BIOLOGY

LIBRARY

G

BACTERIA, YEASTS, AND MOLDS
IN THE HOME

BY

H. W. CONN, PH.D.

PROFESSOR OF BIOLOGY IN WESLEYAN UNIVERSITY, MIDDLETOWN, CONN.

ATITHOR OF "AGRICULTURAL BACTERIOLOGY," " BACTERIA IN

MILK AND ITS PRODUCTS," "THE STORY OF GERM

LIFE," "THE METHOD OF EVOLUTION," ETC.

GINN & COMPANY

BOSTON • NEW YORK • CHICAGO • LONDON

ENTERED AT STATIONERS' HALL

COPYRIGHT, 1903
BY H. W. CONN

ALL RIGHTS RESERVED

Cfte fltbenaum

GINN & COMPANY • PRO-
PRIETORS • BOSTON • U.S.A.

C£

BIOLOGY

LIBRARY

G

PREFACE

The rapidly growing interest in home economics is caus-
ing this subject slowly to assume the aspect of an exact
science. At the present time it is becoming necessary
for those expecting to become housewives to understand
at least the elementary phases of a number of sciences,
most prominent among which are chemistry and bacteri-
ology. The relation of microorganisms to household affairs
has only been recognized in the last few years, but is
now felt to be one of the most important phases in the
study of the problems of the household. The present
work is therefore designed for all interested in household
affairs, including not only students of household econom-
ics but all persons who have practical charge of homes
and are interested in keeping them in the best and most
healthful condition.

238904

iii

TABLE OF CONTENTS

CHAPTER

I. INTRODUCTION

PAGE
I

SECTION I — MOLDS

II. THE GENERAL NATURE OF MOLDS . . . 12

III. CONDITIONS FAVORING MOLD GROWTH . '. . . 32

IV. THE DECAY OF FRUIT; USEFUL MOLDS; MOLD

DISEASES . . * , . » . 40

SECTION II— YEASTS

V. YEASTS AND THEIR DISTRIBUTION .
VI. YEASTS IN THE HOUSEHOLD.
VII. BREAD RAISING; FERMENTED LIQUORS .

56
68
86

SECTION III — BACTERIA

VIII. THE GENERAL NATURE OF BACTERIA . . . 100

IX. BACTERIA WHICH LIVE UPON DEAD FOOD . . 124

X. THE PRESERVATION OF FOOD; DRYING; COOLING 139

XL THE USE OF PRESERVATIVES . V . . . 157

XII. PRESERVATION BY CANNING . . ... . 169

XIII. MILK; EGGS; PTOMAINE POISONING . ... . . 182

XIV. DISEASE BACTERIA 203

Vi CONTENTS

CHAPTER PAGE

XV. PREVENTION OF DISTRIBUTION OF CONTAGIOUS

DISEASES . ... . . . .212

XVI. PRACTICAL SUGGESTIONS . . . . . 241

XVII. DISINFECTION . . . . . . ." . 255

APPENDIX

DIRECTIONS FOR LABORATORY EXPERIMENTS . . . 267

INDEX . ........ 287

BACTERIA,
YEASTS, AND MOLDS

CHAPTER I
INTRODUCTION

Bacteria, yeasts, and molds comprise a series of plants
commonly known as microorganisms, or more popularly as
microbes. It has for some time been recognized that
together they form a group of the utmost importance
not only to the physician but also to the agriculturist.
To-day it is beginning to be appreciated that their rela-
tion to the ordinary household, and hence to the house-
wife, is even more intimate than to the physician. We
are learning that many of the tasks of the housekeeper,
some of which may be more or less unpleasant, have their
foundation in bacteriology, and we are beginning to recog-
nize that these microorganisms constitute the foundation
of the demand for cleanliness so forcibly emphasized in
modern times.

In the household microorganisms have an important
bearing in three directions :

1. They are the cause of the decay and spoiling of foods
and many other products.

2. They are sometimes of value in the preparation of
foods.

3. They are the cause of contagious diseases.

2 BACTERIA, YEASTS, AND MOLDS

i. MICROORGANISMS AND THE PRESERVATION OF FOOD

Although household duties are varied in character, the
larger part of them concern the preparation and the pres-
ervation of foods. The preparation of food belongs pri-
marily to the department of cooking, although certain
other factors are concerned. But the science of cooking
has little to do with the preservation of food. This latter
problem is intimately related to modern bacteriology. It
is largely for this reason that the study of bacteriology
and kindred subjects has in recent years come to be
looked upon as a part of the necessary training of the
housewife.

At the outset we may properly ask, Why is it that food
spoils? Why will not food keep indefinitely without the
many contrivances designed to prevent its spoiling ? The
answer to this question is, briefly, that other living things
besides ourselves are fond of the same foods of which we
are fond, and that these other living beings take every
occasion to consume the material which we design for our
own food. Preserving the food in our pantries, cellars,
and refrigerators, therefore, simply means protecting it
from consumption by other living organisms ; and if we
can keep these organisms away, food may be indefinitely
preserved. On the other hand, if we cannot protect our
food from the attack of these organisms, it spoils ; for the
spoiling of food is simply the result of its consumption by
living beings for whom we have not designed it.

The living beings that endeavor to consume our food
comprise, in the first place, some of the larger animals
with which every one is familiar. Every one knows about

PRESERVATION OF FOODS 3

rats and mice, and the various insects in the home are
only too familiar pests. But not every one understands
that in addition to these large animals there is a great
host of plants and animals which seize every opportunity
of feeding upon that which we intend for our own use.
All such small animals and plants go by the general name
of microbes or microorganisms.

We are chiefly concerned, in this book, with three
important groups of plants, Some of these plants are
large enough to be seen easily and are generally well
known, such as the molds that occur everywhere, and are
always regarded as nuisances in household economy. In
addition to the visible plants there is a still larger num-
ber of others, quite too small to be visible to the naked
eye and, indeed, only seen with the high powers of the
microscope. These invisible organisms are the smallest
living beings of which we have any knowledge, and are
both friends and foes. Not only are they invisible to the
naked eye but to the ordinary housewife they are quite
unknown. Until within recent years they have been
unknown even to scientists, and although science has now
learned to understand quite well what they are and what
they do, to the public in general they are little more than
a name around which cluster various mysteries and in
regard to which there is no general information. Molds
and yeasts have long been known. The term bacteria is new,
and refers to organisms just beginning to claim public
attention but in regard to which there is at present a
large amount of misunderstanding. But even though
they are very minute, and though she knows little about
them, the housewife finds them the most serious, indeed

4 BACTERIA, YEASTS, AND MOLDS

the only serious foe with which she has to contend in her
attempt to keep food in proper condition for use.

These invisible plants are constantly on the alert to con-
sume for themselves the foods which the housewife designs
for the table. If they have a chance to get at the food,
she soon notices that it undergoes a series of changes,
characterized by what we call putrefaction, decay, souring, or
perhaps some other change not properly classed under
any of these terms. The general rotting of fruit, the
decay of meat, the souring of milk, and a host of other
similar phenomena which occur in every pantry if the food
is not carefully protected, represent some of the effects
produced in foods when microorganisms begin to feed
upon them. Thus it is evident that these microscopic
plants play a very great part in domestic economy.
This fact, however, has not been thoroughly appreciated
until recent years, and indeed it is only just beginning
to be recognized to-day that the housewife's knowledge
should comprise an understanding of the nature and hab-
itat of these microscopic foes, their methods of distribu-
tion from place to place, the conditions under which they
grow and fail to grow, together with the various devices
which may be adopted for checking their active growth
where they are not wanted. Although the facts have
only recently been appreciated, it is known to-day that a
very considerable part of the duties in every household is
concerned with these microscopic organisms, known and
unknown.

The chief desire of the housewife is to prevent the
growth of these microorganisms in places where they
are not wanted. For this purpose have been invented

MICROORGANISMS AS USEFUL AGENTS 5

refrigerators and all devices for cold storage and for cool-
ing and keeping cold any food products ; to this end, too,
are designed the various methods of preserving food and
fruits. The immense industry of canning, either on a
large scale as is done in factories, or on a small scale as
is done in the household, is dependent upon the relation
of microorganisms to food. The sterilizing or pasteuriz-
ing of milk, as well as other foods, is also a bacteriological
problem, and, indeed, many other phases of household
life are really bacteriological phenomena. Whether or
not she possesses a scientific knowledge of bacteria and
their allies, the housewife must have a certain practical
knowledge of their nature and of their powers, for this
practical knowledge is absolutely necessary to enable her
to preserve her food successfully from the microorganisms
which are so liable to spoil it.

2. MICROORGANISMS AS USEFUL AGENTS

It must not be understood, however, that micro-
organisms are always our foes. It is true that in the
household they are commonly a source of trouble, but
it is also true that some of them are distinctly friends.
To appreciate that they are sometimes useful, even in our
foods, one needs only to remember that under this head
are included the great group of yeasts that play such an
important part in the household in the raising of bread
and in all types of fermentation. Yeasts, as well as bac-
teria, are microscopic plants, of which the microscopist
recognizes many kinds. Some of these are troublesome,
but, so far as concerns their relations in the household,

6 BACTERIA, YEASTS, AND MOLDS

they are useful servants rather than undesirable foes.
Even bacteria, which are in general looked upon as
dreaded foes, and as agents only of evil, are, under
some circumstances, our friends rather than our enemies.
Bacteria, for example, produce the delicate flavors in
butter and the stronger but equally delicious flavors of
cheese. Bacteria also are solely responsible for the man-
ufacture of vinegar ; for although vinegar might be made
by chemical means, the vinegar of our tables is produced
by the agency of bacteria. Molds also, though generally
looked upon as unmitigated nuisances, are, in some places,
of decided use. The utility of molds, however, has little
to do with household products, being confined chiefly to
the production of certain types of cheeses. The flavor
of Roquefort cheese, for example, is due chiefly, if not
wholly, to the growth of certain types of molds within
the cheese. These illustrations will serve to show that
microorganisms, even in the household, must occasionally
be looked upon as friends rather than enemies.

3. MICROORGANISMS AND DISEASE

Certain species of microorganisms are harmful to
human health and are the cause of contagious diseases.
They are generally known as disease germs or pathogenic
bacteria. Fortunately they are few in number. While
large numbers of species of microorganisms may be
troublesome in the household because of their action
upon our foods, very few species, comparatively, are able
to do harm in the human body or to produce disease if
they should find entrance. The great majority of species

MICROORGANISMS AND DISEASE 7

are, then, harmless to human health, but a small number
are capable of producing disease, and for this reason are
of especial interest.

The study of the causes and cure of disease belongs
primarily to the physician and not to the housewife. The
housewife must, it is true, occasionally act as the nurse of
persons suffering from contagious diseases, and will then
be interested in the treatment of the patient and the cure
of the disease. But even here the question of cure must
be left to the medical profession, while as nurse she should
simply follow the directions given. Yet one phase of the
matter is almost solely hers, for to her must be left the
task of preventing the distribution of contagious diseases.
Many of the diseases produced by microorganisms are
distinctly contagious and, unless the patient and the other
members of the home are properly guarded, a disease
is likely to be carried through a household from one
person to another. To prevent the distribution of such
contagious diseases is the duty of those who care for
the home.

The problem of preventing the distribution of various
diseases is a bacteriological one, for, inasmuch as bacteria
are usually the cause of the disease, the prevention of
contagion is the prevention of the distribution of bac-
teria. In every home such problems are more or less com-
mon. They concern the members of the home far more
materially than they do the physician. Every household
will occasionally have experience with contagious diseases,
and the question of preventing their distribution from a
patient to a healthy individual is sure to arise. The house-
wife who cares for the home year after year will have

8 BACTERIA, YEASTS, AND MOLDS

many experiences where a knowledge of distribution of
diseases is of even more importance to her than to the
physician himself. The physician is directly concerned in
the cure and only indirectly in the prevention of contagion ;
the housewife must always have upon her shoulders the
duty of keeping her family in health, and when an instance
of contagious disease appears she must try to protect the
rest of the household. For these reasons it follows that
a knowledge of disease germs is of more vital significance
to one who cares for the home than it is to the physician,
who is only concerned in curing the disease. The physi-
cian or the Board of Health may give suggestions and
directions, but the successful application of these direc-
tions depends upon the intelligence of the home keeper.

This brief outline of the relation of bacteria to various
household problems is sufficient to show why a knowledge
of microorganisms should be a part of the equipment of
any one who is to conduct the affairs of a well-regulated
household. For the development and preparation of some
foods, for the preservation of all foods, and for the pro-
tection of the health of those under her care, the head of
a modern well-equipped home needs to understand bac-
teria and kindred organisms. A knowledge of molds,
yeasts, and bacteria has become a vital if not a necessary
part of training in domestic economy.

DIFFERENT CLASSES OF .MICROORGANISMS

The microorganisms with which we are concerned all
have one common characteristic : they are what botanists
call colorless plants. This does not mean that they are

CLASSIFICATION OF MICROORGANISMS 9

absolutely without color, for they may be bluish, reddish,
gray, or white, or, indeed, they may show other colors ;
but it means that they do not have the green color char-
acteristic of the majority of plants in nature. The absence
of this green coloring makes them unable to live upon the
food in the soil, and forces them to live upon a kind of
food different from that of ordinary plants. Ordinary
green plants can live upon minerals which they obtain
from the soil, and upon gases which they obtain from the
air, but the colorless plants cannot use such materials
at all. They need a more complex type of food.

The materials in nature are frequently divided into
mineral and organic substances. Mineral, or inorganic, sub-
stances are such' materials as rocks, sand, earth, etc.
Organic substances (wood, bones, fruit, muscle, etc.)
are those which have been produced by animals or by
plants, i.e. by organisms. Evidently the foods we eat —
meats, fruits, vegetables, etc. — are organic, since they all
come from plants or animals. The colorless plants — the
Fungi — are, like animals, obliged to have organic sub-
stances for foods, and therefore feed upon materials essen-
tially similar to those which form the food of animals, i.e.
meats, fats, sugars, etc. Since the colorless plants and
the animals are in need of the same kinds of food they
become rivals in nature. The green plants, on the other
hand, living upon totally different foods, are in no sense
the rivals of animals, but their allies. It is this fact, their
living upon organic foods, that makes the colorless plants
of so much importance for good or ill, and explains their
close relation to the problems of the household with which
we are concerned.

10 BACTERIA, YEASTS, AND MOLDS

Botanists class all colorless plants under one general
group, which they call Fungi. Under this group is a large
variety of plants which show wide differences of structure
in size and general appearance. But inasmuch as they
all agree in lacking green coloring material, they are, at
least from the standpoint of their relations in nature, prop-
erly placed in one general class. The group of fungi as
recognized by botanists is subdivided into, a number of
divisions. A method of dividing them, convenient for
our purposes, is as follows.

FUNGI

Higher Fungi. This includes the forms of large size,
known generally as mushrooms, toadstools, wood fungi,
rusts, smuts, etc. With these plants we are not particu-
larly concerned in the household.

Molds. Fungi of considerable size, easily visible to the
naked eye, composed of threads.

Yeasts. Microscopic plants which multiply by a pro-
cess called budding, composed of oval bodies.

Bacteria. Still smaller plants that multiply by a pro-
cess called fission, composed of spherical, rod-shaped, or
spiral bodies.

Trrb classification is not scientifically accurate. The
higher fungi include a large number of different types
classed by botanists into many subdivisions. But since
they are not concerned in household problems we may
most conveniently group them together and consider them
no further.

The group of molds also is not a proper scientific divi-
sion, since under this head are included several different

CLASSIFICATION OF MICROORGANISMS n

kinds of plants which botanists agree must be separated
into several divisions. Some of the so-called molds really
belong to the higher fungi. But though the term "mold"
is not a good scientific one, practically it is very useful.
It is a common English word, quite generally understood,
and always refers to a variety of plants characterized
by a general appearance so well known as to be easily
recognized by persons who are entirely unfamiliar with
scientific botany. Although admitting that the molds do
not represent any real scientific division of fungi, we may
use the term as referring to colorless plants which every
one recognizes but which cannot be scientifically defined.

The other two groups, yeasts and bacteria, are proper
scientific divisions.

In our study of household problems we are concerned
only with molds, yeasts, and bacteria.

SECTION I --MOLDS

CHAPTER II
THE GENERAL NATURE OF MOLDS

As intimated in the last page, the group of molds does
not form a scientific division. Among the plants grouped
under this popular name are included representatives of
several different groups of fungi. The general character
of molds is a dense mass of fine white threads. But some
of the higher fungi related to the toadstools produce a
white threadlike mass, and if we find this growing in
abundance upon the surface of wood we commonly call
it a mold. Other so-called molds belong to the different
subdivisions related to cup fungi, Ascomycetes, while still
others belong to an order of fungi which includes parasitic
plants like rusts and smuts, and are called JEcidiomycetes.
We must not, therefore, look' upon molds as a division
which would be recognized by any botanist. For house-
hold purposes, however, no term can take the place of this
one, so universally known and so thoroughly understood.
In our studies, therefore, we shall group together as molds
all types of fungi which produce white felted threads, which
have the power of growing in or upon food materials, and
which give rise to the well-known appearance that char-
acterizes the plants going under this common name. Most
of them are closely related to each other.

12

THE GENERAL NATURE OF MOLDS

The general appearance of molds is well known to every
one. At first they are soft, fluffy masses, usually white,
though later they may become blue, green, brown, black,
or red. They grow upon all sorts of material and, under
some conditions, with
very great rapidity.
A typical mold as it
appears to the naked
eye is shown in Fig. 2.
The molds which are
liable to appear on the
foods in the household
are by no means always
alike,thoughthe house-
keeper rarely recog-
nizes any difference
between them. They
differ in many respects,
— in the fineness of
the threads of which
they are made, in the
rapidity of their
growth, in the mate-
rials upon which they
grow, and more partic-
ularly in color ; for while most are white at first, they show
many other colors later. The most common of the house-
hold molds is one which at the time of fruiting becomes
a bluish-green color, and hence is called the "blue mold,"
Penicillium glaucum (see Figs. I and 5). This species
is common upon bread and cheese, but it will grow upon

FIG. i. Two colonies of common mold,
Penicillium, as shown under the micro-
scope on a black background.

14 BACTERIA, YEASTS, AND MOLDS

FIG. 2. A piece of bread upon which one of the common molds
(Mucor) is growing.

FIG. 3. A common mold, Mucor, growing on a bit of banana.

THE GENERAL NATURE OF MOLDS

leather, as well as upon a host of other materials. We
frequently find upon other foods, especially fruits, two or
three kinds of brown molds, and some that even when
fruiting remain pure white. Some, again, become pretty

FIG. 4. The sprouting of the
spores of Penicillium. At b
there is a cluster of seven
spores sprouting to form a
colony.

nearly black, while still
others grow red or pink.
One of the very common
forms consists of a rather
coarse mass of threads,
upon which develop
numerous rounded black
balls about the size of a

period, while another consists of delicate threads with
clusters of white spores looking like snowballs. Each of
these different colors indicates a different species of mold.
There are scores of species known to botanists, but it is
quite unnecessary for the housekeeper to attempt to dis-
tinguish them. Pieces of moldy lemon, banana, apple, and
bread will be quite sure to show different species of molds.

FIG. 6. A cluster
of spores of an
older colony.

FIG. 5. The growth from two spores
two days later than Fig. 4, showing
the beginning of the formation of
spores, showing method of origin at
a, b, c.

16 BACTERIA, YEASTS, AND MOLDS

STRUCTURE OF MOLDS

It requires microscopic study to make out the structure
of molds, but it is important to understand this structure in
order to be able to explain the conditions under which they
grow. If we study a young mold before it has begun to
produce its fruit, it is found to consist of a long, highly
branching thread (Fig. 5). When it begins to grow all
that can be seen is this tangled mass of delicate threads.
The threads are so minute, as a rule, that the individual
fibers are only just large enough to be seen by the naked
eye, and in many cases they are too small to be seen
except with a lens. The thread of the blue mold is too
small to be seen without a microscope. The threads are
practically always of a whitish color, nearly transparent
when examined under the microscope, and appear as
shown in the several figures. In some species of molds
they grow into a very dense, felty, rather tough mass.
In other species they form a loose mass of coarser fibers
(Fig. 2).

An important point to be remembered is that these
threads, by their growth, can penetrate into the depths of
the material upon which they are growing. If they are
upon the surface of bread, the fine fibers push their way
down into the substance of the bread. If they grow upon
cheese, the threads force their way into the body of the
cheese. When growing upon any soft food material, the
mold threads, though visible only on the surface, really
extend into the substance for a considerable distance,
although they are so small and transparent that we cannot
follow them. Of course the readiness with which a mold

THE GENERAL NATURE OF MOLDS 17

can grow through food material will depend upon the tough-
ness or firmness of the material. Upon damp leather the
thread is not capable of growing underneath the surface
so readily as it can upon bread. This thread is known to
botanists by the term mycelium, and by this term we shall
hereafter refer to it. The young mold is a white, loose
mass of mycelium, but as it grows older it becomes denser
by continued branching of the thread.

Fruit. After a while (usually two or three days' growth)
the surface of the mold begins to show some color, —
either blue, brown, red, or some other color. The appear-
ance of the color on the surface indicates that the plant
is fruiting, i.e. producing spores or reproductive bodies.
The spores of different species of mold are produced in
quite different ways, and botanists classify molds by their
methods of forming fruit. It will not be necessary for us
to consider more than one or two of them.

In the common blue mold the spores are produced as
follows. After the mycelium has grown for some time
there arise from its surface tiny threads growing vertically
into the air. These threads, after extending for a very
short distance, divide into little branches (as shown in *
Fig. 5, c), several branches arising from a single stem.
After these branches have grown for a short distance
they begin to be divided by slight constrictions, like rings,
around them, so that each one of them looks like a string
of beads (Fig. 5, c). These rings cut deeper and deeper
into the branch until finally it is broken up into a string
of a dozen or more small round balls (Fig. 6). These
little balls (Fig. 6) are the spores. When seen under the
microscope they appear quite transparent, but when a

18 BACTERIA, YEASTS, AND MOLDS

considerable number of them are seen together they have
a bluish tinge. The spore-bearing branches spring up in
thousands all over the mold, and after a few days its sur-
face is covered with a mass of thousands of spores, giving
to the mold first a slightly blue color and later a darker

blue, until the entire sur-
face finally becomes cov-
ered with the well-known
shade spoken of as blue
mold. These
spores are ex-
tremely light,
are very easily
blown by the
winds and readi-
ly float in the air.
Every breath of

FIG. 7. A colony of Mucor, showing the mycelium , - • i •

, . . /•!/•• air striKinsf a

and the sporangium of the fruit capsules. At a

is a large sporangium filled with spores. mass of molds

in full fruit will

detach some of these minute spores and blow them away.
The species of different molds can easily be distinguished
by their different modes of forming spores. A mold com-
mon on fruit and bread, called .Mucor (Fig. 2), produces
its spores inside of little sacs borne on long stalks. The
mycelium in this mold is coarse and the threads are easily
visible, making a loose mass of delicate fibers, and some-
times forming upon bread a fluffy growth an inch thick
(Fig. 2). When ready to fruit, threads grow vertically
into the air and the end of each thread soon swelh into a
small rounded knob. This knob continues to grow until

FRUITING OF MOLDS

it becomes a ball of considerable size, at first white, but

finally black, and large enough to be seen with the naked

eye (Fig. 7). Inside of this ball the living substance of

the plant soon breaks up into hundreds of minute bodies

(Fig. 7). These are the spores, and after they have

become formed the sacs which hold them (sporangia} burst

and .the little spores are thrown out to be blown about

by the wind.

These molds

are at first soft

and white, but

later black from

the abundance

of these spore

sacs.

Another very
common sort of
mold fruits still
differently^-
pergillus). A

fine threadlike FlG- 8. A colony of Aspergillus, showing mycelium

, . and spore clusters. The lower figures show in

nyC 1S detail the method of spore formation,
produced, as in

the other cases, and from it grow the fruiting branches.
At the end of each fruiting branch grows a little round
ball, from all sides of which project many little knobs
(Fig. 8, a). These knobs lengthen a little, but soon break
up into round spores very much like the branches of blue
mold (Fig. 8, a'-e). The result is that, since they pro-
trude in. all directions, there appears on the end of each
fruiting branch a little rounded mass, looking very much

20

BACTERIA, YEASTS, AND MOLDS

like a corn ball (Fig. 8, d), — a resemblance which is very
striking in some species when the spores are white. This
species of mold, even after producing its fruit, remains
white ; but a careful examination shows it to be covered
all over with minute white balls just big enough to be
seen by the naked eye, but looking very beautiful under

the microscope
(Fig. 9). Each
ball is a mass of
scores of spores.
Some molds of this
last type produce
brown spores in-
stead of white.

Of the scores of
species of molds
each has its own
method of produ-
cing spores. Each
is at first a white,
threadlike myce-
lium, but each in
time shows spots
of color. When the color begins to appear it commonly
means that the mold is producing spores. The spores
are nearly always so small and light as to be blown easily
by the wind, and in this way they are carried to and fro.
The air in any household is almost sure to be filled with
them in greater or less abundance, as can easily be proved
by simple experiment. Figs. 14-17 show a variety of com-
mon molds, with their methods of forming spores.

FIG. 9. A colony of Aspergillus as shown under
the microscope on a black background.

FRUITING OF MOLDS

21

FIG. 10. Mucor, a
common mold.

FIG. ii. Antenaria, a com-
mon mold found upon apples.
Mycelium shown at a, and en-
larged fruiting bodies at b.

FIG. 13. Fruiting bodies
of a mold found upon
apple scab, Cephalo-
thecium.

FIG. 12. Fruiting bodies of another
species of Antenaria,

FIG. 14. Stysanus, a
mold, a, mycelium ;
branch.

common
, fruiting

FIG. 15. A common household mold.

22

BACTERIA, YEASTS, AND MOLDS

Germination of Spores. The function of these spores
is to reproduce the plant. If one of them lights upon a
proper material having sufficient warmth, moisture, and
nourishment for its life, it soon germinates and sends out
from itself a little thread (Fig. 5, a). This thread feeds
upon the material on which it is growing, and continues to

extend and branch until within
« -o "Spores

a tew hours a new mycelium is

produced, thrusting its way into

Spores

FIGS. 1 6 and 17. Two species of molds, Monilia, common in cheese.

the food substance and developing into a typical mold.
After a day or two the spores are again produced (Fig. 5),
and the process is repeated. The air is almost always so
well filled with spores of molds that it is quite impossible
to leave any food product exposed for any length of time
without a number of these living spores falling upon it.
If a piece of moist bread, for example, is exposed to the
air for an hour or so in an ordinary room, and is then cov-
ered with a bell glass in such a way as to keep it moist, it
will, in the course of a day or two, become covered with
molds which have come from the sprouting of spores that

FRUITING OF MOLDS

PLATE I

PLATE II

FIG. 1 8. Plates exposed to the air before and after
sweeping, showing the abundance of mold spores
in the air. The upper plate was exposed before
sweeping, and contains one mold; the lower after
sweeping, and contains numerous molds. Each
was exposed for one minute.

24 BACTERIA, YEASTS, AND MOLDS

fall upon it. These spores — including species already
described, as well as a variety of others — are almost sure
to be floating in the air, and one of the valuable practical
lessons for the housewife to learn is that the ordinary air
of her house is filled with mold spores which are sure to
get upon any food material that is left exposed.

The mold spores, although very light, are slightly
heavier than the air, and after floating awhile they sink
to the floor, if the air is quiet, where they remain until
the air is again disturbed. Sweeping stirs them up, and
so does dusting. Fig. 18 represents two plates filled with
a jelly upon which molds will readily grow. . Plate I was
opened to the air for one minute in an ordinary room and
then closed. The room was then swept and Plate II was
exposed to the air for the same length of time. Both
were then set aside until the spores germinated, when the
photographs were made. The plate exposed to ordinary
air shows only one mold, while that exposed after the room
was swept contained large numbers. Dusting a room pro-
duces similar results. Even walking through a room, espe-
cially with long dresses that sweep the floor, will stir up
mold spores. The practical conclusions are thus taught
that wiping up dust with a damp cloth is far better than
dusting ; that carpet sweepers are better than brooms; and
lastly, that no food should be exposed to the air of a
recently swept room.

PROTECTION OF FOOD FROM MOLDS

The fact that the molding of food starts from spores
that drop upon it from the air suggests protecting the
food by the simple means of keeping the spores away from

PROTECTION OF FOOD 25

it. If we can keep the spores away, no trouble of this
sort will arise. For example, jellies made from the juice
of fruit, which the housewife puts up for winter use, are
excellent material for mold growth, as many a person has
discovered after the jellies have been stored away for a
time. There is, however, little difficulty in preventing the
molding. In making the jelly the material is commonly
heated sufficiently to kill the spores present, and if it
is afterwards properly covered it will keep well enough.
After the jelly has been poured into the jelly tumblers
and has become somewhat hardened, the surface should
be moistened with some alcoholic solution, like brandy, or
even pure alcohol. Then a piece of clean white paper the
size of the tumbler should be placed upon the surface of
the jelly. After this the tumbler should be covered with
a piece of paper tightly glued over its edges ; or tumblers
with special covers may be used instead of ordinary tum-
blers covered with paper. The alcohol aids in destroying
the spores that may have chanced to light on the surface
of the jelly, and the paper, if properly fastened, will pre-
vent the entrance of more. This device is not sufficient
to exclude bacteria, and if the jelly were liable to decay,
the simple paper covers would not protect it from bac-
terial action. But the method is sufficient to prevent
the growth of molds in a majority of cases. Molds fre-
quently grow upon the top of the papers in such jelly
tumblers, but they do no hurt to the contents below.

Other devices for closing the tumblers are also used.
Sometimes a little white of an egg is used instead of alco-
hol. Instead of using paper, a little melted paraffin may
be poured upon the surface of the jelly, thus sealing it

26 BACTERIA, YEASTS, AND MOLDS

effectually. The paraffin should be melted in some dish,
like a cup, at the lowest temperature at which it will melt,
about 140°. The surface of the jelly may then be covered
with a thin layer, which will quickly harden.

These methods of protecting jelly are not sure, and
even after sealing it is necessary to keep the jelly in a
dry place to insure its keeping properly. Spores may be
left under the paraffin, and it is difficult or impossible to
seal so that no mold spore can subsequently enter. Jel-
lies should therefore be stored in dry closets to keep them
from spoiling. If it should happen that no dry closet is
convenient, the air in a damp closet may be partly dried by
keeping unslaked lime in bowls on shelves near the jelly.
These will absorb the moisture and aid in checking the
molding. The lime should be renewed from time to time.

Canned goods will also sometimes mold when the
process of canning has not been thorough. This will
however be considered later. We must notice here, how-
ever, that when cans of fruit are opened and exposed to
the air, mold spores are very likely to drop into them, and
if they are then shut up again the contents of the can are
almost sure to show a fine crop of molds in a few days.
It is almost impossible to open a can of fruit, take out a
part of it, and close again, without allowing mold spores
to drop into it from the air. This must, of course, be
guarded against, and if the whole contents of the can can-
not be used at once, the part that remains should be boiled
and once more closed, as in the original canning. By such
heating the spores that may have dropped in while the
can was opened are destroyed, and it may be closed and
set away safely.

MATERIAL LIABLE TO MOLD 27

MATERIAL WHICH is LIABLE TO MOLD

Since molds are fungi, they require to be fed with organic
food. Hence they are unable to live, as green plants can,
in purely mineral soil. Indeed, they do not grow readily
anywhere except upon rich food, and they grow best when
feeding upon the same kind of foods that animals require.
Whatever contains organic material will support them.
They feed readily upon bread, cheese, or meat, and they
can also support themselves upon leather or upon woolen
or cotton cloth. Some molds grow easily upon damp
wood ; but although thus capable of living upon almost
anything except mineral matter, they grow much more
readily on some materials than on others.

Of common foods, cheese is probably the one that
molds most readily, partly because it is always more or
less moist, and partly because it is quite sure to be inoc-
ulated with mold spores. Wheat flour, or any material
made from it, like bread or cake, is sure to mold if kept
sufficiently moist and warm. The molding of the flour in
the flour barrel is occasionally noticed, and the molding of
bread is a common occurrence. All other forms of flour
and meal, as well as articles made from them, mold readily
enough. Even pickles will occasionally mold ; for the
intense acid of the vinegar, while it quite prevents the
action of the common putrefactive organisms, does not
necessarily stop the growth of molds. In short, almost
any of the foods which are found in the pantry may, under
certain conditions, show mold growth upon their surfaces.

Molding is not confined to food in the pantry, for other
substances which contain organic material can furnish

28 BACTERIA, YEASTS, AND MOLDS

proper sustenance for mold growth. Leather, like that
of old shoes, if kept in a warm, moist atmosphere, becomes
covered with mildew. The same is true of carpets and of
woolen or cotton cloth. Such material does not furnish
a very luxuriant growth, the effect being commonly called
mildew instead of molding. At first sight there seems
little similarity between molding and mildew, but the
microscope tells us that mildew is really nothing more
than the growth of certain species of molds that have
not developed very luxuriantly.

Paper is also liable to mold if kept damp, and certain
molds are occasionally found in and upon books. Even
woodwork will sometimes mold, especially in dark, damp
cellars. In short, almost anything in the household which
is of vegetable or animal nature may, under proper circum-
stances, furnish a substratum which can develop a more or
less luxuriant crop of these plants.

RESULTS OF MOLD GROWTH

The effect of mold growth varies with the species of
the mold and also with the material on which it is grow-
ing. Sometimes molds are useful, as for example in the
ripening of Roquefort cheeses. Upon most of our food
products, however, their action is injurious in at least
four directions, (i) They make the food unsightly, for
few people would be willing to use as food any material
upon which a luxuriant growth has made its appearance.
(2) They generally injure the taste of the foods, for a
peculiar flavor is sure to be imparted to any food product
where mold has grown, and after the mold has a luxuriant
growth the flavor of the food is so modified that we are

RESULTS OF MOLD GROWTH

29

usually not willing to eat it. (3) They affect the odor of
food. Mold is always sure in time to develop a peculiar
smell which we generally speak of as ." musty." Musti-
ness, indeed, is commonly nothing more than the odor that
comes from molds. It is due in part to the presence of
the microscopic spores which arise from the mold mass,
and which, breathed into the nostrils, produce the pecul-
iar effect upon the nose which gives rise to the odor. It

is due also in part to ^..^v?:v:v:n^:^---Tr^-. .^...

gases which arise
from the molding
material as the result
of deccmposition. At
all events, mustiness
is always character-
istic of mold growth,
and whenever any
material or any room
smells musty we may
be confident that it

contains growing FlGt T9- A bit of Stilton cheese. The dark
, , ,T, , parts are masses of mold spores.

molds. We may be

sure also that any material capable of molding, if left in
such a musty room, will be sure to show signs of molding
in a short time. (4) In the end the growth of the molds
results in the total ruin of the food, since after a while
mold growth produces decomposition, putrefaction, and
decay. These later changes are due to the fact that the
molds are consuming the material as their own food.
While they use the food for their own purposes they are
producing chemical changes which result in the production

30 BACTERIA, YEASTS, AND MOLDS

of the peculiarly flavored products characteristic of certain
forms of decay, rot, or putrefaction.

It must not be understood, however, that putrefaction
is produced wholly by the action of molds, even in the
materials on which molds are visibly growing ; for another
class of organisms to be considered later, the bacteria, is
more commonly concerned in putrefaction. But molds
contribute largely to the development of putrefaction, and
in the case of some materials, as fruits, molds are prac-
tically the sole cause of this phenomenon.

MOLDS UPON FOOD NOT NECESSARILY UNWHOLESOME

The result of these various changes is that almost all
foods are soon spoiled if molds are allowed to grow upon

them for any considerable
time. They rapidly change
in flavor, odor, and in ap-
pearance, and eventually
the putrefaction or decay
makes them utterly value-
less. If, however, the
molding is checked quickly
and the food preserved from
A bit of Gorgonzola further molding, or if it is
consumed at once, there

is no reason why the food should not be utilized, for the
mold itself is not particularly unwholesome. We may
consume food that has begun to mold without its produ-
cing any ill effects upon us, provided that the molding has
not extended too far and that we do not eat a great quantity

FIG. 20.

USEFUL MOLDS 31

of it. Indeed, Stilton (Fig. 19), Gorgonzola (Fig. 20), and
Roquefort cheeses owe their delicious flavors to molds.
If a large quantity of moldy material is taken at once, it
is possible that a slight poisonous effect may be produced;
but this practically never occurs in the consumption of
moldy food. It is well to remember, therefore, that molds
are not unhealthful. It is not always necessary to throw
away moldy food ; much of it may be used. Moldy
cheese is by no means ruined, for the moldy surface may
be scraped off and the center will be found as good as
ever. Many samples of preserves or jellies which are
beginning to mold may be utilized if we simply stop the
growth of the mold and preserve the food from further
molding. It may be that the mold has developed a slight
musty odor and taste, which would, perhaps, injure the
value of the food from the standpoint of the palate, but
they will not have injured its ease of digestion or its value
as a food.

It is, however, the desire of the housewife to prevent
molding so far as possible, and to check it quickly if it
begins, in order that she may thus preserve the valuable
foods. To understand the methods by which we may best
prevent the growth of mold, or check it if it once begins,
we must next consider the conditions most favorable for
mold growth.

CHAPTER III
CONDITIONS FAVORING MOLD GROWTH

Moisture. The factor of primary importance is water.
A vigorous growth of molds needs an abundance of mois-
ture, and in dry material they will not grow at all. This
moisture may be supplied by the air in which the food is
kept, or by the food itself.

1. Many materials which do not contain in themselves
enough water to support the development of molds will
serve as a fine locality for mold growth, provided they are
kept in a sufficiently damp atmosphere. If the air of a
room becomes damp or "close," as we say, it is almost
certain that molds will begin to grow upon any organic
substance. Thus a large variety of materials in the house-
hold, ordinarily free from molding, may show signs of
mildew during a damp season. The mustiness of a closed
room is due to the presence of molds and is always an
indication of dampness, for dry rooms neither show signs
of mold nor do they smell musty.

2. Some materials contain within themselves sufficient
water to produce a vigorous development of molds quite
independent of the moisture present in the air. Fruits,
for example, are so fulV of water that it makes little differ-
ence to them whether the atmosphere in which they are
kept is dry or saturated with moisture. If the mold once
gets a start, the fruit itself furnishes all necessary water.

32

EFFECT OF MOISTURE 33

The same might be true of other very moist food materials.
But while a majority of food stuffs are liable to mold in
our houses, they are commonly not moist enough to sup-
port mold growth if kept in a moderately dry atmosphere ;
and even in the case of fruit a moist atmosphere is neces-
sary to start the growth.

From these facts it follows that food capable of being
thoroughly dried may be protected absolutely and per-
manently from molding. Various kinds of flour and meal,
although furnishing excellent food for molds, will keep
indefinitely while dry. This statement is an absolute one
with no exception. It must, however, be remembered
that even the driest of foods may become moist in a
damp atmosphere, and that hence the driest material, if
exposed to a moist atmosphere, may in a short time show
the growth of molds. Flour in a flour barrel, dried apples
packed in a box, and dried meat hung in a shed may all
show signs of mold in damp seasons. Molds will start
upon carpets in damp weather, and upon leather boots or
shoes if they are kept in damp closets sufficiently long for
the germination of the mold spores that are floating in
the air. Books in our libraries and clothes stored away
in closets or drawers are not free from molding in damp
weather. Sometimes leather pocketbooks will develop mold
in our pockets, stimulated by the moisture and heat in our
bodies, and will become covered with the well-known mil-
dew. Boxes of cotton cloth shipped for transport may
mold on their journey if the weather is moist. In short,
in damp weather no animal nor vegetable material is free
from the possibility of molding, and dryness is in all cases
an efficient remedy.

34 BACTERIA, YEASTS, AND MOLDS

It is evident that drying may be conveniently used for
preserving cloth, leather, etc. Thorough airing and drying
by exposure to sunlight, followed by brushing, is the cure
for mildew. It is also wjell to remember that soiled clothes
mold much more readily than clean clothes, probably
because the dirt upon the cloth furnishes a little food for
the molds which suits them better than the cloth itself.
Soiled clothing, if packed away and left undisturbed for a
time, is quite likely to be injured by molding.

While moisture is necessary for mold growth, it is true,
on the other hand, that too much moisture is generally
not favorable to molds. Very wet foods, like fresh meat,
milk,. etc., do not commonly mold, although they readily
decay from the action of bacteria.

Stagnation of the Air. Molds grow better in an atmos-
phere where the air is not freely moving, and therefore
are much more vigorous in foods shut up in tight boxes
than in the same foods when currents of air are allowed
to flow over them. The reason for this is not wholly
known. It may be that the agitation of the thread pro-
duced by the currents of air is injurious to the growth of
molds ; but it is more probable that the air currents simply
tend to evaporate the moisture from the surface too rapidly
to allow the growth of molds. Certain it is that a vigor-
ous growth of mold, upon a bit of cheese for example,
will, when exposed to the air, change from a fine, loose,
fluffy mass to a dense, flat, matted layer, and will soon
almost cease to grow. Whether this is due to evapora-
tion of moisture or to some other cause is a matter of no
great practical importance in the house. The/act is borne
out by long experience, that molds grow in closed vessels

EFFECT OF AIR ON MOLD GROWTH 35

much more rapidly than upon open surfaces. As a result
we find that molding is more likely to take place in food
when a number of pieces are piled together in a heap, as,
for instance, several slices of bread or a number of pieces
of fruit. Such a heap furnishes many little recesses
partly surrounded by walls which prevent the free pas-
sage of air currents, and these little nooks furnish a
sheltered place for the mold spores to germinate. If bits
of bread are spread out on the shelf of a damp closet they
will probably not mold at all, while the same pieces would
mold if piled in a heap. Foods with smooth surfaces are,
for the same reason, not so liable to mold as those filled
with little cavities, like bread.

On the other hand, molds require some air, and molding
almost always begins on the surface. Although, as we
have seen, the mold thread can force its way down into
the solid substance of food, it always starts upon some sur-
face exposed to the air. To grow vigorously, the threads
demand an abundance of air, and, as a consequence, will
never grow in the center of solid food masses, or at least,
if they do, they grow there very slowly. After starting
on the surface they may grow for some distance into solid
food substance. In the manufacture of Roquefort cheese
it is desired that molds should start at the center of a hard
cheese mass. To bring this about the growth is stimu-
lated by piercing the cheeses full of holes by means of long
needles, so that air can penetrate to the center. Air is quite
necessary for the formation of the spores, and the fruiting
of the mold practically always occurs upon the free surfaces.
We need not expect any molding in the center of a mass
of food unless some signs of it are visible externally.

36 BACTERIA, YEASTS, AND MOLDS

Darkness. Molds will grow both in light and darkness,
but on the whole they grow somewhat better in darkness
than in light. Indeed, the action of direct sunlight is
injurious to them, and most species of molds fail to grow
upon the surfaces of material exposed to sunlight. As a
result of this we rarely find molds growing upon the free
surfaces of materials exposed to the sunlight or even to
bright light. This is not universally true, but it is the
common experience of housewives to find that materials,
when shut up in dark closets, are very much more liable
to mold than when left in a light room. This is doubtless
due, in part, to the fact that exposure to sunlight, or even
to the air of a light room, evaporates moisture rapidly
and thus checks molding. But it is not wholly due to
this, for light itself appears to be deleterious to mold
growth.

Temperature. Molds require a moderately warm tem-
perature for vigorous growth. At a temperature in the
vicinity of freezing they will not grow at all, and at a few
degrees above freezing their growth is very slight. Some
species of molds, however, grow readily enough at 40°,
growing better at this than at a warmer temperature.
Hence it follows that the temperature of an ice chest will
not wholly prevent molding. Most common molds, how-
ever, either fail to grow at an ice-chest temperature or
grow very slowly. As the temperature increases, how-
ever, the growth becomes more vigorous, and at tem-
peratures varying from 70° to 100° the growth of these
plants is stimulated to their highest activity. A practical
result from these facts is that any material which can be
kept sufficiently cool will fail to show signs of mold, even

EFFECT OF TEMPERATURE 37

though tightly closed in an atmosphere saturated with
moisture and abundantly sown with mold spores. In cold-
storage houses, where the temperature is below freezing,
there is no molding. If the temperature is just above
freezing, molding is almost prevented. The ice chest also,
though much warmer, very decidedly checks the tendency
in most foods to mold. Cheese, for example, after being
cut, should be kept in a closed dish, to prevent its drying
too rapidly ; but it molds rapidly when thus covered. If
the dish be placed in an ordinary refrigerator, it will keep
a long time.

Killing by Heat. In considering the relation of tem-
perature to molds a fact of great importance is that high
heat will always destroy molds and their spores. A tem-
perature considerably below boiling, 150° or 160°, is quite
sufficient to destroy the mycelium of the molds, although
the spores may resist this temperature ; but a temperature
of boiling is necessary to kill the spores. Hence any
food which has begun to mold, and which is of a character
to allow heating, may be protected from the further growth
of the mold by boiling. A temperature somewhat below
boiling will check mold growth, though not actually kill-
ing the spores. This method of treatment will be possible
for many preserves, canned foods, or any food that has
been previously cooked. It may be applied to preserves,
sauces, jellies, mince-meat, and even pickles. It would
not be practicable, however, with foods whose flavor is
destroyed by cooking. Fresh fruit which has begun to
mold cannot be treated in this way without destroying
the original fruit flavor and giving in its place the taste
of fruit preserves or sauce. It is always necessary to

38 BACTERIA, YEASTS, AND MOLDS

remember that after such heating the food is liable again
to receive more mold spores from the air and may there-
fore later show another growth of molds.

Reaction. By reaction is meant the condition of food
as to its acidity. Some foods are acid (lemons, pickles),
while many may have the opposite reaction, called alkaline.

The reaction of food is a matter of considerable impor-
tance in determining its likelihood to mold. It is true that
both alkaline and acid foods may mold, but in general acid
foods mold more readily. Lemons are very acid, and so
are ordinary fruits, all of which mold very quickly. Molds
may even grow upon such strong acid materials as pickles.
Bacteria, the second great agent in producing decay, grow
in alkaline but not commonly in acid foods. Hence it fol-
lows that materials which are most liable to mold are not
likely to support the growth of bacteria, and vice versa.

PRACTICAL SUMMARY

From these general observations it will be seen that
molds will grow best in dark, damp rooms or in corners
of the rooms where there is not free circulation of air ;
they will flourish in heaps of food where many pieces
are massed together ; they will grow vigorously upon food
inclosed in jars or boxes, and they prefer darkness rather
than light.

From all these facts we may reach practical sugges-
tions as to the methods of avoiding the growth of molds,
(i) The most important of all is that food should, so far
as possible, be kept tolerably dry. If it is of a nature that
will stand drying, it may be protected indefinitely if once

PREVENTING MOLD GROWTH 39

dried and not allowed subsequently to become damp.
Indeed, in a pantry or a cellar, molding commonly means
excessive dampness. (2) Foods are more free from mold
if exposed as much as practicable to light rather than if
kept stored in dark boxes. It is of course necessary to
keep some kinds of food in closed boxes in order to pre-
vent them from becoming too dry, but it is useful to expose
such food occasionally to the air and sunlight in order to
check the development of molds that otherwise might
grow. (3) The growth of molds may be almost com-
pletely stopped by lowering the temperature, and there-
fore foods that are particularly liable to mold may be
prevented from molding for a long time if kept in an
ice chest. The temperature of an ice chest is not low
enough to prevent all mold growth, but it is so low that
some species of molds do not grow at all, while others
grow so very slowly that even a material like cheese,
which is quite sure to mold if shut up in the dark at
ordinary temperatures, may be preserved in a dark ice
chest for many days or even weeks without molding suffi-
ciently to do it injury.

CHAPTER IV

THE DECAY OF. FRUIT; USEFUL MOLDS; MOLD
DISEASES

Of all food materials commonly found in the house-
hold none are so much injured by molds as fruits.

