely upon the surface of the earth. At the
very foundation, the continuation of the present
condition of Nature and the existence of life
during the past history of the world has been
fundamentally based upon the ubiquitous pres-
ence of bacteria and upon their continual action
in connection with both destructive and con-
structive processes.

BACTERIA IN NATURAL PROCESSES. Ill
RELATION OF BACTERIA TO AGRICULTURE.

We have already noticed that bacteria play
an important part in some of the agricultural in-
dustries, particularly in the dairy. From the
consideration of the matters just discussed, it is
manifest that these organisms must have an even
more intimate relation to the farmer's occupation.
At the foundation, farming consists in the culti-
vation of plants and animals, and we have al-
ready seen how essential are the bacteria in the
continuance of animal and plant life. But aside
from these theoretical considerations, a little
study shows that in a very practical manner the
farmer is ever making use of bacteria, as a rule,
quite unconsciously, but none the less positively.

SPROUTING OF SEEDS.

Even in the sprouting of seeds after they are
sown in the soil bacterial life has its influence.
When seeds are placed in moist soil they germi-
nate under the influence of heat. The rich albu-
minous material in the seeds furnishes excellent
food, and inasmuch as bacteria abound in the
soil, it is inevitable that they should grow in and
feed upon the seed. If the moisture is excessive
and the heat considerable, they very frequently
grow so rapidly in the seed as to destroy its life
as a seedling. The seed rots in the ground as a
result. This does not commonly occur, however,
in ordinary soil. But even here bacteria do grow
in the seed, though not so abundantly as to pro-
duce any injury. Indeed, it has been claimed
that their presence in the seed in small quantities
is a necessity for the proper sprouting of the

112 THE STORY OF GERM LIFE.

seed. It has been claimed that their growth tends
to soften the food material in the seed, so that
the young seedling can more readily absorb it for
its own food, and that without such a softening
the seed remains too hard for the plant to use.
This may well be doubted, however, for seeds
can apparently sprout well enough without the
aid of bacteria. But, nevertheless, bacteria do
grow in the seed during its germination, and thus
do aid the plant in the softening of the food ma-
terial. We can not regard them as essential to
seed germination. It may well be claimed that
they ordinarily play at least an incidental part in
this fundamental life process, although it is un-
certain whether the growth of seedlings is to any
considerable extent aided thereby.

THE SILO.

In the management of a silo the farmer has
undoubtedly another great bacteriological prob-
lem. In the attempt to preserve his summer-
grown food for the winter use of his animals,
he is hindered by the activity of common bac-
teria. If the food is kept moist, it is sure to
undergo decomposition and be ruined in a short
time as animal food. The farmer finds it neces-
sary, therefore, to dry some kinds of foods, like
hay. While he can thus preserve some foods,
others can not be so treated. Much of the rank
growth of the farm, like cornstalks, is good food
while it is fresh, but is of little value when dried.
The farmer has from experience and observation
discovered a method of managing bacterial
growth which enables him to avoid their ordinary
evil effects. This is by the use of the silo. The

BACTERIA IN NATURAL PROCESSES. 113

silo is a large, heavily built box, which is open
only at the top. In the silo the green food is
packed tightly, and when full all access of air is
excluded, except at its surface. Under these
conditions the food remains moist, but neverthe-
less does not undergo its ordinary fermentations
and putrefactions, and may be preserved for
months without being ruined. The food in such
a silo may be taken out months after it is packed,
and will still be found to be in good condition foi
food. It is true that it has changed its charac-
ter somewhat, but it is not decayed, and is eagerly
eaten by cattle.

We are yet very ignorant of the nature of the
changes which occur in the food while in the silo.
The food is not preserved from fermentation.
When the silo is packed slowly, a very decided
fermentation occurs by which the mass is raised
to a high temperature (140° F. to 160° F.).
This heating is produced by certain species of
bacteria which grow readily even at this high
temperature. The fermentation uses up the air
in the silo to a certain extent and produces a
settling of the material which still further ex-
cludes air. The first fermentation soon ceases,
and afterward only slow changes occur. Certain
acid-producing bacteria after a little begin to
grow slowly, and in time the silage is rendered
somewhat sour by the production of acetic acid.
But the exclusion of air, the close packing, and
the small amount of moisture appear to prevent
the growth of the common putrefactive bacteria,
and the silage remains good for a long time. In
other methods of filling the silo, the food is very
quickly packed and densely crowded together so
as to exclude as much air as possible from the

114 THE STORY OF GERM LIFE.

beginning. Under these conditions the lack of
moisture and air prevents fermentative action
very largely. Only certain acid-producing organ-
isms grow, and these very slowly. The essential
result in either case is that the common putrefac-
tive bacteria are prevented from growing, proba-
bly by lack of sufficient oxygen and moisture,
and thus the decay is prevented. The closely
packed food offers just the same unfavourable
condition for the growth of common putrefactive
bacteria that we have already seen offered by the
hard-pressed cheese, and the bacteria growth is
in the same way held in check. Our knowledge
of the matter is as yet very slight, but we do
know enough to understand that the successful
management of a silo is dependent upon the
manipulation of bacteria.

THE FERTILITY OF THE SOIL.

The farmer's sole duty is to extract food
from the soil. This he does either directly by
raising crops, or indirectly by raising animals
which feed upon the products of the soil. In
either case the fertility of the soil is the funda-
mental factor in his success. This fertility is a
gift to him from the bacteria.

Even in the first formation of soil he is in a
measure dependent upon bacteria. Soil, as is well
known, is produced in large part by the crum-
bling of the rocks into powder. This crumbling
we generally call weathering, and regard it as due
to the effect of moisture and -cold upon the rocks,
together with the oxidizing action of the air.
Doubtless this is true, and the weathering action
is largely a physical and chemical one. Never-

BACTERIA IN NATURAL PROCESSES. 115

theless, in this fundamental process of rock disin-
tegration bacterial action plays a part, though
perhaps a small one. Some species of bacteria,
as we have seen, can live upon very simple foods,
finding in free nitrogen and carbonates sufficient-
ly highly complex material for their life. These
organisms appear to grow on the bare surface of
rocks, assimilating nitrogen from the air, and car-
bon from some widely diffused carbonates or from
the COa in the air. Their secreted products of
an acid nature help to soften the rocks, and thus
aid in performing the first step in weathering.

The soil is not, however, all made up of dis-
integrated rocks. It contains, besides, various
ingredients which combine to make it fertile.
Among these are various sulphates which form
important parts of plant foods. These sulphates
appear to be formed, in part, at least, by bacterial
agency. The decomposition of proteids gives
rise, among other things, to hydrogen sulphide
(H»S). This gas, which is of common occurrence
in the atmosphere, is oxidized by bacterial growth
into sulphuric acid, and this is the basis of part
of the soil sulphates. The deposition of iron
phosphates and iron silicates is probably also in
a measure aided by bacterial action. All of these
processes are factors in the formation of soil.
Beyond much question the rock disintegration
which occurs everywhere in Nature is chiefly the
result of physical and chemical changes, but there
is reason for believing that the physical and chem-
ical processes are, to a slight extent at least, as-
sisted by bacterial life.

A more important factor of soil fertility is its
nitrogen content, without which it is complete-
ly barren. The origin of these nitrogen ingre-

Il6 THE STORY OF GERM LIFE.

dients has been more or less of a puzzle. Fertile
soil everywhere contains nitrates and other nitro-
gen compounds, and in certain parts of the world
there are large accumulations of these compounds,
like the nitrate beds of Chili. That they have
come ultimately from the free atmospheric nitro-
gen seems certain, and various attempts have been
made to explain a method of this nitrogen fixa-
tion. It has been suggested that electrical dis-
charges in the air may form nitric acid, which
would readily then unite with soil ingredients to
form nitrates. There is little reason, however,
for believing this to be a very important factor.
But in the soil bacteria we find undoubtedly an
efficient agency in this nitrogen fixation. As al-
ready seen, the bacteria are able to seize the free
atmospheric nitrogen, converting it into nitrites
and nitrates. We have also learned that they
can act in connection with legumes and some
other plants, enabling them to fix atmospheric ni-
trogen and store it in their roots. By these two
means the nitrogen ingredient in the soil is pre-
vented from becoming exhausted by the processes
of dissipation constantly going on. Further, by
some such agency must we imagine the original
nitrogen soil ingredient to have been derived.
Such an organic agency is the only one yet dis-
cerned which appears to have been efficient in
furnishing virgin soil with its nitrates, and we
must therefore look upon bacteria as essential to
the original fertility of the soil.

But in another direction still does the farmer
depend directly upon bacteria. The most impor-
tant factor in the fertility of the soil is the part
of it called humus. This humus is very complex,
and never alike in different soils. It contains ni-

BACTERIA IN NATURAL PROCESSES. 117

trogen compounds in abundance, together with
sulphates, phosphates, sugar, and many other sub-
stances. It is this which makes the garden soil
different from sand, or the rich soil different from
the sterile soil. If the soil is cultivated year after
year, its food ingredients are slowly but surely
exhausted. Something is taken from the humus
each year, and unless this be replaced the soil
ceases to be able to support life. To keep up a
constant yield from the soil the farmer under-
stands that he must apply fertilizers more or less
constantly.

This application of fertilizers is simply feed-
ing the crops. Some of these fertilizers the farm-
er purchases, and knows little or nothing as to
their origin. The most common method of feed-
ing the crops is, however, by the use of ordinary
barnyard manure. The reason why this material
contains plant food we can understand, since it
is made of the undigested part of food, together
with all the urea and other excretions of animals,
and contains, therefore, besides various minerals,
all of the nitrogenous waste of animal life. These
secretions are not at first fit for plant food. The
farmer has learned by experience that such excre-
tions, before they are of any use on his fields,
must undergo a process of slow change, which
is sometimes called ripening. Fresh manure is
sometimes used on the fields, but it is only made
use of by the plants after the ripening process
has occurred. Fresh animal excretions are of
little or no value as a fertilizer. The farmer,
therefore, commonly allows it to remain in heaps
for some time, and it undergoes a slow change,
which gradually converts it into a condition in
which it can be used by plants. This ripening is

Il8 THE STORY OF GERM LIFE.

readily explained by the facts already considered.
The fresh animal secretions consist of various
highly complex compounds of nitrogen, and the
ripening is a process of their decomposition. The
proteids are broken to pieces, and their nitrogen
elements reduced to the form of nitrates, leucin,
etc., or even to ammonia or free nitrogen. Fur-
ther, a second process occurs, the process of
oxidation of these nitrogen compounds already
noticed, and the ammonia and nitrites resulting
from the decomposition are built into nitrates.
In short, in this ripening manure the processes
noticed in the first part of this chapter are taking
place, by which the complex nitrogenous bodies
are first reduced and then oxidized to form plant
food. The ripening of manure is both an ana-
lytical and a synthetical process. By the analy-
sis, proteids and other bodies are broken into very
simple compounds, some of them, indeed, being
dissipated into the air, but other portions are re-
tained and then oxidized, and these latter become
the real fertilizing materials. Through the agency
of bacteria the compost heap thus becomes the
great source of plant food to the farmer. Into
this compost heap he throws garbage, straw, vege-
table and animal substances in general, or any
organic refuse which may be at hand. The vari-
ous bacteria seize it all, and cause the decomposi-
tion which converts it into plant food again. The
rotting of the compost heap is thus a gigantic
cultivation of bacteria.

This knowledge of the ripening process is fur-
ther teaching the farmer how to prevent waste.
In the ordinary decomposition of the compost
heap not an inconsiderable portion of the nitro-
gen is lost in the air by dissipation as ammonia

BACTERIA IN NATURAL PROCESSES. 119

or free nitrogen. Even his nitrates may be thus
lost by bacterial action. This portion is lost to
the farmer completely, and he can only hope to
replace it either by purchasing nitrates in the
form of commercial fertilizers, or by reclaiming it
from the air by the use of the bacterial agencies
already noticed. With the knowledge now at his
command he is learning to prevent this waste.
In the decomposition one large factor of loss is
the ammonia, which, being a gas, is readily dis-
sipated into the air. Knowing this common re-
sult of bacterial action, the scientist has told the
farmer that, by adding certain common chemic-
als to his decomposing manure heap, chemicals
which will readily unite with ammonia, he may
retain most of the nitrogen in this heap in the
form of ammonia salts, which, once formed, no
longer show a tendency to dissipate into the air.
Ordinary gypsum, or superphosphates, or plaster
will readily unite with ammonia, and these added
to the manure heap largely counteract the tend-
ency of the nitrogen to waste, thus enabling the
farmer to put back into his soil most of the nitro-
gen which was extracted from it by his crops
and then used by his stock. His vegetable crops
raise the nitrates into proteids. His animals feed
upon the proteids, and perform his work or fur-
nish him with milk. Then his bacteria stock
take the excreted or refuse nitrogen, and in his
manure heap turn it back again into nitrates
ready to begin the circle once more. This might
go on almost indefinitely wpre it not for two
facts : the farmer sends nitrogenous material off
his farm in the milk or grains or other nitro-
genous products which he sells, and the de-
composition processes, as we have seen, dissi-

120 THE STORY OF GERM LIFE.

pate some of the nitrogen into the air as free ni-
trogen.

To meet this emergency and loss the farmer
has another method of enriching the soil, again
depending upon bacteria. This is the so-called
green manuring. Here certain plants which seize
nitrogen from the air are cultivated upon the field
to be fertilized, and, instead of harvesting a
crop, it is ploughed into the soil. Or perhaps
the tops may be harvested, the rest being
ploughed into the soil. The vegetable material
thus ploughed in lies over a season and enriches
the soil. Here the bacteria of the soil come into
play in several directions. First, if the crop
sowed be a legume, the soil bacteria assist it to
seize the nitrogen from the air. The only plants
which are of use in this green manuring are those
which can, through the agency of bacteria, obtain
nitrogen from the air and store it in their roots.
Second, after the crop is ploughed into the soil
various decomposing bacteria seize upon it, pulling
the compounds to pieces. The carbon is largely
dissipated into the air as carbonic dioxide, where
the next generation of plants can get hold of it.
The minerals and the nitrogen remain in the soil.
The nitrogenous portions go through the same
series of decomposition and synthetical changes
already described, and thus eventually the nitro-
gen seized from the air by the combined action
of the legumes and the bacteria is converted into
nitrates, and will serve for food for the next set
of plants grown on the same soil. Here is thus a
practical method of using the nitrogen assimila-
tion powers of bacteria, and reclaiming nitrogen
from the air to replace that which has been lost.

Thus it is that the farmer's nitrogen problem

BACTERIA IN NATURAL PROCESSES. 121

of the fertile soil appears to resolve itself into a
proper handling of bacteria. These organisms
have stocked his soil in the first place. They
convert all of his compost heap wastes into simple
bodies, some of which are changed into plant
foods, while others are at the same time lost.
Lastly, they may be made to reclaim this lost
nitrogen, and the farmer, so soon as he has
requisite knowledge of these facts, will be able
to keep within his control the supply of this im-
portant element. The continued fertility of the
soil is thus a gift from the bacteria.

