ea

xe

——_—

ALBERT R. MANN
LIBRARY

AT

CORNELL UNIVERSITY

3 1924 054 706 191

Cornell University

Library

The original of this book is in
the Cornell University Library.

There are no known copyright restrictions in
the United States on the use of the text.

http://www. archive.org/details/cu31924054706191

THE OLD AND THE NEW

The modern bacteriologist, as he looks through his up-to-date research micro-

scope, might well give a grateful thought to Leeuwenhoek, who in 1683 dis-

covered bacteria with /4is microscope, a crude affair consisting of two screws,
a copper plate with a hole in it, and a single lens mounted in that hole.

BACTERIA, YEASTS, AND MOLDS
IN THE HOME

By H. W. CONN, Pu.D.

THIRD REVISED EDITION

Revised by HAROLD J. CONN, Soil Bacteriologist,
New York Agricultural Experiment Station

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PRESS

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ATHENAUS

GINN AND COMPANY
BOSTON - NEW YORK - CHICAGO - LONDON
ATLANTA + DALLAS - COLUMBUS - SAN FRANCISCO

COPYRIGHT, 1932, BY HAROLD J. CONN
ALL RIGHTS RESERVED

PRINTED IN THE UNITED STATES OF AMERICA

832.3

COPYRIGHT, 1903, 1912, BY
H. W. CONN

COPYRIGHT, 1917, BY
GINN AND COMPANY

The Athenzum Press

GINN AND COMPANY « PRO-
PRIETORS : BOSTON - U.S.A.

PREFACE

At present it is necessary for those expecting to become
housewives to understand the elementary phases of a number
of sciences, most prominent among which are chemistry and
bacteriology. The relation of microérganisms to household
affairs is now felt to be one of the most important phases
of domestic science. The present work is designed for all
interested in household affairs, including not only students
in domestic science but all housewives who are interested in
keeping their homes in the best and most healthful condition.

The present (third) edition has been quite largely revised
in order to bring the subject up to date. The principal
changes made relate to refrigeration, canning, and the spread
of disease. The book has further been changed by adding
a historical introduction in order to give the student an idea
of the historical setting of the subject and at the same time
to introduce it in a way to arouse as much interest as possible.

TABLE OF CONTENTS

SEction I — INTRODUCTION
CHAPTER

I. How ovr KNow.Lepce or Microscopic Lire BEGAN
II. How THe ImporTaANce oF Micro6rGANIsMs was Di1s-
COVERED
ITI. Micro6rGANIsMs IN THE HOUSEHOLD .

Section II— MOLDS

IV. THE GENERAL NATURE oF Mo Lps .
V. CONDITIONS FAVORING Mortp GrowTH
VI. Tue Decay or Fruit; Userut Motps; Mop Dis-

EASES

Section III — YEASTS

VII. YEASTS AND THEIR DISTRIBUTION
VIII. YEASTS IN THE HovusEHOLD
IX.:Breap RaIsiInc; FERMENTED Liquors

Section IV — BACTERIA

X. Tue GENERAL NATURE OF BACTERIA
XI. BACTERIA WHICH LIVE UPON DeEap Foop
XII. THe PRESERVATION OF Foop: Drvyinc; CooLinc

XIII. Tue Use or PRESERVATIVES
vii

PaGE

I

It

21

32
§2

58

74
87

104

118
142
157
177

viii CONTENTS

CHAPTER PAGE
XIV. PRESERVATION BY CANNING . ’ ; ‘ ‘ 189
XV. THe Growrs oF BACTERIA IN Foops . . 203
XVI. DisEASE BACTERIA : , i é P p 228

XVII. PREVENTION OF DISTRIBUTION OF CONTAGIOUS DIS-

EASES. ; ; ; ; : . . 237

XVIII. PracricaL SUGGESTIONS . z ‘ P : 269

XIX. DiIsInFECTION : : ‘ ‘ F . . 283
APPENDIX

DIRECTIONS FOR LABORATORY EXPERIMENTS . F 3 295

INDEX... m % ‘ : * A . ‘ - 315

SECTION I—INTRODUCTION

CHAPTER I

HOW OUR KNOWLEDGE OF MICROSCOPIC LIFE BEGAN

The mother of a large family of children well knows that
she has her hands full in keeping them out of mischief. Gen-
erally by the time the children have grown up she feels she
knows as much on the subject as anyone; and quite possibly
in a practical way she does, even in these days of specialists
in child feeding, children’s diseases, child psychology, and
other studies relating to children. If she lives in the country
her household may include cats, dogs, and possibly other
animals, and she knows that keeping them in their proper
places is almost as much of a task as it is with her own children.

But what about the invisible members of the household,
the bacteria, yeasts, and molds? Does she often stop to
realize what a problem they can be? They are omnipresent ;
they are capable of doing more mischief than a cat in the
larder, more actual harm than a vicious dog; they cannot be
taught obedience like a child or a dog; nor can they be thrown
outdoors like a cat that is in the way. They are too small to
be seen and can be recognized only by what they do; and
for such tiny creatures they can do a lot, either for good or
for bad. The housewife has to learn something about them
in a practical way whether or not she knows anything about
their actual nature. She has to know that milk will sour

I

2 BACTERIA, YEASTS, AND MOLDS

if it is kept warm; while if she bakes her own bread she
must know that the dough has to be warm or it will not
rise. Such practical information as this is possible without
realizing that bacteria sour milk or that yeasts cause bread
to rise; but there is no question that she can control bacteria
and yeasts more intelligently if she knows something about
the habits of these tiny beings.

These microscopic beings, commonly known as micro-
organisms or, more popularly, as microbes or germs, are
minute plants consisting of the three groups— bacteria, yeasts,
and molds — each of which is the subject of one of the later
sections of this book. They have been with mankind since
the earliest days. Some of them have always been spoiling
our food or even bringing sickness upon us; others, in a less
conspicuous way, have been benefiting us by acting as scaven-
gers or by furnishing food for our crops or by giving desirable
flavors to some of our foods. But the human race lived for
thousands of years without knowing of their existence or
realizing how much more comfortable life on earth could be
if we became acquainted with our microscopic friends and
enemies. This acquaintance actually began only about
seventy-five years ago; and during that brief period man has
made more progress in conquering the ills that flesh is heir
to than since human life on earth began. Nevertheless, even
in the earlier days mankind had learned how to control some
of the activities of microdrganisms, although without sus-
pecting that there were any such creatures; and one of the
first practical lessons in their control was probably made by
a housewife.

It is a question whether the housewife or the wine-grower
was the first to obtain practical knowledge of microdrganisms.

DISCOVERY OF LEAVEN 3

It was known in prehistoric times that grape juice would
ferment into wine and that dough would rise on standing,
and one can only guess as to which discovery was made first.
This much, however, is beyond question: back in the days
when wine-making was still an uncontrolled process, yield-
ing a somewhat uncertain product, some housewife had ap-
parently discovered a crude method of cultivating yeast and
controlling the process of bread-raising. She seems, therefore,
to deserve more credit than the wine-maker in the matter;
and one cannot question that her product has been of more
value to mankind than that of the vineyards.

We suppose that the following must have happened. The
early cooks discovered that dough became more palatable
if allowed to stand in a warm place overnight, or possibly
longer, before baking. This simple process may have been
followed for centuries before any attempt to improve it was
made; although it must have been noticed repeatedly that
some batches of bread were better than others. Some batches
would be light and sweet, others heavy, and others sour.
The important discovery came when some cook who had a
lot of dough rise unusually well decided to save a little of that
lot without baking it and to add it to the lot she was going
to make the next day. Much to her delight she found that
in this‘way she could insure good batches of dough every day.
The method was simple enough, and was followed by other
cooks until it became well known, although no one dreamed
that she was actually cultivating a microscopic plant. The
small portion of dough saved over to raise the next batch
was called leaven. That leavening dough was a common
accomplishment in early days is shown by the casual refer-
ences to it in the Bible, such as the well-known passage

4 BACTERIA, YEASTS, AND MOLDS

‘Know ye not that a little leaven leaveneth the whole lump?”’
No important improvement in this process was made until
after the middle of the nineteenth century, when scientists had
discovered with their microscopes bacteria and yeasts. Then
they found out how to isolate the yeast plant from leaven ;
and for the first time were able to teach the housewife
something about bread-making. The modern yeast cake is
a product of the scientific laboratory; and its common use
to-day is one illustration of the way science can assist the
housekeeper in controlling the invisible members of the
household.

Tue DISCOVERY OF BACTERIA

It is not certain who first saw bacteria, but the credit is
sometimes given to a Roman Catholic monk, named Kircher,
who in 1671 used simple lenses of high magnification to
examine various materials such as pus, decaying matter,
blood, and water. He mentioned the discovery of “invisible
worms” in this material and wondered if they could be the
cause of disease. It is very doubtful if he really saw bacteria,
for his lenses were of very low magnifying power as com-
pared with our modern microscopes; and his idea that they
might have anything to do with disease was a mere guess.
Yet it is interesting to know that the existence of micro-
scopic organisms was recognized so long ago and that their
production of disease had been suspected.

Only about twelve years later, however, there is even
better reason to believe that bacteria were really seen. At
this time (1683) a Dutchman, Leeuwenhoek, saw microdr-
ganisms, described them, and drew pictures of them; and
some of his sketches look very much like actual bacteria.

DISCOVERY OF BACTERIA 5

Now Leeuwenhoek was not a scientist in the modern sense
of the word. That is, he did not spend his time in the lab-
oratory and earn his living by scientific work. No one did
in those days. There was no such profession open to any one
in the seventeenth century; and most of the advances in
scientific knowledge made at that time were made by monks
or men of leisure who dabbled in science or by men in some
business pursuit who were curious about nature and studied
its secrets in their odd moments. Thus Leeuwenhoek, besides
some regular trade, had a minor position in one of the pub-
lic buildings of Delft; in addition to all this he became
interested in making lenses and learned how to grind better
lenses than any one had before. He finally made them so
small and of such high magnification that it required a special
holder for the lens in order that he might see anything with
it. The lens was in the round hole near the top. The
platform and screw were for holding the object to be ex-
amined; the microscope was turned toward the light, the
eye placed behind the lens, and the object mounted on the
platform was examined (see Frontispiece).

It seems hard to believe that anything as small as bacteria
could be seen with such a crude microscope; and yet we do
not know what else the objects may have been that he
described. Examining material scraped off the teeth, he
exclaimed: “With greatest surprise I saw that everywhere
in this material many very tiny animalcules were to be
found, which moved around in the most surprising fashion.”
He noticed how abundant they were in water and com-
mented on the enormous number we must swallow in the
water we drink. His chief reaction was one of amazement
that there could be so many and so very small living beings.

6 BACTERIA, YEASTS, AND MOLDS

It is hardly surprising that some one in these early days
should have guessed that these minute creatures, which must
enter our bodies with our food and drink, may have been the
cause of disease. In fact, the first guess of this kind was
made as early as 1546 by one Fracastorio of Verona, who had
never seen any microscopic organism. In spite of this fact,
he proposed a germ theory of disease quite like what we
believe to-day, except that he had no idea what sort of crea-
tures his “living contagious bodies” might be. Two centu-
ries later (1762) an Austrian physician, Plenciz, was able to
go further than this, for it was known by that time that
microérganisms really existed and that there was more than
one kind of them. He suggested, in fact, that each disease
might have its own specific microscopic agent which could
cause that disease and no other. He explained that these
microscopic bodies could be distributed through the air,
enter the body and live there, producing the disease, and
_believed that they might then spread to other hosts by means
of discharges from the body. Plenciz’s theory was not gen-
erally accepted in those days. It was, of course, based on
pure speculation; and neither he nor his followers could
obtain evidence to prove it. So the theory fell into dis-
repute; and as late as 1820 it was casually referred to as
an “exploded theory.”

THE ORIGIN oF LIFE

When a housewife cans a lot of vegetables or fruits, she is
confident that if the canning is well done, the contents of the
can will not spoil. If she is intelligent, she knows that
means that she has killed the microscopic organisms present

THE ORIGIN OF LIFE 7

in the food and has sealed the jar so tightly that no more
microdérganisms can get in. But how would she feel if she
believed that these tiny creatures could spring to life spon-
taneously in any organic material without having to get in
from the outside? Naturally she would think her canning
might be unsuccessful no matter how carefully the work
was done.

And yet that is just what was believed in the eighteenth
century. It was not supposed that these tiny organisms
needed any living parent; in other words, scientists believed
in spontaneous generation. They thought, in fact, they were
being very conservative in limiting this possibility to mi-
croscopic organisms; for at an earlier day it was generally
believed that even moderately large animals could come into
existence without living parents. In the ancient days we
find even intelligent writers giving directions for producing
mice. All you had to do was to put a piece of cheese in a
dark cellar, cover it with rags, and in a few days the cheese
would have turned into mice! The results of this experiment
would often be the same to-day if we selected a cellar not
too tightly constructed, although we should have a slightly
different explanation as to where the mice came from. As
a matter of fact, long before the eighteenth century all
serious;minded people had given up the idea that creatures
as large as mice, eels, or worms could arise spontaneously ;
but only very recently it had been believed that meat turned
into maggots. It took a very clever scientist to think of
keeping meat screened so that flies would not get at it and
then to observe that the maggots did not appear; this same
scientist (Francesco Redi) studied the maggots and dis-
covered that they were immature flies. From that time on

8 BACTERIA, YEASTS, AND MOLDS

(1688) maggots, as well as mice and eels, were understood
to need living ancestors. Redi even went further and made
a statement that was not by any means proved by. his ob-
servations, and which was indeed quite startling to his con-
temporaries ; he claimed, in fact, that life comes only from life.
Nevertheless, the belief in spontaneous generation still
persisted. Microscopes had shown that decaying liquids
were full of minute living creatures. It was observed that
if any organic liquid was kept for a few days, even in a
tightly stoppered bottle, these microscopic beings were sure
to appear in it. Where did they come from if they did not
spring spontaneously into life within it? Of course we do
not believe this to-day; if we did, we should not be so con-
fident that we can save food by canning it. But for about
a century and a half the subject was very hotly disputed.
About the middle of the eighteenth century a scientist by
the name of Needham tried to settle the question by boiling
an infusion of meat, or something of similar nature, in order
to kill all living things in it; he then sealed it hermetically
in the vessel in which it had been boiled and set it aside to
see what happened. Any housewife who has tried to can
some vegetable, which does not contain much sugar or any
acid, by the open-kettle method (or even by the cold-pack
method if the jars were merely allowed to stand in boiling
water) has a fairly good idea of what is likely to happen in
such cases. She knows that her vegetables canned in this way
often go bad; in fact, they practically always go bad unless
she allows them to stand in boiling water for a few hours.
So Needham found that although his boiled infusions some-
times remained clear, they were very often filled with living
organisms after standing a few days. He believed that these

THE ORIGIN OF LIFE 9

must have developed spontaneously in the liquids. He had
plenty of followers in this conclusion ; for the idea was quite
in accord with the views of the day.

Meanwhile another school of scientists, led by Spallanzani,
vigorously opposed Needham and his school. They claimed
that if sufficient pains were taken to kill all the microérgan-
isms, none would develop, and they carried on experiments
to prove their point. The dispute continued unsettled until
about the middle of the nineteenth century. On one side
it was claimed that those who obtained evidence of micro-
scopic life in boiled infusions did not carry on the experiments
carefully enough; on the other side it was claimed that heat
changed the nature of the liquids so that microérganisms
could no longer develop until air was admitted. It seems
strange, indeed, that anything so obvious to us to-day should
have been under dispute among eminent scientists for so
many years.

Oddly enough, the question was settled in a practical way
while this dispute was still raging. Early in the nineteenth
century (1809) a Frenchman, Appert, discovered that if
perishable food was placed’ in proper containers, sufficiently
heated and afterwards hermetically sealed, it would keep
without spoiling. Appert was, in fact, the founder of the
canning industry. Now it was realized even in those days
that the spoilage of food and the development of micro-
scopic organisms in it went hand in hand; and if any scientist
had stopped to think about it, he would have realized that
Appert was successfully keeping living things out of his jars
of preserved food. That this can be done is immensely im-
portant to any housekeeper; and it plainly could not be
done if microscopic life could originate spontaneously in any

10 BACTERIA, YEASTS, AND MOLDS

suitable food, no matter how carefully all microérganisms
had been excluded from it.

Scientists did not regard Appert’s methods of canning food
as being scientific proof of their point, however. It was not
till about 1860 that proof to suit the Needham school was
- furnished. One of those who helped furnish this proof was
Pasteur, the founder of bacteriology, an undoubted genius,
and such a genius that authors never tire of writing about
him. We must give more than passing attention to his work,
of which his refutation of spontaneous generation was a very
small part. He accomplished this in a very simple and yet
conclusive manner. He made a glass flask with a long neck
drawn out into a long and crooked tube. The contents
of such a flask were exposed to the air, which could pass
into the flask without even having to pass through a filter.
Yet no microscopic particles, either living or dead, could be
blown through the long crooked neck, and any such object
falling into the end of it would surely lodge at the bottom
of one of the bends. Pasteur showed that, if the contents
of such a flask were heated hot enough, they could be kept
free from microdrganisms for a long period; although, on
cooling, the contraction of the air in the flask must suck in
a good quantity of air from the outside. Some of these
flasks prepared by Pasteur are still preserved, and the con-
tents are still sterile after these many years. He also
showed that if the neck of a flask were broken off short
so that dust particles could settle into it, the contents
would become cloudy in a very few days and would show
the presence of microscopic organisms. After this demon-
stration by Pasteur no one was able to convince scientists
that spontaneous generation was possible.

CHAPTER II

HOW THE IMPORTANCE OF MICROORGANISMS
WAS DISCOVERED

°

Louis Pasteur, born in 1822 in the family of a simple
French tanner, was destined to become one of the most
picturesque and most famous men of the nineteenth cen-
tury. His keen scientific mind led him to explore new fields
hitherto uninvestigated, and thus he became one of the
world’s leading scientists; while his great depth of feeling
led him into those phases of science which gave most
promise of relieving suffering, and he may well be con-
sidered one of the greatest benefactors to mankind that
the world has ever known. Not many of his discoveries
had a direct bearing on household problems; but indirectly
they are of importance in every home, and every one should
know about him.

Pasteur began his career as a chemist, and he gave
promise, while still a young man, of becoming one of the
leading chemists of his day. But he happened then to get
interested in fermentation, not dreaming that in this way
he was headed away from chemistry. The study of fer-
mentations was a part of chemistry in those days, and it
was not until Pasteur himself had founded the science of
bacteriology that any one thought of the two subjects as
distinct.

His study of fermentations brought him into direct con-

troversy with one of the most prominent chemists of his
II

12 BACTERIA, YEASTS, AND MOLDS

time, the German, Liebig. The history of bacteriology is
full of controversies between the French and the German
scientists; Pasteur, it will be seen, started the fashion
even before bacteriology had really come into existence.
The name of Liebig is best known to the housewife to-day
from the beef extract that bears the name; but his real
reputation is in far different fields. He was, without ques-
tion, one of the greatest chemists of the middle of the
century. By the time Pasteur began his work, Liebig had
won, and thoroughly deserved, an outstanding reputation.
It happened, however, that he made one mistake; and
Pasteur was successful in pointing out Liebig’s error.
Liebig had scoffed at the idea that the microdrganisms
seen in decaying organic matter were the cause of the
fermentations taking place; he insisted that fermentation
was a purely chemical process that took place in organic
matter if conditions were right, just as combustible ma-
terial in which a flame had once started would continue to
burn by purely chemical action. Others before Pasteur
had shown that such material would not decompose if it
was sterilized and the microdrganisms kept out but that
the fermentations would begin as soon as they were intro-
duced. Liebig could easily answer such an argument by
saying that just as a pile of wood could not burn until the
conflagration had been kindled by a small flame, so or-
ganic matter would not begin to decompose until the
process had been started by the spontaneous decomposi-
tion of the dead bodies of these microérganisms. This
answer convinced every one for many years; Liebig was
too great a man to oppose lightly. But Pasteur proved
that he was mistaken. He showed that the same material

PASTEUR AND FERMENTATION 13

could undergo different kinds of fermentation, that each
was associated with a different kind of microscopic or-
ganism, and that he could bring about whichever type of
fermentation he desired by introducing the proper kind of
‘‘veast,’? as he called all such microérganisms.

The housekeeper should remember this. Milk, she well
knows, ordinarily sours with a smooth, firm curd. Occa-
sionally, however, the curd produced is full of bubbles
and has a cheesy odor. On rare occasions milk may go
bad without curdling at all; while if kept in an air-tight
container it may decompose in such a way as to smell like
rancid butter. Each of these types of decomposition is
due to a different kind of microérganism; and it was
Pasteur who first realized this. Pasteur’s demonstration
of the fact completely disposed of Liebig’s theory of
fermentation.