Most pears, plums,
and peacJies decay
rapidly; apples,
oranges, and bananas
keep so m e what
longer, but it is a
universal experience
that none of our
ordinary fruits can
be kept for any con-
siderable length of
time without de-

FIG. 21. An apple beginning to decay under :aymg (F!g- 2l).
the action of certain species of molds. Winter apples, with

their solid flesh and

their tough, smooth skin, can be kept for many months
without rotting, and the thick skins of oranges and lemons
protect them a long time. But thin-skinned fruits, like cher-
ries or berries, can be kept only a comparatively few days.
The decay of fruit is by no means always alike, and it is
produced by a variety of causes. If one simply examines

40

THE DECAY OF FRUIT 41

decaying apples, pears, lemons, and bananas, the differ-
ence in the character of the decay is quite evident both
to the eye and to the smell. Bitter rot, black rot, and
brown rot are three types produced by three different
organisms. It is not within the scope of our study to
describe the different kinds of decay which appear in com-
mon fruit. The causes may be numerous, but in the
majority of the examples of decayed fruit the active agency,

FIG. 22. Monilia, a common species of mold causing fruit decay.

at the start at least, is the growth of molds. In later
stages of the decay bacteria may be concerned, but it is
always molds that begin the process. There are a num-
ber of species of molds intimately associated with the
decay of fruits. The common blue mold (Fig. 7) is one
of the most widely distributed, but there are several others
(Figs. 22, 23, 24).

METHOD OF INFECTION AND DISTRIBUTION

To understand the decay of fruit we must first bear in
mind that mold spores are constantly floating in the air,
and that they may also be carried easily upon the feet of
insects that chance to light upon a bit of spore-bearing
mold. By some such agency mold spores are quite sure

BACTERIA, YEASTS, AND MOLDS

to find their way to the skin of any piece of fruit. But
after they fall upon the fruit they will not grow unless
the conditions are right. If the skin is whole and
smooth they do not readily germinate. Commonly they
start at some small crack in -the skin through which the
thread sprouting from the spore can thrust itself into

the softer parts within.
Hence whole-skinned fruits
are easier to keep than those
with bruises. If the spores
find sufficient moisture on the
skin, and a convenient crack,
they soon send a tiny myce-
lium thread into the fruit.
This grows luxuriantly,
branching profusely, and
presently pushes its way in
every direction through the
soft pulp of the fruit. The
fruit begins to soften and
decay. The rotting is caused

fe fc {h Qf ^ mo]d

mation of spores at c and the *

sprouting of spores at a and b. mycelium in the flesh, the

visible decaying spots being

simply the external evidence of the mold growing within.
After a time the mold begins to form its spores. To
do this it generally breaks through the skin so that the
spores may be formed in the air. These spores can easily
be seen in a well-decayed apple (Fig. 25). The spores
thus produced are then scattered into the air from the
broken skin of the fruit. They are carried either by air

F,G.23.

showing the for-

DISTRIBUTION OF SPORES

43

currents or by insects, or, if the pieces of fruit are in
direct contact with each other, as is almost always the
case when packed, one piece of fruit will directly infect
the next and thus start a new center of decay. In this
way decay which begins with a single piece of fruit is

FIG. 24. Another species of Monilia taken from a decaying apple,
showing formation of spores.

sure in a short space of time to extend to the neighbor-
ing pieces. From a single decaying apple, infection may
spread from apple to apple until a whole barrel speedily
becomes decayed and ruined. It is an example of direct
contagion.

A practical suggestion arising from these facts is the
wisdom of removing from the vicinity of sound fruits all

44

BACTERIA, YEASTS, AND MOLDS

that show signs of decay, since decaying fruit will surely
be shedding spores which will infect the sound fruit.
Such fruit, therefore, should not be allowed to remain in
a pantry with other fruit, nor in a cellar. Nor should
it be allowed to accumulate in heaps near the home, for
insects and air currents are sure to distribute the spores.
The removal of all decaying fruit, or its total destruction,
therefore, is a necessary safeguard to protect the sound
fruit that remains.

PROTECTION OF FRUIT FROM DECAY

There is no thoroughly successful remedy for the decay

of fruit. It is true that
fruit may be preserved
absolutely from such de-
cay ; but this can only
be done by the process
of canning, or by some
other method of preserv-
ing which involves oper-
ations totally changing
the character of thefruit.
These we shall consider
in a later chapter. It is

FIG. 25. A small bit of an apple under a not possible by any

microscope, showing the molds breaking known meansto preserve

through the skin to produce spores, and fruit indefinitely from
showing the mycelium running through

the substance of the apple. the attack °f molds and

at the same time to re-
tain its original, natural, fresh condition. Even the hardiest
and toughest of fruits will, in the course of months, begin to

PROTECTING FRUITS FROM DECAY 45

show signs of decay, though some kinds may be preserved
much longer than others. But although it is not possible
to prevent absolutely the growth of molds, it is quite pos-
sible to delay it very materially if proper care is taken of
the fruit. Fruit which would ordinarily keep only a few
weeks may, if properly treated, be kept through the winter
until the spring. Different fruits vary much in their ease
of preservation. Peaches, cherries, and berries can hardly
be preserved at all ; pears only a little longer. Grapes
can be kept a few weeks or longer if special care is taken.
Apples, oranges, and lemons can be kept many weeks or
even months.

Moisture. We have seen that plenty of moisture is a
necessary condition of mold growth. But in considering
the application of this fact to the decaying of fruit we
must remember that the interior of fresh fruit itself is
always moist, containing, indeed, quite sufficient water for
the development of the molds, provided they can once get
through the skin. Hence the decay of fruit goes on
about equally well in moist and in dry air, provided the
molds once get a start, and it cannot be prevented by keep-
ing the fruit dry.

But the moisture which accumulates upon the skin of
the fruit is a most important factor in its tendency to
decay. The mold spores are quite incapable of germinat-
ing unless they are moistened, and any fruit, the skin of
which is kept perfectly dry, is very largely protected
from decay, because the spores get no opportunity for
germinating. If the skin of the fruit can be kept clean
as well as dry, the rotting may be delayed for a very
long time.

46 BACTERIA, YEASTS, AND MOLDS

This is no easy matter, for there are almost sure to be
some depressions in the skin, such as cracks or dents, and
in these moisture is sure to accumulate. The depressions
around the stem or the eye of an apple serve the same
end, and, in damp air, water is so likely to accumulate
here that molding starts readily. Once germinated the
threads quickly force their way into the apple around the
stem and find plenty of moisture in the flesh of the fruit.
Hence any devices which tend to keep the skin of the
fruit dry are at the same time devices for checking the
first steps of decay. Fruit whose skin is wiped frequently
with a dry cloth will keep better than fruit that is not
thus wiped. This question of moisture explains also
why it is that fruits begin to decay first at points where
two pieces come in contact with each other, since here
there is a much better opportunity for moisture to con-
dense. We also learn why fruit which has been cooled
to a very low temperature — as in cold storage — and
subsequently warmed, may decay more quickly than fruit
which has not been cooled. The cold skin of the fruit
taken from cold storage causes a slight condensation of
water, and then when subsequently warmed this water
furnishes a favorable starting point for the germination
of mold spores. This explains also why covering with
sawdust or charcoal is of great value in checking the
decay of fruit. If packed in sawdust, fruit may be pre-
served a long time, because the sawdust absorbs moisture
and prevents the accumulation of water upon the fruit
skin. Charcoal serves the same purpose. For some
fruits, like pears, oat chaff or rye chaff serves better
than sawdust.

VALUE OF CLEAN SKIN 47

This absorption of moisture explains also the efficacy
of one of the best means known for preventing the decay
of fruits. Experience of recent years has shown that the
wrapping of fruits with paper is a more efficient means
of protecting them from the ordinary rot than almost any
device that has ever been adopted. There may be two
reasons for this. Wrapping the fruit with paper protects
it to a considerable extent from mold spores, which would
drop upon the skin from the air if it were not thus pro-
tected. But this is doubtless not the chief reason for
the value of the paper wrapper, since the fruit is almost
sure to be infected with the mold spores while still on the
trees, and certainly before it can be wrapped in the paper.
The paper used is of a soft, porous nature, and, when prop-
erly wrapped around the fruit, absorbs quickly any mois-
ture that may be upon the skin, and prevents moisture from
further condensation.

Clean Skin. The facts mentioned also clearly explain
the value of a smooth skin. Since decay always starts
from spores that lodge on the skin, any method of pre-
venting their lodging or of removing them will protect
the fruit ; hence the wiping of fruit with a clean cloth
will be useful in protecting it from decay. Wiping can-
not, indeed, wholly remove the spores, but it aids materi-
ally. Moreover, if the wiping is done with a dry cloth, it
will also remove the moisture, a matter of no small impor-
tance. Fruit dealers, who have learned by experience how
to handle fruit, understand well that a frequent wiping of
fruit till it is dry and clean is a necessity for its best
preservation. It is sometimes surprising to see in what
fine condition some dealers can keep fruit far into the

48 BACTERIA, YEASTS, AND MOLDS

spring months by the simple devices of low temperature
and clean, dry skins.

Temperature. We have already noticed how effectively
low temperatures check the growth of molds, and this
applies of course to their growth in fruit as well as else-
where. If fruits could be actually frozen, the decay could
be indefinitely prevented. But this is not possible with
common fruit, since the freezing injures its character. All
that can be done, therefore, is to- cool the fruit to as near
the freezing point as possible without actually freezing it.
If the temperature is lowered until the fruit is near to the
freezing point, the growth of the molds may be so delayed
as effectually to prevent the fruit from decaying for very
many months. This can be done readily in the modern
cold-storage plant, and in the last few years fruit growers
have been learning that cold storage furnishes a means
of keeping fruit for the spring market. To be sure the
expense of such storage is a considerable item, but the
extra price that may be received in the spring may more
than make it good. If one has not the opportunity for
cold storage, it is best to keep fruit in cool cellars where
the temperature does not go down to freezing and is toler-
ably constant. The lower the temperature (above freez-
ing) the better. The temperatures of cool cellars are not,
however, low enough to prevent mold growth wholly.
They will not prevent the final decay of the fruit, but
they are very useful in delaying it. When fruits are
removed from such cellars it must be remembered that
they are cold and will condense water rapidly on their
surfaces. They should be wiped dry after being in the
warm air a few hours, or they will decay quickly.

DECAY DUE TO DISEASE

49

ROTTING OF FRUIT DUE TO DISEASES OF THE
FRUIT TREE

In addition to the rotting of fruit due to the growth
of common molds, it is important to know that many
diseases are caused by certain
microorganisms that attack the
plants upon which they are
growing, or attack the fruits
themselves while still growing
upon the fruit trees. These
sometimes produce various
kinds of rots and decay in the
fruit even before it is plucked
(Fig. 26, 27). In some cases the
fruit may appear to be perfectly
sound when picked from the
tree, but it is really already in-
fected with molds which cause
it later to show signs of decay
(Fig. 21). Nearly all of the
diseases in question are caused
by molds somewhat similar to
those we have already con-
sidered, but of different species.
Botanists know a large number
of species of molds which grow upon different fruit trees,
producing diseases of the tree and accompanied by decay
of the fruit. So far as concerns affairs of the household
these imperfections are quite beyond the reach of efficient
remedies. If the fruit which we buy at the market and

FIG. 26. Peaches turned into
a hard mass (mummified) by
the action of fungi.

BACTERIA, YEASTS, AND MOLDS

bring to our houses is already infected with the molds in
question, nothing that we can do will protect it from their
subsequent growth and consequent decay. The only
alleviating remedy is, as mentioned in other cases, to
keep the fruit cool, because none of these microorganisms
grow readily while in low temperatures. Dryness is of
no value, since the molds are already within the fruit,

where there is moisture
enough.

This cause of the de-
cay of fruit is, however,
of no very great signifi-
cance to the ordinary
household, because in a
great majority of cases
the fruits infested with
these troubles will show
some signs of decay be-
fore they reach the mar-
ket. The loss comes

FIG. 27. Peaches decaying on the tree. uPon tne fruit grower,

upon the person who buys

the fruit for storing, or upon the dealer ; rarely will the
decay thus produced be delayed sufficiently for the fruit to
be marketed, sold, and carried away by the customers. The
consumer would not distinguish this from the more com-
mon types of decay. For this reason this species of fruit-
disease, while of great significance to the farmer and to
the one who handles fruits, is of no very great impor-
tance in the ordinary household and need not here be
further considered.

USEFUL MOLDS 51

UTILITY OF MOLDS

We never look upon molds as of any particular utility.
Nevertheless, when we study their relations in nature we
find that they are of the utmost importance. In the pro-
cesses which are going on in nature the molds form a very
important link, aiding in furnishing different kinds of liv-
ing beings with food. The woody part of trees contains
a large amount of material which cannot be used as food
by either plants or animals. Were it not for some agent
which brings this material into condition for subsequent
use by plants and animals, the food material of the world
would in time become stored away in the form of wood,
and the world would materially suffer as the result. But
the tree trunk does not remain a hard, solid mass very
long after it has fallen to the ground. It slowly softens
and decays, until eventually it assumes a condition in
which it can again be used for food by various animals
and plants. Insects, for example, feed upon the decaying
wood until, in time, the tree trunk is all consumed. In
this process a group of fungi similar to molds plays an
important part, for it is a mold-like mycelium growing
through the hard surface of the wood that begins the
softening necessary to make its utilization possible. With
this we are not particularly concerned, for the household
is not usually concerned in the decay of wood. Wood in
the household may occasionally decay, but it is such a rare
circumstance that the housewife pays little attention to it.

Outside of their agency in producing the decay of woods,
molds are of no great utility, so far as we know at the
present time. A few of our food products are, however,

52 BACTERIA, YEASTS, AND MOLDS

benefited by the development of molds. As already
noticed, the peculiar flavor of certain cheeses is due to the
growth of molds. Roqtiefort cheese, by a special device
of the manufacturer, is caused to mold. When cut open
this cheese shows green spots extending through its sub-
stance, and these little green masses are simply the spores
of molds which have developed in the cheese during its
ripening. Stilton cheese, a variety made in England, and
Gorgonzola are also ripened by molds. Camembert cheese,
a type of soft cheese very popular in Europe and begin-
ning to obtain a considerable market in the United States,
is always covered with molds which have developed dur-
ing the ripening of the cheese, and have contributed to
its flavor. Brie cheese is another type whose flavors are
due to molds, and there are several others less well known.

DISEASES OF ANIMALS PRODUCED BY MOLDS

Some species of molds may live a parasitic life. Many
species live as parasites upon plants, sending their myce-
lium into the leaves or stems of the plants, and produ-
cing thus a variety of diseases. With these we are not
concerned in this work. A few molds can live a parasitic
life upon animals, and there are consequently a few animal
diseases produced by molds. The mold diseases of man-
kind are confined to two or three common skin diseases,
which sometimes become quite troublesome.

The most common of these mold diseases in man is
called ringworm, an affection of the skin which produces
open sores. These sores spread in all directions from a
central starting point, and as they spread they heal in

MOLD DISEASES

53

the center, though continuing to spread at the edge, thus
producing a ringlike growth that has given origin to the

FIG. 28. A mold (Trie hop hy ton) which produces ringworm. At a
is a bit of hair with the mold spores on the outside, and at b a
figure of the mold itself highly magnified.

name. The affection is a
troublesome one to heal,
especially when it gets into
the scalp ; but it never pro-
duces any very serious
trouble. Two or three types
of this disease have been
found to be produced by
two or three kinds of molds.
Fig. 28 shows one of the
common species that is the FlG-,29: . T™ pi\ces of ^r 'rom the

scalp infested with a mold (Mtcrospo-

cause of ringworm.

At a

is shown a bit of hair with
the mold fungus and mold
spores growing upon it, and
at b the fungus more highly
magnified. Of the several species of molds that produce
this trouble some are more liable to grow upon the hair

ron) producing ringworm. The upper
figure shows the masses of spores
attached to the outside of the hair;
the lower figure shows the mold
thread lying beneath the spores.

54

BACTERIA, YEASTS, AND MOLDS

and others upon the smooth skin, the latter proving less
troublesome to heal. A second skin disease is favus, some-
times difficult to distinguish from ringworm, although it is
produced by a different species of mold, shown in Fig. 30.
In the case of both of these diseases the affection is
spread by means of mold spores discharged through the

skin. They are liable to be
carried from person to person
by the use of combs or towels,
or even cloths and sponges
used in washing or bathing
the skin. If, therefore, there
is an example of ringworm in
a family, it is imperative, in
order to prevent the spread
of the disease from one to
FIG. 30. A mold (Achorion) pro- another, that the person suf-
ducing a second type of skin fering from the attack should

disease known as favus. At a . . . i i •

.. . , . ... have his own combs, his own

the mycelium is shown, at b the

spores as found on hair. towels, his Own Sponges, and

even his own soap for washing.

By this means the disease can usually be confined to the
person in whom it originally appears. The cure of such
diseases, must be left to a physician.

MOLD-INFECTED ROOMS

Sometimes a room, like a pantry, may become badly
infested with molds, so that all sorts of food become
rapidly infected by them. This is an indication that the
room is filled with mold spores in such numbers that they

MOLD-INFECTED ROOMS 55

drop into everything exposed. The remedy for such con-
dition is to get rid of the spores. The room should be
vigorously swept and dusted, a windy day being chosen,
and all windows and doors should be left wide open to
blow out the dust. After a thorough airing the room
should be closed again and left undisturbed until the
remaining dust settles ; then the floor, shelves, window
sills, etc., should be wiped with a damp cloth. This will
usually remove the spores, and food will subsequently be
less liable to mold.

SECTION II- -YEASTS

CHAPTER V

YEASTS AND THEIR DISTRIBUTION
FERMENTATION

Yeasts are the natural agents which produce the phe-
nomenon called fermentation. This term has several mean-
ings to the scientists, but as the word is commonly used
it refers to a process by which alcoholic liquors are pro-
duced from sugary solutions. Fermentation is therefore
the basis of the various popular beverages known to
civilized as well as to uncivilized races. Fermentation is
also the foundation of another phenomenon apparently
quite different in its character ; for the raising of bread by
yeast is just as truly a fermentation as is the manufacture
of beer.

The essential phenomena of fermentation are the
destruction of sugar and the production from it of two
other substances. The sugar is originally a solid, although
it is very easily dissolved in water. It is a somewhat com-
plex body, but by the action of yeasts it is easily broken
to pieces to form two simpler ones. One of these, alcohol,
is a liquid and remains in solution ; the other, carbon dioxide,
is a gas and usually passes off from the solution in the
form of bubbles (Fig. 31). It is this production of alcohol

56

FERMENTATION

and carbon dioxide that is the foundation of all fermenta-
tive phenomena. Chemists represent the action that takes
place as follows.

(sugar)

(alcohol) (carbon dioxide)

The phenomenon of alcoholic fer-
mentation has been known for many
centuries, traces of such knowledge
being found as far back as we have
any recorded history. Back in the
earliest historical days mankind was
familiar with certain fermented drinks.
At the present time we find that the
phenomena of fermentation are known
by nearly all races of men, and there
is hazily a tribe of savages without
its own kind of fermented drink.
These "stimulating" beverages are ob-
tained from a variety of different
materials by different races. The
juice of grapes has long been used
for the purpose, but various other
fruits serve equally well. The juice
of the palm tree is used by some
races, and sweet juices of various

•gas

FIG. 31. Fermenting so-
lution of molasses,
showing at a the grow-
ing yeast with the bub-
bles of carbon dioxide
arising, and also the
arrangement for con-
ducting the gas under-
neath limewater at b,
for the purpose of de-
termining the nature
of the gas.

other plants are also used. In all
cases the material must contain sugar, or something that
can be converted into sugar ; for it is always sugar which
undergoes the fermentation, no other source of alcohol
being practical for producing intoxicating beverages. In

58 BACTERIA, YEASTS, AND MOLDS

the process of bread making, too, fermentation has been
known almost as long; for we read in literature of
leavened and unleavened bread at least three thousand
years ago.

Although fermentation was thus long known, its cause
remained a mystery until the nineteenth century. The
type of fermentation which we are considering is in all
Ceases produced by essentially the same agency, a group
of plants called yeasts. It is not always the same species
of yeast, for the group includes quite a large number of
different species. The commercial product is simply one
kind that has been cultivated for commercial purposes ;
but there are many others in nature not under cultivation
which may conveniently be called wild yeasts. All of the
kinds are, however, very similar in appearance, have the
same general characters, and are closely related to each
other.

Yeast was discovered about two centuries ago by a
Dutch microscopist, who found fermented liquors filled
with minute bodies, the significance of which he did not
understand. Nor were they really appreciated until about
the third decade of the nineteenth century. At that time
it was quite conclusively demonstrated that these minute
bodies were living organisms, capable of feeding, growing,
and multiplying, and having a very close relation to the
phenomena of fermentation. It was soon shown also
that it was their growth that produced the fermentation,
since this phenomenon would not occur unless these
organisms were not only present but also growing and
multiplying. In our study we must first learn the nature
of the yeast plant.

STRUCTURE OF YEASTS

59

WHAT ARE YEASTS

Yeast plants are always microscopic, no species being
large enough to be seen with the naked eye. When these
tiny plants are massed together, as in a yeast cake, the
mass may form a bulk large enough to be seen. We can
see a yeast cake,
but the individual
yeast plant is not
more than ^ of an
inch in diameter,
and this is far be-
low the power of
the unaided vision.
By the microscope
alone we learn that
the yeast mass is
made up of millions

Of minute bodies, FlG; 32- Common yeast very highly magnified.
. Figs, a and b show vacuoles; c shows a nucleus

each of which is an n inside of the yeast cell; d shows a budding

individual yeast cell with the nucleus dividing ; e shows the cell
r>lant divided, the new cell containing a bit of the

old nucleus.

The yeast plants

are much simpler than the molds. If a bit of a yeast
cake be mixed with a little water and examined under
the microscope, there will be found what is shown in
Fig. 32. There will be seen large numbers of minute
oval bodies, sometimes very nearly spherical or sometimes
considerably longer than broad. They are quite color-
less and nearly transparent, as seen under the micro-
scope, but whitish when seen in bulk. They have a

60 BACTERIA, YEASTS, AND MOLDS

uniform, smooth outline, but inside of them may com-
monly be seen some smaller bodies. There is usually
a somewhat rounded clear spot, as shown in Fig. 32, a>
although in many cases instead of one we find two, three,
or four smaller ones (Fig. 32, b). These apparently rep-
resent only little drops of an oily liquid and have, so far
as we know, nothing very particular to do with the life of
the yeast plant. These drops are called vacucles. No
further bodies can be seen in the yeast cell by ordinary
methods of study, although special microscopic devices
show that there are other bodies inside (Fig. 32, c). These
other smaller bodies need not, however, concern us. The
yeast cell thus described is quite unlike ordinary plants,
showing less resemblance to them than molds. But though
they bear no likeness to what we commonly call plants,
biologists are unanimous in their opinion that they are to
be classed with the molds as colorless plants and, hence,
as fungi.

Yeast exists in three somewhat different states: (i) the
resting state ; (2) the growing state ; (3) the spore-
bearing state. The yeast in an ordinary yeast cake
already described is in the resting state. Such yeast
appears as in Fig. 32, a, each plant being a single oval
body or cell. It is alive but is not actively growing.

The Growing State. When a little resting yeast is
placed in a solution which contains proper material for
food it begins at once to consume the food and grow.
As it grows it multiplies by a method known as budding.
Upon the sides of the yeast plants appear small buds (Fig.
33, a). Each bud at first appears as a little swelling on
the side of the larger yeast cell. This little bud increases

STRUCTURE OF YEASTS

6l

in size until finally it may be as large as the original plant
(Fig. 33, c). Usually by this time, if the growth is vigor-
ous, there may have appeared a second bud. The latter
sometimes arises from the side of the first cell and some-
times from the side of the first bud, giving an appearance
such as is shown at Fig. 33, c. This budding continues,
the little buds appearing one after the other, until there
are produced irregular-shaped groups like those shown at
Fig. 33, d. For a considerable time the cells in these
groups remain attached to each other, so that a little of
the sediment from
a fermenting liquid
will appear under
the microscope as
shown in Fig. 33,^.
After a while, how-
ever, the different
cells drop apart
and may go into
a resting stage, each cell remaining by itself. These
cells are capable of growth and development, either imme-
diately or subsequently, when again placed in a solution
which furnishes them food. This method of multipli-
cation, which is distinctly characteristic of yeasts and
separates them sharply from bacteria, the next group of
plants to be studied, is known as budding. "The yeast
plants are therefore sometimes called the budding fungi.

The Spore-bearing State. Under some conditions yeast
plants produce a different kind of reproductive body known
as spores. If a lot of yeast is placed where it has mois-
ture but insufficient food, it does not grow by the normal

FIG. 33. Growing yeast cells, showing method
of budding and forming groups of cells.

62

BACTERIA, YEASTS, AND MOLDS

FIG. 34.

containing four
spores.

method of budding, but its contents break up into several

parts. In Fig. 34 is shown one of these yeast cells which
has been growing on a porcelain plate
without sufficient nourishment, and it
will be seen that four small bodies
have formed inside of the cell. These
bodies are spores and are capable of
A yeast cell resisting for a long time a variety of
adverse conditions, such as drying,
heating, etc., without being injured.

When the yeast cell breaks, the little spores burst forth

ready to be distributed by the winds or by any other

convenient means.

Not all species of

yeasts are yet

known to produce

spores of this kind,

although it is a

characteristic pos-
sessed by a large

number (Fig. 35).

Botanists divide FlG- 35- Three species of yeast each contain-
ing spores.

yeasts into two

divisions in accordance with their power of producing such
spores. The genus Saccharomyces includes yeasts which
produce spores, while the genus Torula includes those that
do not. The number of spores formed in a single yeast
cell is not always the same, although commonly three or
four. It may not always be the same for the same species
of yeast.

DISTRIBUTION OF YEASTS 63

WHERE YEASTS ARE FOUND

From the facts just mentioned it will readily be under-
stood that yeasts have a wide distribution, even though
they do not grow luxuriantly except in sugar solutions.
The spores are excessively minute and are capable of
being thoroughly dried without injury, in which condition
they will remain alive for months. These spores are
easily blown by the winds and distributed far and wide.
Even the bodies of the yeast cells in their resting stage,
before they have produced spores, may be dried, and for
considerable time suffer no injury. These dry yeast cells
will keep for weeks and sometimes for months without
losing their power of growth. The commercial dried
yeast cake, which will be referred to presently, contains
not yeast spores but simply dried yeast cells. These are
still alive and remain for a long time capable of growing
if placed in proper conditions of food and moisture. Such
dried yeast cells are very light and easily distributed by
currents of air. In such dried form yeast is distributed
in dust by the winds, and may be found almost univer-
sally present over the surface of the earth, except in the
middle of oceans and deserts. Elsewhere the air, the
soil, and the water are practically sure to contain yeast
in greater or less abundance.

Such yeast plants, or yeast spores, blowing around in the
air have sometimes been called wild yeast, a name quite
convenient for distinguishing plants which are indiscrimi-
nately scattered in the air from those which we cultivate in
great masses for purposes of brewing, bread making, etc.

64 BACTERIA, YEASTS, AND MOLDS

Spontaneous Fermentation. These wild yeasts are so
common in the air that they are sure to be present in
most localities, and they fully explain certain phenomena
of fermentation that seem at first sight somewhat puz-
zling. Almost any sugary solution will contain them. If
the juice of an apple is squeezed from the pulp, it forms
a sweet liquid which tastes at first almost exactly like
the apple from which it is taken. But if it is allowed to
stand in a warm place a fermentation begins in it which
rapidly changes its character, pro-
ducing in a few hours what we call
cider. A typical alcoholic fermen-
tation has started, just as truly due
to the growth of yeast as are similar
fermentations in a brewery. Since
the yeast has not been planted con-

FIG. 3^ Wild yeast from Sci°Uslv in the dder> the fermenta-
the juice of an apple, tion must be due to the wild yeasts
which causes the fermen- which find their way into the juice,

tation of cider. either ^^ ^ ^ been squeezed

from the apple pulp or afterwards. The apple has been
growing in the air for many weeks, and the wild yeasts
have had plenty of chances to lodge on its skin. When the
juice is squeezed from the pulp it is sure to contain these
yeasts, and they promptly start a fermentation (Fig. 36).

In a similar way other spontaneously fermented prod-
ucts are made from the juice of various plants or fruits ;
for any sweet juice from such natural sources will be sure
to become inoculated with wild yeast and will consequently
undergo fermentation. This fact has been learned by
almost all people from experience. Most savage tribes

SPONTANEOUS FERMENTATION 65

have learned to make fermented drinks from the juices of
plants or fruits by simply collecting the sweet liquor and
allowing it to stand until it ferments.

These wild yeasts explain another phenomenon occa-
sionally seen in the household. The housewife finds that
some of her preserved fruits or jellies at times undergo
an alcoholic fermentation. This is quite different from
molding or decay, and is found only in sugar-holding
materials. The preserve develops a peculiar, sharp, pun-
gent taste, easily recognized but difficult to describe. It
is particularly liable to occur in jellies, partly because
they contain much sugar and partly because, even when
covered in jelly tumblers, they are still somewhat exposed
to the air and hence are liable to inoculation with wild
yeast. Sometimes this phenomenon is also found in
canned foods that have not been properly protected. It
is not uncommon to find a similar fermentation occurring
in certain types of sugar. Maple sugar which is kept in
the pantry for weeks until it becomes moist, may ferment
and develop the peculiar sour taste characteristic of this
phenomenon. In all such cases the trouble is due to
the presence of the wild yeasts which are floating in
the air and which settle and grow upon any proper food.
These wild yeasts are so sure to be present in the air
that it is very difficult to protect a fermentable material
from their action unless the air is completely excluded.

Such wild yeasts do not, of course, live permanently in
the air, since the air would itself furnish no food for them.
They live and grow in the soil, in decaying fruit on the
ground, on the surface of fruit on the trees, and in a
variety of other 'places. The air simply distributes them.

66 BACTERIA, YEASTS, AND MOLDS

FOOD REQUIRED BY YEAST

All common species of yeast require sugar for food,
and therefore will not grow rapidly unless sugar is pres-
ent in abundance. Bread dough ferments because it con-
tains some sugar. Flour itself contains a large amount
of starch, which is not fermentable ; but in the bread
dough some of the starch is changed to sugar by a chem-
ical process, so that fermentation is possible. Almost all
sugar solutions furnish a proper medium for yeast growth,
provided the solution is not too dense. Yeast cannot live
upon absolutely pure sugar, since it needs certain other
materials for food ; but all natural sugar solutions, such
as molasses, grape juice, etc., contain quite enough other
material for the yeasts to feed upon, and they ferment
readily enough. A high percentage of sugar is injurious
to the growth of yeasts, a fact that explains why almost
anything can be preserved if it is saturated with a large
amount of sugar. (See Preserves, p. 163.)

Food is required for yeasts during the fermentation,
since they are growing and rapidly increasing in abun-
dance. The simple presence of yeasts produces no fer-
mentation. If anything prevents the growth of the yeast
plants, no fermentation occurs, and it is always found that
the yeast increases in bulk during the process. In the
large fermentative industries there is consequently pro-
duced a large quantity of yeast, which accumulates in
bulk at the close of the fermentations.

This material has been mostly a waste product, although
a considerable amount of it has been utilized for bread
raising, as shown in the next chapter. Recently a new

FOOD OF YEAST 67

use for such masses of yeast plant has been suggested.
The yeast mass must contain considerable food material,
and the question has been raised whether it is not pos-
sible to utilize it as a food product. By simple means
extracts of such yeasts have been made and have lately
been placed upon the market. These materials, known
as ovits, wukj and siris, have not yet appeared in America
but are found in the European trade. They have a value
almost the same as that of ordinary beef extracts. They
make an appetizing bouillon which may be a useful stimu-
lant, but since they are only extracts, they contain practi-
cally no real food. They may therefore easily take the
place of such substances as Liebig's beef extract and similar
products, but like them they do not contain real food and
must not be regarded as nutritious.

CHAPTER VI
YEASTS IN THE HOUSEHOLD

As Enemies. Yeast must, in general, be looked upon as
the housewife's friend, since in almost all its relations to
household affairs it produces only desirable results. In a
few instances we find yeast producing trouble. Its occa-
sional presence in jellies and preserves has already been
noticed, as well as in the fermentation of maple sugar.
*• Any sirup containing fruit sugar, cane sugar, or beet
sugar may undergo spontaneous fermentation in our
homes. In dairy products yeasts occasionally produce
mischief, since the bitter tastes of milk and cheese are
sometimes caused by their growth. This will rarely if
ever trouble the housewife, although it may cause mis-
chief for the dairymen. * It is only in the fermentation of
sugary substances, like jellies and sirups, th#t the house-
wife is troubled with undesired fermentation. One prac-
tical suggestion in this connection may be of use. Since
boiling will kill yeasts, any material which shows the easily
recognized sign of fermentation — the peculiar, sharp,
pungent taste — can be preserved from further injury if
it is merely heated to the temperature of boiling. No
further fermentation will then occur, provided the subse-
quent entrance of yeast is prevented by protecting the
material from the air. If the material cannot be heated,
there is no satisfactory remedy for a fermentation once
started.

68

YEASTS A SOURCE OF ALCOHOL 69

As Friends. Yeasts must usually be looked upon as
servants rather than as enemies. They are the allies of
the housewife in a number of directions. We have
noticed above that when they grow in sugar solutions
they give rise to two new substances, carbon dioxide and
alcohol, and in various domestic affairs sometimes the
one, sometimes the other, and sometimes both of these
products are utilized.

THE USE OF YEASTS AS A SOURCE OF ALCOHOL

The alcohol produced by yeasts is the foundation of the
great fermentative and distillery industries, for common
yeasts are the agents which produce the alcohol found in
all alcoholic beverages. The fermentative industries, of
immense extent all over the civilized world, are dependent
upon yeasts. In the manufacture of fermented and dis-
tilled liquors these little plants are used in all cases for
the production of alcohol out of various sugar solutions.
The fermentative industries, therefore, involving the invest-
ment of hundreds of millions of dollars, are founded upon
the growth and powers of these microscopic plants. The
struggle with gigantic evils resulting from these industries
forms one of the greatest problems of civilization. This,
however, is a matter- which does not belong to our
immediate subject.

In breweries and distilleries some material containing
sugar (molasses, preparations from rye, corn, barley, etc.)
is inoculated with a quantity of yeast, a species being-
chosen which experience has shown to be well adapted
to the purpose. The mixture is warmed slightly and a

70 BACTERIA, YEASTS, AND MOLDS

vigorous fermentation is started. The fermented mass
may subsequently be used directly for a beverage — fer-
mented drinks, like beer, ale, etc. — or the water may be
partly separated from the alcohol by distillation, produ-
cing a liquor with a much higher percentage of alcohol, —
the distilled liquors, like rum, brandy, whisky, etc.

In the making of wines the process is, in a way, simpler,
and reliance is usually placed upon the wild yeasts which
produce a spontaneous fermentation. The skin of the
grape becomes the lodging place of numerous micro-
organisms which collect there while the grape is growing.
These include molds and bacteria as well as yeasts, and
when the juice is squeezed from the grape it is certain to
contain some of this wild yeast. Fig. 37 shows some of
the wild yeast thus spontaneously inoculated into grape
juice. The juice is set aside and a spontaneous fermen-
tation begins. The fermentation is not very vigorous and
may require many weeks for its completion. In recent
years some vintners have adopted the plan of adding to
the grape juice cultures of chosen varieties of yeast for
the purpose of hastening the fermentation and making it
more reliable. The success of the plan is still somewhat
doubtful, and this method of wine making has not been
very widely adopted up to the present time.

So sure is the grape juice to contain yeasts that unless
some means of preventing their growth is adopted fer-
mentation cannot be avoided. In making what is called
unfermented grape juice the yeasts are destroyed by heat.
The grape juice is heated to a temperature of about
170° for a few minutes. This operation is usually per-
formed twice, after which the wine is bottled and sealed.

YEASTS A SOURCE OF ALCOHOL 71

The process is really the same as that of preserving
food by canning, which will be described later, the only
essential difference being that the grape juice does not
require boiling for its preservation. It will be noticed
from Fig. 37 that there are other organisms besides
yeasts upon the grape skin. These may have some effect
upon the wine, but very little is known in regard to the
matter.

In the household yeasts are occasionally used in the
same way, solely for the alcohol they develop. This use
is practically confined to the
manufacture of a few of the
homemade wines which are
produced from juices of fruit
such as grapes, elderberries,
blackberries, currants, rasp-
berries, etc. Cider also is an
apple wine. The principles
in the manufacture of these
homemade wines are the FIG. 37. Organisms found upon the

same as in the production of skin of a grape and concerned in
the commercial wines. The the fermentation of wine.

fruit juice, which contains a considerable quantity of easily
fermentable sugar, is expressed from the fruits and mixed
with water. Commonly the fruit juice is not sweet enough,
particularly if a sweet wine is desired. In the manufac-
ture of most homemade wines, therefore, sugar is added.
The amount varies widely with the kind of fruit used,
being greater for sour fruits, and it varies also according
to whether a sweet or sour wine is wanted. The juice is
then left to ferment spontaneously under the influence of

72 BACTERIA, YEASTS, AND MOLDS

wild yeasts. The juice must not, of course, be heated,
for this would kill the yeasts and prevent fermentation.
The fermentation is not very vigorous, and the amount
of alcohol developed not very great. After the fermenta-
tion has about stopped, the wine is placed in bottles or in
closed casks. The time required for fermentation may be
a few weeks (currant wine) or many months (grape wine).
In making cider nothing is necessary except to press the
juice from the apples and allow it to ferment sponta-
neously. Fermentation in any of these cases might be
hastened by the addition of yeast. This is occasionally
done, but is not a common practice.

Whatever be the source of the yeast, the process of
wine making is simply an ordinary fermenting of the
sugar. The carbon dioxide that is produced is allowed to
pass off into the air undisturbed during the fermentation,
and the liquid gradually becomes filled with alcohol. The
final result is the wine, which always contains alcohol in
small percentage. After the yeasts stop growing, bacteria
may develop in the product and cause further changes,
so as to injure its taste, or even totally change its nature,
as in the formation of vinegar. (See Chapter IX.)

Y THE USE OF YEASTS AS A SOURCE OF CARBON
DIOXIDE

The chief use of yeasts in the household is not to pro-
duce fermented drinks but to raise bread. The raising
of bread by means of yeast has been brought to a state of
great perfection, so that the method of producing a desir-
able fermentation in bread dough by means of this product

YEAST AS A SOURCE OF CARBON DIOXIDE 73

is now extremely simple. But it has taken many centuries
of experiment and trial to understand the subject well
enough to bring it under proper control

In all nations, and apparently in all ages, people have
been accustomed to make bread from meals obtained from
the different kinds of grain. The earliest method of cook-
ing such material was simply to mix it with water and
then bake it, the result being a rather hard, tough material
known as unleavened bread.

The next step consisted of a spontaneous raising of the
dough. If dough is left in a warm place for a number of
hours, it becomes somewhat swollen with gas, appears
lighter in character, and when baked produces a type of
bread more easily masticated, better in flavor, and more
easily digested. Flour from most cereals, if mixed with
water and kept for a few hours in a warm place, will
undergo a fermentation, due to the wild yeasts that may
have found entrance to the meal. This method of fer-
menting the dough gave the first form of raised, or leav-
ened bread.

Very early, even before historical records, it was dis-
covered that a little of the dough thus raised would serve
as a starter for a second batch, resulting in a quicker and
more satisfactory raising than that obtained by spontane-
ous fermentation. This was known as leaven, and as far
back as the time of Lot we read of leavened and unleav-
ened bread. The Egyptians also knew of this process.
Leaven has been used from those early days to the pres-
ent time. Even to-day leaven consists of a little dough
which has already fermented and hence contains yeasts,
and which is saved to be used in fresh dough for the

74 BACTERIA, YEASTS, AND MOLDS

purpose of starting fermentation. Although its use has
largely given way to cultivated yeast, it has been employed
in the baking of bread up to very recent times, and to a
limited extent is still used in France. The difficulty
with leaven is that its action is unreliable. The leaven
contains bacteria as well as yeast, and these may make the
bread sour, or sometimes bitter; and unless the very
greatest care is taken in its manipulation the bread pro-
duced by means of it is not good. Only very skillful
bakers can use it satisfactorily. The use of leaven has,
therefore, almost wholly been replaced by the far more
easy and reliable method of raising dough with cultivated
yeasts.

The use of yeast instead of leaven in bread making is
also old. In the time of the Roman empire it is apparent,
from a few references in literature, that the use of yeast
was understood. It is stated that the Romans in baking
their bread sometimes used a leaven made of grape juice
and millet for the purpose of hastening fermentation.
We have already seen that grape juice is sure to contain
yeast, and this phenomenon, whose nature the Romans,
of course, did not understand, is perfectly intelligible
to-day. The Romans were unconsciously using yeast for
raising their bread. The early bakers soon learned to use
yeast in a more accurate and satisfactory manner, and
from the time of Rome down through the centuries the
use of cultivated yeast products for the purpose of raising
bread was more or less common. The methods of pro-
ducing and cultivating yeast during these various ages are
not known at the present time. It is known, however,
that later the use of yeast declined, and bakers returned

METHODS OF OBTAINING YEAST 75

to the old method of using leaven. In the seventeenth
century the use of yeast began again, and from that
time on it has been used more and more widely. As
methods of cultivating yeast developed it became pos-
sible to obtain a more reliable product, and as the relia-
bility of the product increased so did its usefulness in a pro-
portionate degree. At the present time yeast has very
largely taken the place of leaven in baking, because it has
proved easier to handle and more reliable in its results.

METHODS OF OBTAINING YEAST

The original source of all forms of cultivated yeast is
wild yeast, which, as we have seen, may easily be obtained
by exposing any sugary solution to the air. To obtain
such yeast in quantity sufficient for the purposes of house-
hold fermentation, various devices have been practiced.
Some of these, though little* used at present, are instruct-
ive. A very interesting method of obtaining yeast called
"salt raising" was frequently practiced by housewives
before the introduction of compressed yeast. To a quan-
tity of milk was added a little salt, sufficient to delay
the growth of the common bacteria which otherwise
quickly sour it. The milk was then placed in a warm
place for several hours. The yeasts which found entrance
from the air were not injured by the salt, and grew rapidly.
The milk soon began to froth from the carbon dioxide thus
developed. This material was then used to mix with the
dough for the raising. The method here described has
nearly gone out of use, and no study has been made of
the kinds of microorganisms actually concerned in the

76 BACTERIA, YEASTS, AND MOLDS

process, though it probably involved both yeasts and bac-
teria. It is interesting to-day simply because it was a
method of utilizing the wild microorganisms for the pur-
pose for which we now use cultivated yeasts.

Other devices obtained by spontaneous fermentation
have frequently been practiced. Bakers sometimes make
a brew which is allowed to ferment spontaneously, and
use the product for bread raising. In making the Scotch
barms, a brew is prepared containing hops and flour, with
other ingredients, and this, at least in making " virgin
barm," is allowed to ferment spontaneously.

In all such cases yeasts are obtained, but they are
always mixed with bacteria, which may materially inter-
fere with their successful working. The uncertainty of
results due to these impurities has led to cultivating yeasts
especially for household purposes. Cultivated yeasts are
simply wild yeasts from the air which have been freed
from impurities and planted in some pure food material,
where they grow in abundance, giving finally a mass
of pure yeast. Cultivated yeasts are now used almost
universally by all bread makers because of their greater
reliability.

FERMENTING POWER OF DIFFERENT YEASTS

The cultivated yeast used to-day in bread raising has
been gradually selected from a large variety of species.
The microscopist recognizes many different kinds of
yeasts, varying in their microscopic appearance, their
rapidity of growth, and their power of producing fermen-
tation, as well as in other important characteristics. Most

FERMENTING POWER OF DIFFERENT YEASTS 77

of them will raise bread, but some of them are poorly
adapted to this purpose. Some of them, like brewer's
yeast, act so slowly
that the bread will not
rise rapidly enough.
The use of yeast
in bread making is
dependent entirely
upon its fermenta-
tive power, and con-
sequently the value
of any type of yeast
will depend upon
the energy of its
fermentation. Some
types of yeast pro-
duce a more vigor- FIG. 38.
ous fermentation
than others. The
cake of compressed
yeast, for example,
produces a more vig-
or ous fermentation
in bread than either the brewer's yeast or the dried cake.
The relative value of the three types in fermenting flour
is shown in Fig. 38. In each tube was placed a mixture
of flour and water so as to fill completely the closed arm
on the right. Each was then inoculated with a different
yeast, the same quantity in each. As they fermented
the sugar in the flour, the gas given off collected in the
closed arm as shown, and the vigor of the fermentation

Three fermentation tubes inocu-
lated with different varieties of yeast, show-
ing the differences in fermenting power, as
indicated by the amount of gas collected in
the closed tube. The tube on the right was
inoculated with dried yeast, the middle tube
with brewer's yeast, and the left-hand tube
with compressed or distillery yeast.

78 BACTERIA, YEASTS, AND MOLDS

may be inferred from the amount of gas produced. It will
be seen that the tube on the left has in the inclosed arm
a much larger amount of gas than is found in either of
the other samples. This tube was inoculated with a dis-
tillery yeast (compressed yeast), and the experiment shows
that this type of yeast has a greater fermentative power
upon flour than either of the other two forms. It sug-
gests also that this yeast will be the most satisfactory
for the ordinary domestic purpose of bread raising.

There are also other factors concerned in the choice of
a proper species of yeast. Some kinds of yeast give a
sour or otherwise unpleasant taste to bread, and others
give to the bread an undesirable color. From the many
varieties of yeast which might be used for this purpose
certain ones have been chosen by the brewers as par-
ticularly well adapted for their type of fermentation ;
others are commonly used in distilleries. But this does
not necessarily make them the best for bread raising. A
long experience in baking has resulted in the selection
of the type best adapted for bread raising, and this is
a species that grows quickly in dilute sugar solutions
and hence raises the bread in a few hours. At the same
time it gives rise to a pleasant, agreeable taste, and pro-
duces no color. Consideration of all these phenomena
has been clearly essential in selecting a yeast which is
best adapted for bread making.

All of the yeasts used by brewers and distilleries
to-day belong to the same species, and this species is also
the best for bread raising. But although all one species
there are several quite distinct varieties having different
fermenting powers.

DIFFERENT KINDS OF YEAST 79

DIFFERENT KINDS OF COMMERCIAL YEAST
PREPARATIONS

In the early periods of bread making there were no
means of obtaining pure yeast. Gradually, however, we
have learned to cultivate the yeasts by themselves, until
at the present time there are quite a number of methods
for producing tolerably pure masses of yeast. The chief
preparations of this sort are given in the following pages
and all one species, known as Saccharomyces cerevisice ; but
although belonging to one species there are a number of
varieties differing in several characters.

Compressed Yeast. At the present time the yeast most
commonly used by the housekeeper is the compressed
yeast cake. This well-known commercial article consists
of a soft, somewhat soggy material, composed of large
quantities of yeast plants mixed together with a certain
amount of starch and a varying quantity of other material.
This yeast is originally a distillery yeast, which the manu-
facturers of certain alcohol products sow in large vats
containing materials upon which the plant feeds readily.
The yeast grows vigorously and after a time collects as a
scum on the surface of the vat. This is removed, washed,
and the water partly removed ; then the mass is pressed
into cakes and sold to the public.

This compressed yeast is the most convenient and reli-
able type of yeast culture that has been produced. In
the fresh cake nearly all of the yeast plants are alive and
vigorous, and the results obtained from their use are almost
uniformly satisfactory. Compressed yeast has one disad-
vantage : it will not keep long, and hence must be used

80 BACTERIA, YEASTS, AND MOLDS

while fresh or the proper results will be lacking. If the
yeast cake is kept for a day or two only, the plants begin
to die, and after three or four days only a small number
of them may be left alive. Such yeast when a few days
old will not produce as quick a raising of the bread as
the fresh cake. More than this, a result is frequently
experienced in old cakes that is worse than the loss of
activity. The commercial compressed yeast is never a
pure yeast, but contains a variety of other microscopic
plants, among which are bacteria as well as other yeasts.
These other organisms are liable to grow in the cake if
kept for a few days. The yeast may even decay, which
indicates an excessive growth of bacteria ; but if it does
not decay it is quite certain that in an old cake other
kinds of yeast or bacteria are relatively more abundant
than they are in the fresh cake. When such an old
yeast cake is used it may give rise to undesirable fermen-
tations in the bread, resulting in unpleasant flavors. If
it is necessary to keep a compressed yeast cake some
days before using it, it is best preserved by placing it
in cold water and keeping it in an ice chest, but it should
never be allowed to freeze.