BACTERIA AS SOURCES OF TROUBLE TO THE
FARMER.

While the topics already considered comprise
the most important factors in agricultural bacte-
riology, the farmer's relations to bacteria do
not end here. These organisms come incidentally
into his life in many ways. They are not always
his aids as they are in most of the instances thus
far cited. They produce disease in his cattle, as
will be noticed in the next chapter. Bacteria are
agents of decomposition, and they are just as
likely to decompose material which the farmer
wishes to preserve as they are to decompose ma-
terial which the farmer desires to undergo the
process of decay. They are as ready to attack
his fruits and vegetables as to ripen his cream.
The skin of fruits and vegetables is a moderately
good protection of the interior from the attack
of bacteria; but if the skin be broken in any
place, bacteria get in and cause decay, and to
prevent it the farmer uses a cold cellar. The
bacteria prevent the farmer from preserving

122 THE STORY OF GERM LIFE.

meats for any length of time unless he checks
their growth in some way. They get into the
eggs of his fowls and ruin them. Their trouble-
some nature in the dairy in preventing the keep-
ing of milk has already been noticed. If he
plants his seeds in very moist, damp weather,
the soil bacteria cause too rapid a decomposition
of the seeds and they rot in the ground instead
of sprouting. They produce disagreeable odours,
and are the cause of most of the peculiar smells,
good and bad, around the barn. They attack
the organic matter which gets into his well or
brook or pond, decomposing it, filling the water
with disagreeable and perhaps poisonous products
which render it unfit to drink. They not only aid
in the decay of the fallen tree in his forests, but
in the same way attack the timber which he
wishes to preserve, especially if it is kept in a
moist condition. Thus they contribute largely
to the gradual destruction of wooden structures.
It is therefore the presence of these organisms
which forces him to dry his hay, to smoke his
hams, to corn his beef, to keep his fruits and
vegetables cool and prevent skin bruises, to ice
his dairy, to protect his timber from rain, to use
stone instead of wooden foundations for build-
ings, etc. In general, when the farmer desires
to get rid of any organic refuse, he depends upon
bacteria, for they are his sole agents (aside from
fire) for the final destruction of organic matter.
When he wishes to convert waste organic refuse
into fertilizing material, he uses the bacteria of
his compost heap. On the other hand, whenever
he desires to preserve organic material, the
bacteria are the enemies against which he must
carefully guard.

BACTERIA IN NATURAL PROCESSES. 123

Thus the farmer's life from year's end to year's
end is in most intimate association with bacteria.
Upon them he depends to insure the continued
fertility of his soil and the constant continued
production of good crops. Upon them he de-
pends to turn into plant food all the organic ref-
use from his house or from his barn. Upon
them he depends to replenish his stock of nitrogen.
It is these organisms which furnish his dairy with
its butter flavours and with the taste of its cheese.
But, on the other hand, against them he must be
constantly alert. All his food products must be
protected from their ravages. A successful farm-
er's life, then, largely resolves itself into a skilful
management of bacterial activity. To aid them
in destroying or decomposing everything which he
does not desire to preserve, and to prevent their
destroying the organic material which he wishes to
keep for future use, is the object of a considerable
portion of farm labour ; and the most successful
farmer to-day, and we believe the most successful
farmer of the future, is the one who most intelli-
gently and skilfully manipulates these gigantic
forces furnished him by the growth of his micro-
scopical allies.

RELATION OF BACTERIA TO COAL.

Another one of Nature's processes in which
bacteria have played an important part is in the
formation of coal. It is unnecessary to emphasize
the importance of coal in modern civilization.
Aside from its use as fuel, upon which civilization
is dependent, coal is a source of an endless variety
of valuable products. It is the source of our
illuminating gas, and ammonia is one of the prod-

124 THE STORY OF GERM LIFE.

ucts of the gas manufacture. From the coal
also comes coal tar, the material from which such
a long series of valuable materials, as aniline
colours, carbolic acid, etc., is derived. The list of
products which we owe to coal is very long, and
the value of this material is hardly to be over-
rated. In the preparation of these ingredients
from coal bacteria do not play any part. Most
of them are derived by means of distillation. But
when asked for the agents which have given us
the coal of the coal beds, we shall find that here,
too, we owe a great debt to bacteria.

Coal, as is well known, has come from the ac-
cumulation of the luxuriant vegetable growth of
the past geological ages. It has therefore been
directly furnished us by the vegetation of the
green plants of the past, and, in general, it repre-
sents so much carbonic dioxide which these
plants have extracted from the atmosphere. But
while the green plants have been the active
agents in producing this assimilation, bacteria
have played an important part in coal manufac-
ture in two different directions. The first ap-
pears to be in furnishing these plants with
nitrogen. Without a store of fixed nitrogen in
the soil these carboniferous plants could not have
grown. This matter has already been considered.
We have no very absolute knowledge as to the
agency of bacteria in furnishing nitrogen for this
vegetation in past ages, but there is every reason
to believe that in the past, as in the present, the
chief source of organic nitrogen has been from
the atmosphere and derived from the atmos-
phere through the agency of bacteria. In the
absence of any other known factor we may be
pretty safe in the assumption that bacteria played

BACTERIA IN NATURAL PROCESSES. 125

an important part in this nitrogen fixation, and
that bacteria must therefore be regarded as the
agents which have furnished us the nitrogen
stored in the coal.

But in a later stage of coal formation bacteria
have contributed more directly to the formation of
coal. Coal is not simply accumulated vegetation.
The coal of our coal beds is very different in its
chemical composition from the wood of the trees.
It contains a much higher percentage of carbon
and a lower percentage of hydrogen and oxygen
than ordinary vegetable substances. The conver-
sion of the vegetation of the carboniferous ages
into coal was accompanied by a gradual loss of
hydrogen and a consequent increase in the per-
centage of carbon. It is this change that has
added to the density of the substance and makes
the greater value of coal as fuel. There is little
doubt now as to the method by which this woody
material of the past has been converted into coal.
The same process appears to be going on in a
similar manner to-day in the peat beds of various
northern countries. The fallen vegetation, trees,
trunks, branches, and leaves, accumulate in
masses, and, when the conditions of moisture and
temperature are right, begin to undergo a fer-
mentation. Ordinarily this action of bacteria,
as already noticed, produces an almost complete
though slow oxidation of the carbon, and results
in the total decay of the vegetable matter. But
if the vegetable mass be covered by water and
mud under proper conditions of moisture and tem-
perature, a different kind of fermentation arises
which does not produce such complete decay.
The covering of water prevents the access of
oxygen to the fermenting mass, an oxidation of

126 THE STORY OF GERM LIFE.

the carbon is largely prevented, and the vegetable
matter slowly changes its character. Under the
influence of this slow fermentation, aided, proba-
bly by pressure, the mass becomes more and more
solid and condensed, its woody character becomes
less and less distinct, and there is a gradual loss
of the hydrogen and the oxygen. Doubtless
there is a loss of carbon also, for there is an evo-
lution of marsh gas which contains carbon. But
in this slow fermentation taking place under the
water in peat bogs and marshes the carbon loss
is relatively small ; the woody material does not
become completely oxidized, as it does in free
operations of decay. The loss of hydrogen and
oxygen from the mass is greater than that of
carbon, and the percentage of carbon therefore in-
creases. This is not the ordinary kind of fermen-
tation that goes on in vegetable accumulations.
It requires special conditions and possibly special
kinds of fermenting organisms. Peat is not
formed in all climates. In warm regions, or
where the woody matter is freely exposed to the
air, the fermentation of vegetable matter is more
complete, and it is entirely destroyed by oxida-
tion. It is only in colder regions and when cov-
ered with water that the destruction of the organic
matter stops short of decay. But such incom-
plete fermentation is still going on in many parts
of the world, and by its means vegetable ac-
cumulations are being converted into peat.

This formation of peat appears to be a first
step in the formation of denser coal. By a con-
tinuation of the same processes the mass becomes
still more dense and solid. As we pass from the
top to the bottom of such an accumulation of
peat, we find it becoming denser and denser, and

BACTERIA IN NATURAL PROCESSES. 127

at the bottom it is commonly of a hard consist-
ence, brownish in colour, and with only slight
traces of the original woody structure. Such
material is called lignite. It contains a higher
percentage of carbon than peat, but a lower per-
centage than coal, and is plainly a step in coal for-
mation. But the process goes on, the hydrogen
and oxygen loss continuing until there is finally
produced true coal.

If this is the correct understanding of the for-
mation of coal, we see that we have plainly a pro-
cess in which bacterial life has had a large and
important share. We are, of course, densely
ignorant of the exact processes going on. We
know nothing positively as to the kind of micro-
organisms which produce this slow, peculiar fer-
mentation. As yet, the fermentation going on in
the formation of the peat has not been studied
by the bacteriologists, and we do not know from
direct experiment that it is a matter of bacterial
action. It has been commonly regarded as sim-
ply a slow chemical change, but its general simi-
larity to other fermentative processes is so great
that we can have little hesitation in attributing it
to micro-organisms, and doubtless to some forms
of plants allied to bacteria. There is no reason
for doubting that bacteria existed in the geologi-
cal ages with essentially the same powers as
they now possess, and to some forms of bacteria
which grow in the absence of oxygen can we
probably attribute the slow change which has
produced coal. Here, then, is another great
source of wealth in Nature for which we are de-
pendent upon bacteria. While, of course, water
and pressure were very essential factors in the
deposition of coal, it was a peculiar kind of fer-

128 THE STORY OF GERM LIFE.

mentation occurring in the vegetation that
brought about the chemical changes in it which
resulted in its transformation into coal. The vege-
tation of the carboniferous age was dependent
upon the nitrogen fixed by the bacteria, and to
these organisms also do we owe the fact that this
vegetation was stored for us in the rocks.

CHAPTER V.

PARASITIC BACTERIA AND THEIR RELATION TO
DISEASE.

PERHAPS the most universally known fact in
regard to bacteria is that they are the cause of
disease. It is this fact that has made them ob-
jects of such wide interest. This is the side of
the subject that first attracted attention, has been
most studied, and in regard to which there has
been the greatest accumulation of evidence. So
persistently has the relation of bacteria to disease
been discussed and emphasized that the majority
of readers are hardly able to disassociate the two.
To most people the very word bacteria is almost
equivalent to disease, and the thought of swallow-
ing microbes in drinking water or milk is decid-
edly repugnant and alarming. In the public mind
it is only necessary to demonstrate that an article
holds bacteria to throw it under condemnation.

We have already seen that bacteria are to be
regarded as agents for good, and that from their
fundamental relation to plant life they must be
looked upon as our friends rather than as our
enemies. It is true that there is another side to

PARASITIC BACTERIA. 129

the story which relates to the parasitic species.
These parasitic forms may do us direct or indi-
rect injury. But the species of bacteria which are
capable of doing us any injury, \.\\t pathogenic bac-
teria, are really very few compared to the great
host of species which are harmless. A small
number of species, perhaps a score or two, are
pathogenic, while a much larger number, amount-
ing to hundreds and perhaps thousands of species,
are perfectly harmless. This latter class do no in-
jury even though swallowed by man in thousands.
They are not parasitic, and are unable to grow in
the body of man. Their presence is entirely con-
sistent with the most perfect health, and, indeed,
there are some reasons for believing that they
are sometimes directly beneficial to health. It is
entirely unjust to condemn all bacteria because a
few chance to produce mischief. Bacteria in gen-
eral are agents for good rather than ill.

There are, however, some species which cause
mankind much trouble by interfering in one way
or another with the normal processes of life.
These pathogenic bacteria, or disease germs, do
not all act alike, but bring about injury to man in
a number of different ways. We may recognise
two different classes among them, which, how-
ever, we shall see are connected by intermediate
types. These two classes are, first, the patho-
genic bacteria, which are not strictly parasitic but
live free in Nature; and, second, those which live
as true parasites in the bodies of man or other ani-
mals. To understand the real relation of these
two classes, we must first notice the method by
which bacteria in general produce disease.

130 THE STORY OF GERM LIFE.

METHOD BY WHICH BACTERIA PRODUCE
DISEASE.

Since it was first clearly recognised that cer-
tain species of bacteria have the power of pro-
•ducing disease, the question as to how they do
so has ever been a prominent one. Even if they
do grow in the body, why should their presence
give rise to the symptoms characterizing dis-
ease ? Various answers to this question have
been given in the past. It has been suggested
that in their growth they consume the food of
the body and thus exhaust it ; that they produce
.an oxidation of the body tissues, or that they
produce a reduction of these tissues, or that
they mechanically interfere with the circulation.
None of these suggestions have proved of much
value. Another view was early advanced, and has
stood the test of time. This claim is that the
bacteria while growing in the body produce poi-
sons, and these poisons then have a direct action
on the body. We have already noticed that bac-
teria during their growth in any medium produce
a large number of biprodiicts of decomposition.
We noticed also that among these biproducts
there are some which have a poisonous nature ;
so poisonous are they that when inoculated into
the body of an animal they may produce poison
ing and death. We have only to suppose that the
pathogenic bacteria, when growing as parasites in
man, produce such poisons, and we have at once
an explanation of the method by which they give
rise to disease.

This explanation of germ disease is more than
simple theory. It has been in many cases clearly
demonstrated. It has been found that the bac-

PARASITIC BACTERIA. 131

teria which cause diphtheria, tetanus, typhoid,,
tuberculosis, and many other diseases, produce,
even when growing in common culture media,
poisons which are of a very violent nature. These
poisons when inoculated into the bodies of ani-
mals give rise to much the same symptoms as
the bacteria do themselves when growing as para-
sites in the animals. The chief difference in the
results from inoculating an animal with the poison
and with the living bacteria is in the rapidity of
the action. When the poison is injected the poi-
soning symptoms are almost immediately seen ; but
when the living bacteria are inoculated the effect
is only seen after several days or longer, not, in
short, until the inoculated bacteria have had time
enough to grow in the body and produce the poi-
son in quantity. It has not by any means been
shown that all pathogenic germs produce their
effect in this way, but it has been proved to be
the real method in quite a number of cases, and
is extremely probable in others. While some
bacteria perhaps produce results by a different
method, we must recognise the production of poi-
sons as at all events the common direct cause of
the symptoms of disease. This explanation will
enable us more clearly to understand the relation
of different bacteria to disease.

PATHOGENIC GERMS WHICH ARE NOT STRICTLY
PARASITIC.

Recognising that bacteria may produce poi-
sons, we readily see that it is not always neces-
sary that they should be parasites in order to
produce trouble. In their ordinary growth in
Nature such bacteria will produce no trouble.