Pasteur regarded this work as a mere side line, and
planned shortly to get back to his chosen field. But the
Fates willed differently. For at about this time (1865)
France was quite suddenly threatened with the loss of
one of its chief industries, silk-raising, on account of the
ravages of a disease among the silkworms. This disease,
known as pébrine, had baffled some of the best minds of
France, and its ravages were becoming so serious as to
cause widespread alarm. Then some one thought of Pasteur,
and he was asked to study the problem. He hesitated for
some time; for he foresaw that if he went so far afield
in his work he might never get back to chemistry. But he
finally agreed. And he solved the problem — not in a day,
or a month, or a year even, but soon enough to save the
silkworm industry. It took him five years, and dis-

14 BACTERIA, YEASTS, AND MOLDS

couraging years they were, too — saddened by the death
of his daughter, an attack of paralysis which left him lame
for the rest of his life, a burst of skepticism which greeted
his discoveries when first announced, and finally by his
country’s defeat in war with Prussia. To overcome the
skepticism and to prove that he had actually controlled
the disease, he finally had to hire a silk farm which had
been abandoned on account of pébrine, and to show that
he could bring it back into healthy condition again.

Thus Pasteur saved the silk industry for France; but
better yet, he had proved the' germ theory of disease. For
a century or more it had been guessed that diseases might
be caused by germs; now Pasteur had proved it. This
discovery led to the study of other diseases, and even
more important results were brought about. The first of
these diseases was anthrax, an extremely serious disease
of cattle and sheep. Pasteur conquered this disease by
showing how to inoculate animals against it.

Vaccination for anthrax was an entirely new idea at
that time. Smallpox vaccination had been known for half
a century, ever since the famous discovery of Jenner.
Dr. Jenner, a physician practicing in the latter part of the
eighteenth century, had happened to hear a remark by a
country girl: “I can’t take smallpox because I have had
cowpox”; and from that had been born his idea of in-
tentionally inoculating people with cowpox to prevent their
getting smallpox. As a result, this most dreaded disease
of the eighteenth century had been almost wiped out from
civilized Europe before the time of Pasteur. So vaccination
was well known to Pasteur’s contemporaries; but who had
ever heard of vaccinating for anthrax?

ANTHRAX AND CHICKEN CHOLERA 15

Pasteur would not have thought of trying it if he had
not made an accidental discovery along the same line
several years before. In the early ’7o’s he had been work-
ing with a disease of poultry known as chicken cholera,
which he had concluded was caused by some microérgan-
ism. He had a culture of this organism, in fact, and used
it again and again to produce the disease in healthy fowls.
But one time, on returning to his laboratory after a vaca-
tion, he found it had lost its power of causing the disease ;
but before learning the fact he had inoculated several
chickens with it. He then obtained a fresh culture, and
much to his surprise discovered that although it would
produce the disease in other chickens, it had no effect on
those which had been inoculated with the old culture.
This was the accidental observation that has nearly revo-
lutionized the practice of medicine. To a mind less keen
than Pasteur’s it might have merely suggested that these
particular chickens were “tough old birds” not susceptible
to the disease. But no such explanation satisfied Pasteur ;
he wondered why they were not susceptible, and imme-
diately made the right guess — they had become immune
because he had first inoculated them with an old culture,
one too weak to cause the disease. Thus he concluded
that an animal could be made immune to a disease by
inoculating it with a weakened culture of the organism
causing that disease. That is probably what is done in the
case of smallpox vaccination. Cowpox is probably a modi-
fied form of smallpox, weakened by passage through cattle
and no longer capable of giving a human being a real at-
tack of the disease, but capable of making him immune.
This possible identity of cowpox and smallpox is still noth-

16 BACTERIA, YEASTS, AND MOLDS

ing but a guess; but here in the case of chicken cholera
Pasteur had shown definitely that a weakened culture could
give immunity without causing the disease. It was a mo-
mentous discovery, not because chicken cholera is a disease
of much importance, but because the same principle could
be applied to other diseases.

He first applied this same principle to anthrax. In this
case he found that old cultures were just as virulent as
fresh ones; but he soon discovered that he could weaken
the anthrax germ by growing it at a high temperature. A
culture weakened in that way could be used to vaccinate
cattle against the disease. He proved this to his own satis-
faction; but he had found other scientists so skeptical
about his earlier discoveries that he decided to arrange a
public experiment to show that he had conquered anthrax.
For this purpose he obtained fifty sheep, and in the pres-
ence of an assembly that had come to watch the experi-
ment he inoculated them all with virulent anthrax bacteria.
Now, anthrax is a severe disease, and any sheep thus in-
oculated could hardly be expected to escape; but, as
Pasteur informed the crowd, twenty-five of the sheep had
been vaccinated against anthrax and were immune. He
urged the assemblage to return in two days to see the
result. On the third day, therefore, a large crowd, com-
posed of farmers, physicians, veterinarians, scientists, and
journalists, was present, and their impressions of the
sight that greeted them were so strong that the world is
never likely to hear the last of Pasteur’s experiment.
Twenty-five sheep were dead or dying; the other half of
the fifty were in perfect health. The success of the vac-
cination was perfectly demonstrated.

THE CONQUEST OF RABIES 17

Thus far Pasteur’s discoveries had not saved a single
human life, while Jenner’s one discovery had saved hun-
dreds of thousands. And yet Pasteur had really made
a discovery of greater value to mankind than Jenner’s.
This is true even though smallpox had been one of the
worst scourges of the seventeenth and eighteenth centuries,
while anthrax was a disease of sheep and cattle rarely
attacking human beings. Jenner had made a chance dis-
covery and did not know how to apply the same method
to the attack of other diseases. Pasteur, on the other
hand, had reasoned out the control of anthrax from a
theory already in his mind, and since the theory had
worked once, there was no reason why it could not work
again. And it has; disease after disease has since yielded
to a similar line of attack. The first human disease to be
conquered in this way was rabies; and again it was Pasteur
who made the conquest. He is said to have attacked that
disease first because of a horror of hydrophobia which had
persisted in his mind ever since losing a boyhood friend by
this disease following the bite of a rabid wolf.

He used the same principle to control rabies that he had
with anthrax, but his methods had to be different. After
experimenting in various ways, he finally discovered that
if he ‘removed the spinal cord of a rabbit dead of this
disease, it would cause the disease in another animal; but
if dried under certain conditions for a number of days, the
germs in it lost their virulence and yet caused an animal
inoculated with them to become partly immune so that
fresher material could be used without producing the dis-
ease. In this way Pasteur found that an animal could be
made immune to rabies.

18 BACTERIA, YEASTS, AND MOLDS

He supposed that the treatment would also work on a
human being. But his problem was far from solved. Con-
sider the difficulties still ahead. Who would undergo the
risky experience of being vaccinated against rabies on the
bare chance that some day a mad dog might bite him?
Or if he had agreed to be vaccinated, would he let a mad
dog bite him so that Pasteur could test his theory? Hardly!
Pasteur’s only hope of making the treatment a practical
success was the possibility that it would be effective if
applied after the bite. That seemed illogical; but the
long period which elapses between bite and appearance of
symptoms made him hope that such might be the case.
Fortunately his hope was justified, and the treatment to-day
is used in just that way.

But Pasteur did not know the treatment would work if
applied after the bite, and the only way to find out was
to try it. To try it he had to apply it to some one who
had been bitten by a rabid dog, and the only way to
secure such a patient was to announce the treatment to
the world. He hated to do this, for he was afraid it would
prove a failure. But he announced it, and felt he had
staked his reputation on a very uncertain hope. To make
things even harder for a man of his sensitive nature, his
first patient was a little boy, who had perfect confidence
that the famous Pasteur would keep him from getting sick.
Pasteur had the boy live with him during the treatment,
and no patient was ever watched more closely. When the
time for the appearance of symptoms came around Pasteur
could hardly sleep, but was up at all hours to watch for
the slightest sign of sickness. By this time it was much
more than the success of his experiment and the effect of

ROBERT KOCH 19

its failure upon his personal fame that concerned him; he
had become genuinely attached to the little boy and was
praying with all his heart that he might be saved. The
boy lived. All the world to-day has heard of those sleepless
nights of Pasteur and how he finally became convinced that
either his treatment or some unknown miracle had saved
the boy. To-day the Pasteur treatment is used so generally
that we know it was no miracle; human ingenuity had
conquered a dreaded disease.

While Pasteur in France was making these discoveries,
Germany also produced a bacteriologist who achieved in-
ternational reputation, Robert Koch. Koch has never been
called the father of bacteriology; but he made great dis-
coveries. He learned the cause of tuberculosis, among
other things; but in another way he made a still greater
contribution, which the public has never appreciated. Bac-
teria are such tiny objects that, when they were discovered,
it was a puzzle how any one could ever study them. You
cannot pick one up with your fingers or even with the
tiniest forceps made; you can barely see it with the
-highest-powered microscope. It took a genius like Pasteur
to study them. Then Koch showed a simple method. To
be sure you cannot handle a single bacterium; but Koch
showed how you could fasten it down on a plate of jelly
so that it could not move and its descendants could not
swim away from it until finally a mass of bacteria (a
colony) developed large enough to be seen with the naked
eye. There was something large enough to handle; you
could not pick up a single organism, but you could make
a culture from one of these colonies, and if the work were
done carefully you could be reasonably sure that the cul-

20 BACTERIA, YEASTS, AND MOLDS

ture contained the descendants of one organism only. That
simple little method revolutionized the study of bacteria
and opened up the field to any one who wanted to explore it.

Some of these new students were French and some were
German. The rivalry between the two schools became even
more intense as discovery after discovery was made, first
in one country and then in the other. It was at its height,
perhaps, when diphtheria antitoxin was discovered. Here
the honors were very evenly divided. A Frenchman,
Emile Roux, first discovered that diphtheria germs pro-
duce a poison which we call diphtheria toxin. His work
was quickly followed up by Behring, a German, who,
by the use of this diphtheria toxin, actually produced
antitoxin on a small scale, enough to cure a small animal,
but hardly enough to be of practical value to a human
being. Then Roux went further and produced it on a
practical scale.

Discoveries came rapidly thereafter. The first bacteria
to be studied were naturally those of disease, because
every one was afraid of diseases and wanted to see mankind
rid of them. But later other kinds of bacteria were given
attention. Even before Pasteur’s day it had been learned
why milk soured; but now it was learned how to keep it
sweet and how to prevent other foods from spoiling. It
was found that bacteria are everywhere, and that no
household can be run in such a cleanly way as to exclude
them. Many of these discoveries have practical value to
the housekeeper. Since she has bacteria around her on
every hand, since they may be mischievous or may be
among her best friends, it behooves her to learn how to
keep these invisible members of the household under control.

CHAPTER III

MICROORGANISMS IN THE HOUSEHOLD

Thanks to these discoveries it is now well recognized
that bacteria, yeasts, and molds together form a group of
utmost importance in human welfare. Although far too
small to*be seen, their rapid rate of reproduction makes
them one of nature’s strongest forces either for weal or for
woe. Their importance in connection with disease and the
practice of medicine was recognized many years ago; and
a little later their significance in agriculture was understood.
Still: more recently it has come to be appreciated that their
relation 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 microdrganisms constitute the foundation
of the demand for cleanliness so forcibly emphasized in
modern times. Thus the vague knowledge of the past is
growing into a scientific understanding of the subject.

In the household microérganisms 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 and infectious diseases.
21

22 BACTERIA, YEASTS, AND MOLDS

1. MICROORGANISMS AND THE PRESERVATION OF Foop

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 23

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 refers
to organisms which began to claim public attention much
more recently but in regard to which there is at present a
large amount of misunderstanding. Even though these or-
ganisms are very minute, and though she knows little about
them, the housewife finds them the most serious, indeed

24 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 microérganisms 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 microérganisms in places where they
are not wanted. For this purpose have been invented

MICROORGANISMS AS USEFUL AGENTS 25

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 microédrganisms 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 microédrganisms
which are so liable to spoil it. x

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,

26 BACTERIA, YEASTS, AND MOLDS

they are usually 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
microérganisms, even in the household, must occasionally
be looked upon as friends rather than enemies.

3. MICROORGANISMS AND DISEASE

Certain species of microdrganisms 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 microérganisms 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 27

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 microdérganisms 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.

In preventing the distribution of diseases the primary
problem is a bacteriological one, for, since microorganisms
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

28 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 microérganisms 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

Nearly all the microdrganisms with which we are here
concerned have this characteristic: they are what botanists
call colorless plants. This does not mean that they are

CLASSIFICATION OF MICROORGANISMS 29

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 oxganisms. Evidently the foods we eat —
meats, fruits, vegetables, etc. — are organic, since they all
come from plants or animals. Colorless plants, such as fungi
and bacteria, are, like animals, obliged to have organic sub-
stances for foods, and therefore feed upon materials es-
sentially 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,

30 BACTERIA, YEASTS, AND MOLDS

Among the colorless plants are a great variety of forms
which show wide differences in structure, size, and general
appearance. But inasmuch as they all agree in lacking
green coloring material, they are, at least from the stand-
‘point of their relations in nature, properly placed in one
general class. A method of dividing them, convenient for
our purposes, is as follows.

CoLorLEss PLaNts

Higher Fungi. This includes the forms of larger 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 small size, but yet easily visible to the
naked eye, composed of threads.

Yeasts. Microscopic plants which multiply by a process
called budding, composed of oval bodies.

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

This 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. Scientists also classify yeasts and bacteria
still further into smaller groups; but one does not need
to learn them to understand the behavior of these micro-
organisms in the home.

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

CLASSIFICATION OF MICROORGANISMS 31

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.

PROTOZOA

One or two diseases referred to in later chapters are
caused by animals rather than plants. Malaria is certainly
so caused, and possibly smallpox. These animals are uni-
cellular and belong to the group Protozoa.

SECTION II— MOLDS

CHAPTER IV
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
ita 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 4Acidiomycetes.
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.

32

THE GENERAL NATURE OF MOLDS 33

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,though the 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, Ste minke Fic. 1. Two colonies of common mold,
‘ * Penicillium, as shown under the micro-
rials upon which they scope on a black background.

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. 1 and 5). This species
is common upon bread and cheese, but it will grow upon

34 BACTERIA, YEASTS, AND MOLDS

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

Fic. 3. A common mold, Aducor, growing on a bit of banana.

THE GENERAL NATURE OF.MOLDS 35

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

Fic. 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 Cae ee en
others grow red or pink. of spores of an
One of the very common older colony.
forms consists of a rather ye, 5. The growth from two spores
coarse mass of threads, __ two days later than Fig. 4, showing
upon which develop numer- the beginning of the formation of
Bee spores, showing method of origin at
ous black balls containing 2.
spores, 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.

36 BACTERIA, YEASTS, AND MOLDS

STRUCTURE OF MoLps

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 37

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

38 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 inthe air.
Every breath of
air striking a

Fic. 7. A colony of Mucor, showing the mycelium
and the sporangium of the fruit capsules. Ata
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 swells into a
small rounded knob. This knob continues to grow until

FRUITING OF MOLDS 39

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 blackfrom
the abundance
of these spore
sacs.

Another very
common sort of
mold fruits still
differently (As-
pergillus), A
fine, threadlike Fic. 8. A colony of Aspergillus, showing mycelium

and spore clusters. The lower figures show in
detail the method of spore formation.

mycelium is
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, 2). 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

40 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. See
experiments 6-8, pp. 272-273. Figs. 14-17 show a variety
of common molds, with their methods of forming spores.

Fic. 9. A colony of Aspergil/us as shown under
the microscope on a black background.

FRUITING OF MOLDS 41

Fic. 10. Mucor,a
common mold.

Fig. 11. Alternaria, a com-
mon mold found upon apples.
Mycelium shown at a, and en-
larged fruiting bodies at 4.

Fic. 12. Fruiting bodies of another
Fic. 13. Fruiting bodies species of Alternarin.
of a mold found upon
apple scab, Cephalo-
thectum.

Fic. 14. Stysanus, a common
mold. a, mycelium; 4, fruiting
branch. Fic. 15. A common household mold.

42 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, 2). This thread feeds
upon the material on which it is growing, and continues to
extend and branch until within
a few hours a new mycelium is
produced, thrusting its way into

0 9% Spores

Fics. 16 and 17. Two species of molds, Afonz/ia, 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 spares falling upon it,
If a piece of moist bread, for example, is éxposed to the
air for a few moments 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

PuaTE I

PLaTE II

Fic. £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.

43

44 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
vacuum cleaners better yet; and lastly, that no food should
be exposed to the air of a recently swept room.

PROTECTION OF Foop From Mo.Lps

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 45

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.

In protecting jelly from the growth of microdrganisms
there are several facts to bear in mind. Jelly contains too
much sugar and is often too acid to permit the growth of
ordinary bacteria. Molds and yeasts, which can grow in
it, do not produce spores that are specially resistant to
heat; and these organisms, moreover, cannot grow in the
absence of oxygen. Several methods have been proposed
for preventing spoilage. One of the most popular in for-
mer years was to pour a little pure alcohol or some distilled
liquor such as brandy over the top of the hardened jelly
to kill mold spores that had lodged there and then to seal
with a paper cover. For obvious reasons this method is
not in wide use in the United States at present.

The most common method now employed in the home
to seal tumblers of jelly is to pour a little melted paraffin
upon the surface of the jelly. 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.
The object of this method of sealing is not so much to
exclude mold spores as to keep out air. The molds, un-
like many of the bacteria, are unable to grow unless they

46 BACTERIA, YEASTS, AND MOLDS

have sufficient air. Hence if the seal is good they will not
grow on the jelly even though spores are present under the
paraffin. This is the reason why tumblers of jelly can be
allowed to stand overnight to harden before pouring on
the paraffin.

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 are often
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
be considered in a later chapter. We must notice here,
however, 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. This must, of course, be guarded against,
and if the whole contents of the can cannot 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 47

MATERIAL WHICH 1S LIABLE TO MoLp

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. A “mustiness” 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

48 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.

ReEsuLts oF Motp 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. (1) 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 49

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
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
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

Fic. 19. A bit of Gorgonzola cheese. Dark
spot at right on top is mass of mold spores.

SO 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.

Mops upon Foop 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
andthe food preserved from

Fic. 20. A bit of American cheese. further molding, or if it is
No molds are present.

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

USEFUL MOLDS 5I

of it. Indeed, Stilton cheese, Gorgonzola (Fig. 19), 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 materially 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 V
CONDITIONS FAVORING MOLD GROWTH

When a piece of bread or cheese goes bad, it gets moldy ;
when a bottle of fruit juice spoils, the organisms growing in
it (as we shall learn later) are either yeasts or molds; but
the spoilage of a can of vegetables, like corn or beans, is
almost invariably due to bacteria. Why can molds grow
in the first two instances but not in the third? The answer
to this question is important, for it shows how to control
their growth.

Food Requirements. Like nearly all other kinds of
‘ microdrganisms, molds require organic matter. As food is
always composed of organic matter, they have no trouble
in meeting this requirement. Were this the only peculiarity
of their food needs, all food would mold; but there are
certain other respects in which they prefer quite different
food from ordinary bacteria. They like a large amount of
sugar. Most bacteria can use sugar; but if a fluid contains
as much as two per cent of sugar the growth of ordinary
bacteria is decidedly inhibited. Quite the contrary with
molds. They grow well even with larger percentages of
sugar. One reason for this difference is that when a micro-
organism grows in the presence of sugar, this substance is
converted into acids; and it requires only a small amount
of acid to prevent the growth of the ordinary decomposition
bacteria. Molds, however, grow best if there is a little acid
present, and they tolerate a considerable amount of it.

52

FOOD REQUIREMENTS OF MOLDS 53

From this it is easy to understand why certain kinds of
food mold while certain others spoil from the growth of
bacteria. If a food contains much sugar, like jelly, or much
acid, like lemons, bacteria cannot grow in it; while molds,
if neither the sugar content nor the acid is too high, are
not inhibited. If, on the other hand, a moist food is low in
sugar and acid, ordinary decay bacteria are likely to grow
so rapidly in it that the molds cannot get started.

This is not the whole story, however. Yeasts, as well as
molds, like much sugar and tolerate considerable acid. We
must look further into the peculiarities of these organisms
before we can learn why some foods spoil from the action
of molds and others from that of yeasts.

Moisture. A factor of primary importance in the
growth of all microérganisms-is water. A vigorous growth
of molds requires an abundance of moisture, and in dry
material they will not grow at all. There is, however, a
very distinct difference in this respect between molds and
either bacteria or yeasts. Bacteria and yeasts ordinarily
prefer liquids to solids, and grow only in solids that have a
high percentage of moisture. If, therefore, the moisture con-
tent of any material is quite low, like that of flour stored
in a damp place, molds can grow but neither yeasts nor
bacteria. This particular illustration is interesting: flour
is not acid and contains practically no sugar, but molds will
grow in it because its low moisture content prevents the
growth of bacteria or yeasts.