Where the compressed yeast cake can be obtained fresh,
however, it is the most convenient form in use. It is so
cheap that the expense need not be considered in the
household, where only a small amount is needed. But
where large quantities of bread are to be made, com-
pressed yeast is somewhat expensive, and it is cheaper
then to brew one's own yeast. Consequently bakers
long adhered to their own methods of making yeast, to
be referred to presently, instead of depending upon the

DIFFERENT KINDS OF YEAST

8l

FIG. 39. Yeast from
a dried yeast cake.

commercial product. For the ordinary housekeeper the
bother of making the yeast brew is so great, the results so
unreliable, and the expense of compressed yeast so slight,
that the latter is now almost universally
used. To-day many bakers have given
up making their own yeast brews and
depend upon compressed yeast.

Dried Yeast. A second type of com-
mercial yeast is the dried yeast cake.
This is prepared by cultivating yeast,
mixing the product with certain ingredients, chiefly starch,
pressing into cakes, and then drying the product at a low
heat. The drying perhaps injures or kills some of the
yeast plants, but a great many of them remain uninjured,
and may be found for a long time in the dried yeast cake,
still alive and capable of growing if placed under proper
conditions (Fig. 39). In order that they may begin to

grow again they must be mois-
tened, and in using a dried yeast
cake it is best to soak it in
warm water to which has been
added a small amount of sugar.
The sugar furnishes food for
the yeast plants, and by soak-
ing them in warm water they
are soon brought to a con-
dition of growth, so that when
added to the bread dough they readily enough produce a
fermentation (Fig. 40).

The dried yeast cakes are not quite so convenient to
use as the compressed, but a little experience will enable

FIG. 40. The same yeast after a
few hours' growth.

82 BACTERIA, YEASTS, AND MOLDS

any one to obtain good results with them. Their great
advantage is that they need not be absolutely fresh. The
cakes may be preserved for many weeks or even months,
and their powers will not be destroyed. They cannot
decay or mold, since they contain no water. It is always
well to remember, in using them, that the drying of the
yeast destroys some of the yeast plants and in time kills
them all. If such a yeast cake is examined week after
week, an increasingly smaller number of living yeast
plants will be found, and finally they will all disappear.
The fresher the cakes are the better, and those that are
very old are useless. But in spite of this fact these dried
yeast cakes may be kept for many weeks, and for persons
who have not a ready access to a market they are much
more convenient than the compressed cakes.

Sometimes yeast is prepared in the form of a dry powder.
It is not a very common form, and the statements made
concerning dried yeast cakes will apply equally well to
yeast powder.

Brewer's Yeast. Yeast has frequently been sold in a
liquid form by brewers to bakers, to be used in raising
bread. Yeast from such a source is different in variety
and action from that of the compressed or dried yeast
cake. It grows in the brewer's fermenting vats, either as
the "top" yeast or the "bottom" yeast. The former
grows as a scum on the top of the vat, while the latter
sinks to the bottom, the former alone being used for bread
raising. The first that appears on the surface of the vat
is commonly removed, since it is liable to be filled with
dirt and harmful bacteria. The flavor of bread raised
with brewery yeast is a little different from that raised by

YEAST BREWS 83

other kinds, and is sometimes slightly bitter, thus explain-
ing the difference sometimes noticed in the flavor of baker's
and homemade bread. This type of yeast does not pro-
duce so vigorous a form of fermentation in flour as com-
pressed yeast, and is less satisfactory in a household. Its
use even by bakers has largely ceased.

Cultivation of Yeast Brews. When one is near a mar-
ket, by far the most convenient method of obtaining yeast
for bread making is to purchase the compressed cake ;
but when one is far from market a fresh supply is not
easily obtained. Moreover, we have noticed that if yeast
is needed in large quantities the compressed yeast is some-
what expensive. It is then certainly cheaper and may
sometimes be more convenient to brew one's own yeast.
Brewing yeast is a very easy process if one will exercise
a little care.

First one prepares a mixture known as the brew, in
which the yeast will grow readily; and then he inoculates
this mixture with a small quantity of yeast from some
good source and allows the material to grow. Many
varieties of mixtures are in use for the development of
yeast. Two good formulae are as follows.

(i) i lb. potatoes (2) l/2 Ib. of malt

l/2 oz. hops y2 oz. of hops

i gal. water i gal. of water

To prepare the first of these mixtures, boil the potatoes
and remove the skins ; boil again until thoroughly soft, and
then mash finely. Meantime the hops are to be heated
with the water to nearly the boiling point for a couple
of hours, to dissolve the hop extract. After this the

84 BACTERIA, YEASTS, AND MOLDS

liquid is to be strained and mixed with the mashed pota-
toes. It is well to boil again for a few moments to
destroy any microscopic organisms (bacteria or molds)
that may have found entrance into the brew during its
preparation. The material is then to be cooled and may
be allowed to ferment spontaneously. But, since the
results are then unreliable, there is usually added to it,
after it is cooled to the temperature of 70° to 80°, a small
quantity of pure yeast from some reliable source. The
whole is to be stirred occasionally and allowed to stand
until the yeast has developed for a few days. The yeast
will then be present in large quantity in the brew, and
can be used for any desirable purpose.

In making the second of the above brews, the process
is nearly the same. The hops are steamed or heated with
the water, as in the first case, and then mixed with the
malt according to the proportions given in the formula.
The subsequent treatment is identical in both cases.

Some such method of preparing yeast was in former
years almost universally used for baking. Brewing yeast
is inexpensive, simply requiring a little care ; but with the
introduction of the convenient compressed yeast at a small
price this method of making yeast has practically disap-
peared from the household. It is still retained, however,
in some places where large quantities of yeast are used.

The hops are added to these brews, not as food for the
yeast, but for two other purposes : (i) They give a slight
nutty flavor which is subsequently imparted to the bread,
somewhat improving its taste. (2) The extract of hops is
a partial antiseptic, in a measure preventing the growth of
bacteria, though not injuriously affecting yeast. Without

YEAST BREWS 85

the hops various mischievous bacteria would be almost
sure to develop in the brew, injuring or perhaps ruining
it. The slimy-bread bacterium, for example (see page 93),
is liable to grow in these brews, but the hop extract has a
decidedly antiseptic power against it.

By a method somewhat similar to the above, breweries
and distilleries cultivate yeast ; but in these large estab-
lishments, where there is a demand for large quantities of
yeast of the highest grade, a care is given to the brewing
impossible in the home. The brewer uses a microscope
to test his product, and exercises a care in cultivating his
yeast which insures its purity. Yeast from such sources
is therefore more reliable than any other, and consequently
most yeast in use to-day comes from breweries or dis-
tilleries, or from institutions where it is grown upon a
large scale. Home brewing of yeast is unreliable and
unsatisfactory.

CHAPTER VII

BREAD RAISING; FERMENTED LIQUORS
WHAT is BREAD RAISING?

The method by which yeast makes bread light is very
simple and easily understood. There is present in the

bread dough, at the start, a
small amount of sugar which
comes from the flour; but
there is, in addition, a con-
siderable quantity of starch,
and with the starch there is
also present in the flour a
small amount of a material
known as diastase. By the
action of this diastase in
the dough, part of the starch
is converted into sugar.
Thus there is present in
the dough, after it is mixed,
a sufficient quantity of sugar

FIG. 41. Recently mixed dough in-
oculated with yeast, but before
the yeast has grown.

to furnish proper ferment-
able material for the yeast.

The baker mixes the fresh, active yeast with the dough,
and places the whole in a warm place where the yeast
will be stimulated into active growth (Fig. 41).

86

WHAT IS BREAD RAISING

The yeast begins to feed upon the materials in the
dough and ferments the sugar, producing carbon dioxide
and alcohol. Both of these materials remain for a while
in the dough, the alcohol dissolving in the water, and the
carbon dioxide accumulating as a gas in small bubbles.
The dough is so sticky and heavy that it is not possible
for these bubbles to rise up
through the dough as it does
in ordinary fermented liquids
(Fig. 31). The gas, there-
fore, simply collects as small
bubbles in the midst of the
dough, causing the dough
to swell. This is the so-
called raising of the bread,
and the bread maker must
learn from experience when
it has progressed suffi-
ciently. After the dough
has been properly " raised " FlG. 42. The same dough after

by the yeast, it may be yeast has grown and caused the

seen to be filled with holes
occupied by the gas bub-
bles (Fig. 42). Now, after the proper kneading, it is put
in the oven for baking. The heat of baking drives off
the small amount of alcohol which is contained in the
bread. The heat also expands the bubbles of gas so as
to enlarge the little holes in the dough, thus causing
it to swell still more ; but while this is being done
the heat hardens the dough into the firm texture of the
baked bread, and the holes previously occupied by the

dough to swell up by the accumu-
lation of carbon dioxide.

88

BACTERIA, YEASTS, AND MOLDS

carbon dioxide gas are left as pores in the bread (Fig. 43).
This makes the bread light and porous, and gives it the
character that every one is familiar with in properly raised
bread. If it were not for these holes, the dough would
be a hard, tough mass, difficult to bake and more difficult

to digest.

The purposes of the

raising of bread by yeast

are three.

1. It makes the ma-
terial Lighter, i.e. more
porous, and hence easier
of mastication and more
palatable.

2. It renders it more di-
gestible, because the por-
ous material is more easily

FIG. 43. The same material after bak- acted Upon by the digest-
ing, showing the cavities left after iye jukes than the mQre
the carbon dioxide is expelled.

solid unleavened bread.

3. The yeast imparts a certain flavor to the bread
which enhances its value. This flavor, due to yeast, is
well shown by the difference in the flavor of bread raised
in the ordinary household and that sometimes raised by
bakers, where a different species of yeast is used.

That the flavor produced -by yeast is an important
factor may be realized also by comparing the flavor of
bread raised by yeast with that made light by chemical
or mechanical means. Any process which will fill the
dough with bubbles will make it light. In one type of
bread, known as aerated bread, the spaces or cavities in

* ' *I

""•?

-*••-*.- ;-&

RELATION OF BREAD RAISING TO TEMPERATURE 89

the dough are produced by mechanically mixing air with
the dough. The result is a bread that is light enough
but lacks the peculiar flavor present in ordinary raised
bread. In another type of bread (qtdck biscuits] chemical
means are relied upon to produce the gas. A small quan-
tity of cream of tartar and saleratus is mixed with the
dough. These two materials act upon each other chem-
ically and give rise to a quantity of carbon dioxide gas,
which appears very quickly, and rapidly fills the dough
with bubbles of gas. The dough> when subsequently
baked, is light, but has a flavor quite different from that
which would be produced in the same dough if it were
raised by the action of yeast. No other method of pro-
ducing lightness in the dough gives quite so good flavors
as can be obtained by the use of yeast, and none is thought
to make bread quite so easy of digestion.

RELATION TO TEMPERATURE

The growth of yeast, and hence the raising of bread, is
very closely dependent upon temperature. Yeasts grow
readily in warm temperatures, less readily in low tempera-
tures, and not at all if the temperature is in the vicinity
of freezing. Common yeast grows best if kept between
75° and 90° F. At higher temperatures the yeast does
not produce such good results, since certain other injurious
microorganisms (bacteria} are then likely to grow. If
the dough is kept at a temperature above 90°, there is
almost sure to be trouble from the growth of undesired
organisms which give rise to unpleasant flavors. Bread
made from such dough is very apt to be sour. The

90 BACTERIA, YEASTS, AND MOLDS

temperature should be higher in winter than in sum-
mer, owing partly to the fact that flour in winter is
quite sure to be cold and to require some time to become
warm. In winter a temperature of 95° is not too great
for the proper raising of the dough, while in summer a
temperature of 70° is more satisfactory. In the raising
of bread dough it is always far better to use a ther-
mometer and to determine the exact temperature. This
is rarely done in the ordinary kitchen. It is more com-
mon to place the dough near the stove and trust that
the temperature will be close enough to that desired.
It is not possible, under these circumstances, to depend
absolutely upon the results. In the majority of cases
the dough is fermented satisfactorily, but bad batches
of bread from this cause are a frequent experience of
the housewife. To produce uniform results it is quite
necessary to use a thermometer, and then the dough may
surely be kept within the limits of temperature above
mentioned.

The length of time for yeast to grow in the dough before
baking is dependent upon the temperature of the fermen-
tation ; but it is important that it should not be too long.
If the temperature is low (below 70°), so that it requires
a longer time than usual for the dough to rise sufficiently,
the texture of the bread is apt to be crumbly and brittle,
and a sour taste is very likely to develop, due to the
growth of other microorganisms besides the yeast. If,
on the other hand, the bread rises too quickly, owing to
too high a temperature, an abundance of gas is produced
which makes the dough rise rapidly; but the bread will
be inferior in flavor, texture, and color. The best results

IMPURITIES IN COMMERCIAL YEAST 91

are obtained by a moderately active growth of the yeast,
which will produce a sufficient amount of lightness in the
dough in the course of eight or ten hours.

IMPURITIES IN COMMERCIAL YEAST

One factor largely determining the value of commercial
yeast is its purity. It rarely or never happens that a
yeast cake, or yeast culture of any form, is composed
purely of yeast. There is almost certain to be mixed with
it a quantity of bacteria. Frequently there is also pres-
ent a variety of mold spores, and the yeast cake is also
likely to contain other species of yeast besides the one
desired for bread raising. These impurities maybe abun-
dant or scanty in any cake of yeast. If they are present
at all, they may produce trouble, but this will depend upon
circumstances. The yeast plants themselves are present
in such overwhelming proportions that, under ordinary cir-
cumstances, the impurities get little opportunity to develop.
If the raising is conducted at a proper temperature, the
impurities will rarely do much injury. In the common
use of yeast, therefore, in spite of the fact that various
bacteria and mold spores may be mixed with the dough
when the yeast is added, the bread rises in a normal way,
and the impurities produce no trouble.

These foreign bacteria in the yeast cake are quite sure
to increase with its age. While the yeast plants do not
multiply in the compressed yeast cake, the bacteria are
almost sure to do so, especially if the cake is kept in a
moist condition for some days before using. An old yeast
cake is therefore quite sure to contain more of these

92 BACTERIA, YEASTS, AND MOLDS

impurities than a fresh one. Moreover, in an old cake,
as we have seen, the number of living yeast cells is less
than in a fresh one, and so the undesirable germs have a
better chance to grow in the dough. The use of an old
yeast cake is therefore unwise, since the bread may thus
be ruined. The fermentation does not progress rapidly
enough, the bread must be kept longer at a warm tem-
perature, and during this whole period the other yeasts or
bacteria have a chance to develop and produce a variety
of bad flavors. If one uses fresh yeast cakes, there is little
probability that any trouble will arise from the action of the
smaller number of bacteria or molds that may be present.
Sour Bread. The impurities from the yeast or from
some other source do, however, occasionally produce
trouble, two types of which are so common as to demand
notice. The raising of dough by means of yeast some-
times causes it to become sour. The dough rises in the
proper manner apparently, but the bread when baked is
found to have an unpleasant, sour taste. This is espe-
cially likely to happen if the bread is raised too long.
By some this sour taste is regarded as an improvement to
the flavor. It is due to the development, during the fer-
mentation, of certain acids in the dough, which come, not
from the action of yeasts, but from the growth of bacteria
that are present either in the yeast or flour. It has been
a disputed question whether the acid produced is lac-
tic, acetic, or butyric. (Lactic acid is like that formed in
sour milk, acetic acid is formed in vinegar, and butyric
acid is the acid found in old rancid butter.) It is fre-
quently a mixture of all three, but ordinarily it is prob-
ably mostly lactic acid. Each of these acids is known

SOUR BREAD 93

to be produced by bacteria. Since the acids are caused
by bacteria, this subject really belongs to a later division
of our discussion ; but its close relation to bread making
leads to its introduction at this point.

Recognizing that the cause of sour bread is due to
the growth of bacteria, it is not difficult to suggest the
proper means of avoiding it. Fresh yeasts only should
be employed. A good quality of flour should be used, and
the dough should be mixed in clean utensils. After mix-
ing, the dough should be placed in a clean dish at a proper
temperature (75° in summer, 90° in winter), so that the
bread will rise in about eight hours. Dough should never
be allowed to ferment too long. Strict attention to these
details will commonly remove the trouble.

The bacteria which produce sour bread do not, however,
come wholly from the use of impure yeasts, for the flour
itself is likely to contain some organisms which may cause
this trouble. A sour taste is much more likely to be
found in bread made from poor grades of flour than in
that made from the higher grades. This is perhaps due
to the fact that, owing to difference in the method of
manufacture, the lower grades of flour contain a larger
number of bacteria. The same trouble is also sometimes
caused by the use of unclean utensils in the mixing of the
dough, or by leaving the dough to rise in a dish not thor-
oughly washed. Unclean utensils are sure to have a large
number of bacteria attached to them, and these bacteria,
becoming mixed with the dough, grow there readily side
by side with the yeast.

Slimy Bread. In recent years it has been noticed that,
a few hours after baking, bread sometimes becomes slimy.

94 BACTERIA, YEASTS, AND MOLDS

When perfectly fresh it does not show any sliminess, but
after standing a few hours the inside of the loaf appears
more or less moist, and shows a slimy texture when broken,
looking as if permeated with cobwebs. This trouble is
occasionally met with in the household, but more commonly
in bakeries. Indeed, sometimes sliminess has become so
troublesome in certain bake shops as nearly to ruin the
business, the trouble reappearing day after day and prov-
ing extremely difficult to remedy.

The cause of the trouble is known to be the develop-
ment of certain bacteria, one species of which is shown in
Fig. 44. These bacteria are capable
of growing in the dough, and are
not killed during the baking. After
the bread is removed from the oven
they begin a rapid growth, if the
bread is kept warm, and in a few
hours produce the trouble de-
FIG. 44. A species of bac- scribed These bacteria frequently

tenum which produces *

slimy bread. come from the yeast, but in some

cases, where the subject has been

studied in detail, it has appeared that the source is the
flour rather than the yeast. Certain samples of flour con-
tain these mischievous organisms, and when bread is made
from such flour it is difficult to avoid their presence and
growth. A change to a new brand of flour will then
obviate the trouble. If a housewife should experience
this slimy bread fermentation, the proper method of pro-
cedure is (i) to use a new brand of flour for bread mak-
ing, (2) to sterilize, by methods to be referred to later,
all utensils that are used in connection with bread making,

ALCOHOL AND CARBON DIOXIDE 95

and (3) to get a fresh supply of yeast. After this the
trouble ought to disappear. It is also important to
remember that the sliminess only occurs if the bread is
kept warm, and hence chiefly in the summer. If the
bread is cooled at once and kept in a cool place until it is
eaten, the trouble is not likely to manifest itself even
though the slimy bacteria are present. The bread is
wholesome enough even though slimy.

THE UTILIZATION OF BOTH ALCOHOL AND CARBON
DIOXIDE

In the immense fermentation industries involving the
production of beers, porters, ales, etc., both of the products
of fermentation are commonly utilized. The general char-
acter and effect of beer are due partly to the alcohol pres-
ent and partly to the presence of a quantity of the car-
bon dioxide, which gives to the beer its sparkle. In the
manufacture of such a product the fermentable material,
usually some form of grain, is inoculated with a large
quantity of a vigorous yeast, a species being chosen that
has been found by experience to produce the desired
results. A fermentation starts up which progresses rap-
idly if the temperature is kept warm, as it is in the man-
ufacture of common beer. The fermentation lasts a few
days. If the temperature is low, as in the production of
the so-called lager beer, the fermentation lasts many weeks.
During this fermentation alcohol accumulates in the liquid,
and the carbon dioxide gas escapes into the air, forming
a froth in the fermenting vat. The yeast increases in
amount, and either collects on the surface or sinks to

96 BACTERIA, YEASTS, AND MOLDS

the bottom. Most of the yeast is then removed, and
the liquid stored in casks or bottles. Here the fermen-
tation continues for a time, but rather slowly. Since the
vessels are closed the carbon dioxide gas cannot escape,
but, accumulating in the vessel, is partly dissolved in the
liquid itself. The gas exerts considerable pressure inside
the bottle or cask, and when it is opened the expansion
of the gas gives rise to the popping of the corks and the
bubbling and frothing of the beer ; in other words, to the
sparkle. Beers are usually drunken while they are toler-
ably fresh, and sometimes before fermentation has wholly
ceased, though some types of beer are kept for months.
In all such fermented products the carbon dioxide is
desired no less than the alcohol, since it contributes
materially to the flavor of the product. In the production
of sparkling wines a similar effect is produced by a sec-
ondary fermentation, forming carbon dioxide in the wine
after it is placed in the bottles (Fig. 45, b).

For those interested simply in home problems the fer-
mentation of beers is of little importance. It is carried
on chiefly in the great breweries, where beer is made on a
large scale, but only to a very limited extent in the house-
hold itself. It has been, however, a somewhat common
procedure in certain households to make homemade beer
on a small scale. In previous years this was made from
certain roots and extracts of strongly flavored plants.
For example : home beers have been made from a mixture
of molasses and hops flavored with spruce extract ; or
sugar and ginger with lemon for flavor ; or a mixture of
sugar, crushed raisins, and lemon; but to-day highly
flavored extracts are purchasable at stores for a small

BREAD RAISING; FERMENTED LIQUORS 97

price. These flavoring extracts are mixed at home with
a quantity of sugar and water (two pounds sugar to ten
quarts water). To the mixture is added a considerable
amount of yeast (one cake for the above quantity), and the
whole material, closed in bottles or other vessels, is then
set aside in a
warm place for
fermentation.
The fermenta-
tion goes on
rapidly, and in
the course of a
couple of days
a beverage is
produced, rilled
with carbon di-
oxide, which
causes a bub-
bling and froth-
ing when the
vessel is opened,

and containing FIG. 45. Miscellaneous species of yeast.

a Small quantity a, S. cerevisice; b, S. pastorianus /, from wine; c, S. pastoria-
c i i-i T>I_ nus HI > d> S- ellipsoideus II; e, S. cerevisice, from beer;

of alcohol. The ^ s apiculatus. ^ s. minor,
amount of alco-
hol in such beverages is small if the fermentation is not
kept up too long ; but in old homemade beer the alcohol
may be considerable.

Such home-brewed beer has come to be somewhat
extensively used in recent years. In its manufacture it
must be remembered that the fermentation, which results

98 BACTERIA, YEASTS, AND MOLDS

in the production of carbon dioxide and alcohol, is due to
the action of the yeast upon the sugar and not to the
beer extract. The extract is added in these cases chiefly
to produce a peculiar flavor in the product, which renders
it palatable. The commercial beer extracts simply give a
pungent taste and perhaps stimulate the growth of the
yeast ; but it is the fermentation of the sugar that causes
the sparkle due to the carbon dioxide, and any sugary
solution will ferment in a similar way if yeast is added.
The product is not palatable, however, unless something
is present to give it a flavor. The only reason why such
homemade beers are less intoxicating than commercial
beers is because the fermentation is allowed to continue
but a short time, long enough to produce an abundance
of carbon dioxide but only a little alcohol.

Fermented Milk. A mild fermented beverage is occa-
sionally made from milk by means of a yeast. It is called
kumiss, and is regarded as useful for invalids, since it
is supposed to be more easy of digestion than raw milk.
Its preparation is as follows. Into a quantity of milk is
placed a little common sugar, — from four to eight table-
spoonfuls to a gallon of milk, — and yeast is added just as in
homemade beer, one fourth of a cake of compressed yeast
in a little water being sufficient for a gallon of milk. The
mixture is put in a warm place and fermentation sets in.
After twenty-four hours' fermentation the material is
bottled and placed on ice ; when cool it is ready for use.
The milk becomes slightly soured, giving a taste much
relished by some people. It is filled with carbonic diox-
ide and contains a small amount of alcohol, and is thus a
sort of beer made from milk. It is not much used in this

BREAD RAISING; FERMENTED LIQUORS 99

country except for invalids. Other types of fermented
beverages, kefir, mazoon, and some others, are made from
milk by the use of special ferments, always containing
yeast, but whose preparation is hardly within the reach
of the ordinary household.

SECTION III — BACTERIA

CHAPTER VIII
THE GENERAL NATURE OF BACTERIA

Our study of bacteria must be more extended than that
which we have given to either molds or yeasts. While
molds and yeasts are of significance in the household, the
action of bacteria is much more fundamental and universal.

i/ Bacteria are far smaller
than yeasts or molds
(Fig. 46). They are com-
monly unknown to the
housewife even by name,
and rarely does she under-
stand that they have any

FIG. 46. Showing the comparative size relation to household
of molds (a), yeast (b and c], and bac-
teria (d) economy, or concern her

very closely. Few have

ever seen them or been aware of their existence. Never-
theless they are so constantly at work upon all kinds of
food products in the pantry, that the affairs of the house-
hold are in a state of more or less constant warfare against
these invisible, unrecognized, and unknown foes. They
are more serious enemies than molds or yeasts. Chiefly
to their presence and activity is due the fact that the
preservation of foods, even for a few days, is frequently

100

STRUCTURE OF BACTERIA IOI

difficult, while special devices are required to preserve
food indefinitely.

To the housewife bacteria are of little value and are
foes, like the molds, rather than allies, like the yeasts.
This does not mean that they have no utility. On the
contrary, they are of the most fundamental importance in
nature, and it is no exaggeration to say that the very con-
tinuation of life is dependent upon their activity. To the
agriculturist
they are abso-
lutely essen-
tial. They
are the dairy-
man's close FIG. 47. Comparative size of the point of the finest
allies and cambric needle (£), a particle of dust (a), and bac-
teria (c).

they are in-
dispensable friends of many industries. By their action
are produced some of the articles for our tables (vinegar)
and also the flavor of butter and cheese. However, these
phenomena do- not directly concern the housewife, and,
with a few individual exceptions, bacteria are her foes.

STRUCTURE OF BACTERIA

Size. Bacteria are much smaller than yeasts, and only
the high powers of the microscope can disclose their
presence (Fig. 47). Many are not more than a fifty
thousandth of an inch in diameter, and even the larger
ones are not much more than a ten thousandth of an
inch. But bacteria are far more abundant in nature than
yeasts. They are present in great numbers in the earth,

102 BACTERIA, YEASTS, AND MOLDS

the air, and the water, and are sure to find their way into
every kind of food or anything else that may be exposed
to the air. They are also much more troublesome than
molds for two reasons : (i) they multiply with a rapidity
that is quite inconceivable; (2) they are quite invisible
to the naked eye, and their presence is not suspected
until they become numerous enough to produce undesired
changes in the material upon which they are growing.
As a result they present a vast number of problems to
the housewife, which she has dimly seen for years, but
for which science has only in the last few years begun to
offer solutions. They are much more difficult to handle
than either molds or yeasts, because they are smaller,
more numerous, and more vigorous, and for these reasons
it is almost impossible to exterminate them. It is an
impossibility to free a pantry from bacteria and very diffi-
cult to guard food from their action.

Shape. Bacteria are very simple, and there are such
slight differences between the various kinds that in many
cases it is quite impossible by microscopic study to dis-
tinguish one species from another. The bacteriologist
knows to-day that many bacteria which when studied under
the microscope appear absolutely identical, are totally
unlike in their general characters. It frequently happens
that perfectly harmless bacteria cannot by ordinary micro-
scopic study be distinguished from those that are very harm-
ful. For example, the bacillus which produces typhoid fever
cannot be distinguished microscopically from another com-
mon but harmless species found in water. For this reason
the microscopic study of these plants gives only a small
part of the facts that we need to know in regard to them.

CLASSIFICATION OF BACTERIA 103

Classification. A consideration of the classification of
bacteria is quite unnecessary for the purpose of our work,
inasmuch as they are so minute that no one without the
aid of a powerful microscope will ever be likely to see
these organisms. Their activities are seen on all sides,
but the organisms themselves are totally below the reach
of our vision. It is sufficient, therefore, to give a few
facts concerning their general appearance.

Bacteria are the simplest organisms known. They are
far simpler than molds and even simpler than yeasts. So
minute are they, and so simple in their structure, that
very little is known in regard to them at the present time
except their general external appearance. They are uni-
versally regarded as plants, although many of them are
endowed with a power of motion and for this reason might
readily be mistaken for animals. Biologists have learned,
however, that many plants can move, and they are univer-
sally agreed that bacteria must be classed with plants
rather than animals.

Flagella. The fact that many bacteria are endowed
with the power of motion suggests that they must have
locomotive organs, and these, indeed, are easily seen by
proper microscopic study. They consist of minute hairs
which project from the body of the bacteria. Sometimes
there is a single one from one end, sometimes they occur
in tufts, and occasionally they may be scattered all over
the bodies of the bacteria as shown in Fig. 48. These
little hairs are capable of waving to and fro, and by this
motion they drive the bacteria through the water. Not
all bacteria possess such locomotive organs, and one
means by which scientists classify these organisms is by

104

BACTERIA, YEASTS, AND MOLDS

the presence or absence of these motor hairs. They

are known by the name of flagella.

Spherical Bacteria: Cocci.
The simplest type of bac-
teria consists of those that
are in the shape of a minute
sphere. Their size differs
somewhat, but they are
always extremely minute, and
about all that can be said in
regard to them is that they
are spherical organisms,
sometimes possessing flagella
and sometimes apparently

FIG. 48. Cocci, bacilli, and bac- without them. No internal
teria. a (Coccus), b and c (Badi- structure is known. They

/us), show flagella ; d(Bacterium) multiply sometimes in SUCh

**»

has no flagella.

a way as Q OQ
°

to produce long chains (Fig. 49, a),

sometimes so as to produce groups of a(

fours or groups of eight or sixteen ^^

(Fig. 49, b, c, d). The general name fcp

given to spherical bacteria is coccus, and

to this name are sometimes prefixed FlG" 49' Cocci>show-

ing methods of mul-

certam other syllables to indicate certain tiplication. a, strep-
characters. Streptococcus is a name tococcus; b, Micro-
given to cocci forming chains (Fig. 49,
a), and Micrococcns to those forming
fours or irregular masses as at b. The term Sarcina is
the name given to those that form solid masses such as
shown in Fig. 49, c and d.

coccus; c and
Sarcina.

CLASSIFICATION OF BACTERIA

105

Rod-shaped bac-
teria.

Rod-shaped Bacteria. These are in the shape of rods
of greater or less length. They are usually somewhat
rounded at the ends and may be only a little longer than
they are broad, or they may be Q
very many times as long as broad
(Fig. 50). When one of these grows
it lengthens and commonly soon
divides into two, but they may con-
tinue to lengthen for a time without FIG. 50.
manifesting any signs of division.
In such a case they form long slender threads, as shown
in Fig. 50, b. These threads, however, eventually break
up -into short sections (Fig. 50, c). Some of these rod-
shaped bacteria have flagella and are capable of active
motion, in which case they form the species of Bacillus
(Fig 48, c) ; others have no flagella and are quite with-
out the power of motion, in which case they constitute the
species Bacterium (Fig. 48, d).

Spiral Bacteria. A third type of bacteria is in the form
of a spiral rod, shown in Fig. 51. These, however, are
somewhat uncommon and of less
importance than the others. Like
the other forms they may possess
flagella or they may be without
them.

Multiplication. The growth and
multiplication of bacteria is ex-
tremely simple and consists in a
lengthening of the individual followed by its division. A
sphere becomes slightly oval in shape and then divides in
the middle to produce two spheres, as shown in Fig. 52, a.

FIG. 51. Spiral bacteria.

io6

BACTERIA, YEASTS, AND MOLDS

OOCDOO

One of the rod-shaped forms lengthens itself and divides
in the middle and produces two individuals, each of which
again lengthens and divides (Fig. 52, b). The same method
is found in the spiral bacteria. This manner of division,
which is characteristic of all bacteria, will be seen to be
quite different from the method we have already noticed
in the yeasts. Indeed, the distinction between yeasts and
bacteria is based upon this method of multiplication. The

method of multi-
plication in bac-
teria is known as
fission, and this
group of fungi are
called fission fungi
in distinction
from the yeasts,
which are called
budding fungi. The
difference between
these two classes
can be distin-

FIG. 52. Showing the method of multiplication
by fission, a, a coccus form ; 6, a short rod ;
c, d, and e, showing the method of growth into
long chains and the consequent breaking into
sections.

guished only by careful microscopic study, but it is the
scientific distinction between the two groups.

Spore Formation. Under some circumstances bacteria
have a different method of multiplication. Inside of the
body of a single individual bacterium appears a little
rounded mass which is known as a spore (Fig. 53). This
spore may be broader than the rod which produced it,
or it may be narrower ; but it finally breaks out, the
bacterium itself disappearing and the spore then coming
out freely in the medium in which it lives. These

GROWTH OF BACTERIA

107

spores are capable of subsequently germinating into
new individuals like those that produced them and thus
continuing the race (Fig. 53, b}.

Not all bacteria produce spores, and the question
whether any species of bacteria forms spores is a matter
of most extreme significance in connection with its func-
tions ; for these spores are covered by a little shell which
is hard and tough and capable of
resisting various adverse condi-
tions. Spore-bearing bacteria
may be dried without injury, for
their spores protect them from
destruction. They may be heated
to a high temperature, even to
boiling, without being killed.
Thus the presence of spores will
make a great difference in the
ease with which any material can
be sterilized by heat. Bacteria

FIG. 53. Showing the forma-
tion of spores. At a is a
free spore and at b a germi-
nating spore.

not capable of producing spores are very easily killed by
heat, while the spore-bearing forms are destroyed with
much greater difficulty.

GROWTH OF BACTERIA

Rapidity of Growth. The most striking fact in regard
to bacteria is their wonderful rapidity of multiplication ;
for upon this are dependent their extraordinary powers.
Bacteria growth and multiplication mean the same thing,
and the rapidity with which they can multiply is almost
inconceivable. Certain kinds of common bacteria can

108 BACTERIA, YEASTS AND MOLDS

reproduce themselves once every half hour, the result of
which is that a single bacterium will have become two in
a half hour, four in an hour, eight in an hour and a half,
and so on. This increase of progeny by geometrical pro-
gression results in the production of descendants with
immense rapidity. If the rate of multiplying above men-
tioned should continue for twelve hours, the result would
be the production of about seventeen million offspring.
Such a rapid production as this does not continue very
long, through lack of food and other adverse conditions.
If it did, the world would soon become filled with bacteria,
crowding everything else out of existence.

Recognizing that they have this wonderful power of
multiplication, we can readily see that bacteria represent
a force in nature of almost inconceivable magnitude.
This rate of growth is a possibility for a while at least,
and in order that such a multiplication should continue
it is only necessary that the bacteria should be given
proper food and proper conditions. The results are mar-
velous. Although they are so small that a single one
can accomplish practically nothing in nature, the fact that
this single one can in twenty-four hours produce millions
of descendants gives to bacteria almost unlimited power.
An appreciation of this fact is fundamental to an under-
standing of the action of bacteria. Since one in the
course of a few hours may become hundreds of thousands,
and a little later its progeny may be millions, it is clear
that in order to protect any material from the action of
bacteria something more is necessary than simply to
reduce the number of microorganisms. If the material
is to be protected from them, every single bacterium must

GROWTH OF BACTERIA 109

be destroyed, for if but one be left alive it will require
only a few hours for its descendants to become so numer-
ous as to be able to accomplish almost anything in the
way of chemical destruction.

Relation of Growth to Temperature. This great power
of growth is dependent upon many factors, most promi-
nent among which is temperature. Like all living things,
bacteria will not grow at the temperature of freezing or
below, but will develop
at nearly all temperatures
above, some species even
growing at 140.° Certain a* %
species grow best at a
temperature that is not
much above freezing ;
others grow best at

higher temperatures. ^^ showing the effect f variations
Most of the common in temperature on bacteria growth, a,
household types require a single bacterium; b, its progeny in

considerable warmth for twentyfour hours at 5o° ; *, its progeny

in twenty-four hours at 70°.

their proper growth, and

the warmer the temperature, up to a certain limit, the more
rapid their growth. The relation of temperature to the
rapidity of multiplication, for common species, is shown
by the accompanying figure (Fig. 54). At a is repre-
sented a single bacterium ; at b is the progeny of this bac-
terium when kept twenty-four hours at a temperature of
50°, a little above that of the ordinary ice chest ; at c is the
progeny of this bacterium kept the same time at 70°,
the ordinary temperature of a living room. A glance at
the figure will show what an extraordinary influence a few

1 10 BACTERIA, YEASTS, AND MOLDS

degrees of temperature may have upon the rate of growth
of this bacterium. The figure teaches a very practical
lesson in regard to the influence of cold in delaying the
growth of bacteria and thus protecting food from spoiling.

If the temperature is raised too high, it has an injurious
action upon the growth of bacteria. Each species of bac-
teria grows best at a certain temperature, growing less
rapidly if warmed above this point or cooled below it.
Most, though not all, of the bacteria against which the
housewife has to contend grow best at temperatures
between 70° and 95°. If the temperature is raised above
95°, many cease to grow so rapidly, and at still higher tem-
peratures— between 12 5° and 140°-— a large majority are
quite incapable of growing at all. At the higher temper-
atures food would hardly decay. There are, however, a
few species which grow only at very high temperatures,
not developing at all unless it is above 125°.

It is perfectly evident that all problems connected with
the protection of food from the action of microorganisms
will be dependent upon the temperature at which the bac-
teria grow most rapidly. Food which is kept in an ice
chest, although it may be protected from the action of
those bacteria which grow only at room temperatures, will
be exposed to other species that grow best at lower tern
peratures. When we remember that some kinds of bac-
teria grow at temperatures close to freezing, we can readily
see that no method of cooling food short of actually
freezing it will totally protect it from decay.

Death Temperatures. All bacteria are killed by excess-
ive heat, but the temperature which kills them is some-
what variable. Bacteria exist, as we have seen, in two

DEATH TEMPERATURE III

forms. One is the active, growing form, in which they
feed and multiply rapidly ; the other is the spore form, in
which they are at rest, neither feeding nor growing. In
the former condition they are easily killed by moderate
heat, a temperature of 149° to 160°, if continued for an
hour (usually a much shorter time), being quite sufficient
to destroy them. In the form of spores, however, such a
temperature has little value in destroying them. Bacteria
can resist without being killed a higher temperature than
can any other known form of living matter. Spores of
certain bacteria can be boiled for a long time without
being killed, and if subsequently cooled they will grow
and multiply. To destroy the vitality of such spores
requires a temperature above that of boiling water, a
temperature rather difficult to obtain, at least for liquids,
in an ordinary kitchen. It is, however, important to
remember that although many kinds of bacteria spores
are not killed by a short boiling, a boiling of an hour or two
is sufficient to destroy even the most resisting spores. Any
material, therefore, that can be boiled for a considerable
length of time may thus be thoroughly sterilized, that is,
may have all its actively growing bacteria and all its
spores destroyed at the same time. This great resist-
ance to heat on the part of bacteria spores is a matter
of much importance to the housewife, and she should fully
realize it. All canning processes, as we shall see, depend
upon the destruction of bacteria, and the resistance of
spores to boiling is a factor that should always be
remembered.

A practical lesson to be drawn from these facts is that
food heated to boiling in its preparation is thereby, in a

112 BACTERIA, YEASTS, AND MOLDS

measure, protected from spoiling, since the bacteria are
mostly killed. But if the food is simply warmed, the
spoiling is hastened instead of delayed. For example,
in making beef tea, if the liquid is boiled, it will keep
easily; but since boiling precipitates the proteids and
deprives the material of most of its food value, it is better
to make it by warming without boiling. Such material
decays very rapidly, and, if set on the back of the stove to
keep warm, will be spoiled in a short time. Moderate heat
hastens bacteria growth. Boiling kills all but spores.

Light. Direct sunlight rapidly kills bacteria (except
some spores) and daylight in general has an injurious
effect upon them in proportion to its intensity. They
grow best in darkness. Dust or dirt exposed to sun-
light soon loses most of it's living bacteria, while in dark
cellars, dark corners, and cracks they may remain alive a
long time. Hence the rooms in our houses should be
kept light. The too frequent habit of closing blinds and
using heavy curtains or shutters to keep out the light
is a great mistake. Pantries and kitchens should have
all the light possible. A sick room particularly should
have all possible sunlight ; and bright colors for wall
paper, curtains, etc., will aid not only in making it cheer-
ful but in actually destroying the disease bacteria. Sun-
light and fresh air should everywhere take the place of
the darkened, closed rooms which have been only too
common in our houses in past years.

Relation to Air. Most living things require oxygen
and therefore demand air for their growth. This is true
of a majority of bacteria. Most bacteria like to feed
where they can have plenty of air. Hence decay is apt

RELATION TO AIR 113

to begin on the surface of things, extending towards the
interior. This is not true, however, of all bacteria. Some
species can grow perfectly well without air, and others,
indeed, cannot grow at all if they are in contact with
air. The latter bacteria, which live without oxygen, are
known as anaerobic ; the former, which demand oxygen,
are called aerobic. The aerobic bacteria are by far the most
important in the affairs of the household, but the anae-
robic bacteria, on the other hand, produce certain types of
putrefaction which are sometimes more serious, inasmuch
as the products of putrefaction which take place without
air are likely to be more poisonous than those products
of decay taking place in contact with the air. We must
remember, then, that whereas most bacteria grow best in
the air, we cannot protect any material from the growth
of microorganisms simply by keeping air away from it,
inasmuch as some species grow perfectly well, and even
better, out of contact with the air. Hence, in canning
food, it is not the exclusion of air that makes preserva-
tion of food possible, but the exclusion of bacteria.

Moisture. Like yeast and molds, bacteria require
water. Dry food is protected from their action because
they cannot obtain water sufficient for their life processes.
Bacteria, in general, require more water than molds. Vari-
ous materials, if simply damp, will mold or mildew, but
they will not support bacteria life unless the amount of
water is considerable, 25 % to 30% of water being necessary
for any growth, and a larger amount still for vigorous
growth. Hence they may be expected to grow in all
kinds of food which are thoroughly wet, but they will not
grow in any of the dried forms of food which we keep

114 BACTERIA, YEASTS, AND MOLDS .

in our houses, a fact of much importance in connection
with the problem of food preservation.

Acidity. For still another reason molds and bacteria
do not commonly flourish upon the same material. The
former, as we have seen, grow best upon acid substances;
but most bacteria cannot endure acids, preferring a slightly
alkaline food. Hence fruits, which are acid, decay by
molding, while meats, which are not so acid or are alka-
line, decay by bacterial action. The presence of acid or
sourness in food will check its decay. Some food (cran-
berries) may be actually too sour for bacteria growth.

WHERE BACTERIA MAY BE FOUND

We may almost say they are to be found everywhere
upon the surface of the earth. This is not strictly true,
since a few places seem to be free from them ; for exam-
ple, the middle of deserts and the bottom of the deep
oceans. But wherever on the surface of the earth ani-
mals or plants are found, there, in the earth, the air, and
all bodies of water, are also found bacteria.

Air. Bacteria are so extremely minute that they are
capable of floating in the air for a long time and of being
blown by the winds almost indefinitely. Consequently it
is almost impossible, at least in inhabited localities, to
find any air that does not contain them. The number
that may be present in the air varies with the density of
human population. We find them more abundant in city
than in country air ; more abundant, as a rule, in houses
than out of doors ; more abundant in the air of rooms
well filled with people than in empty rooms, since they

DISTRIBUTION OF BACTERIA 115

arise from clothes and skin. In the air of schoolrooms
or audience rooms the number of bacteria is very great,
and there are more at the close of a school session than
at the beginning. There are more bacteria in the air
of a poorly ventilated schoolroom than in the air of a
sewer. The presence of animals as well as of men
always increases the number of bacteria in the air.
Wherever we find dust, there we find bacteria. By this
it is not meant that dust is composed wholly of bacteria,
for many other things go to
constitute what we know as OQ o •*?
dust; but among the dust abed

particles we may be sure to _

x? =» a <?ff *=-, x//-
find bacteria in great num- Jj|/ £^jJ ~"5^

bers. In short, all air in the e ^ '

vicinity of habitation contains

* FIG. 55. A group of bacteria in

bacteria. The air of high water.

mountains far from the habi-

tat ion of animals is found lans'> c> bacillus **t*rficiaiis ; <t, ba-

cillus rubescens ; e, bacillus hyalinus ;

to be moderately free from /, badiius deiicatuius •, g, badiiusjan-
these ubiquitous organisms.

Elsewhere they are present in abundance. Since this is
the case it is quite impossible for any material exposed to
the air for even a short time to escape a rapid contami-
nation with microorganisms.

Water. Practically all bodies of water on the surface
of the earth are filled with bacteria (Fig. 55). The
number found in water, however, is widely variable. In
spring water which comes fresh from the ground the
number is small, and in some cases they may be wholly
absent. The same thing is true of the water of artesian

Il6 BACTERIA, YEASTS, AND MOLDS

wells, drawn from a depth of a hundred feet or more.
All surface waters are sure to contain them, for they
are present in lakes, ponds, pools, rivers, and in the ocean.
They are more abundant in flowing streams than in water
standing in lakes or reservoirs, quite contrary to the usual
belief. We commonly look upon running waters as purer
than standing waters, but, so far as concerns bacteria, the
reverse is usually the case. Rivers or brooks contain them
in large numbers ; lakes in which the water has stood for
a long time contain a far smaller quantity. The reason
is that rivers and brooks collect the bacteria from the
surface of the ground, from sewage, etc., and the longer
they flow the greater the number of bacteria they con-
tain, since they are great draining agents for the country.
When water stands in lakes or ponds the bacteria, which
are slightly heavier than the water, have a chance to settle
to the bottom. This they do in the course of a few days,
and after a time the water in such standing reservoirs
becomes far purer than in the supply streams. It will
easily be understood that the greater the amount of
decaying matter entering any stream the larger will be
the number of bacteria in its waters. The rivers of civi-
lized countries, that receive the sewage from cities, not
only contain these little organisms in immense numbers,
but contain some of the most dangerous kinds, since they
are the disease germs discharged from human patients.

From these general facts we reach the conclusion that
no water at our command upon the surface of the earth is
absolutely free from bacteria. Spring water is the purest,
and water from deep artesian wells is about equally pure.
Water from lakes and reservoirs is the next in purity, and

BACTERIA IN THE SOIL

n;

water derived directly from flowing streams and rivers is
most likely to contain these organisms in greatest num-
bers. The most dangerous water for drinking pur-
poses is that of rivers which have been contaminated in
any way by sewage material, a condition of things true of
the water used in some cities.

Soil. Soil on the surface of the earth is usually filled
with bacteria (Fig. 56). They are usually abundant in
the superficial layers, decreasing
rapidly as we pass below the sur-
face, until at the depth of a com-
paratively few feet they practi-
cally disappear. They are more
abundant in some kinds of soil
than in others. Where the soil
is dry and sandy the number is
comparatively small; where it is
moist and loamy they are more
abundant. They are found pro-
fusely around buried bodies of
animals, or in soil that contains
decaying roots of ordinary plants.
They are immensely numerous
in the vicinity of earth closets
or privies, and the soil near sink drains and manure heaps
is filled with them. Indeed, any soil which contains the
remains of animal or vegetable matter and a considerable
amount of moisture will have bacteria in inconceivable num-
bers, while in cleaner soils they will be much less abundant.

They are sure to be abundant in all dirt which accu-
mulates in a household, for nearly all such dirt contains

FIG. 56. A group of soil
bacteria.

fusiformi*-, e, B.subtms-, /,

terium pasteuriana.

n8

BACTERIA, YEASTS, AND MOLDS

organic material in a state of partial decay. Any dirt
which collects in corners of rooms, in the cracks of floors,
or upon shelves in pantries, cellars, etc., is sure to contain
bacteria in great quantities. The dirt that clings to the
walls and ceilings of rooms is also quite sure to contain

FIG. 57. A bit of decaying meat highly magnified, show-
ing the bacteria feeding upon the material.

them, and the dirt collected by sweeping the floors is filled
with them.

Bacteria in Food. Bacteria are found in all moist foods,
especially in those undergoing the process commonly
spoken of as spoiling (Fig. 57). Indeed it is the bac-
teria, as we shall presently see, that ordinarily cause
this spoiling. Any meat which develops the gamy flavor

BACTERIA IN FOOD 119

is filled with them ; sour milk contains them in immense
numbers ; moldy bread and bad eggs hold millions of them,
and decaying fruit may show bacteria as well as molds.
All types of food which develop peculiar taints and tastes
characteristic of putrefaction contain great numbers of
bacteria. Long before these taints are appreciable to
the senses the bacteria that produce them are abundant.
No moist food can be exposed on pantry shelves or in
ice chests, even for an hour, without containing bacteria,
and after it has remained there for
a day or two the number of bac-
teria present in it becomes very
great indeed, because of the multi-
plication of those that have found
entrance.