132 THE STORY OF GERM LIFE.

The poisons will be produced in decaying mate-
rial but will seldom be taken into the human
body. These poisons, produced in the first
stages of putrefaction, are oxidized by further
stages of decomposition into harmless products.
But should it happen that some of these bacteria
obtained a chance to grow vigorously for a while
in organic products that are subsequently swal-
lowed as man's food, it is plain that evil results
might follow. If such food is swallowed by man
after the bacteria have produced their poisonous
bodies, it will tend to produce an immediate poi-
soning of his system. The effect may be sudden
and severe if considerable quantity of the poison-
ous material is swallowed, or slight but protracted
if small quantities are repeatedly consumed in
food. Such instances are not uncommon. Well-
known examples are cases of ice-cream poison-
ing, poisoning from eating cheese or from drink-
ing milk, or in not a few instances from eating
fish or meats within which bacteria have had
opportunity for growth. In all these cases the
poison is swallowed in quantity sufficient to give
rise quickly to severe symptoms, sometimes re-
sulting fatally, and at other times passing off as
soon as the body succeeds in throwing off the
poisons. In other cases still, however, the
amount of poison swallowed may be very slight,
too slight to produce much effect unless the same
be consumed repeatedly. All such trouble may
be attributed to fermented or partly decayed
food. It is difficult to distinguish such instances
from others produced in a slightly different way,
as follows :

It may happen that the bacteria which grow
in food products continue to grow in the food

PARASITIC BACTERIA. 133

even after it is swallowed and has passed into
the stomach or intestines. This appears particu-
larly true of milk bacteria. Under these condi-
tions the bacteria are not in any proper sense
parasitic, since they are simply living in and
feeding upon the same food which they consume
outside the body, and are not feeding upon the
tissues of man. The poisons which they produce
will continue to be developed as long as the bac-
teria continue to grow, whether in a milk pail or
a human stomach. If now the poisons are ab-
sorbed by the body, they may produce a mild or
severe disease which will be more or less lasting,
continuing perhaps as long as the same food and
the same bacteria are supplied to the individual.
The most important disease of this class appears
to be the dreaded cholera infantum, so common
among infants who feed upon cow's milk in warm
weather. It is easy to understand the nature of
this disease when we remember the great number
of bacteria in milk, especially in hot weather,
and when we remember that the delicate organ-
ism of the infant will be thrown at once into
disorder by slight amounts of poison which would
have no appreciable effect upon the stronger
adult. We can easily understand, further, how
the disease readily yields to treatment if care
is taken to sterilize the milk given to the pa-
tient.

We do not know to-day the extent of the
troubles which are produced by bacteria of this
sort. They will, of course, be chiefly connected
with our food products, and commonly, though
not always, will affect the digestive functions. It
is probable that many of the cases of summer
diarrhoea are produced by some such cause, and

134 THE STORY OF GERM LIFE.

if they could be traced to their source would be
found to be produced by bacterial poisons swal-
lowed with food or drink, or by similar poisons
produced by bacteria growing in such food after
it is swallowed by the individual. In hot weather,
when bacteria are so abundant everywhere and
growing so rapidly, it is impossible to avoid such
dangers completely without exercising over all
food a guard which would be decidedly oppress-
ive. It is well to bear in mind, however, that
the most common and most dangerous source of
such poisons is milk or its products, and for this
reason one should hesitate to drink milk in hot
weather unless it is either quite fresh or has been
boiled to destroy its bacteria.

PATHOGENIC BACTERIA WHICH ARE TRUE
PARASITES.

This class of pathogenic bacteria includes
those which actually invade the body and feed
upon its tissues instead of living simply upon
swallowed food. It is difficult, however, to draw

any sharp line sep-
arating the two
classes. The bac-
teria which cause
diphtheria (Fig.
28)> for instance,
do not really in-

FlG. ^.-Diphtheria bacillus. vade the body.

They grow in the

throat, attached to its walls, and are confined to
this external location or to the superficial tissues:
This bacillus is, in short, only found in the mouth
and throat, and is practically confined to the so-*

PARASITIC BACTERIA. 135

called false membranes. It never enters any of
the tissues of the body, although attached to the
mucous membrane. It grows vigorously in this
membrane, and there secretes or in some way
produces extremely violent
poisons. These poisons
are then absorbed by the
body and give rise to the
general symptoms of the
disease. Much the same is
true of the bacillus which
causes tetanus or lockjaw YIG. ^.-Tetanus bacillus,
(Fig. 29). This bacillus is

commonly inoculated into the flesh of the victim
by a wound made with some object which has
been lying upon the earth where the bacillus
lives. The bacillus grows readily after being in-
oculated, but it is localized at the point of the
wound, without invading the tissue to any extent.
It produces, however, during its growth several
poisons which have been separated and studied.
Among them are some of the most violent poi-
sons of which we have any knowledge. While
the bacillus grows in the tissues around the
wound it secretes these poisons, which are then
absorbed by the body generally. Their poison-
ing effects produce the violent symptoms of the
disease. Of much the same nature is Asiatic
cholera. This is caused by a bacillus which is
able to grow rapidly in the intestines, feeding
perhaps in part on the food in the intestines and
perhaps in part upon the body secretions. To
a slight extent also it appears to be able to in-
vade the tissues of the body, for the bacilli are
found in the walls of the intestines. But it is
not a proper parasite, and the fatal disease it

136 THE STORY OF GERM LIFE.

produces is the result of the absorption of the
poisons secreted in the intestines.

It is but a step from this to the true parasites.
Typhoid fever, for example, is a disease produced
by bacteria which grow in the intestines, but
which also invade the tissues
more extensively than the
cholera germs (Fig. 30). They
do not invade the body gen-
erally, however, but become
somewhat localized in special
glands like the liver, the
spleen, etc. Even here they
do not appear to find a very
favourable condition, for they
do not grow extensively in
these places. They are likely
to be found in the spleen in
small groups or centres, but
stained, showing the not generally distributed
cSres^b0 staged tnrough it:- Wherever they
toshowthe'flageiTa! grow they produce poison,
which has been called typho
toxine, and it is this poison chiefly which gives
rise to the fever.

Quite a considerable number of the patho-
genic germs are, like the typhoid bacillus, more
or less confined to special places. Instead of
distributing themselves through the body after
they find entrance, they are restricted to special
organs. The most common example of a para-
site of this sort is the tuberculosis bacillus, the
cause of consumption, scrofula, white swelling,
lupus, etc. (Fig. 31). Although this bacillus is
very common and is able to attack almost any
organ in the body, it is usually very restricted in

PARASITIC BACTERIA.

137

growth. It may become localized in a small
gland, a single joint, a small spot in the lungs, or
in the glands of the mesentery, the other parts
of the body remaining free from infection. Not
infrequently the whole trouble is thus confined

flG. 31. — Tuberculosis bacillus: a, As seen in lung tissue ; b,
More magnified ; c, As sometimes seen in sputum of con-
sumptive patients.

to such a small locality that nothing serious re-
sults. But in other instances the bacilli may after
a time slowly or rapidly distribute themselves
from these centres, attacking more and more of
the body until perhaps fatal results follow in the
end. This disease is therefore commonly of very
slow progress.

Again, we have still other parasites which are
not thus confined, but which, as soon as they
enter the body, produce a general infection, at-
tacking the blood and perhaps nearly all tissues
simultaneously. The most typical example of
this sort is anthrax or malignant pustule, a disease
fortunately rare in man (Fig. 32). Here the
bacilli multiply in the blood, and very soon a
general and fatal infection of the whole body
arises, resulting from the abundance of the ba-

THE STORY OF GERM LIFE.

cilli everywhere. Some of the obscure diseases
known as blood poisoning appear to be of the same
general nature,
these diseases re-
sulting from a very
general invasion of
the whole body by
certain pathogenic
bacteria.

In general, then,
we see that the so-
called germ diseas-
es result from the

FIG. v.-Antkrax bacillus (splenic aCtj°n ,UP°n . the

fever). body of poisons

produced by bac-
terial growth. Differences in the nature of these
poisons produce differences in the character of
the disease, and differences in the parasitic pow-
ers of the different species of bacteria produce
wide differences in the course of the diseases and
their relation to external phenomena.

WHAT DISEASES ARE DUE TO BACTERIA?

It is, of course, an extremely important matter
to determine to what extent human diseases are
caused by bacteria. It is not easy, nor indeed
possible, to do this to-day with accuracy. It is
no easy matter to prove that any particular dis-
ease is caused by bacteria. To do this it is neces-
sary to find some particular bacterium present in
all cases of the disease ; to find some method of
getting it to grow outside the body in culture
media; to demonstrate its absence in healthy ani-
mals, or healthy human individuals if it be a hu-

PARASITIC BACTERIA,

139

man disease ; and, finally, to reproduce the disease
in healthy animals by inoculating them with the
bacterium. All of these steps of proof present
difficulties, but especially the last one. In the
study of animals it is comparatively easy to re-
produce a disease by inoculation. But experi-
ments upon man are commonly impossible, and
in the case of human diseases it is frequently
very difficult or impossible to obtain the final
test of the matter. After finding a specific bac-
terium associated with a disease, it is usually pos-
sible to experiment with it further upon animals
only. But some human diseases do not attack
animals, and in the case of diseases that may be
given to animals it is frequently uncertain wheth-
er the disease produced in the animal by such in-
oculation is identical with the human disease in
question, owing to the difference of symptoms in
the different animals. As a consequence, the proof
of the germ nature of different diseases varies all
the way from absolute demonstration to mere
suspicion. To give a complete and correct list
of the diseases caused by bacteria, or to give a
list of the bacteria species pathogenic to man, is
therefore at present impossible.

The difficulty of giving such a list is rendered
greater from the fact that we have in recent years
learned that the same species of pathogenic bac-
terium may produce different results under differ-
ent conditions. When the subject of germ dis-
ease was first studied and the connection between
bacteria and disease was first demonstrated, it
was thought that each particular species of
pathogenic bacteria produced a single definite
disease ; and conversely, each germ disease was
supposed to have its own definite species of bac-

140 THE STORY OF GERM LIFE.

terium as its cause. Recent study has shown,
however, that this is not wholly true. It is true
that some diseases do have such a definite rela-
tion to definite bacteria. The anthrax germ, for
example, will always produce anthrax, no matter
where or how it is inoculated into the body. So,
also, in quite a number of other cases distinct
specific bacteria are associated with distinct dis-
eases. But, on the other hand, there are some
pathogenic bacteria which are not so definite in
their action, and produce different results in ac-
cordance with circumstances, the effect varying
both with the organ attacked and with the condi-
tion of the individual. For instance, a consider-
able number of different types of blood poison-
ing, septiccemia, pycemia, gangrene, inflammation of
wounds, or formation of pus from slight skin
wounds — indeed, a host of miscellaneous trou-
bles, ranging all the way from a slight pus forma-
tion to a violent and severe blood poisoning — all
appear to be caused by bacteria, and it is impos-
sible to make out any definite species associated
with the different types of these troubles. There
are three common forms of so-called pus cocci,
and these are found almost indiscriminately with
various types of inflammatory troubles. More-
over, these species of bacteria are found with al-
most absolute constancy in and around the body,
even in health. They are on the clothing, on the
skin, in the mouth and alimentary canal. Here
they exist, commonly doing no harm. They have,
however, the power of doing injury if by chance
they get into wounds. But their power of doing
injury varies both with the condition of the indi-
vidual and with variations in the bacteria them-
selves. If the individual is in a good condition

PARASITIC BACTERIA. 141

of health these bacteria have little power of in-
juring him even when they do get into such
wounds, while at times of feeble vitality they
may do much more injury, and take the occasion
of any little cut or bruise to enter under the skin
and give rise to inflammation and pus. Some
people will develop slight abscesses or slight in-
flammations whenever the skin is bruised, while
with others such bruises or cuts heal at once
without trouble. Both are doubtless subject to
the same chance of infection, but the one resists,
while the other does not. In common parlance,
we say that such a tendency to abscesses indi-
cates a bad condition of the blood — a phrase
which means nothing. Further, we find that the
same species of bacterium may have varying
powers of producing disease at different times.
Some species are universal inhabitants of the
alimentary canal and are ordinarily harmless,
while under other conditions of unknown char-
acter they invade the tissues and give rise to a
serious and perhaps fatal disease. We may thus
recognise some bacteria which may be compared
to foreign invaders, while others are domestic
enemies. The former, like the typhoid bacillus,
always produce trouble when they succeed in
entering the body and finding a foothold. The
latter, like the normal intestinal bacilli, are al-
ways present but commonly harmless, only under
special conditions becoming troublesome. All
this shows that there are other factors in deter-
mining the course of a disease, or even the exist-
ence of a disease, than the simple presence of a
peculiar species of pathogenic bacterium.

From the facts just stated it will be evident
that any list of germ diseases will be rather un-
10

142 THE STORY OF GERM LIFE.

certain. Still, the studies of the last twenty years
or more have disclosed some definite relations of
bacteria and disease, and a list of the diseases
more or less definitely associated with distinct
species of bacteria is of interest. Such a list,
including only well-known diseases, is as follows :

Name of disease. Name of bacterium producing the disease.

Anthrax (Malignant pustule). Bacillus anthracis.

Cholera.
Croupous pneumonia.
Diphtheria.
Glanders.
Gonorrhoea.
Influenza.
Leprosy.
Relapsing fever.
Tetanus (lockjaw).
Tuberculosis (including con-
sumption, scrofula, etc.)
Typhoid fever.

Spirillum cholera asiatica.
Micrococcus pneumonia croufoseE.
Bacillus diphtheria.
Bacillus mallei.
Micrococcus gonorrhoea.
Bacillus of influenza.
Bacillus lepra.
Spirillum Obermeieri.
Bacillus tetani.

Bacillus tuberculosis.
Bacillus typhi abdominalis.

Various wound infections, including ^/fc^/mia,

pyaemia, acute abscesses, ulcers, erysipelas, etc., are pro-
duced by a few forms of micrococci, resembling
each other in many points but differing slightly.
They are found almost indiscriminately in any of
these wound infections, and none of them appears
to have any definite relation to any special form
of disease unless it be the micrococcus of erysip-
elas. The common pus micrococci are grouped
under three species, Staphylococcus pyogenes aureus,
Staphylococcus pyogenes, and Streptococcus pyogenes.
These three are the most common, but others are
occasionally found.

In addition to these, which may be regarded as
demonstrated, the following diseases are with
more or less certainty regarded as caused by dis-
tinct specific bacteria : Bronchitis, endocarditis,

PARASITIC BACTERIA. 143

measles, whooping-cough, peritonitis, pneumonia,
syphilis.

Still another list might be given of diseases
whose general nature indicates that they are
caused by bacteria, but in connection with which
no distinct bacterium has yet been found. As
might be expected also, a larger list of animal
diseases has been demonstrated to be caused by
these organisms. In addition, quite a number
of species of bacteria have been found in such
material as faeces, putrefying blood, etc., which
have been shown by experiment to be capable of
producing diseases in animals, but in regard to
which we have no evidence that they ever do
produce actual disease under any normal con-
ditions. These may contribute, perhaps, to the
troubles arising from poisonous foods, but can
not be regarded as disease germs proper.

VARIABILITY OF PATHOGENIC POWERS.

As has already been stated, our ideas of the
relation of bacteria to disease have undergone
quite a change since they were first formulated,
and we recognise other factors influencing dis-
ease besides the actual presence of the bac-
terium. These we may briefly consider under
two heads, viz., variation in the bacterium, and
variation in the susceptibility of the individual.
The first will require only a brief consideration.