It must be emphasized, however, that some moisture is
necessary even for molds. Flour that is stored in a dry
place can be kept indefinitely without molding. In fighting
molds, therefore, one line of attack is to exclude all moisture,

54 BACTERIA, YEASTS, AND MOLDS

Water for their growth may be supplied by the air in
which the food is kept, or by the food itself.

1. The air is the source of the water when flour, which
naturally does not contain enough moisture to support
even molds, becomes covered with a growth of these organ-
isms. Flour is not the only material thus affected. A large
variety of materials in the household, 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. Fruits,
for example, are so full of moisture that they are equally
good food for molds whether kept in a dry or a moist
place. If the mold once gets a stari (which, by the way, is
very difficult in a dry atmosphere), the fruit itself furnishes
all necessary water. Jellies and other similar preserves also
contain sufficient moisture.

From this it follows that food capable of being thoroughly
dried may be protected absolutely from molding if stored
in a dry place. It also follows that any condition which
favors moisture, such as darkness, stagnation of the air,
proximity to the soil (as in cellars), is likely to permit the
growth of molds. Under such conditions not only food,
but also leather-covered books, shoes, pocketbooks, and
even carpets or clothes may become covered with mildew.
In damp weather no animal or vegetable material is beyond
the possibility of molding ; but if it is placed in a dry atmos-
phere the growth of molds may be entirely prevented.

MOLDS IN RELATION TO AIR 55

Aération. We have just seen that molding is stimulated
by stagnation of the air. This is not because molds do not
like air, but because air currents cause drying and deprive
them of the necessary moisture. Molds need oxygen, just
as we do, and hence require some air; thus molding almost
always begins on the surface of any substance attacked.

In this matter of aération molds are quite different from
either bacteria or yeasts. Bacteria and yeasts, like fishes
and other aquatic animals, can live on the oxygen dissolved
in the water around them; some bacteria can even grow
in the entire absence of free oxygen. Molds, on the other
hand, can never grow in its entire absence; and although
they can probably use dissolved oxygen to some extent,
they apparently prefer to obtain it from the air. Some-
times one can actually drown a mold by keeping it beneath
the surface of a liquid in which it could grow well if it were
allowed to float on the surface.

These facts show why molds do not cause the spoilage
of canned vegetables. A can of vegetables is ordinarily
sealed too tightly to allow the entrance of air; so some
kinds of bacteria may grow, but molds cannot. Further-
more, if air is able to get in, the bacteria can grow so well
in such material that they prevent mold growth. In canned
fruits or fruit juice molds cannot grow unless air gets in;
but if the seal is not tight they can grow, because the
abundance of sugar and acid in such material prevents the
growth of bacteria which would keep down mold growth
if they could flourish. In jellies molds. are ordinarily
the only microdrganisms capable of growing, because of the
high acid content and large amount of sugar. Hence in
making jelly one does not have to be careful to keep out

56 BACTERIA, YEASTS, AND MOLDS

microérganisms but merely has to seal it in such a way as
to keep out air and thus to prevent mold growth.

Temperature. Molds, like bacteria and yeasts, require a
moderately warm temperature for vigorous growth. At a
temperature slightly below 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. The still
lower temperatures of mechanical refrigerators are more
efficient, while those of cold storage (slightly below freez-
ing) prevent mold growth almost entirely. Most common
molds, however, either fail to grow at an ice-chest tempera-
ture or grow very slowly. As the temperature increases,
however, 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
though tightly closed in an atmosphere saturated with
moisture and abundantly sown with mold spores.

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. Boiling or-
dinarily kills spores as well as mycelium. 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. 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,

PREVENTING MOLD GROWTH 57

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 pre-
serves or sauce. It is always necessary to remember that
after such heating the food is liable again to receive more
mold spores from the air and may therefore later show an-
other growth of molds.

r

PRACTICAL SUMMARY

From all these facts we may reach practical sugges-
tions as to the methods of avoiding the growth of molds.
(x) 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
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 and air 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 remove
such food occasionally, to scald the container, and to ex-
pose it to the air and sunlight in order to prevent any great
accumulation of mold spores. (3) The growth of molds
may be almost completely stopped by lowering the tem-
perature, and therefore foods that are particularly liable to
mold may be prevented from molding for a long time if
kept in a refrigerator.

CHAPTER VI

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 peaches decay
rapidly; apples,
_ oranges, and bananas
keep somewhat
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-
caying (Fig. 21).
Fic. 21. An apple beginning to decay under Winter apples, with

the action of certain species of molds. 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 thema longtime. 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
58

THE DECAY OF FRUIT 59

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. Bztter 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,

Fic. 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

60 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
and dry, 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
Fic. a3: Monilia, showing the for- by the growth of the mold
mation of spores at ¢ and the 3
sprouting of spores at 2 and 4. 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

DISTRIBUTION OF SPORES 61

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

Fic. 24. Another species of Moni/ia 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

62 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
thecharacterof thefruit.
These we shall consider
inalaterchapter. It is
Fic. 25. A small bit of an apple under a not possible by any

microscope, showing the molds breaking knownmeans to preserve
through the skin to produce spores, and fruit indefinitely from

showing the mycelium running through
the substance of the apple. the attack of 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 63

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 learned that some 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.

64 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 65

This absorption of moisture explains also the efficacy
of one of the best means known for preventing the decay
of fruits. Experience in past years has showri 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

66 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. Al!
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 fruit growers have now learned by
practical experience 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 67

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
microérganisms 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). Insome 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 cf decay
(Fig. 21). Nearly all of the
diseases in question are caused
by molds somewhat similar to
those we have already con- fic. 26. Peaches tumed into
sidered, but of different species, 2 b#"d mass (mummified) by

the action of fungi.
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

68 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 microdrganisms
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-
HES ae 2 ....| ket. The loss comes

Fic. 27. Peaches decaying on the tree. UPON the fruit grower,

upon the person whobuys
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 bythe customers. The
consumer would not distinguish this from the more com-
mon types of decay. For this reason this type 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 69

Utitity oF Mo.tps

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, much of 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.

In recent years it has been learned that molds are valuable
commercially in the production of certain chemicals which
have industrial uses, A few food products, moreover, are

7O 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. Roguefort 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. S¢z/ton 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 MoLps

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 comprise 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

71

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

Fic. 28. A mold (Zrichophyton) which produces ringworm. At a
is a bit of hair with the mold spores on the outside, and at da
figure of the mold itself highly magnified.

name. The affection is a
troublesome one to heal,
especially when it gets into
the scalp; it may produce
bald spots, but is never very
serious. 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
cause of ringworm. At @
is shown a bit of hair with
the mold fungus and mold
spores growing upon it, and
at 6 the fungus more highly

Fic. 29. Two pieces of hair from the
scalp infested with a mold (Microspo-
ron) producing ringworm. Theupper
figure shows the masses of spores
attached to the outside of the hair;
the lower figure shows the mold
thread lying beneath the spores.

magnified. Of the several species of molds that produce
this trouble some are more liable to grow upon the hair

72 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
Fic. 30. Amold (Achorion) pro- another, that the person suf-
ducing a second type of skin fering from the attack should
disease known as favs. At@ hoe his own combs, his own
the mycelium is shown, at éthe id
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.

MOoLD-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 73

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. A far better method is to use a vacuum
cleaner, which removes the mold spores without scattering
them in the air.

SECTION III— YEASTS

CHAPTER VII
YEASTS AND THEIR DISTRIBUTION

FERMENTATION

Yeasts are the most important among the natural agents
which bring about fermentation. This term has several mean-
ings to 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 alcoholic 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

74

FERMENTATION

75

and carbon dioxide that is the foundation of all fermenta-

tive phenomena.
place as follows.

C,H,,0, =2 C,H,O + 2 co,

(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 hardly a tribe of savages without
its own kind of fermented drink.
These intoxicating 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
other plants are also used. In all

Chemists represent the action that takes

Fic. 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 4,
for the purpose of de-
termining the nature
of the gas.

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

76, 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
cases 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.
The yeast plant was first seen two centuries ago by a Dutch
microscopist, who found fermented liquors filled with minute
bodies, the significance of which he did not understand;
nor was it known that they cause fermentation 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 77

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 yedst mass is
made up of millions
of minute bodies,

é

Fic. 32. Common yeast very highly magnified.
if Figs. 2 and 6 show vacuoles; ¢ shows a nucleus
each of which is an 2 inside of the yeast cell; ¢ shows a budding
individual yeast cell with the nucleus dividing; ¢ shows the cell
divided, the new cell containing a bit of the
old nucleus.

plant.

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

78 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, 4). 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 vacuoles. 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,¢). 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: (1) 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 79

in size until finally it may be as large as the original plant
(Fig. 33, ¢). 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, ¢. This budding continues,
the little buds appearing one after the other, until there
are produced irregular-shaped groups like those shown at
Fig. 33, 2. 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, d.
After a while, how-
ever, the different

Fic. 33. Growing yeast cells, showing method
cells dro p apart of budding and forming groups of cells.
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

80 BACTERIA, YEASTS, AND MOLDS

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

Fic. 34. A yeast cell resisting for a long time a variety of

ee four 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 ee) es)

characteristic pos-

sessed by a large (3) ese

number (Fig. 35).

Botanists divide F1¢.35. Three species of yeast each contain-

c 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 Zoruéa 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 81

WHERE YEASTS ARE FOUND

From the fact that sugar solutions will always ferment, it
will readily be understood that yeasts have a wide distribu-
tion, 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.

82 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-
Hig. 36: ‘Wild yeast from sciously in the cider, 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,

pao BE calere either before it has 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 83

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 con-
densed milk and in canned foods that have not been properly
protected. It is not uncommon to find a similar fermen-
tation 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 characteris-
tic 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 multiply upon any food suited to
their gfowth. These wild yeasts are so sure to be present in
the air that it is very difficult to protect a fermentable mate-
rial 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.

84 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. 183.)

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

YEAST AS A FOOD 85

use for such masses of yeast plant has been found. In the
course of its growth the yeast plant stores up considerable
food material, and the masses of yeast that accumulate’
prove to be a useful food material. It contains not only
the well-known types of food substance, proteins, fats, and
carbohydrates, but also is well supplied with vitamins.:
Vitamins, as is well known today, are very necessary food
substances, but of rather mysterious nature in that chem-
ists have never analyzed them. It is known, however, that
there are several vitamins, each serving its particular pur-
pose in animal nutrition; not all of them are present in
yeast, but enough to make it a useful article of diet. The
various vitamins are distinguished by scientists by the
letters A, B, C, and so forth. Our knowledge of them is con-
stantly growing, and if recent claims are correct, that one of
the vitamins has been isolated in chemically pure form, more
accurate information about them will soon be forthcoming.
In spite of all the recent investigations, however, it must
still be admitted that our knowledge of their behavior in
the body, as well as of their chemical nature, is still very
imperfect. But it is known that they are necessary for
health; and a diet without fresh vegetables, fruit, or milk
is likely to be deficient in them. It is now well known that,
when necessary, this deficiency may be made up, in part
at least, by eating yeast; although for this purpose alone
there is little demand for it in ordinary civilized communi-
ties, because it is much less palatable than fruits, vege-
tables, or milk products.

It is coming to be believed, however, that yeast has
other properties as a food less well understood even than
vitamins. Claims are even made that it overcomes con-

86 BACTERIA, YEASTS, AND MOLDS

stipation, controls certain stomach disorders, and improves
the general tone of the body. To what extent these claims
are based on fact and how far they are merely advertising
propaganda cannot now be told for certain. It can, how-
ever, be safely stated that yeast is now being used to some
extent as a food and is being widely advertised for the pur-
pose. Commercial preparations containing yeast, so fla-
vored as to be palatable, are now available, and may well in
many cases be a desirable addition to the diet. Extracts of
yeasts, under various trade names, have for some time
been placed on the market in Europe, although not well
known in this country. It is, however, doubtful whether
they have the nutrient value of the yeast itself, any more
than beef extract is as good a food as the beef.

CHAPTER VIII
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. Ina
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, that 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.
87

88 BACTERIA, YEASTS, AND MOLDS

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 and industrial processes sometimes the
one, sometimes the other, and sometimes both of these
products are utilized. .

Tue Use oF YEASTS AS A SOURCE OF ALCOHOL

The alcohol produced by yeasts is the foundation of the
fermentative and distillery industries, for common yeasts
are the agents which produce the alcohol found in all
alcoholic beverages. The fermentative industries, which
were important in this country before prohibition and are
still of immense extent all over the rest of the world,, are
dependent upon yeasts. In the manufacture of fermented
and distilled liquors these little plants are used in all cases
for the production of alcohol out of various sugar solutions.
The struggle with gigantic evils resulting from these in-
dustries 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 vig-
orous fermentation is started. The fermented mass may
subsequently be used directly for a beverage — fermented
drinks, like beer, ale, etc. — or the water may be partly

FERMENTED DRINKS 89

separated from the alcohol by distillation, producing 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.

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 performed
twice, after which the wine is bottled and sealed. 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 boil-
ing 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,
and various devices are used to get rid of them.

Yeasts are also used in the manufacture of homemade
wines which are produced from juices of fruit such as grapes,

go BACTERIA, YEASTS, AND MOLDS

elderberries, blackberries, currants, raspberries, etc. Cider also
isan apple wine. The principles in the manufacture of these
homemade wines are the same as in the production of the
commercial wines. It must be remembered that in the United
States their sale or transportation is distinctly illegal.
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 undis-
turbed during the fermenta-
tion, 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 grow-
ing, bacteria may develop in

Fic. 37. Organisms found upon the

skin of a grape and concerned in
the fermentation of wine. the product and cause fur-

ther changes, so as to injure
its taste, or even totally change its nature, as in the forma-
tion of vinegar. (See Chapter XI.)

Tue 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 QI

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 ualeavened 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

92 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; but when successful, some
think it makes better bread. The use of leaven has there-
fore been almost wholly 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. Inthe 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 93

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 present in the milk
were not injured by the salt, and therefore 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 microérganisms actually concerned in the

94 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 microédrganisms 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 95

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- Fic. 38. Three fermentation tubes inocu-
ous fermentation lated with different varieties of yeast, show-

ing the differences in fermenting power, as
than others. The indicated by the amount of gas ne in
cake of compressed the closed tube. The tube on the right was
yeast, for example, inoculated with dried yeast, the middle tube
with brewer’s yeast, and the left-hand tube
with compressed or distillery yeast.

produces a more vig-
orous 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

96 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 97

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 cerevisia ; 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 multiplies rapidly and after a few hours collects
as a scum on the surface of the vat. This is removed,
washed, and the water partly removed by heavy pressure ;
then the mass is formed 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

98 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 on the ice; 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 rather expensive, and it may be 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 99

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 fA &
up making their own yeast brews and GG
depend upon compressed yeast. eo”

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

Fic. 39. Yeast from
a dried yeast cake.

Fic. 40. The same yeast after a
few hours’ growth.

100 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 little 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, a decreasing 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 con-
venient 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 Iol

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 drew, 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 formule are as follows.

(1) 1 lb. potatoes (2) ¥% Ib. of malt
¥% oz. hops ¥ oz. of hops
1 gal. water 1 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

102 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: (1) 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 103

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 111),
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 IX
BREAD RAISING; FERMENTED LIQUORS
Wuat 1s BreapD 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

Fic. 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),

104

WHAT IS BREAD RAISING Ios

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 vazsing of the bread,
and the bread maker must
learn from experience when
it has progressed suff-
ciently. After the dough

has been properly “raised ”’
by the yeast, it may be
seen to be filled with holes

Fic. 42. The same dough after
yeast has grown and caused the
dough to swell up by the accumu-
lation of carbon dioxide.

occupied by the gas bub-

bles (Fig. 42). Now, after the proper kneading, it is
sometimes baked at once and sometimes given a second
raising. The heat of baking drives off the small amount
of alcohol. 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

106 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 Aghter, i.e. more
porous, and hence easier
of mastication and more
palatable. :

2. Itrenders it move di-
gestible, because the por-
ous material is more easily
Fic. 43. The same material after bak- acted upon by the digest-

ing, showing the canlies left after jve juices than the more
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
dcugh with bubbles will make it light. In one type of
bread, known as aévated bread, the spaces or cavities in

RELATION OF BREAD RAISING TO TEMPERATURE I107

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 (quick 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 such 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 go’ 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

108 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 microdrganisms 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 109g

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 present a variety of
mold spores, and especially in summer the yeast cake is
likely to contain other species of yeast besides the one
desired for bread raising. These impurities may be 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

IIo 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 /ac-
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 III

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. It has been noticed that, a few hours
after baking, bread sometimes becomes slimy in consistency.

112 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
Fic. 44. A species of bac: scribed. These bacteria frequently
terium which produces ;

slimy bread. come from the yeast cake, 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 (1) 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,

FERMENTED DRINKS 113

and (3) to get a fresh supply of yeast. After this the
trouble ought to disappear. It is also important to re-
member that the sliminess occurs only 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.

Tue UTILIZATION OF BOTH ALCOHOL AND CARBON
DIoxIDE

In the production of beers, porters, ales, etc., both of the
products of fermentation are commonly utilized. The gen-
eral character and effect of beer are due partly to the
alcohol present and partly to the presence of a quantity of
the carbon dioxide, which gives to the beer its sparkle.
In the manufacture of such a product the fermentable ma-
terial, 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 manu-
facture of common beer. The process lasts from a few days
to several weeks according to temperature and the kind of
beer being made. During this fermentation alcohol accumu-
lates 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 the bottom. Most of the yeast is then removed,
and the liquid stored in casks or bottles. Here the fermen-

114 BACTERIA, YEASTS, AND MOLDS

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. In beers the carbon dioxide is desired no less than
the alcohol, since it contributes materially to the flavor of
the product. In ordinary wines, however, the fermentation
is allowed to continue for a much longer period and the
gas permitted to escape; hence the alcohol content be-
comes high and the drink has no sparkle.

Such fermentations form the basis of immense indus-
tries in other countries, and did in the United States before
prohibition. The present law has resulted in much more
home production of fermented drinks in this country than
ever before, especially of wines. The fermentative process,
however, should be given more careful control than can
ordinarily be managed in the home; and such home brew
seldom recommends itself to any except those who crave
alcohol in any form.

There is, however, a type of homemade beer which is
easy to make and is ordinarily too low in alcohol to be in-
toxicating or to come within the scope of prohibition
legislation.

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,

ROOT BEER 1is

and lemon; but to-day highly flavored extracts are pur-
chasable at stores for a small price. These flavoring ex-
tracts are mixed at home with a quantity of sugar and
water (two pounds sugar to ten quarts water). To the
mixture is added a small amount of yeast (one cake of dried

yeast or 4 cake

of compressed

0) . ON yeast for the
ox? oP above quantity),
. and the whole

gis ( ine material, closed

SS in bottles or
other vessels, is

then set aside in

Wo , doo a warm place
for fermenta-

4 tion. The fer-
WR : mentation goes

EM on rapidly, and
a oow, in the course of
one) g acouple of days

Fic. 45. Miscellaneous species of yeast. a beverage is

a, S. corevisia; b, S. pastorianus I, from wine; c S. pastoria- produced, filled
nus III; d, S. ellipsoideus II; e, S. cerevisia, from beer; . *

A, S\ apiculatus; g, S. minor. with carbon di-

oxide, which

causes a bubbling and frothing when the vessel is opened,
and containing a small quantity of alcohol. To keep the
alcoholic content low one should consume the beverage
promptly, or one should put it in a very cold place after
one or two days’ fermentation. As a matter of fact, although
the fermentation may be allowed to continue longer, this is

116 BACTERIA, YEASTS, AND MOLDS

hardly a desirable way to obtain an alcoholic drink if one
is desired; for the flavor of such a brew after longer fer-
mentation in no way resembles that of commercial beer, and
is generally regarded as rather unpleasant.

In making such home-brewed beer it must be remem-
bered that the fermentation, which results in the produc-
tion 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 intoxi-
cating 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.

Homemade beers of this type are probably less popular
to-day than formerly, largely because of the wide variety of
comparatively inexpensive charged drinks sold in bottled
form. These bottled drinks are not fermented, but are
artificially charged with carbon dioxide so as to give them
the sparkle of beers without the alcohol. Some of these
charged drinks, like ginger ale, birch beer, and root beer,
are much the same in taste as the old-fashioned homemade
beers; while others of the “‘near-beer” type more closely
resemble the commercial beer now forbidden in this coun-

FERMENTED MILK I17

try by law, having the flavor and the sparkle, but lacking
the 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 bot-
tled 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 carbon dioxide
and contains a small amount of alcohol, and is thus a sort
of beer made from milk. It is not much used in this coun-
try except for invalids. Other types of fermented beverages,
kefir, maizoon, and some others, are made from milk by the
use of special ferments, always containing yeast, whose
preparation is hardly within the reach of the ordinary
household.

SECTION IV— BACTERIA

CHAPTER X

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.