In the Body. The presence of
bacteria in food leads us to expect FIG- 58- Bacteria from the
to find them in our mouths, stom- teeth of a health? mouth'
achs, and intestines. Our whole digestive tract is crowded
with them. Fig. 58 represents a bit of the scrapings from
the teeth, highly magnified, and containing hundreds of
several different species of bacteria. They are equally or
more abundant in the stomach and intestines. This is
the normal condition of things, and these bacteria do us
no injury, but are probably of direct use.

The substance of the matter is that bacteria are practi-
cally everywhere on the surface of the earth. They are
in immense numbers in the household, on the walls and
ceilings of our rooms, upon our pantry shelves ; they
are present in every bit of food which remains exposed
to the air for a short time ; they are in all liquid foods,

120 BACTERIA, YEASTS, AND MOLDS

particularly milk. So ubiquitous are they that it is an
absolute impossibility for the housewife, by any means
at her command, to keep her pantry and food free from
them.

These facts forcibly emphasize the futility of the com-
mon method of sweeping and dusting rooms. Bacteria
are heavier than the air and if undisturbed settle and lie
quietly upon floors, tables, etc. Every sweeping the room
receives stirs them up. A dustbrush sends them flying

FIG. 59. Petri dishes exposed, one, a, before, and the other, 3,
after a class has occupied a schoolroom.

through the room only to settle down again later. On the
other hand, wiping with damp cloths removes the bacteria
and is the only proper method of cleaning. This is espe-
cially true for kitchens and pantries where food is exposed
to the air, and for schoolrooms where there is likely to be
a collection of numerous kinds of bacteria, including some
disease germs brought by the many children. Fig. 59
shows two plates, one exposed to the air before and the
other after a school session. The relative abundance of
bacteria floating in the air is clearly shown.

RESULTS OF BACTERIA GROWTH 121

These facts, too, show the desirability of having the
walls of kitchens and pantries smooth and glazed, in order
that they may not furnish lodging places for air bacteria
and may be cleaned readily with a damp cloth. They also
show us that lace curtains and heavy hangings around
rooms will be lurking places for numerous organisms.
This may do no harm in ordinary parlors, rooms where
the bacteria are mostly harmless and where no food is
kept, but should never be allowed in kitchens, and should
be most emphatically forbidden in sick rooms where dis-
ease germs are likely to be floating about in the air.

THE RESULTS OF BACTERIA GROWTH

The bacteria with which we are concerned all require
complex foods. Some species can live upon simple min-
erals from the soil, but these are of no importance in the
household. All that are of interest for our purposes feed
upon substances quite similar, in general, to those upon
which animals subsist. Any materials containing sugars,
starches, proteids (albumen, lean meat, etc.), or other ani-
mal foods, furnish excellent nourishment for bacteria.
For this reason the bacteria are in a sense the rivals of
the animal kingdom. Both animals and bacteria feed upon
the same kind of food, and both are, therefore, constantly
seeking to obtain and use it for their own purposes.

When we bear in mind the facts thus far outlined we
can easily understand why bacteria play such an important
part in the affairs of everyday life. They are too small to
see, but are capable of inconceivably rapid multiplication.
They are all about us in great numbers, in earth, air, and

122 BACTERIA, YEASTS, AND MOLDS

water. Some can be dried without injury, others frozen
for months without losing their vitality, and even a short
boiling fails to kill many species. With all these wonder-
ful properties it is not strange that they are constantly at
work all around us modifying the nature of all substances
upon which they feed.

PARASITES AND SAPROPHYTES

The food upon which bacteria feed may be either living
or dead. If bacteria are capable of feeding upon the
living body of an animal or plant, we call them parasites.
Such bacteria quite naturally produce injury to the life
of the individual upon which they feed. In mankind they
produce a great variety of abnormal results which we call
diseases. The parasitic bacteria, therefore, are commonly
called disease germs, and are the cause of most of our con-
tagious diseases. Many 'of them feed upon animals, pro-
ducing animal diseases, while others live upon plants,
giving rise to diseases in the plant world.

Fortunately only a comparatively small number of spe-
cies of bacteria are capable of existing upon living bodies
of animals. The great majority are incapable of feeding
upon living tissue, although they feed upon it readily
enough after it is dead. Those dependent upon the dead
bodies of animals or plants cannot live a parasitic life.
When bacteria feed upon such nonliving materials we call
them saprophytes. They are, like animals in general, depend-
ent for sustenance upon dead animal and vegetable food
The saprophytic bacteria, while they may be rivals of ani-
mals for food, are not the cause of diseases. These harmless

SAPROPHYTES AND PARASITES 123

bacteria far outnumber the disease germs. We should
not therefore be frightened when we learn that bacteria
are all around us, in the food we eat, the water we drink,
and the air we breathe. Most of them are harmless or
beneficial, and need cause us no uneasiness.

It should also be noted, finally, that some bacteria can
live both upon living tissues, like parasites, and upon
dead material, like saprophytes. Such microorganisms
are partly parasitic and hence are capable of producing
disease. They are also capable of living outside the body
in various localities in nature. They may be of serious
importance to the health of man, inasmuch as they are
capable of living a parasitic life if they can get into the
living body ; but are also able to live an independent life
in nature. All disease bacteria either belong to this class
or are strict parasites, while the harmless bacteria belong
to the class of saprophytes.

CHAPTER IX

BACTERIA WHICH LIVE UPON DEAD FOOD:
SAPROPHYTES

These include the bacteria found living freely in nature,
in the air, in water, and in the soil. Since they live upon
dead organic material they may be expected in any kind
of food upon which the human being lives, as well as in
other substances that do not serve us as food.

MATERIALS THAT SERVE BACTERIA AS FOOD

Some kinds of food are very readily attacked by bac-
teria, others with more difficulty, and some hardly at all.
Pure sugars are, as a rule, not attacked by them, although
if the sugar is in water solution certain bacteria may some-
times feed upon it, and raw sugar is sometimes injured
by bacterial growth. The same is true of pure starches,
since most bacteria are quite incapable of making use of
pure starch. It happens, however, that nearly all of our
food materials containing starch and sugar contain also
other substances upon which bacteria can feed, so that
the sugary and starchy foods in our households are by no
means exempt from them. Fats are also attacked by bac-
teria, although less readily than some foods. By bacterial
action the fat is made rancid and undergoes other less
familiar changes.

124

FOODS OF BACTERIA 12$

The food most readily attacked by the majority of bac-
teria is the class known as proteids. Proteid materials
are foods for nearly all species of bacteria, are most easily
attacked by them, and are sure to be consumed if exposed
to the air under proper conditions. By proteid food is
meant a class of chemical substances, highly complex in
nature, which may best be understood by illustrations.
The best known examples are the following : the white
of egg, named albumen; the lean part of meat, known
by chemists as myosin ; the curd of milk, called casein;
gluten, which is the gummy substance present in wheat
flour ; a similar substance present in beans, known as
legumen. All of these substances will be recognized as
liable to putrefy rapidly. Nearly all of our foods contain
either these proteids or others in greater or less abun-
dance. Anything made of flour contains gluten ; any-
thing that has milk in it contains casein ; all meats
contain myosin ; anything made of beans or peas contains
the legumen, while eggs always furnish albumen. Since
most foods contain some of these substances, and since
cooking does not change their nature, practically all foods
hold some of these proteids.

Proteids are of all foods the most necessary for the
human body. While the body might live on proteids
alone, it could not live entirely on any other kind of food,
and proteids therefore are absolutely necessary for the
human body. Most bacteria flourish upon proteids as well
as we do, and inasmuch as practically all of our food
products contain a certain quantity of proteids, it follows
that nearly all of our foods are readily consumed by the
great host of saprophytic bacteria.

126 BACTERIA, YEASTS, AND MOLDS

THE EFFECT OF BACTERIAL GROWTH UPON FOOD

If any common food product is sufficiently moist, bac-
teria which get into it from some source are sure to grow
and in the course of a few hours will produce marked
changes therein. But bacteria do not consume food as
large animals do by taking it bodily inside of themselves.
They are quite too small to do this. To the eye it does not
seem that the bacteria are actually consuming the food
but that they are simply producing noticeable changes
within it. In reality, however, they are consuming it
and in the end cause its almost complete disappearance.
The essential effect that they produce is the chemical
decomposition of the material upon which they are feed-
ing. Bacteria do not consume the whole food but use
only a part of it. An illustration may make clear their
mode of action. If a house is built with a wooden
frame and brick walls, and the wood is burned away, the
house is sure to tumble to pieces, because the wooden
framework is necessary to hold the building together.
Much the same thing is true of a chemical molecule, which
is a structure made of a variety of substances bound
together to form a unit. Bacteria, as they utilize foods,
have the power of taking some of these materials out of
the molecule, but cannot consume the whole. The result
of extracting some of the material from a molecule is that
the entire structure will fall to pieces, just as the house
falls whose framework has been burned away. The meat
becomes putrid, the milk sours, the egg rots, and any
other material containing proteid undergoes a similar type
of spoiling.

PRODUCTS OF BACTERIAL GROWTH I2/

NEW PRODUCTS

Decomposition Products. When a house falls to pieces
after burning, a mass of debris is left lying in the old cellar.
So, when the chemical molecule is broken to pieces, as
described above, there will remain certain fragments of
the original molecule. Although really fragments of the
original substances they are quite different in nature from
the original material. They are known as by-products of
decomposition, or simply as decomposition products. When-
ever bacteria grow in a mass of food, destroying the
chemical nature of the food molecules, there is sure to be
produced a variety of materials representing the de"bris
from the destruction of the molecule. These materials
are by-products of decomposition and are always of a
nature quite different from the original food substance.
They are, as a rule, simpler in their chemical nature than
the original food, and are quite different in their physical
characters.

From the original food, which may have been a partly
solid material, like a bit of meat, there arises as the result
of its destruction a number of these by-products, some of
which are in the form of gases and pass off into the air,
some of which are more or less liquid and remain behind
in the food mass. Others are easily soluble in water and
dissolve in the liquids of the food. Thus the food material
is almost sure to soften gradually and to become of a more
or less fluid nature. There is likely to be a considerable
variety of these by-products, some of them having new
odors and tastes. The new materials give to the food
mass as it is consumed by bacteria wholly new flavors ;

128 BACTERIA, YEASTS, AND MOLDS

and since some of them are vapors they may give it a
strong odor. Consequently the food material which is
being consumed by bacteria soon begins to have a very
strong taste and odor, due to some of these decomposition
products. The character of the food changes very greatly,
and after the bacteria have had an opportunity of feeding
upon the material for a comparatively few hours no resem-
blance to the original food mass remains, in appearance,
taste, or smell.

This whole phenomenon is spoken of as putrefaction, or
decay. There is, however, a slight difference between
these two terms. By putrefaction we commonly mean a
change in food masses by which a series of very unpleas-
ant odors and tastes make their appearance in the putre-
fying mass. By the term "decay" we properly mean a
more complete destruction of the food material, in which
the unpleasant odors and flavors finally disappear, leaving
behind a comparatively odorless material which represents
the final debris remaining from the total destruction of
the food masses. Putrefaction, with its high flavors and
odors, is an incomplete process ; decay, a more complete
process of destruction. Putrefaction is produced in gen-
eral by bacteria when they do not have an abundance of
air or oxygen, whereas decay occurs when the amount of
air or oxygen present is abundant. In other words, when
a bit of food is being consumed by bacteria without suffi-
cient oxygen it putrefies and becomes offensive in taste
and smell ; when, however, the oxygen is abundant, the pro-
cess of putrefaction goes on to a more complete destruc-
tion, ending finally in what is known as decay, by which
the material is converted into inoffensive substances.

BACTERIAL SECRETIONS 129

Bacterial Secretions. Besides the decomposition prod-
ucts just referred to, another class of new substances is
found in the putrefying and decaying food, and these are
to be regarded as secretions from the bacteria. Bacteria are
living organisms and, like larger animals and plants, are con-
stantly emitting from their bodies certain secretions. Our
own bodies are constantly secreting materials, like perspira-
tion, urea, etc. ; and bacteria, as the result of their activity,
are also constantly producing a small amount of secretions.
These secretions are totally different products from the
original food. The secretions from some species of bac-
teria are quite harmless, although others are of an intensely
poisonous nature. As a result, a bit of food that is under-
going putrefaction may in the course of time become
highly poisonous because of the appearance of poisonous
materials, part of which may be decomposition products
but most of which are probably bacterial secretions.

Chemists and bacteriologists are not able to separate
very clearly decomposition products from the secretions
of bacteria, and for our purpose it is quite unnecessary.
We need only remember that as the bacteria consume our
food products they produce profound chemical changes
which we call putrefaction and decay. As the result of
these changes not only is a host of highly flavored prod-
ucts developed but also another series with strong odors.
Some of these new products are poisonous, others are not.
All of them have a tendency to be softer than the original
food and more easily dissolved in water; the result of which
is that as the food is consumed by the bacteria it becomes
softer and more liquid. In the end it largely disappears,
being dissolved into gases which pass off into the air and

130 BACTERIA, YEASTS, AND MOLDS

liquids that soak down into the soil or evaporate, leaving
only a small residue. This is the general phenomenon of
putrefaction, ending in complete decay.

Advantages from Incipient Decay. Although this pro-
cess of decay may be a somewhat rapid one, it actually
takes place by steps, one after another. The breaking
down of the food under the action of bacteria is not a
sudden falling of the molecules into fragments but a pro-
cess that takes considerable time and presents a number
of intermediate steps between the original food and the
final condition of decay. As the bacteria begin to act
upon the food it is not at first necessarily ruined or even
injured. At the beginning of the process the new prod-
ucts are quite different from those that appear later, and
it may happen that those first produced give to the food
a slight flavor which, instead of injuring its character,
actually improves it.

The presence of a certain amount of flavor in our foods
is very desirable, and even necessary. Pure foods with-
out flavors cannot be properly digested and absorbed, a
certain amount of flavor being needed to stimulate the
digestive organs. Some of the flavors arising in the early
stage of decomposition are of a character that is enjoyed
by the human palate. For example, the so-called gamy
taste of meat is a flavor which some people enjoy very
much, while others dislike it. This gamy taste is simply
the beginning of decomposition, and is due to the fact
that the meats have been kept until the bacteria have
begun to act upon them and to produce the incipient
stages of putrefaction. In this early period the flavors
are not very strong and not particularly unpleasant ; but

FLAVORS FROM INCIPIENT DECAY 131

if the process is allowed to go a little farther the taste of
putrefaction becomes too strong for any palate. Another
example is Limburger cheese, in which a strong flavor
of incipient putrefaction is produced by the development
of bacteria in the cheese mass. Any one who has ever
known the flavor or taste of Limburger cheese will easily
believe that it is incipient putrefaction. Other forms of
soft cheeses show the same feature in less degree. A
great variety of flavors and odors is found in the so-called
soft cheeses, nearly every one of which
represents a certain type of incipient pu-
trefaction. Even the hard cheeses show
this same characteristic, though there is
less similarity to putrefaction. Neverthe-
less the taste of the hard cheese is prob- FlG- 6o- Bacterium
ably, at least in part, due to the beginning ^r° mgKg*?C

' flavors in butter.

of this process of chemical destruction
produced by bacteria. If the cheese has become over-
ripened, a very strong decayed taste may be apparent.
In the making of butter the same phenomenon occurs, for
the extremely delicate flavor of a high quality of butter
is due to the action of bacteria upon the cream before
the butter is made, and the butter flavor is thus one of
incipient decay (Fig. 60). It is one of the most exquisitely
delicate of all our food flavors, and is highly enjoyed by
all people.

VINEGAR

Another example of a benefit derived from bacterial
action is in the manufacture of vinegar. This is a mate-
rial which, though not a real food, is used in considerable

132 BACTERIA, YEASTS, AND MOLDS

quantities as a condiment and preservative. As ordinarily
made it is simply a product of bacterial growth. The
basis of vinegar is acetic acid, and this is produced from
alcohol by certain changes brought about in it through
the action of microorganisms. The source of vinegar is
always some weak alcoholic solution, commonly cider or
weak wine; but any liquid that contains a moderate
quantity of alcohol may be a source of vinegar. This
material is caused to undergo a chemical change which
converts the alcohol into acetic acid, and when this occurs
it becomes vinegar.

* The change of the alcohol into acetic acid is brought
about by the presence of a material, a brownish, felted,
slimy mass, which increases in amount as the vinegar is
made, and upon whose presence the conversion of alcohol
into vinegar seems to depend. This has long been known
as mother of vinegar. „ Good vinegar will always contain such
mother. The study of this mother of vinegar shows it
to be a mass of bacteria (Fig. 61). They are crowded
together in countless millions to form this slimy mass,
and during the production of the vinegar multiply rapidly
and finally become excessively numerous. The growth of
the bacteria produces the change in the alcohol which con-
verts it into acetic acid. The formation of common vinegar
is therefore due to the development of microorganisms.
Some types of a cheap product are made by a chemical
process, but all good table vinegar is produced by bacteria.
A knowledge of the manufacture of vinegar is to-day a
matter of little importance in the household, for the mate-
rial is commonly made either in large factories or in a
farmer's cellar. The housewife is simply concerned in

VINEGAR

133

purchasing a good product, and in its use. The type of
vinegar commonly regarded as the best is that which is
made from cider, although a large part of the vinegar used
in the world is made from some other source of alcohol
(wine, beer, etc.). Thevalue
of vinegar is in a measure
dependent upon its flavor,
which differs according to
the material from which
it is made. Vinegar, of
course, has always an in-
tensely sour taste from the
presence of acetic acid, but
in addition to this there
are other flavors, due to
the original material from
which it is produced, and
these affect its value.
Vinegar also varies in color
according to the substance
from which it is made.
Cider vinegar is of a rich
brown color, while if made
from other materials it
may have a reddish or whitish color, or may be almost
black. The color, therefore, is no indication of the char-
acter of the vinegar, for a perfectly good product may be
white, red, or brown. The market value of vinegar is
dependent chiefly upon the amount of acid it contains.
The higher the percentage of acid (the sourer it is), other
things being equal, the greater its value.

FIG. 61. Bacteria producing vinegar.

134 BACTERIA, YEASTS, AND MOLDS

Although they are not bacteria a word may be said in
regard to the vinegar eels frequently found in good cider
vinegar. These are minute little worms, just visible to the
naked eye, which are frequently seen swimming near the
surface. Their presence may be consistent with a good
quality of vinegar. They do not themselves have much
influence upon vinegar, although if abundant they weaken
its strength. They are quite harmless to the person using
the vinegar, and one need never be suspicious or throw
away any because it contains large numbers of these eels.
They must be looked upon as present in ordinary good
cider vinegar, and must be classed among the perfectly
harmless organisms which are sure to occur in some of
our food products.

FOOD EVENTUALLY RUINED BY BACTERIA

These illustrations are sufficient to show that the by-
products of decomposition are not always necessarily dis-
advantageous to our foods. If the chemical destruction
is only beginning, the result may be of a pleasant nature,
and the food may be actually benefited by the action of
the bacteria. If, however, this process is allowed to go
farther, most foods are entirely ruined. Gamy food soon
becomes putrescent ; soft cheeses of all kinds soon undergo
putrefaction and decay, and even the hard cheese in the
end will become ruined by the development of too strong
a flavor of putrefaction. Butter in the course of time is
also ruined, although bacteria do not grow readily in butter
and it may be kept a long time without undergoing putre-
faction. It is, however, really impossible to draw any

GARBAGE 135

due between the incipient decomposition that benefits
the flavor of food and the later stages which utterly
destroy it.

Although the flavors of incipient decomposition may be
pleasant and useful, the taste produced by later stages is
offensive. In the end the food is always totally ruined,
for bacteria will finally produce the complete destruction
of the materials upon which they feed. The kinds of
putrefaction, that is, the odors and tastes that develop, are
by no means always the same. Different species of bac-
teria produce different results, and the same species of
bacteria produces a quite different kind of decay in differ-
ent sorts of food material. But it is a matter of little
significance what type of putrefaction occurs, for all of
them are equally sure to destroy the food. It is useful to
remember, however, that the kind of decomposition which
is produced when bacteria grow without sufficient air is
always more unpleasant and more dangerous than that
which takes place where there is plenty of air. Any food
material which is closed in tight bottles or jars and under-
goes putrefaction is sure to give rise to more unpleasant
odors and tastes and to decidedly more unpleasant types
of decomposition than food material which decays in the
open air.

GARBAGE

All the refuse from our tables or our kitchens is just
as good food for bacteria as is the material which we
actually consume, and all of this waste material, after we
have discarded it, is attacked by bacteria. This is shown
simply enough by the odors arising from garbage if it is

136 BACTERIA, YEASTS, AND MOLDS

allowed to stand, the putrefaction and decay that set in
being sure indications of the presence of bacteria and
proofs that the bacteria are decomposing the material.
Such waste material is, of course, of no use in the house-
hold, since it is not in a condition to attract the palate of
man ; but there is a large amount of food material left
in these waste products which is very useful for feeding
certain animals. It has commonly been used for feeding
hens and hogs, and the recognition of its food value has
in recent years made the garbage of our large cities a
very valuable product. This use of garbage is being
abandoned as unhealthful, and the practice of burning the
material is becoming common.

The housewife is not, however, concerned in this prob-
lem but only in the proper disposal of the waste material
from her kitchen and her table. This she simply desires
to get rid of, and its tendency to rapid putrefaction makes
it imperative that it be disposed of at once and not allowed
to accumulate. She can adopt a variety of methods for
this purpose. She may burn it, provided it is not too large
in quantity, is not too moist, and she has a fire hot enough
for the purpose. As a rule, however, burning garbage
in an ordinary kitchen stove is not very feasible. It is
commonly too moist to be easily consumed in a moderate
fire ; but where possible this is the best means of getting
rid of the waste.

The usual method of disposing of garbage in a city is
to allow it to be removed by those who pay for the privi-
lege because of the value of the material for feeding hogs.
The household waste is placed in receptacles, which are
emptied by the garbage collectors. In order that such

GARBAGE 137

receptacles may be kept in a tolerably wholesome con-
dition, the garbage should be removed frequently, and
for this we must depend upon the faithfulness of the col-
lectors. The vessels themselves should occasionally be
cleaned. If not cleaned, they give rise to unpleasant,
unwholesome odors in or around the house. They may
become the breeding places for flies and prove to be in
general a considerable nuisance.

The chief trouble with such garbage cans is their smell
and unsightliness, but these difficulties are removed if the
cans are kept clean. It is not difficult to clean them. Cold
water for washing garbage cans is of very little use ; but if
they are thoroughly washed with very hot water they can be
kept so clean that they emit no odor and are not unpleas-
ant. Since putrefaction is due to bacterial growth it is of
course possible to prevent the smell and decay of the gar-
bage by the use of disinfectants. Borax might be used for
the purpose, but it is expensive ; and the use of more vigor-
ous disinfectants is likely to make the material poisonous
to hogs subsequently fed upon it, or to dogs who very fre-
quently feed upon the contents of the garbage receptacle.
Such disinfectants are quite unnecessary, and the only
thing that the housewife needs to do is to keep the garbage
can tolerably clean, and to see that it is emptied as fre-
quently as possible. She should remember, however, that
she cannot depend upon the garbage man to clean the recep-
tacle. He will simply empty it. If the garbage can gets
to smelling offensively, a thorough washing with hot water
and sal soda applied vigorously with an old broom will make
a great improvement. Naturally greater attention must
be given to the matter in the summer than in the winter.

138 BACTERIA, YEASTS, AND MOLDS

Closely associated with these problems are certain other
minor questions relating to the kitchen sink. In the
ordinary sink a considerable amount of organic material is
liable to find its way into the drain and trap. The cloths
used for washing dishes are also quite sure to become
soiled with various forms of organic material from the food.
These materials are liable to bacterial action and uierefore
will decay and become offensive. Consequently boiling
water should be occasionally poured down the sink drain
to disinfect the trap as far as possible, and the cloths used
in dishwashing should be thoroughly washed in boiling
water and dried to prevent them from becoming offensive
by furnishing a chance for bacterial growth.

CHAPTER X
THE PRESERVATION OF FOOD: DRYING; COOLING

The growth of bacteria in food is nearly always unde-
sirable and the housewife must always aim to prevent it.
Even where the incipient decomposition products are
useful because pleasant to taste, this taste is developed
in the food before it is received into the house, so that
the housewife is not concerned in the methods adopted
to produce the flavors. Her sole aim must be to prevent
the food from spoiling. To do this she must constantly
bear in mind that putrefaction is always due to the growth
of microorganisms, and that all types of putrefaction and
decay may be prevented by stopping the growth of such
organisms, and delayed by decreasing its rapidity. Any-
thing which will check the activity of bacterial growth will
delay the spoiling of food products. In order to know
how to treat food for this purpose it is most useful to
bear in mind the facts already mentioned in regard to the
growth of bacteria.

To the housewife of to-day the problem of food preser-
vation is of less significance than it was fifty years ago.
To-day, at least in all communities of even moderate size,
these problems have been largely solved for her by the
marketman, and she can buy her food in such small quan-
tities that frequently she does not need to consider the
problem of preservation. The housekeeper of fifty years

139

140 BACTERIA, YEASTS, AND MOLDS

ago was confronted with many problems in the preserva-
tion of meats, vegetables, and fruits, because she was
likely to have large quantities brought to her hands at
once for immediate disposal. But though the questions
are not so pressing in the modern home, they are still con-
stantly arising in the well-regulated house. A somewhat
extended notice of the subject is therefore necessary.

The Use of Foods while Fresh. The first thing that
must always be borne in mind is that nearly all kinds of
food are better when used as fresh as possible. The
earlier food is consumed after it reaches the household,
the surer it is to be free from the troublesome action of
bacteria and the more certain it is not to develop decom-
position tastes and flavors. The necessity of using food
while fresh is much more imperative with some foods
than with others. Meats are especially liable to spoil, the
meat of immature animals more quickly than that of adult
animals, and must be used promptly. Many fruits, like
cherries, berries, peaches, and pears, keep only a short
time, and beans and peas spoil very quickly if kept moist.
The endeavor should always be to use such materials
at once.

The housewife in our modern community should remem-
ber that a small proportion of the food she buys is really
fresh. The crowding of people together into cities de-
mands a food supply coming from long distances, and
the constantly open markets twelve months in the year
require some food to be preserved for weeks and months
before use. Hence our markets are filled and our tables
loaded with various forms of preserved foods ; and whether
she buys canned or salted goods, or meats or poultry, the

PRESERVATION BY DRYING 141

housewife may be confident that some device for preser-
vation has likely been used in their preparation. The
modern city is possible only because we have learned
methods of food preservation.

It is of course not always possible to use all kinds of
food in a fresh condition, and it becomes quite necessary
to have some means devised for their preservation. The
means adopted for preservation are always to subject the
food to conditions unfavorable for bacteria growth.

DRYING

Since bacteria require a considerable quantity of water
for their growth and multiplication, they will not develop
at all in foods that are even moderately dry. Molds will
grow upon a food that has only a small amount of water,
but bacteria require from 25^ to 30^) of water in their
foods in order that they may grow. Molds will grow
upon damp floors, damp cloth, or paper, but bacteria can
attack these materials only when soaked with water.

A practical application of this fact is drying, — one of
the most widely used methods of preserving food. This is
adopted by nature for the purpose of preserving many
food products, like corn, wheat, oats, rye, etc. Nature
wants to keep such seeds from decaying for some time,
perhaps during the winter season, in order that they may
be in good condition for the growth of the young seedlings
in the spring. To accomplish this the seed, when it ripens,
is deprived of its moisture, so that when fully ripe and
ready to be shed from the plant it has become a dry,
hard, tough mass, forming the grain of wheat or corn, or

142

BACTERIA, YEASTS, AND MOLDS

the dry pea or bean. Such a food material is beyond the
reach of bacterial action, and, unless these grains become
subsequently soaked with water, they are protected from
decay (Fig. 62). Bacteria grow in them readily enough in
the spring when they are moistened and begin to sprout.
This drying of the grains protects all kinds of flours
and meals made from them. The wheat is ground into

flour, and the corn into
meal, each of which con-
tains but a small amount
of moisture, far too little
to allow bacteria to feed
upon the material.

RW 1 _-*&^ Flour is Perfectly good

food for bacteria, and if
we only moisten it with
water, putrefaction and
decay begin in a short
time; but as it is
ordinarily prepared the
amount of moisture is too slight for bacteria. The same
is true of all flours or meals prepared by grinding dried
seeds furnished by plants. To a less extent the same is
true of various food preparations made from these flours.
In making bread or cake dried flour is mixed with water
and subsequently baked. The mixing of the flour with
water brings it into a condition for bacterial action, but
the baking dries up enough of the water to preserve it.
If the baking is so thorough that the water is almost
completely driven off, as in the case of dried bisctiits, or
crackers as they are called in the United States, the

FIG. 62. Showing nature's method of
preserving seeds by drying. The upper
figures are the fresh seed, the lower
figures the same after drying for winter
preservation.

PRESERVATION BY DRYING 143

material is left so completely dry that bacteria cannot
consume it at all. Dried crackers, if kept dry, can be pre-
served indefinitely, neither decaying nor molding. In the
case of bread and soft cakes the water is not wholly driven
off ; hence these foods are not protected entirely from
the action of microorganisms. As a rule bacteria cannot
attack them and the housewife hardly fears their decay;
but molds can grow upon them readily, and they must
therefore be protected by means already suggested.

In addition to foods that are naturally dry, a large
variety of others may be preserved completely from bac-
terial action by artificial drying. This method of pre-
serving has been known for centuries and is understood
by both civilized people and savages. Most kinds of meat
can be treated in this way, and the drying of meat is
carried on to a large extent in different parts of the world.
The frontiersman and the hunter in the woods sometimes
cut the flesh of deer, bears, and other animals into thin
strips and hang it where it will be dried by the heat of the
sun. This dried meat is called pemmican, a tough, hard,
dry substance which can be kept for months without
danger of decay. It is good food, though somewhat less
digestible than fresh meat. A similar drying could' be
adopted in the household to preserve meats, but it is
rarely worth while.

Usually the efficacy of the drying is increased by the
use of salt. This plan for the preservation of meat is
adopted in many parts of the world where cattle are plenty
and the market is distant. In South America thousands of
tons of dried flesh are prepared each year, the drying in
this case being produced artificially, and the meat being

144 BACTERIA, YEASTS, AND MOLDS

still further protected from- decay by the addition of a
small quantity of salt. Such preserved meats are then
shipped all over the world and form an excellent food
which can be kept indefinitely. The commercial names
under which this dried meat is sold are several ; the more
common ones are charque and tassajo. Such meats, though
useful, do not take the place of the fresh product. Their
flavor is changed ; they are tough and not easy to digest.
A more familiar method of preserving meat is the cur-
ing of hams, bacon, etc. In such cases the flesh is first
salted thoroughly by soaking in a brine, and then sub-
jected to the action of smoke from burning wood. Such
smoked food is thoroughly protected from bacterial action
by at least three factors : (i) The material becomes some-
what dry, so that the bacteria cannot readily act upon it.

(2) The action of the smoke is in a measure antiseptic,
partly destroying bacterial life upon the surface, and at the
same time so impregnating the meat with injurious vola-
tile products that bacteria cannot ordinarily grow in it.

(3) The salt is itself injurious to bacterial life. The ham is
thus preserved from the action of bacteria by a combina-
tion of drying, smoking, and salting, all of which processes
together are sufficient to prevent completely the subse-
quent growth of bacteria, although molds may grow upon
it if it is not properly protected. The same thing is true of
dried beef, a material preserved from decay partly by a pre-
liminary soaking in brine and partly by a subsequent drying.
The methods of preparing dried beef vary. Sometimes the
process is one of artificial drying simply, but commonly
smoking and salting are adopted to aid in the process. The
drying of flesh is sometimes carried out so completely that

PRESERVATION BY DRYING 145

the mass can be reduced to a powder. Powdered meat,
however, is an article of commerce not very widely used.

Drying is adopted extensively for a variety of other
animal foods. It is much used in preserving fish, some-
times without salting, sometimes with an abundance of
salt. The heat of the sun, artificial heat, and smoking
are all employed. Mussels and other shellfish are some-
times preserved by drying.

One of the most recent and useful applications of dry-
ing is in evaporating muk. Milk is now easily dried by
special devices and is put upon the market at a low price.
The dried product will keep indefinitely, and is an extremely
valuable food, since it is one of the cheapest as well as
the most nutritious that can be bought. It will not take
the place of fresh milk, for when subsequently dissolved
in water it has a peculiar flavor, not unpleasant, but not
like milk. For baking and for many other purposes, how-
ever, it has proved to be one of the most useful as well as
one of the cheapest of foods. It is as nutritious as milk,
is easily digested, and has the great advantage of keeping
indefinitely without decaying, souring, or molding.

In the drying of flesh, milk, etc., it must be remembered
that the process simply checks the growth of bacteria, but
does not necessarily kill them. Hence, if the meat con-
tained any disease germs at the time of drying, the process
itself would not remove the danger of eating it. Meat
from diseased animals cannot, therefore, be rendered fit
to eat by drying. Even the parasitic worm, Trichina, can
withstand the smoking in the curing of ham. Unless the
temperature is raised quite high during the drying, the
process does not, therefore, remove dangers attending

146 BACTERIA, YEASTS, AND MOLDS

the use of food procured from diseased animals. In the
process commonly adopted for drying milk, sufficient heat
is used to render harmless any disease germs it may have
originally possessed.

A large variety si fruits, berries, and vegetables are also
capable of preservation indefinitely by the simple process
of drying. The farmer's wife has long known that she
can preserve apples by cutting them into small pieces and
hanging them in strings over her kitchen fire to dry. The
same thing is possible for many vegetables, like squashes,
pumpkins, and even potatoes. Many kinds of berries —
blackberries, blueberries, strawberries, and some others
— can be preserved by merely extracting from them a
large part of their water. This drying of fruits and vege-
tables is often accomplished by subjecting them to artificial
heat, but more commonly in recent years the materials
are subjected to hydraulic pressure, by means of which
the water is actually squeezed out. A slight subsequent
drying is then sufficient to preserve the material almost
indefinitely.

Some fruits are preserved by a combination of drying
and the presence of considerable sugar. Raisins, for
example, are dried grapes, but they are not dried so com-
pletely as berries, for some moisture is left in them. The
preservation of the raisin from decay is due in part to
the lack of water, but chiefly to the presence of a high
per cent of sugar, which is in itself deleterious to bac-
terial action. So, too, with other sweet fruits like prunes,
apricots, figs, dates, currants, etc. Their preservation is
partly a matter of drying and partly the result of the
sugar present.

PRESERVATION BY DRYING 147

A large variety of fruits may be preserved by drying
if we only have proper means for extracting the water.
Indeed, probably any fruit could be thus preserved for
future use if we could find a practical method of drying
it. To do this the fruit, divided into small pieces, must
be subjected to a heat sufficient to dry it rapidly so as
to prevent decay, but not sufficient to cook it. It is
hardly worth while to attempt such work in the ordinary
home, for the results are not entirely satisfactory, and
dried fruits are easily purchased. Some such method is
practical with certain fruits and impractical with others ;
but it always greatly changes the nature of the fruit.
Before it can be used the dried fruit must be soaked
with water to soften it, after which it rarely bears much
resemblance to the original fruit. Dried apples are quite
different from fresh ; the taste of the fresh apple has wholly
disappeared, leaving in its place an entirely different flavor.
The same is true of practically all fruits preserved by dry-
ing. Their food value has not been reduced, for a bit of
dried apple is just as nutritious as the fresh ; but fruits
have very little food value at any time, and are eaten
mostly for their flavors. Dried fruit is much inferior in
taste and cannot be used for so many purposes as fresh
fruit. The drying of fruits and vegetables leaves a pulpy,
somewhat tasteless substance, which, although it still
retains its original food material, has lost the peculiar
charm which gives value to the fresh fruit.

It must be evident, then, that drying is the most widely
adopted method of preserving foods, but it is not equally
useful for all kinds. With some it works to perfection.
For grains or other foods obtained from seeds it leaves

148 BACTERIA, YEASTS, AND MOLDS

nothing to be desired. It is useful for meats and many
other kinds of animal foods. For vegetables and fruits
its value is far less, and sometimes very doubtful. For
them it should be used only where there is a large quantity
of fresh material for which no better method of preserva-
tion can be found.

USE OF Low TEMPERATURES

The value of low temperatures in preserving all forms
of food is familiar to every one. Microorganisms are
stimulated into active growth by high temperatures and
checked by low temperatures. It must be remembered,
however, that the temperature at which bacteria grow
most readily is not always the same ; for although some
species flourish only at warm temperatures, from 70° to
1 00°, others grow best at temperatures only a few degrees
above freezing. While, then, a low temperature will check
the development of most bacteria, it will not, unless it
is actually below freezing, wholly prevent it, since some
species grow readily enough at low temperatures. In the
consideration of the use of low temperatures, therefore,
three phases of the subject may be considered, based
upon the degree of cold obtained.

i. Cold Storage. By cold storage is meant the use of
storehouses which are cooled artificially, and where a very
low and constant temperature is maintained for months
at a time. In some compartments the temperature is
held at a few degrees above freezing, while in others
it is even below freezing. These low temperatures are
commonly produced by the use of artificial-ice machines,

COLD STORAGE 149

based upon the vaporization of ammonia, and kept con-
stant in spite of great changes in the temperature of the
air outside. Cold-storage plants are a modern device,
and only within comparatively recent years have they
come to be used to any considerable extent for the pres-
ervation of food. They are now found in all our large
cities, and they are being utilized more and more each
year, producing profound modifications of the conditions
of civilized life. By means of them a large variety of
foods can be preserved for many months without any
tendency toward putrefaction and decay, and may be used
at any time with the confidence that they have been kept
in a perfectly good condition. The cold-storage plants
make it possible to keep fresh for winter or spring use a
large quantity of the perishable products which previously,
if not capable of preservation by canning, it was necessary
to throw away because of the certainty of putrefaction and
decay. Such devices are producing a far more equitable
condition in the food supply of modern communities. It
is now possible to have fresh at any season of the year
the perishable food products produced at almost any other
season, provided we take the trouble to preserve them in
cold-storage plants, and our city markets can furnish fresh
fruits at almost any time.

The length of time during which food can be preserved
by cold storage depends upon the temperature. If actually
frozen, as is commonly the case with fish, fowl, and flesh
generally, food may be preserved indefinitely. Frozen
food in the arctic regions keeps for years, and will indeed
keep as long as it remains frozen. The same would be
true of frozen food in cold storage. But some kinds of

150 BACTERIA, YEASTS, AND MOLDS

food, particularly fruits, are ruined by freezing. In these
cases the temperature may approach freezing but must
never quite reach it. Such food will be preserved for a
while, perhaps for months if the temperature is low, but
not indefinitely.

The cold-storage plant cannot be utilized by the house-
wife, and need not therefore be further considered here.
She should always remember, however, that during the
winter and spring a considerable part of the perishable
food products purchased in markets has come from cold-
storage plants, where they have been retained for a long
period at a temperature in the vicinity of freezing, or even
below it. If she buys fish, fowl, or fruit during the win-
ter, in a city market, she may regard it as probable that
they have come from cold storage. This is a matter of
considerable importance because of the practical question
of the keeping property of such material.

The question has frequently been raised whether foods
from cold storage is not subject to exceptionally rapid
decay after being brought again to a warm temperature.
It is a general belief that meats and other materials that
have been frozen decay very rapidly after they are thawed
out, and hence that food taken from cold storage must
be used quickly, since it will putrefy more rapidly than
when fresh. This belief seems to be well founded, but
the reason for it is not clear. Possibly the food is slightly
changed in its physical nature by the freezing so that
bacteria can more readily act upon it when it is thawed.
In many cases, however, especially with fruits, which are
not actually frozen, the rapid decay which follows re-
moval from cold storage is due to the large amount of

THE ICE CHEST 151

moisture which condenses upon the surface of the cold
fruit when it is placed in warm or damp air. Such sur-
face moisture, as we have seen, furnishes the necessary
condition for the starting of mold growth. The prac-
tical lesson to be learned is that after the material has
been removed from the cold storage and warmed up to
ordinary room temperatures it should be consumed as
rapidly as possible, because putrefaction and decay are
sure to take place speedily. If not used at once, it must
be kept in an ice chest. There is practically as much
difficulty in keeping food bought in the markets from
decay in the winter, if kept in a warm house, as there
is in the summer.

Cold-storage plants are hardly found outside of large
cities, and persons at a distance must depend upon other
means of producing low temperatures. These are easy
to obtain in winter, but difficult in summer.

2. Temperature of an Ice Chest. A far less efficient
means of obtaining low temperature is by the use of the
ordinary ice chest, — less efficient than cold storage simply
because the temperature is higher. The temperature of
ice chests is variable, depending upon the size of the chest
and the amount of ice in it. It will sometimes be as low
as 40°, or even lower, but never quite reaches the freezing
point ; at other times it will run up to 50°, and as the ice
melts the temperature rises to that of the outer air. Food
preserved in an ice chest is far less thoroughly protected
than in cold-storage plants. The use of the ice chest is
simply a means of checking the development of bacteria,
but it by no means stops their growth. At the tem-
perature of 40° most bacteria, if they grow at all, grow

152 BACTERIA, YEASTS, AND MOLDS

very slowly, and the food may therefore be preserved for
quite a long period, although it is sure in the end to
undergo certain forms of putrefaction.

The type of putrefaction that occurs in material kept
in an ice chest is usually somewhat different from that
which occurs in the same material at an ordinary room
temperature. The common putrefactive bacteria grow
readily at high temperatures, but hardly at all at the
temperature of the ice chest. Other types of bacteria,
however, grow more readily at the lower than at the
higher temperatures, and meat or other food kept in the
refrigerator will in the course of time undergo a type
of decay due to the microorganisms favored by the low
temperature. This decayed meat appears somewhat dif-
ferent from decayed meat at higher temperatures and has
a different odor, — a fact indicating a different type of pu-
trefaction. Certain peculiar kinds of decay are seen at
these low temperatures which are hardly found under
other conditions. Occasionally, for example, fleshy foods,
particularly those from salt water, like lobsters or fish,
develop a peculiar phosphorescence if kept in an ice chest.
If examined in the dark they will be seen to glow with a
somewhat brilliant greenish light. This phosphorescence
is due to the development of certain very interesting kinds
of bacteria, and always appears if they grow luxuriantly
at low temperatures. They grow chiefly upon foods which
contain considerable salt, and hence particularly in marine
foods. They are more likely to be found in meat pre-
served in an ice chest, since the more common decay
produced by other bacteria will at higher temperatures
mask the growth of the phosphorescent bacteria. It is

THE ICE CHEST 153

not necessary to throw such food away, since the phos-
phorescence does not appear to r,encler it unwholesome,
and it may be eaten with impunity.

Although far less efficient than cold storage, the ice
chest is a means of preserving for a short time food that
would otherwise quickly spoil. Its efficiency depends
upon its temperature. The larger the amount of ice in
an ice chest the lower its temperature and the greater its
efficiency. If the amount of ice is very small there will
be such a rise in the temperature that food placed in the
ice chest will spoil. In spite of its drawbacks the ice chest
has become a necessity in the well-ordered household. It
is frequently necessary to preserve foods for a few hours
before they can be used, and in the warmer temperature
of spring, summer, or autumn this is frequently impos-
sible without the use of ice. In particular is this true of
the preservation of milk, a topic .vhich we shall notice
by itself.

In many parts of America the ice chest has become an
almost universal aid in the housekeeping of families in
moderate circumstances, and has greatly simplified prob-
lems of home economics. To the poorer families, how-
ever, it is hardly known. The home with an ice chest
may purchase food to advantage in quantity and preserve
it for a few days till used. The poorer families must rely
upon their food being preserved by dealers in food sup-
plies, and can therefore buy only such small quantities as
can be used at once.

To keep an ice chest in good condition it must be
frequently cleaned. The inside is sure to be damp, and
dirt is quite likely to collect in the cracks and corners.

154 BACTERIA, YEASTS, AND MOLDS

This dirt will furnish a good place for the growth of such
bacteria as thrive in low temperatures, and thus the ice
chest in time becomes unfit for use. Food will not keep
well under such conditions, becoming infected with bac-
teria as well as affected by the odors given off from
the decaying material. A frequent cleaning is necessary
to keep the ice chest sweet and thus make it possible to
preserve food properly.

3. Temperature of a Cool Cellar. — It sometimes hap-
pens that the only place for storing the autumn products
is a cool cellar. This is frequently the case on the farm,
especially when considerable material is to be preserved.
A cool cellar is of use in any home, for it makes possible
the purchasing of fruits and vegetables in bulk during the
fall, when they are cheap, and their preservation for use
till a later season when they are more expensive.

The value of a cool cellar rests upon two facts : (i) The
temperature is usually lower than in other parts of the
house. (2) It is more likely to be uniform. A cellar under-
neath a house will have during the winter season, at least
in cool climates, a temperature not much above freez-
ing. For reasons which we have already considered such a
temperature will preserve fruits and vegetables from bac-
terial action or other types of decay. Where such a cellar
is at hand it is, therefore, very well adapted to the preser-
vation of fruits. Any other room, if its temperature could
be controlled, would be just as good, and if it were light
would be somewhat better than a cellar, which is usually
dark. But rooms above ground are generally lighted by
windows, which make it difficult to control the tempera-
ture. In the winter such rooms are pretty sure to have

THE COOL CELLAR 155

a temperature below freezing in the cold climates, and
this is sufficient to ruin fruits, most of which are spoiled
by freezing.

Since the value of the cellar in preserving fruits and
vegetables is simply in its uniform and low temperature,
the lower the temperature — provided it is above freez-
ing— and the more even it is, the more satisfactory are
the results. On the other hand, a warm cellar, so char-
acteristic-of most modern houses heated by furnaces, is
of very little use in preserving foods, for decay occurs
about as rapidly in such a cellar as it would elsewhere in
the house, more rapidly, indeed, than in a cold pantry.
Since one can purchase large quantities of many foods
more reasonably in the fall by taking advantage of the
low market rates, it is economy to have a compartment
partitioned off from the heating apparatus in the cellar
where fruits and vegetables can be stored. A cold closet
is, indeed, almost necessary for the keeping of preserves.

In the use of a cold cellar to preserve vegetables it is
well to bear in mind that many of them — parsnips, car-
rots, beets, turnips — are better preserved if buried in
sand, and that fruits keep better in sawdust, oat chaff, or
some other material which absorbs moisture.

Other Devices. Any device for cooling will of course
be useful in preserving foods. Cold running water, spring
houses, submerging in iced water, are all used for the pur-
pose. Suspension in deep wells is one of the most com-
mon methods of obtaining a low temperature for milk,
butter, etc., and is widely adopted in houses where ice is
not at hand. Even the scheme of packing material in
damp leaves may be of some value, since the evaporation

156 BACTERIA, YEASTS, AND MOLDS

of the water from the leaves lowers the temperature. In
warm climates this principle is made use of to cool drinks
by keeping them in earthenware receptacles the surfaces
of which are constantly moistened. The evaporation of
the water on the outside cools the inclosed liquids.

Cooling may be used for any kind of food. Three
general rules should always be followed where food is
put aside for preservation at a low temperature.

1. Cool the food as quickly as possible. This should
be done before covering and setting aside for keeping.

2. Use every possible device for avoiding moisture.

3. Use food quickly after taking it from its place of
storing, for such food when warmed decays rapidly.

THE USE OF HEAT

The easy destruction of bacteria by heat suggests a
means for increasing the keeping properties of many
foods. Liquid foods may first be boiled and then cooled
as quickly as possible, after which they may be put away
in cold places for preservation. It is necessary that the
material should actually be boiled, since a lower tempera-
ture is not only useless but frequently detrimental. If a
putrescible material is simply steeped in warm water and
then put away, it will spoil rapidly ; if it is boiled it may
be preserved for some time. Boiling is useful for such
materials as soups, stews, or any liquid not injured by
boiling. It must be remembered, however, that boiling
will not preserve the material indefinitely ; it simply delays
the spoiling.

CHAPTER XI

THE USE OF PRESERVATIVES

In early years the only means adopted for preserving
food were drying and cooling, both of which have been
known and used for many centuries. Within the last
fifty years other methods have been used for the same
purpose, and for some kinds of food they are far more
satisfactory and valuable than those just mentioned. The
first which we shall notice is the use of preservatives.

The explanation of using preservatives is that it adds
to the food something which will check the growth of
microorganisms and thus prevent decay. Such preserv-
atives must fulfill two conditions : (i) They must have
some antiseptic power. (2) They must be comparatively
harmless to man.