That the same species of pathogenic bacteria
at different times varies in its powers to produce
disease has long been known. Various con-
ditions are known to affect thus the virulence of
bacteria. The bacillus which is supposed to give
rise to pneumonia loses its power to produce the

144 THE STORY OF GERM LIFE.

disease after having been cultivated for a short
time in ordinary culture media in the laboratory.
This is easily understood upon the suggestion
that it is a parasitic bacillus and does not thrive
except under parasitic conditions. Its patho-
genic powers can sometimes be restored by pass-
ing it again through some susceptible animal.
One of the most violent pathogenic bacteria is
that which produces anthrax, but this loses its
pathogenic powers if it is cultivated for a con-
siderable period at a high temperature. The
micrococcus which causes fowl cholera loses its
power if it be cultivated in common culture media,
care being taken to allow several days to elapse
between the successive inoculations into new
culture flasks. Most pathogenic bacteria can
in some way be so treated as to suffer a dimi-
nution or complete loss of their powers of pro-
ducing a fatal disease. On the other hand, other
conditions will cause an increase in the virulence
of a pathogenic germ. The virus which produces
hydrophobia is increased in violence if it is
inoculated into a rabbit and subsequently taken
from the rabbit for further inoculation. The
fowl cholera micrococcus, which has been weak-
ened as just mentioned, may be restored to its
original violence by inoculating it into a small
bird, like a sparrow, and inoculating a second
bird from this. A few such inoculations will
make it as active as ever. These variations
doubtless exist among the species in Nature as
well as in artificial cultures. The bacteria
which produce the various wound infections and
abscesses, etc., appear to vary under normal con-
ditions from a type capable of producing violent
and fatal blood poisoning to a type producing

PARASITIC BACTERIA. 145

only a simple abscess, or even to a type that is
entirely innocuous. It is this factor, doubtless,
which in a large measure determines the severity
of any epidemic of a bacterial contagious dis-
ease.

SUSCEPTIBILITY OF THE INDIVIDUAL.

The very great modification of our early
views has affected our ideas as to the power
which individuals have of resisting the invasion
of pathogenic bacteria. It has from the first
been understood that some individuals are more
susceptible to disease than others, and in attempt-
ing to determine the significance of this fact
many valuable and interesting discoveries have
been made. After the exposure to the disease
there follows a period of some length in which
there are no discernible effects. This is followed
by the onset of the disease and its development
to a crisis, and, if this be passed, by a recovery.
The general course of a germ disease is divided
into three stages: the stage of incubation, the
development of the disease, and the recovery. The
susceptibility of the body to a disease may be
best considered under the three heads of Inva-
sion, Resistance, Recovery.

Means of Invasion. — In order that a germ dis-
ease should arise in an individual, it is first ne-
cessary that the special bacterium which causes
the disease should get into the body. There
are several channels through which bacteria can
thus find entrance ; these are through the
mouth, through the nose, through the skin, and
occasionally through excretory ducts. Those
which come through the mouth come with the

146 THE STORY OF GERM LIFE.

food or drink which we swallow ; those which
enter through the nose must be traced to the air;
and those which enter through the skin come in
most cases through contact with some infected
object, such as direct contact with the body of
an infected person or his clothing or some objects
he has handled, etc. Occasionally, perhaps, the
bacteria may get into the skin from the air, but
this is certainly uncommon and confined to a few
diseases. There are here two facts of the utmost
importance for every one to understand: first,
that the chance of disease bacteria being carried
to us through the air is very slight and confined
to a few diseases, such as smallpox, tuberculo-
sis, scarlet fever; etc., and, secondly, that the un-
injured skin and the uninjured mucous membrane
also is almost a sure protection against the in-
vasion of the bacteria. If the skin is whole,
without bruises or cuts, bacteria can seldom, if
ever, find passage through it. These two facts
are of the utmost importance, since of all sources
of infection we have the least power to guard
against infection through the air, and since of all
means of entrance we can guard the skin with
the greatest difficulty. We can easily render
food free from pathogenic bacteria by heating it.
The material we drink can similarly be rendered
harmless, but we can not by any known means
avoid breathing air, nor is there any known
method of disinfecting the air, and it is impos-
sible for those who have anything to do with
sick persons to avoid entirely having contact
either with the patient or with infected clothing
or utensils.

From the facts here given it will be seen that
the individual's susceptibility to disease produced

PARASITIC BACTERIA. 147

by parasitic bacteria will depend upon his habits
of cleanliness, his care in handling infectious
material, or care in cleansing the hands after such
handling, upon his habit of eating food cooked
or raw, and upon the condition of his skin and
mucous membranes, since any kind of bruises
wjll increase susceptibility. Slight ailments,
such as colds, which inflame the mucous mem-
brane, will decrease its resisting power and ren-
der the individual more susceptible to the entrance
of any pathogenic germs should they happen to
be present. Sores in the mouth or decayed teeth
may in the same way be prominent factors in- the
individual's susceptibility. Thus quite a number
of purely physical factors may contribute to an
individual's susceptibility.

Resisting Power of the Body. — Even after the
bacteria get into the body it is by no means cer-
tain that they will give rise to disease, for they
have now a battle to fight before they can be sure
of holding their own. It is now, indeed, that the
actual conflict between the powers of the body
and these microscopic invaders begins. After
they have found entrance into the body the bac-
teria have arrayed against them strong resisting
forces of the human organism, endeavouring to
destroy and expel them. Many of them are rapid-
ly killed, and sometimes they are all destroyed
without being able to gain a foothold. In such
cases, of course, no trouble results. In other
cases the body fails to overcome the powers of
the invaders and they eventually multiply rapidly.
In this struggle the success of the invaders is not
necessarily a matter of numbers. They are sim-
ply struggling to gain a position in the body, where
they can feed and grow. A few individuals may

148 THE STORY OF GERM LIFE.

be entirely sufficient to seize such a foothold, and
then these by multiplying may soon become in-
definitely numerous. To protect itself, therefore,
the human body must destroy every individual
bacterium, or at least render them all incapa-
ble of growth. Their marvellous reproductive
powers give the bacteria an advantage in the bat-
tle. On the other hand, it takes time even for
these rapidly multiplying beings to become suf-
ficiently numerous to do injury. There is thus an
interval after their penetration into the body
when these invaders are weak in numbers. Dur-
ing this interval — the period of incubation — the
body may organize a resistance sufficient to ex-
pel them.

We do not as yet thoroughly understand the
forces which the human organism is able to array
against these invading foes. Some of its meth-
ods of defence are, however, already intelligible
to us, and we know enough, at all events, to give
us an idea of the intensity of the conflict that is
going on, and of the vigorous and powerful forces
which the human organism is able to bring against
its invading enemies.

In the first place, we notice that a majority of
bacteria are utterly unable to grow in the human
body even if they do find entrance. There are
known to bacteriologists to-day many hundreds,
even thousands of species, but the vast majority
of these find in the human tissues conditions so
hostile to their life that they are utterly unable to
grow therein. Human flesh or human blood will
furnish excellent food for them if the individual
be dead, but living human flesh and blood in some
way exerts a repressing influence upon them which
is fatal to the growth of a vast majority of spe-

PARASITIC BACTERIA. 149

cies. Some few species, however, are not thus
destroyed by the hostile agencies of the tissues
of the animal, but are capable of growing and
multiplying in the living body. These alone are
what constitute the pathogenic bacteria, since, of
course, these are the only bacteria which can pro-
duce disease by growing in the tissues of an ani-
mal. The fact that the vast majority of bacteria
can not grow in the living organism shows clearly
enough that there are some conditions existing in
the living tissue hostile to bacterial life. There
can be little doubt, moreover, that it is these same
hostile conditions, which enable the body to resist
the attack of the pathogenic species in cases
where resistance is successfully made.

What are the forces arrayed against these in-
vaders ? The essential nature of the battle ap-
pears to be a production of poisons and counter
poisons. It appears to be an undoubted fact that
the first step in repelling these bacteria is to flood
them with certain poisons which check their
growth. In the blood and lymph of man and
other animals there are present certain products
which have a direct deleterious influence upon the
growth of micro-organisms. The existence of
these poisons is undoubted, many an experiment
having directly attested to their presence in the
blood of animals. Of their nature we know very
little, but of their repressing influence upon bac-
terial growth we are sure. They have been named
alexines, and they are produced in the living tis-
sue, although as to the method of their pro-
duction we are in ignorance. By the aid of
these poisons the body is able to prevent the
growth of the vast majority of bacteria which
get into its tissues. Ordinary micro-organisms

150 THE STORY OF GERM LIFE.

are killed at once, for these alexines act as anti-
septics, and common bacteria can no more grow
in the living body than they could in a solution
containing other poisons. Thus the body has a
perfect protection against the majority of bac-
teria. The great host of species which are found
in water, milk, air, in our mouths or clinging to
our skin, and which are almost omnipresent in
Nature, are capable of growing well enough in or-
dinary lifeless organic foods ; but just as soon as
they succeed in finding entrance into living human
tissue their growth is checked at once by these
antiseptic agents which are poured upon them.
Such bacteria are therefore not pathogenic germs,
and not sources of trouble to human health.

There are, on the other hand, a few species of
bacteria which may be able to retain their lodg-
ment in the body in spite of this attempt of the
individual to get rid of them. These, of course,
constitute the pathogenic species, or so-called
" disease germs." Only such species as can over-
come this first resistance can be disease germs,
for they alone can retain their foothold in the
body.

But how do these species overcome the poi-
sons which kill the other harmless bacteria ?
They, as well as the harmless forms, find these
alexines injurious to their growth, but in some
way they are able to counteract the poisons. In
this general discussion of poisons we are dealing
with a subject which is somewhat obscure, but
apparently the pathogenic bacteria are able to
overcome the alexines of the body by producing
in their turn certain other products which neu-
tralize the alexines, thus annulling their action.
These pathogenic bacteria, when they get into

PARASITIC BACTERIA. 151

the body, give rise at once to a group of bodies
which have been named lysines. These lysines
are as mysterious to us as the alexines, but they
neutralize the effect of the alexines and thus
overcome the resistance the body offers to bac-
terial growth. The invaders can now multiply
rapidly enough to get a lasting foothold in the
body and then soon produce the abnormal symp-
toms which we call disease. Pathogenic bacteria
thus differ from the non-pathogenic bacteria
primarily in this power of secreting products
which can neutralize the ordinary effects of the
alexines, and so overcome the body's normal re-
sistance to their parasitic life.

Even if the bacteria do thus overcome the
alexines the battle is not yet over, for the indi-
vidual has another method of defence which is
now brought into activity to check the growth of
the invading organisms. This second method of
resistance is by means of a series of active cells
found in the blood, known as white blood-cor-
puscles (Fig. 33 a, fr). They are minute bits of
protoplasm present in the blood and lymph in
large quantities. They are active cells, capable
of locomotion and able to crawl out of the blood-
vessels. Not infrequently they are found to take
into their bodies small objects with which they
come in contact. One of their duties is thus to en-
gulf minute irritating bodies which may be in the
tissues, and to carry them away for excretion.
They thus act as scavengers. These corpuscles
certainly have some agency in warding off the at-
tacks of pathogenic bacteria. Very commonly
they collect in great numbers in the region of
the body where invading bacteria are found. Such
invading bacteria exert upon them a strong attrac-

THE STORY OF GERM LIFE.

Pie. 33. — White blood corpuscles and other phagocytes : a, A sta-
tionary form ; b, Motile form ; c, Phagocyte with a bacterium
half engulfed ; d, Phagocytes containing bacteria either dead
or alive ; e, Phagocyte loaded with bacteria.

PARASITIC BACTERIA. 153

tion, and the corpuscles leave the blood-vessels
and sometimes form a solid phalanx completely
surrounding the invading germs. Their collec-
tion at these points may make itself seen exter-
nally by the phenomenon we call inflammation.

There is no question that the corpuscles en-
gage in conflict with the bacteria when they thus
surround them. There has been not a little dis-
pute, however, as to the method by which they
carry on the conflict. It has been held by some
that the corpuscles actually take the bacteria into
their bodies, swallow them, as it were, and subse-
quently digest them (Fig. 33 c, d, e). This idea
gave rise to the theory of phagocytosis, and the
corpuscles were consequently named phagocytes.
The study of several years has, however, made it
probable that this is not the ordinary method by
which the corpuscles destroy the bacteria. Ac-
cording to our present knowledge the method is
a chemical one. These cells, when they thus col-
lect in quantities around the invaders, appear to
secrete from their own bodies certain injurious
products which act upon the bacteria much as do
the alexines already mentioned. These new bod-
ies have a decidedly injurious effect upon the
multiplying bacteria ; they rapidly check their
growth, and, acting in union with the alexines,
may perhaps entirely destroy them.

After the bacteria are thus killed, the white
blood-corpuscles may load themselves with their
dead bodies and carry them away (Fig. 33 d, e).
Sometimes they pass back into the blood stream
and carry the bacteria to various parts of the
body for elimination. Not infrequently the white
corpuscles die in the contest, and then may ac-
cumulate in the form of pus and make their way

1 54 THE STORY OF GERM LIFE.

through the skin to be discharged directly. The
battle between these phagocytes and the bacteria
goes on vigorously. If in the end the phagocytes
prove too strong for the invaders, the bacteria
are gradually all destroyed, and the attack is re-
pelled. Under these circumstances the individual
commonly knows nothing of the matter. This
conflict has taken place entirely without any con-
sciousness on his part, and he may not even know
that he has been exposed to the attack of the
bacteria. In other cases the bacteria prove too
strong for the phagocytes. They multiply too
rapidly, and sometimes they produce secretions
which actually drive the phagocytes away. Com-
monly, as already noticed, the corpuscles are at-
tracted to the point of invasion, but in some cases,
when a particularly deadly and vigorous species
of bacteria invades the body, the secretions pro-
duced by them are so powerful as actually to
drive the corpuscles away. Under these circum-
stances the invading hosts have a chance to mul-
tiply unimpeded, to distribute themselves over the
body, and the disease rapidly follows as the result
of their poisoning action on the body tissues.

It is plain, then, that the human body is not
helpless in the presence of the bacteria of disease,
but that it is supplied with powerful resistant
forces. It must not be supposed, however, that
the outline of the action of these forces just given
is anything like a complete account of the matter;
nor must it be inferred that the resistance is in all
respects exactly as outlined. The subject has only
recently been an object of investigation, and we are
as yet in the dark in regard to many of the facts.
The future may require us to modify to some ex-
tent even the brief outline which has been given.

PARASITIC BACTERIA. 155

But while we recognise this uncertainty in the de-
tails, we may be assured of the general facts.
The living body has some very efficacious resist-
ant forces which prevent most bacteria from
growing within its tissues, and which in large
measure may be relied upon to drive out the true
pathogenic bacteria. These resistant forces are
in part associated with the productions of body
poisons, and are in part associated with the active
powers of special cells which have been called
phagocytes. The origin of the poisons and the
exact method of action of the phagocytes we may
well leave to the future to explain.