Bacteria are far smaller
than yeasts or molds
(Fig. 46). Some house-
wives do not know of their
existence, while even those
of the more intelligent class
often fail to appreciate their
Fic. 46. Showing the comparative size close relation to household

of molds (a), yeast (6 and c), and bac- ‘

terla (2). economy. Few housewives,
it is safe to say, 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
118

STRUCTURE OF BACTERIA 119

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
continuation of life is dependent upon their activity. To
the farmer
they are abso-
lutely essen-
tial. They
are the dairy-

man’s close Fic. 47. Comparative size of the point of the finest
allies, and cambric needle (4), a particle of dust (a), and bac-
4 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,

120 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: (1) 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 121

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 external appearance. They are almost 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; bacteria need not,
therefore, be classed with animals on that account if they
resemble plants more closely in other respects.

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

122 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-

“ @0 Ya . :
a F teria consists of those that
eg 2te in the shape of a minute
lf sphere. Their size differs
yp § somewhat, but they are
always extremely minute, and
rt about all that can be said in
H regard to them is that they
are spherical organisms,
sometimes possessing flagella
and sometimes apparently
Fic. 48. a, cocci; 4 (Pseudomonas), without them. No internal
rods with polar flagella; ¢, rods structure is known. They
with peritrichiate flagella; ¢, im- multiply sometimes in such

motile rods. Se Ripa ae
oo pee Ra a ees
to produce long chains (Fig. 49, 2), 0 CO
sometimes so as to produce groups of Cae
fours or groups of eight or sixteen B >
(Fig. 49, 4, c, d). The general name jd
given to spherical bacteria is coccus, and
to this name are sometimes prefixed FS 49. Cocci, show-
; mains ‘ ing methods of mul-
certain other syllables to indicate certain —tiptication. a, Strep-
characters. Streptococcus is a name ‘tococcus; 6, Micro-
given to cocci forming chains (Fig. 49, <i © and 4
. a Sarcina.
a), and Micrococcus to those forming
fours or irregular masses as at 6. The term Savcina is
the name given to those that form solid masses such as
shown in Fig. 49, ¢ and d.

ce d

¢

CLASSIFICATION OF BACTERIA 123

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 o0_9

very many times as long as broad # © ° AES
(Fig.50). When one of these grows f=)
it lengthens and commonly soon ¢ if
divides into two, but they may con- AS
tinue to lengthen for a time without Fic. 50. Rod-shaped bac-
manifesting any signs of division. or
In such a case they form long slender threads, as shown
in Fig. 50, 6. These threads, however, eventually break
up into short sections (Fig. 50, c). Some of these rod-
shaped bacteria have flagella ard are capable of active
motion (Fig. 48, 4, ¢); others have no flagella and are quite
without the power of motion (Fig. 48, @). Several names
are given to bacteria of this shape; Bacterium and Bacillus
are two of those most commonly used.

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

So 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.

Fic. 51. Spiral bacteria.

124 BACTERIA, YEASTS, AND MOLDS

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, c, 2). 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

20 OOWas«0 method of multi-

plication in bac-
bQ000 ©0Q0 coDdaD 0000000 teria is known as

CeO: Co). Cx CS Cac fission, and this
daoOD GD GW OO group of fungi are

-— 9 0) called fission fungi
OD c om vA in distinction

OC eo eocs ce from the yeasts,

Fic. 52. Showing the method of multiplication winch aps : called
by fission. w, a coccus form; 4, a strepto- budding fungi. The
coccus; ¢ and d, short rods; e, showing suc- difference between
cessive stages: in the formation of chains, these two classes
arising by fission from single cells. a

can be distin-

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 reproduction. 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

e

GROWTH OF BACTERIA 125

spores are capable of subsequently germinating into
new individuals like those that produced them and thus
continuing the race (Fig. 53, 4).

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 QOD Gp re
by a little shell which is hard

and tough and capable of resisting <> oO Pe)

various adverse conditions. Spore-

bearing bacteria may be dried with- Pe) “<

out injury, for their spores protect

them from destruction. They may

be heated to a high temperature, a Xe) Q C
even to boiling, without being killed.

Thus the presence of spores will 44 b (Co
make a great difference in the ,,, +e Showing Geom
ease with which any material can with spores. Ataare free
be sterilized by heat. Bacteria not spores, and at 4 germi-
capable of producing spores are "#8 Spores:

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

126 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 Jack 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 Jittle 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 microdrganisms. If the material
is to be protected from them, every single bacterium must

GROWTH OF BACTERIA 127

be destroyed, for if but one be left alive it may 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 at140.° Certain ,' %
species grow best ata
temperature that is not
much above freezing ;
others grow best at
higher temperatures. Fic. 54. Showing the effect of variations
Most of the common in temperature on bacteria growth. a,
household types require a single bacterium; 4, its progeny in
considerable warmth for twenty-four hours at 50°; ¢, its progeny

7 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 @ is repre-
sented a single bacterium; at 4 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 ¢ 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

we ag ®
ete

128 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 125° 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 microérganisms
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 tem-
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 129

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 140° to 160°, if continued an hour
(usually a much shorter time), being ordinarily 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 skort boiling, a boiling of a few hours
is sufficient to destroy all but the most resistant spores.
Any material, therefore, that can be boiled for a consider-
able length of time may ordinarily be thus sterilized, that
is, may have its actively growing bacteria and their spores
destroyed at the same time. This great resistance to
heat on the part of bacterial spores is a matter of much
importance to the housewife, and she should fully
realize it. 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 do¢/ing in its preparation is thereby, in a

130 BACTERIA, YEASTS, AND MOLDS

measure, protected from spoiling, since the bacteria are
mostly killed. But if the food is simply wavmed,' 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 its 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 once common habit of closing blinds and
using heavy curtains or shutters to keep out the light
was 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 were too common in our
houses in former 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 131

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 anaérobic; the former, which demand oxygen,
are called aérobic. The aérobic bacteria are by far the most
important in the affairs of the household, but the anaé
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 microérganisms 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 ordinary
canning it is not the exclusion of air that makes pres-
ervation 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 much growth, and a still larger amount 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

132 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 133

arise from clothes and skin. In the air of schoolrooms
or audience rooms the number of bacteria is large, 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 Cae BG
dust; but among the dust @ } lex
f

particles we may be sure to
find bacteria in great num- a
bers. In short, all air in the d ®e

vicinity of habitation contains
bacteria. The air of high
mountains far from the habi-

. ‘ i a, Pseudomonas fluorescens ; b, Bacillus
tation of animals is found prodigiosus; c, Pseudomonas janthi-
to be moderately free from =; @, Proteus vulgaris; ¢, Micro
these ubiquitous organisms, “7% @@H# f Bacillus col
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 microdérganisms.

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 artestan

Fic. 55. A group of bacteria
from water.

134 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 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 135

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 ag } 99@em
rapidly as we pass below the sur- ee POCO
face, until at the depth of a com- G72 00 ip
paratively few feet they practi- WY 1
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 Fic. 56. Soil organisms.
animals, or in soil that contains 4, Bacilles subtilis; 6, B. cereus ;
decaying roots of ordinary plants. oo
They are immensely numerous _ ganism; / nitrite organism; g,
in the vicinity of earth closets — ##aeters 4; an Actinomyces
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

136 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

Fic. 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 137

is filled with them; sour mi/k 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 may become 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 Fic. 58. Bacteria from the
to find them in our mouths, stom- **¢th of @ healthy 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.

Can we escape from Bacteria? Bacteria, in short, are
practically 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,

138 BACTERIA, YEASTS, AND MOLDS

particularly milk. So ubiquitous are they that it is an abso-
lute 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 common
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 through the room,
only to settle down again later. On the other hand, wiping

Fic. 59. Petri dishes exposed, one, a, before, and the other, 4
after a class has occupied a schoolroom.

with damp cloths removes the bacteria and this is a proper
method of cleaning. This is especially true for kitchens and
pantries where food is exposed to the air, and for school-
rooms 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. These facts forcibly show the advantage of vacuum
cleaners, which remove the dirt without stirring up the dust.

RESULTS OF BACTERIA GROWTH 139

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, protetds (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

140 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 hodies
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 I4!

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 microdrganisms
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 XI

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 ot
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. ads 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.

142

FOODS OF BACTERIA 143

The food most readily attacked by the majority of bac-
teria is the class known as protezds. 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.

144 BACTERIA, YEASTS, AND MOLDS

Tue EFFect oF BACTERIAL GROWTH UPON Foop

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 todo 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 145

New Propucts

Decomposition Products. When a house falls to pieces
after burning, a mass of débris 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 débris
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;

}
J

146 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 débris 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 147

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

148 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 flevor 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 149

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- es
trefaction. Even the hard cheeses show SMS
this same characteristic, though there is (.3=
less similarity to putrefaction. Neverthe-

less the taste of the hard cheese is prob- Fi6.60. Bacterium
ably, at least in part, due to the beginning setae Nate
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
incipieht 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

150 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 microérganisms. 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 microdrganisms.
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 151

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 uport-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.

Fic. 61. Bacteria producing vinegar.

152 BACTERIA, YEASTS, AND MOLDS

Although they are not bacteria a word may be said in
regard to the vznegar 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 153

fine 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 ditfer-
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

.

154 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. Household
incinerators specially designed for consuming moist garbage
and similar material are now available. Where possible this
is the best means of getting rid of the waste.

A common 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 155

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.

156 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 therefore
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 XII
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 microdérganisms, 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 formerly. To-day,
at least in all communities of even moderate size, these
problems have been largely solved for her by the market-
man, and she can buy her food in such small quantities
that frequently she does not need to consider the prob-
lem of preservation. The housekeeper of earlier days

157

158 BACTERIA, YEASTS, AND MOLDS

was confronted with many problems in the home 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 constantly
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
sooner 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 and milk 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 only a small proportion of the food she buys is
really fresh. The crowding of people together into cities
demands 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 city 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 159

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

160 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.
Flour is perfectly good
food for bacteria, and if
we only moisten it with

Fic. 62. Showing nature’s method of .
preserving seeds by drying. The upper Water, putrefaction and

figures are the fresh seed, the lower decay begin in a short

figures the same after drying for winter

preservation. 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 biscuits, or
crackers as they are called in the United States, the

PRESERVATION BY DRYING 161

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 microérganisms. 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. 7

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

162 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 ¢assajo. 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: (1) 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 163

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 /fishk, some-
times without salting, sometimes with an abundance of salt.
The heat of the sun, artificial heat, and smoking are all
employed. ussels and other shellfish are sometimes pre-
served by drying.

One of the most recent and most useful applications of
drying is in evaporating mz/k. Skim milk is easily dried
into a powder and will keep indefinitely without decaying,
souring, or molding. It is one of the cheapest as well as
most nutritious of foods. It does not quite take the place
of fresh milk, for when dissolved in water most dried milks
have a taste unlike milk. For baking, it is as good as fresh
milk, and is most excellent for camping parties. Whole
milk, when dried, does not keep so well, since the fat in it
becomes rancid in time.

The drying of eggs to a powder form has been success-
fully accomplished, and in this form they may be used for
all cooking purposes.

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 milk 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, 77ichina, 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

164 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 of fruzts, 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 todry. 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 165

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 mineral content has not been reduced, and
this is one of the most valuable aspects of fruit in our
diet. But most of us eat fruit for their flavors, rather than
for the sake of their dietary value. Dried fruit is much
inferior in taste and cannot be used for so many purposes
as fresh fruit. The drying of fruits and vegetables often
leaves a pulpy, somewhat tasteless substance, which 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

166 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.

UsEe oF Low TEMPERATURES

The value of low temperatures in preserving all forms
of food is familiar to every one. Microérganisms 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
100°, 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.

1. 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 167

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 preservation
of food. They are now found in all our large cities, and
they are being utilized more and more each year, pro-
ducing 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 being used more and more, and are produc-
ing a far more stable condition in the food supply. 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,
it makes little difference how long it is kept. 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

168 BACTERIA, YEASTS, AND MOLDS

food, particularly fruits, are ruined by freezing under or-
dinary conditions. 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. It has re-
cently been found that even fruit—or at least many
kinds of fruit — can be kept frozen indefinitely if kept in
a sirup containing the right amount of sugar. Another
method of freezing, applicable to fruit as well as various
other kinds of food, is a recently developed process known
as quick freezing. In this process the food is frozen almost
instantaneously by passing between two sheets of very cold
metal. Such frozen fruits taste almost like fresh fruit, but
must be consumed immediately after thawing, as they spoil
rapidly.

The cold-storage plant cannot be utilized by the house-
wife, although temperatures nearly as low can be obtained
in modern mechanical refrigerators. 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 winter, in a city market, she may
regard it as probable that they have come from cold stor-
age. This is a matter of considerable importance, because
of the practical question of the keeping properties of such
material.

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

MECHANICAL REFRIGERATION 169

must be used quickly, since it will putrefy more rapidly
than when fresh. This is partly due to the fact that food
just ready to spoil is placed in cold storage to preserve it.
Such food will spoil at once when removed from the freez-
ing temperature. Possibly, also, 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 actu-
ally frozen, the rapid decay which follows removal from
cold storage is due to the large amount of moisture which
condenses upon the surface of the cold fruit when it is
placed in warm or damp air. Such surface moisture, as
we have seen, furnishes the necessary condition for the
starting of mold growth. The practical 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 soon as possible, because putrefac-
tion and decay are sure to take place speedily. If not used
at once, it must be kept in an ice chest.

Properly controlled, cold-storage plants are of very great
value to the public. The objections to them are chiefly
two. They enable unscrupulous people to freeze food that
is ready to spoil, and therefore not fit for eating, and sub-
sequently to put it on the market. They also make it easier
to gather great quantities of foods in the hands of a few
persons, who, controlling so large a supply, can manipulate
prices. Except for these misuses, which can be controlled by
law, the cold-storage plant is a great boon to the consumer.

2. Mechanical Refrigeration in the Home. Of all house-
hold devices, the mechanical refrigerator gives the nearest
approach to cold-storage conditions. Several types of these

170 BACTERIA, YEASTS, AND MOLDS

are now on the market, differing considerably in detail but
alike in general principles. They all function through the
condensation and vaporization of a gas, the cooling being
effected by the drop in temperature produced upon vapor-
ization. The condensation is generally brought about
mechanically by means of an electrically driven pump,
although in one type the object is secured by heating the
gas at one point of the system by means of a flame and
cooling it at another by means of water. Whatever prin-
ciple is employed, the device enables the housekeeper to
obtain much lower temperatures than by means of ice.
Hence much more efficient refrigeration is available in the
household today than was possible in former years.

In the mechanical refrigerator the temperature within
the freezing coil is below freezing. That place is, therefore,
not suitable for preserving many kinds of food; but is
rather used for freezing water and desserts. A frozen des-
sert may, however, be preserved almost indefinitely if
placed in a pan inside the freezing coil. Just below or just
beside the coil, a temperature as low as 35° is easily ob-
tained ; in fact an electric refrigerator may easily be set so
that freezing temperatures are secured just beneath it.
Accordingly the space either below or beside the coil (de-
pending on the model of refrigerator) is designed for storing
very perishable foods, such as milk and cream. Milk kept
at a few degrees above freezing practically never sours, and
it is always a surprise to the housewife who has had no
previous experience with such low temperatures to discover
how long it will remain sweet in this type of refrigerator.
Other undesirable changes may occur at this temperature,
however; so it is hardly desirable to use, without cooking,

THE ICE CHEST 171

milk that has been kept more than three or four days in
such a refrigerator, even though it is still perfectly sweet
and shows no signs of decomposition.

In a well-constructed mechanical refrigerator the tem-
perature should not be over 40° anywhere. At such tem-
peratures most bacteria, if they grow at all, grow very
slowly; and kinds of food less subject to rapid decom-
position than milk (such as meat, vegetables, fruits, and
preserves) may be kept for a long time — as long as the
housekeeper ordinarily needs to preserve them. The atmos-
phere in a mechanical refrigerator is usually rather dry,
and vegetables are likely to wilt; so it is generally recom-
mended that they be kept in a tight container. Practically
all other kinds of food keep better than on ice.

3. 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 simply because the tem-
perature is higher. The temperature of ice chests is vari-
able, 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 tem-
perature 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. Food may be preserved for quite
a while, 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

172 BACTERIA, YEASTS, AND MOLDS

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 microdrganisms favored by the low tem-
perature. This decayed meat appears somewhat different
from decayed meat at higher temperatures and has a dif-
ferent odor — a fact indicating a different type of putre-
faction. Certain peculiar kinds of decay are seen at these
low temperatures which are hardly found under other
conditions. Occasionally, for example, fleshy foods, par-
ticularly those from salt water, like lobsters or fish, develop
a peculiar phosphorescence if kept in an ice chest. If exam-
ined 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 tem-
peratures. They grow chiefly upon foods which contain
considerable salt, and hence particularly in marine foods.
They are more likely to be found in meat preserved 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 not necessary to throw such
food away, since the phosphorescence does not appear to
render 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

THE ICE CHEST 173

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 slight lowering of the temperature that food in the
ice chest will spoil. Some form of refrigeration is almost a
necessity in the household in order to preserve foods which
must be kept from a few hours to a day or two before they
can be used. This is especially true of the preservation of
milk, a topic which we shall notice by itself.

In much of America the ice chest has long been an
almost universal aid in the housekeeping of families in
moderate circumstances, but at present, in the homes of
considerable means, it is being largely replaced by the
electrical refrigerator. Very few families now have to do
without either type of refrigeration. The home with a re-
frigerator 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 supplies, and can therefore buy only such small quan-
tities 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.
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 pre-
serve food properly.

174 BACTERIA, YEASTS, AND MOLDS

4. 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: (1) The
temperature is usually Jower 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 freezing.
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
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-

THE COOL CELLAR 175

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.

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
of the water from the leaves lowers the temperature. This
principle is often made use of to cool drinks and small
lots of food by keeping them in unglazed earthenware
receptacles the surfaces of which are constantly moist.
The evaporation of the water on the outside cools the in-
closed liquids. In the same way automobile tourists keep
water cool by suspending it outside the car in porous
canvas bags.

Cooling may be used for any kind of food. Three gen-

176 BACTERIA, YEASTS, AND MOLDS

eral 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 stor-
ing, for such food when warmed decays rapidly.

THe Usre or 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 insufficient heat 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 pre-
served 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 pre-
serve the material indefinitely; it simply delays the
spoiling. It kills the bacteria present, but others can get
in later.

CHAPTER XIII
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
co the food something which will check the growth of
microédrganisms and thus prevent decay. Such preserv-
atives must fulfill two conditions: (1) 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 microdrganisms 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 microdrganisms are also poison-
ous to man and therefore cannot be used in his foods.

177

178 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 prevent
decay 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. These various commercial products differ in their
chemical 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. At one time a num-
ber of such products were sold quite generally, under special
trade names; but to-day one rarely finds them offered for
sale by retailers in the United States. They are now known
to be of questionable value. They are undoubtedly effi-
cient in protecting food from putrefaction and decay, for
they all check bacterial growth. If used in sufficient quan-

COMMERCIAL PRESERVATIVES 179

tity 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. It is
easy to see how a housewife, after trying them once, might
find them so convenient as to give up entirely the use of
a refrigerator or other devices for keeping food cool, be-
lieving it cheaper as well as more convenient and more
satisfactory to employ a preservative than to use ice. The
various forms of preservatives may be used for almost any
kind of food,— for canning fruits or vegetables, for preserv-
ing 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 was 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 Canada 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

180 BACTERIA, YEASTS, AND MOLDS

own country is less necessary, 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 181

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, have 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,! and they must also be condemned in the house, since
even in small quantities it is possible that their daily use
may cause trouble. No housewife should therefore depend
upon any of these forms of preservation for her food. They
are unwholesome and even dangerous, and their use is
likely 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. It is a very mild preservative, however, and there is some question
as to its value. Some states still forbid its use; and products, such as to-
mato ketchup, on the markets of these states seem to keep as well as those
with a benzoate as sold in other states.

182 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.

Nonroisonous 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
microdrganisms 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 183

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% 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. Ata moderate heat the
fruit is so thoroughly impregnated with the preservative
that no putrefactive organisms are subsequently able to
growin it, and it may then be preserved almost indefinitely.
Marmatades 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, plums, 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

184 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 dine, 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.
ffams 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 duz¢er 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 microérganisms.

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

VINEGAR AS A PRESERVATIVE 185

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. This is especially true since
they are lacking in the vitamin which prevents scurvy,
a trouble frequently met with among sailors who have
subsisted too largely upon salt foods. Nevertheless such
foods are very useful, and if a sufficient quantity of fresh
food (or even powdered lemon, as used by recent polar
expeditions) is consumed 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: (1) 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,
the microdrganisms will be destroyed, the trouble may

186 BACTERIA, YEASTS, AND MOLDS

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. Metal covers
are especially undesirable, for the same reason. 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. Sauerkraut,
for example, is cabbage protected from putrefactive fer-
mentation by allowing it to sour in the presence of con-
siderable salt, with the production of acetic and lactic
acids. 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 putre-
faction. Here we actually have an instance of a harmless
kind of microédrganism 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 pre-
served from further decay, while dill pickles are similarly
made from cucumbers.

