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Title: A Civic Biology - Presented in Problems
Author: Hunter, George William
Language: English
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[Illustration: Compare the unfavorable artificial environment of
a crowded city with the more favorable environment of the
country.]
A CIVIC BIOLOGY
Presented in Problems
BY
GEORGE WILLIAM HUNTER, A.M.
HEAD OF THE DEPARTMENT OF BIOLOGY, DE WITT CLINTON
HIGH SCHOOL, CITY OF NEW YORK.
AUTHOR OF "ELEMENTS OF BIOLOGY," "ESSENTIALS OF
BIOLOGY," ETC.
[Illustration: Printer's Logo]
AMERICAN BOOK COMPANY
NEW YORK CINCINNATI CHICAGO
COPYRIGHT, 1914, BY
GEORGE WILLIAM HUNTER.
COPYRIGHT, 1914, IN GREAT BRITAIN.
* * * * *
HUNTER, CIVIC BIOLOGY.
W. P. 3
Dedicated
TO MY
FELLOW TEACHERS
OF THE DEPARTMENT OF BIOLOGY
IN THE DE WITT CLINTON HIGH SCHOOL
WHOSE CAPABLE, EARNEST, UNSELFISH
AND INSPIRING AID HAS MADE
THIS BOOK POSSIBLE
FOREWORD TO TEACHERS
A course in biology given to beginners in the secondary school should have
certain aims. These aims must be determined to a degree, first, by the
capabilities of the pupils, second, by their native interests, and, third,
by the environment of the pupils.
The boy or girl of average ability upon admission to the secondary school
is not a thinking individual. The training given up to this time, with but
rare exceptions, has been in the forming of simple concepts. These concepts
have been reached didactically and empirically. Drill and memory work have
been the pedagogic vehicles. Even the elementary science work given has
resulted at the best in an interpretation of some of the common factors in
the pupil's environment, and a widening of the meaning of some of his
concepts. Therefore, the first science of the secondary school, elementary
biology, should be primarily the vehicle by which the child is taught to
solve problems and to think straight in so doing. No other subject is more
capable of logical development. No subject is more vital because of its
relation to the vital things in the life of the child. A series of
experiments and demonstrations, discussed and applied as definite concrete
problems which have arisen within the child's horizon, will develop power
in thinking more surely than any other subject in the first year of the
secondary school.
But in our eagerness to develop the power of logical thinking we must not
lose sight of the previous training of our pupil. Up to this time the
method of induction, that handmaiden of logical thought, has been almost
unknown. Concepts have been formed deductively by a series of comparisons.
All concepts have been handed down by the authority of the teacher or the
text; the inductive search for the unknown is as yet a closed book. It is
unwise, then, to directly introduce the pupil to the method of induction
with a series of printed directions which, though definite in the mind of
the teacher because of his wider horizon, mean little or nothing as a
definite problem to the pupil. The child must be brought to the
appreciation of the problem through the deductive method, by a comparison
of the future problem with some definite concrete experience within his own
field of vision. Then by the inductive experiment, still led by a series of
oral questions, he comes to the real end of the experiment, the conclusion,
with the true spirit of the investigator. The result is tested in the light
of past experiment and a generalization is formed which means something to
the pupil.
For the above reason the laboratory problems, which naturally precede the
textbook work, should be separated from the subject matter of the text. A
textbook in biology should serve to verify the student's observations made
in the laboratory, it should round out his concept or generalization by
adding such material as he cannot readily observe and it should give the
student directly such information as he cannot be expected to gain directly
or indirectly through his laboratory experience. For these reasons the
laboratory manual has been separated from the text.
"The laboratory method was such an emancipation from the
old-time bookish slavery of pre-laboratory days that we may
have been inclined to overdo it and to subject ourselves to
a new slavery. It should never be forgotten that the
laboratory is simply a means to the end; that the dominant
thing should be a consistent chain of ideas which the
laboratory may serve to elucidate. When, however, the
laboratory assumes the first place and other phases of the
course are made explanatory to it, we have taken, in my
mind, an attitude fundamentally wrong. The question is, not
what _types_ may be taken up in the laboratory to be fitted
into the general scheme afterwards, but what _ideas_ are
most worth while to be worked out and developed in the
laboratory, if that happens to be the best way of doing it,
or if not, some other way to be adopted with perfect
freedom. Too often our course of study of an animal or plant
takes the easiest rather than the most illuminating path.