These resisting powers of the body will vary
with conditions. It is evident that they are
natural powers, and they will doubtless vary with
the general condition of vigour of the individual.
Robust health, a body whose powers are strong,
well nourished, and vigorous, will plainly furnish
the conditions for the greatest resistance to bac-
terial diseases. One whose bodily activities are
weakened by poor nutrition can offer less resist-
ance. The question whether one shall suffer
from a germ disease is not simply the question
whether he shall be exposed, or even the question
whether the bacteria shall find entrance into his
body. It is equally dependent upon whether he
has the bodily vigour to produce alexinesin proper
quantity, or to summon the phagocytes in suffi-
cient abundance and vigour to ward off the attack.
We may do much to prevent disease by sanitation,
which aids in protecting the individual from at-
tack ; but we must not forget that the other half
of the battle is of equal importance, and hence
we must do all we can to strengthen the resist-
ing forces of the organism.

156 THE STORY OF GERM LIFE.

RECOVERY FROM GERM DISEASES.

These resisting forces are not always sufficient
to drive off the invaders. The organisms may
retain their hold in the body for a time and
eventually break down the resistance. After this
they may multiply unimpeded and take entire
possession of the body. As they become more
numerous their poisonous products increase and
begin to produce direct poisoning effects on the
body. The incubation period is over and the dis-
ease comes on. The disease now runs its course.
It becomes commonly more and more severe until
a crisis is reached. Then, unless the poisoning is
so severe that death occurs, the effects pass away
and recovery takes place.

But why should not a germ disease be always
fatal ? If the bacteria thus take possession of the
body and can grow there, why do they not always
continue to multiply until they produce sufficient
poison to destroy the life of the individual ?
Such fatal results do, of course, occur, but in by
far the larger proportion of cases recovery finally
takes place.

Plainly, the body must have another set of
resisting forces which is concerned in the final
recovery. Although weakened by the poisoning
and suffering from the disease, it does not yield
the battle, but somewhat slowly organizes a new
attack upon the invaders. For a time the multi-
plying bacteria have an unimpeded course and
grow rapidly ; but finally their further increase is
checked, their vigour impaired, and after this they
diminish in numbers and are finally expelled from
the body entirely. Of the nature of this new re-
sistance but little is yet known. We notice, in

PARASITIC BACTERIA. 15 »

the first place, that commonly after such a recov-
ery the individual has decidedly increased resist-
ance to the disease. This increased resistance
may be very lasting, and may be so considerable
as to give almost complete immunity from the
disease for many years, or for life. One attack
of scarlet fever gives the individual great immu-
nity for the future. On the other hand, the re-
sistance thus derived may be very temporary, as
in the case of diphtheria. But a certain amount
of resistance appears to be always acquired.
This power of resisting the activities of the para-
sites seems to be increased during the progress
of the disease, and, if it becomes sufficient, it
finally drives off the bacteria before they have
produced death. After this, recovery takes place.
To what this newly acquired resisting power is
due is by no means clear to bacteriologists, al-
though certain factors are already known. It
appears beyond question that in the case of cer-
tain diseases the cells of the body after a time
produce substances which serve as antidotes to
the poisons produced by the bacteria during their
growth in the body — antitoxines. In the case of
diphtheria, for instance, the germs growing in the
throat produce poisons which are absorbed by the
body and give rise 'to the symptoms of the dis-
ease; but after a time the body cells react, and
themselves produce a counter toxic body which
neutralizes the poisonous effect of the diphtheria
poison. This substance has been isolated from
the blood of animals that have recovered from an
attack of diphtheria, and has been called diphthe-
ria antitoxine. But even with this knowledge the
recovery is not fully explained. This antitoxine
neutralizes the effects of the diphtheria toxine,
11

158 THE STORY OF GERM LIFE.

and then the body develops strength to drive off
the bacteria which have obtained lodgment in the
throat. How they accomplish this latter achieve-
ment we do not know as yet. The antitoxine
developed simply neutralizes the effects of the
toxine. Some other force must be at work to get
rid of the bacteria, a force which can only exert
itself after the poisoning effect of the poison is
neutralized. In these cases, then, the recovery is
due, first, to the development in the body of the
natural antidotes to the toxic poisons, and, second,
to some other unknown force which drives off the
parasites.

These facts are certainly surprising. If one
had been asked to suggest the least likely theory
to explain recovery from disease, he could hardly
have found one more unlikely than that the body
cells developed during the disease an antidote to
the poison which the disease bacteria were pro-
ducing. Nevertheless, it is beyond question that
such antidotes are formed during the course of
the germ diseases. It has not yet been shown in
all diseases, and it would be entirely too much to
claim that this is the method of recovery in all
cases. We may say, however, in regard to bacte-
rial diseases in general, that after the bacteria en-
ter the body at some weak point they have first a
battle to fight with the resisting powers of the body,
which appear to be partly biological and partly
chemical. These resisting powers are in many
cases entirely sufficient to prevent the bacteria
from obtaining a foothold. If the invading host
overcome the resisting powers, then they begin
to multiply rapidly, and take possession of the
body or some part of it. They continue to grow
until either the individual dies or something oc-

PARASITIC BACTERIA. 159

curs to check their growth. After the individual
develops the renewed powers of checking their
growth, recovery takes place, and the individual
is then, because of these renewed powers of re-
sistance, immune from a second attack of the dis-
ease for a variable length of time.

This, in the merest outline, represents the rela-
tion of bacterial parasites to the human body.
But while this is a fair general expression of the
matter, it must be recognised that different dis-
eases differ much in their relations, and no general
outline will apply to all. They differ in their
method of attack and in the point of attack. Not
only do they produce different kinds of poisons
giving rise to different symptoms of poisoning ;
not only do they produce different results in dif-
ferent animals ; not only do the different patho-
genic species differ much in their power to de-
velop serious disease, but the different species are
very particular as to what species of animal they
attack. Some of them can live as parasites in
man alone; some can live as parasites upon man
and the mouse and a few other animals; some
can live in various animals but not in man ; some
appear to be able to live in the field mouse, but
not in the common mouse ; some live in the horse;
some in birds, but not in warm-blooded mammals ;
while others, again, can live almost equally well
in the tissues of a long list of animals. Those
which can live as parasites upon man are, of
course, especially related to human disease, and
are of particular interest to the physician, while
those which live in animals are in a similar way
of interest to veterinarians.

Thus we see that parasitic bacteria show the
widest variations. They differ in point of attack,

160 THE STORY OF GERM LIFE.

in method of attack, and in the part ot the body
which they seize upon as a nucleus for growth.
They differ in violence and in the character of the
poisons they produce, as well as in their power of
overcoming the resisting powers of the body.
They differ at different times in their powers of
producing disease. In short, they show such a
large number of different methods of action that
no general statements can be made which will ap-
ply universally, and no one method of guarding
against them or in driving them off can be hoped
to apply to any extended list of diseases.

DISEASES CAUSED BY OTHER ORGANISMS THAN
BACTERIA.

Although the purpose of this work is to deal
primarily with the bacterial world, it would hardly
be fitting to leave the subject without some refer-
ence to diseases caused by organisms which do
not belong to the group of bacteria. While most
of the so-called germ diseases are caused by the
bacteria which we have been studying in the
previous chapters, there are some whose inciting
cause is to be found among organisms belonging
to other groups. Some of these are plants of a
higher organization than bacteria, but others are
undoubtedly microscopic animals. Their life
habits are somewhat different from those of
bacteria, and hence the course of the diseases is
commonly different. Of the diseases thus pro-
duced by microscopic animals or by higher plants,
one or two are of importance enough to deserve
special mention here.

Malaria. — The most important of these dis-
eases is malaria in its various forms, and known

PARASITIC BACTERIA.

161

under various names — chills and fever, autumnal
fever, etc. This disease, so common almost
everywhere, has been studied by physicians and
scientists for a long time, and many have been
the causes assigned to it. At one time it was
thought to be the result of the growth of a bacte-
rium, and a distinct bacillus was described as pro-
ducing it. It has finally been shown, however,
to be caused by a microscopic organism belong-
ing to the group of unicellular animals, and some-

FlG. 34.— Malarial organism : Figs, a to g show the growth of
the parasite within the blood corpuscle ; o is the organism in
all cases ; s, the spores. Fig. i is the so-called cresentic body
which develops through Fig. 2, into the flagellate form, shown
at 3. The significance of i, 2, and 3 are not known.

what closely related to the well-known amoeba.
This organism is shown in Fig. 34. The whole
history of the malarial organism is not yet known.
The following statements comprise the most im-
portant facts known in regard to it, and its rela-
tion to the disease in man.

Undoubtedly the malarial germ has some
home outside the human body, but it is not yet
very definitely known what this external home is;
nor do we know from what source the human para-

162 THE STORY OF GERM LIFE.

site is derived. It appears probable that water
serves in some cases as its means of transference
to man, and air in other cases. From some ex-
ternal source it gains access to man and finds
its way into the blood. Here it attacks the
red blood-corpuscles, each malarial organism
making its way into a single one (Fig. 34 a).
Here it now grows, increasing in size at the
expense of the substance of the corpuscle
(Fig. 34 a-f). As it becomes larger it becomes
granular, and soon shows a tendency to separate
into a number of irregular masses (Fig. 34 /).
Finally it breaks up into many minute bodies
called spores (Fig. 34^). These bodies break out
of the corpuscle and for a time live a free life in
the blood (Fig. 34 ti). After a time they make
their way into other red blood-corpuscles, develop
into new malarial amoeboid parasites, and repeat
the growth and sporulation. This process can ap-
parently be repeated many times without check.

These organisms are thus to be regarded as
parasites of the red corpuscles. It is, of course,
easy to believe that an extensive parasitism and
destruction of the corpuscles would be disastrous
to the health of the individual, and the severity
of the disease will depend upon the extent of the
parasitism. Corresponding to this life history of
the organism, the disease malaria is commonly
characterized by a decided intermittency, periods
of chill and fever alternating with periods of in-
termission in which these symptoms are abated.
The paroxysms of the disease, characterized by
the chill, occur at the time that the spores are
escaping from the blood-corpuscles and floating
in the blood. After they have again found their
way into a blood-corpuscle the fever diminishes,

PARASITIC BACTERIA. 163

and during their growth in the corpuscle until
the next sporulation the individual has a rest
from the more severe symptoms.

There appears to be more than one variety of
the malarial organism, the different types differ-
ing in the length of time it takes for their growth
and sporulation. There is one variety, the most
common one, which requires two days for its
growth, thus giving rise to the paroxysm of the
disease about once in forty-eight hours ; another
variety appears to require three days for its
growth ; while still another variety appears to be
decidedly irregular in its period of growth and
sporulation. These facts readily explain some of
the variations in the disease. Certain other ir-
regularities appear to be due to a different cause.
More than one brood of parasites may be in the
blood of the individual at the same time, one
producing sporulation at one time and another at
a different time. Such a simultaneous growth of
two independent broods may plainly produce al-
most any kind of modification in the regularity of
the disease.

The malarial organism appears to be very
sensitive to quinine, a very small quantity being
sufficient to kill it. Upon this point depends the
value of quinine as a medicine. If the drug be
present in the blood at the time when the spores
are set free from the blood-corpuscle, they are
rapidly killed by it before they have a chance to
enter another corpuscle. During their growth in
the corpuscle they are far less sensitive to qui-
nine than when they exist in the free condition as
spores, and at this time the drug has little effect.

The malarial organism is an animal, and can
not be cultivated in the laboratory by any arti-

1 64 THE STORY OF GERM LIFE.

ficial method yet devised. Its whole history is
therefore not known. It doubtless has some
home outside the blood of animals, and very
likely it may pass through other stages of a meta-
morphosis in the bodies of other animals. Most
parasitic animals have two or more hosts upon
which they live, alternating from one to the other,
and that such is the case with the malarial para-
site is at least probable. But as yet bacteriolo-
gists have been unable to discover anything very
definite in regard to the matter. Until we can
learn something in regard to its life outside the
blood of man we can do little in the way of devis-
ing methods to avoid it.

Malaria differs from most germ diseases in the
fact that the organisms which produce it are not
eliminated from the body in any way. In most
germ diseases the germs are discharged from the
patient by secretions or excretions of some kind,
and from these excretions may readily find their
way into other individuals. The malarial organ-
ism is not discharged from the body in any way,
and hence is not contagious. If the parasite does
pass part of its history in some other animal
than man, there must be some means by which it
passes from man to its other host. It has been
suggested that some of the insects which feed
upon human blood may serve as the second host
and become inoculated when feeding upon such
blood. This has been demonstrated with start-
ling success in regard to the mosquito (Anopheles),
some investigators going so far as to say that this
is the only way in which the disease can be com-
municated.

Several other microscopic animals occur as
parasites upon man, and some of them are so
definitely associated with certain diseases as to

COMBATING PARASITIC BACTERIA. 165

lead to the belief that they are the cause of these
diseases. The only one of very common occur-
rence is a species known as Amoeba coli, which is
found in cases of dysentery. In a certain type
of dysentery this organism is so universally found
that there is little doubt that it is in some very
intimate way associated with the cause of the dis-
ease. Definite proof of the matter is, however,
as yet wanting.

On the side of plants, we find that several
plants of a higher organization than bacteria may
become parasitic upon the body of man and pro-
duce various types of disease. These plants be-
long mostly to the same group as the moulds,
and they are especially apt to attack the skin.
They grow in the skin, particularly under the hair,
and may send their threadlike branches into some
of the subdermal tissues. This produces irrita-
tion and inflammation of the skin, resulting in
trouble, and making sores difficult to heal. So
long as the plant continues to grow, the sores, of
course, can not be healed, and when the organ-
isms get into the skin under the hair it is fre-
quently difficult to destroy them. Among the
diseases thus caused are ringworm, thrush, alopecia,
etc.

CHAPTER VI.

METHODS OF COMBATING PARASITIC BACTERIA.

THE chief advantage of knowing the cause of
disease is that it gives us a vantage ground from
which we may hope to find means of avoiding its
evils. The study of medicine in the past history

1 66 THE STORY OF GERM LIFE.

of the world has been almost purely empirical,
with a very little of scientific basis. Great hopes
are now entertained that these new facts will place
this matter upon a more strictly scientific foun-
dation. Certainly in the past twenty-five years,
since bacteriology has been studied, more has
been done to solve problems connected with dis-
ease than ever before. This new knowledge has
been particularly directed toward means of avoid-
ing disease. Bacteriology has thus far borne
fruit largely in the line of preventive medicine,
although to a certain extent also along the line
of curative medicine. This chapter will be de-
voted to considering how the study of bacteriol-
ogy has contributed directly and indirectly to
our power of combating disease.

PREVENTIVE MEDICINE.