Any substance can be preserved from bacterial action
if it can be soaked in vinegar or other acid, and it is there-
fore possible in the household to convert into either sour
or sweet pickles a considerable variety of vegetables.
In actual practice the use of vinegar for this purpose is
very limited, mostly confined to green fruits and vegeta-
bles, 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 187

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 microdrgan-
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

188 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 XIV
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.
189

190 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: (1) 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 zudefinitely. 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 microérganisms. 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.

1. 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 19t

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 heated. 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. 1. It must be remembered that the destruction of
the organisms capable of growing in the particular food to
be canned must be absolute. If a single individual micro-
organism is left alive in the food after the boiling, and finds
conditions favorable to its growth, the whole process is use-
less and the canning will be a total failure. One live bac-
terium, capable of growing and multiplying, can produce
a subsequent putrefaction and destruction of the food with
just as great certainty, though not so quickly, as if a million
of them were left alive. Therefore, unless the food contains
substances which inhibit bacterial growth, the preliminary
heating must be a complete sterilization, that is, a heating
so thorough that every individual bacterium is destroyed.
No halfway 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

Ig2 BACTERIA, YEASTS, AND MOLDS

this complete destruction. If a housewife finds that a portion
of her canned preserves is spoiled, she may infer 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 acids that act as partial anti-
septics, 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 ¢omatoes has always given trouble to the
housewife. In former years it was thought to be an

DIFFICULTIES OF CANNING 193

impossibility to can green corn, and the preservation of peas
and deans has proved to be even more difficult. These
products are successfully preserved to-day, but until home
canning was stimulated by the war-time food shortage they
were rarely canned except in factories, for they are far
more difficult to preserve in this way than foods containing
considerable amounts of sugar or acid. The problem of
canning any product, whether it be fruit, tomatoes, corn, or

peas, is simply that of totally destroy. WH
——]

ing the microorganisms present that @
. . SS 2
are capable of growing in that par- A, oo fe
ticular food. If the material, like a2 ~
P 7 6
most fruits, contains so much sugar geo is S598

or acid that only yeasts or molds are @ UM, OP BBB
able to grow in it, preserving is quite “¢ r)
easy, because simple boiling kills Fic. 63. Spore-producing
these organisms. Corn, peas, and _ >acteria found in canned
beans, however, not only furnish a wee
favorable environment for the growth of bacteria, but also
are sure to contain bacteria which develop spores (Fig. 63)
and can therefore resist considerable boiling. If two or three
or even one of these highly resisting spores survives, the
canning may prove quite ineffectual. Tomatoes contain con-
siderable acid but little sugar, and therefore stand midway
between these two groups of foods. Ordinary boiling is
generally sufficient to preserve them, especially if sugar be
added, but they are more likely to spoil than are fruits.
The remedy in all such cases is higher or longer heating,
since no satisfactory means of destroying bacteria is known
except the application of heat. Even spores may be destroyed
if the proper method is adopted,

194 BACTERIA, YEASTS, AND MOLDS

Higher Heat. Common liquids, when boiled in open ves-
sels, 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. If the material is
boiled under pressure of a few pounds only, a sufficient tem-
perature is obtained to destroy the spores in a comparatively
short time. Household devices for cooking under pressure
are now on the market, but as they are rather expensive,
this method of sterilizing is in common use only in canning
factories. This method of heating is called “ processing”
and is very efficient.

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 material
is boiled for a sufficient time, the spores are- eventually
totally destroyed. The length of the time necessary is often
as much as two or three hours and depends very largely
upon the vigor of the boiling and the nature of the food
(see page 201),

Intermittent Heating. Sometimes a better product is
obtained if, instead of boiling once for a long time, the
food be boiled for shorter periods on three successive days.
The principle upon which this method depends is that the
spores not killed by the first day’s boiling will germinate
and be in a condition to be readily destroyed the second
day, while the third day’s heating takes care of the few that
escape both previous heatings. This is known as “‘ frac-
tional” sterilization, because only a part of the bacteria are
destroyed at each heating. The length of boiling necessary
on each of the three days varies with the kind of food it
is desired to preserve.

HERMETICAL SEALING

195

2. Preservation. After the food has once been deprived
of bacteria (sterilized), it must be protected from the

subsequent access of all kinds of microérgan-
isms. Since bacteria are always present in the
air, any of these sterilized products will surely
be reinoculated if exposed, and the new bac-
teria would soon spoil the food. Therefore
the practical method of keeping bacteria out is
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. Bacteriologists
have found that the air which passes through
cotton is deprived of all bacteria. If, there-
fore, any sterilized material is placed in bottles,
tubes, or vials which are tightly plugged with
cotton, as shown in Fig. 64, it will be per-
fectly protected from the invasion of bacteria.
A knowledge of this fact may be of some
practical 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
ordinary canning of food. At best it is of
only temporary utility, for though cotton keeps
all bacteria away from the sterilized material,

WF “Regs bie

Fic. 64. Pre-
served cher-
ries, showing
that the ex-
clusion of air
is not neces-
sary for pres-
ervation.

it will not wholly exclude molds, and, moreover, allows the
material to become dry. Hermetical sealing keeps food

moist as well as sterile.

196 BACTERIA, YEASTS, AND MOLDS

Hermetical sealing, which will prevent all subsequent
access of air, is extremely easy to accomplish and is thor-
oughly effective. The material must be sealed in some
proper receptacle whzle 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 numerous. In
earlier days the housewife employed ordinary bottles, which
were filled with the material, then plugged tightly with corks,
and sealed with rosin
or something of the
sort to exclude all air,
The invention of the
modern fruit jar with
its rubber ring and con-
venient top has done

Fic. 65. The top of a common fruit jar; « away with all such
is the rubber ring upon which the success crude devices. The

of the sealing is dependent. ie sale he .
fruit jar with its vari-

ously devised top (Fig. 65) is a perfectly effectual means of
excluding air and hence for keeping out all microdrganisms.
The significant feature of these fruit jars is the rubber ring
a, which is clamped tightly upon a flat ledge on the jar ¢
by means of the cover 4, so made that heavy pressure can
be exerted upon the rubber. This pressure upon the rubber
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 softness and elas-
ticity of the rubber; if this gets hard, as it will in a few
months, the sealing will not be as effectual. Of course com-
plete sterilization of the jar must be assured. In the cold-pack

THE FRUIT JAR 197

method (see page 200) this takes care of itself, as jar and
contents are sterilized together. In the open-kettle method it
is best to place the jar in cold water before filling, to bring
the water to a vigorous boil, and then to fill the jar while
still hot. Pouring boiling water into the jar is a simpler
method, but is not quite so certain.

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, however, 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 into
the tin can, upon which a cover is placed and sealed firmly,
the whole now being closed to the air except for a small
opening in the cover. Then the can, with its contents, is
placed in a convenient heating apparatus for thorough sterili-
zation. Open boiling or pressure heating is used, according
to the temperature desired; in the former case the small
opening in the cover is not sealed until after heating, to
allow the escape of steam, while in the latter case the cans
are entirely sealed before processing. Cans are kept under
observation for a while to make sure that sterilization has
been complete, and any cans found to be swollen from the
accumulation of gas within are discarded as ruined. Canning
factories have sometimes suffered great financial loss from
the spoiling of their products, ordinarily because some highly
resistant spores have survived. Canners know to-day that
the remedy in such cases is the application of greater heat,
and thus are able now to avoid in great measure their losses
of previous years,

198 BACTERIA, YEASTS, AND MOLDS

In canning certain kinds of food it has been customary
to add some mild antiseptic to aid in the subsequent pres-
ervation. Borax, for instance, has frequently been used to
check the development of any bacteria that may be left in
meat after the process of canning. 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, although benzoate of soda is
allowed in certain foods. In household canning it may be
given as a universal rule that no preservatives of any sort
should be used.

Practical Suggestions. Nearly any type of food can be
preserved by canning. Some materials, however, are very
much more easily preserved than others. Meats are pre-
served 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

PRACTICAL SUGGESTIONS FOR CANNING 199

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 ordinarily of corn, peas, and beans.
All these materials may be canned successfully in an ordinary
household, but it requires long heating and special care, and
at best there will be many failures. Consequently such mate-
rials, 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. When more of these
vegetables are raised in the home garden than can be eaten
during the summer, it may become profitable to can them at
home. During the last war and a few years immediately fol-
lowing this was particularly true because of the food shortage
caused by the war, But except under such conditions it is
better and cheaper to depend upon the market for canned
corn, peas, and beans. The market products are more reli-
able, under ordinary conditions considerably cheaper, and
usually nearly or quite as good as those obtained by home
canning.

Most forms of fruit— apples, pears, cherries, peaches,
grapes, berries, etc., and even tomatoes—are so easy to
can that it is generally economical and advantageous to
preserve them at home. Material canned at home is usu-
ally of a better flavor, because more carefully prepared, and
is more satisfactory than much that can be bought in the
markets, in the preparation of which wholesale methods are
necessary. For the household, therefore, canning is most
satisfactory in the case of fruits, and it furnishes a means
of kééping for winter use many delightful delicacies,

200 BACTERIA, YEASTS, AND MOLDS

The Open-Kettle Method. The old household method of
canning is to stew the material to be preserved, generally
with the addition of considerable sugar, and then after a
short boiling to pour it while still hot into jars that have
previously been sterilized by boiling. The jars are sealed
and the process is complete. This method is applicable
principally to fruits that contain so much acid and sugar
that the bacteria whose spores resist the boiling are unable
to grow. Tomatoes are generally put up successfully by this
method, although not so easily as fruits.

The Cold-Pack Method. By the newer methods of canning,
as recently advocated by the Department of Agriculture, the
food is placed in the jars before heating and is sterilized
in the jars. Sterilization is accomplished by heating under
steam pressure, by protracted boiling, or by the intermittent
method (see p.194). The finished product is generally im-
proved if the food is dlanched before packing in the jars,
that. is, immersed in boiling water for a short time and then
dipped: once or twice into cold water. This method is appli-
cable to fruits. and to nearly all vegetables, but for fruits its
advantages over the hot-pack method are perhaps not suffi-
cient to recommend it to the housewife who is familiar with
the older method. For different foods different periods of
heating are recommended, as shown for some of the more
important fruits and vegetables on the next page. For full
particulars the reader is referred to the circulars of the
Department of Agriculture. :

Even the cold-pack method does not. susie assure pres-
ervation. Some loss must be expected, both through spores
that escape sterilization and through bacteria that find en-
trance on account of careless handling or poorly sealed jars.

COLD-PACK METHOD 201

TIME TABLE FOR COLD-PACK METHOD OF CANNING, AS
RECOMMENDED BY THE DEPARTMENT OF AGRICULTURE

(Time given in minutes)

sTo1 | so TOs | INTERMITTENT, IN
Hot- | Pounns | Pounps | Hor-Warer Batu
Foop BLancy| WaTER pt
BATH Steam | Stream | yop 2p 3D
Pressurz| Pressure] Day | Day | Day
Corn (sweet) . . . 5 180 go 60 go | 60 | 60
Corn (field). . . .| 10 180 60 50 go | 60 | 60
String beans . . . | 5-10 | 120 60 40 60 | 60 | 60
Shell beans and peas | 5-10 | 180 60 40 60 | 60 | 60
Squash and pumpkin 3 120 60 40 60 | 60 | 60
Asparagus . . . .| 15 120 60 40 60 | 60 | 60
Root vegetables . . 5 go 60 40
Tomatoes ... . th 22 15 10
Apricots and peaches | 1-2 16 10 5
Cherries and berries 16 Io 5
Apples and pears .| I¢ 20 8 6
Preserves. a 20 10

In canning some kinds of food (dried beef, jellies, etc.)
that would be injured by the high heat necessary for sterili-
zation, certain packers assist preservation by partially extract-
ing the air from the jar. Such food keeps fairly well, though
it is not sterile. It will spoil rapidly if air be admitted to
the jar, and at best does not keep quite as well as foods that
have been actually sterilized.

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 upon salted foods,
which were the staple diet on shipboard before the extended
adoption of canning. Canned foods are not so rich in vita-
mins as fresh foods, but their vitamin content is seldom

202 BACTERIA, YEASTS, AND MOLDS

completely destroyed. Different kinds of foods differ in this
respect. Thus the vitamins of tomato seem especially re-
sistant to heat and are present in abundance in the canned
product. As explained on page 85, there are several kinds
of vitamins, each with its own function in physiology, and
their exact chemical nature is not yet wholly understood.
More accurate information is gradually accumulating in
regard to them; and it is not impossible that we will soon
know more definitely which foods suffer most in this respect
on heating, and why their vitamins are more readily de-
stroyed than those of other foods.

For the present one can merely speak a word of caution
against making canned food one’s only diet; but as this
is never done in ordinary civilized life, canned goods can
be regarded as very useful and perfectly safe food products.

CHAPTER XV
THE GROWTH OF BACTERIA IN FOODS

BaAcTERIA IN MILK

It is more difficult to maintain a supply of good milk
than of almost any other food product. This is due to
three reasons: (1) 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 comprise many kinds (Fig. 66). Milk may contain
bacteria while still in the udder, and it has a further
chance of contamination with microédrganisms from a vari-
ety of sources, so that a few minutes after the milk has
been drawn it may contain organisms in large numbers.
The chief sources of these organisms are (1) the bacteria
in the milk ducts, which are washed into the milk can
during the milking; (2) the dust that is likely to be float-
ing 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
203

204 BACTERIA, YEASTS, AND MOLDS

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 incredible
numbers. The
exact numbers,

Fic. 66. Milk as seen under the microscope, show-

ing numerous bacteria. a, common lactic acid
however, are mat- bacteria; 4, gas-forming bacteria; c, strepto-
ters of no special cocci, causing mastitis; ¢, fat globules; ¢, a cell.
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

BACTERIA IN MILK

205

milk belong to a type known as /actic-acid 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,
can be kept out of the milk.

ca)
Hee R80 “Been
886 RPO §yo%0
7 fo) ae
2 3
“ee
‘RY LG
¢ “2F EES
Py ¢ ad
ao”, —_ =,
a ae ze
Ro, 7 AGS
ce °
By ee
9 = fo
Fic. 67. Group of milk bacteria.

x, the most common lactic bacterium, 2B. Zactis
acidi; 2, a less common lactic bacterium,
B. aerogenes; 3, common cocci found
in milk; 4, a bacillus producing cheese
flavors; 5, a common bacillus with no action
on milk, B. subtilis; 6, a bacillus causing
slimy milk, B. Zactis viscosus ; 7 and 8, com-
mon organisms with no action on milk; 9,
bacillus causing swelling of cheese; 10, a
bacillus causing milk to become putrid.

Curdling and souring will never occur if bacteria

Although the souring is a
nuisance, it'does not injure
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
putrefaction is far more
unpleasant and unwhole-
some than ordinary sour-
ing. The souring of milk,
therefore, is a natural phe-
nomenon, and one that
should be expected and

desired in milk after it has become a day or two old.
Milk which will not sour is suspzczous, unless it has been
kept at a very low temperature for preservation.
Sometimes milk a day or two old becomes sdmy or
slippery to the touch, rather sweetish to the taste, and is

206 BACTERIA, YEASTS, AND MOLDS

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 dlue
or ved, 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 microdrganisms 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.

1. 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

TYPES OF CITY MILK 207

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 milk, 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 proportion
to its cost, we notice the kinds of milk that are to be had
in the modern city.

Grocery Milk. The poorest kind of milk that can be
purchased is that which the poorer classes use in a few of
our large cities. It is bought in small quantities from
grocery stores. This method of. purchasing is perhaps a
necessity for the poorer classes who have no refrigerators,
for in warm weather it is quite impossible to keep milk
without ice. The store keeps the milk on ice, and the
customer buys it in such quantities as can be consumed at
once. This would not be a bad arrangement if it were not
for the fact that the poorer kinds of milk generally reach
these stores, and that the milk is likely to be kept in the
stores till it is old, under conditions which make contamina-
tion and even watering very easy. As a rule this grocery
milk is the least reliable of any milk on the market. It is
sold for a small price but is proportionately of poor qual-
ity, and it would be better economy for the poorer classes
to purchase a better grade. Its sale is now forbidden by
law in most of the large cities of the United States.

208 BACTERIA, YEASTS, AND MOLDS

Milk from Ordinary Milkmen. The milk from the or-
dinary milkmen varies very greatly in quality, sometimes
being of a very high quality and sometimes very poor.
There is no way in which the consumer can tell by look-
ing at the milk whether it is good or not. Public statutes
and public officials endeavor to guard the milk supply for
the benefit of the public, and have so far succeeded that in
general the watering and skimming of milk are rare. Chemi-
cally, market milk is usually well standardized; but cleanli-
ness, freshness, and general wholesomeness are more difficult
to guarantee by any form of public inspection. As a result
much filthy milk, quite unfit for consumption, is constantly
sold. It is certain that a considerable part of the deaths
of infants is directly caused by old or filthy milk.

A method of meeting this difficulty has now been adopted
in many progressive communities by a system of grading.
This consists of having each bottle labeled with a large
letter which indicates its grade. The grades adopted are
A, B, and C. The exact meaning of these grades varies
slightly in different localities, but in general they signify
the following: Grade A is milk of the best quality, pro-
duced in a cleanly fashion, free from disease germs and
fitted to be used raw as an infant food. It may be sold
either raw or pasteurized, but must be marked to show
whether or not it has been submitted to pasteurization.
In many communities Grade A pasteurized milk is not
sold, as there seems little object in taking expensive pre-
cautions to prevent contamination of the milk if it is to be
pasteurized and the disease germs in it thus killed. Grade B
is milk of an equal food value, but the production of which
has not been surrounded by quite so great precautions.

GRADING OF MILK 209

Its pasteurization is required; and therefore, although
perhaps not so clean or fresh as Grade A milk, it is safe
to drink and generally contains fewer living bacteria than
Grade A raw. In many communities it is really preferable
to the latter, although it costs less. It is usually a good food
even for infants, provided some other article (for example,
orange juice) is included in the diet to make up for any
deficiency in the milk due to the heating. Grade C milk is
that of lower quality, which is sold for cooking purposes
but not for drinking. In many communities Grade C milk
is not sold; and thus the purchaser finds himself limited
to a choice between Grade A raw and Grade B pasteur-
ized milk. This grading system enables the purchaser to
know what he is buying, and has proved a great benefit to
the consumer as well as to the milk industry wherever it is
adopted. It is necessary, however, to learn whether the
grading is done by public officials or by the milkman. If
the milk producer or the dealer places the label ‘“‘Grade A”
on his bottles, it means nothing; if the grading is done by
official inspectors, it means much. We cannot rely upon a
Grade A label unless it is authorized by the public milk
inspector.

Certified Milk. In most places in this country it is pos-
sible to buy what is called certified milk. The meaning of
the term is this: A small group of men, largely doctors,
constitute themselves a certifying board. Where any milk
dealer desires to use the label, this board carefully examines
the condition of the dairies from which the milk is pro-
duced, together with all methods of handling the milk, and
also makes frequent chemical and bacteriological analyses
of the milk. If the analysis of the milk and the conditions

210 BACTERIA, YEASTS, AND MOLDS

of its production come up to a specified very high standard,
the board gives the milkman the right to use the label
“Certified.” This label, therefore, carries with it the guar-
anty of extreme care in production. To carry out all the
requirements which these boards make involves much
expense in the production of the milk, and as a result the
milk sells for a very high price, two or three times the price
of ordinary milk. Such milk is certainly of the highest
grade, but it is doubtful whether it is any more valuable,
and it is certainly no safer, than pasteurized milk of either
A or B grade, provided it is protected by proper official
inspection.

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 clean-
liness 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
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 frequently
overlooks. Milk vessels should be cleaned with the greatest
of care and should be thoroughly washed with boiling
water (not simply hot) 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-

PRESERVATION OF MILK 211

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. Drying the milk vessels after wash-
ing is a process in which perhaps more care is necessary
than in the actual washing. If a well cleaned milk pail or
bottle is closed tightly immediately after washing and
wiping (or even inverted unclosed on a flat surface in such
a way as to exclude the air) enough moisture remains in
it to permit the growth of bacteria. Such a vessel after a
few hours is in a more filthy condition than before wash-
ing; if any one questions the statement, let him leave a
freshly washed milk vessel tightly closed half a day, then
open it and smell the interior! A milk vessel after scald-
- ing should be thoroughly wiped, and then allowed to
stand right side up and open to the air until next
used.