What is easier, for instance, particularly with large
classes of restless pupils who apparently need to be kept in
a condition of uniform occupation, than to kill a supply of
animals, preferably as near alike as possible, and set the
pupils to work drawing the dead remains? This method is
usually supplemented by a series of questions concerning the
remains which are sure to keep the pupils busy a while
longer, perhaps until the bell strikes, and which usually
are so planned as to anticipate any ideas that might
naturally crop up in the pupil's mind during the drawing
exercise.
"Such an abuse of the laboratory idea is all wrong and
should be avoided. The ideal laboratory ought to be a
retreat for rainy days; a substitute for out of doors; a
clearing house of ideas brought in from the outside. Any
course in biology which can be confined within four walls,
even if these walls be of a modern, well-equipped
laboratory, is in some measure a failure. Living things, to
be appreciated and correctly interpreted, must be seen and
studied in the open where they will be encountered
throughout life. _The place where an animal or plant is
found is just as important a characteristic as its shape or
function._ Impossible field excursions with large classes
within school hours, which only bring confusion to
_inflexible_ school programs, are not necessary to
accomplish this result. Properly administered, it is without
doubt one of our most efficient devices for developing
biological ideas, but the laboratory should be kept in its
proper relation to the other means at our disposal and never
be allowed to degenerate either into a place for vacuous
drawing exercises or a biological morgue where dead remains
are viewed."--_Dr. H. E. Walter._
For the sake of the pupil the number of technical and scientific terms has
been reduced to a minimum. The language has been made as simple as possible
and the problems made to hinge upon material already known, by hearsay at
least, to the pupil. So far as consistent with a well-rounded course in the
essentials of biological science, the interests of the children have been
kept in the foreground. In a recent questionnaire sent out by the author
and answered by over three thousand children studying biology in the
secondary schools of Connecticut, Massachusetts, New Jersey, and New York
by far the greatest number gave as the most interesting topics those
relating to the care and functions of the human body and the control and
betterment of the environment. As would be expected, boys have different
biological interests from girls, and children in rural schools wish to
study different topics from those in congested districts in large
communities. The time has come when we must frankly recognize these
interests and adapt the content of our courses in biology to interpret the
_immediate_ world of the pupil.
With this end in view the following pages have been written. This book
shows boys and girls living in an urban community how they may best live
within their own environment and how they may coöperate with the civic
authorities for the betterment of their environment. A logical course is
built up around the topics which appeal to the average normal boy or girl,
topics given in a logical sequence so as to work out the solution of
problems bearing on the ultimate problem of the entire course, that of
preparation for citizenship in the largest sense.
Seasonal use of materials has been kept in mind in outlining this course.
Field trips, when properly organized and later used as a basis for
discussion in the classroom, make a firm foundation on which to build the
superstructure of a course in biology. The normal environment, its relation
to the artificial environment of the city, the relations of mutual give and
take existing between plants and animals, are better shown by means of
field trips than in any other way. Field and museum trips are enjoyed by
the pupils as well. These result in interest and in better work. The course
is worked up around certain great biological principles; hence insects may
be studied when abundant in the fall in connection with their relations to
green plants and especially in their relation to flowers. In the winter
months material available for the laboratory is used. Saprophytic and
parasitic organisms, wild plants in the household, are studied in their
relations to mankind, both as destroyers of food, property and life and as
man's invaluable friends. The economic phase of biology may well be taken
up during the winter months, thus gaining variety in subject matter and in
method of treatment. The apparent emphasis placed upon economic material in
the following pages is not real. It has been found that material so given
makes for variety, as it may be assigned as a topical reading lesson or
simply used as reference when needed. Cyclic work in the study of life
phenomena and of the needs of organisms for oxygen, food, and reproduction
culminates, as it rightly should, in the study of life-processes of man and
man's relation to his environment.
In a course in biology the difficulty comes not so much in knowing what to
teach as in knowing what _not_ to teach. The author believes that he has
made a selection of the topics most vital in a well-rounded course in
elementary biology directed toward civic betterment. The physiological
functions of plants and animals, the hygiene of the individual within the
community, conservation and the betterment of existing plant and animal
products, the big underlying biological concepts on which society is built,
have all been used to the end that the pupil will become a better, stronger
and more unselfish citizen. The "spiral" or cyclic method of treatment has
been used throughout, the purpose being to ultimately build up a number of
well-rounded concepts by constant repetition but with constantly varied
viewpoint.
The sincere thanks of the author is extended to all who have helped make
this book possible, and especially to the members of the Department of
Biology in the De Witt Clinton High School. Most of the men there have
directly or indirectly contributed their time and ideas to help make this
book worth more to teachers and pupils. The following have read the
manuscript in its entirety and have offered much valuable constructive
criticism: Dr. Herbert E. Walter, Professor of Zoölogy in Brown University;
Miss Elsie Kupfer, Head of the Department of Biology in Wadleigh High
School; George C. Wood, of the Department of Biology in the Boys' High
School, Brooklyn; Edgar A. Bedford, Head of Department of Biology in the
Stuyvesant High School; George E. Hewitt, George T. Hastings, John D.