In the study of medicine in the past centuries
the only aim has been to discover methods of
curing disease ; at the present time a large and
increasing amount of study is devoted to the
methods of preventing disease. Preventive medi-
cine is a development of the last few years, and
is based almost wholly upon our knowledge of
bacteria. This subject is yearly becoming of
more importance. Forewarned is forearmed, and
it has been found that to know the cause of a
disease is a long step toward avoiding it. As
some of our contagious and epidemic diseases
have been studied in the light of bacteriological
knowledge, it has been found possible to deter-
mine not only their cause, but also how infection
is brought about, and consequently how conta-
gion may be avoided. Some of the results which

COMBATING PARASITIC BACTERIA. 167

have grown up so slowly as to be hardly appre-
ciated are really great triumphs. For instance,
the study of bacteriology first led us to suspect,
and then demonstrated, that tuberculosis is a
contagious disease, and from the time that this
was thus proved there has been a slow, but, it is
hoped, a sure decline in this disease. Bacterio-
logical study has shown that the source of chol-
era infection in cases of raging epidemics is, in
large part at least, our drinking water ; and since
this has been known, although cholera has twice
invaded Europe, and has been widely distributed,
it has not obtained any strong foothold or given
rise to any serious epidemic except in a few cases
where its ravages can be traced to recognised
carelessness. It is very significant to compare
the history of the cholera epidemics of the past
few years with those of earlier dates. In the epi-
demics of earlier years the cholera swept ruth-
lessly through communities without check. In
the last few years, although it has repeatedly
knocked at the doors of many European cities, it
has been commonly confined to isolated cases,
except in a few instances where these facts con-
cerning the relation to drinking water were ig-
nored.

The study of preventive medicine is yet in its
infancy, but it has already accomplished much.
It has developed modern systems of sanitation,
has guided us in the building of hospitals, given
rules for the management of the sick-room which
largely prevent contagion from patient to nurse;
it has told us what diseases are contagious, and in
what way ; it has told us what sources of conta-
gion should be suspected and guarded against,
and has thus done very much to prevent the

j68 THE STORY OF GERM LIFE.

spread of disease. Its value is seen in the fact that
there has been a constant decrease in the death
rate since modern ideas of sanitation began to
have any influence, and in the fact that our
general epidemics are less severe than in former
years, as well as in the fact that more people
escape the diseases which were in former times
almost universal.

The study of preventive medicine takes into
view several factors, all connected with the
method and means of contagion. They are the
following :

The Source of Infectious Material. — It has been
learned that for most diseases the infectious ma-
terial comes from individuals suffering with the
disease, and that except in a few cases, like ma-
laria, we must always look to individuals suffering
from disease for all sources of contagion. It is
found that pathogenic bacteria are in all these
cases eliminated from the patient in some way,
either from the alimentary canal or from skin se-
cretions or otherwise, and that any nurse with
common sense can have no difficulty in deter-
mining in what way the infectious material is
eliminated from her patients. When this fact is
known and taken into consideration it is a com-
paratively easy matter to devise valuable precau-
tions against distribution of such material. It is
thus of no small importance to remember that the
simple presence of bacteria in food or drink is of
no significance unless these bacteria have come
from some source of disease infection.

The Method of Distribution. — The bacteria must
next get from the original source of the disease to
the new susceptible individual. Bacteria have no
independent powers of distribution unless they

COMBATING PARASITIC BACTERIA. 169

be immersed in liquids, and therefore their pas-
sage from individual to individual must be a pas-
sive one. They are readily transferred, however,
by a number of different means, and the study of
these means is aiding much in checking contagion
Study along this line has shown that the means
by which bacteria are carried are several. First
we may notice food as a distributor. Food may
become contaminated by infectious material in
many ways; for example, by contact with sewage,
or with polluted water, or even with eating uten-
sils which have been used by patients. Water is
also likely to be contaminated with infectious
material, and is a fertile source for distributing
typhoid and cholera. Milk may become contam-
inated in a variety of ways, and be a source of dis-
tributing the bacteria which produce typhoid
fever, tuberculosis, diphtheria, scarlet fever, and
a few other less common diseases. Again, in-
fected clothing, bedding, or eating utensils may
be taken from a patient and be used by another
individual without proper cleansing. Direct con-
tact, or contact with infected animals, furnishes
another method. Insects sometimes carry the
bacteria from person to person, and in some dis-
eases (tuberculosis, and perhaps scarlet fever and
smallpox) we must look to the air as a distribu-
tor of the infectious material. Knowledge of
these facts is helping to account for multitudes
of mysterious cases of infection, especially when
we combine them with the known sources of con-
tagious matter.

Means of Invasion. — Bacteriology has shown us
that different species of parasitic bacteria have
different means of entering the body, and that
each must enter the proper place in order to get

170 THE STORY OF GERM LIFE.

a foothold. After we learn that typhoid infec-
tious material must enter the mouth in order to
produce the disease; that tuberculosis may find
entrance through the nose in breathing, while
types of blood poisoning enter only through
wounds or broken skin, we learn at once funda-
mental facts as to the proper methods of meeting
these dangers. We learn that with some diseases
care exercised to prevent the swallowing of infec-
tious material is sufficient to prevent contagion,
while with others this is entirely insufficient.
When all these facts are understood it is almost
always perfectly possible to avoid contagion ; and
as these facts become more and more widely known
direct contagion is sure to become less frequent.

Above all, it is telling us what becomes of the
pathogenic bacteria after being eliminated from
the body of the patient; how they may exist for
a long time still active ; how they may lurk in
filth or water dormant but alive, or how they may
even multiply there. Preventive medicine is tell-
ing us how to destroy those thus lying in wait for
a chance of infection, by discovering disinfect-
ants and telling us especially where and when to
use them. It has already taught us how to crush
out certain forms of epidemics by the proper
means of destroying bacteria, and is lessening
the dangers from contagious diseases. In short,
the study of bacteriology has brought us into a
condition where we are no longer helpless in the
presence of a raging epidemic. We no longer sit
in helpless dismay, as did our ancestors, when an
epidemic enters a community, but, knowing their
causes and sources, set about at once to remove
them. As a result, severe epidemics are becoming
comparatively short-lived.

COMBATING PARASITIC BACTERIA. 171

BACTERIA IN SURGERY.

In no line of preventive medicine has bacteri-
ology been of so much value and so striking in
its results as in surgery. Ever since surgery has
been practised surgeons have had two difficulties
to contend with. The first has been the shock
resulting from the operation. This is dependent
upon the extent of the operation, and must always
be a part of a surgical operation. The second
has been secondary effects following the operation.
After the operation, even though it was success-
ful, there were almost sure to arise secondary
complications known as surgical fever, inflamma-
tion, blood poisoning, gangrene, etc., which fre-
quently resulted fatally. These secondary com-
plications were commonly much more serious
than the shock of the operation, and it used to be
the common occurrence for the patient to recover
entirely from the shock, but yield to the fevers
which followed. They appeared to be entirely
unavoidable, and were indeed regarded as neces-
sary parts of the healing of the wound. Too fre-
quently it appeared that the greater the care taken
with the patient the more likely he was to suffer
from some of these troubles. The soldier who
was treated on the battlefield and nursed in an
improvised field hospital would frequently re-
cover, while the soldier who had the fortune to
be taken into the regular hospital, where greater
care was possible, succumbed to hospital gangrene.
All these facts were clearly recognised, but the
surgeon, through ignorance of their cause, was
helpless in the presence of these inflammatory
troubles, and felt it always necessary to take them
into consideration.

172 THE STORY OF GERM LIFE.

The demonstration that putrefaction and de-
cay were caused by bacteria, and the early proof
that the silkworm disease was produced by a
micro-organism, led to the suggestion that the in-
flammatory diseases accompanying wounds were
similarly caused. There are many striking sim-
ilarities between these troubles and putrefaction,
and the suggestion was an obvious one. At first,
however, and for quite a number of years, it was
impossible to demonstrate the theory by finding
the distinct species of micro-organisms which pro-
duced the troubles. We have already seen that
there are several different species of bacteria which
are associated with this general class of diseases,
but that no specific one has any particular relation
to a definite type of inflammation. This fact made
discoveries in this connection a slow matter from
the microscopical standpoint. But long before
this demonstration was finally reached the theory
had received practical application in the form of
what has developed into antiseptic or aseptic
surgery.

Antiseptic surgery is based simply upon the
attempt to prevent the entrance of bacteria into
the surgical wound. It is assumed that if these
organisms are kept from the wound the healing
will take place without the secondary fevers and
inflammations which occur if they do get a chance
to grow in the wound. The theory met with de-
cided opposition at first, but accumulating facts
demonstrated its value, and to-day its methods
have been adopted everywhere in the civilized
world. As the evidence has been accumulating,
surgeons have learned many important facts, fore-
most among which is a knowledge of the common
sources from which the infection of wounds oc-

COMBATING PARASITIC BACTERIA. 173

curs. At first it was thought that the air was the
great source of infection, but the air bacteria have
been found to be usually harmless. It has ap-
peared that the more common sources are the
surgeon's instruments, or his hands, or the cloth-
ing or sponges which are allowed to come in con-
tact with the wounds. It has also appeared that
the bacteria which produce this class of troubles
are common species, existing everywhere and uni-
versally present around the body, clinging to the
clothing or skin, and always on hand to enter the
wound if occasion offers. They are always pres-
ent, but commonly harmless. They are not for-
eign invaders like the more violent pathogenic
species, such as those of Asiatic cholera, but may
be compared to domestic enemies at hand. It is
these ever-present bacteria which the surgeon
must guard against. The methods by which he
does this need not detain us here. They consist
essentially in bacteriological cleanliness. The
operation is performed with sterilized instruments
under most exacting conditions of cleanliness.

The result has been a complete revolution in
surgery. As the methods have become better
understood and more thoroughly adopted, the in-
stances of secondary troubles following surgical
wounds have become less and less frequent until
they have practically disappeared in all simple
cases. To-day the surgeon recognises that when
inflammatory troubles of this sort follow simple
surgical wounds it is a testimony to his careless-
ness. The skilful surgeon has learned that with
the precautions which he is able to take to-day
he has to fear only the direct effect of the shock
of the wound and its subsequent direct influence;
but secondary surgical fevers, blood poisoning,
12

174 THE STORY OF GERM LIFE.

and surgical gangrene need not be taken into con-
sideration at all. Indeed, the modern surgeon
hardly knows what surgical gangrene is, and bac-
teriologists have had practically no chance to
study it. Secondary infections have largely dis-
appeared, and the surgeon is concerned simply
with the effect of the wound itself, and the power
of the body to withstand the shock and subse-
quently heal the wound.

With these secondary troubles no longer to
disturb him, the surgeon has become more and
more bold. Operations formerly not dreamed of
are now performed without hesitation. In former
years an operation which opened the abdominal
cavity was not thought possible, or at least it was
so nearly certain to result fatally that it was re-
sorted to only on the last extremity; while to-day
such operations are hardly regarded as serious.
Even brain surgery is becoming more and more
common. Possibly our surgeons are passing too
far to the other extreme, and, feeling their power of
performing so many operations without inconven-
ience or danger, they are using the knife in cases
where it would be better to leave Nature to her-
self for her own healing. But, be this as it may,
it is impossible to estimate the amount of suffer-
ing prevented and the number of lives saved by
the mastery of the secondary inflammatory trou-
bles which used to follow surgical wounds.

Preventive medicine, then, has for its object
the prevention rather than the cure of disease.
By showing the causes of disease and telling us
where and how they are contracted, it is telling
us how they may to a large extent be avoided.
Unlike practical medicine, this subject is one
which has a direct relation to the general public.

COMBATING PARASITIC BACTERIA. 175

While it may be best that the knowledge of cura-
tive methods be confined largely to the medical
profession, it is eminently desirable that a knowl-
edge of all the facts bearing upon preventive
medicine should be distributed as widely as pos-
sible. One person can not satisfactorily apply
his knowledge of preventive medicine if his
neighbour is ignorant of or careless of the facts.
We can not hope to achieve the possibilities lying
along this line until there is a very wide distribu-
tion of knowledge. Every epidemic that sweeps
through our communities is a testimony to the
crying need of education in regard to such sim-
ple facts as the source of infectious material, the
methods of its distribution, and the means of ren-
dering it harmless.

PREVENTION IN INOCULATION.

It has long been recognised that in most cases
recovery from one attack of a contagious disease
renders an individual more or less immune against
a second attack. It is unusual for an individual
to have the same contagious disease twice. This
belief is certainly based upon fact, although the
immunity thus acquired is subject to wide varia-
tions. There are some diseases in which there is
little reason for thinking that any immunity is ac-
quired, as in the case of tuberculosis, while there
are others in which the immunity is very great
and very lasting, as in the case of scarlet fever.
Moreover, the immunity differs with individuals.
While some persons appear to acquire a lasting
immunity by recovery from a single attack, others
will yield to a second attack very readily. But
in spite of this the fact of such acquired immu-

176 THE STORY OF GERM LIFE.

nity is beyond question. Apparently all infec-
tious diseases from which a real recovery takes
place are followed by a certain amount of pro-
tection from a second attack ; but with some dis-
eases the immunity is very fleeting, while with
others it is more lasting. Diseases which pro-
duce a general infection of the whole system are,
as a rule, more likely to give rise to a lasting
immunity than those which affect only small
parts. Tuberculosis, which, as already noticed,
is commonly quite localized in the body, has lit-
tle power of conveying immunity, while a disease
like scarlet fever, which affects the whole system,
conveys a more lasting protection.

Such immunity has long been known, and in
the earlier years was sometimes voluntarily ac-
quired ; even to-day we find some individuals
making use of the principle. It appears that a
mild attack of such diseases produces immunity
equally well with a severe attack, and acting
upon this fact mothers have not infrequently
intentionally exposed their children to certain
diseases at seasons when they are mild, in or-
der to have the disease " over with " and their
children protected in the future. Even the more
severe diseases have at times been thus vol-
untarily acquired. In China it has sometimes
been the custom thus to acquire smallpox. Such
methods are decidedly heroic, and of course to be
heartily condemned. But the principle that a
mild type of the disease conveys protection has
been made use of in a more logical and defensible
way.

The first instance of this principle was in vac-
cination against smallpox, now practised for more
than a century. Cowpox is doubtless closely re-

COMBATING PARASITIC BACTERIA. 177

lated to smallpox, and an attack of the former
conveys a certain amount of protection against
the latter. It was easy, therefore, to inoculate
man with some of the infectious material from
cowpox, and thus give him some protection
against the more serious smallpox. This was a
purely empirical discovery, and vaccination was
practised long before the principle underlying it
was understood, and long before the germ nature
of disease was recognised. The principle was re-
vived again, however, by Pasteur, and this time
with a logical thought as to its value. While
working upon anthrax among animals, he learned
that here, as in other diseases, recovery, when it
occurred, conveyed immunity. This led him to
ask if it were not possible to devise a method of
giving to animals a mild form of the disease and
thus protect them from the more severe type.
The problem of giving a mild type of this extraor-
dinarily severe disease was not an easy one. It
could not be done, of course, by inoculating the
animals with a small number of the bacteria, for
their power of multiplication would soon make
them indefinitely numerous. It was necessary
in some way to diminish their violence. Pas-
teur succeeded in doing this by causing them to
grow in culture fluids for a time at a high tem-
perature. This treatment diminished their vio-
lence so much that they could be inoculated into
cattle, where they produced only the mildest type
of indisposition, from which the animals speedily
recovered. But even this mild type of the dis-
ease was triumphantly demonstrated to protect
the animals from the most severe form of an-
thrax. The discovery was naturally hailed as a
most remarkable one, and one which promised

178 THE STORY OF GERM LIFE.

great things in the future. If it was thus possi-
ble, by direct laboratory methods, to find a
means of inoculating against a serious disease
like anthrax, why could not the same principle be
.applied to human diseases ? The enthusiasts be-
gan at once to look forward to a time when all
diseases should be thus conquered.