3. Temperature. The effect of temperature upon the
keeping of milk is more striking than its effect upon that
of any other food. Since milk may be frozen, it may be
kept in that condition for weeks, months, or even years
without change. Freezing has not, however, proved a prac-
tical method of preserving milk. But other means of cool-
ing are in constant use. Milk is frequently placed in a
cellar, since the temperature is lower there than in the rest
of the house. Another widely adopted plan, though not a
satisfactory one, is to lower the milk into a well, where,
since it is near the water, it is cooled. A more practical and
widely used device is the refrigerator, in which low tempera-

212 BACTERIA, YEASTS, AND MOLDS

ture can easily be maintained. The lower the temperature
the better the results; and, consequently, the more ice used
the better. The refrigerator has become a practical neces-
sity 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 sometimes sour almost as soon
as delivered to the customer. The housewife should there-
fore place the milk in as cold a place as she can find, im-
mediately after receiving it from the milkman. If she
does not do this, she must not blame the milkman if the
milk does not keep.

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 wholesome 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.
Now, although the lactic-acid 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 per-
fectly sweet and showing no trace of souring or curdling,
usually contains great numbers of bacteria. The bacteria
that grow under these circumstances may cause the milk
to become unwholesome, while the lactic-acid bacteria
are not injurious, although they render the milk unpleas-
ant. 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
undoubtedly wisest to discard the milk.

STERILIZATION OF MILK 213

In a mechanical refrigerator milk can be kept longer
than in an ice chest. The temperature close to the cooling
coil in such a refrigerator is only a degree or two above
freezing, so low as to prevent the growth of practically all
bacteria. Milk can retain its fresh taste seven days or more
under such circumstances, although it is not well to make
a practice of keeping it that long, as it may no longer be
safe to drink even though it is unchanged in flavor and
appearance.

4. Use of Preservatives. The facts given elsewhere con-
cerning the use of preservatives apply equally in the case
of milk. The use of any preservative is always to be dep-
recated, 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 possible
to keep the milk longer, but do not make it more whole-
some if it chances at the outset to contain any harmful
bacteria.

5. Preservation of Milk by Heat. Long before modern
bacteriology had explained the reasons for it, heat had
been used for keeping milk; and physicians had long
recommended the boiling of milk which invalids were to
drink, though they did not understand that the reason for
the heat was that it destroyed bacteria. In the use of heat
for this purpose two different methods may be mentioned.

(a) Sterilization. By sterilization, strictly speaking, is
meant the application of sufficient heat to kill ail bacteria
present in the milk. This can be done only by the use of
temperatures above boiling, by methods beyond the reach

214 BACTERIA, YEASTS, AND MOLDS

of a household. While a few years ago there were dairies
that did this, to-day the plan has been abandoned except for
certain forms of milk put up in cans, like unsweetened con-
densed milk. Such high heat makes decided chemical changes
in the milk which lower its food value.

A far more common method is simply to doz? the milk.
While this temperature does not kill all bacteria, still it has
been quite common to speak of it as sterilizing. In hot
weather milk is very often boiled to prevent its souring, and
in some European countries milk is never drunk without
boiling.

The purpose of sterilization is twofold. (1) It delays
the souring of the milk. Milk that has been boiled may
keep from souring for several days, whereas without boiling
it will keep only a few hours. With the poorer families 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 pro-
duced by bacteria in the milk, and boiling destroys them.
This is the ground upon which physicians and health boards
have in the past so widely advocated the boiling of milk
that is to be used for drinking. Since boiling does destroy
practically all the disease germs liable to be in milk, it
makes it incapable of distributing 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

PASTEURIZATION OF MILK 215

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 endure 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 diges-
tive powers, and many children are satisfactorily brought up
on it; nevertheless it is somewhat 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 fact has prevented the widely extended use of
sterilized milk.

(6) Pasteurization, The objections to boiling milk have
led to a different method of using heat for milk preser-
vation. Pasteurization has come into wide use in the last
few years. It consists of heating milk to a temperature of
145° to 170° and maintaining this temperature for from ten
minutes to half an hour, according to the temperature used.
In this country it is most common to use the lower temper-
ature of 145° for half an hour. After heating, the milk must
be cooled rapidly.

It may seem strange that the use of a lower temperature
should be more satisfactory than boiling, but the reasons
are simple. The chief results to be accomplished are to
make it possible to keep the milk longer and to kill all
disease germs, and at the same time not to affect the chem-
ical nature of the milk. A temperature of 145° for half an
hour destroys all the disease germs liable to be in milk,
kills most of the lactic-acid bacteria so that the milk will

216 BACTERIA, YEASTS, AND MOLDS

keep longer, and at the same time does not produce the
chemical changes which a higher temperature will. Pasteur-
ized milk at this temperature does not have the taste of
boiled milk and is as easily digested as raw milk.

In an ordinary household it is almost impossible to find
any servant in the kitchen who can satisfactorily use a ther-
mometer, and even the housewife herself would hardly under-
take to heat milk at a temperature of 145° for half an hour.

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

The only way it can be accomplished is by some device which
will bring about the result in a simpler way. The most con-
venient 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 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 proportioned to the bottles that, when properly
used, the milk is heated to about the temperature desired

PASTEURIZATION OF MILK 217

before it begins to cool. The method of using this pasteur-
izing apparatus is extremely simple and can be followed
satisfactorily in any kitchen.

Where such an apparatus is not obtainable, the same ob-
ject 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
occasionally be 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. :

The adoption of pasteurization has been very rapid in
recent years. The primary reason for this is the growing
realization of the fact that in no other way can the public be
protected from diseases distributed by milk. That it has been
found impossible to guard the milk supply so as to avoid
such dangers is shown by the fact that epidemics of scarlet
fever, septic sore throat, etc. have been traced to certified
milk, which has had almost all conceivable safeguards thrown
around it. Pasteurization alone renders it safe. Hence
we find some cities passing ordinances requiring all milk
to be pasteurized, except such as comes from tuberculin-
tested cattle. Hence too we find as a rule that Grade A
milk is sometimes pasteurized, while milk of Grades B and
C is always thus treated, to give the milk a guaranty of
safety. It is certainly unsafe to feed babies upon ordinary
unpasteurized market milk. For these reasons the pasteuri-
zation of market milk on a large scale has been rapidly

218 BACTERIA, YEASTS, AND MOLDS

adopted in the larger cities, until it is possible to purchase
pasteurized milk in almost any large community.

Pasteurization, to be really efficient, must be carefully done.
A lower temperature than 145° would be useless and indeed
sometimes might increase rather than decrease the numbers
of bacteria. One of the objections raised against the practice
is that in large dairy concerns the pasteurization is done
hastily and carelessly, so that the milk is injured rather than
benefited. To meet this objection various communities are
requiring that the pasteurizing apparatus and process shall
be under official supervision and control, thus insuring its
thoroughness. When pasteurization is carried out under
official inspection, the milk may be relied upon as safe. In
no other way can the public be guaranteed that its milk
supply may not spread contagious diseases.

Two objections have been urged against pasteurized milk.
The first is that it has a tendency to encourage carelessness
in handling the milk. The dairyman might feel that since
the milk is to be pasteurized, it is not necessary for him to
be particularly careful in its production and handling, since
any bacteria that get into it will be subsequently killed. This
objection is met by the growing requirement that the milk
must reach a certain standard of cleanliness and freedom
from bacteria before it is submitted to pasteurization.

A second widespread objection has been that pasteurized
milk is not quite so good a food as raw milk. This objec-
tion has been based chiefly upon the fact that pasteurization
as carried out in earlier years, at temperatures as high as
170° or more, did produce changes in the milk similar to
those produced by boiling, which rendered the milk less
easily assimilated by infants. This objection hardly holds

PASTEURIZATION OF MILK 219

against the American pasteurization temperature of 145°.
But even against this low temperature it has been insisted
that pasteurized milk is not suitable for infants as a sole
article of food. It has been claimed that pasteurization
destroys some of the vitamins normally present in milk,
those poorly understood bodies whose presence in our food
is so necessary. Hence it is insisted that babies brought up
on such pasteurized milk have a tendency to develop a mild
form of scurvy which children given raw milk do not have.
Whether this is true or not, it is no argument against the
use of pasteurization. It is an argument simply against milk
as a sole article of diet for infants; for when other foods
are included in the diet, or when vitamin-rich materials
such as orange juice or even extract of potato peelings are
added, the objection disappears. Doctors to-day, there-
fore, quite generally recommend that when pasteurized
milk is to be fed to babies orange juice should be given
either with it or separately. For adults nothing of this
kind is necessary, since adults feed upon a mixed diet.

It will be perfectly clear that the fact that pasteurization
of milk is the only way of insuring its safety is a sufficient
answer to the arguments against it, especially since all ob-
jections may be readily met by the methods above men-
tioned. Pasteurization is not a substitute for cleanliness,
but an added safeguard. The best milk for the home is the
cleanest milk obtainable, which should be subsequently
pasteurized to remove accidental dangers that may have
reached it, and used with a little orange juice if it is to be
fed to young children.

One caution should be given regarding the use of pasteur-
ized milk ; the milk must be used quickly after pasteurizing.

220 BACTERIA, YEASTS, AND MOLDS

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 method
of keeping it can prevent all bacteria from growing, and
although the use of refrigeration, pasteurization, or steriliza-
tion may keep it in a drinkable condition for a day, two days,
or even longer, it is always open to suspicion 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.

PRESERVATION OF Eccs

Eggs prove to be particularly difficult to preserve. They
are sure to contain bacteria inside the shell, deposited 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 certain 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

BACTERIA AND THE WHOLESOMENESS OF FOOD 221

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 THE GROWTH OF BACTERIA UPON THE
WHOLESOMENESS OF Foop

The question whether the growth of bacteria in the food
necessarily renders it unwholesome remains yet to be con-
sidered. 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
likely to eat food which has begun 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. A/cohol is in a sense a decomposition prod-
uct produced by yeast. It certainly is used to a very great
extent, and probably, when used only in small quantity, causes
no very considerable injury. Vinegar is also a decomposi-
tion product from the growth 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 developed in the curd of milk by

222 BACTERIA, YEASTS, AND MOLDS

the action of certain microérganisms. Sauerkraut is a
preparation which is allowed to undergo an incipient de-
composition the flavors of which give the peculiar character
to this food. That sauerkraut is a harmless food product
is, of course, perfectly evident. In gamy meat we have
flavors of decomposition produced by microérganisms. 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
harmful. These illustrations are sufficient to show that
the simple fact that food contains decomposition products
is not sufficient to make it unwholesome, since many de-
composition products are distinctly desirable in our foods.
The flavors of cheese in particular are very useful, for when
eaten with coarse bread they give relish to otherwise rather
tasteless foods.

ENCOURAGING THE GROWTH OF BACTERIA IN Foop

In all the food products mentioned in the previous sec-
tion, cheese, vinegar, and so on, the growth of bacteria is
actually encouraged. To what extent is the housewife
concerned in learning how to use bacteria in the manu-
facture of these foods? Vinegar is never made in the city
home, butter seldom, and few kinds of cheeses are home-
made products. Nevertheless certain of these processes
are useful to the housewife and should be understood.

Cottage cheese is often made at home. It is a very use-
ful way of saving milk that has soured. If the milk has
already soured before the housewife decided to make the
cheese she does not have to encourage the growth of bac-

BACTERIA IN THE PRODUCTION OF FOOD 223

teria, because they are not concerned in the manufacture
of cottage cheese except in the souring and curdling of the
milk. If the milk is sweet, it first has to be soured, which
should be done by placing it at a temperature of about
70 degrees for a day or two. The rest of the process is to
remove the curd and press out the whey. Other kinds of
cheeses are made from milk curdled with rennet instead
of by the action of bacteria, and these microérganisms
grow subsequently in the curd, and thus produce the flavors ;
but the process involved is not well adapted to home
manufacture.

Butter is seldom made at home, except on the farm.
When it is, little attention is paid to control of the bac-
teria. The cream is soured (ripened) by bacterial action,
and after that the process of churning is mechanical. If
the wrong bacteria take part in the ripening, the flavor is
bad; but a good flavor can be brought about without real
souring. In modern creameries the ripening process is
being continually shortened, till at present much cream is
churned while still sweet.

A food-making process dependent upon bacteria which
the housekeeper is much more apt to undertake is the
manufacture of sauerkraut or dill pickles. The principle
involyed in making both is the same. The cucumbers or
the shreds of cabbage are packed in a jar, with considerable
salt, and allowed to stand under a weight so that the juices
will be extracted. Fermentation then takes place. On
account of the salt, few of the decomposition bacteria can
grow, and acid-forming types develop something like those
that sour milk, although not the ordinary lactic-acid bac-
teria. These gradually change the nature of the cabbage

224 BACTERIA, YEASTS, AND MOLDS

or the cucumber until the flavors characteristic of sauerkraut
or dill pickles develop.

There is a trick to making sauerkraut, and by no means
all the homemade or even the factory product is satisfac-
tory. Sometimes it putrefies instead of merely souring, and
the flavor becomes disagreeable. One important factor in
preventing putrefaction is the quantity of salt employed;
one should use 2.5 per cent, that is, four tenths of an ounce
for each pound of cabbage. A second important factor is
the exclusion of air, as the desired bacteria grow in the
absence of air and the growth of other kinds must be
prevented. This can well be done by covering the jar with
a piece of cloth on top of which is placed a paraffined
board cut just to fit the jar. Weights are placed on this
to the extent of bringing the level of the juices up to the
board, but no higher. It should be watched carefully for
a few days, and weights removed or added so as to maintain
the proper level of the liquid. Using these simple precau-
tions any one should be able to make good sauerkraut.

BACTERIAL Potsons IN Foops

But, on the other hand, there are unquestionably such
products which are harmful and which, even though
present in small quantity, may be decidedly harmful or
even poisonous. When certain kinds of microdrganisms
grow in food material, they give rise to a class of decom-
position products which are sometimes, although from the
chemical standpoint incorrectly, called ptomaines. They
are usually the result of bacteria growing in animal prod-
ucts; and while some of them are quite harmless, others

BACTERIAL POISONS 225

are of an intensely poisonous nature. If such substances
develop in food, they may render it unwholesome or even
fatally poisonous. To such poisonous decomposition prod-
ucts are due instances of poisoning from eating cheese,
quite a number of which are on record. A similar cause
explains the still larger number of cases of ice-cream poison-
ing, when many people have been rendered seriously and
even fatally sick by the eating 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 XVI.) But in cases of
poisoning from eating food the bacteria grow simply im the
food. They do not live in the body nor do they produce
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 unknown 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 prob-

226 BACTERIA, YEASTS, AND MOLDS

ably due to the development of toxic substances in some
food products, since almost any of the putrescible foods
which come upon our tables may, in warm weather and
under certain circumstances, undergo a type of putrefac-
tion which gives rise to these poisons. When this occurs,
‘**ptomaine poisoning” is quite likely to follow the use of
the foods. It is probable that a large part of the summer
diarrhea so common in warm weather is due to poisonous
decomposition products developed in some of our foods.

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 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 sufficiently cold. We know that decomposition
products are more likely to give rise to toxic substances 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 prevent
bacteria from growing will prevent “‘ptomaine poisoning.”
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 well
remember that such poisoning is most likely to occur in
foods that have been kept for some time in a moderately
warm temperature.

BACTERIAL POISONS 227

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 preventing
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. When food begins to have the smell
of decomposition it becomes open to suspicion, although
this does not mean that it is necessarily dangerous, since
many of these decomposition products are quite harmless.
The food products that seem to give the largest amount of
trouble are ice cream and fish, and it is therefore desirable
to be particularly on one’s guard about their use in warm
weather and, if possible, to use only that which is fresh or
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 XVI
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 BActTERIA PRODUCE DISEASE

The disease germs are all capable of growing and multi-
plying in the body, but the habits of different species of
disease bacteria are widely different. Sometimes they be-
come 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 potsoning, or septicemia.
On the other hand, it sometimes happens that the micro-

organisms become located in very definite parts of the
228

DISEASES, HOW PRODUCED 229

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 ¢orzns. 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 (Aszatze 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.

230 BACTERIA, YEASTS, AND MOLDS

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, — an hour or two 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 day 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:

DISEASE BACTERIA 231

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 crists 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,

232 BACTERIA, YEASTS, AND MOLDS

whooping cough, typhoid fever, diphtheria, grippe, tonsilitis,
etc., protects the individual for a time from a second attack.
The protection lasts much longer in séme 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 virulent 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

DISTRIBUTION OF CONTAGIOUS DISEASES 233

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 ConTaGiousS DISEASES

While these problems are of the utmost importance in
every household, hygiene does not properly belong to
the field of our study. 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 microérganisms, 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 microdrganisms are so abundant in the air that they
are sure to get into any exposed bit of food, and we have

234 BACTERIA, YEASTS, AND MOLDS

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.

DISTRIBUTION OF CONTAGIOUS DISEASES 235

1. The causes of these diseases are veal ¢hings 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 moisture in the air
may harbor 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 aive; 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

236 BACTERIA, YEASTS, AND MOLDS

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 and grow.

CHAPTER XVII

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
237

238 BACTERIA, YEASTS, AND MOLDS

sense contagious but produced by parasitic organisms which
may under peculiar conditions pass from individual to indi-
vidual. Prominent among this last class are malaria and
yellow fever, diseases 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, indeed, like measles and mumps,
while almost certainly caused by microérganisms of some
sort living in the human body, have not yet been satis-
factorily 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 likely 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: (1) The
microérganisms which produce the disease must find some
means of exi¢ 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. For a proper understand-
ing, therefore, of the way to handle contagious diseases
in the home we need to consider these three factors.

MALARIAL PARASITES 239

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.

1. 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
this should always be the first point inquired into in the
practical study of any contagious disease. 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 a second. Malaria,
chills and fever, and fever and ague are all names for
the same disease, produced by a microscopic parasite living
in the human blood. Growing there, it develops poison-
ous 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, 1) which enters the blood corpuscle. Inside this
corpuscle it grows, and finally breaks up into many little
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

240 BACTERIA, YEASTS, AND MOLDS

(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

Fic. 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 9a, which develop in the mosquito.
10 shows the union of the female sex body, 9, with one of the flagella of 9a. 11-15
show the development of the united mass, 10, in the body of the mosquito, finally
producing spores such as shown at 1. 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

MOSQUITOES AND MALARIA 241

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

o” avr
4 XX Yt ie F ad
a { | °
Ee;

Fic. 70. a@, the harmless mosquito (Culex); 4, the malarial
mosquito (Anopheles). a’ and a” show the position of the
harmless mosquito when lighting on the floor or on the
wall; &, 3” and 6’” 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, 4) 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

242 BACTERIA, YEASTS, AND MOLDS

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 one special kind of
mosquito, and at the present time it seems as if all 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, 6, 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 jive delicate hairlike

MOSQUITOES AND MALARIA 243

feelers on the head of the dangerous speciés, rather than
three, as in the harmless form (Fig. 70, a and 6), and the
method of lighting with the body held in a straight line
(Fig. 70, 6’, 6”, 6"), rather than bent, as in the harmless spe-
cies (Fig. 70, a’ and a'’). It must also be remembered that
not all mosquitoes, even of the harmful species, will be dan-
gerous. Only those that have sucked the blood from mala-
rial 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
belief that night air is dangerous. It is not the night air that
produces the trouble, but the mosquitoes in the air. It is also
evident that the best method of protecting a household from
malaria is by the use of screens. It is a curious fact that their
use at our windows and doors is the best protection from these
microscopic parasites, inasmuch as screens or mosquito net-
tings 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 experi-
ment that the simple procedure of covering doors and win.
dows of houses with mosquito netting has produced a marked
decrease in the amount of malaria in these dwellings.

244 BACTERIA, YEASTS, AND MOLDS

It has been proved recently that yellow fever also is dis-
tributed by mosquitoes rather than by direct personal con-
tagion. 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 pre-
venting the mosquitoes from biting them and becoming
infected with the germs which they might carry to other
persons. It has also been banished from the Panama
Canal zone by draining the swamps and closing up the
breeding places of mosquitoes ; and the last time that yellow
fever invaded the United States it was speedily crushed out as
soon as active measures were taken to destroy mosquitoes
and prevent their breeding.

In all truly contagious diseases the parasites have some
means of leaving the body of the patient. Their methods
of exit are numerous, but are not very diffi-

» (>. cult to determine in the case of any particular
i «ru? 4 disease. Most es of contagious diseases
’ P §
\ § have suggestive symptoms. For example, in
XQ 88 ymp Pp
eras smallpox, there is an eruption of the skin,

Fic. 71. Bacillus

i is
oA atpheiatie and it becomes probable at once that th

eruption is a means of elimination of micro-
organisms. 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 eliminating

ELIMINATION OF GERMS FROM PATIENTS 245

the infectious organisms. The same is true, probably, of
measles, tonsilitis, and grippe. In consumption, infectious
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.
In typhoid fever and cholera the most dis- .
tinctive characteristic of the disease is the Daa
diarrheal discharges from the alimentary canal, py¢ 72. Mos-
and this suggests that the feeces may be the quito that
source of exit of infectious material. Thus, spreads yeh
though contagious diseases differ very much Ren
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 bé
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

246 BACTERIA, YEASTS, AND MOLDS

by direct contact. In such a disease as smallpox, 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, isola-
tion is rightly considered of the greatest importance (see
page 269).