POISONOUS PRESERVATIVES

Since we know that the spoiling of food is due to the
growth of microorganisms it is easy to find chemical sub-
stances which will be perfect preservatives. If it were
simply a matter of protecting food from decay, it would
be the easiest thing in the world to bring about the
result. But it chances that most of the materials fatal
to the life and growth of microorganisms are also poison-
ous to man and therefore cannot be used in his foods.

158 BACTERIA, YEASTS, AND MOLDS

This greatly restricts the number of materials that can be
used for food preservation. Some it is quite impossible
to use because of their violently poisonous nature. For
example, carbolic acid and corrosive sublimate will preserve
food perfectly, since they are fatal to bacterial growth ;
but they are also violent poisons to man and hence must
not be put in his foods. There are other chemicals, how-
ever, of a less poisonous nature which are frequently used
for the preservation of foods.

The milder drugs in use to-day for this purpose are
chiefly borax, benzoic acid, salicylic acid, and formalin.
Although these substances are poisonous and injurious
to man when used in considerable quantity, they may be
swallowed in small quantities without any appreciable
effect upon the individual. But even in small quantities
they have the power of checking the growth of bacteria,
and they are frequently used for protecting various kinds
of food from the spoiling that would otherwise occur.

These materials, put up into proper form for use, can
be found in our markets under a variety of commercial
names. They usually go under special trade names, — pre-
servaline, fruit preservaline, antifermentine, freezine, etc.
These various commercial products differ in their chem-
ical analyses, but are all made up of mildly poisonous
materials. No two of these preservatives are exactly
alike, but most of them are made up, wholly or in part, of
the chemical substances above mentioned. The preserva-
line products, for example, are largely borax, while the
basis of freezine is formalin. They are undoubtedly effi-
cient in protecting food from putrefaction and decay, for
they all check bacteria growth. If used in sufficient

COMMERCIAL PRESERVATIVES 159

quantity they will wholly prevent putrefaction, and even
in small quantities they may so check the growth as to pre-
serve the food much longer than usual. For this reason
they are extremely convenient and have been widely used
by people who do not understand what they are. Some
have found them so convenient that they have given up
the use of the refrigerator or other devices for producing
cool temperatures, feeling that it is much cheaper, as well
as more convenient and more satisfactory, to keep their
food by adding a small quantity of preservaline or similar
substance, than to use ice. The various forms of pre-
servatives may be used for almost any kind of food, — for
canning fruits or vegetables, for preserving milk, meat,
etc., — and, so far as concerns the actual protection of food
from decay, they certainly accomplish their purpose.

But the important question arises whether it is health-
ful to use such materials in our food. Every one of them
is of a more or less injurious nature, and if taken into the
body in any considerable amount will produce poisonous
effects. This has led to much experimenting and discus-
sion. In past years a considerable portion of the food
products on the market has been treated with some of these
food preservatives, — borax being widely used for this pur-
pose. In the markets of Europe some of these substances
are used to preserve a large part of the meats, butter, milk,
etc. England obtains great quantities of her provisions
from America and even Australia, and it seems difficult,
or impossible, to deliver them at such long distances with-
out treating them with preservatives. At all events, the
foods coming from Australia to the markets of England
are usually so treated. The use of preservatives in our

l6o BACTERIA, YEASTS, AND MOLDS

own country is less common, because our markets are nearer
the sources of supply. The national Pure Food Law,
making these preservatives illegal, has greatly reduced
their use, and to-day the food on our markets is mostly
free from them.

It has been an open question for some years whether
borax used in small quantities under such conditions is
injurious to the consumer. Nor is the question yet posi-
tively settled. It has become in a measure an interna-
tional question, involving the importation of American beef
and other products into foreign markets, and a great deal
of contradictory evidence has been advanced. The fact that
people have for years been unconsciously using food preserved
by means of such substances, without any apparent injuri-
ous effects, seems prima facie evidence that no harm results ;
but it is possible, of course, to say that the harmful effects
are not at first discernible, and that many of the digestive
and other troubles of man are due to this unconscious con-
sumption of such drugs. No positive answer can be given
to the question. Although it is certain that many people in
large cities have occasionally, or even constantly, consumed
them without any apparent injury, the general belief is that
they are injurious.

Moreover, when such materials are used for preserving
food, it frequently happens that a considerable quantity
is unconsciously used. Our foods usually pass through
the hands of several people before they are consumed.
The original producer may put in a little preservative, the
middleman adds more in order that the material may not
spoil on his hands, and the householder, in ignorance of
these additions, may put in a little more. By the time it

PRESERVATIVES IN FOOD l6l

reaches the table it may be so filled with some of these
poisonous articles as to be decidedly unwholesome. In-
stances are known where violent sickness, and even death,
especially among children, has been traced to the use of
such preservatives, which had been added by one person
and another until the food contained them in large quan-
tity. This is particularly true of milk, because it spoils
so easily and quickly.

For these various reasons the use of such preservatives is
to-day forbidden by law in any food materials offered for sale,1
and they must also be condemned in the house, since even
in small quantities it is possible that their daily use may
cause trouble. It is also quite certain that if a preservative
is used at all, the food will occasionally contain so much of
it as to be decidedly unwholesome, disastrous, or perhaps
even fatal. No housewife should therefore depend upon any
of these forms of preservation for her food. They are un-
wholesome and even dangerous, and their use is liable
to be followed by ill health and possibly by fatal sickness.
Particularly should it be understood that it is dangerous
to add preservatives to food that has previously passed
through the hands of others who may have already used
preservatives, — a condition of things especially likely to
occur with milk. Nothing but universal condemnation
for the use of the commercial materials can be given the
householder. If any preservative is to be used, it is far
cheaper and better to buy pure borax from the druggist.
For milk or cream this may be used in the proportion
of one quarter to one half ounce to six quarts of milk or

1 By a recent ruling a small amount of benzoic acid is allowed in certain
foods.

162 BACTERIA, YEASTS, AND MOLDS

cream ; for preventing hams or bacon from molding or
becoming slimy, the borax may be dusted on the surface,
not more than one quarter of an ounce being used for
each pound of meat.

But any one of these materials, if used in considerable
quantity, is certainly injurious, and this fact makes it
quite out of the question to recommend them for home
use. It is quite impossible for the physician, much less
the housewife, to know how much may be used without
danger.

NONPOISONOUS PRESERVATIVES

In protecting food by preservatives we are not confined
to poisons, since there are a few materials capable of pre-
serving food that are not poisonous but are, on the con-
trary, beneficial to us. The use of such preservatives is
of course perfectly proper. Some of them have been in
use for many years and at the present time are more used
than ever. The chief ones are mentioned below.

Sugar. As already indicated, bacteria do not grow
readily in pure sugar solutions, and if the solutions are
very strong they do not grow at all. The other forms of
microorganisms also, molds and even yeasts, fail to grow
readily in solutions containing a considerable quantity of
sugar. It is therefore quite feasible to preserve many
of our foods from putrefaction by simply mixing them
with a considerable quantity of sugar. Since sugar is an
excellent food for man it does not injure the material but
increases the food value of the product. As a preserva-
tive sugar has more value against bacteria and molds than
against yeast. It is the material which readily supports

SUGAR AS A PRESERVATIVE 163

yeast life, and it occasionally happens that materials pre-
served by it will ferment. But this does not commonly
occur if the percentage of sugar is high, i.e. 40^6 to 50^.

The use of sugar as a preservative is adopted in a
number of well-known products. Fresh fish is occasion-
ally preserved by rubbing with sugar. Condensed milk is
preserved by the addition of 30^ to 40^ of it. It changes
the nature of the milk, rendering it somewhat less digest-
ible, but does not materially injure it as a food product.
Jellies are also preserved from bacterial action, though
not wholly from fermentation, by the large amount of sugar
which they contain ; for decay would take place quickly
if it were not present. It has been used for a long time
to protect fruits, in making what are known as preserves.
Almost any kind of fruit may be preserved by stewing it
with a large amount of sugar, equal parts by weight of fruit
and sugar being commonly used. At a moderate heat the
fruit is so thoroughly impregnated with the preservative
that no putrefactive organisms are subsequently able to
grow in it, and it may then be preserved almost indefinitely.
Marmalades are also preserved by the same preservative.
This is also, in a measure, as we have seen, the reason for
the preservation of raisins, figs, flhtms,etc., which are pre-
served partly by drying and partly by the presence of sugar.
In these cases the fresh fruit contains so much of it that
none is artificially added. But most fruits contain too
little to be preserved without the special treatment above
described. There are of course decided limitations to the
use of sugar for this purpose, for the flavors of most of our
fruits are changed when mixed with a great deal of it.
They cease to have fruit flavors and become a sort of

164 BACTERIA, YEASTS, AND MOLDS

candied material which can be used only as a sweetmeat
or a sauce. This method of preservation is used to-day
much less than in earlier years before the wide extension
of the process of canning.

Salt. A more common, harmless preservative is salt.
Materials thoroughly salted are completely protected from
bacterial growth. Since salt is harmless and, indeed, a
necessary ingredient in our food, such a method of pre-
serving is quite legitimate. Salt is used as a preservative
for a variety of food products. Fat pork is very easily pre-
served by keeping it immersed in a strong salt solution
called brine, producing what is known as salt pork. Corned
beef and corned bacon are also preserved in the same way.
Cheeses are sometimes preserved in brine, and the same is
true of eggs. In other cases the salt is mixed with the food.
Hams and some other meats are preserved partly by salt-
ing, and in most forms of dried beef salt is added to assist
in the preserving. It is used for the preservation of great
quantities of fish, particularly marine fish, which may in
this way be preserved indefinitely from bacterial action.
Fresh-water fish could be preserved equally well, but since
they are not generally caught in large numbers they are
rarely salted. The salting of butter is a procedure adopted
partly for the purpose of giving a salty flavor and partly
for the purpose of its preservation. In the preparation of
cheeses salt is almost always used, for after their manufac-
ture they are usually kept for weeks or months before they
are ready for market, and salt is rubbed into their surfaces
to prevent the growth of undesirable microorganisms.

It must be remembered that, while salting preserves the
material from decay, it does not preserve its fresh form.

SALT AS A PRESERVATIVE 165

The flavor is much changed, and too large a quantity of
salt meat is not wholesome. Moreover, salt somewhat
changes the physical nature of food, so that it is not
quite so easily digested. Salt foods, therefore, cannot
wholly take the place of fresh foods. Experience has
shown that when used in large quantities and unaccom-
panied by plenty of fresh food they give rise to a kind
of digestive derangement known as scurvy, a trouble fre-
quently met with among sailors who have subsisted too
largely upon salty foods. Nevertheless such foods are
very useful, and if a quantity of fresh food is used with
them they may be used very advantageously as part of
our diet. In preparing such foods for the table they
should be soaked in water to remove as much of the salt
as possible.

Vinegar. Acetic acid is another material used legiti-
mately for the preservation of certain kinds of food prod-
ucts. In its best known form, vinegar, it is the basis
of the preservation of all kinds of pickles. The acetic
acid in these cases serves two purposes : (i) It gives a new
flavor to the material, rendering it very sour. (2) It pro-
tects the product almost totally from the action of bacteria.
The pickling of cucumbers has become a great industry,
green cucumbers being more extensively used for the pur-
pose than any other material. The vinegar is frequently
mixed with spices, both for the purpose of added flavor
and to aid in the preservation. Although pickled vegetables
keep well, they do not keep indefinitely. Pickle brine
sometimes becomes covered with a scum composed of bac-
teria, and the pickles themselves may grow soft from decay.
If the pickles are taken out and boiled for a few minutes,

166 BACTERIA, YEASTS, AND MOLDS

the microorganisms will be destroyed, the trouble may
be checked and the pickles preserved. It is practically
important to know that pickles should not be kept in
glazed ware, since the acetic acid may unite with the
glazing and make unwholesome products. Glassware
receptacles are best for the holding of pickles.

In a somewhat modified way acetic acid or lactic acid
is the basis of certain other preserved foods. Saner-
kraut, for example, is cabbage protected from putre-
factive fermentation by allowing it to sour and develop
acids. Among these, acetic acid is somewhat prominent,
but lactic acid is also found. The acid in this case is
formed in the cabbage by the growth of acid-producing
bacteria, and after it is formed it prevents the growth
of other putrefactive bacteria, thus making it possible
to preserve for a long time the vegetable material which
would otherwise undergo putrefaction. Here we actually
have an instance of one kind of harmless microorgan-
ism protecting food from the action of other species. A
similar food product is sometimes made from beans which
are allowed to sour and are thus preserved from further
decay.

Any substance can be preserved from bacterial action
if it can be soaked in vinegar or other acid, and it is
therefore possible in the household to convert into either
sour or sweet pickles a considerable variety of vegetables.
The use of vinegar for this purpose is very limited,
mostly confined to green fruits and vegetables, although
fish or flesh is occasionally treated in the same way. The
product obtained is used as a flavor to our diet rather than
as a food.

SPICES AS PRESERVATIVES 167

Spices. Many of the spices common in the household
are more or less efficient as antiseptics, and when added
to food material will preserve it from putrefaction. Their
use is quite general in certain household products. For
example, mince-meat is a watery mixture which under
ordinary circumstances would readily putrefy. Both the
meat and the apple in it would by themselves undergo
putrefaction and decay ; but when they are made into
mince-meat, and spices, boiled cider, and some other mate-
rials added, the entire mixture forms a mass which, though
not absolutely protected from the growth of microorgan-
isms, is ordinarily incapable of supporting the growth of
the putrefactive and decaying bacteria which would natu-
rally appear in the ingredients. The antiseptic effect is
produced chiefly by the spices, and if the housewife should
leave these out she would have a putrefying mass in a short
time. Such material is not, however, completely protected
from mold growth. It will keep longer if the apple is left
to be added at the time of using, and, of course, it will keep
best in a cool temperature. In a warm temperature the
effect of the spices is not sufficient to prevent a more or
less troublesome fermentation and decay, and particularly
molding.

In ordinary sausages and salads the same principle is
concerned. Sausage meat is made of material which is
subject to rapid putrefaction, but in cool weather it may
be preserved for a long time. Here we have again an
example of a readily putrescible material prevented from
decay by the presence of the slightly antiseptic spices,
like salt, sage, etc. The spices in the sausages have
really a twofold purpose. Not only do they protect the

168 BACTERIA, YEASTS, AND MOLDS

materials for a time from putrefaction, but they give to
them the peculiar flavor which is desired. In the case of
sausages, as in mince-meat, the spices are not sufficient
to prevent putrefaction absolutely, and consequently in
the warm summer weather it is not very easy to preserve
them. Sausages, like mince-meat, are generally made in
cold weather, for under such circumstances they may be
preserved without trouble for a considerable length of
time.

In a somewhat similar way, as we have already noticed,
hops are used for aiding in the preservation of a yeast
brew. They are also frequently used in making beer, to
which they not only impart a desired flavor but also aid
in preventing the decay of materials present which would
readily support the growth of bacteria. Fruit cake of
certain grades is preserved from spoiling chiefly by the
spices it contains. Nearly all strong spices have an anti-
septic power when mixed with foods, and protect them to
a greater or less extent from bacterial action. This fact
is made use of quite extensively by different nations ;
for most countries have special spiced foods preserved in
this way, many of which are not known to people outside
of the localities where they are made. Spices are thus of
much value both as a means of imparting flavor and as
a preservative, but they never preserve the original taste
of the foods. Many spiced foods are used simply as
condiments rather than as nourishment.

CHAPTER XII
PRESERVATION BY CANNING

The addition of mild preservatives like sugar, salt,
spices, vinegar, etc., while it makes possible the preser-
vation of many kinds of food, very decidedly changes
their nature. The flavor is totally changed, and in some
cases the food is rendered less digestible ; hence its food
value is lowered. These methods of preserving food are
very useful for some purposes, but they cannot be used
for all kinds of food. In many cases the change of flavor
would be so decided and the change in the nature of the
food so great as largely to destroy the material for subse-
quent purposes. None of the methods preserve the food
in anything like its natural condition.

WHAT is CANNING ?

A method of preservation based upon the simple plan
of keeping bacteria away from food products has been
devised in the last century. This has come more and more
into common use, until to-day it is employed to an almost
incredible extent. The method is spoken of as canning.
The food is not treated by any antiseptic for the pre-
vention of bacterial growth, but reliance is placed simply
upon devices for keeping all bacteria from it. If this can
be done, the food will not be subject to their action, and
will never spoil.

169

I/O BACTERIA, YEASTS, AND MOLDS

We have already noticed that bacteria are almost uni-
versally distributed in earth, air, and water. This fact
makes it extremely difficult to protect food from their
action, and, indeed, without special devices it is quite
impossible to do so. All food material — meats, fruits, or
vegetables — is sure to contain bacteria when it reaches
the home or the canning factory. From some source,
either air, water, or earth, every kind of food material is
sure to become contaminated. Every one must recognize,
then, that bacteria will be found with absolute certainty in
every kind of fresh food.

Hence the process of keeping food by protecting it from
bacteria must consist of two steps : (i) Some means must
be devised for removing the bacteria already present in
the food. (2) The access of all other bacteria must be
absolutely prevented. If these two objects can be accom-
plished, the food will be protected from bacterial action
and, thus protected, may be preserved indefinitely. Food
thus guarded may be kept for any number of months. No
limit has ever been found, and we have no reason for ques-
tioning that it might be preserved for centuries without
any subsequent change, provided it could be kept abso-
lutely free from the attack of microorganisms. This
method, therefore, offers almost unlimited possibilities in
the way of preserving food for future use. It demands
care in its application, but the results, when properly
obtained, are permanent.

i. Destroying the Bacteria Present. The removal from
any food material of bacteria already present is generally
brought about by the action of high heat. We have
already noticed that a sufficiently high heat is fatal to all

STERILIZATION FOR CANNING 171

forms of life, and hence the simple heating of food will
destroy all bacteria. The material to be canned must be
cut up into pieces of convenient size, which will depend
somewhat upon the kind of material. In general, the
larger the pieces, the more attractive the appearance of
the product when finished but the greater the difficulty
of canning. Cherries, plums, and berries can be left
whole. Pears are cut into halves or quarters, while apples
are commonly cut into smaller pieces. These pieces are
to be placed in water and the whole brought to a brisk
boil, — this temperature being chosen because it is easily
obtained and because it is sufficient in most cases to destroy
the bacterial life. The process of canning is, therefore,
applicable only to materials that are not greatly injured by
immersion in water and subsequent boiling. Hence it is
useful for foods which cannot be well preserved by drying.
In the application of heat several points must be borne
in mind. I. It must be remembered that the destruc-
tion of the bacteria must be absolute. If a single indi-
vidual bacterium is left alive in the food after the boiling,
the whole process is useless, and the canning will be a
total failure. One live bacterium will be capable of grow-
ing and multiplying, producing a subsequent putrefaction
and destruction of food with just as great certainty, though
not so quickly, as if a million of them were left alive. The
preliminary heating must therefore be a complete sterili-
zation, that is, a heating so thorough that every individual
bacterium is destroyed. No half-way processes are of any
use whatsoever; it must be total and absolute. This is
by no means easy, and most failures in canning are due
to the inability to bring about this complete destruction.

BACTERIA, YEASTS, AND MOLDS

If a housewife finds that a portion of her canned preserves
is spoiled, she may be sure that the original heating was
insufficient.

2. It must be remembered that the amount of heat
required to destroy different species of bacteria is not
always the same. While most actively growing bacteria
are destroyed by a moderate heat, and quickly killed by
boiling, certain bacteria spores, as already noticed, are
capable of standing much greater heat. Some kinds of
bacteria produce spores that may be boiled for a few
moments, or, indeed, for an hour, without being wholly
destroyed. From this it follows that a short boiling
is not always sufficient to destroy bacterial life. If the
food material chances to contain some of these resisting
spores, the brief boiling commonly adopted in the pro-
cess of canning will not kill them, and it will inevitably
happen that the food, if canned, will undergo putrefac-
tion because of the growth of the spores that were left
uninjured. If on the other hand the food in question
does not chance to contain such spores, a few moments'
boiling is quite sufficient to protect the material perfectly
from later decay.

It is a well-known fact that the process of canning is
not equally successful with all kinds of foods. Some sub-
stances (rhubarb} contain a material that acts as a par-
tial antiseptic and can be preserved very easily. Others,
like most fruits, require a little more care, but are easily
preserved ; while others, in spite of the ordinary precau-
tions, will frequently show subsequent signs of decay.
The canning of tomatoes has always given trouble to the
housewife. In former years it was thought to be an

DIFFICULTIES OF CANNING 173

impossibility to can green corn, and the preservation of peas
and beans has proved to be even more difficult. While
all of these products are successfully preserved by canning
to-day, it is chiefly done in factories ; for they are far more
difficult to preserve in this way than a large number of
other foods which are more commonly preserved in the
home. The problem of canning any product, whether it
be fruit, tomatoes, corn, or peas, is simply that of totally
destroying the bacteria that may be
present. If the material chances to
contain only the bacteria that are
unable to produce spores, as with
most fruits, it is quite easy to
destroy them by simple boiling.
Green corn, however, has been *V
found by microscopic study to con- FIG. 63. Spore-producing
tain a considerable number of a cer- bacteria found in canned
tain kind of bacteria which develop

spores capable of resisting very high heat (Fig. 63). These
bacteria have been found on the corn husks while grow-
ing in the field, on the corn cobs, and also in the green
corn. They are difficult to destroy by heat, and hence
the successful canning of corn has been regarded in
past years as an impossibility. The presence of two or
three or even one of these highly resisting spores may
be quite sufficient to make the ordinary method of can-
ning quite ineffectual. Although little microscopic study
has been directed to other similar problems, like the can-
ning of tomatoes and peas, there is no doubt that the
trouble is due to the presence of spore-bearing bacteria
which resist the temperature of ordinary boiling.

1/4 BACTERIA, YEASTS, AND MOLDS

The remedy in all such cases is greater heat, since no
satisfactory means of destroying bacteria is known except
the application of heat. Even spores may be perfectly
destroyed if the proper method is adopted.

Higher Heat. Common liquids, when boiled in open
vessels, cannot be heated above 212°, no matter how brisk
the boiling ; but if boiled in closed vessels under pressure
the temperature may be raised much higher. A tempera-
ture of 212° does not destroy spores, but a few degrees
higher will do so. If the material is boiled under pressure
of a few pounds only, such a temperature is easily obtained,
and if it is maintained for a short time the spores will be
destroyed. In the household it is rarely possible to use
apparatus for this purpose; but in canning factories there
is no difficulty in constructing and using devices for heat-
ing under pressure. This method of heating is commonly
adopted for the sterilization of food products which are
difficult to can because of the presence of spores.

Longer Heating. Higher temperatures are not easily
obtained in the household, but the spores may be killed
by simply prolonging the boiling. If spore-bearing mate-
rial is boiled for a sufficient time, the spores are eventually
totally destroyed. The length of time necessary for the
purpose cannot be stated exactly, for it will depend very
largely upon the vigor of the boiling and the nature of the
food. For the thorough sterilization of peas an hour, or
even two hours, may be needed, and an equal time is
required for corn or beans. Tomatoes do not require
quite so much time. Any material will be more surely
sterilized if placed at first in cold water and then brought
to a boil, than if placed immediately in boiling water.

HERMETICAL SEALING 175

Nearly all failures in canning are due to an insufficient
amount of heating at the outset. In the canning of
fruits, which is the kind of preserving most commonly
performed at home, there is seldom any special difficulty,
since fruits do not as a rule contain resisting spores.
In the majority of cases, therefore, a vigorous boiling of
fruits for a few moments is sufficient to destroy bacterial
life, after which the materials can be canned with perfect
success. It must be remembered, however, that absolute
certainty cannot be reached by simple boiling, and that
the employing of this method will result in occasional
failures. Once in a while a can will become decayed,
though the rest of the same lot will be preserved in the
proper fashion. The difference in these cases is doubt-
less due to the accidental presence of some spore-producing
bacterium which happened to get into one of the cans and
not into the others.

2. Preservation. , After the food has once been de-
prived of bacteria (sterilized), it must be protected from
the subsequent access of all kinds of microorganisms.
Since bacteria are always present in the air, any of
these sterilized products will surely be reinoculated if
exposed, and the new bacteria would soon spoil the food.
The practical method of keeping bacteria out is, there-
fore, that of sealing the contents hermetically. In the
laboratory it is possible to preserve foods without sealing
by simply filtering all the air that reaches them through
something fine enough to 'exclude bacteria. Bacteriolo-
gists have found that the air which passes through cotton
is deprived of all bacteria. If, therefore, any sterilized
material is placed in bottles, tubes, or vials which are

BACTERIA, YEASTS, AND MOLDS

tightly plugged with cotton, as shown in Fig. 64, it will
be perfectly protected from the invasion of bacteria. A
knowledge of this fact may be of some practi-
cal importance, even in the household, in case
it is desired to preserve something for a short
time only and one does not want to go to the
trouble of hermetical sealing. But such a
method is quite impracticable for the ordi-
nary canning of food. At best it is of only
temporary utility, for, though cotton keeps
all bacteria away from the sterilized material,
it will not wholly exclude molds, and there-
fore cannot preserve indefinitely.

Hermetical sealing, which will prevent all
subsequent access of air, is extremely easy to
accomplish and is thoroughly effective. The
material must be sealed in some proper re-
ceptacle while still hot from the boiling, for
it is at this time sterile, and if sealed at once
has no opportunity of becoming inoculated
with more bacteria.

The devices for hermetical sealing are
served cher- numerous. In earlier days the housewife
ries, showing employed ordinary bottles, which were filled

that the ex-
clusion of air with the material, then plugged tightly with

is not neces- corks, and sealed with rosin or something of
saryforpres- the sort to exciucie an air The invention

ervation.

of the modern fruit jar with its rubber ring
and convenient top has done away with all such crude
devices. The fruit jar with its variously devised top is
a perfectly effectual means for excluding air and hence

FIG. 64. Pre-

THE FRUIT JAR 177

for keeping out all microorganisms (Fig. 65). The sig-
nificant feature of these fruit jars is the rubber ring a,
which is clamped tightly upon a flat ledge on the jar c, by
means of the cover b, so made that heavy pressure can be
exerted upon the rubber. This pressure upon the rub-
ber effectually excludes all air and all bacteria. Fresh
rubber rings should be used each time the jar is filled,
since the efficiency of the sealing depends upon the soft-
ness and elasticity of ^— — ====.
the rubber; if this
gets hard, as it will
in a few months, the
sealing will not be
effectual. Of course
the whole jar must

be Sterilized before FIG. 65. The top of a common fruit jar.

being filled. To do At a is the rubber rins uPon which the suc'

cess of the sealing is dependent.

this it is best to place

it in cold water, bringing the water to a vigorous boil, and

then fill the jar while it is still hot.

The glass fruit jar is almost universally used in the
home, is very convenient, and can be used again and
again. But in canning factories the use of tin cans is
largely adopted, since they are less expensive and are
to be used but once. The principle of their use, how-
ever, is exactly the same as that of the glass jar, although
the details are different. The material to be canned,
with or without previous boiling, is put in the tin can,
upon which a cover is placed and sealed firmly by sol-
dering, the whole now being closed to the air except
for a small opening in the cover. Then the can, with

1/8 BACTERIA, YEASTS, AND MOLDS

its contents, is placed in a convenient heating appa-
ratus for thorough sterilization, the opening in the top
being sufficient for the exit of steam and for preventing
internal pressure, which might give rise to an explosion.
In some factories it is sometimes customary to heat the
product in a bath of CaCl, which makes it possible to
obtain a temperature of 260°- — quite sufficient to sterilize
the contents of the can, even though it contain resisting
spores, as will be the case with peas or corn. While the
material is still hot a drop of solder is placed upon the
opening in the top of the can. This thoroughly seals it
and the work is done. It is customary to keep the cans
in the factory for a while in order to test the efficacy
of the work. Any cans which later are found to be
swollen, indicating the accumulation of gas on the inside,
are discarded as ruined. In the ordinary process it fre-
quently happens that an occasional can either fails of ster-
ilization or of complete sealing; the result of which is a
subsequent ruin of the product. Canning factories some-
times suffer great loss from the spoiling of their products.
In all these cases the cause is probably the presence
of resisting spores, and the remedy is the application of
greater heat. A knowledge of this fact has enabled can-
ning establishments in recent years to avoid in great
measure their previous losses.

In certain kinds of canned food it has been customary to add
some mild antiseptic to aid in the subsequent preserva-
tion. The material most commonly used for this purpose
is borax, which is frequently found in cans of meat. Its
purpose is to check the development of any bacteria that
may be left in the meat after the process of canning.

PRESERVATIVES USED IN CANNING 179

From the facts already given it will be seen that the
presence of borax in canned foods is totally unnecessary,
provided sufficient care is taken in the canning. Its
use was a means of covering up a lack of thoroughness
in canning, and it has been found in the cheaper products.
If the material had not been heated enough to produce
complete sterilization, it might still be preserved in cans
if sufficient borax were added. In large packing factories
where a great amount of food, particularly meat, is to
be canned at once, it had become quite common to use
a certain amount of such a preservative to cover up this
lack of complete sterilization and prevent subsequent loss.
The method is of course more economical, because it does
not require so much heat and because there is a very
much smaller per cent of loss. Whether the material thus
preserved is unwholesome is a question that has not yet been
positively settled, but the sale of it is to-day forbidden by
the national Pure Food Law. In fruit canning in the
household it may be given as a universal rule that no dis-
infectants of any sort should be used. If the housewife
cannot satisfactorily preserve her fruits without them, she
would do very much better to depend upon the commercial
products which she can buy at the store. At all events, no
one should under any circumstances resort to the use of
borax, preservaline, antifermentine, or any of the other
materials put upon the market for preventing fermentation.
They are dangerous to use, they are at least partly poisonous,
and their use in any form should be absolutely avoided in
domestic work.

Practically any type of food can be preserved by can-
ning. Some materials, however, are very much more

180 BACTERIA, YEASTS, AND MOLDS

easily preserved than others. Meats are preserved with
great ease, but it is rarely worth while in the household
to can meat, since fresh meat can be bought in civilized
countries at all seasons of the year. When one wants
canned meats it is better to depend upon the product
bought in the market than to go to the trouble of canning.
The same may be said of tomatoes, corn, peas, or beans. All
of these materials may be canned successfully in an ordi-
nary household, but it requires long heating and special
care, and at best there will be many failures. Consequently
such materials, when canned in the home, may be very
expensive because of the considerable amount that must
be thrown away. In the canning factory, however, because
of greater experience and better facilities, these foods
can be preserved much more successfully and cheaply.
Moreover the commercial products in these cases are of a
very satisfactory quality and very cheap. If for any reason
a housewife has on hand a large quantity of tomatoes
which must be canned or thrown away, it may be econom-
ical to can them at home, always remembering that they
require more heat and more care than most other fruits.
But except under such conditions it is better and cheaper
to depend upon the market for canned tomatoes, peas, and
corn. The market products are more reliable, consider-
ably cheaper, and usually nearly or quite as good as those
obtained by home canning.

Concerning other materials, however, it is economical
and frequently advantageous to adopt the process of can-
ning in the household. Most forms of fruit — apples,
pears, cherries, peaches, grapes, berries, etc. — are canned
without much difficulty, requiring only a moderate boiling

VALUE OF CANNED GOODS l8l

and a careful sealing in fruit jars. The material thus
prepared is usually of a better flavor, because more care-
fully prepared, and more satisfactory than much that can
be bought in the markets, in the preparation of which
wholesale methods have been necessary. For the house-
hold, therefore, canning is chiefly applicable to fruits, and
it furnishes a means of keeping for winter use many
delightful delicacies.

The process of canning has wrought a wonderful change
in civilization. It has made possible the use of great
quantities of material which previously were sure to decay
before they could be used. It is possible to take any crop
which is produced in abundance during a short season and
preserve it indefinitely for future use. It has brought
about a great expansion of the food possibilities of the
human race and -a very great change in the habits of
civilization.

Canned food is, however, always changed in character
by cooking, although materials which are ordinarily cooked
before they are eaten may, of course, be canned without
further change. The most noticeable effect of the process
is the total disappearance of the original flavors. Canned
fruit has a flavor of its own and oftentimes a very pleas-
ant one, but the flavor of the fresh fruit is usually more
agreeable. Experience has shown that a diet of canned
foods alone is not wholly satisfactory, although arctic
explorers have learned that they can live upon them much
more healthfully than they can upon salt foods, which
were the staple diet on shipboard before the extended
adoption of canning. Canned foods are valuable, but
they should not be used exclusively.

CHAPTER XIII

MILK; EGGS; PTOMAINE POISONING
BACTERIA IN MILK

It is more difficult to preserve a supply of good milk
than of almost any other food product. This is due to
three reasons : (i) The number of bacteria, under ordinary
circumstances, is greater than in any other food product.
(2) Milk furnishes an exceptionally favorable food for
bacteria. (3) The changes which these bacteria produce in
milk are very decided and take place with great rapidity.
These three factors together make it difficult to preserve
milk in the household without exceptional precautions.

The bacteria present in milk are not only numerous,
but they comprise many kinds (Fig. 66). Milk as it is
secreted by the healthy cow does not contain bacteria, but
it has a chance of contamination with microorganisms
from a variety of sources, and even a few moments after
the milk has been drawn it contains organisms in large
numbers. The chief sources of these organisms are :
(i) the bacteria in the milk ducts which are washed into
the milk can during the milking ; (2) the dust that is likely
to be floating in the air of the barn or milking stall where
the milk is drawn ; (3) the milk vessels, which are rarely
washed perfectly clean ; (4) the dirt and filth that are
always clinging to the hairs of the cow and which fall into

182

PTOMAINE POISONING

183

the milk pail during the milking ; (5) bacteria from the
hands and clothing of the milker.

The number of bacteria found even in fresh milk is
extremely great, particularly if the milk be drawn without
special precautions for cleanliness. Thousands and even
hundreds of thousands are sometimes found in each cubic
inch. These
bacteria grow
rapidly, inasmuch
as milk is warm
when drawn
from the cow,
and by the time it
reaches the con-
sumer in the city
the milk is likely
to contain these
microorganisms
in in cred ible
numbers. The

exact numbers, FIG. 66. Milk as shown under the microscope, show-
however, are mat- ing numerous bacteria, a, common lactic bacteria ;
ters of no Special b> common cocci ; c, fat globules ; d, cells.

importance to us, for fortunately most of the bacteria in
milk are harmless. Some of them, indeed, are useful, and,
while occasionally troublesome bacteria get into milk, as a
rule we may look upon the milk bacteria as doing no injury
to the health of the person drinking it (Fig. 67).

Effect of Bacteria upon the Milk. But the housewife
is interested in the effect of the growth of bacteria upon
the milk itself. The bacteria which grow most rapidly in

1 84

BACTERIA, YEASTS, AND MOLDS

milk belong to a type known as lactic bacteria (Fig. 67).
These produce a change in the milk sugar, converting it
into lactic acid, which causes the milk to taste sour and
curdle. Curdling and souring will never occur if bacteria
can be kept out of the milk. Although the souring is a
oo n nuisance, it does not injure

>g« 9qrf>_ the wholesomeness of the
milk, and sour milk could
be used freely were it not
for its unpleasant taste.
Indeed, souring is, under
some circumstances, desir-
able, since milk properly
soured is protected from a
variety of other changes
far less agreeable. If the
lactic bacteria do not cause
the milk to sour, it is
almost sure to putrefy, and

i , the most common lactic bacterium, B. lactis putrefaction is far more

acidi; 2, a less common lactic bacterium unpleasant and Unwhole-
n. lactis aerogenes ; 3, common cocci found

in milk; 4, a bacillus producing cheese SOmC than Ordinary SOlir-

flavors ; s, a common bacillus with no action . .-p., . r .,,

on milk, *. «*,7«; 6, a bacillus causing "lg. The SOUring of milk,

slimy milk, B. lactis viscosus ; 7 and 8, com- therefore, is SL natural phe-
mon organisms with no action on milk; 9,

bacillus causing swelling of cheese; 10, a n O m 6 n O n, and OttC that

bacillus causing milk to become putrid. should be expected and

desired in milk after it has become a day or two old.
Milk which will not sour is suspicious, unless it has been
kept at a very low temperature for preservation.

Sometimes milk a day or two old becomes slimy or
slippery to the touch, rather sweetish to the taste, and is

9 ^ fo

FIG. 67. Group of milk bacteria.

PRESERVATION OF MILK 185

ruined for all practical purposes. There is no special rea-
son for believing that such milk is unwholesome ; but
people will not drink it since it is not normal milk. Milk
occasionally undergoes a sort of putrefaction, becoming
tainted in smell and taste. Sometimes it becomes blue
or red, and occasionally other changes take place in it.
Practically all of these phenomena are due to different
species of bacteria, and they may all be prevented if the
growth of the microorganisms can be held in check.
None of them, however, produce so much trouble in the
household as souring, and although, from the standpoint
of health, some of these other types of bacterial action
are more serious than the souring, the latter is the phe-
nomenon which produces the greatest inconvenience.

PRESERVATION OF MILK

The preservation of milk, which commonly means pre-
venting the milk from souring within too short a time, is
accomplished only by checking the growth of bacteria.
In considering the question of furnishing the household
with good, sweet, wholesome milk, several factors are
involved which must be considered separately.

i. Source. Every housewife should be very particular
about the source from which she obtains her milk. This
is a matter frequently overlooked, and milk is obtained
without special consideration as to its source, upon the
general assumption that all milk is alike and that it makes
little difference from whence it comes. This is common
in the families of the rich and the poor, because the
former leave the purchase to servants, and the latter are

186 BACTERIA, YEASTS, AND MOLDS

likely to buy the cheapest quality. No article of food
should be so closely scrutinized, for, although the legal
safeguards which the public milk inspection places around
our milk supplies insure a tolerably good chemical quality,
there is a great difference in the product from different
sources. It is an absolute rule that cheap milk is always
poor milky and the cheaper the less its value. It is not
economy to purchase poor milk, for, although there may
be a saving in the original purchase, the amount of food
bought is less and the danger attending its use is much
greater. Recognizing, then, that its value is in propor-
tion to its cost, we notice the kinds of milk that may be
purchased in the modern city.

Sanitary Dairies. Certified Milk. The most expensive
milk comes from special dairies where great care is taken
to keep everything in proper sanitary condition. The
cows are kept in first-class health and are under the care
of a veterinarian. Every precaution is taken to exclude
contagious diseases from contact with the dairy, and care
is taken to keep everything clean and sanitary. For all
this care the dairyman must of course be reimbursed by
the consumer, and he is obliged to charge a higher price.
In the vicinity of our larger cities many of these dairies
have grown up in the last few years and are to-day furnish-
ing an exceptionally high grade of sanitary milk, for which
the charge is commonly from twelve to fifteen cents per
quart. Such milk, though the most expensive, is undoubt-
edly the best and is far safer than the ordinary milk.

A modification of this method is the sale of what is
called certified milk. This is milk that is sold with the cer-
tificate of a special commission, commonly composed of

TYPES OF CITY MILK 187

physicians. This commission, by means of chemical and
bacteriological tests and sometimes by visits to the dairies,
insures itself that certain dairies produce milk of good
character and under unexceptionable conditions. Exam-
inations and tests of the milk are made frequently, and if
it comes up to the high standard which is set, the com-
mission gives the dairy its certificate, which is then placed
upon each bottle of milk sold. Such a certificate assures
the customer that the milk is thoroughly reliable.

Milk from the Ordinary Milkman. Milk from the com-
mon milk supply is less reliable and costs correspondingly
less. Sometimes this milk is of a good character, perhaps
of as high a grade as that from the sanitary dairies. At
other times, however, such milk is not satisfactory, because
it is produced under conditions of unimaginable filth.
There is no way for the consumer in a large city to deter-
mine whether the milk from the milkman is reliable; and
if milk is to be purchased from an ordinary milk supply,
one .must be content with such legal regulations as the
state can devise for protecting the quality of milk. If one
lives in a small community where the milk is distributed
by the producer himself, it is quite possible to know more
about its quality ; for a little care in selecting the most
cleanly milkman will ordinarily result in obtaining milk
that is thoroughly satisfactory.

Grocery Milk. The poorest kind of milk that can be
purchased is that upon which the poorer classes in cities
largely depend. This is obtained from groceries, and is
bought in small quantities. This method of purchasing
is a necessity with the poorer classes who have no re-
frigerators, for in warm weather it is quite impossible to

188 BACTERIA, YEASTS, AND MOLDS

preserve milk in a tenement house without the use of ice.
The grocer keeps the milk on ice, and the customer buys
it in small quantities to be consumed at once. This would
be a proper arrangement if it were not for the fact that
poorer kinds of milk find their way into these groceries,
and are likely to be kept until old, so that as a rule the
milk thus purchased is the poorest grade that reaches the
market. It is usually sold at a small price, but is of such
poor quality that the poorer classes themselves would be
much wiser to purchase a better grade.

By the removal of part of its water the keeping property
of milk may be increased. Condensed milk is such a prod-
uct, which, after condensation, is commonly preserved by the
addition of about 40^) sugar or by sterilizing. It is a useful
product, but cannot exactly replace fresh milk. A type
sometimes called concentrated milk has three quarters of
its water removed by evaporation at 140°. This destroys
disease germs and brings the milk into a condition in
which it will keep for many days. When, subsequently,
the water is restored, the material is indistinguishable from
fresh milk and will be easily substituted for it.

But our care should not cease with the scrutiny of its
source. Even though originally of the highest character,
milk will not keep in our homes unless properly treated.
The keeping of milk depends upon temperature and
cleanliness in the pantry.

2. Milk Vessels. Special care should be given to the
vessels in which milk is received and kept. A large part
of the trouble which the housewife experiences in keeping
milk is due, not to the milkman, nor to the character of
the milk which she purchases, but to the condition of the

PRESERVATION OF MILK 189

vessel in which she places it. A milk pitcher used day
after day becomes filled with lactic acid bacteria, and any
fresh milk poured into such a receptacle will be sure to
sour in a very short time. This fact a housewife fre-
quently overlooks. Milk vessels should be cleaned with
the greatest of care and should be thoroughly scrubbed
with boiling water in which there is considerable soap.
The soap "cuts" the grease and cleans the dirt from the
milk vessels, and the boiling water kills part of the bac-
teria ; so that through the agency of the soap and the
boiling water the milk receptacles are pretty thoroughly
cleaned. Glass vessels are more satisfactory than others,
since it is much easier to tell whether they are clean.
Glass, however, is easily broken in hot water, and care
must be taken in the cleaning.

3. Temperature. The effect of temperature upon the
keeping of milk is more striking than upon that of any
other food product. Since milk may be frozen, it may be
kept in that condition for weeks, months, or even years
without change. It is rarely possible to preserve milk in
this way, however, although freezing has recently been
adopted in some communities as a means of furnishing
fresh milk to the public. But other means of cooling are
in constant use. Milk is frequently placed in a cellar, since
the temperature is lower than in the rest of the house.
Another widely adopted plan is to lower the milk into a
well, where, since it is near the water, it is cooled. An
even more practical and widely used device is the ice
chest, in which low temperature can be easily maintained.
The lower the temperature the better the results, and con-
sequently the more ice used the better. The ice chest has

IQO BACTERIA, YEASTS, AND MOLDS

become a practical necessity for families who try to keep
milk for even a few hours in hot weather. If not cooled,
milk will sour very rapidly. In a moderately warm room it
will keep for a few hours only, and in summer it will some-
times sour almost as soon as delivered to the customer.
The housewife should, therefore, place the milk in as cold
a place as she can find immediately after receiving it from
the milkman.

One caution must be given in regard to milk preserved
at low temperatures. If milk is put in an ice chest
with a temperature in the vicinity of 40°, it may keep
for many days or even weeks without souring. It is
usually assumed that milk is perfectly good and whole-
some so long as it is not sour. This is based upon the
assumption that the only important change to be feared
is souring ; so that if it is not sour it is almost universally
regarded as wholesome. Nothing could be further from
the truth, for, although the lactic bacteria do not grow at
low temperatures, certain other species do grow readily
enough. Milk kept in an ice chest for many days, even
though perfectly sweet and showing no trace of souring
or curdling, usually contains great numbers of bacteria.
The bacteria that grow under these circumstances are
likely to be more injurious to health than the lactic bac-
teria. The latter are not injurious, although they render
the milk unpleasant ; while the bacteria that grow at low
temperatures are, some of them at all events, mischie-
vous forms, and the milk may, therefore, be made very
unwholesome by them. If any unusual smell or taste
should appear in milk which has been kept for a day or
two in an ice chest, it is not fit to drink, for this means

STERILIZATION OF MILK 191

that unusual types of bacteria have developed to great
extent and have probably made it unwholesome.

4. Use of Preservatives. The facts given elsewhere
concerning the use of preservatives apply equally in the
case of milk. The use of any preservative is always to
be deprecated, and, so far as concerns the housewife, the
rule should be that no preservatives should ever under
any circumstances be used in milk.

It should be borne in mind that none of these devices
remove dangerous disease germs. They make it pos-
sible to keep the milk longer, but do not make it more
wholesome if it chances at the outset to contain any
mischievous bacteria.

5. Sterilization. Sterilization of milk has become
extremely common in the last fifteen years. It has been
recommended widely by physicians, it has been introduced
by milk-supply companies, and it has very frequently been
adopted in private families. In our large cities, during
hot weather, families unable to obtain ice protect their
milk by heating it. The most common method is that
of simple boiling, a boiling temperature being sufficient
to kill most of the bacteria present. Not all of the bac-
teria are killed by this method, and hence the milk is
not strictly sterilized, for this term means the destruc-
tion of all bacteria. But the boiling does destroy most
of them, and since it is an extremely easy method to use,
the boiling of milk is a very general practice. Absolute
sterilization is possible by using a heat higher than that of
boiling, but this cannot be done in the ordinary kitchen.
In common use sterilizing simply means boiling, and we
$hall so use the word, although it is not strictly correct,

192 BACTERIA, YEASTS, AND MOLDS

The purpose of sterilization is twofold, (i) It delays
the souring of the milk. Milk that has been boiled may
keep from souring for several days, whereas without boil-
ing it will keep only a few hours. With the poorer fami-
lies in cities this is the chief purpose of boiling the milk,
since it will not keep more than a few hours without ice,
and they have no ice chests where it can be preserved
from souring. (2) The destruction of disease germs. Milk
is a common means by which certain contagious diseases
are distributed through a community. The diseases in
question are produced by bacteria in the milk, and boiling
destroys them. This is the ground upon which physicians
and health boards have in the past few years so widely
advocated the boiling of milk that is to be used for drink-
ing. Since boiling does destroy practically all the disease
germs liable to be in milk, it makes it incapable of dis-
tributing contagious diseases.

There are certain disadvantages in boiling milk. The
taste is wholly changed, for boiled milk is quite a different
article from raw milk. Most people do not enjoy the
taste of boiled milk, and the adoption of sterilizing or
boiling will, therefore, greatly reduce the amount of milk
used as a food. It might indeed be possible to learn to
enjoy the taste of boiled milk. Children brought up on
it like it, while they cannot tndure the taste of raw milk.
A more serious objection to sterilization is that the heating
so changes the nature of the milk that it is less easily
digested and assimilated. Boiled or sterilized milk can
be digested and assimilated readily enough by persons
with strong digestive powers, and many children are satis-
factorily brought up on it ; nevertheless it is somewhat

PASTEURIZATION OF MILK 193

more difficult to digest and assimilate than raw milk, and
frequently children with weak digestive powers do not
flourish when fed upon such milk. This is a serious
matter and has prevented the widely extended use of
sterilized milk. Because of these objections the practice
of sterilizing has not increased in the last few years as it
was once believed it would.

6. Pasteurization. — The objections to boiling have led
to the adoption of a different method of treating milk for
the purpose of accomplishing the same results. Pasteur-
izing is also dependent upon the use of heat, but a lower
degree than that of boiling is used. The temperature
adopted for this purpose is commonly between 155° and
170°, sometimes running slightly above or below these
limits, and the milk should be kept at this temperature
from ten minutes to half an hour. // must then be cooled
rapidly.

It may seem strange that the use of a lower tempera-
ture than boiling should be more satisfactory than boiling.
The reasons, however, are simple enough. The bacteria
which sour the milk do not produce spores and are, there-
fore, nearly all killed at a temperature of 155°. Conse-
quently pasteurized milk will keep much longer than
unpasteurized milk. Furthermore, all disease germs that
are most liable to be present are also destroyed by this
low temperature. The diseases ordinarily distributed by
milk are produced by bacteria that do not develop spores,
and a temperature of 160° is sufficient to destroy such
bacteria. Moreover, the disagreeable changes produced
by boiling do not appear at the pasteurizing temperatures.
Pasteurized milk does not have the taste of boiled milk,

194

BACTERIA, YEASTS, AND MOLDS

and is nearly as easily digested and assimilated as raw
milk; hence the objections raised against sterilization
do not apply to pasteurization.