McCarthy, and Frank M. Wheat, all of the Department of Biology in the De
Witt Clinton High School.
Thanks are due, also, to Professor E. B. Wilson, Professor G. N. Calkins,
Mr. William C. Barbour, Dr. John A. Sampson, W. C. Stevens, and C. W.
Beebe, Dr. Alvin Davison, and Dr. Frank Overton; to the United States
Department of Agriculture; the New York Aquarium; the Charity Organization
Society; and the American Museum of Natural History, for permission to copy
and use certain photographs and cuts which have been found useful in
teaching. Dr. Charles H. Morse and Dr. Lucius J. Mason, of the De Witt
Clinton High School, prepared the hygiene outline in the appendix. Frank M.
Wheat and my former pupil, John W. Teitz, now a teacher in the school, made
many of the line drawings and took several of the photographs of
experiments prepared for this book. To them especially I wish to express my
thanks.
At the end of each of the following chapters is a list of books which have
proved their use either as reference reading for students or as aids to the
teacher. Most of the books mentioned are within the means of the small
school. Two sets are expensive: one, _The Natural History of Plants_, by
Kerner, translated by Oliver, published by Henry Holt and Company, in two
volumes, at $11; the other, _Plant Geography upon a Physiological Basis_,
by Schimper, published by the Clarendon Press, $12; but both works are
invaluable for reference.
For a general introduction to physiological biology, Parker, _Elementary
Biology_, The Macmillan Company; Sedgwick and Wilson, _General Biology_,
Henry Holt and Company; Verworn, _General Physiology_, The Macmillan
Company; and Needham, _General Biology_, Comstock Publishing Company, are
most useful and inspiring books.
Two books stand out from the pedagogical standpoint as by far the most
helpful of their kind on the market. No teacher of botany or zoölogy can
afford to be without them. They are: Lloyd and Bigelow, _The Teaching of
Biology_, Longmans, Green, and Company, and C. F. Hodge, _Nature Study and
Life_, Ginn and Company. Other books of value from the teacher's standpoint
are: Ganong, _The Teaching Botanist_, The Macmillan Company; L. H. Bailey,
_The Nature Study Idea_, Doubleday, Page, and Company; and McMurry's _How
to Study_, Houghton Mifflin Company.
CONTENTS
CHAPTER PAGE
FOREWORD TO TEACHERS 7
I. SOME REASONS FOR THE STUDY OF BIOLOGY 15
II. THE ENVIRONMENT OF PLANTS AND ANIMALS 19
III. THE INTERRELATIONS OF PLANTS AND ANIMALS 28
IV. THE FUNCTIONS AND COMPOSITION OF LIVING THINGS 47
V. PLANT GROWTH AND NUTRITION--THE CAUSES OF GROWTH 58
VI. THE ORGANS OF NUTRITION IN PLANTS--THE SOIL AND
ITS RELATION TO ROOTS 71
VII. PLANT GROWTH AND NUTRITION--PLANTS MAKE FOOD 84
VIII. PLANT GROWTH AND NUTRITION--THE CIRCULATION AND
FINAL USES OF FOOD BY PLANTS 97
IX. OUR FORESTS, THEIR USES AND THE NECESSITY OF THEIR
PROTECTION 105
X. THE ECONOMIC RELATION OF GREEN PLANTS TO MAN 117
XI. PLANTS WITHOUT CHLOROPHYLL IN THEIR RELATION TO
MAN 130
XII. THE RELATIONS OF PLANTS TO ANIMALS 159
XIII. SINGLE-CELLED ANIMALS CONSIDERED AS ORGANISMS 166
XIV. DIVISION OF LABOR, THE VARIOUS FORMS OF PLANTS AND
ANIMALS 173
XV. THE ECONOMIC IMPORTANCE OF ANIMALS 197
XVI. AN INTRODUCTORY STUDY OF VERTEBRATES 232
XVII. HEREDITY, VARIATION, PLANT AND ANIMAL BREEDING 249
XVIII. THE HUMAN MACHINE AND ITS NEEDS 266
XIX. FOODS AND DIETARIES 272
XX. DIGESTION AND ABSORPTION 296
XXI. THE BLOOD AND ITS CIRCULATION 313
XXII. RESPIRATION AND EXCRETION 329
XXIII. BODY CONTROL AND HABIT FORMATION 348
XXIV. MAN'S IMPROVEMENT OF HIS ENVIRONMENT 373
XXV. SOME GREAT NAMES IN BIOLOGY 398
APPENDIX 407
SUGGESTED COURSE WITH TIME ALLOTMENT AND SEQUENCE
OF TOPICS FOR COURSE BEGINNING IN FALL 407
SUGGESTED SYLLABUS FOR COURSE IN BIOLOGY BEGINNING
IN FEBRUARY AND ENDING THE NEXT JANUARY 411
HYGIENE OUTLINE 415
WEIGHTS, MEASURES, AND TEMPERATURES 417
SUGGESTIONS FOR LABORATORY EQUIPMENT 418
INDEX 419
A CIVIC BIOLOGY
I. THE GENERAL PROBLEM--SOME REASONS FOR THE STUDY OF BIOLOGY
What is Biology?--_Biology is the study of living beings, both plant and
animal._ Inasmuch as man is an animal, the study of biology includes the
study of man in his relations to the plants and the animals which surround
him. Most important of all is that branch of biology which treats of the
mechanism we call the human body,--of its parts and their uses, and its
repair. This subject we call _human physiology_.