With many diseases, however, other means of transference
are more common, The microdrganisms 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

oe malaria and yellow fever has been mentioned,

° Bsa) and lies have a very close relation to the dis-
00S tribution of typhoid fever. So close is this rela-
cl ans tion that it is now urged that the name ¢yphoid
onic plagaa, Jy should be used. Fleas, also, distribute the
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 and
lice, to shun mosquito bites and flea bites, and, in short, to
avoid insects as much as possible. Mosquito netting has,
therefore, 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 at will about the
house. The bubonic plague, which, fortunately, is as yet
rare in this country but which is producing great ravages

WATER AS A SOURCE OF DISEASE 247

in Europe, Asia, and Africa, is known to be transmitted by
fleas carried 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, ¢yphord
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),
aud 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, andis |
liable in either case to percolate through Cie.
the soil or be washed by rains into wells or rs
streams. Wells are filled with water that ’
Fic. 74. Bacillus
has soaked through the soil, and are quite of typhoid fever.
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 intoa
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

248 BACTERIA, YEASTS, AND. MOLDS

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,
720 ro as the disease is hardly known in America.

3B But in the event of a cholera epidemic
it should be remembered that the majority
of cases are due to drinking water that
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

Fic.75. Bacillus
of cholera.

FILTERING OF DRINKING WATER - 249

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 a
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. Some of these are no more than strainers.
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, 2) 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

250 ° BACTERIA, YEASTS, AND MOLDS

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, zt zs
better not to use tt 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

Fic. 76. Pasteur filter, ‘
showing the filter itself, by which the water supply of a

#, made of unbaked whole city may be purified by filter-

porcelain, and the metal

Se ; : .
een 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 purefying suspicious water is by boiling.

Aérated Waters. The recognition of danger connected

with ordinary drinking water has led to the extension of

the use of a variety of aérated waters, Apollinaris water,

ICE AS A DISTRIBUTER OF DISEASE 251

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 aération, 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 aéra-
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 xaturally aérated waters are, so far as
known, never likely to be impregnated with disease germs.
We may then conclude that naturally aérated water is safe
from disease bacteria, and that other forms of aérated
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.

252 BACTERIA, YEASTS, AND MOLDS

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, five of
them being very definite specific diseases and one of a
somewhat obscure type. The five definite diseases are
tuberculosis, diphtheria, scarlet fever, septic sore throat,
and typhoid fever. The other disease referred to is the
indefinite series of intestinal troubles known as summer
complaint, summer diarrhea, cholera infantum, etc., all
characterized by the presence of diarrhoea and 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 children.
Pure milk, however, is never the cause of any of these
troubles. Clean milk fresh from a healthy cow is never
the source of any of the diseases above mentioned. Some
cows have tuberculosis, and the milk of such a cow may be
dangerous; diseased udders are believed to be sometimes
the source of the bacteria which cause septic sore throat;

MILK AS A DISTRIBUTER OF DISEASE 253

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:
(1) 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? 1. 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

254 BACTERIA, YEASTS, AND MOLDS

as to whether he is careful or careless in handling it.
In general it is well not to buy milk from a dirty or
careless 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 milk,
Grade A milk, or certified milk. The latter are higher
grades of milk, coming from special farms, and should
have a proper certificate or an official grading. They cost
more than the ordinary grade, but are safe, 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 pasteurization 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 pasteurization has in recent years come to be
so widely adopted. The same end is less satisfactorily
reached by boiling.

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

MILK AS A DISTRIBUTER OF DISEASE 255

general question cannot be answered and it will always bea
matter for individual decision. That there is some danger
is certain. Whether the danger is sufficient to warrant
or demand the pasteurization of a/ 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,
To guard against diseases distributed by the air is particularly

256 BACTERIA, YEASTS, AND MOLDS

difficult. Fortunately this is not a common method of dis-
tribution, for all recent experience tends to show that it is
tare and that the danger is confined to the immediate
vicinity of the patient. The germs given off from him
soon settle to the floor, and as a rule live only a short
time. Measles, scarlet fever, and smallpox may be thus dis-
tributed, and a person may take them without coming in
actual contact with the patient, when no other means of
infection is known save that of air currents. The distribu-
tion of disease bacteria by means of air, however, does not
extend very far from the patient. It is, in fact, questioned
to-day whether air plays an important part in the distri-
bution of even these diseases. It was once blamed in the
case of almost any disease whose distribution seemed mys-
terious. If, however, we stop to realize how easy it is to
come into indirect contact with a patient through articles
contaminated with his discharges, it is doubtful whether
one need take the air into account at all as an agent of
dissemination. If, moreover, bacteria are thrown off into
the air by a patient they must rapidly settle to the floor,
and the danger of taking such disease decreases rapidly as
we pass from the immediate vicinity of the patient.

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

AIR AS A DISTRIBUTER OF DISEASE 257

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 meas/es 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
being usually sufficient to free the air from
such floating microédrganisms. 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.

of tuberculosis.

258 BACTERIA, YEASTS, AND MOLDS

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 evety 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 and brooms could be dis-
carded, their places being taken by damp cloths and vac-
uum cleaners, 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

BACTERIA IN UNCOOKED FOOD 259

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

260 BACTERIA, YEASTS, AND MOLDS

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 overalarmed 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.

Bacillus Carriers. It frequently happens that persons who
have had germ diseases continue for some time after recovery
to carry around in their bodies the bacteria of the disease.
Although the germs no longer do any harm to the recovered
patient, they are still as dangerous as ever if by any chance
they should reach another individual. Such persons are
called ‘bacillus carriers,” and as long as they continue to
harbor these disease germs they are a source of danger to
their associates. Such bacillus carriers are particularly com-
mon after cases of typhoid fever and diphtheria. Recovered
typhoid patients have been known to carry active typhoid
bacilli for many years. In one famous case such a person
was employed as a cook, and for a period of twelve years
cases of typhoid fever appeared in all families shortly after
she was first employed by them as cook. Such bacillus car-
riers in a dairy have also been known to infect the milk and

BACILLUS CARRIERS 261

produce a typhoid epidemic, distributed by the milk supply.
Even more common is the distribution of diphtheria by
carriers. While the diphtheria germs do not remain in the
patient’s mouth for any such length of time as those of
typhoid fever linger in the body, they do remain there from
three to six weeks, and sometimes for some months. As
long as they are present the person is a source of danger to
his associates. A person may become a carrier of diphtheria
germs who has not himself had the disease. It frequently
happens in a school that after one or two cases of diphtheria
have appeared, quite a number of the children will be found
to have diphtheria germs in their throats, having obtained
them, doubtless, from associating with the patients. To
these carriers the bacilli may not be doing injury, since some
children are immune; but as long as the germs are present in
their mouths the carriers are a source of danger to others who
may not be immune. The most efficient method of prevent-
ing the distribution of this disease through a school, or any
institution, is to examine the throats of all children who
are associated with cases of true diphtheria, and then tem-
porarily to isolate those whom a microscopic examination
shows to be carriers. By such means it is practically always
possible to check the spread of diphtheria and to prevent
epidemics in schools, and the method is more effective than
that of closing the schools.

Against some diseases we do not yet know how to
protect ourselves. The best known of these is infantile
paralysis, the method of its distribution not being positively
known. It is certainly distributed by people either directly
or indirectly, and the wise precaution is to keep away from
patients or from those who have been in contact with them.

262 BACTERIA, YEASTS, AND MOLDS

One thing to remember in the spread of disease, whether
from bacillus carriers or from active cases, is the ease with
which our usual habits allow us to contaminate our hands
with saliva or nasal discharges and then to transfer this
contamination to others. Many sanitarians insist that this
is the most important form of direct contagion, and that
if we could all manage to keep our hands away from mouth
and nose, the spread of disease would be reduced to a
minimum. Unfortunately, however, in the case of a head
cold, when the danger of infection is greatest, it is almost
impossible to avoid thus contaminating the hands. We
should, nevertheless, learn to regard our hands as con-
taminated at such times and should be careful not to
handle food or to touch other people (as in shaking hands)
without first washing our hands.

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

INVASION THROUGH THE SKIN 263

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

sD stomach, and, indeed, we are swallowing them
. » allthe time, The mouth contains great num-
a°v$ = ~=bers of these bacteria, as well as numerous
other species, but they do us no injury. Skin
30 oO diseases like ringworm, favus, etc., enter in
¢%e2t *9 the sameway. This is likewise the case with
ssi lockjaw (Fig. 79), erysipelas (Fig. 78, 5), and
_ various forms of blood poisoning, some of
ae 4 7 which are of comparatively little importance,
WY while others may be serious and fatal. It is
Fic. 78. Vari. Possibly also true of some other diseases; in
ous patho- some cases we have really no knowledge of the
genic cocci. matter,
i ae But though these diseases enter through

ducing pneu-
monia; ¢,
erysipelas
cocci.

the skin, it should be remembered that the
surface of the body is commonly quite well
protected against the invasion of microérgan-
isms. We have already seen that the skin of

truits, if uninjured, protects the softer portion of the
interior from decay to a considerable extent, and that the

organisms which produce decay usually enter Be)
through bruises, cracks, or cuts in the skin. Vie Li;
: . : : 4 Ww =
Precisely the same thing is true, probably to °{NWS%
an even greater extent, in the case of the fig. a9.
human body. The outer layer of the skin isa Bacillus of
tetanus

protection which the bacteria cannot ordinarily

penetrate. If therefore the skin is unbroken and unin-
‘ jured, a person is almost perfectly protected against the

264 BACTERIA, YEASTS, AND MOLDS

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 microérganisms 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 /ockjaw (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 and treated with tinc-
ture of iodine. 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

ENTRANCE OF BACTERIA THROUGH THE MOUTH 265

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 inthecase of diphtheria, where thecontagion
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.

266 BACTERIA, YEASTS, AND MOLDS

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. Especial care is
needed to guard school children in these respects, for
their ignorance and thoughtlessness lead to many chances
of contagion from mouth to mouth. 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 ‘udberculosis.
Diphtheria is probably contracted in the same way, and
possibly the grippe, whooping cough, and measiles, 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

BREATHING 267

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 near the patient are exposed
to the disease by breathing the air, while those at some dis-
tance are but slightly exposed, and those at a greater dis-
tance, 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.

SUMMARY

It is plain, then, that there are various facts the house-
wife should know in order to help prevent the distribution
of contagious diseases. It is especially important to remem-
ber that no contagion can take place unless three conditions
are fulfilled: (1) the disease germs must be eliminated from
the patient’s body; (2) they must be carried to a healthy
individual; and (3) they must have some means of invad-
ing the second individual. If this chain of events is broken
at any point, the spread of the disease can be prevented.

Realizing this, it is well to remember the important means
of elimination, of carriage, and of invasion. Elimination
may take place through saliva or body discharges (especially
from nose and throat), through forcible breathing (such as
coughing), and through skin eruptions. With disease germs
that cannot infect a new human being directly, exit may be

268 BACTERIA, YEASTS, AND MOLDS

brought about by the bite of an insect. Carriage from one
individual to another may take place through other animals,
especially insects, through water, ice, milk, uncooked vege-
tables, or sometimes by direct contact of one person with
another. Sometimes diseases are also spread through
“carriers,” healthy individuals who harbor the germs and
can transmit them to others without being sick themselves.
Some diseases are spread ‘by one of these means, others by
different ones; and in the case of an epidemic it is important
to know the exact facts, so that one may be on his guard
against the true channel of infection and not be afraid of
others. Invasion of a new host may occur through a broken
skin (rarely through an uninjured skin), through the mouth,
or through the respiratory tract. Here again each disease
has its own method of entrance, and in the fight against it
its peculiarities should be taken into account. With an in-
telligent understanding of these factors a housewife can do
much toward keeping her family in good health.

CHAPTER XVIII
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 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

269

270 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 varies from two to six weeks, and a laboratory
examination is necessary to determine when a convalescent
patient ceases to be able to transmit the disease to other
children. Measles is only contagious in its early stages, anda
week after the patient “breaks out”’ is no longer communi-
cable. 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 and all eating utensils be thoroughly disinfected
by placing them for ten minutes in boiling water.

TREATMENT OF INFECTED ARTICLES 271

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

272 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. (1) 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 Jozdzmg, 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 273

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

274 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 of the approved type does this satis-
factorily. All bowls, sinks, and closets should be con-
nected 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 filled with water no
bacteria and no gas can pass from the sewer into the sink.

SEWAGE 275

To be efficient a trap should remain full of water. The
traps, however, occasionally get emptied of water, and
then gases may pass up from the sewers. Such gases are
offensive in odor and used to be regarded as dangerous
to health. It is now realized that these gases do not bring
bacteria into the house with
them and hence are harm-
less although undesirable. The
insides of the traps, however,
become breeding places for cer-
tain kinds of bacteria, though
rarely disease bacteria, and may
in time become full of them. It
is therefore desirable to pour
some kind of disinfectant occa-
sionally into the bowls and
sinks. A weak solution of car- , E
bolic acid, one part to twenty, Fic. 80. Diagram showing the
or a solution of chloride of lime, P*inciple of two kinds of traps
. separating washbowls from
one part to twelve, put into .overs.
bowls and sinks will disinfect
the traps. It is also an excellent plan to pour boiling water
frequently down sinks, bowls, and closets, for this not
only ‘helps to clean but helps also to disinfect.

Leaky sewer pipes in a house are a serious menace. 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. For this reason it is desirable
to have sewer pipes laid where they may be easily inspected.
When the pipes are laid above the cellar floor, leaks are
more likely to be noticed and to receive attention at once.

276 BACTERIA, YEASTS, AND MOLDS

Where sewage leaks, flies are sure to gather, and disease
may be carried by them even to people outside the imme-
diate household. The evils from sewer gas have, however,
been overrated. Sewer gas itself is not capable of producing
any specific disease. At one time it was thought that sewer
gas was a great menace and likely to produce various diseases
in those breathing it. Further experience has shown that
this is not true. The gas is unpleasant but not in itself harm-
ful. The diseases are caused not by gases but by living
bacteria, and sewer gas 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 ; in other cases it may last only a few years; in some
cases perhaps only a few months or weeks ; but a temporary
protection is always gained. The reason why one is thus
protected from a second attack scientists have not yet
wholly explained, but its practical importance is beyond
question.

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

VACCINATION 277

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

278 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 gen-
eral protection against this extremely violent and fre-
quently fatal disease.

Modern physicians have two splendid weapons in fight-
ing diphtheria, one a cure, the other a preventive. The
cure is diphtheria antitoxin, a preparation that has been
known since a little before the beginning of this century.
If it is injected into the patient sufficiently early in the
disease, it is an almost certain cure. The preventive is
toxin-antitoxin, a mixture of antitoxin with the toxin (ie.
poison) produced by the diphtheria bacilli. If a child is
treated with this mixture under proper conditions, he is
protected against diphtheria many years, perhaps for life.
The use of these two products is being adopted very widely
by physicians, and every housewife should understand that
it is a precautionary measure that is perfectly safe, and the
only known means of protecting a family where complete
isolation of a diphtheria patient js impossible.

A method of vaccinating against typhoid fever has also
been devised and is coming to be extensively used. The
treatment is perfectly harmless, and it gives a very high
degree of protection against the disease. It is so efficient
that since 1914 it has effectually protected the armies of
the world from typhoid fever, the disease that previously
devastated army camps. This anti-typhoid vaccination is

PHYSICAL VIGOR A PROTECTION 279

becoming more and more common among people at large
as well as in armies, and is a wise precaution to all. The
protection does not last more than two or three years.

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
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. 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

280 BACTERIA, YEASTS, AND MOLDS

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
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
ownway. 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 vaccination, by a
guard placed over the water and the milk supplies, and by
fighting flies; malaria by destroying the breeding places of
mosquitoes and protecting the body 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

GENERAL CONCLUSIONS 281

parts of the body, producing other diseases, such as scvofula,
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 such 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
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.

282 BACTERIA, YEASTS, AND MOLDS

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.

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 XIX
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 microdrgan-
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 materiai
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 microérganisms.
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

283

284 BACTERIA, YEASTS, AND MOLDS

be considered: (1) 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 microérganisms
have already been considered in previqus chapters, and
a summary only is here needed. They are briefly the
following :

Heat. All active and growing forms of bacteria are de-
stroyed by moderate heat. In liquids a temperature of
140°, maintained for half an hour, is usually capable of
destroying 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 microérganisms that do not produce spores. Conse-
quently lower temperatures than boiling are commonly
sufficient for disinfection. The only common disease that

PHYSICAL DISINFECTING AGENTS 285

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 160°, 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.

286 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. (1) 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 (1 gram)
Common salt . . . . . . 30 grains (2 grams)
Water... . . . . . I quart(1ooo 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 287

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 havea 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 totally 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

288 BACTERIA, YEASTS, AND MOLDS

applied dry if the material which is to be disinfected con-
tains moisture, but it acts only in the presence of mois-
ture and should usually be dissolved in water. A solution
of one part to twenty-five of water (one pound to six
gallons) will be found to be very efficient in disinfecting
walls, floors, furniture, etc. Chloride of lime is also one
of the most efficient disinfectants for water. When added
in very minute quantities, only one part of chlorine to a
million of water, it kills the disease germs and is perfectly
harmless in the water. It is very widely used to-day for this
purpose and its use is extending rapidly. Common slacked
lime, which is occasionally used, is of little value as a
disinfectant.

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 forma-
lin to ten thousand parts of water being sufficient to destroy
the vitality 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 ma-
terial 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. It is also quite irritating
to the skin, and must be carefully handled. For these
reasons it is less widely used in the home than certain
other disinfectants.

Creosote Disinfectants. A class of products derived from
coal tar and going under the general name of creosote
preparations are sold under a great variety of trade des-
ignations. They are all much alike in appearance and
properties,— brown, oily-looking liquids, having a strong,

APPLICATION OF DISINFECTANTS 289

tarry odor and forming a milky solution when diluted in
water. They are very powerful disinfectants even when
many times diluted, and are harmless to the skin unless
applied too strong. They are, therefore, much better than
any of the germicides just listed for disinfecting hands or
for application to scratches and cuts in the skin. Their
only disadvantages are that they have a strong odor and
that they stain clothing which is disinfected in them.

Other Skin Disinfectants. Iodine has been used for
years to disinfect small skin wounds, and is still favored
by many physicians. It is so irritating, however, that a
search has been made for something to take its place.
Two proprietary disinfectants which are designed for just
such usage are now on the market. Both are dyes, one
yellow (acriflavine), the other red (mercurochrome). Neither
is quite as effective as iodine; but for the treatment of
minor skin injuries they are undoubtedly satisfactory, and
are much more popular than iodine, as their use is not
painful. Like iodine they stain the skin, a fact which is
often of advantage to the physician, as it shows just what
area has been covered with the disinfectant. A disinfect-
ant of this type, therefore, is often used before vaccination
or before making a hypodermic injection.

#

APPLICATION OF DISINFECTANTS

In determining the application of disinfectants two ques-
tions arise: (1) 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

290 BACTERIA, YEASTS, AND MOLDS

should be applied. We should look in at least four dif-
ferent directions : (1) 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.

Excreta. Jl discharges from a patient suffering from
any infectious disease should be disinfected at once, since
they will always contain infectious microérganisms. This
would apply to the feeces, 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
frequently 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

DISINFECTING OF CLOTHING AND BEDDING 291

for a moment in strong alcohol, and 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
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 doc/ing 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,

292 BACTERIA, YEASTS, AND MOLDS

and may be employed for soaking blankets and other
articles not injured by water. 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 of formalin to ten gal-
lons of water. A soaking in such a solution will be a
thorough disinfection. For heavier articles like mat-
tresses and comfortables, which cannot be soaked, complete
sterilization is difficult. If there are at hand facilities for
steaming, these articles may be disinfected in that way; 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. They may,
however, be protected considerably by covering them with a
rubber blanket, which will prevent their becoming contami-
nated. Whenever possible, one should use an old mattress
of little value on the bed of a contagious patient, so that it
can subsequently be destroyed. At present, however, health
authorities recommend sunning and airing for disinfecting
mattresses, rugs, and heavy bedding. Exposure to the sun
and air for four successive days seems to be as efficient as
more expensive methods of sterilizing. Disease bacteria
ordinarily die when dried, and are quickly killed by sunlight.

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

TREATMENT OF THE SICK ROOM 293

totally different. While the room is occupied by the patient
not very much can be done to control the contagion.
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 room
is occupied for some time, it may be well to wash occa-
sionally 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 having infectious material float from his skin around the
room. All contaminated cloths should be burned imme-
diately, 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 Vacating. After a room is vacated by. the
patient it must be disinfected before using it again. Con-
cerning the proper treatment of such a room there have
been many differences of opinion. For a considerable time
it has been a common custom to treat such rooms by a
gaseous disinfectant, the general practice being to close the
room, sealing all cracks around windows and doors, and
then to liberate the disinfectant. For this purpose formalde-
hyde gas has been most commonly used, although the fumes
of burning sulphur have also been employed. Where such
a method is employed it is always best to have it done by
a health officer.