On the other hand, there is one practical objection. In
an ordinary household it is almost impossible to find one
employed in the kitchen who can satisfactorily use a ther-
mometer, and it is out of the question to expect any ordi-
nary servant to heat milk at a temperature of 160° for

FIG. 68. Apparatus for home pasteurization of milk. The figure on
the right shows method of cooling the milk by running water.

half an hour. The only way it can be accomplished is by
some device which will bring about the result in a simpler
way. The most convenient apparatus for this purpose is
that shown in Fig. 68. This consists of a series of bottles
which readily fit into cylinders placed in a larger vessel.
This receptacle is to be filled with boiling water and the
bottles, filled with milk, are placed in the cylinders. The
whole is set aside to cool. The milk is warmed by the
hot water surrounding it, and the water is at the same
time cooled by the milk. The size of the vessel is so

PASTEURIZATION OF MILK 195

proportioned to the bottles that, when properly used, the
milk is heated to about the temperature desired before it
begins to cool. The use of this pasteurizing apparatus is
extremely simple and can be followed satisfactorily in any
kitchen.

Where such an apparatus is not obtainable the same
object can be accomplished in a still simpler way. Place
the milk in quart glass jars. Fill a pail with boiling water
and place the jars of milk in it. The amount of water
should be such as to come nearly up to the top of the
jars. The pail should then be set aside to cool, and the
milk should be occasionally stirred. The result is that
the milk is warmed to about the temperature desired
before it begins to cool. After the heating, the milk
should be cooled rapidly by running cold water into the
pail, this step being as important as the heating.

Pasteurization has been adopted widely in the last few
years and its use is increasing. It is possible to purchase
pasteurized milk at the present time in many of the larger
cities. Milk-supply companies frequently adopt the prac-
tice of pasteurizing milk on a large scale and furnishing
it to their customers. Pasteurization is also extremely
useful in the household where milk is used for food, espe-
cially where there are children. It is certainly not safe at
the present time to feed young children milk from the ordi-
nary milk supply. Such milk, however, may be rendered
safe by pasteurization, and, since this does not materially
injure the ease of digestion, it is an extremely wise pre-
caution to pasteurize all milk which is to be used for
children, especially if the source of the milk is not known
to be reliable.

196 BACTERIA, YEASTS, AND MOLDS

One caution should be given regarding the use of pas-
teurized milk : the milk must be used quickly after pas-
teurizing. It is true that such milk may keep for two
days without difficulty, but bacteria are growing in it all
the while, and although the milk does not sour it soon
becomes unfit to drink. Hence pasteurized milk must be
used quickly, at least within twenty-four hours from the
time when it was pasteurized, and meantime it should be
kept cool just as if it had not been pasteurized.

The most important rule in regard to the use of milk
in the household is that it should be used fresh. No satis-
factory method of keeping it can prevent all bacteria from
growing, and although the use of ice and of pasteurization
or sterilization may keep it in a drinkable condition for a
day, two days, or even longer, it is always suspicious after
it has been kept for this length of time. Milk is plenty
old enough by the time it reaches the house, and it should
therefore always be used fresh. It is far better to obtain
it frequently, in small quantities, using it up as soon as
possible after it reaches the home.

Above all it should be emphasized that clean milk is
better than pasteurized milk. The proper procedure is to
obtain milk in good condition and then pasteurization is
unnecessary. Pasteurization is not a guard against filth,
but only an unsatisfactory means of destroying the dis-
ease germs which may chance to be in the milk from
some source of accidental contamination. When young
children must be fed upon cow's milk probably the only
safe procedure is to adopt home pasteurization or to use
concentrated milk, unless one can afford the expense of
purchasing milk from sanitary dairies.

PRESERVATION OF EGGS 197

EGGS

Eggs prove to be particularly difficult to preserve.
They are sure to contain bacteria inside the shell, depos-
ited there before the egg was laid. These will in time
cause the egg to spoil. Eggs cannot be sterilized by
heat, for this cooks them. Drying, of course, alters their
nature. The use of low temperatures will preserve eggs
as well as fruit. They may be protected from actual
spoiling for some time by placing them in some liquids
that keep away the air. Brine is used, and water glass
is even more successful. To use the latter, mix the water
glass purchased at the drug store with ten times its bulk
of water, and keep the eggs in the mixture. They will
remain in a usable condition for a long time, though they
lose their fresh taste. No means are known by which this
can be preserved.

EFFECT OF BACTERIA GROWTH UPON THE WHOLESOME-
NESS OF FOOD

The question whether the growth of bacteria in the
food necessarily renders it unwholesome remains yet to
be considered. It is evident that after any food material
has become completely putrefied it is quite ruined for all
food purposes. The vile tastes and odors become so
strong that no one can relish food that has entered the
later stages of putrefaction. But how about the earlier
stages, when the flavors and odors are so slight as to
indicate that bacteria have only begun their action ? In
other words, are we liable to eat food which has begun

198 BACTERIA, YEASTS, AND MOLDS

to be decomposed by bacteria, and if so, is such food
unwholesome in any respect ?

We cannot regard any material as harmful simply
because it is a product of decomposition or contains such
products. A number of such decomposition products are
in more or less constant use. Alcohol is in a sense a
decomposition product of yeast. It certainly is used to
a very large extent, and probably, when used only in small
quantity, causes no very considerable injury. Vinegar
is also a decomposition product of bacteria, and is used
freely by the human race without injury. The flavors
of our high-priced butter are due to bacteria, and the
extremely valuable flavors of cheeses are due, in many
cases and perhaps in all, to decomposition products devel-
oped in the curd of milk by the action of certain micro-
organisms. Sauerkraut is a preparation which is allowed
to undergo an incipient decomposition the flavors of which
give the peculiar character to this food. That sauerkraut
is a harmless food product is, of course, perfectly evident.
In the general class of flavors known as gamyvto. have fla-
vors of decomposition produced by microorganisms. The
very common use of such partially decomposed meats, and
the fact that many persons are exceptionally fond of them,
are indications enough that they are not appreciably harm-
ful. These illustrations are sufficient to show that the
simple fact that food contains decomposition products
is not sufficient to make it unwholesome, since many
decomposition products are distinctly desirable in our
foods. The flavors of cheese in particular are very use-
ful, for when eaten with coarse bread they give relish
to otherwise rather tasteless foods.

PTOMAINE POISONING 199

BACTERIAL POISONS IN FOODS

But, on the other hand, there are unquestionably some
such products which are harmful and which, even though
present in small quantity, may be decidedly harmful, or
even poisonous. When certain kinds of microorganisms
grow in food material they give rise to a class of decom-
position products which have been known under the gen-
eral name of ptomaines. These ptomaines are chemical
bodies of great complexity with whose chemical nature we
are not in this work concerned. It is sufficient for our
purpose to know that they are usually the result of bac-
teria growing in animal products, and, while some of them
are quite harmless, others are of an intensely poisonous
nature. If such bodies develop in food they may render it
unwholesome, or even fatally poisonous. To such poison-
ous decomposition products are due instances of poison-
ing from eating cheese, quite a number of which are on
record. A similar cause explains the still larger number
of cases of ice-cream poisoning, when many people have
been rendered seriously and even fatally sick by the eat-
ing of ice cream. Similar effects have sometimes resulted
from the use of milk, although such cases are rare. Many
cases of poisoning are recorded from the use of meats, fish,
and sometimes other foods.

The poisoning in all such cases must not be confused
with diseases produced by bacteria. Sometimes food may
contain disease germs, and these may enter the body when
the food is swallowed, and by growing inside of our bodies
produce disease. (See Chapter XIV.) But in cases of
poisoning from eating food the bacteria grow simply in

200 BACTERIA, YEASTS, AND MOLDS

the food. They do not live in the body, nor do they pro-
duce any definite bacterial disease. The effects are due
simply to the products of decomposition which have been
developed in the foods by certain kinds of bacteria.

These troubles are much more common than we are apt
to realize. Since bacteria grow best at high temperatures,
it is not surprising to find more cases of food poisoning in
warm weather. It is not an infrequent occurrence to have
a general poisoning follow any one of the innumerable
banquets held in our communities. Hundreds of cases
of intestinal trouble occasionally follow such banquets.
The illnesses resulting are rarely serious, but temporarily
they produce great inconvenience and trouble. They are
due to the development of ptomaines in some food prod-
ucts, since almost any of the putrescible foods which come
upon our tables may, in warm weather and under certain
circumstances, undergo a type of putrefaction which gives
rise to these poisonous ptomaines. When this occurs pto-
maine poisoning is quite likely to follow the use of the
foods. Such ptomaines are known to be developed quite
readily in materials that have been preserved in cold stor-
age and then removed to warm rooms. Hence it is desir-
able to consume cold-storage material as soon as possible.
It is almost certain that a large part of the summer
diarrhoea so common in warm weather is due to poison-
ous decomposition products developed in some of our foods,
milk being particularly likely to cause such trouble.

Unfortunately we know very little concerning the con-
ditions under which such poisonous materials appear.
Not all bacteria produce them, and it is only rarely that
food is thus rendered unwholesome by bacteria. We

PTOMAINE POISONING 2OI

know that strictly fresh foods never contain these poisons.
We know that their development is dependent in a measure
upon temperature, inasmuch as they do not develop in food
that is kept cool. We know that decomposition products
are more likely to give rise to poisonous ptomaines in the
absence of oxygen than in its presence. We know, lastly,
that injurious substances are produced by bacteria; but
we do not yet know the source of the bacteria, nor have
we, for this reason, discovered any methods for keeping
them from our foods other than those ordinarily adopted
for checking bacterial growth. Anything that will pre-
vent bacteria from growing will prevent ptomaine poison-
ing. Consequently low temperature, drying of foods, and
the other devices already suggested are the only means we
have for guarding ourselves from such troubles. We may
wisely remember that ptomaine poisoning is most likely
to occur in foods that have been kept for some time in a
moderately warm temperature. Fresh foods never contain
poisonous ptomaines.

The use of fresh foods and the preservation at low tem-
peratures of any food that must be kept for some time are
the only rules that can be given at present for prevent-
ing such instances of poisoning. Eat food fresh when
possible ; keep it cold if it must be preserved ; do not
keep it any longer than necessary, and be particularly
careful to consume quickly any material taken from cold
storage. When food begins to have the smell of decom-
position, it becomes suspicious, although this does not
mean that it is necessarily dangerous, since many of these
decomposition products are quite harmless. The food
product that seems to give the largest amount of trouble is

202 BACTERIA, YEASTS, AND MOLDS

ice cream, and it is therefore desirable to be particularly
on one's guard against its use in warm weather and, if
possible, to use only that which has been made from fresh
materials. Since the dangers are greatest in summer we
should be particularly careful at this season not to allow
any putrescible food to be warmed by the sun or by
standing near a stove.

CHAPTER XIV
DISEASE BACTERIA

The bacteria hitherto studied are all saprophytes. There
remain for consideration those that can carry on their life
within the body of living animals and plants, namely, the
parasites. The distinction between parasites and sapro-
phytes is not a sharp one, for while some species can live
only in lifeless material, and others only in living material,
there are many that can live either a parasitic or sapro-
phytic life. When the bacteria grow in the body of a
living animal or plant, they may give rise to disease, and
these parasitic bacteria are therefore called disease germs,
pathogenic bacteria, disease bacteria, etc.

How BACTERIA PRODUCE DISEASE

The parasitic bacteria are all capable of growing and
multiplying in the body, but the habits of different species
of disease bacteria are widely different. Sometimes they
become distributed all over the body, developing rapidly in
any part, perhaps even in the blood. In such cases the
disease produced by them is not located at any particular
point, but distributed all through the body. This is true
of certain forms of so-called blood poisoning, or septiccemia.
On the other hand, it sometimes happens that the micro-
organisms become located in very definite parts of the

203

204 BACTERIA, YEASTS, AND MOLDS

body, and while able to grow in certain places are unable
to grow elsewhere. In these cases the disease produced
may be local, although secondary general symptoms may
appear, as is true of diphtheria. Between these two
extremes are many intermediate types.

Whenever bacteria obtain a foothold in the body they
multiply more or less rapidly, and have the same general
power of forming decomposition products and secretions
as they have when growing in lifeless food. These new
substances arising in the body are as varied in nature as
are those produced by the common saprophytes. Among
them are almost sure to be some that are distinctly poi-
sonous, which we call toxins. These toxins may be either
decomposition products or bacterial secretions ; but how-
ever they are produced they are liable to be absorbed
by the blood, and the body may thus be directly poi-
soned by them. If the bacteria are in the blood itself,
this poisoning is easy to understand ; but localized dis-
eases are similarly explained. Diphtheria, for example, is
produced by bacteria growing on the inside surface in the
throat. The bacteria themselves do not enter the body,
but their excretions are absorbed rapidly enough. Grow-
ing in the throat, the bacteria develop very powerful
toxins, and these are absorbed from the throat into the
blood, producing a general poisoning of the whole body.
Sometimes the germs grow in the intestine (Asiatic chol-
era), and their poisonous secretions are absorbed with the
digested food. Something similar is true of practically all
disease germs. All produce poisonous materials which are
absorbed by the body, and these cause the direct injury
characteristic of the various diseases.

DISEASES, HOW PRODUCED 205

Not all the bacteria which secrete poisons are disease
germs. Some saprophytes may produce deadly poisons,
but since they are not able to grow in the living body
they are never in a proper sense the causes of disease.
They might, however, grow in our food and render that
poisonous, so that if it were subsequently eaten it would
give rise to cases of food poisoning such as already
noticed. Such troubles are cases of toxic poisoning but
not true diseases. A true germ disease is caused by
the germs themselves entering and multiplying within
the body. When the poisons and not the bacteria are
absorbed by the body, the sickness comes on very quickly
and violently, — a few hours after the poisonous food is
consumed. But it is also of short duration, for, if the
amount of poison absorbed is not sufficient to produce
death, it is quickly excreted from the body, and a clay or
two afterward the person will have perfectly recovered,
except for the weakening effects of the poisoning. This
is the general history of cases of poisoning from ice cream,
etc. A true disease acts very differently. It is slow in
appearing, gradual in its development, and very slow in
disappearing.

The Course of Bacterial Diseases. The diseases pro-
duced by bacteria have different histories in the body ;
but a considerable number of them, with many of which
the housewife is intimately concerned, have a course some-
what as follows. For some days after the bacteria enter
the body they have difficulty in maintaining a foothold.
Sometimes, indeed, even though they succeed in entering,
they are driven out by resisting powers which the body
possesses but which we cannot here particularly consider.

206 BACTERIA, YEASTS, AND MOLDS

If, however, they overcome these resisting forces and gain
a foothold, they then begin to develop, so that in the
course of a few days they become quite numerous. As
they grow they produce their toxins, and these, devel-
oped at first in small quantity, are absorbed by the body
and give rise to the first slight symptoms characteristic
of the particular disease. But the bacteria continue to
multiply and produce their poisons in greater and greater
abundance. As a natural consequence the body becomes
more and more influenced by them, the symptoms of the
disease become more and more violent, the person becomes
more and more ill. This continues until death occurs or
a crisis is reached. After the crisis the bacteria begin to
disappear, and are finally driven from the body, while the
poisons they produced become less capable of causing
injury and are eventually excreted. The person may then
recover entirely from the attack.

RESISTANCE AGAINST DISEASE

In most cases the body in driving off the bacteria
acquires the power of guarding itself from a second attack
of the same species, and the individual, for a time at least,
is not liable to a second attack of the same disease. The
whole explanation of how the body protects itself, drives
off the invading bacteria, counteracts their toxins, and
retains this power of protection in the future, is one of
the interesting problems upon which bacteriologists are
still studying. We cannot here enter into the subject, but
it is well to remember that a recovery from common con-
tagious diseases, like smallpox, scarlet fever, measles, mumps,

DISEASE BACTERIA 2O/

whooping cough, diphtheria, grippe, tonsilitis, typhoid fever,
etc., protects the individual for a time from a second attack.
The protection lasts much longer in some cases than in
others, and whereas the protection against the diseases at
the beginning of the above list lasts for years or for life,
the protection against those at the end of the list lasts
for only a few months or weeks.

Two important facts in regard to the resistance against
disease must be mentioned. The ability of a person to
resist an attack of any kind of disease germ is dependent
upon two things.

1. The vigor of the bacteria. It has been learned by
experience that the bacteria reproducing any definite dis-
eases are more vigorous at some seasons than at others.
A very vigorous lot of bacteria will give rise to a more
serious attack of the disease, and will be more difficult to
drive out than a lot of the same kind of bacteria that
have been weakened by some unknown conditions. It
is a well-known fact that some epidemics of smallpox,
measles, etc., are milder than others ; not simply because
fewer people are attacked, but because those who are sick
have the disease in a milder form. This difference in the
severity of the attack is due in part to a difference in
the vigor and activity of the bacteria that make entrance
into the body, and is a matter beyond our control.

2. The vigor of the body itself. A vigorous, healthy,
active body has a power of resistance sufficient to drive off
most kinds of these invading parasites. If, however, the
body is less vigorous, less active, i.e. in a low state of
physical health, its resisting power is less and the body has
great difficulty in driving off the invaders. This resisting

208 BACTERIA, YEASTS, AND MOLDS

power, then, depends upon the vigor of the physical
health. Hence it is of the greatest practical importance
for every one to remember that robust physical health is
the best protection against many types of disease due to
the invasion of bacteria. It is true that persons in appar-
ently perfect health may take these diseases, but it is never-
theless the rule that the stronger the physical vigor the
less is the likelihood of being attacked. At any rate a
person of strong constitution will have a milder attack of
the disease than one whose physical activity is weakened.

DISTRIBUTION OF CONTAGIOUS DISEASES

While these problems are of the utmost importance in
every household, hygiene does not properly belong to
the study of bacteria. There is one phase of the subject
of bacterial diseases, however, that is of vital interest to
every housewife. If contagious diseases are due to the
growth of bacteria or other microorganisms, it is clear
that they may be avoided if we can prevent the disease
germs from reaching the healthy individual. We have
already noticed how one bit of decaying fruit contaminates
another, the spores passing to the perfect fruit and caus-
ing that also to decay. We have seen how the minute
spores of molds and yeasts are scattered through the air
and blown about by the winds until they are almost sure
to be found everywhere. We have noticed, also, how
readily bacteria are distributed, and how surely the air
of our houses is filled with them. We have learned that
these microorganisms are so abundant in the air that they
are sure to get into any exposed bit of food, and we have

DISTRIBUTION OF CONTAGIOUS DISEASES 209

seen that one of the housewife's duties is to protect her
food from their action.

Very similar but more serious problems arise in the
household in connection with the distribution of disease
germs. If a disease is produced only by the development
of bacteria, of course it may be prevented if we can
discover some means of keeping the disease bacteria
from the body. In canning fruit the housewife tries to
prevent bacteria from reaching it. Can she not by a
similar principle protect her children from contagious
diseases ? This problem is the one feature of contagious
diseases that belongs primarily to the housewife. The pre-
vention of the distribution of such diseases is a subject
which the physician can handle only indirectly, because
it depends upon conditions in the home which he can-
not control. The modern trained nurse may be able to
do this ; but in the majority of cases the whole problem
of the prevention of the distribution of contagious dis-
eases from individual to individual must rest upon the
home maker. The doctor comes in for a few moments
only, the nurse is only occasionally at hand, and the duty
of protecting the inmates of the home from disease must
fall upon the one who is at the head of it. To do it she
must proceed according to the same principles by which
she protects her food from decay. As she is obliged to
use devices to keep bacteria away from all putrescible food
materials, and as she must keep decaying apples away
from the perfect ones, so it is her duty to guard the mem-
bers of her family from the invasion of the disease germs.

In her battle against disease the housewife should
remember three things.

210 BACTERIA, YEASTS, AND MOLDS

1 . The causes of these diseases are real tilings and not
simply matters of imagination. They can be seen with
the microscope ; they feed ; they grow and multiply like
larger animals and plants. Contagious diseases are not
mere nervous affections that may be banished by forget-
ting them and believing in their nonexistence. They are
produced by definitely known living beings, and can be
avoided only by keeping our bodies free from them.

2. The causes of the diseases in question are always
microscopic, and can never be detected by the naked eye.
Material which cannot be seen may therefore be filled
with microscopic parasites which are capable of producing
fatal diseases. An invisible particle of dust may harbor
numbers of deadly germs ready to invade the living body
and produce trouble. Since the foes cannot be seen, the
battle is a blind and therefore a difficult one.

3. These agents are alive ; they grow and multiply.
Thus it follows that infectious material may rapidly
increase in quantity. A particle of dust containing only
a few parasitic bacteria may be the starting point of a
disease which may spread widely until it shall become an
epidemic with its scores of victims. The problem to be
dealt with is something like that of fire. The flame of
a single match is very slight and may do little injury ;
but this same flame may start a conflagration that will
burn an entire city. So with the disease bacteria. Each
of them, although extremely minute, is capable of develop-
ing with wonderful rapidity, and a single one may develop
sufficiently in the course of a few days to be scattered
far and wide, causing a great epidemic. The extreme
minuteness of these foes and their wonderful power of

DISTRIBUTION OF CONTAGIOUS DISEASES 211

multiplying are the most prominent facts to be borne in
mind when contending with contagious diseases. We
must not, therefore, think that anything is safe from
contamination with bacteria because it looks clean. The
eye may not see the contamination even when it is present.
Clear, sparkling water may sometimes contain deadly bac-
teria, while dirty water may be perfectly safe to drink.
Nor must we think any substance safe because it has only
an extremely small quantity of infectious material upon it,
for bacteria can grow so rapidly that a half dozen may
become millions in a few hours if they have a chance
to feed arid grow.

CHAPTER XV

PREVENTION OF DISTRIBUTION OF CONTAGIOUS
DISEASES

What are the diseases against which the housewife must
be on her guard lest they distribute themselves through
her home? They are evidently those due to microscopic
parasites, either bacteria or other forms of living things.
Not all forms of sickness are due to parasites, for some
have an entirely different cause. But the diseases with
which we are here concerning ourselves — the so-called
contagious diseases, which are well known to be " catch-
ing " and which pass from the patient to a healthy indi-
vidual— are due to parasites.

The chief of these diseases are smallpox, scarlet fever,
diphtheria, measles, mumps, whooping cough, tonsilitis, and
influenza or grippe, — all known to be contagious. In addi-
tion there are other diseases, serious but much less con-
tagious ; so slightly contagious, indeed, that until quite
recently they have not been looked upon as being capable
of passing from individual to individual. The most prom-
inent and important are typhoid fever and tuberculosis.
The best-known form of the latter disease is commonly
known by the name of consumption. Formerly neither
typhoid fever nor consumption was supposed to be con-
tagious, but it is now known that under some conditions
they pass from patient to healthy individual. Lastly
may be mentioned a class of diseases not in any proper

212

CONDITIONS OF CONTAGION 213

sense contagious but produced by parasitic organisms
which may under peculiar conditions pass from individ-
ual to individual. Most prominent among this last class
is malaria, a disease never known to pass directly from
one person to another but which may be distributed from
individual to individual through an agency to be noticed
presently. It must not be assumed that science at the
present time knows, the cause of all the diseases here
listed. Some of them, like measles, scarlet fever, whoop-
ing cough, and mumps, while almost certainly caused
by microorganisms living in the human body, have not
yet been satisfactorily explained, and we do not know
the actual germs which cause them. There are some
other contagious diseases besides those mentioned, for
almost any trouble that produces open sores anywhere
on or in the body is liable to be distributed from person
to person. Those mentioned are, however, the most
important.

CONDITIONS OF CONTAGION

To make it possible for a disease to pass from one person
to another, three conditions must be fulfilled: (i) The
microorganisms which produce the disease must find some
means of exit from the patient. (2) The organisms must in
some way be carried from the patient to the healthy indi-
vidual. (3) The organisms must find some means of enter-
ing the body of the healthy individual. If the parasites
can meet these three conditions, the disease will be carried
from patient to well person, and thus will be contagious.
For a proper understanding, therefore, of the way to han-
dle contagious diseases in the home we need to consider

214 BACTERIA, YEASTS, AND MOLDS

these three factors. If we know how the bacteria leave
the body of the patient, how they are distributed, and how
they enter the body of another, we are well equipped to
guard against them.

I. The Means of Elimination from the Body

A knowledge of the means by which the contagious
material leaves the body of the patient is of first impor-
tance in preventing the distribution of such material,
and should always be the first question asked. There
are several different methods.

The parasites that produce certain diseases do not find
any direct means of being eliminated from the body, and
when this is the case the disease is not in any proper
sense contagious. Malaria is the best example of this
class of diseases, and yellow fever is probably a second.
Malaria, chills and fever, or fever and ague, are all the
same disease, and are produced by a microscopic parasite
living in the human blood. Growing there, it develops
poisonous secretions, and these acting upon the body give
rise to the symptom of chill followed by fever only too
well known in this disease. The parasite is a minute little
body (Fig. 69, i) which enters the blood corpuscle. Inside
this corpuscle it grows, and finally breaks up into many lit-
tle bodies, or spores. As soon as the spores are formed
the blood corpuscle breaks to pieces, setting the spores
free and at the same time liberating the secreted poisons.
These poisons cause the chill followed by fever well
known in malaria. The spores may then enter into other
blood corpuscles and go through the same history again

MALARIAL PARASITES

(Fig. 69, 1-7). It takes about forty-eight hours for them
to complete their history, and hence the chills, in the
common form of malaria, occur every other day. One

FIG. 69. Malarial organism.

2-7 show the stages that occur in ordinary blood, 7 representing the spores which appear
after the blood corpuscle breaks to pieces. These spores are like 2 and immediately
enter into fresh corpuscles, as at 3. 8 shows a so-called crescent body in the corpuscle.
The crescent bodies become the sexual bodies, 9 and ga, which develop in the mosquito.
10 shows the union of the female sex body, 9, with one of the flagella of go.. 11-15
show the development of the united mass, 10, in the body of the mosquito, finally
producing spores such as shown at i. 16, the intestine of the mosquito, showing the
malarial organism attached.

form of the parasites, however, requires three days to com-
plete the cycle. The malarial parasites remain in the blood
and never pass out of the body by any of the ordinary
excretions. There is therefore no direct means by which

2l6 BACTERIA, YEASTS, AND MOLDS

they can pass from one person to another, and conse-
quently malaria is not a contagious disease. This fact
has been known for many years, and no instances of
direct contagion have been noted.

The last few years, however, have disclosed the fact that
there is a means by which malaria is transmitted indi-
rectly from man to man, and have shown us how the

FIG. 70. a, the harmless mosquito (Culex) ; b, the malarial
mosquito (Anopheles), a' and a" show the position of the
harmless mosquito when lighting on the floor or on the
wall ; £', b" and b'" show the position of Anopheles when
lighting on the floor, wall, and ceiling.

human body usually becomes infected with this disease. A
certain kind of mosquito (Fig. 70, b) forms an interme-
diate connection between a malarial patient and another
individual. This kind of mosquito may bite the patient,
sucking into its body at the time a considerable quantity
of blood. Inasmuch as the blood contains the malaria para-
sites, the mosquito will become filled with them. The little
organisms live in the mosquito as readily as they do in the

MOSQUITOES AND MALARIA 217

human body, undergoing a different history, however. In
the mosquito they pass through a new series of changes
(Fig. 69, 8-15), finally lodging in the glands around the
mouth (salivary glands). If this mosquito with its sali-
vary glands thus loaded with these little parasites chances
to bite another individual, thrusting its proboscis in
through the skin, these parasites will pretty surely be
forced into the body of that individual. When the mos-
quito flies away it will leave the blood of the one bitten
inoculated with the parasites. They are now in a loca-
tion adapted to their life and they begin to develop. In
a few days they are abundant enough to produce a poi-
sonous effect upon their victim and he develops an attack
of malaria. Thus this particular disease is transmitted
from person to person by means of mosquitoes, and at the
present time it seems as if most, and perhaps all, of the
cases of malaria start originally from mosquito bites.
Malaria is most prevalent at the seasons of the year when
mosquitoes are abundant ; it is most abundant in parts
of the world where mosquitoes are most common ; and
it is most likely to be caught at night, the time when
mosquitoes are the liveliest.

It should be noted, however, that not all kinds of mos-
quitoes are capable of carrying this malarial parasite.
Fortunately the most common mosquito is quite free
from them and is, therefore, not a source of danger. Only
one group of mosquitoes is associated with this trouble.
Fig. 70, bt shows the common form of this species, and
also the ordinary, harmless mosquito, a. The differences
between them are shown in the figures. The most easily
distinguished differences are the five delicate hairlike

2l8 BACTERIA, YEASTS, AND MOLDS

feelers on the head of the dangerous species, rather than
three as in the harmless form (Fig. 70, a and b), and the
method of lighting with the body held in a straight line
(Fig. 70, b', b", b'")y rather than bent as in the harmless
species (Fig. 70, a' and a"). It must also be remembered
that not all mosquitoes, even of the harmful species, will
be dangerous. Only those that have sucked the blood
from malarial patients will contain the parasites and be
able to transmit the disease. In other words, of all the
mosquitoes that may bite us in summer only a few are
likely to be infected and produce any trouble. We may
be bitten thousands of times and still be free from malaria,
while the next mosquito that bites us may inoculate us
with these parasites.

That family is the best protected against malaria that
is the best protected against mosquitoes. If we live in
a region where malaria abounds, it is somewhat dangerous
to remain out of doors during the night, or even in the early
part of the evening, unless properly protected. At this
time mosquitoes are most likely to be flying about. From
this fact arises the ground for belief that night air is
dangerous. It is not the night air but the mosquitoes
in the air that produce the trouble. It is also evident
that the best method of protecting a household from
malaria is the use of mosquito netting. It is a curious
fact that its use at our windows and doors is the best
protection from these microscopic parasites, inasmuch as
mosquito nettings will keep mosquitoes from the houses
and will reduce the chances of contagion. This is not a
matter of theory only, for it has been found by careful
observation and experiment that the simple procedure

ELIMINATION OF GERMS FROM PATIENTS 219

of covering doors and windows of houses with mosquito
netting has produced a marked decrease in the amount
of malaria in these dwellings.

It has been proved recently that yellow fever also is
distributed by mosquitoes rather than by direct personal
contagion. The species of mosquito is different from
either of those shown in Fig. 70, and lives only in warm
climates. Mosquito netting is the best check for this
disease. Yellow fever has been almost wholly stamped
out of Havana by simply surrounding the patients with
netting, thus preventing the mosquitoes from biting them
and becoming infected with the germs which they might
carry to other persons.

In all truly contagious diseases the parasites have some
means of leaving the body of the patient. Their methods

of exit are numerous, but it is not very

V V
difficult to determine, in the case of any fX jf'^*"'

particular disease, the methods by which I **^* \
the parasites leave the body. Most types . ^SJ '
of contagious diseases have suggestive >k**r

symptoms. For example, in smallpox, scar- FlG-7l> Bacillus

, , - 1^.1 ' •• .. °f diphtheria.

let fever, or measles, there is an eruption
of the skin, and it becomes probable at once that this
eruption is a means of elimination of microorganisms.
In diphtheria (Fig. 71) the germs grow in the mouth,
clinging to the surfaces inside the mouth and throat, and
it is quite evident that the breath, or at all events the
forcible breath that comes with coughing, will detach
the bacteria from their position in the throat and blow
them into the air. In the case of whooping cough the
violent paroxysms of coughing are probably a means of

220 BACTERIA, YEASTS, AND MOLDS

eliminating the infectious organisms. The same is true,
probably, of tonsilitis and grippe (Fig. 72). In consump-
tion, discharges from the lungs pass into the mouth and
are voided in the sputum. It becomes evident, therefore,
that here is a disease the contagion of which is found in
the sputum and also in the breath exhaled when cough-
ing. The ordinary breath does not contain the germs.
^'IQ, In typhoid fever and cholera the most dis-
•Vik tinctive characteristic of the disease is the
FIG. 72. Ba- diarrheal discharges from the alimentary canal,
cillus causing and this suggests that the faeces may be the
influenza or source of exit of infectious material. Thus,
though contagious diseases differ very much
from each other, it is rarely difficult to determine by
observation the method by which the infectious matter
leaves the body in the case of any particular contagious
disease. The practical fact to bear in mind is that dur-
ing the progress of an infectious disease any unusual
discharges from the body, mouth, skin, or elsewhere are
almost always the means of exit of the parasites, and from
such excretions all members of a household should be
most carefully guarded. Special attention should be given
to the care of the various discharges from the patient, and
if this is done the contagion may be reduced very largely,
and in many cases be absolutely prevented.

2. How Disease Germs are carried to and fro

There are several methods by which infection may
be carried from the body of the patient to that of the
healthy person. In the case of some diseases it is chiefly

HOW DISEASE GERMS ARE CARRIED 221

by direct contact. In such diseases as smallpox or scar-
let fever, where the infectious material is probably on the
skin, contact with the patient would be very likely to
infect a healthy individual. Hence, with all diseases of
this character, isolation is rightly considered of the greatest
importance (see page 241).

With most diseases, however, other means of transference
are more common. The microorganisms are not able to
travel of their own accord, and are always carried about by
some other agencies, the chief of which are the following.

Insects. Insects are occasionally the means of carrying
infectious material. The relation of the mosquito to
malaria has been mentioned, and flies have a 00
very close relation to the distribution of
typhoid fever. So close is this relation that

it is now urged that the name typhoid fly FlG- 73- Ba-
cillus of bu-
should be used. Fleas, also, distribute the bonicpiague.

bubonic plague, which has recently produced
so many deaths in the Old World (Fig. 73). It is quite
possible that insects may carry the infection of cholera
and some other diseases ; but we know little upon these
matters at present. We are thus taught to avoid flies, to
shun mosquito bites and flea bites, and, in short, to avoid
insects as much as possible. Mosquito netting has, there-
fore, an actual sanitary value.

Larger Animals. Occasionally larger animals transmit
infectious microorganisms. It is believed that diphtheria
is sometimes carried from the patient in the sick room to
another person by cats which wander about the house at
will. The bubonic plague which, fortunately, is as yet
rare in this country but which is producing great ravages

222 BACTERIA, YEASTS, AND MOLDS

in Europe, Asia, and Africa, is known to be transmitted by
rats. Tuberculosis is sometimes transmitted by cattle,
through their milk, to children drinking it. There may
be other instances not so well known where larger animals
are the means of distributing infectious material.

Water. The distribution of disease germs by means of
drinking water is chiefly confined to two diseases, typhoid
fever and Asiatic cholera. Typhoid fever is very common
and many epidemics are due to polluted drinking water.
The disease is caused by a well-known bacillus (Fig. 74),
and the method by which the water becomes contaminated
is very easy to understand. The bacilli live in the intes-
tines of the patient and are carried from him by the
excreta. This material may be thrown
upon the soil or into earth closets, and is
liable in either case to percolate through
the soil or be washed by rains into wells or

streams. Wells are filled with water that
FIG. 74. Bacillus

of typhoid fever. nas soaked through the soil, and are quite
readily contaminated with typhoid germs.
Hence well water has been a very common source of the
distribution of this disease. In most cities the excreta are
thrown into sewers and the sewage may empty later into a
river. Hence the drinking water of cities may sometimes
present very great danger. Cities frequently depend upon
the water of running streams, and nearly all streams of any
size in civilized communities are more or less contaminated
by sewage from houses or towns on their banks. Such
water will be likely occasionally to become infected with
typhoid bacilli ; so that rivers and streams are positive
sources of danger to communities that depend upon them

WATER AS A SOURCE OF DISEASE 223

for their drinking supplies. The result of drinking such
contaminated water is the development of many cases of
typhoid fever. A large part of the cases of this disease in
cities are due to the contamination of drinking water. Many
epidemics have been traced to just such a source.

The Asiatic cholera bacillus (Fig. 75) has also in recent
years been shown to be distributed by means of the water
supply. The practical result of this discovery has been
that, since cities have learned to guard their water sup-
plies, severe epidemics of cholera have been prevented.
This subject, however, need not detain us,
as the disease is hardly known in America.
But in the event of a cholera epidemic
it should be remembered that the majority
of cases are due to drinking water that

of cholera.

has been contaminated with cholera bacilli.

There are some other diseases occasionally distributed
by water, but they are rare or little known. We need not
consider them in our discussion.

The practical question how to avoid such dangers must
face the head of every household. To answer this we
must first fully realize that any water which has oppor-
tunity for sewage contamination is dangerous for drink-
ing, and cities supplied only with water directly from
rivers or streams have a supply that is frequently unsafe
for use. Those cities, however, which have large reser-
voirs where the water stands for some time will have
more reliable water, since the standing of water will in
time always purify it of typhoid bacilli. The danger that
the water supply may become a source of typhoid fever is,
therefore, confined to those cities that use the water of

224 BACTERIA, YEASTS, AND MOLDS

running streams, or those that pour their sewage into a lake
and then pump the water out for drinking purposes. The
housewife in the city cannot control her water supply.
This must be left to health boards and water commissions.
But she should learn whether the water is from a source
liable to be contaminated with sewage. If so, she must
regard it as dangerous and bestir herself to treat it in
some way that will make it safe for drinking. This can
be easily done by simply boiling the water, since even a
brief boiling destroys typhoid bacteria. This is the only
satisfactory method of rendering such water harmless.
After boiling, the water may be cooled with ice and used
for drinking.

Many households are supplied with various kinds of fil-
ters attached to their faucets for the purpose of purifying
the water. The ordinary filters are worse than useless.
They may make the water look clear and may remove
some of the solid material ; but, while it looks pure, such
water is no safer after filtering than before. Filters in
ordinary use have no value whatsoever in removing typhoid
germs. They do remove large particles of dirt, but bac-
teria pass through them as easily as dust through mos-
quito netting ; and though they make the water clear they
do not make it a whit less dangerous.

One type of water filter (the Pasteur, the Berkefeld, and
the Chamberland) is able to remove bacteria from water
and thus remove all danger. Such a filter is shown -in
Fig. 76. The actual filter is a cylinder (Fig. 76, a) made
of unbaked porcelain which is placed inside of a metal
covering. The water enters the metal tube and is filtered
through into the inside of the filter. These filters have

FILTERING OF DRINKING WATER

225

been in use for several years and are quite efficient if prop-
erly cared for. But in the ordinary home they are apt to
be worse than useless, since bacteria lodge in the porcelain
filter and grow there, so that the water passing through
will be actually contaminated in filtering. To prevent
this requires more careful attention
than will generally be given in a
house. The filtering cylinder should
be removed every day and carefully
cleaned by a thorough brushing, and
about every fourth day it should be
sterilized by boiling in water for five
minutes. This kills the bacteria in
the pores of the filter and renders
it safe for a few days. Unless one
is willing to adopt this plan of regu-
lar sterilization of the filter, it is
better not to use it at all. There
is no other means in the household
of filtering water which will remove
from it the danger of distributing
typhoid fever. There is a method
by which the water supply of a
whole city may be purified by filter-
ing on a large scale ; but this again
must be left to the public officials,

and is not within the reach of the housewife. Her sole
method of purifying suspicious water is by boiling.

Aerated Waters. The recognition of danger connected
with ordinary drinking water has led to the extension of
the use of a variety of aerated waters, Apollinaris ivater,

f

FIG. 76. Pasteur filter,
showing the filter itself,
a, made of unbaked
porcelain, and the metal
cover.

226 BACTERIA, YEASTS, AND MOLDS

Seltzer water, etc. Such beverages are not bacteria free,
and a study of a large variety has shown that occasion-
ally the number of bacteria they contain is considerable.
Artificial aeration, that is, charging the water with carbon
dioxide, does not at once destroy germs, and if the water
thus charged contained disease germs at the outset, the
water is not rendered any safer than it was before aera-
tion. Such artificially prepared waters, therefore, are,
while fresh, no safer than the original water from which
they are made. After they have stood for a few weeks
the disease germs seem to die and the water becomes
wholesome. The naturally aerated waters are, so far as
known, never likely to be impregnated with disease germs.
We may then conclude that naturally aerated water is safe
from disease bacteria, and that other forms of aerated
water are practically safe if they are not too fresh. In
general, such waters are, therefore, more reliable than
drinking water which has an opportunity for sewage
contamination.

Ice. The question has been raised in the last few years
whether ice made from sewage-contaminated water is safe
to use for cooling drinking water. Typhoid bacilli are not
killed by freezing, and it has been claimed, therefore, that
such ice is as dangerous as water. A more careful study
of the subject has shown, however, that although the
bacilli are not killed by simple freezing, they are mostly
rendered harmless if they remain frozen in ice for several
weeks. Ice harvested in the winter is therefore safe to
use the following summer. This statement applies to
clear ice, but not to snow ice sometimes found on the
surface of frozen ponds.

MILK AS A DISTRIBUTER OF DISEASE 227

Milk. Milk is a means of distributing certain diseases ;
not, indeed, a vehicle by which a contagious disease in a
household is carried from one member of the family to
another, but rather a source by which diseases from out-
side may find entrance into the family. The diseases com-
monly attributable to milk are not very numerous, four of
them being very definite and one of a somewhat obscure
type. The four definite diseases are tuberculosis, diph-
theria, scarlet fever, and typhoid fever. The other one
referred to is the indefinite series of intestinal troubles
known as summer complaint, summer diarrhea, cholera
infantnm, etc. These are all characterized by the pres-
ence of diarrhea, and are particularly common in warm
weather.

There is no doubt that all of these diseases are occa-
sionally distributed by milk. The one most commonly
attributed to this source is typhoid fever, and many
instances have been recorded where epidemics of typhoid
have been due directly to milk contaminated with typhoid-
fever bacteria. Epidemics of diphtheria and scarlet fever
have also been traced to the same source, though more
rarely. The question whether any considerable amount
of tuberculosis is attributable to milk has not been
settled positively, but the probability seems to be that
milk is a source of this disease, especially for young chil-
dren. Pure milk, however, is never the cause of any
of these troubles. Milk fresh from a healthy cow is
never the source of any of the diseases above mentioned,
nor indeed do any of them, except tuberculosis, come
directly from the animal producing the milk. Some
cows have tuberculosis and their milk may be dangerous ;

228 BACTERIA, YEASTS, AND MOLDS

but cows probably do not have diphtheria, typhoid, or
scarlet fever. Danger from these diseases lies in the pos-
sibility that between the time of milking and the time
when it reaches the consumer the milk may have been con-
taminated with the bacteria which produce these troubles,
and that these bacteria, growing in the milk, may render
it a source of hidden danger.

The relation of milk bacteria to the production of
summer complaint and similar diseases is not so well
understood. The only points that we need notice are :
(i) Such troubles are doubtless due to the bacteria present
in the milk. (2) They are consequently much more likely
to be associated with milk in summer than in winter, since
bacteria grow much faster in warm than in cold weather.
(3) Fresh milk which has been kept cool is less liable to
produce such troubles than older milk which has been
kept warm, partly, no doubt, because the latter contains
more bacteria than the former. Practically, then, the
housewife should remember that old milk that has been
kept warm is a source of danger, and that occasionally
even fresh milk may be the cause of the diseases above
mentioned unless some precautions can be adopted.

How can precautions be taken in the household against
these possible dangers? i. We notice again that the milk
that costs the most is the best and most reliable, while
the cheapest milk is not only the poorest food but also
the most dangerous. 2. Where it is possible to obtain
information in regard to the character of the source of
milk, the danger of contracting disease may be lessened.
For in a small community knowledge concerning the man
who delivers the milk should enable one to get some idea

MILK AS A DISTRIBUTER OF DISEASE 229

as to whether he is careful or careless in handling it.
In general it is well not to buy milk from a dirty or care-
less milkman, for such a man is much more likely to sell
milk that is a source of danger. For this reason milk
distributed in glass bottles is more reliable than that
distributed from metal cans. 3. Practically all of these
dangers may be avoided by the use of pasteurized, con-
centrated, or certified milk. The latter is a higher grade
of milk, coming from special farms, and should have a
certificate from a medical commission. They cost more
than the ordinary grade, but are safe to use, and may be
given to infants without fear of contagious diseases. In
general, then, the first factor to be considered in guard-
ing the family from disease through milk is the obtaining
of the supply from reliable sources only, even though the
price may be higher. This will give a more reliable prod-
uct, one that is more valuable as a food and less liable to
produce disease.

But in many households this may not be possible, and
the family may be obliged to depend upon the ordinary
milk supply without any knowledge of its source. What
should be done under these circumstances? Such milk
can be rendered harmless, so far as concerns the diseases
referred to, by the processes of sterilization mentioned on
another page. Since milk from an unknown source may
be rendered safe for use in this way, it is easy to under-
stand why sterilization has in recent years come to be
so widely adopted. The same end is more satisfactorily
reached by pasteurization.

Every housekeeper will ask, however, whether such a
precaution is necessary under ordinary conditions. This

230 BACTERIA, YEASTS, AND MOLDS

general question cannot be answered and it will always be a
matter for individual decision. That there is some danger
is certain. Whether the danger is sufficient to warrant
or demand the pasteurization of all ordinary market milk
is a matter of opinion upon which bacteriologists are not
yet agreed. For young children who must be fed upon
cow's milk it is, under the conditions of modern life,
not safe to use the ordinary milk supply. Many children
are brought up on such milk without suffering materially
therefrom ; but if it is used with young children there is
considerable danger of the diseases mentioned, especially
diarrheal troubles. In feeding young children, therefore,
it is wise, and almost necessary, to adopt some method,
preferably pasteurization, of destroying the disease germs
that may be present. If the milk is to be used by adults,
the necessity is not so great, for adults are not as a rule
so liable to diseases from this source. Nevertheless milk
from the common milk supply, unless pasteurized, must
be looked upon as a possible source of typhoid fever and
some other troubles. It should be emphasized especially
that milk is not necessarily harmless because it has not
soured. It is true that soured milk contains more bacteria
than sweet milk, but most of them are harmless, while a
sample of milk that is perfectly sweet may contain disease
bacteria and be unsafe to use.

The Air. The readiness with which bacteria can float
in the air suggests that they may be easily distributed by
this means. The agency of air in distributing diseases
has been somewhat overrated, but it occurs in a few dis-
eases which we usually look upon as extremely contagious.
Skin diseases, like measles, scarlet fever, and smallpox, are

AIR AS A DISTRIBUTER OF DISEASE 231

distributed by the air, and a person can take them with-
out coming in actual contact with the patient, when no
other means of infection is known save that of air cur-
rents. The distribution of disease bacteria by means of
air, however, does not extend very far from the patient.
If bacteria are thrown off into the air, a second person in
the same room and in the immediate vicinity may become
affected by them. But the danger is confined chiefly to
the room occupied by the patient. It is true that the
germs may pass into other rooms or out of doors, but
they usually cease to be dangerous, partly because they
become mixed with such large amounts of pure air, and
partly because they soon settle to the floor or ground
and are destroyed by sunlight. The danger of taking
such diseases decreases rapidly as we pass from the
immediate vicinity of the patient. The danger may be
much decreased if the skin of the patient be kept moist
by a mixture of glycerine and water, or by a little oil
rubbed on the skin. This may be done in scarlet fever,
during the later stage, when the skin is peeling, and the
danger of contagion will thereby be lessened.

From these facts we can conceive that the dust and
dirt collecting on the floor of the sick room will be likely
to become a source of trouble. The dust that accumu-
lates on the floors, walls, or ceilings, on the window sills or
the doors, or on any article of furniture in the room occu-
pied by a patient, is likely to contain the living disease
bacteria. Such material is therefore a source of con-
tagion, and in protecting a family from attacks of conta-
gious diseases the dust accumulations of the sick room
must be looked upon as a special source of danger.

232 BACTERIA, YEASTS, AND MOLDS

In a few diseases characterized by coughing the germs are
distributed by air from the mouths of the patients. The
most noticeable of these are consumption (Fig. 77), whoop-
ing cough, and very likely measles at certain stages. The
air coughed from the mouth in these cases contains small
particles of moisture which float around for some time,
and these particles are likely to be laden with disease
germs. As long as this water is floating the air 'may be
dangerous to another person breathing it. In these cases
also the danger is practically confined to the immediate
vicinity of the patients, for these particles
of moisture do not float very long but soon
sink to the ground or come in contact with
the walls of the room. Danger is confined
to within a few feet of the patient, a dis-
tance as great as that of the next room
FIG. 77. Bacillus .. __ . ,

of tuberculosis. being usually sufficient to free the air from

such floating microorganisms. The only
way to avoid such dangers is to insist upon plenty of fresh
air in the sick room, and to air the rest of the house
frequently and thoroughly.