But the principle has not borne the fruit at
first expected. There is little doubt that it might
be applied to quite a number of human diseases
if a serious attempt should be made. But several
objections arise against its wide application. In the
first place, the inoculation thus necessary is really
a serious matter. Even vaccination, as is well
known, sometimes, through faulty methods, re-
sults fatally, and it is a very serious thing to
•experiment upon human beings with anything so
powerful for ill as pathogenic bacteria. The seri-
ousness of the disease smallpox, its extraordinary
contagiousness, and the comparatively mild results
of vaccination, have made us willing to undergo
vaccination at times of epidemics to avoid the
somewhat great probability of taking the disease.
But mankind is unwilling to undergo such an op-
eration, even though mild, for the purpose of
avoiding other less severe diseases, or diseases
which are less likely to be taken. We are un-
willing to be inoculated against mild diseases,
•or against the more severe ones which are
uncommon. For instance, a method has been
devised for rendering animals immune against
lockjaw, which would probably apply equally
well to man. But mankind in general will never
adopt it, since the danger from lockjaw is so
small. Inoculation must then be reserved for
•diseases which are so severe and so common, or

COMBATING PARASITIC BACTERIA. 179,

which occur in periodical epidemics of so great
severity, as to make people in general willing to
submit to inoculation as a protection. A further
objection arises from the fact that the immunity-
acquired is not necessarily lasting. The cattle
inoculated against anthrax retain their protective-
powers for only a few months. How long similar
immunity might be retained in other cases we can
not say, but plainly this fact would effectually
prevent this method of protecting mankind from
being used except in special cases. It is out of
the question to think of constant and repeated
inoculations against various diseases.

As a result, the principle of inoculation as an
aid in preventive medicine has not proved of very
much value. The only other human disease in
which it has been attempted seriously is Asiatic
cholera. This disease in times of epidemics is so-
severe and the chance of infection is so great as
to justify such inoculation. Several bacteriolo-
gists have in the last few years been trying to
discover a harmless method of inoculating against
this disease. Apparently they have succeeded,,
for experiments in India, the home of the chol-
era, have been as successful as could be antici-
pated. Bacteriological science has now in its
possession a means of inoculation against chol-
era which is perhaps as efficacious as vaccination
is against smallpox. Whether it will ever be used
to any extent is doubtful, since, as already pointed
out, we are in a position to avoid cholera epidemics
by other means. If we can protect our commu-
nities by guarding the water supply, it is not
likely that the method of inoculation will ever be
widely used.

Another instance of the application of pre-

180 THE STORY OF GERM LIFE.

ventive inoculation has been made, but one based
upon a different principle. Hydrophobia is cer-
tainly one of the most horrible of diseases, al-
though comparatively rare. Its rarity would ef-
fectually prevent mankind from submitting to
a general inoculation against it, but its severity
would make one who had been exposed to it
by the bite of a rabid animal ready to submit
to almost any treatment that promised to ward
off the disease. In the attempt to discover a
means of inoculating against this disease it was
necessary, therefore, to find a method that could
be applied after the time of exposure — i. e., after
the individual had been bitten by the rabid ani-
mal. Fortunately, the disease has a long period
of incubation, and one that has proved long
enough for the purpose. A method of inocula-
tion against this disease has been devised by Pas-
teur, which can be applied after the individual
has been bitten by the rabid animal. Apparently,
however, this preventive inoculation is dependent
upon a different principle from vaccination or in-
oculation against anthrax. It does not appear to
give rise to a mild form of the disease, thus pro-
tecting the individual, but rather to an acquired
tolerance of the chemical poisons produced by
the disease. It is a well-known physiological fact
that the body can become accustomed to tolerate
poisons if inured to them by successively larger
and larger doses. It is by this power, apparently,
that the inoculation against hydrophobia produces
its effect. Material containing the hydrophobia
poison (taken from the spinal cord of a rabbit
dead with the disease) is injected into the indi-
vidual after he has been bitten by a rabid animal.
The poisonous material in the first injection is

COMBATING PARASITIC BACTERIA. 181

very weak, but is followed later by a more powerful
inoculation. The result is that after a short time
the individual has acquired the power of resisting
the hydrophobia poisons. Before the incubation
period of the original infectious matter from the
bite of the rabid animal has passed, the inoculated
individual has so thoroughly acquired a tolerance
of the poison that he successfully resists the attack
of the infection. This method of inoculation thus
neutralizes the effects of the disease by anticipat-
ing them.

The method of treatment of hydrophobia met
with extraordinarily violent opposition. For sev-
eral years it was regarded as a mistake. But the
constantly accumulating statistics from the Pas-
teur Institute have been so overwhelmingly on
one side as to quiet opposition and bring about a
general conviction that the method is a success.

The method of preventive inoculation has not
been extensively applied to human diseases in ad-
dition to those mentioned. In a few cases a similar
method has been used to guard against diphtheria.
Among animals, experiment has shown that such
methods can quite easily be obtained, and doubt-
less the same would be true of mankind if it was
thought practical or feasible to apply them. But,
for reasons mentioned, this feature of preventive
medicine will always remain rather unimportant,
and will be confined to a few of the more violent
diseases.

It may be well to raise the question as to why
a single attack with recovery conveys immunity.
This question is really a part of the one already
discussed as to the method by which the body
cures disease. We have seen that this is in part
due to the development of chemical substances

1 82 THE STORY OF GERM LIFE.

which either neutralize the poisons or act as
germicide upon the bacteria, or both, and perhaps
due in part to an active destruction of bacteria
by cellular activity (phagocytosis). There is little
reason to doubt that it is the same set of activi-
ties which renders the animal immune. The forces
which drive off the invading bacteria in one case
are still present to prevent a second attack of the
same species of bacterium. The length of time
during which these forces are active and sufficient
to cope with any new invaders determines the
length of time during which the immunity lasts.
Until, therefore, we can answer with more exact-
ness just how cure is brought about in case of
disease, we shall be unable to explain the method
•of immunity.

LIMITS OF PREVENTIVE MEDICINE.

With all the advance in preventive medicine
we can not hope to avoid disease entirely. We
are discovering that the sources of disease are on
all sides of us, and so omnipresent that to avoid
them completely is impossible. If we were to
apply to our lives all the safeguards which bac-
teriology has taught us should be applied in order
to avoid the different diseases, we would surround
ourselves with conditions which would make life
intolerable. It would be oppressive enough for
us to eat no food except when it is hot, to drink
no water except when boiled, and to drink no
milk except after sterilization ; but these would
not satisfy the necessary conditions for avoiding
disease. To meet all dangers, we should handle
nothing which has not been sterilized, or should
•follow the handling by immediately sterilizing the

COMBATING PARASITIC BACTERIA. 183;

hands; we should wear only disinfected clothes;
we should never put our fingers in our mouths
or touch, our food with them ; we should cease
to ride in public conveyances, and, indeed,
should cease to breathe common air. Absolute
prevention of the chance of infection is impos-
sible. The most that preventive medicine can
hope for is to point out the most common and
prolific sources of infection, and thus enable
civilized man to avoid some of his most common
troubles. It becomes a question, therefore, where
we will best draw the line in the employment of
safeguards. Shall we drink none except sterilized
milk, and no water unless boiled ? or shall we put
these occasional sources of danger in the same
category with bicycle and railroad accidents, dan-
gers which can be avoided by not using the bicycle
or riding on the rail, but in regard to which the
remedy is too oppressive for application ?

Indeed, when viewed in a broad philosophical
light it may not be the best course for mankind
to shun all dangers. Strength in the organism
comes from the use rather than the disuse of our
powers. It is certain that the general health and
vigour of mankind is to be developed by meeting
rather than by shunning dangers. Resistance to
disease means bodily vigour, and this is to be de-
veloped in mankind by the application of the
principle of natural selection. In accordance
with this principle, disease will gradually remove
the individuals of weak resisting powers, leaving
those of greater vigour. Parasitic bacteria are
thus a means of preventing the continued life of
the weaker members of the community, and so
tend to strengthen mankind. By preventive med-
icine many a weak individual who would other-

1 84 THE STORY OF GERM LIFE.

wise succumb earlier in the struggle is enabled to
live a few years longer. Whatever be our humani-
tarian feeling for the individual, we can not fail
to admit that this survival of the weak is of no
benefit to the race so far as the development of
physical nature is concerned. Indeed, if we were
to take into consideration simply the physical
nature of man we should be obliged to recom-
mend a system such as the ancient Spartans de-
veloped, of exposing to death all weakly individ-
uals, that only the strong might live to become
the fathers of future generations. In this light,
of course, parasitic diseases would be an assist-
ance rather than a detriment to the human race.
Of course such principles will never again be
dominant among men, and our conscience tells us
to do all we can to help the weak. We shall
doubtless do all possible to develop preventive
medicine in order to guard the weak against para-
sitic organisms. But it is at all events well for us
to remember that we can never hope to develop the
strength of the human race by shunning evil, but
rather by combating it, and the power of the
human race to resist the invasions of these or-
ganisms will never be developed by the line of
action which guards us from attack. Here, as in
other directions, the principles of modern humanity
have, together with their undoubted favourable
influence upon mankind, certain tendencies toward
weakness. While we shall still do our utmost to
develop preventive medicine in a proper way, it
may be well for us to remember these facts when
we come to the practical question of determining
where to draw the limits of the application of
methods for preventing infectious diseases.

COMBATING PARASITIC BACTERIA. 185

CURATIVE MEDICINE.

Bacteriology has hitherto contributed less to
curative than to preventive medicine. Neverthe-
less, its contributions to curative medicine have
not been unimportant, and there is promise of
much more in the future. It is, of course, unsafe
to make predictions for the future, but the accom-
plishments of the last few years give much hope
as to further results.

It was at first thought that a knowledge of
the specific bacteria which cause a disease would
give a ready means of finding specific drugs for
the cure of such disease. If a definite species of
bacterium causes a disease and we can cultivate
the organism in the laboratory, it is easy to find
some drugs which will be fatal to its growth, and
these same drugs, it would seem, should be valu-
able as medicines in these diseases. This hope
has, however, proved largely illusive. It is very
easy to find some drug which proves fatal to the
specific germs while growing in the culture media
of the laboratory, but commonly these are of little
or no use when applied as medicines. In the first
place, such substances are usually very deadly poi-
sons. Corrosive sublimate is a substance which
destroys all pathogenic germs with great rapidity,
but it is a deadly poison, and can not be used as a
drug in sufficient quantity to destroy the parasitic
bacteria in the body without at the same time
producing poisonous effects on the body itself.
It is evident that for any drug to be of value in
thus destroying bacteria it must have some spe-

1 86 THE STORY OF GERM LIFE.

cially strong action upon the bacteria. Its germi-
cide action on the bacteria should be so strong
that a dose which would be fatal or very injurious
to them would be too small to have a deleterious
influence on the body of the individual. It has
not proved an easy task to discover drugs which
will have any value as germicides when used in
quantities so small as to produce no injurious
effect on the body.

A second difficulty is in getting the drug to
produce its effect at the right point. A few
diseases, as we have noticed, are produced by
bacteria which distribute themselves almost
indiscriminately over the body ; but the majority
are somewhat definitely localized in special
points. Tuberculosis may attack a single gland
or a single lobe of the lung. Typhoid germ is
localized in the intestines, liver, spleen, etc.
Even if it were possible to find some drug which
would have a very specific effect upon the tuber-
culosis bacillus, it is plain that it would be a very
questionable method of procedure to introduce
this into the whole system simply that it might
have an effect upon a very small isolated gland.
Sometimes such a bacterial affection may be local-
ized in places where it can be specially treated, as
in the case of an attack on a dermal gland, and in
these cases some of the germicides have proved to
be of much value. Indeed, the use of various dis-
infectants connected with abscesses and super-
ficial infections has proved of much value. To
this extent, in disinfecting wounds and as a local
application, the development of our knowledge
of disinfectants has given no little aid to curative
medicine.

Very little success, however, has resulted in the

COMBATING PARASITIC BACTERIA. 187

attempt to find specific drugs for specific diseases,
and it is at least doubtful whether many such will
ever be found. The nearest approach to it is qui-
nine as a specific poison for malarial troubles.
Malarious diseases are not, however, produced by
bacteria but by a microscopic organism of a very
different nature, thought to be an animal rather
than a plant. Besides this there has been little
or no success in discovering specifics in the form
of drugs which can be given as medicines or inocu-
lated with the hope of destroying special kinds of
pathogenic bacteria without injury to the body.
While it is unwise to make predictions as to future
discoveries, there seems at present little hope for
a development of curative medicine along these
lines.

VIS MEDICATRIX NATURAE.

The study of bacterial diseases as they pro-
gress in the body has emphasized above all things
the fact that diseases are eventually cured by a
natural rather than by an artificial process. If a
pathogenic bacterium succeeds in passing the
outer safeguards and entering the body, and if it
then succeeds in overcoming the forces of resist-
ance which we have already noticed, it will begin
to multiply and produce mischief. This multi-
plication now goes on for a time unchecked, and
there is little reason to expect that we can ever
do much toward checking it by means of drugs.
But after a little, conditions arise which are hos-
tile to the further growth of the parasite. These
hostile conditions are produced perhaps in part
by the secretions from the bacteria, for bacteria
are unable to flourish in a medium containing
much of their own secretions. The secretions

1 88 THE STORY OF GERM LIFE.

which they produce are poisons to them as well
as to the individual in which they grow, and
after these have become quite abundant the fur-
ther growth of the bacterium is checked and
finally stopped. Partly, also, must we conclude
that these hostile conditions are produced by
active vital powers in the body of the individual
attacked. The individual, as we have seen, in
some cases develops a quantity of some substance
which neutralizes the bacterial poisons and thus
prevents their having their maximum effect. Thus
relieved from the direct effects of the poisons, the
resisting powers are recuperated and once more
begin to produce a direct destruction of the bac-
teria. Possibly the bacteria, being now weakened
by the presence of their own products of growth,
more readily yield to the resisting forces of the
cell life of the body. Possibly the resisting forces
are decidedly increased by the reactive effect of
the bacteria and their poisons. But, at all events,
in cases where recovery from parasitic diseases
occurs, the revived powers of resistance finally
overcome the bacteria, destroy them or drive
them off, and the body recovers.