The use of gaseous disinfectants for this purpose is, how-
ever, going out of practice and has been largely abandoned
by modern health officials. It has been found both useless

294 BACTERIA, YEASTS, AND MOLDS

and inefficient, and it is believed to give to the inmates of
the house a feeling of false security. It is the convalescing
patient that ts the source of danger to the rest of the house-
hold, not the room he has vacated, and to allow him to leave
the room and mingle with the family, giving them a feeling of
security by disinfecting his room, is the height of unwisdom.
Then, too, experiment has shown that these gaseous dis-
infectants cannot be relied upon as actually disinfecting the
room. To treat a room by this method is very easy and
therefore widely adopted, but it is not regarded to-day as of
much value and is being abandoned.

The best method of preparing a room for reoccupancy is
as follows: Carpets, bedding, curtains, and all cloth material
should be removed and disinfected as above mentioned.
Then all surfaces of the room, including walls, ceilings, floor,
tables, chairs, and especially cracks around mopboards and
floor, should be washed freely with chloride-of-lime solution,
about one pound to six gallons of water. The room should
then be aired by having the windows open for a day, after
which it is ready for occupancy. Such a room is safer than
one which has been “‘fumigated”’ by any gaseous disinfectant.
It is well to remember that while most disease germs die
quickly upon being dried, the tuberculosis bacillus may remain
alive in a room for weeks or even months, and for this
reason more care should be exercised in the room occupied
by a consumptive than in the case of any other disease.

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. Ahot-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 @2-——

£

STERILIZING CHAMBER

glass dishes, Fig. 83, several dozen of
which should be at hand.

4. Glass pipettes to hold 1 cc.

5. A few fermentation tubes, shown 5,, 9, steam ste Hiuane
in Fig. 38. apparatus.

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.

STEAM
Wa TER

295

296 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
microérganisms 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

Fic. 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. Pr,

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

L 2p
em

a

Fic. 83. A petri dish for
plate cultures.

APPENDIX 297

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.

298 BACTERIA, YEASTS, AND MOLDS

Preparation of Agar 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 15 grams of agar add 985 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 absorbent cotton
placed in it. The liquid agar is poured into the cotton, and it will run
through readily, coming out as a tolerably clear solution. 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 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
agar, she can buy it of dealers in bacteriological supplies. The agar
culture medium which is sold by such dealers is slightly alkaline,
and should be rendered a little acid by adding HCl 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 agar in three or four of the test
tubes prepared as above described, and pour it from each into a steril-
ized petri dish. Replace the cover upon the dish and allow the agar
to harden. Sweep a little dust from the floor and scatter over the sur-
face of the agar 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 agar. 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
agar, as in Experiment 6, and, after removing the cover, shake the dust

APPENDIX 299

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 distribu-
tion of mold spores ?

8. Molds in the Air (a). Prepare four dishes of hardened agar.
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 (6). Repeat the above experiment, using moist
bread instead of the petri dishes of agar. 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.

1o. Growth from Spores. Prepare a petri dish of hardened agar.
‘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 agar. Touch the agar 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 trans-
ferred 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 agar, 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 agar as follows: Select one of the

300 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 agar, 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 agar
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. Inthe 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 agar, 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. 1o-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 agar place a small quantity of mold spores. Melt the agar 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 301

a. beaker of boiling water and allow the water to boil briskly for half
an hour, after which the agar 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
agar 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 azy molds grow upon the dish placed in the ice
chest?

16. 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 agar 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(@). 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 (6). Make a cut through the skin of an apple
with a knife blade that has been previously dipped into the midst of

302 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 agar 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 @ 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 (CO,).

APPENDIX 303

23. CO, 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 Stupy or 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 2-inch objective. Note that the water seems to be filled with
very minute dots. Study with a higher power (tinch objective).
Examine the yeast ce//s, noting the skafe, comparative szze, 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 yousee 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

304 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
microérganisms are growing in the solution. Commonly Jdacteria
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 fewdays. 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 305

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 4 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 4 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 4 have risen under the influence of the yeast,
bake 4 at once in the oven, while ¢ is to be thoroughly kneaded and
then baked. Compare the results of a, 4, and ¢, 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.

306 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 307

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, 4, c,d. Bring
a2 to a boil for five minutes, 4 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
preyenting 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.

308 BACTERIA, YEASTS, AND MOLDS

Microscopic Stupy 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 34-inch objective
is required to study them, but a j-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 s¢azzed in order that they may be more
clearly visible. Staining fluids may be bought or a convenient one
be prepared as follows:

Ziehl’s Carbol-Fuchsin

Saturated alcoholic solution of fuchsin. . . . . . Soc.
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 to 7x 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 309

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. Ifa 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:

1 liter of water.
5 grams of Liebig’s extract of beef.
Io 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 to 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

310 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 most 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 1.5 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 agar 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 agar 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 of 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 311

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. (4) 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. (c) 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. (a) 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 agar 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
inthe 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

312 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.

6o. 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 313

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 6; take out a second
the moment the water boils and label ¢; remove a third after the
water has boiled half an hour and label @ 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

Acidity, bacteria and, 132

Zcidiomycetes, 32

Air, bacteria and, 130, 132; bacteria
in, 138; distribution of disease
and, 257; molds and, 44-46, 55

Alcohol, 221; yeasts as source, 88

Alcoholic beverages, 88

Alcoholic fermentation, 74, 82, 88

Alternaria, 41

American cheese, 50

Animals, distribution of disease and,
246

Anthrax, 14, 16

Antiseptic, 283

Antitoxin, Behring and, 20; diph-
theria, 20, 278

Apparatus for pasteurization of
milk, 216

Appert, canning industry and, 9

Apple, molds and, 62

Apple scab, mold on, 41

Apples, canning of, 199

Ascomycetes, 32

Aspergillus, colony of, 39, 40

Aspergillus spores, 39

Bacillus, 123

Bacillus carriers, 260

Bacon, 162

Bacteria, 30, 118-294; acidity and,
132; aérobic, 131; air and, 130,
132; anaérobic, 131; classifica-
tion of, 121; death temperature
of, 128; discovery of, 4; disease,
228-268; effect of growth upon
the wholesomeness of food, 221;
effect upon milk, 204; encourag-
ing growth of, in food, 222; fats
and, 142; flagella, 121; food
flavors and, 149; food ruined
by, 152; from the mouth, 137;

315

general nature of, 118-141; in
air, 138; in body, 137; in butter,
149; in cheese, 149; in food, 136,
203-227; in milk, 137, 203-220;
in soil, 135; in uncooked food,
259; in water, 133; invasion
through the mouth, 265; lactic-
acid, 205; light and, 130; means
of invasion, 262; moisture and,
131; multiplication and growth,
123; organic substances and, 29;
producing vinegar, 151; proteids
and, 139, 143; rapidity of growth,
125; results of growth, 139; rod-
shaped, 123; secretions of, 147;
shape of, 120; size of, 119;
spherical, 122; spiral, 123; spore
formation of, 124; spores and,
125; starches and, 142; structure
of, 119; sugars and, 142; tem-
perature and, 127; where found,

132

Bacterial growth upon food, effect
of, 144

Bacterial invasion through the skin,
262

Bacterial poisons in foods, 224-227

Bacterium, 123

Banana, mold on, 34

Beans, canning of, 193

Bedding and clothing, disinfection,
291

Beef, dried, 162

Beer, 88; homemade, 114

Behring and antitoxin,’ 20

Benzoic acid, 178, 181

Berries, canning of, 199

Beverages, alcoholic, 88

Blood poisoning, 228, 263

Blue mold, 33, 37, 59

Body, bacteria in, 137, 263

316

Boiling of milk, 214

Borax, 178

Bread, mold on, 34, 137; raised or
leavened, gt; raising of, 3, 90,
104-113; slimy, 111; souring of,
110; unleavened, 91

Breathing and bacterial invasion, 266

Brewer’s yeast, 100

Brie cheese, molds and, 70

Bubonic plague, 246

Budding fungi, 79

Budding of yeasts, 78

Butter, bacteria in, 149, 221

Camembert cheese, molds and, 70

Canned vegetables, molds and, 55

Canning, Appert and, 9; cold-pack
method of, 200; of apples, 199;
of beans, 193; of berries, 199; 0:
cherries, 199; of grapes, 89, 199;
of green corn, 193; of meats, 198;
of peaches, 199; of pears, 199;
open-kettle method of, 200; pres-
ervation by, 189-201

Canning industry, Appert and, 9

Carbolic acid, 178; as nicintehtant,
286

Carbon dioxide, yeasts as source of,
go

Carriers, bacillus, 260

Cellar, cool, 174

Certified milk, 209

Cheese, American, 50; bacteria in,
149, 221; Brie, molds and, 70;
Camembert, molds and, 70; cot-
tage, 222; Gorgonzola, 49; Gor-
gonzola, molds and, 70; molds in,
42, 47; Roquefort, molds and, 48,
51,70; Stilton, molds and, 51, 70

Cherries, canning of, 199

Chicken cholera, Pasteur and, 15

Chloride of lime as disinfectant, 287

Cholera, Asiatic, 229; bacillus of,
248; water and, 247, 248

Cider, 90

Clothing and bedding, disinfection,
291

Cocci, 122

Cold-pack method of canning, 200,
201

BACTERIA, YEASTS, AND MOLDS

Cold storage, 166

Colonies, 19; of Aspergillus, 39, 40;
of mold, 33; of Mucor, 38

Compressed yeast, 97

Contagion, conditions of, 238

Contagious diseases, 237-282; dis-
tribution of, 233; prevention of
distribution, 237-268

Cooling, devices for, 174; rules for,
176 :

Corn, canning of, 193

Corrosive sublimate, 178; as disin-
fectant, 286

Cowpox, 14, 15

Creosote disinfectants, 288

Decay, 21, 24, 146; of fruit, 58; of
peaches on tree, 68; protection of
fruit from, 62

Decomposition products, 145

Diastase, 104

Dill pickles, 186, 223

Diphtheria, 229; antitoxin for, 20,
278; bacillus, 244; carriers of,
261; toxin-antitoxin, 278

Disease, germ theory of, 6; micro-
organisms and, 26; resistance
against, 231

Disease bacteria, 228-268

Disease distribution, air and, 257;
animals and, 246; by water, 247;
ice and, 251; insects and, 239,
246; milk and, 252, 253; mosqui-
toes and, 239

Disease germs, 26, 140, 228; elimi-
nation of, 239; how carried, 245

Diseases, distribution of, 233; how
produced, 229; of fruit tree, 67;
prevention of distribution of, 237-
268; produced by molds, 70

Disinfectant, application of, 289;
carbolic acid as, 286; chloride of
lime as, 287; cold as, 285; cor-
rosive sublimate as, 286; creo-
sote as, 288; formalin as, 288;
heat as, 284; sunlight as, 285

Disinfection, 283-294

Distribution of disease, 233-236;
air and, 257; animals and, 246;
by water, 247; ice and, 251;

INDEX

insects and, 239, 246; milk and,
252, 253; mosquitoes and, 239;
prevention of, 237-268

Distribution of yeasts, 14

Dried fish, 163

Dried fruit, 164, 165

Dried milk, 163

Dried yeast, 99

Drinks, fermented, 89, 113-117

Drying, preservation by, 159-166

Eggs, preservation of, 220
Elimination of disease germs, 239
Erysipelas, cocci of, 263

Fats and bacteria, 142

Favus, 72, 263

Fermentation, alcoholic, 74, 75, 82,
88; Liebig and, 12; Pasteur and,
Ir; yeasts and, 74

Fermented drinks, 89, 113-117

Filtering of drinking water, 249

Fish, dried, 163

Fission fungi, 124

Flagella, bacteria and, 121

Flavors, food, bacteria and, 149

Fleas, bubonic plague and, 246

Flies, typhoid fever and, 246

Food, bacteria in, 136, 203-227 ;
bacterial poisons in, 224, 227;
effect of bacterial growth upon,
144; effect of bacterial growth on
wholesomeness of, 221; encourag-
ing growth of bacteria in, 222;
freshness of, 158; preservation
of, 22, 157-202; protection from
molds, 44; Yuined by bacteria,
452; uncooked, bacteria in, 259

Food flavors, bacteria and, 149

Formalin, 178; as disinfectant, 288

Fracastorio, 6

Fruit, canning of, 199; decay of, 58;
dried, 164, 1653 ; mold and, 54;
protection from decay, 62

Fruit jar, 197

Fruit tree, diseases of, 67

Fruiting of mold, 37-41

Fungi, 30; budding of, 79; fis-
pon a, peaches, mummified
by, 6

317
Garbage, 153
Germ theory of disease, 6
Germicide, 283
Germs, disease, 140; elimination

of, 239; how carried, 245
Gorgonzola cheese, molds and, 49,

51, 79
oe of milk, 208

rapes, canning of, 89, 199
Grocery milk, 207 ne

Ham, 162
Heat, for preservation, 176, 190;
preservation of milk by, 213

Ice and distribution of disease, 251

Ice chest, 171

Ice-cream poisoning, 225

Immunity, 276; Pasteur and, 16

Importance of microdrganisms, dis-
covery of, 11-20

Infantile paralysis, 261

Infected articles, treatment of, 271

Insects, disease distribution and,
239, 246; malaria and, 246

Isolation, 269

Jar, fruit, 197

Jelly, protection from microérgan-
isms, 45

Jenner, vaccination and, 14

Koch, Robert, 19
Kumiss, 117

Lactic-acid bacteria, 205

Leather, mildew on, 48

Leaven, 3, 91

Leeuwenhoek, discovery of micro-
organisms by, 4

Liebig, fermentation and, 12; Pas-
teur and, 12

Life, origin of, 6-10

Limburger cheese, 149

Lockjaw (tetanus), 264

Low temperatures, preservation by,
166-176

Malaria, 239; insects and, 246;
mosquitoes and, 242, 243

318

Malarial mosquito, 241

Malarial organism, 240

Meat, decay in, 148

Meats, canning of, 198

Micrococcus, 122

Microérganisms, 2, 23; classes of,
28; disease and, 26; importance
of, discovered, 11-20

Microscope, milk under, 204

Microscopic life, knowledge of, 1-10

Mildew, 48, 54; on leather, 48

Milk, apparatus for pasteurization,
216; bacteria in, 203-220; _boil-
ing of, 214; certified, 209; distri-
bution of disease and, 247, 252;
dried, 163; effect of bacteria on,
204; fermented, 117; from milk-
men, 208; grading of, 208; gro-
cery, 207; keeping of, in relation
to temperature, 211; pasteuri-
zation of, 215, 216, 219; pres-
ervation by heat, 213; preser-
vation of, 206-220; preservatives
for, 213; slimy, 205; source of,
206; sterilization of, 213; under
the microscope, 204

Milk vessels, care of, 210

Milkmen, 208

Moisture, bacteria and, 131; molds
and, 53

Mold, blue, 33, 59

Mold growth, conditions favoring,
52-59; results of, 48

Mold spores, 37; germination of, 42;
in air, 43

Molds, 30; air and, 44-46, 55; apple
and, 62; Brie cheese and, 70;
canned vegetables and, 55; colo-
nies of, 33; diseases produced by,
yo; food requirements of, 52;
fruits and, 54; general nature of,
32-51; Gorgonzola cheese and,
49, 51, 70; in cheese, 42, 47; in
rooms, 72; moisture and, 53; on
banana, 34; on bread, 34; pro-
tection of foods from, 44; Roque-
fort cheese and, 48, 51, 70; Stilton
cheese and, 51, 70; structure of,
36; temperature and, 56; utility
of, 69

BACTERIA, YEASTS, AND MOLDS

Monilia, 42, 59, 60, 61

Mosquito, harmless, 241, 242; ma-
larial, 241, 242, 243; of yellow
fever, 244, 245

Mosquitoes, disease distribution and,
239-245

Mother of vinegar, 150

Mouth, bacteria in, 137; bacterial
invasion through, 265

Mucor, 34, 41; colony of, 38; spores
of, 38

Mustiness, 47, 49

Mycelium, 37

Needham, 8-9

Open-kettle method of canning, 200
Organic substances, bacteria and, 29

Parasites, 140, 228

Pasteur, 8, 9, 10-18; anthrax and, 14;
chicken cholera and, 15; fermen-
tation and, 11; immunity and,
16; Liebig and, 12; pébrine and,
13; rabies and, 17; spontaneous
generation and, 10

Pasteur’s flasks, 10

Pasteurization of milk, 215-220; ap-
paratus for, 216

Pathogenic bacteria, 26

Peaches, canning of, 199; decaying
on tree, 68; mummified by fungi,
67

Pears, canning of, 199

Pébrine, Pasteur and, 13

Pemmican, 161

Penicillium, 33; spores of, 35

Pickles, 185

Plague, bubonic, bacillus of, 246

Pneumonia, cocci of, 263

Poisoning from ice cream, 225

Poisons, bacterial, 224, 225, 227

Preservation, by canning, 189-201;
by drying, 159-166; by low tem-
peratures, 166-176; by salting,
184; of eggs, 220; of food, 157-
202; of food, heat for, 176, 213;
of food, microdrganisms and, 22;
of milk, 206-220; sugar and, 182;
vinegar and, 185

INDEX

Preservatives, 177-188; commer-

cial, 179; nonpoisonous, 182; 3, of
k, 213; poisonous, 1773; spices

as, 107

Protection of fruit from decay, 62

Proteids, bacteria and, 139, 143

Protozoa, 31

Ptomaine poisoning, 226

Ptomaines, 224

Putrefaction, 24, 49-50, 146

Rabies, Pasteur and, 17-19

Raising of bread, 90, 91, 104-113

Rapidity of growth of bacteria, 125

Redi, Francesco, 7

Refrigeration in home, mechanical,
169; by ice, 171

Resistance against disease, 231

Ringworm, 70, 71, 263

Roquefort cheese, 51, 70;
and, 26, 48, 51

Roux, Emile, 20

molds

Saccharomyces cerevisiz, 97

Salicylic acid, 178

Salt as preservative, 184

Salt raising and yeasts, 93

Saprophytes, 140, 142-227

Sarcina, 122

Sauerkraut, 186, 222, 223

Sealing, hermetical, 196

Secretions of bacteria, 147

Septicemia, 228

Sewage, 259, 274

Sick room, treatment of, 273, 292

Silkworm, disease of, 13-14

Skin, bacterial invasion through, 262

Slimy bread, 111

Slimy milk, 205

Smallpox, vaccination for, 14

Soil, bacteria in, 135

Source of milk, 206

Souring, 24, 111

Spallanzani, 9

Spices as preservatives, 187

Spontaneous generation, 7; Pasteur
and, Io

Spore formation of bacteria, 124

Spores, bacterial, 125; of Aspergil-
lus, 39; of mold, 37; of mold,

319

germination of, 42; of Penicil-
lium, 35; of yeast, 80
Starches and bacteria, 139, 142
Sterilization, 129, 191; of milk,
213
Stilton cheese, molds and, 51, 70
Streptococcus, 122
Sugars and bacteria, 139, 142

Temperature, bacteria and, 127;
keeping of milk and, 211; molds
and, 56; yeast and, 107

Tetanus, 264; bacillus of, 263

Toxin, diphtheria, 20

Toxin-antitoxin, diphtheria, 278

Toxins, 229

Trichina, 163

Tuberculosis, bacillus of, 257

Typhoid fever, flies and, 246; water
and, 247, 248

Typhoid-fever bacillus, 247

Typhoid vaccination, 278

Unleavened bread, 91

Vaccination, 276; for anthrax, 14;
for smallpox, 14; for typhoid, 278;
Jenner and, 14

Vegetables, canned, mold and, 55

Vinegar, 90, 149, 221; as preserva-
tive, 185; bacteria producing,
151; mother of, 150

Vinegar eels, 152

Vitamines, 185, 201, 219; yeast and,
85

Water, Asiatic cholera and, 247, 248;
bacteria in, 133; distribution of
disease by, 247; filtering of, 249;
typhoid fever and, 247, 248

Wine, fermentation of, 3

Wines, homemade, 89

Yeast, brewer’s, 100; compressed,
97; dried, 99; food required by,
84; impurities in, 109; methods
of obtaining, 93; spores of, 80;
temperature and, 107; vitamins
and, 85; wild, 81, 82

Yeast brews, ror

320 BACTERIA, YEASTS, AND MOLDS

Yeasts, 25, 30, 87-117; as enemies, tation and, 74; in the household,
87; as friends, 88; as source of 87-117; salt raising and, 93; struc-
alcohol, 88; as source of carbon ture of, 77; where found, 81; wild,

dioxide, 90; budding of, 78; dif- 7
ferences in ‘fermenting powers of, Yellow fever, 239; mosquitoes and,
95; distribution, 74-86; fermen. 244, 245

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