Tuberculosis (Fig. 77), or consumption, has a special
source of danger in the sputum of the patient. This
material is filled with the dangerous bacilli. As long as
it is kept moist they have little chance of distribution ; but
if the sputum is voided on the floor or where it can dry,
the dried material will blow around as dust, still contain-
ing active bacilli. The sputum of consumptive patients
should be received in old cloths which can be burned,
thus destroying all danger, or in special cups which can
be sterilized by disinfectants.

DUST OF SCHOOLROOMS 233

It is extremely important, also, to remember the sig-
nificance of dust in a schoolroom. A schoolroom with
children from many homes is likely to be a collecting
place of disease germs. The children frequently bring
such germs to the schoolroom, where they are distrib-
uted through the air, float around for a while, and even-
tually settle on the floor. If they remained on the floor
they would be harmless, but every time the room is
swept or dusted the germs are stirred up again. Sweeping
and dusting a schoolroom decidedly increases the danger
of contagion. If feather dusters could be discarded and
brooms also dispensed with, their places being taken by
damp cloths, the amount of contagion would be materially
reduced. If the floors, window sills, desks, and tables
were wiped each day, the dust, instead of being scattered
through the room, would be collected and removed by the
damp cloth. The cloth should subsequently be rinsed and
occasionally washed in hot water. Where this method
has been adopted the results have been surprising. One
school, for example, with over four hundred pupils, burned
up the feather dusters and used damp cloths for cleaning.
During the following year there was not a single case of
contagious disease among the scholars, an altogether new
experience for the school. The same general facts would
apply equally well to the household. Brooms and dusters
simply distribute germs through the air, and should be
dispensed with as far as possible. Vacuum cleaners and
damp cloths should, where possible, take the place of brooms
and dusters. Woodwork should always be cleaned with a
damp cloth rather than by dusting. No simple rule will
be more useful in checking the distribution of contagious

234 BACTERIA, YEASTS, AND MOLDS

diseases than that of discarding the old-fashioned method
of dusting and replacing the same with the more sani-
tary one of wiping. It is much better to have bacteria in
the carpets, where they will die after a time, than to have
them in the air that we breathe.

Uncooked Food. Some of the foods that come upon our
tables without cooking may be the means of distributing
disease. This is not, however, very common, and is men-
tioned only as a possibility. If fruit has a chance to
become contaminated with infectious material (such as
sewage, or sewage-infected water, or consumptive sputum),
and is eaten uncooked, the person eating it is in danger
of contracting disease. The chance, however, of fruit
becoming contaminated with disease germs is not very
great, and we cannot therefore look upon it as a very
serious source of danger in a household. Lettuce, celery,
or radishes grown on sewage farms have a chance of
contamination from typhoid germs in the sewage used
for fertilizing the soil, and have been pointed out as pos-
sible dangers. Troubles from these sources are, however,
rare and may be commonly neglected, but in times of epi-
demics it is always wise to guard against even this pos-
sible source of danger by avoiding the consumption of
fruit or vegetables that have in any way whatever been
exposed to a chance of contamination.

Although it is thus seen that quite a number of our
foods are sources of possible danger, it is not wise to be
too fearful over the matter. The fact that certain dis-
eases under certain conditions are caused by some of our
commonly consumed foods must be admitted ; but it
must also be remembered that the chances in each case

MEANS OF BACTERIAL INVASION 235

are small ; that our fathers and grandfathers have con-
sumed similar foods for generations and have suffered
only occasionally therefrom. It is therefore wiser not to
be over alarmed or to make life burdensome by too great
precautions, but simply to use such care as may seem
feasible and possible in our homes, and not give up the
use of any desirable food because we know that it may
be an occasional source of danger. Some people have
actually given up the use of butter and milk because it
has been shown that they contain so many bacteria. Such
a procedure is sheer nonsense. The facts here outlined
have been given, not for the purpose of inducing people
to avoid the use of such materials, but merely to suggest
to them the wisdom of adopting possible precautions
against consuming contaminated foods.

3. Means of Invasion

A matter of almost equal importance in considering the
distribution of disease is the means by which the bacteria
get into the body. Each species may have its own means
of entering, and frequently each can find entrance in only
one way. If it should get in by other means it would pro-
duce no injury. Some species, however (tuberculosis), pro-
duce' trouble, no matter how or where they enter. If we
know the means of entrance of any contagious material,
we are of course in a much better position to guard our-
selves against it. The important means of entrance are
as follows.

The Skin. Some diseases find entrance chiefly through
the skin. This is true of the bacteria which cause the

236 BACTERIA, YEASTS, AND MOLDS

many little sores, festers, boils, and abscesses, all of which
are commonly due to bacteria entering through the skin
(Fig- 78)- These bacteria are harmless in the
stomach, and, indeed, we are swallowing them
all the time. The mouth contains great num-
bers of these bacteria, as well as numerous
other species, but they do us no injury. Skin
diseases like ringworm, favus, etc., enter in
the same way. This is likewise the case with
lockjaw (Fig. 79), erysipelas (Fig. 78, b), and
various forms of blood poisoning, some of
which are of comparatively little importance,
while others may be serious and fatal. It is
FIG. 78. Vari- possibly also true of measles, scarlet fever,
ous pat ho- and smallpox, although in these latter cases
gemc cocci. we nave really no knowledge of the matter.

a, pus cocci;

b cocci pro- But tnough these diseases enter through
ducingpneu- the skin, it should be remembered that the
monia; c, surface of the body is commonly quite well
protected against the invasion of microorgan-
isms. We have already seen that the skin of
fruits, if uninjured, protects the softer portion of the
interior from decay to a considerable extent, and that the
organisms which produce decay usually enter
through bruises, cracks, or cuts in the skin.
Precisely the same thing is true, probably to
an even greater extent, in the case of the FlG ?9
human body. The outer layer of the skin is a Bacillus of
protection which the bacteria cannot ordinarily tetanus
penetrate. If therefore the skin is unbroken and unin-
jured, a person is almost perfectly protected against the

INVASION THROUGH THE SKIN 237

invasion of the particular kinds of bacteria which pass in
through the skin. A person whose skin is not broken can
without danger handle infectious material which might pro-
duce fatal results were the skin cut or bruised. It is, how-
ever, hardly ever the case that a person's skin is unbroken
over his entire body. Cuts, bruises, and scratches break
the skin, and through such openings microorganisms may
find entrance into the body. A little sliver in the skin is
frequently the starting point of a fester, a boil, or an
abscess, or even of a severe and perhaps fatal case of
blood poisoning. So small a thing as a pin prick may
sometimes allow entrance to mischievous bacteria.

The conclusion of all this is that a whole skin is a
protection which can almost absolutely be relied upon ;
but a more important lesson is that any break in the
skin should be more or less carefully protected. The
almost surely fatal disease lockjaw (tetanus) comes from
soil bacteria getting into the body through the skin, and
is apt to occur in wounds made by rusty nails, etc., which
have been lying a long time on the earth and have become
contaminated with the lockjaw bacillus. All cuts and
bruises should be carefully washed with boiled, i.e. steril-
ized, water. The fear of bacteria explains why the sur-
geon endeavors to clean the surfaces of wounds by some
disinfectant which will prevent the growth of micro-
organisms. Here, too, is the reason for protecting from
further contamination a wound thus cleansed, by covering
with bandage or plaster. All of these devices are for the
purpose of protecting the body from the entrance of bac-
teria, and make it possible for the wound to heal readily
without the disturbance which would be produced if

238 BACTERIA, YEASTS, AND MOLDS

bacteria got into the wound. Modern surgery is based on
the simple plan of keeping bacteria out of wounds. The
frequent efficacy of treating wounds by such crude meth-
ods as covering them with tobacco juice or even mud
is due to the fact that these act as mild antiseptics and
protect wound surfaces from the entrance of dangerous
organisms.

The skin should therefore be carefully guarded, and in
all cases of diseases connected with the skin, a list of
which has been given above, special care should be taken
that no part of the body which is cut or bruised or
scratched, or has sores upon the surface, should be
allowed to come in contact with infectious material. If
this is done, the danger of contagion will be greatly
reduced. Though a person with whole skin may safely
handle infectious material, no matter how dangerous it is,
one whose hands contain even the smallest pin scratch
might contract contagion and suffer illness'or death from
such procedure.

The Mouth. Some diseases find entrance through the
mouth by means of the food or drink swallowed. They
are chiefly typhoid fever, tuberculosis, diphtheria, and cholera,
although there are some others. It is manifest that not
only is the chance of contagion through the mouth less
than when a disease is borne by air currents and enters
through the skin, but it is more easily prevented. The
diseases mentioned are not usually regarded as very con-
tagious, except in the case of diphtheria, where the contagion
may be through food (milk) or air. To prevent contagion
from most of these diseases it is only necessary to guard
all that enters the mouth, keeping it free from infection.

ENTRANCE OF BACTERIA THROUGH THE MOUTH 239

Food served hot is free from danger. Food and liquids
should be specially guarded from contamination in the
sick room, especially in cases of typhoid fever. The
utensils used by the sick patient should never be used by
other inmates of the house. Those who have anything to
do with nursing the patient or handling soiled bedding
should be especially careful that nothing has an oppor-
tunity of getting into their mouths. Contagion in these
diseases may be carried by the fingers ; for if a person
touches the patient he is likely to have his fingers con-
taminated with infectious material, and should he subse-
quently place his fingers in his mouth, infection would be
very likely to follow. If one guards everything that goes
into the mouth, the chance of infection is slight. It is a
significant fact that in cases of typhoid and cholera — the
most typical diseases of this sort — nurses and doctors
rarely take the disease from their patients. They have
learned the method of infection, and guard themselves
by keeping infectious material from their mouths.

Breathing. Some diseases undoubtedly enter the body
with the breath. Fortunately the diseases thus contracted
are few. Foremost among them stands tuberculosis.
Diphtheria is probably contracted in the same way, and
possibly the grippe, whooping cough, and measles, although
in regard to the last two we know almost nothing. There
is no means of protecting ourselves against this method of
infection except to keep away from individuals suffering
from the diseases. As already mentioned, the bacteria
that pass into the air fill the space in the immediate
vicinity of the patient, but do not disseminate themselves
to a very great distance. Hence persons in the immediate

240 BACTERIA, YEASTS, AND MOLDS

vicinity of the patient are exposed to the disease by
breathing the air, while those at some distance are but
slightly exposed, and those at a greater distance not at all.
The danger is mostly confined to the room in which the
patient is kept, and hardly extends to the rest of the
household. The only protection against this method of
invasion, then, is to avoid the immediate vicinity of the
patient, and to keep the air of the room and the rest of
the house as fresh as possible. If one who is obliged to
breathe such air will take the opportunity frequently to
breathe fresh air out of doors, his danger will be reduced.

CHAPTER XVI
PRACTICAL SUGGESTIONS

From the facts outlined it is very easy to draw certain
practical suggestions for dealing with contagious diseases.

Isolation. In the case of highly contagious skin diseases,
such as scarlet fever, measles, smallpox, etc., the patient
must be isolated from the rest of the household as com-
pletely as possible. This should be done by confining
him to one room and allowing no one to enter except
those necessarily engaged in caring for him.

The same general treatment may be applied in diseases
characterized by coughing, like whooping cough and con-
sumption. Diphtheria, also, though not distinctly a cough-
ing disease, is distributed by breath that is forcibly exhaled
by the patient, and the seriousness of the disease makes
it necessary to adopt isolation. While it is manifest that
the only means of absolutely avoiding contagion from
tuberculosis and whooping cough is to isolate the patient,
it is also clear that complete isolation of a sufferer from
whooping cough or tuberculosis is rarely possible in an
ordinary household. Diphtheria is such a serious disease,
so rapidly fatal, and its course is usually so brief, that com-
plete isolation is not only feasible but necessary. The
other two diseases last so long that isolation is generally
very burdensome, difficult, or impossible. It is well to
remember that in such diseases periods of coughing are

241

242 BACTERIA, YEASTS, AND MOLDS

the times when there is most chance of contagion, and
that all well persons should, so far as possible, be kept
away from the vicinity of these patients at the time of
coughing. If this is done and the sputum is cared for,
the chance of contagion is much reduced.

The question often arises how long the isolation should
be continued. One must usually depend upon the physi-
cian or board of health for an answer to this question,
since the period of isolation varies with different diseases.
For scarlet fever it is about six weeks ; for whooping cough
it is certainly as long ; for diphtheria the time of necessary
isolation is very variable, and our health boards and physi-
cians have not yet determined how long an isolation is neces-
sary to prevent a convalescent patient from transmitting
the disease to other children. Upon this matter nothing
positive can be said at the present time. In general, the
period of isolation must be determined for each disease
by the advice of physician or board of health.

Excreta. In the case of diseases located in the alimen-
tary canal, and distributed by excreta, isolation of the
patient is not so necessary, but everything that comes in
contact with the discharges from the alimentary canal
should be carefully guarded. This will include not only
the discharges from the intestine but also those from
the mouth. All possible precautions should be taken to
prevent any such material from being distributed through
the household. Such diseases can very easily be confined
to the patient and the sick room if care be taken with
the excreta, if all soiled materials coming in contact with
the patient be properly treated, and all eating utensils
thoroughly disinfected.

TREATMENT OF INFECTED ARTICLES 243

Clothing and Bedding. Any articles of clothing that
come in contact with a patient, any towels or cloths
used in bathing him, are very likely to be mediums for
the distribution of disease. If it is a skin disease, the
clothing is sure to become infected. If the disease bac-
teria are eliminated through the sputum or the excre-
ment, it is almost inevitable that the clothing, especially
the bedding, will be contaminated with infectious material.
In all skin diseases, as well as in cases of typhoid, diph-
theria, tuberculosis, and indeed most contagious diseases,
clothing and bedding are sources of infection and must
be guarded carefully. The clothing and bedding should
not be sent to the general laundry but washed separately
and thoroughly boiled. Nothing should be worn in the
sick room by nurse or patient that cannot be washed,
and all unwashable fabrics, curtains, carpets, etc., should
be removed from the room where there is a contagious
disease.

Eating Utensils, etc. The eating utensils used by a
patient, or indeed anything that he handles or uses dur-
ing his sickness, may be very easily contaminated with
the infectious material. It is perfectly evident that a
diphtheria patient who has the bacilli in his mouth will
contaminate the spoons, knives, and forks which he uses
with the bacteria that are producing the trouble in his
throat. The same thing would be true, though perhaps
to a less extent, of all contagious diseases, for a patient
cannot handle anything without danger of thus infecting
it. Consequently all utensils from the sick room and
all articles handled by the patient must be looked upon
as means of distributing the disease. The practice of

244 BACTERIA, YEASTS, AND MOLDS

taking the spoons, knives, cups, and plates from which
the patient has taken his meals, and carrying them into
the kitchen to be washed with the other household uten-
sils for subsequent use by the rest of the family, is a dan-
gerous one and is one of the easiest and perhaps most
common means of distributing the disease from the sick
room to the rest of the household. Doubtless many times
the distribution of diseases is attributable to the indiscrim-
inate use of the same eating utensils by the family. It
is easy to avoid this danger, (i) Allow no one to use the
eating utensils which the patient has during his sickness.
(2) After his recovery put them into boiling water and
leave them for several minutes. Do not wash them
with the eating utensils of the rest of the household.
Thorough boiling will render them harmless, and there-
fore even a knife or a spoon coming from the sick room
should be placed in boiling water before it is used by any
other person. It must be borne in mind that water that
is simply hot is not sufficient for this purpose. The
water must be boiling, and it is better if the articles are
placed in the water and the water boiled for five or ten
minutes before they are taken out to be used. The state-
ments made concerning eating utensils apply also to any
articles handled by the patient.

Books used by children recovering from diphtheria or
scarlet fever and then returned to a public library may
distribute disease through a community. In cities where
the schools furnish supplies children should be cautioned
against putting into their mouths pencils, etc., particularly
those belonging to other children. If a person has a scalp
disease, like ringworm, he should not be allowed to use

TREATMENT OF THE SICK ROOM 245

combs or brushes used by other members of the family,
for other cases of the disease would be sure to follow.

Nurses. Those who nurse the patient should take
special care in a number of directions. They should
have a change of clothing to put on when they leave the
sick room to mingle with the rest in the house ; they
should wash their hands frequently with some disin-
fectant to be mentioned later, especially after handling
the patient, his bedding or his clothes. They should be
especially careful to avoid putting their fingers into their
mouths, for in many diseases this is a common means of
infection. A nurse who carefully observes these precau-
tions is much less liable to infection from any of the
diseases. The face also requires frequent washing. The
hair is a particularly good lodging place for bacteria, and
a good nurse wears a cap to protect her head in cases of
contagious diseases.

Treatment of the Sick Room. After the recovery of
the patient it is necessary that the room he has occupied
should be thoroughly disinfected before any other mem-
bers of the household are allowed to enter it. The method
of disinfection will be found in another place. We will
here only emphasize the fact that in order to prevent the
appearance of other cases of the disease such disinfection
is absolutely necessary before the room is occupied by other
people.

The treatment after recovery from a contagious disease
is sometimes difficult to determine. So far as concerns
the patient himself, the proper procedure after recovery
is to bathe himself thoroughly in a disinfectant solution
suitable for this purpose, the disinfection or bathing

246 BACTERIA, YEASTS, AND MOLDS

including the hair as well as the rest of the body. The
person should be given clean clothes that have not only
been thoroughly washed but disinfected by proper means ;
after which there is no danger of his transmitting the
disease to others.

Sewage. Since the discharges from patients find their
way into sewage, this material is extremely dangerous,
indeed from the standpoint of human health one of the
most dangerous of all substances. Every effort should
be made in the household to guard against it. Par-
ticular attention should be given to keeping the drinking-
water supply from becoming contaminated with sewage.
In cases where the water is from a well there should be
especial precautions against contamination from privies or
sewage. The health of the family depends upon having
the well a long distance from sewage and privies.

In cities the sewage empties commonly into one gen-
eral system, and most of the houses are connected by a
series of underground channels. These sewers carry the
discharges from all the patients in the city, and hence
contain the dangerous disease germs. Since each house
is connected with this system of sewerage, it is of the
greatest importance in modern cities that the connections
with the sewer pipes should be most carefully guarded.
Proper plumbing does this satisfactorily, but it is neces-
sary that the plumbing should be thorough and that it
should occasionally be inspected. All bowls, sinks, and
closets should be connected with the sewer by traps.
The general design of such a trap is shown in Fig. 80.
Between the bowl or sink and the sewer is a bent tube
filled with water. As long as this trap is thoroughly

SEWAGE

247

filled with water no bacteria and no gas can pass from
the sewer into the sink. If the joints of the sewer pipes
are tight and the traps are full of water, there is no dan-
ger that anything from the sewage can come into the
rooms. The traps, however, occasionally get emptied of
water, and then gases may pass up from the sewers.
Moreover, the insides of these
traps become breeding places
for certain kinds of bacteria,
though rarely disease bacteria,
and may in time become full
of them. It is therefore de-
sirable to pour some kind of
disinfectant occasionally into
the bowls and sinks. A weak
solution of carbolic acid, one
part to twenty, or a solution
of chloride of lime, one part
to twelve, put into bowls and Fla 8a Diagram showing the

sinks will disinfect the traps. principle of two kinds of traps
It is also an excellent plan to separating washbowls from

.,. r sewers.

pour boiling water frequently

down sinks, bowls, and closets, for this not only helps

to clean but helps also to disinfect.

A worse danger to a household are leaky sewer pipes.
If these are poorly laid, the contents of the sewer
may ooze out into the cellar or soil under the cellar
and become a source of considerable danger. Leaking
sewer pipes in a house are a serious menace. The
evils from sewer gas have, however, been overrated. Sewer
gas itself is not capable of producing any specific disease.

248 BACTERIA, YEASTS, AND MOLDS

If it is constantly escaping into a house, the members of
the family may perhaps become weakened by constantly
breathing such gas, and may be more liable to the attack
of parasitic diseases. Such persons might perhaps have
a tendency to throat troubles ; but there is no evidence
in our possession that sewer gas can cause any particular
disease. The diseases are caused not by gases but by
living bacteria ; and while sewer gas may be deleterious
in its weakening action upon individuals breathing it, it
can never produce disease.

Protection following Cure ; Immunity. The recovery
from a contagious disease, as a rule, protects the indi-
vidual more or less perfectly from a second attack of
the same disease. But the amount of protection differs
with different diseases. After recovery from some of our
contagious diseases, like scarlet fever, a person rarely
has a second attack during life. With other diseases a
second attack is more likely to follow, but in all cases
there is at least a temporary protection following the
recovery. In other words, after a person has recovered
from a contagious disease he is not, at least for some
time, liable to the same disease again. This protection
lasts in some cases for many years and perhaps through
life (scarlet fever) ; in other cases it may last only a few
years (measles?); in some cases perhaps only a few
months or weeks (diphtheria); but a temporary protec-
tion is always gained. The reason why one is thus pro-
tected from a second attack scientists have not yet wholly
explained.

Vaccination. A word must be given in regard to the
method of protecting the body against smallpox known

VACCINATION 249

as vaccination. This method has been in use over a
hundred years, but there is a vast deal of misunderstand-
ing in regard to it. The fact of the case is that
vaccination gives to the individual a certain amount of
protection against the dreaded and frequently fatal dis-
ease, the protection being due to about the same cause
as that which produces the immunity following recovery
from germ diseases. The protection is not an absolute
one, since vaccinated persons do occasionally take the
disease. But for a time after vaccination one is almost
surely protected against smallpox. How long this protec-
tion may last no one knows. It certainly does not last
forever, and if one wishes to remain immune it is neces-
sary to repeat the vaccination occasionally. For a year or
two after vaccination the protection is strong and nearly
absolute. But after a couple of years it gradually becomes
reduced, and after ten or fifteen years the amount of
protection afforded is very slight. The proper method,
therefore, of guarding against smallpox is vaccination in
childhood, followed by vaccination some years later, and
perhaps again at intervals in later life. Experience has
shown over and over again that proper attention to vacci-
nation will check smallpox epidemics, and no other means
has hitherto been satisfactory.

It must be recognized, however, that vaccination is not
always harmless. In the vast majority of cases the per-
son suffers nothing except a very trifling inconvenience
from the treatment. In extremely rare cases, perhaps,
more serious results arise. If these secondary troubles
do occur, they are usually not due directly to the vaccina-
tion but to the vaccination wound becoming contaminated

250 BACTERIA, YEASTS, AND MOLDS

with bacteria. It is therefore necessary to protect the
wound carefully against possible contamination. This is
done by the physician in various ways. Although there
is thus some danger in vaccination, the chances of trouble
are very slight indeed, whereas the protection afforded
against smallpox is so great as to lead scientific men
and physicians to recommend its use unhesitatingly as
a general protection against this extremely violent and
frequently fatal disease.

Modern physicians have means of almost perfectly
protecting the members of the household from the con-
tagion of diphtheria by means of the product known as
diphtheria antitoxin. Where a family is unable to isolate
a patient from other children, an injection of antitoxin is
almost certain to prevent the distribution of the disease.
Its use is being adopted very widely by physicians, and
every housewife should understand that it is a precaution-
ary measure that is eminently wise, perfectly safe, and the
only known means of protecting a family where complete
isolation of a diphtheria patient is impossible. Many phy-
sicians, indeed, adopt it as a precautionary measure in
households where there are several children, even though
the patient is isolated.

PHYSICAL VIGOR A PROTECTION AGAINST CONTAGION

The best protection against contagion is robust health-
A person in strong, vigorous health is much less liable to
yield to disease than one less robust. Consequently in
the attempt to protect the household from contagious
diseases special emphasis should be placed upon methods

PHYSICAL VIGOR A PROTECTION 251

of increasing the physical vigor of its members. This can
be done by wholesome food, by exercise, and by fresh air.
An active body is far less liable to disease than one more
or less passive, and vigorous exercise in the open air,
accompanied by plenty of wholesome but not too rich
food, will be the most thorough safeguard an individual
can have against the attack of some infectious diseases,
especially tuberculosis. The need of fresh air should be
emphasized, perhaps, more than any other point, for the
air in houses, for reasons already indicated, is much more
liable to be filled with infectious material than the out-
door air, and a person who constantly remains in the
house is much more liable to yield to contagion. ,If,
however, he is careful to exercise in the open air, he will
ward off attacks to which otherwise he might yield.
This applies even more forcibly to the air of our sleeping
rooms than to that of our living rooms, for fresh air in
the sleeping room is one of the greatest desiderata in
maintaining good health. The belief that night air is
injurious is responsible for much ill health. Sleeping in
close rooms without sufficient air causes a general lower-
ing of bodily vigor. Our sleeping rooms should have
the windows open even in cold weather, and, provided
there be mosquito nettings at the windows to keep out
insects, there is absolutely nothing to be feared in night
air. While vigorous health is a protection against some
diseases (tuberculosis), it is far less efficient against others
(smallpox).

It should always be borne in mind that contagious
diseases are real things, and not the result of imagination.
They are produced in our bodies by the growth of certain

252 BACTERIA, YEASTS, AND MOLDS

microscopic animals and plants in our blood, muscles, or
elsewhere. They cannot be warded off by simply disbe-
lieving in their existence, and the sooner the housewife
learns that a contagious disease is due to distinct living
beings which are transported from one person to another
and live as parasites in the patient, the sooner will she be
in a position to protect her family from the spread of
contagion.

GENERAL CONCLUSIONS

Each type of infectious disease must be fought in its
own way. The so-called children's diseases are so decidedly
contagious that isolation alone is capable of preventing
their distribution. Of the adult diseases, however, the
most serious may be largely checked by proper means.
Smallpox must be fought with vaccination and isolation,
diphtheria by antitoxin and isolation, typhoid fever by
a guard placed over the water and the milk supplies,
malaria by destroying the breeding places of mosquitoes
and protecting oneself from mosquito bites.

Of all diseases, however, tuberculosis is most widespread
and demands most attention. The common form of this
disease is consumption, but the bacteria may attack other
parts of the body, producing other diseases, such as scrofula,
hip disease, etc. Consumption must be guarded against
by destroying the sputum of patients and avoiding their
breath while coughing, and in any form of the disease
that produces open sores the discharges from the sores
must be carefully destroyed. In spite of the long-accepted
belief, consumption is not hereditary but is contagious.
Its spread through families is due to the close association

GENERAL SANITARY RULES 253

of patients with the other members of the family. It is
a disease associated with small rooms, poor ventilation,
and crowded houses where the healthy members of the
family live with consumptive patients and frequently sleep
with them. Under such conditions contagion is almost
sure, and the disease spreads from person to person just
as decay spreads from apple to apple in a barrel. More
air, more light, more care of the sputum and other dis-
charges, greater attention given to guarding against the
coughing of the patient, as for example inducing him to
cough into cloths that can be burned, — these are the
remedies against the spread of the contagion, and strict
attention to these facts would soon convince any one that
the disease is not hereditary but due to infectious matter
disseminated from the patient. The child of a consump-
tive mother may even nurse at his mother's breast with
little danger of contagion ; but sleeping with her and
breathing her breath while she is coughing is very likely
to give him the disease and lead to the erroneous belief
that he inherited it from his mother.

GENERAL RULES

There are a few simple rules whose observance will
reduce the chances of contagion. These rules should be
followed by all, but it is particularly important that chil-
dren in every household, and especially children in schools,
should be taught their significance. The most important
rules are :

Do not spit on the floor.

Do not put the fingers in the mouth.

254 BACTERIA, YEASTS, AND MOLDS

Do not wet the fingers in the mouth for the purpose
of turning the leaves of books, especially library books,
inasmuch as book leaves are sometimes the lurking places
of disease bacteria.

Do not put pencils in the mouth.

Do not put money in the mouth. This is extremely
important, because money is liable to come in contact
with all sorts of people and to become contaminated with
many kinds of disease bacteria.

Do not put into the mouth anything that another per-
son has had in his mouth. This refers to gum, apple
cores, candy, whistles, bean blowers, drinking cups, etc.

Turn the face aside from others when coughing. This
will sometimes prevent contagion passing from one per-
son to another, inasmuch as the breath in coughing
distributes disease germs.

Be always particular about personal cleanliness, fre-
quently washing the face and hands.

CHAPTER XVII
DISINFECTION

In every household the problem of disinfection is sure
to arise in connection with contagious diseases, and it is
a question of more or less serious import according to the
seriousness of the disease and the number of inmates in
the house. The purpose of all disinfection is to prevent
the spread of contagious diseases from one person to
another. Hence it is desired to destroy the microorgan-
isms which cause the disease. If this can be done there
will be no chance of contagion, but until it is done there
is always a possibility that a healthy person may contract
disease by coming in contact with the germs.

In connection with the treatment of infected material
two terms are frequently confused. An antiseptic is a
material or a treatment which checks the growth of bac-
teria, though it does not necessarily kill them all. It
may prevent their development without destroying their
life. The term germicide, when properly used, refers
to treatment which totally destroys all microorganisms.
The agents which are used as antiseptics are also
commonly capable of acting as germicides if they are
used in larger quantities, and, on the other hand, germi-
cidal substances may be only antiseptic if used in small
quantities.

In considering the question of disinfection in the
household there are always two important questions to

255

256 BACTERIA, YEASTS, AND MOLDS

be considered : (i) What disinfectants are capable of
destroying the bacteria ? (2) How can these agents be
most practically applied ? It is of course manifest that
not all germicides can be used under all conditions. Vio-
lent poisons, like corrosive sublimate, might be used in
some cases, while it would be out of the question to use
them in others. The question, therefore, of the appli-
cation of the disinfectants is of even more importance
than a knowledge of these antiseptics themselves.

DISINFECTING AGENTS — PHYSICAL

The physical agencies which destroy microorganisms
have already been considered in previous chapters, and
a summary only is here needed. They are briefly the
following :

Heat. All active growing forms of bacteria are
destroyed by moderate heat. A temperature of 140°,
maintained for half an hour, is usually capable of de-
stroying them, and a higher temperature quickly kills
them. Spores, however, are not killed by a temperature
short of actual boiling, and some spores are killed only
by prolonged boiling. Moist heat of steam is more effi-
cacious than dry heat. Bacteria spores may withstand a
dry heat of 280° for some hours, but they cannot with-
stand a moist heat of steam that is much above boiling.

A matter of practical importance is the recognition of
the fact that most of our contagious diseases are caused
by microorganisms that do not produce spores. Conse-
quently lower temperatures than boiling are commonly
sufficient for disinfection. The only common disease that

PHYSICAL DISINFECTING AGENTS 257

is known to produce spores is lockjaw; for while there are
some other disease germs which do produce spores, the ordi-
nary diseases of the household which we look upon as con-
tagious are not, so far as we know to-day, disseminated
by means of spores. Hence the practical conclusion is
that for all of the common household diseases a moist tem-
perature of 150° or 1 60°, maintained for half an hour,
is sufficient for disinfection ; but it must always be
borne in mind that this will not disinfect spore-producing
material.

Sunlight. Bacteria cannot stand direct sunlight for more
than a few hours without being killed, — the brighter
the light the more efficacious its action. While sunlight
is thus an acceptable germicide, its practical value is
limited because it has little power of penetration. Thin
materials, like sheets, which can be exposed to direct sun-
light, will be disinfected in the course of a few hours, but
heavier materials, like blankets, will be disinfected only
on their surface. Anything on which the sunlight can
shine directly may easily be disinfected by this means,
but in dimly lighted rooms light is of little value as a
disinfectant. Its use is therefore limited to such articles
as can be removed from the rooms and exposed to the
sun's rays.

Cold. Cold is almost useless as a disinfectant. It
delays the growth of bacteria for a while, but does not
destroy them. We have already seen that long-continued
freezing in ice will, after some months, destroy typhoid
bacilli, but, except in the case of a few diseases, like
yellow fever, freezing is of no value as a -disinfecting
agent.

258 BACTERIA, YEASTS, AND MOLDS

DISINFECTING AGENTS — CHEMICAL

The most common methods of disinfection employ
certain chemical agents known to have the power of
destroying bacteria. There is a long list of germicidal
substances. We need notice only those few agents that
are in common use.

Corrosive Sublimate. This is one of the most efficient
germicides, and its small cost has given it wide use. The
most common strength for using it in ordinary conditions
is one part of sublimate to one thousand parts of water. At
this strength it rapidly kills bacteria. This strength may
be used for washing floors or walls of infected rooms. It
may be used for washing the hands after touching infec-
tious materials. It is an excellent antiseptic, but there
are two objections to it. (i) It is intensely poisonous, and
the greatest care must be exercised in handling it, to pre-
vent it from reaching the mouth. (2) It has a strong cor-
rosive action on metals and cannot be used on anything
made of iron or steel. These facts limit its use, but never-
theless it is one of the best and most widely used of chem-
ical disinfectants. A solution of proper strength, one to
one thousand, may be made by dissolving one quarter of
an ounce of corrosive sublimate in two gallons of water.
A more effective solution is as follows.

Corrosive sublimate . . . .15 grains (i gram)

Common salt 30 grains (2 grams)

Water i quart (1000 grams)

Carbolic Acid. This material has been used longer than
any other disinfectant, and is very efficient, though less
so than corrosive sublimate. It is commonly used in a

CHEMICAL DISINFECTING AGENTS 259

proportion of about one part acid to twenty parts water,
although sometimes it may be weaker and sometimes
stronger. A solution of one part to twenty may be used
for washing the hands, but stronger solutions will produce
a burning of the skin. It may be employed for almost any
of the purposes for which corrosive sublimate is used, but
its value is less and its cost is considerably greater. One
of the reasons for its popularity is the fact that it pos-
sesses a distinct odor, and people who do not properly
understand the matter of disinfection have an impression
that a disinfectant ought to have a strong odor. It should
be understood thoroughly at the outset that deodorants
are not disinfectants. Substances with strong smells do not
ordinarily have any value as disinfectants. The odor of
carbolic acid is almost without value, and the security
which people feel when a disinfected room is filled with
carbolic acid fumes is wholly misplaced. To disinfect
the air requires materials of a different nature, and car-
bolic acid is not more useful as a disinfectant than are
many other antiseptics that emit no odor at all. Corro-
sive sublimate, for example, is very much more effica-
cious than carbolic acid, although it is totally without
odor. It may frequently be desirable in a sick room to
have a deodorant as well as a disinfectant ; but this is for
comfort rather than for safety, and other deodorants can
be employed which are equally as efficacious as carbolic
acid. The burning of coffee grains in a room will usu-
ally destroy offensive smells and serve as a deodorant,
although it is valueless as a disinfectant.

Chloride of Lime. This is one of the cheapest and at
the same time one of the best disinfectants. It may be

260 BACTERIA, YEASTS, AND MOLDS

applied dry if the material to be disinfected contains mois-
ture, but it acts only in the presence of moisture and should
usually be dissolved in water. A solution of one part to
twenty-five of water (one pound to six gallons) is proper for
use, and is extremely efficient in disinfecting walls, floors,
furniture, etc. Its efficacy is due to the chlorine gas liber-
ated from it. Common slacked lime, which is occasionally
used, is of little value as a disinfectant.

Sulphur. The fumes of burning sulphur have been
widely employed for disinfecting rooms, partly because of
its efficacy and partly because of ease of application. The
common method of procedure is to shut up in a room the
articles to be disinfected, tightly closing all cracks around
doors, windows, keyholes, etc., and to burn a quantity of
sulphur in the room. Sulphur can be used only in spaces
that can be tightly closed, and this of course materially
limits its application. It has the disadvantage of not
readily destroying bacteria spores, and therefore not being
absolutely effective. In spite of this fact it is found to
be of great practical value, and has been very widely and
successfully used by boards of health.

Formalin. The desirability of some disinfectant in the
form of a gas that can be used for disinfecting rooms, etc.,
has led to the use of a new disinfectant known as formalin.
This material, as purchased, looks like water, and consists
of a poisonous gas dissolved in water. The liquid itself
is a very effective germicide, one part of formalin to ten
thousand parts of water being sufficient to destroy the vital-
ity of bacteria. Formalin has no more injurious action
upon clothing than common water would have. Hence
it may be used very freely in disinfecting any material

APPLICATION OF DISINFECTANTS 261

that can be soaked in water. Its general use for washing
is hardly practicable, because it gives off a gas that is very
injurious to the eyes and must be carefully handled. In
recent years it has come to be used extensively by health
boards for disinfecting rooms. Formaldehyde gas is liber-
ated in considerable quantity and allowed to act in closed
rooms for a number of hours. To liberate the gas in
quantity various devices have been adopted. One of the
simplest means is burning what are known as formalin
candles, which can be lighted and left to burn in a room,
giving out quantities of formalin gas. Other methods
require special apparatus in the form of lamps, etc., and
are not within the reach of the ordinary householder.
The efficacy of this gas in disinfecting has been ques-
tioned. It appears to be about as efficient as sulphur,
and under some circumstances more so, though not an
absolute germicide in every case. It is probably the best
gas disinfectant known.

APPLICATION OF DISINFECTANTS

In determining the application of disinfectants two ques-
tions arise : (i) Where should the disinfectant be applied?

(2) What is the proper disinfectant to apply? In most
problems that confront the household there is little diffi-
culty in determining the place where the disinfectant
should be applied. We should look in at least four dif-
ferent directions : (i) the excreta and all discharges from the
patient ; (2) the person of the patient or of the attendant ;

(3) clothing, including all bedding, wearing apparel, etc. ;

(4) the sick room itself while occupied and after it is vacated.

262 BACTERIA, YEASTS, AND MOLDS

Excreta. All discharges from a patient suffering from
any infectious disease should be disinfected at once, since
they will always contain infectious microorganisms. This
would apply to the faeces, and all discharges from the mouth,
as well as from sores on the skin, etc. Such discharges
should be placed in a solution of corrosive sublimate, one
part sublimate to five hundred parts water, or of chloride of
lime, six ounces to a gallon. The quantity of the disin-
fectant should be large, and the material should be allowed
to soak in it for at least an hour before it is thrown into
closet or sewer. Such treatment effectually destroys its
pathogenic nature. It is of course difficult to disinfect
discharges from the skin, but all pus that exudes from
such sores should be collected and thoroughly disinfected.

The Person. The disinfection of the patient during
disease is rarely possible, and all that need be here stated
is that the skin should be kept clean by bathing in water
to which has been added a little glycerine. The disinfec-
tion of the person of nurse or attendant, however, should
be most carefully attended to in cases of serious infectious
diseases. The hands in particular are liable to become
infected with the pathogenic germs, because they are used
in handling the patient and his bedding. They should be
carefully washed in soap and water, special attention being
given to brushing the finger nails and removing all possible
dirt from them. Afterwards it is well to put the hands
for a moment in strong alcohol, then, before drying, in
a corrosive-sublimate solution, one part sublimate to one
thousand parts water. After this the hands should be
washed again in clean water. Other parts of the body
should also be washed, although no part needs it so much

DISINFECTION OF CLOTHING AND BEDDING 263

as the hands. The hair should occasionally be washed
in the same way, although, as already stated, the nurse
should use a cap to protect the hair from infection as far
as possible. These disinfections should be frequent in
cases of serious contagious diseases, and should always
be attended to when the nurse leaves the sick room to
mingle with the rest of the family.

Clothing, Bedding, etc. These articles almost always
offer difficult problems. The following general directions
are all that can be given.

1. Burn everything which is not of very great value.
This is the most thorough method of disinfection, and
therefore care should be taken to use old, worthless
articles as much as possible, in order that they may
subsequently be burned without too great loss.

2. All of the articles that can be boiled should be sub-
jected to a vigorous boiling for at least half an hour. This
is sufficient for complete disinfection. It will apply to all
forms of thin clothing, like cotton, and may be used for
sheets, pillow cases, etc.

3. Articles too heavy for boiling, or those that would
be ruined by boiling, cannot be so easily treated. Any-
thing that can be soaked in water without injury can be
disinfected by soaking it for three or four hours in a solu-
tion containing one part of formalin to five thousand parts
of water. This is extremely cheap as well as easy to make,
and may be employed for blankets and other articles
capable of soaking in water without ruin. The blankets
should be placed in a tub, the tub filled with water, and
formalin added in the proportion mentioned above, or even
as strong as one quarter of a pint formalin to ten gallons of

264 BACTERIA, YEASTS, AND MOLDS

water. A soaking in such a solution will be a thorough
disinfection. For heavier articles like mattresses and
comfortables, which cannot be soaked, there is no satis-
factory method of disinfection. If there are at hand facili-
ties for steaming, these articles may be disinfected ; but
this is never possible at home, and can only be done by
health boards. Mattresses in particular are difficult to
disinfect and cannot be rendered perfectly safe. For this
reason care sho,uld be taken that only mattresses of little
value are used in contagious diseases, so that later they may
be destroyed. They may, however, be protected consider-
ably by covering them with a rubber blanket, which will
prevent their becoming contaminated. Carpets and heavy
curtains can be disinfected satisfactorily only by means of
superheated steam, and this is rarely possible in a private
house. Care should be taken, therefore, to remove such
articles from a room in which there is any contagious
disease.

TREATMENT OF THE SICK ROOM

While occupied. A room in which there is a case of
contagious disease is, under the very best circumstances,
a source of danger to all persons within the house, and it
must be most carefully guarded to protect the other mem-
bers of the family from danger. The treatment of the
room during its occupancy and after its vacation must be
totally different. While the room is occupied by the
patient not very much can be done to control the conta-
gion. Plenty of fresh air should be insisted upon, and
obtained by the proper opening of windows, care being
taken, of course, to shield the patient from draughts. If the

TREATMENT OF THE SICK ROOM 265

room is occupied for some time, it may be well to wash
occasionally all surfaces of furniture, floors, window sills,
etc., with corrosive sublimate solution as described above.
The patient himself, in case of skin disease, may be bathed
and his skin be kept moist with water containing a little
glycerine or with vaseline. This will materially diminish
the chance of infectious material floating from his skin
around the room. All contaminated cloths should be
burned immediately, and care should be taken that no
one passes from the sick room to mingle with the other
members of the family until he has changed his clothes.

Care after Vacation. After the room is vacated by the
patient it is necessary to disinfect it thoroughly before
using it again. The disinfection of such a room is a matter
of some difficulty and many methods have been adopted
for the purpose. One that is perhaps as satisfactory as
any is as follows.

Carpets, curtains, bedding, and all cloth material should
be removed and disinfected as above mentioned. All
surfaces in the room, including walls, ceiling, floor, tables,
chairs, and especially cracks around mopboards and floor,
should be washed freely with the corrosive sublimate solu-
tion or with the chloride of lime solution.

If this washing is thorough, including all surfaces in
the room, the room will be well disinfected ; but it is
wise and customary to complete the process by the use
of some gaseous disinfectant. One occasionally used is sul-
phur fumes. The best method of applying it is, first, to
close tightly all cracks and then to place the sulphur in a
metal dish in the middle of the room, preferably putting
the vessel in a tub containing an inch or two of water.

266 BACTERIA, YEASTS, AND MOLDS

A little alcohol is poured upon the sulphur, which is then
ignited and the room quickly closed. Five pounds of sul-
phur should be burned for every thousand feet of space,
and the room should be left closed for twenty-four hours.
While such sulphur fumes are not a perfect disinfectant,
in practice the method has been found satisfactory.

In these days formalin gas is being used, more than
sulphur. The method of obtaining the gas is either
through the burning of formalin candles or the using of
one of the machines devised for producing such gas.
These, however, are always handled by boards of health,
and details of their use need not be given here. After
the use of the gaseous disinfectant all windows should
be thrown open to allow a free access of air.

Disinfection by gas cannot be absolutely relied upon,
and there are always possibilities of a disease reoccurring
in the room if it is occupied immediately. It is therefore
wise, where possible, to leave the room unoccupied for
some time after it is vacated by the patient, but this is
not absolutely necessary. It should perhaps also be stated
that if the room is thoroughly washed with a disinfectant
solution and thoroughly aired, the use of the gaseous dis-
infectant is unnecessary; and if the gaseous disinfectant
is thoroughly applied, the washing is unnecessary ; either
one, if thorough, is sufficient. But the chance of some
slip in the application makes it wise to use both methods,
at least in the case of serious contagious diseases. Dis-
infection should always follow smallpox, measles, diph-
theria, tuberculosis, and typhoid fever, and it is wise to
adopt it in cases of mumps, whooping cough, and the
other lighter contagious diseases.

APPENDIX

DIRECTIONS FOR LABORATORY EXPERIMENTS

Apparatus. The experiments here described are all of a simple
character. Many of them can be performed without any special
apparatus ; but some would need, in addition to test tubes, flasks, and
other simple glassware found in any
laboratory, a few pieces, as follows.

1. A steam sterilizer. An ordinary
steamer such as used in the kitchen
will do. A better form is shown in
Fig. 81.

2. A hot-air sterilizer. The best form
is shown in Fig. 82. Some sort of sheet-
iron box which will serve the purpose
may be found in almost all chemical
laboratories.

3. Petri dishes. These are double
glass dishes, Fig. 83, several dozen of
which should be at hand.

4. Glass pipettes to hold i cc.

5. A few fermentation tubes, shown
in Fig. 38.

6. Pieces of platinum wire fused

into glass rods are convenient for transferring bacteria.

7. To carry out the microscopic studies there will be needed a
microscope with a two-thirds and a one-sixth inch objective. A higher
power is desirable though not necessary. In addition, glass slides
and cover glasses will be needed.

The apparatus above listed (except the microscope) costs little,
and many of the experiments can be performed with even simpler

improvised material.

267

FIG. 8 1. Steam sterilizing
apparatus.

268

BACTERIA, YEASTS, AND MOLDS

Method of Experimenting. The order in which the experiments
are given is the one which most naturally follows the subjects treated
in the body of the text, and should be followed as closely as possible.

Where possible each
scholar should perform
the experiments, but
this will be found imprac-
ticable in most cases. In
such cases the experi-
ment must be performed
by the teacher in the
presence of the class.

Most experiments with
microorganisms require
two or three days for the
bacteria to grow, and
the observations must
therefore be made some
time after the prepara-
tion is made. Hence it
is especially important

FIG. 82. Hot-air sterilizing apparatus.

that everything should
be carefully and intel-
ligibly labeled and that the scholars understand the meaning of the
labels. When the teacher performs the experiments the scholars
should see the preparation as well as the final results, and each
scholar should make careful notes.

Sterilizing. • All glassware must be
sterilized before it is used. This is abso-
lutely necessary and the success of the
experiments will depend upon it. The
glassware should be first washed clean.
Then all test tubes, flasks, and fermenta-
tion tubes should be tightly plugged with
cotton, as shown in Figs. 38 and 64, and then placed, with all
other glass apparatus, in the dry sterilizer. By means of a Bunsen
flame the sterilizer should then be heated to a temperature of about

FIG. 83. A petri dish for
plate cultures.

APPENDIX 269

340° (170° C.) and kept at this temperature for one hour. After cool-
ing they are ready for use. In the following experiments it will be
understood that all glassware should be sterilized before using.

EXPERIMENTS ILLUSTRATING THE MOLDS

1. Mold on Bread. Place several slices of bread under a bell glass
or any dish that will protect it from evaporation. Battery jars, large
beakers, or even common bowls will answer. Moisten the bread with
water and put aside in a warm place (80° to 95°). After two or three
days the bread will usually show signs of white mold. Allow the
mold to grow until some color appears and then determine, if possible,
whether there are more than one species of mold on the bread.

2. Molds on Different Foods. Under separate bell glasses place
bits of cheese, some pieces of lemon, and a bit of banana. Each of
these should be moist. Cover and set aside as in the last experiment.
Molds will grow in a few days, but probably different species will grow
upon the different materials. Compare the molds and determine how
many kinds can be seen.

3. Experiment to show the Mycelium. Place a little fruit juice,
such as may be obtained from canned fruit, in test tubes or in homeo-
pathic vials, and drop a few mold spores from the last experiment, or
a little dust from the floor, upon the surface of the liquid. Set aside
to grow, and notice how the molds spread and send fine threads into
the liquid. Later notice that colored masses of spores grow in the
air upon the surface but not in the liquid below.

4. Spores. After the molds of the previous experiments have
begun to produce spores, as shown by the appearance of some color,
remove a little spore material from the surface with a knife blade or
a platinum wire and examine under a microscope. For this purpose
a compound microscope is necessary, since the spores are very small.