All this is, of course, a natural process. The
recovery from a disease produced by the invasion
of parasitic bacteria depends upon whether the
body can resist the bacterial poisons long enough
for the recuperation of its resisting powers. If
these poisons are very violent and produced rap-
idly, death will probably occur before the resisting
powers are strong enough to drive off the bacteria.
In the case of some diseases the poisons are so
violent that this practically always occurs, recov-
ery being very exceptional. The poison produced
by the tetanus bacillus is of this nature, and recov-

COMBATING PARASITIC BACTERIA. 189

ery from lockjaw is of the rarest occurrence. But
in many other diseases the body is able to with-
stand the poison, and later to recover its resisting
powers sufficiently to drive off the invaders. In
all cases, however, the process is a natural one and
dependent upon the vital activity of the body. It
is based at the foundation, doubtless, upon the
powers of the body cells, either the phagocytes
or other active cells. The body has, in short, its
own forces for repelling invasions, and upon these
forces must we depend for the power to produce
recovery.

It is evident that all these facts give us very
little encouragement that we shall ever be able
to cure diseases directly by means of drugs to
destroy bacteria, but, on the contrary, that we
must ever depend upon the resisting powers of
the body. They teach us, moreover, along what
line we must look for the future development
of curative medicine. It is evident that scien-
tific medicine must turn its attention toward
the strengthening and stimulating of the resist-
ing and curative forces of the body. It must
be the physician's aim to enable the body to re-
sist the poisons as well as possible and to stimu-
late it to re-enforce its resistant forces. Drugs
have a place in medicine, of course, but this place
is chiefly to stimulate the body to react against
its invading hosts. They are, as a rule, not spe-
cific against definite diseases. We can not hope
for much in the way of discovering special medi-
cines adapted to special diseases. We must sim-
ply look upon them as means which the physician
has in hand for stimulating the natural forces of
the body, and these may doubtless vary with dif-
ferent individual natures. Recognising this, we
13

I pO THE STORY OK GERM LIFE.

can see also the logic of the small dose as com-
pared to the large dose. A small dose of a
drug may serve as a stimulant for the lagging
forces, while a larger dose would directly repress
them or produce injurious secondary effects. As
soon as we recognise that the aim of medicine is
not to destroy the disease but rather to stimulate
the resisting forces of the body, the whole logic
of therapeutics assumes a new aspect.

Physicians have understood this, and, espe-
cially in recent years, have guided their practice
by it. If a moderate dose of quinine will check
malaria in a few days, it does not follow that
twice the dose will do it in half the time or with
twice the certainty. The larger doses of the
past, intended to drive out the disease, have been
everywhere replaced by smaller doses designed
to stimulate the lagging body powers. The mod-
ern physician makes no attempt to cure typhqid
fever, having long since learned his inability to
do this, at least if the fever once gets a foothold ;
but he turns his attention to every conceivable
means of increasing the body's strength to resist
the typhoid poison, confident that if he can thus
enable the patient to resist the poisoning effects
of the typhotoxine his patient will in the end re-
act against the disease and drive off the invading
bacteria. The physician's duty is to watch and
guard, but he must depend upon the vital powers
of his patient to carry on alone the actual battle
with the bacterial invaders.

ANTITOXINES.

In very recent times, however, our bacteriolo-
gists have been pointing out to the world certain

COMBATING PARASITIC BACTERIA. 191

entirely new means of assisting the body to fight
its battles with bacterial diseases. As already
noticed, one of the primal forces in the recovery,
from some diseases, at least, is the development
in the body of a substance which acts as an anti-
dote to the bacterial poison. So long as this anti-
toxine is not present the poisons produced by the
disease will have their full effect to weaken the
body and prevent the revival of its resisting
powers to drive off the bacteria. Plainly, if it is
possible to obtain this antitoxine in quantity and
then inoculate it into the body when the toxic
poisons are present, we have a means for de-
cidedly assisting the body in its efforts to drive
off the parasites. Such an antidote to the bac-
terial poison would not, indeed, produce a cure,
but it would perhaps have the effect of annulling
the action of the poisons, and would thus give the
body a much greater chance to master the bac-
teria. It is upon this principle that is based the
use of antitoxines in diphtheria and tetanus.

It will be clear that to obtain the antitoxine
we must depend upon some natural method for
its production. We do not know enough of the
chemical nature of the antitoxines to manufacture
them artificially. Of course we can not deny the
possibility of their artificial production, and cer-
tain very recent experiments indicate that per-
haps they may be made by the agency of elec-
tricity. At present, however, we must use natural
methods, and the one commonly adopted is sim-
ple. Some animal is selected whose blood is
harmless to man and that is subject to the dis-
ease to be treated. For diphtheria a horse is
chosen. This animal is inoculated with small
quantities of the diphtheria poison without the

192 THE STORY OF GERM LIFE.

diphtheria bacillus. This poison is easily ob-
tained by causing the diphtheria bacillus to grow
in common media in the laboratory for a while,
and the toxines develop in quantity ; then, by
proper filtration, the bacteria themselves can be
removed, leaving a pure solution of the toxic
poison. Small quantities of this poison are inocu-
lated into the horse at successive intervals. The
effect on the horse is the same as if the animal
had the disease. Its cells react and produce a
considerable quantity of the antitoxine which
remains in solution in the blood of the animal.
This is not theory, but demonstrated fact. The
blood of a horse so treated is found to have the
effect of neutralizing the diphtheria poison, al-
though the blood of the horse before such treat-
ment has no such effect. Thus there is developed
in the horse's blood a quantity of the antitoxine,
and now it may be used by physicians where
needed. If some of this horse's blood, properly
treated, be inoculated into the body of a person
who is suffering from diphtheria, its effect, pro-
vided the theory of antitoxines is true, will be to
counteract in part, at least, the poisons which are
being produced in the patient by the diphtheria
bacillus. This does not cure the disease nor in
itself drive off the bacilli, but it does protect the
body from the poisons to such an extent as to
enable it more readily to assert its own resisting
powers.

This method of using antitoxines as a help in
curing disease is very recent, and we can not even
guess what may come of it. It has apparently
been successfully applied in diphtheria. It has
also been used in tetanus with slight success.
The same principle has been used in obtaining an

COMBATING PARASITIC BACTERIA. 193

antidote for the poison of snake bites, since it has
appeared that in this kind of poisoning the body
will develop an antidote to the poison if it gets a
chance. Horses have been treated in the same
way as with the diphtheria poison, and in the
same way they develop a substance which neu-
tralizes the snake poison. Other diseases are
being studied to-day with the hope of similar
results. How much further the principle will go
we can not say, nor can we be very confident that
the same principle will apply very widely. The
parasitic diseases are so different in nature that
we can hardly expect that a method which is satis-
factory in meeting one of the diseases will be very
likely to be adapted to another. Vaccination has
proved of value in smallpox, but is not of use in
other human diseases. Inoculation with weak-
ened germs has proved of value in anthrax and
fowl cholera, but will not apply to all diseases.
Each of these parasites must be fought by special
methods, and we must not expect that a method
that is of value in one case must necessarily be
of use elsewhere. Above all, we must remember
that the antitoxines do not cure in themselves;
they only guard the body from the weakening
effects of the poisons until it can cure itself, and,
unless the body has resisting powers, the anti-
toxine will fail to produce the desired results.

One further point in the action of the anti-
toxines must be noticed. As we have seen, a
recovery from an attack of most germ diseases
renders the individual for a time immune against
a second attack. This applies less, however, to a
recovery after the artificial inoculation with anti-
toxine than when the individual recovers without
such aid. If the individual recovers quite inde-

194 THE STORY OF GERM LIFE.

pendently of the artificial antitoxine, he does so
in part because he has developed the antitoxines
for counteracting the poison by his own powers.
His cellular activities have, in other words, been
for a moment at least turned in the direction of
production of antitoxines. It is to be expected,
therefore, that after the recovery they will still
have this power, and so long as they possess it
the individual will have protection from a second
attack. When, however, the recovery results from
the artificial inoculation of antitoxine the body
cells have not actively produced antitoxine. The
neutralization of the poisons has been a passive
one, and after recovery the body cells are no
more engaged in producing antitoxine than be-
fore. The antitoxine which was inoculated is
soon eliminated by secretion, and the body is
left with practically the same liability to attack
as before. Its immunity is decidedly fleeting,
since it was dependent not upon any activity on
the part of the body, but upon an artificial inocu-
lation of a material which is rapidly eliminated
by secretion.

CONCLUSION.

It is hoped that the outline which has been
given of the bacterial life of Nature may serve to
give some adequate idea of these organisms and
correct the erroneous impressions in regard to
them which are widely prevalent. It will be seen
that, as our friends, bacteria play a vastly more
important part in Nature than they do as our
enemies. These plants are minute and extraor-
dinarily simple, but, nevertheless, there exists a
large number of different species. The number

COMBATING PARASITIC BACTERIA. 195

of described forms already runs far into the hun-
dreds, and we do not yet appear to be approach-
ing the end of them. They are everywhere in
Nature, and their numbers are vast beyond con-
ception. Their powers of multiplication are in-
conceivable, and their ability to produce profound
chemical changes is therefore unlimited. This
vast host of living beings thus constitutes a force
or series of forces of tremendous significance.
Most of the vast multitude we must regard as
our friends. Upon them the farmer is dependent
for the fertility of his soil and the possibility of
continued life in his crops. Upon them the
dairyman is dependent for his flavours. Upon
them important fermentative industries are de-
pendent, and their universal powers come into
action upon a commercial scale in many a place
where we have little thought of them in past
years. We must look upon them as agents ever
at work, by means of which the surface of Nature
is enabled to remain fresh and green. Their
power is fundamental, and their activities are
necessary for the continuance of life. A small
number of the vast host, a score or two of spe-
cies, unfortunately for us, find their most favour-
able living place in the human body, and thus
become human parasites. By their growth they
develop poisons and produce disease. This small
class of parasites are then decidedly our enemies.
But, taken all together, we must regard the bac-
teria as friends and allies. Without them we
should not have our epidemics, but without them
we should not exist. Without them it might be
that some individuals would live a little longer, if
indeed we could live at all. It is true that bac-
teria, by producing disease, once in a while cause

196 THE STORY OF GERM LIFE.

the premature death of an individual ; once in a
while, indeed, they may sweep off a hundred or a
thousand individuals; but it is equally true that
without them plant and animal life would be im-
possible on the face of the earth.

INDEX.

Acetic acid, 51.
Alcohol, 48.
Alexines, 149.
Amoeba coh, 165.
Animals or plants ? 31.
Anthrax, 137, 177.
Antitoxmes, 157, 100.
Aroma of butter, 76.

Bacillus acidi lactici, 71.
Bacillus, definition of, 33.
Bacteria, defined by Hoffman, 15.
Beer, bacteria in the manufacture

of, 50.

Blood poisoning, 138, 140.
Blue milk, 72.

study of, by Fuchs, 12.

Bitter milk, 72.
Butter making, 75, 78.
Butyric acid, 56.

Canning industry, 64. <
Capsule around bacteria, 24.
Cheese ripening, 86 ; bacteria in,

90.

Cholera Asiatica, 133.
Cholera, fowl, 144.

Classification of bacteria, 33, 36.

Cleavage products, 41.

Coal, relation of bacteria to, 123.

Cocoanut fibre, 44.

Colony of bacteria, 25.

Compost heap, 118.

Cream ripening, 75, 77.

Curative medicine. 185.
Cure of disease by natural processes,
187.

D.

Dairy industry, 66.
Decomposition products, 41.
Diphtheria, 134.

Disease, method of production, 130.
Diseases produced by bacteria, 139,

Distribution of disease germs, 168.
Division of bacteria, method of, 18,

rapidity of, 21.

Drugs in germ diseases, 185.
Dysentery, 165.

F.

Farmer's life, relation to bacteria,

121.

Fermentative industries, 48.
Fermentation, theory of Liebig, 13.
Fertilizers, ripening of, 117.
Flagella, 29.
Flavour of butter, 76 ; of cheese,

88.

Food cycle of Nature, 97.
Food, relation of bacteria to, 22.

G.

Generic names, 37.
Green manuring, 120.

H.

Habitat of bacteria, 38.

Hemp, 44.

Henle, general theory of disease, 12.

Hydrophobia, 180.

198

INDEX.

I.

Pathogenic bacteria, abundance of,

Indigo, preparation of, 57.
Inflammation in surgery, 153.
Internal structure of bactena, 30.
Invasion, means of, 145, 169.

129.
Pathogenic bacteria not true para-
sites, 131.
Phagocytes, 151.
Poisons produced by bacteria, 130,

J-

132.
Preventive inoculation, 175.

Jute, 44.

Preventive medicine, 166 ; limits of,

K.

182.
Products of bacterial life, 41, 47.

Koch, contribution to bacteriology,

Pure cultures, 15 ; in vinegar mak-

16.

butter making, 82 ; in cheese mak-

L.

„ 'ng, 93-
Pus, 153 ; pus cocci, 142.

Lactic acid, 55.

Leather, 46.

R.

Leeuwenhoek, studies of, 10.
Legumes in nitrogen fixation, 108.
Liebig, theory of fermentation, 13.
Limits of preventive medicine, 182.

Recovery from germ diseases, 156.
Red milk, 72.
Resistance to disease, 147.

Linen, 42.

Lockjaw, 135.

S.

Lysines, 151.

Sarcina, defined, 19.

Sauer Kraut, 65.

M.

Scavengers, bacteria as, 95, 101. _

Maceration industries, 42.

Schwann, studies on fermentation,

Maceration of skeletons, 46.

12.

Malaria, 160.
Malignant pustule, 137.
Microbe, definition of, 9.
Micrococcus, defined, 18.

Seeds, sprouting of, in.
Shape of bactena, 17.
Silo, bacteria in, 112.
Size of bacteria, 17.

Milk bacteria, 67, 70.
Milk, effect of bacteria on, 70.
Milk handling, 74.
Mosquitoes and malaria, 164.
Motion of bacteria, 28.
Muller. studies of, n.
Multiplication, rapidity of, 21.
Mycoderma aceti, 52.

Skeletons, 46.
Slimy milk, 72.
Snuff, preparation of, 59.
Soapy milk, 72.
Soil, fertility of, 114.
Sources of infectious material, 168.
Souring of milk, 70.
Species, differences between, 23, 34 ;

N.

Sponges, 45.

Spores, 25.

Nitrate beds, 116.
Nitrifying bacteria, 103.
Nitrogen fixation, 107.
Nitrogen loss, 104.

O.

Staphylococcus pyogenes, 142.
Streptococcus, defined, 19.
Streptococcus pyogenes, 142.
Surgery, bactena in, 171.
Susceptibility of the individual, 145.

Opium, 63.
Oscillaria?, as allies of bacteria, 32.

T.
Tainted milk, 72.

p

Tetanus, 135.
Tobacco curing, 58.

Parasitic bacteria, 134.
Pasteur, contributions of, 14.

Troublesome fermentations, 63, 121.
Tuberculosis, 136.
Typhoid fever, 136.

Vaccination, 176.

INDEX. 199

W.

Wine, bacteria in manufacture of,

Variation among bacteria, 35. 50.

Vinegar, 51. Y.

Virulence of pathogenic germs, 140, I Yellow milk, 72.

Vis inedicatrix naturae, 187. I Zougloea, 24.

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