5. Growth of Mold from Spores. Moisten a bit of bread and trans-
fer with a platinum wire a little bit of the spore mass from a vigor-
ously growing mold to the surface of the bread. Cover with a bell
glass and set aside for growth. Examine every day, and note that
molds start from the points where the bread was inoculated with the
mold spores.

270 BACTERIA, YEASTS, AND MOLDS

Preparation of Gelatin Culture Medium

For the following experiments it is necessary to prepare a jelly
upon which molds will grow. A satisfactory jelly for this purpose is
as follows.

To 100 grams of gelatin add 900 cc. of water and about 5 grams
of Liebig's Extract of Beef, and boil for half an hour. While still
hot filter the material through absorbent cotton. In using absorbent
cotton for this purpose a large funnel should be used and the absorb'
ent cotton placed in it. The liquid gelatin is poured into the cotton,
and it will run through readily, coming out as a tolerably clear solu-
tion. Some of the filtered jelly is to be placed in sterilized flasks and
some in test .tubes, about 10 cc. in each. Plug the flasks and test tubes
with cotton, and steam the jelly in a common steamer for about twenty-
five minutes. The jelly is to be cooled and put aside for twenty-four
hours. At the end of that time it should again be placed in the
steamer and steamed for half an hour. Once more set it aside for
twenty-four hours, and upon the third day steam it again for half an
hour and cool. Material thus prepared should give a clear, slightly
brownish jelly, which, if properly sterilized, will keep indefinitely. It
should be acid to litmus paper.

If the teacher does not care to go to the trouble of making the
gelatin, she can buy it of dealers in bacteriological supplies. The
gelatin culture medium which is sold by such dealers is slightly
alkaline, and should be rendered a little acid by adding HC1 until
the mixture will just turn blue litmus paper red. Molds require an
acid medium, though bacteria need one with an alkaline reaction.

6. Mold Spores in Dust. Melt the gelatin in three or four of the
test tubes prepared as above described, and pour it from each into a
sterilized petri dish. Replace the cover upon the dish and allow the
gelatin to harden. Sweep a little dust from the floor and scatter over
the surface of the gelatin in one petri dish. Scrape some dust from
a crack in the floor and sow on another dish. In the same way sow
dust from other places upon the gelatin. Set aside until the molds
begin to grow, and examine the mold colonies.

7. Molds in a Dust Cloth. Prepare two petri dishes of hardened
gelatin, as in Experiment 6, and, after removing the cover, shake

APPENDIX 271

the dust from a dry dust cloth over one of them. After leaving it
thus exposed to the air for two minutes replace the cover. Over a
second dish shake a damp dust cloth. Set both aside and compare
the number of molds that grow in the two plates. Has the dampness
prevented the distribution of mold spores ?

8. Molds in the Air. Prepare four dishes of hardened gelatin.
Expose two of them to the air of an ordinary room that has been
quiet for some hours, for example a schoolroom before the school
has assembled, by leaving the cover off for two minutes and then
replacing it. Expose two other plates for the same length of time
at the close of the school session after the air has become stirred up.
Another pair of plates may be advantageously exposed in the hall
while the scholars are passing. All plates should be exposed for the
same length of time, carefully labeled, and set aside at the ordinary
room temperature for growth. Count the number of molds that
grow in each plate. A few bacteria colonies will be likely to appear
on some of the plates, but these can easily be distinguished from
molds since they do not have the fuzzy appearance due to the mold
mycelium.

9. Molds in the Air. Repeat the above experiment, using moist
bread instead of the petri dishes of gelatin. After exposure, place
under bell glasses and set aside for growth. The results will be
essentially the same as in the last experiment, though less striking.

10. Growth from Spores. Prepare a petri dish of hardened gela-
tin. With a platinum wire or the tip of a knife blade remove a bit
of the spore mass from some mold obtained in a previous experiment,
and transfer it to the surface of the gelatin. Touch the gelatin in
this way in several places and then cover and set aside for growth.
After two or three days note that a mold colony begins to grow from
each spot where the wire touched, indicating that spores have been
transferred to the jelly. Allow the molds to grow for two or three
days, examining them each day with a microscope or, if a microscope
is not at hand, with a hand lens. Note the extension of the mycelium
through the gelatin, and later the development of minute tufts of
spores on the surface. -. .

11. Germination of Spores. Sow mold spores upon the surface
of a petri dish of hardened gelatin as follows. Select one of the

272 BACTERIA, YEASTS, AND MOLDS

dishes previously inoculated and showing mold colonies in vigorous
growth, some of which bear spores. Remove the cover, invert it
over a second dish of hardened gelatin and gently tap the dish con-
taining the molds. This will cause the spores to fall in a shower into
the second dish. Replace the cover and set the newly inoculated
dish aside for growth. After one day examine the surface with a
microscope to see if the spores have begun to germinate. Usually
they will not show much growth before two days. When they begin
to germinate study carefully with a microscope. This may be best
done by dropping a thin cover glass upon the surface of the gelatin
and then studying the spores with a high-power objective (£-inch).
The germinating spores will show threads protruding from them, as
shown in Fig. 4, p. 15. Examine daily for several days. After about
three days it will be possible to see the fruiting branches beginning
to grow from the ordinary threads, as shown in Fig. 5, p. 15. This
study is very instructive, but cannot of course be made without a
good microscope.

12. Fruiting of Molds. In the same way study a variety of molds.
To obtain a variety is usually easy. One needs only to expose to the
ordinary air two or three of the petri dishes and several species of
mold spores are almost sure to drop in. They cannot be distinguished
until they begin to develop their fruit, when they can readily be sep-
arated by a low-power microscope or a hand lens. If the spores
are sown on gelatin, as above described, the method of development
of the fruit may be studied. Methods of producing fruit in the com-
mon molds are shown in Figs. 10-17. The study of two or three species
is sufficient, although the larger the number of studies the better.

13. The Effect of Drying. Place under a bell glass two slices of
bread, one of which is damp, either naturally or by being slightly
moistened with water, and the other dried. Leave for two or three
days and notice the effect of drying in preventing the growth of
molds. If one slice remains dry, no molds will grow upon it though
the other soon becomes covered.

14. The Effect of Boiling Temperature. In each of two test tubes
of gelatin place a small quantity of mold spores. Melt the gelatin in
the tubes at as low a heat as will melt it. Pour the contents of one
tube into a petri dish and cover at once. Place the other tube in

APPENDIX 273

a beaker of boiling water and allow the water to boil briskly for half
an hour, after which the gelatin is to be poured into a petri dish and
treated like that in the first tube. Set both dishes aside for mold
growth, and examine at intervals for several days, noticing whether
molds develop in both dishes or only in the first. If they grow in
both, note the relative abundance in the two dishes.

15. Effect of Low Temperatures. Prepare two plates of hardened
gelatin and sow mold spores upon the surface of each. Leave one in
the ordinary room temperature and place the other in an ice chest or
some other place where the temperature is low. Compare day by day,
and determine the effect of low temperatures in checking or stopping
mold growth. Do any molds grow upon the dish placed in the ice
chest?

1 6. Effect of Air Currents. Moisten a slice of bread and sow mold
spores "upon it, or allow it to mold spontaneously under a bell glass.
After it shows a luxuriant growth of mold remove the bell glass and
leave it exposed to the currents of the air. Notice how the growth
of the mold ceases and the delicate mycelium flattens down close to
the bread.

17. Molds in Cheese. Obtain a bit of Roquefort cheese. Cut it
open and remove a bit of the green mass in the middle by means of
a knife point or a platinum wire. Sow this substance upon the sur-
face of a dish of hardened gelatin and set aside for growth. After
two or three days the molds will begin to develop and may be studied
with a microscope. When they begin to produce fruit they should,
if possible, be studied sufficiently to determine the species. This
species of mold is figured in Chapter II and should be easily identified.

18. Decay of Fruit (a). Place in a jar a number of apples that have
been bruised or cut, packing them in rather tightly. Scatter in the
jar some spores of the common blue mold which will usually be found
on some of the petri dishes already prepared. Close the jar and set
aside. Prepare a second jar with some whole clean apples and treat
in the same way. Compare the two jars for a week or two to see if
decay makes its appearance in either or in both of the jars. Does
bruising hasten the decay of the fruit?

19. Decay of Fruit (£). Make a cut through the skin of an apple
with a knife blade that has been previously dipped into the midst of

274 BACTERIA, YEASTS, AND MOLDS

a mass of mold spores, preferably the common blue mold. Put the
apple aside in a jar and examine carefully until it decays. Note that
the decay begins rather quickly and starts at the point of the cut
where the spores were inoculated.

20. Molds in Decaying Fruit. Obtain some thoroughly decayed
fruit, several different kinds if possible. Remove a bit of the
decayed material with a knife blade and plant it in gelatin in a
petri dish. Replace the cover and set aside until the molds begin to
germinate. Allow them to grow for a number of days and then study
with a microscope, determining if possible the method of forming
spores and comparing them with the figures of molds given in the
previous pages. Is the species found similar to any described in
this work?

EXPERIMENTS ILLUSTRATING YEASTS

21. Fermentation of Molasses. Into a common test tube or any
glass vial place a solution made by mixing one spoonful of molasses
with ten spoonfuls of water. Rub up a little compressed yeast in
water and put a few drops into the tube of molasses water. Set aside
in a warm place and let it stand for about twenty-four hours. At the
end of this time a vigorous fermentation will be seen. The liquid will
have become somewhat cloudy, numerous bubbles can be seen rising
through it, a froth forms on top, and a mass of sediment soon
collects at the bottom. The bubbles are the carbon dioxide which
is escaping into the air, the sediment at the bottom is the growing
mass of yeast, and the alcohol, which looks just like water, is
dissolved in the liquid and is of course invisible.

22. Proof of the Nature of the Gas. Prepare two tubes, as shown
in Fig. 31. In tube a place molasses and water inoculated with sev-
eral drops of yeast, as in the last experiment. Put the cork in place
and insert the other end of the tube into a second tube underneath
the surface of some clear limewater, as shown in Fig. 31. Set aside
in a warm place until vigorous fermentation occurs. Note the bubbles
of gas that arise from the fermenting tube and bubble up through
the limewater. The limewater soon becomes turbid, showing that the
gas contains carbon dioxide (CO2).

APPENDIX 2/5

23. C02 produced chemically. In test tube a of a pair of tubes
similar to those used in the last experiment place a little cream of
tartar in water; in another test tube dissolve some saleratus in water.
Pour the saleratus solution into test tube a, close at once with a cork,
and allow the gas produced to pass into limewater as before.

MICROSCOPIC STUDY OF YEASTS

24. Resting Stage. Rub a bit of yeast cake in a little water so
as to make a slightly cloudy solution. Place a drop of the solution
upon a microscope slide, cover with a cover glass, and examine first
with a f-inch objective. Note that the water seems to be filled with
very minute dots. Study with a higher power (|-inch objective).
Examine the yeast cells, noting the shape, comparative size, and the
vacuoles inside of the cells, as shown in Fig. 32. Are the cells
attached or are they mostly separate? Hunt for small buds upon
the sides of the larger cells. Proceed in the same way with a little
dried yeast cake and compare the yeast cells in size and appearance
with those of compressed yeast.

25. Growing Yeast. With a pipette remove a drop of the sedi-
ment from growing yeast prepared as in Experiment 21. Place
the drop on a slide, cover with a cover glass, and study as in the
previous case. Remove some of the yeast found floating on the sur-
face, and study in the same way. Note that the yeast cells are in
groups. Make a sketch of several groups, showing buds of various
sizes. Can you see the vacuoles in the cells, as in the first specimen ?
Note any other differences you can see between this growing yeast
and the compressed yeast cake.

26. Staining Yeast. Place a drop of yeast upon a slide and cover
with a cover glass. Place a drop of stain upon the slide beside the
specimen. (Almost any stain will do. Eosin dissolved in water is
satisfactory.) With a bit of blotting paper applied to the edge of
the cover glass opposite to the stain, draw the water out so as to
suck the stain under the glass. Allow the stain to remain about two
minutes, and then place a drop of clear water beside the cover glass
and with a blotter draw this under until it washes out the stain.
Then examine the specimen and determine whether the yeast cells

2/6 BACTERIA, YEASTS, AND MOLDS

are stained red. It should be found that most of them are unstained,
although a few are stained deep red.

27. Staining Boiled Yeast. Put some yeast in a test tube with
some water. Heat to boiling for a few seconds and then remove
Some of the yeast with a pipette and stain it as above described.
After washing, study to see if the yeast which has been killed by
boiling stains better than the living yeast.

28. Effect of Boiling. Prepare two test tubes of molasses and
water and inoculate both with a drop of yeast. Plug with cotton.
Place one test tube in water and boil for ten minutes, and then leave
both test tubes side by side in a warm place for two days, and deter-
mine whether the boiling has been sufficient to kill the yeast.

29. Wild Yeast. Prepare several test tubes of molasses and
water as described and, without plugging with cotton, leave exposed
in various places for two or three days. Determine by the appear-
ance of bubbles whether fermentation occurs. If any change takes
place in the liquids, examine with a microscope to determine whether
yeasts have found entrance from the air or whether some other
microorganisms are growing in the solution. Commonly bacteria
will be found more abundantly than yeasts.

30. Fermentation of Cider. Grind up a few apples and strain the
juice from the same by squeezing through cheese cloth. Collect the
juice in test tubes and allow it to stand for a few days. A fermenta-
tion soon appears and the juice turns into cider. Examine the sediment
with a microscope and detect the presence of yeast. Close up the tube
with a cotton plug and leave it for a number of weeks, determining
whether it subsequently becomes acid by the development of acetic acid.

31. Fermentation of Grape Juice. Proceed as above, using grapes
instead of apples. The juice will become wine if fermentation occurs
properly.

32. Effect of Temperature. Fill three test tubes with molasses and
water as above described and inoculate each with three drops of
yeast in water. Place one tube in a refrigerator, a second in a
moderately warm temperature, about 70°, and a third in a warmer
place, near a stove or radiator (temperature about 90°). Compare
the three at the end of three, six, and twenty-four hours, and note
the effect of temperature upon growth.

APPENDIX 277

33. Effect of Light. Prepare two tubes in the same way and set
one in a bright light and the other in a dark place. This may
be best done by wrapping the tube in velvet or heavy black paper
to keep out the light. Keep both tubes at the same temperature
and determine whether light has any effect upon the rapidity of
growth.

34. Effect of Age on Yeast. Obtain an old sample of dried yeast
cake. Prepare two tubes of molasses and water and inoculate one
with a small quantity of the old yeast cake and two others with a
similar quantity of a fresh cake. Set aside in a warm place and
determine in which the fermentation starts sooner, and in which it is
the more vigorous. Examine with a microscope after fermentation
begins, to see if either contains other organisms besides yeast.

35. Comparative Fermenting Power. Make a dilute mixture of
flour and water. Fill three fermentation tubes with the mixture, as
shown in Fig. 38. Inoculate one with compressed yeast, a second
with dried yeast cake, and a third with brewer's yeast, if it can be
obtained. Set all three aside in a warm place for one day, and
determine the relative fermenting power of the different yeasts by
comparing the quantities of gas that collect in the closed tubes..

36. Action of Yeast on Bread. Mix up a little flour and water to
about the consistency of dough for bread making, and divide into
three lots. Into a and b place a little compressed yeast. This may
best" be done by dissolving the yeast in water and stirring it into the
dough during the mixing, a and b are then to be placed in a warm
place for five or six hours, while c, without the yeast, is to be baked
at once. After a and b have risen under the influence of the yeast,
bake b at once in the oven, while c is to be thoroughly kneaded and
then baked. Compare the results of #, b, and c, noticing the differ-
ence in the textures of the bread.

37. Overraising. Mix another lot of dough with yeast in the
same way and allow it to rise in a warm place for twelve hours or
more. Test with litmus paper to see if it is acid. Bake and taste
to see if it has become sour.

38. Bread raised by Wild Yeast. Put a small amount of salt in a
little milk and then allow it to stand in a warm place until a froth
appears. Mix it with flour to make a dough and set aside to rise.

2?8 BACTERIA, YEASTS, AND MOLDS

Does the dough rise as rapidly and as satisfactorily as when yeast is
used? Does the baked dough have the same taste?

39. Kumiss. Into a quart of milk put two tablespoonfuls of com-
mon sugar and add about one sixteenth of a compressed yeast cake.
Put in a warm place and leave for twenty-four hours. Cool and
taste. It will be kumiss, or fermented milk. Is it sour?

EXPERIMENTS ILLUSTRATING BACTERIA

40. Putrefaction. Place in a series of test tubes, with a little
cold water, the following : (a) a bit of raw meat ; (b) some white of
egg ; (c) some flour ; (d) some crushed beans ; (e) sugar ; (f) starch ;
(g) a bit of melted butter. Set all of these tubes in a warm place
for two or three days and determine which will putrefy and which
will not.

41. Effect of Moisture. Place a little of the following foods in test
tubes: (a) dry beans; (b) Indian meal; (c) a piece of dry bread;
(d) graham meal ; (e) flour; (f) common crackers. In another series
of test tubes place the same materials moistened with water. Set
all aside in a warm place and notice the effect of water in bringing
about putrefaction.

42. Effect of Temperature. Place bits of meat with a little water
in three test tubes. Put the first tube in an ice chest, the second in
ordinary room temperature, and the third close to a stove or radiator,
where the temperature is high. Notice the rapidity of putrefaction
in each case.

43. Effect of Boiling. Chop finely some raw beef and place it in
water, warming slightly but not heating it to more than 130°. Divide
into two parts, place each in a test tube, setting one aside without
further treatment, but bringing the other to a brisk boil for a moment
and then setting beside the first. At the end of twenty-four hours
examine to determine if putrefaction has occurred.

44. Effect of Freezing. The following experiment can be per-
formed only in cold weather. Place a little hay in water and heat to
a lukewarm temperature, leaving the same to steep for half an hour.
Filter through filter paper into two test tubes. Plug with cotton
and set one of the test tubes in a warm place. Put the other out of

APPENDIX 279

doors where the liquid will freeze. Allow it to remain frozen for a
few hours, and then bring it back into a warm room, leaving it there
for a few days to see if it putrefies, in order to determine whether
freezing destroys the life of the bacteria in the hay infusion. For
this experiment it will be better to use a metal dish instead of a test
tube, since freezing might break the test tube.

45. Effect of Boiling upon Spores. Put some hay into a dish and
steep with warm water at about 120°. After an hour's steeping
filter through filter paper into four test tubes, filling each half full,
plugging the same with cotton, and labeling them a, b, c, d. Bring
a to a boil for five minutes, b for ten minutes, c for twenty, and leave
d without boiling. Set aside for a few days to determine whether
the material in all cases putrefies. Does the hay infusion contain
bacteria spores that are not killed by boiling?

46. Action of Disinfectants. Mix the white of an egg with ten
times its bulk of water and place the material in a series of test tubes,
filling each about one third full. To the tubes add the following
disinfectants : (a) no addition ; (b) one quarter of a gram of salt ;
(c) one gram of salt ; (d) one gram of sugar ; (e) five grams of
sugar ; (f) two drops of a corrosive-sublimate solution (one part
sublimate to one thousand parts water) ; (g) six drops of corrosive-
sublimate solution ; (h). one drop of formalin ; (i) two drops of
formalin ; (j) three drops of formalin ; (k) one eighth of a gram of
borax ; (1) one fourth of a gram of borax ; (m) four drops of carbolic-
acid solution (one part acid to twenty parts water) ; (n) ten drops of
carbolic-acid solution. Set all test tubes in a warm place side by side
and examine daily, noticing the effect of the various ingredients in
preventing decay, and noting how much more powerful some disin-
fectants (corrosive sublimate) are than others (carbolic acid). Num-
bers h, i, j, m, and n should be closed with a cork to prevent the
disinfectant from evaporating.

47. Vinegar. Soak a bit.of raw meat in vinegar, warming it some-
what and leaving it for several hours. Remove the bit of meat,
placing it in a test tube plugged with cotton, and leave for a few
days, to determine whether it putrefies or whether the vinegar acts
as a disinfectant. The vinegar will prevent putrefaction if enough
is used.

280 BACTERIA, YEASTS, AND MOLDS

MICROSCOPIC STUDY OF BACTERIA

It is rarely feasible to carry on any extended microscopic study of
bacteria with ordinary classes. The organisms are so minute that
they require very high powers and expensive microscopes, and are so
simple that the scholar can learn very little by their study. A brief
examination of a few bacteria may, however, be useful. If desired it
can be done as follows.

48. Study of Living Bacteria. Obtain a bit of decaying meat,
decaying egg, or some other proteid material, and place a minute
drop of it upon a slide in a drop of water; cover with a cover glass
and study with the highest objective obtainable. A TVinch objective
is required to study them, but a ^-inch will usually be sufficient
to show the bacteria as minute specks, many of which will commonly
be seen swimming rapidly under the field of the microscope. If
decaying material from different sources is studied, there will usually
be found several kinds of bacteria, as indicated by the different sizes
and shapes.

49. Staining Bacteria. To make a more careful study of these
organisms, they must be stained in order that they may be more
clearly visible. Staining fluids may be bought or a convenient one
be prepared as follows:

ZiehVs Carbol-Fuchsin

Saturated alcoholic solution of fuchsin 5 cc.

Five per cent, solution of carbolic acid 45 cc.

To stain bacteria place a very small drop of some decaying mixture
upon a cover glass in a drop of clear water. Spread it over the cover
glass in as thin a layer as possible, and then allow it to dry in the air.
After drying take the cover glass in a pair of forceps and pass it rap-
idly through a gas flame three times. This is \tofix the bacteria upon
the slide. Place a few drops of the staining fluid upon the bacteria
on the cover glass and allow the stain to remain for five minutes.
Then wash thoroughly in a stream of running water and place the
cover glass upon a slide in a drop of water, bacteria side down.
Study with the highest-power objective. The bacteria will be found

APPENDIX 28l

to be stained brilliant red. It is instructive to examine a number of
decaying fluids in this way.

50. Bacteria from the Teeth. Scrape a little tartar from the teeth,
spread upon a cover glass, and stain in a similar manner.

Further microscopic study of bacteria requires higher-power objec-
tives and more apparatus than can be found in ordinary schools.

CULTURE EXPERIMENTS WITH BACTERIA

Nearly all experiments in bacteriology involve the use of culture
media prepared for the purpose. Such culture media may be made
by any one who has at his command a laboratory with proper appa-
ratus for sterilizing. If a teacher does not have facilities for making
culture media, they may be bought from the dealers in bacteriological
apparatus. The following is easy to prepare.

Gelatin Culture Medium
Mix together in a common stew pan the following:

i liter of water.

5 grams of Liebig's extract of beef.
10 grams of peptone.
100 grams of gelatin.

Carefully weigh the mixture in the dish in which it is to be boiled.
Heat the mixture at about 140° until the gelatin is thoroughly melted,
and then boil briskly for a few moments. Test with litmus paper.
It will be found to be acid. Add to it, drop by drop, a solution of
caustic soda (NaOH) until it is slightly alkaline to litmus paper.
Boil briskly for half an hour. Weigh once more, add enough water
to bring it up to the original weight, and test again with litmus
paper. If the reaction is still slightly alkaline, the material is ready
for filtering. Filter through absorbent cotton, as already described,
and collect the clear liquid in a sterilized liter flask. Fill with the
material as many sterilized test tubes as it is desired to use, putting
about 10 cc. in each, which should fill them about two inches deep.
Replace the plugs and then steam all of the gelatin in a steamer for

282 BACTERIA, YEASTS, AND MOLDS

about half an hour. Set aside for twenty-four hours, and steam
again; and after another twenty-four hours steam a third time. If
properly made, the material will still be clear, and, being now sterile,
will remain clear indefinitely. It differs from the medium prepared
for molds chiefly in being alkaline instead of acid.

Agar Culture Medium

For some purposes a modification of the above is desirable. It is
made in the same way, except that, instead of using 100 grams of
gelatin, there are placed in the mixture i .8 grams of agar-agar (a prep-
aration from a sea moss which may be purchased from dealers). This
is known as agar culture medium. In other respects it is made pre-
cisely as above, except that more heat is required to melt agar than
to melt gelatin.

51. Bacteria in Tap Water. Melt six of the gelatin tubes by mod-
erate heat. By means of a sterilized pipette, preferably one that holds
exactly one cubic centimeter, place in each of the six tubes a cubic
centimeter of water drawn directly from the tap. Mix the water thor-
oughly with the gelatin and pour the contents of each tube into a
petri dish, covering it at once and allowing it to cool. Set aside
at a temperature not above 70°. In about two days the dishes will
be found to be covered with little dots known as colonies. These
will be somewhat variable in appearance, but since each colony repre-
sents what was a single bacterium in the original drop of water, the
counting of these colonies in the plate will give the number of bac-
teria in the tap water.

52. Bacteria in Well Water. Proceed in the same way with the
water drawn from a well if it is obtainable.

53. Bacteria in Miscellaneous Waters. Obtain samples cf water
in sterilized bottles from several sources — horse troughs, gutters, run-
ning water of the streets, snow, etc. — and treat them in the same way
as described above. Comparison of the plates will give an idea of
the relative number of bacteria in water from different sources.

54. Bacteria in Ice. Obtain a piece of ice and melt it in a steril-
ized beaker. Place a cubic centimeter of the water in gelatin and
proceed as above described.

APPENDIX 283

55. Bacteria from Various Sources, (a) Into three tubes of melted
gelatin culture medium place a small drop of saliva. Mix thoroughly
with the gelatin and pour into petri dishes. (<£) Place in other tubes
of melted gelatin, and also of melted agar, very small bits of decaying
meat or decaying egg. Mix thoroughly in the gelatin by rubbing
with a sterilized glass rod and pour out into a petri dish. (V) Into a
third set of tubes place small pieces of dirt swept up from the floor
or picked out of cracks in the floor. Mix with the gelatin and pour
into petri dishes. (W) Into a fourth set of tubes place a little dirt from
the street and proceed as before. Allow all plates to grow till the
colonies are visible. Note any differences between them.

56. Bacteria on the Fingers. Pour gelatin into some petri dishes.
After it has hardened touch its surface with the fingers, replace the
cover, and set aside for bacterial growth. Wash the hands thoroughly
in clean water, wiping with a clean towel, and then proceed in the
same way with a second petri dish, touching the surface with the
fingers and setting aside for growth.

57. Bacteria in the Air. Melt the contents of four tubes of gelatin
and four of agar. Pour each into a petri dish, replace the cover, and
allow the contents to harden without inoculation. Expose one gelatin
and one agar plate to the air of a schoolroom before the school ses-
sion, by removing the covers and leaving the plates uncovered for three
minutes. Expose two similar plates at the close of the school session
in the same way. Expose two in the hall at the time when many schol-
ars are passing through it. Expose two in a room after sweeping or
dusting. In all cases the plates are to be exposed the same length of
time, carefully labeled, and set aside for the bacteria to grow. The
relative number of bacteria is readily determined by an examination of
the plates. Molds will grow upon the surface of the plates, but a little
study will make it possible to distinguish them from bacteria. The
bacteria will commonly be more numerous than the molds. Similar
plates exposed in a variety of locations will be very instructive as
indicating the abundance of bacteria in the air.

58. Bacteria in Milk. In an ordinary flask place one hundred
cubic centimeters of water and sterilize by steaming for two hours.
After cooling place one cubic centimeter of ordinary milk in the flask
and mix thoroughly by shaking. Melt three tubes of gelatin and three

284 BACTERIA, YEASTS, AND MOLDS

of agar. Into one tube of each place one cubic centimeter of the
diluted milk ; into a second tube of each place one half of a cubic
centimeter, and into a third a single drop. Mix thoroughly, pour
into petri dishes as usual, harden, and set aside for growth. If
possible, count the number of bacteria on the plates and estimate the
number per cubic centimeter (a single drop is about one fifteenth of
a cubic centimeter). The number will sometimes be too large to
make this possible.

59. Effect of Temperature upon Milk. Fill six test tubes full of
milk. Place two of them in an ice chest, two at ordinary room tem-
perature, and two close to a stove or radiator where the temperature
is very warm. Examine at intervals of three or four hours and note
the time at which the tubes become sour and curdle. Determine, if
possible, whether there is any difference in the appearance or smell
of the curdled milk in the three samples.

60. Effect of boiling Milk. Fill two test tubes one third full of
milk. Place one of them in water and allow the water to boil briskly
for five minutes. The second one is not to be boiled. At the close
of the boiling plug both test tubes with cotton and set side by side
in a warm place. Examine each day and notice the difference in
the changes that take place in the milk. One sample will probably
sour quickly ; the other will keep very much longer and will not sour,
even after many days, although it will spoil. Test both samples with
litmus paper, after they have spoiled, to see if both are acid.

61. Growth of Bacteria in Milk. Obtain some absolutely fresh
milk. This experiment may be difficult in a city where fresh milk is
not easy to obtain. Place one cubic centimeter of the milk in one
hundred cubic centimeters of boiled and cooled water, mix thoroughly,
and then with a clean sterilized pipette place one cubic centimeter of
the diluted milk in each of six test tubes of melted agar culture
medium. Mix thoroughly, pour into petri dishes, and set aside for
the bacteria to grow. Place the milk at a warm temperature near
a radiator for six or eight hours, and repeat the experiment, making
six more petri dishes in the same way. Set all aside, and after the
bacteria have grown count the number of colonies in each, thus
determining the rate of multiplication of bacteria between the first
and last experiments.

APPENDIX 285

62. Washing of Milk Vessels. Place some ordinary milk in two
test tubes and set aside until the milk sours. Pour out the milk from
all the test tubes and wash one with cold water and the other with hot
water and soap. Hold the tubes up to the light and notice the dif-
ference in the cleanliness of the two test tubes. Now fill each tube
with fresh milk and set aside in a moderately cool place and notice in
which of the tubes the milk sours first.

63. Vinegar Bacteria. Obtain a little good vinegar containing
some of the mother of vinegar. Put a bit of the mother upon a glass
slide, cover with a cover glass to spread in a thin layer, and study
with a high-power microscope.

64. Effect of Heat in sterilizing Fruit. Fill four test tubes about
half full of water. In each place a few small berries, like blackber-
ries or blueberries, or pieces of cherry, apple, or pear. Plug each
tightly with cotton. Put one aside and label a. Place the others
in cold water and gradually bring the water to a boil. Before the
water boils take out one test tube and label it b ; take out a second
the moment the water boils and label c ; remove a third after the
water has boiled half an hour and label d. Set all tubes aside in a
warm place and watch for several days, determining which are suc-
cessfully sterilized, which will be indicated by their not spoiling.

INDEX

Abscesses, 236.

Acetic acid, 132; as a preservative,
165; in bread, 92.

Acidity, effect of, upon bacterial
growth, 114; effect of, on mold
growth, 38.

^Ecidiomycetes, 12.

Aerated, bread, 88 ; waters, 225.

Aerobic bacteria, 113.

Air, as a distributer of disease, 230 ;
bacteria in, 1 14 ; its effect on bac-
terial growth, 112, 114; on mold
growth, 34.

Albumen, 125.

Alcohol, 56, 198.

Anaerobic bacteria, 113.

Anopheles, 216.

Antenaria, 21.

Antifermentine, 158.

Antiseptic, 255 ; use of, in canning,
178.

Antitoxin, 250.

Apollinaris water, 225.

Apple, fermentation of, 64.

Ascomycetes, 12.

Aspergillus, 19.

Bacillus, 105.

Bacon, curing of, 144.

Bacteria, classification of, 103; dis-
tribution of, 114 ; growth of, 107 ;
in bread, 93 ; in yeast cultures, 91 ;
multiplication of, 105 ; relation of,

287

to air, 112; shape of, 102 ; size of,
100, 101.

Bacterial growth, results of, 121,
126.

Bacterium, 105.

Beans, canning of, 173, 174, 178,
180; soured, 166.

Bedding, treatment of, 243.

Beef, dried, 144.

Beer, fermentation of, 95 ; home-
made, 96.

Berries, drying of, 146.

Biscuits, preservation of, 142.

Bitter rot, 41.

Black rot, 41.

Blood poisoning, 203, 236.

Blue milk, 185.

Blue mold, 13; fruit of, 17.

Boiling as a preservative, 156, 161.

Boils, 236.

Books, a source of contagion, 244 ;
molding of, 33.

Boracic acid, 158.

Borax, use as a preservative, 158,
159, 178.

Bread, molding of, 27 ; raising of,
72, 86.

Bread raising, purpose of, 88 ; rela-
tion to temperature, 89.

Breathing, a source of infection,

239-

Brewer's yeast, 77, 82, 83.
Brie cheese, 52.

288

BACTERIA, YEASTS, AND MOLDS

Brown rot, 41.
Bubonic plague, 221.
Budding, 10, 60; fungi, 61.
Butter, flavor of , 6, 131, 198 ; ruined

by bacteria, 134; salting of, 164.
By-products, 127.

Camembert cheese, 52.
Canned foods, value of, 181 ; mold-
ing of, 26.
Canning, 5, 169 ; failures, cause of,

i?5-

Canning in factories, 177.

Carbolic acid, as a disinfectant, 258 ;
as a preservative, 1 58.

Carbon dioxide, 56,

Carpets, molding of, 33.

Casein, 125.

Cats, as distributers of disease, 221.

Cattle, as distributers of tuberculo-
sis, 222.

Celery, 234.

Cellar, use of, for preserving food,

154.

Cephalothecium, 21.

Certified milk, 186, 229.

Charque, 144.

Cheese, flavor of, 6, 198 ; molding
of, 27, 37; poisoning, 199; pres-
ervation of, in brine, 164.

Chills and fever, 214.

Chloride of lime, 259.

Cholera, 204, 220, 222, 223, 227, 238.

Cider, 64, 71 ; as a source of vine-
gar, 133.

Cloth, molding of, 33.

Clothing, disinfection of, 243, 263.

Coccus, 104.

Cold, as a disinfectant, 257; as a
preservative, 148.

Cold storage, 148 ; effect of, on
molds, 37 ; food from, 1 50.

Cool temperatures, devices for, 155.

Commercial yeast, impurities in, 91.

Compressed yeast, 78 ; keeping of,
80.

Consumption, 212, 220, 232, 241,
252.

Contagion, conditions of, 213.

Contagious diseases, i, 6; distribu-
tion of, 7, 208, 212.

Corn, canning of, 173, 174, 178, 180.

Corned beef, 164.

Corrosive sublimate, as a disinfect-
ant, 258 ; as a preservative, 158.

Coughing, a means of distributing
bacteria, 232.

Crackers, preservation of, 142.

Curtains, in sick rooms, 121.

Darkness, effect on mold growth,

36.

Death of bacteria by heating, no.

Decay, i, 4, 128, 129; advantages
of, 130.

Decay of fruit, 41, 49; prevention
of, 44.

Decomposition of food, 126; prod-
ucts, 127.

Deodorants, 259.

Diastase, 86.

Diphtheria, 204, 219, 227, 238, 239,
241, 243, 244, 248, 250, 252.

Dirt, bacteria in, 118.

Disease bacteria, 203 ; vigor of, 207.

Disease germs, 6, 122.

Diseases, caused by molds, 53 ; cause
of, 210, 212 ; course of, 205; how
produced, 203 ; prevention of, 7.

Dishcloths, 138.

INDEX

289

Disinfectants, application of, 261.

Disinfection, 255.

Distilled liquors, 70.

Distillery yeast, 78, 79.

Dried yeast, 81.

Drinking water a source of disease,

222.

Drying as a preservative, 33, 141.
Dust, in the schoolroom, 233 ; in the

sick room, 231.

Eating utensils, treatment' of, 243.
Eggs, bacteria in, 119; preservation

of, 164, 197.
Elimination of germs from body,

214.

Epidemics, 210.
Erysipelas, 236. •
Excreta, 242, 262; as a source of

infection, 220.

Fats as bacterial foods, 1 24.

Favus, 54, 236.

Fermentation, 56 ; checked by boil-
ing, 68; of jellies, 65.

Fermentative industries, 95.

Fermented beverages, 57, 70.

Fermenting power of yeasts, 76.

Figs, 163.

Filtering water, 224.

Fish, poisoning from eating, 199 ;
preserving of, 145, 163.

Fission, 10, 106.

Flagella, 103, 105.

Flavors, from bacterial growth, 127,
130; of butter, 6; of cheese, 6;
produced by yeasts, 88.

Fleas as distributers of disease, 221.

Flies as distributers of disease, 221.

Floors, bacteria on, 118.

Flour, molding of, 27,33 > preserved

by drying, 142.
Food as a distributer of disease,

234-

Foods, bacteria in, 118; of bacte-
ria, 121, 124; preservation of, 139;

ruined by bacteria, 134; use of,

while fresh, 140.
Formalin, 158; as a disinfectant,

260, 264, 266.
Freezine, 158.
Freezing of food, 149.
Fresh air, need of, 251 ; in sick

room, 265.
Fruits, canning of, 172, 180; decay

of, 40, 42, 119; drying of, 146;

moisture in, 32 ; packing of, 46 ;

wrapping in paper, 47.
Fungi, 9, 10.

Gamy flavors, 118, 130, 198.
Garbage, 135; cans, 137.
Germicide, 255.
Gluten, 125.

Gorgonzola cheese, 31, 52.
Grippe, 220, 239.

Hair, a lodging place for bacteria,
245 ; disinfection of, 263.

Hams, curing of, 144, 164.

Hands, disinfection of, 262.

Hangings in sick rooms, 121.

Heat, as a disinfectant, 256; as a
preservative, 156; killing molds
by, 37 ; required for canning, 172,
174.

Hip disease, 252.

Home brewing of yeast, 83.

Hops,.as a preservative, 168 ; use of,
in yeast, 84.

290

BACTERIA, YEASTS, AND MOLDS

Ice a source of disease germs, 226.

Ice chest, 151 ; cleaning of, 153; ef-
fect of, on molds, 36 ; use of, in
preserving milk, 190.

Ice cream, 202, 205.

Immunity, 248.

Impurities in yeast, 91.

Insects as distributers of disease,
221.

Intestines, bacteria in, 119.

Invasion, means of, 235.

Isolation, necessity for, 241.

Jellies, fermentation of, 65; preser-
vation of, 163; protection of, 25.

Kefir, 99.
Kumiss, 98.

Lactic acid, a preservative, 166 ; in

bread, 92.

Lactic bacteria, 184.
Lakes, bacteria in, 116.
Leather, molding of, 33.
Leaven, 73.
Legumen, 125.
Lettuce, 234.
Light, as a disinfectant, 257 ; effect

of, on bacteria, 112.
Limburger cheese, 131.
Lockjaw, 236, 237, 257.

Malaria, 213, 252; cause of, 214;

distribution of, 216.
Maple sugar, fermentation of, 65.
Marmalades, 163.
Mattresses, 264.
Mazoon, 99.
Measles, 212, 213, 219, 230, 232,

236, 239, 241, 248.

Meats, canning of, 179, 180; mold-
ing of> 33-

Micrococcus, 104.

Microorganisms, and disease, 6 ; and
preservation of food, 2 ; classes
of, 8.

Microsporon, 53.

Mildew, 28, 32, 34.

Milk as a distributer of disease,
222, 227 ; methods of guarding
against, 228.

Milk bacteria, 182 ; effect of, on milk,
183.

Milk, condensed, 163 ; drying of,
145 ; fermented, 98 ; from gro-
ceries, 187; from milkmen, 187;
poisoning from, 199; preservation
of, 185 ; preserved at low temper-
atures, 190; sources of, 185;
vessels, 188.

Mince-meat, 167.

Mineral substances, 9.

Moisture, and decay, 45; effecting
mold growth, 26, 32 ; in fruit,
46; required for bacteria, 113.

Mold growth, results of, 28.

Molding, prevention of, by heat,

37-
Molds, color of, 15; fruit of, 17;

general nature of, 12; meaning

of the term, n ; structure of, 16;

wholesomeness of, 30.
Moldy bread, bacteria in, 119.
Monilia, 22, 41.
Mosquito netting, 218.
Mosquitoes and malaria, 216.
Mother of vinegar, 132.
Mouth, bacteria in, 119; a source foi

entrance of germs, 238.
Mucor, 14, 1 8, 21.

INDEX

29I

Multiplication of bacteria, 105 ;
rapidity of, 107 ; relation to tem-
perature, 109.

Mushrooms, 10.

Mussels, drying of, 145.

Mustiness, 29, 32.

Mycelium, 17.

Myosin, 125.

Night air, 218, 251.
Nurses, care of person of, 245 ; disin-
fection of, 262.

Odors from bacterial growth, 127.

Organic substances, 9.

Ovus, 67.

Oxygen, relation of bacteria to, 128.

Paper, molding of, 28.

Parasites, 122, 203.

Pasteur filter, 224.

Pasteurization of milk, 5, 193, 229.

Pasteurizing apparatus, 195.

Pathogenic bacteria, 6, 203.

Patient, disinfection of, 262 ; care of

person of, 245, 262, 265.
Peas, canning of, 173, 174, 178,

1 80.

Pemmican, 143.
Penicillium glaucum, 13, 15.
Phosphorescence of food, 1 52.
Physical vigor a protection against

disease, 250.

Pickles, 165; molding of, 27.
Plums, 163.
Poison secreted by bacteria, 129,

199.
Poisoning from cheese and ice

cream, 199.
Pork, preservation of, 164.

Preservaline, 158.
Preservation of food, 2.
Preservatives, in canning, 179; in

milk, 191 ; poisonous, 157 ; use of

condemned, 161.
Preserved foods, 140.
Preserves, 163.

Protection of food from mold, 24.
Proteids as bacterial food, 121, 125.
Ptomaine poisoning, 201.
Ptomaines, 199.
Putrefaction, 4, 119, 128, 129, 134;

at low temperatures, 152 ; caused

by molds, 30; of milk, 184, 185.

Quick biscuit, 89.

Radishes, 234.

Raising of bread, 87.

Raisins, 146, 163.

Rancidity due to bacteria, 124.

Rats as distributers of disease, 221.

Reaction, effect of, on molds, 38;

effect of, on bacteria, 114.
Red milk, 185.
Reservoirs, bacteria in, 116.
Resistance against disease, 206.
Rhubarb, canning of, 172.
Ringworm, 52, 236, 244.
Rivers, bacteria in, 116.
Rod-shaped bacteria, 105.
Rooms infected with molds, 54.
Roquefort cheese, 6, 28, 31, 52.
Rotting. See Decay.
Rusts, 10.

Saccharomyces, 62, 79.

Salads, 167.

Salicylic acid, 158.

Salt as a preservative, 164.

292

BACTERIA, YEASTS, AND MOLDS

Salt raising of bread, 75.

Salt used in drying meat, 144.

Sanitary, dairies, 186; milk, 229.

Saprophytes, 122, 124, 203.

Sarcina, 104.

Sauerkraut, 166, 198.

Sausages, 167.

Scarlet fever, 212, 213, 219, 221,

227, 230, 236, 241, 244, 248.
Schoolrooms, bacteria in, 115.
Scotch barms, 76.
Scrofula, 252.
Scurvy, 165.

Secretions from bacteria, 129.
Seeds, preservation of, 141.
Seltzer water, 226.
Septicaemia, 203.
Sewage, 116, 222, 246; farms, 234;

gas, 247.

Shellfish, drying of, 145.
Sick room, disinfection of, 264;

treatment of, 245.
Sink, care of, 138.
Siris, 67.
Skin, a means of invasion, 235;

a protection, 236; diseases, 230;

value of clean, 47.
Slacked lime, 260.
Slimy, bread, 93; milk, 184.
Smallpox, 219, 221, 230, 236, 241,

251, 252.
Smuts, 10.

Soil, bacteria in, 117.
Sour bread, 92.

Sour milk, bacteria in, 119, 184.
Souring of foods, 4.
Sparkling wines, 96.
Spherical bacteria, 104.
Spices as preservatives, 167.
Spiral bacteria, 105.

Spoiling of foods, i, 2, 118.

Spontaneous fermentation, 64.

Sporangia, 19.

Spores, 17, 37, 106, 256; germina-
tion of, 22; of yeast, 62; resist-
ance of, to heat, 107, in, 172.

Spring houses, 155.

Spring water, bacteria in, 116.

Sputum a source of infection, 220,
232.

Starch as bacterial food, 121, 124.

Sterilization, in, 229; before can-
ning, 171; of milk, 5, 191, 192;
purpose of, 192.

Stilton cheese, 31, 52.

Stomach, bacteria in, 119.

Streptococcus, 104.

Stysanus, 21.

Sugar, a bacterial food, 121, 124;
as a preservative, 66, 162 ; in
fruits, 146.

Sulphur as a disinfectant, 260, 265.

Summer diarrhea, 200, 227.

Sunlight as a disinfectant, 257.

Sweeping, 120.

Tassajo, 144.

Temperature, effect of, on decay of

fruit, 48 ; effect of, on milk, 189 ;

effect of, on molds, 36 ; relation of,

to bread raising, 89 ; relation of,

to growth, 109.
Tetanus, 237.
Toadstools, 10.
Tomatoes, canning of, 172, 174,

1 80.

Torula, 62.
Toxic poisoning not a disease,

205.
Toxins produced in the body, 204.

INDEX

293

Transportation of disease germs,

220.

Traps, 246.
Trichina, 145.
Trichophyton, 53.
Tuberculosis, 212, 222, 227, 232,

235, 238, 239, 243, 251, 252.
Typhoid fever, 102, 212, 220, 221,

222, 227, 238, 243, 252.

Unfermented grape juice, 70.
Unleavened bread, 73.
Utility of molds, 51.

Vaccination, 248.

Vacuoles, 60.

Vegetables, drying of, 146 ; preser-
vation of, 155.

Vinegar, 6, 72, 131, 198 ; as a pre-
servative, 165; eels, 134.

Water, as a distributer of disease,

222; bacteria in, 115.
Wells, a source of infection, 222;

for preserving food, 155.

Wholesomeness of bacterial prod-
ucts, 197.

Whooping cough, 212, 213, 219, 232,
239, 241.

Wild yeasts, 58, 63, 65, 70.

Wines, homemade, 71 ; method of
making, 70 ; sparkling, 96.

Wood, decaying of, 51.

Wounds, treatment of, 238.

Wuk, 67.

Yeast, as a cause of bitter milk,

68 ; as an enemy, 68 ; as a friend,

69 ; brewk, 83 ; cultivated, 76 ;
differentSJdnds of, 77 ; discovery
of, 50 ; distribution of, 63 ; food of,
66 ; growing state of, 60 ; in bread
making, 74 ; method of obtaining,
75 ; powder, 82 ; preparations, 79 ;
selection of best species of, 78 ;
species of, 61 ; structure of, 59;
used as a source of alcohol, 69 ;
as a source of carbon dioxide, 7 2 ;
waste as a food, 67.

Yellow fever, 214, 219.

ANNOUNCEMENTS

.05

EXPERIMENTAL DAIRY
BACTERIOLOGY

By H. L. RUSSELL, Dean of the College of Agriculture, University of Wisconsin,

and E. G. HASTINGS, Assistant Professor of Agricultural

Bacteriology, University of Wisconsin

Newizmo. Cloth. 147 pages. Illustrated. List price, $1.00; mailing price, $i.

THE purpose of the course here outlined is to train the
student in those bacteriological processes that are
necessary for him to comprehend thoroughly before
he is in a position to appreciate the relation of microorganisms
to dairy processes. This work is of fundamental importance
to the student who wishes to learn the nature of the biological
changes going on in milk and its products, whether he is con-
cerned purely with the practical sideof dairying or is interested
in the cognate work of dairy chemistry or dairy bacteriology.

The attempt has been made to keep the scope of this work
within the realm of dairy bacteriology, and not to encroach
upon the field of dairy manufactures.

The methods presented are believed to be the best in use
at the present time. A committee of the American Public
Health Association now has under consideration the formu-
lation of standard methods for milk analysis, but these have
not as yet been published. The methods of media making
are those recommended by the Laboratory Section of the
American Public Health Association, and, while more com-
plicated than those usually described in text-books, are surely
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A plate counter, which will be found of much practical
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166%

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CIVICS AND HEALTH

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York City. With an Introduction by Professor WILLIAM T. SEDGWICK,

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The book is alive from cover to cover. It breathes reform but not
of the platform variety. It abounds in ugly facts but superabounds in
ihe statement of best methods of getting rid of this ugliness. As
claimed by the publishers, it is preeminently a book on " getting things
done." — Hygiene and Physical Education, Springfield, Mass.

GINN AND COMPANY PUBLISHERS

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SEP 03 1996

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