Why study Biology?--Although biology is a very modern science, it has found
its way into most high schools; and an increasingly large number of girls
and boys are yearly engaged in its study. These questions might well be
asked by any of the students: Why do I take up the study of biology? Of
what practical value is it to me? Besides the discipline it gives me, is
there anything that I can take away which will help me in my future life?
Human Physiology.--The answer to this question is plain. If the study of
biology will give us a better understanding of our own bodies and their
care, then it certainly is of use to us. That phase of biology known as
_physiology_ deals with the uses of the parts of a plant or animal; human
physiology and hygiene deal with the uses and care of the parts of the
human animal. The prevention of sickness is due in a large part to the
study of hygiene. It is estimated that over twenty-five per cent of the
deaths that occur yearly in this country could be averted if _all_ people
lived in a hygienic manner. In its application to the lives of each of us,
as a member of our family, as a member of the school we attend, and as a
future citizen, a knowledge of hygiene is of the greatest importance.
Relations of Plants to Animals.--But there are other reasons why an
educated person should know something about biology. We do not always
realize that if it were not for the green plants, there would be no animals
on the earth. Green plants furnish food to animals. Even the meat-eating
animals feed upon those that feed upon plants. How the plants manufacture
this food and the relation they bear to animals will be discussed in later
chapters. Plants furnish man with the greater part of his food in the form
of grains and cereals, fruits and nuts, edible roots and leaves; they
provide his domesticated animals with food; they give him timber for his
houses and wood and coal for his fires; they provide him with pulp wood,
from which he makes his paper, and oak galls, from which he may make ink.
Much of man's clothing and the thread with which it is sewed together come
from fiber-producing plants. Most medicines, beverages, flavoring extracts,
and spices are plant products, while plants are made use of in hundreds of
ways in the useful arts and trades, producing varnishes, dyestuffs, rubber,
and other products.
Bacteria in their Relation to Man.--In still another way, certain plants
vitally affect mankind. Tiny plants, called _bacteria_, so small that
millions can exist in a single drop of fluid, exist almost everywhere about
us,--in water, soil, food, and the air. They play a tremendous part in
shaping the destiny of man on the earth. They help him in that they act as
scavengers, causing things to decay; thus they remove the dead bodies of
plants and animals from the surface of the earth, and turn this material
back to the ground; they assist the tanner; they help make cheese and
butter; they improve the soil for crop growing; so the farmer cannot do
without them. But they likewise sometimes spoil our meat and fish, and our
vegetables and fruits; they sour our milk, and may make our canned goods
spoil. Worst of all, they cause diseases, among others tuberculosis, a
disease so harmful as to be called the "white plague." Fully one half of
all yearly deaths are caused by these plants. So important are the bacteria
that a sub-division of biology, called _bacteriology_, has been named
after them, and hundreds of scientists are devoting their lives to the
study of bacteria and their control. The greatest of all bacteriologists,
Louis Pasteur, once said, "It is within the power of man to cause all
parasitic diseases (diseases mostly caused by bacteria) to disappear from
the world." His prophecy is gradually being fulfilled, and it may be the
lot of some boys or girls who read this book to do their share in helping
to bring this condition of affairs about.
The Relation of Animals to Man.--Animals also play an important part in the
world in causing and carrying disease. Animals that cause disease are
usually tiny, and live in other animals as _parasites_; that is, they get
their living from their hosts on which they feed. Among the diseases caused
by parasitic animals are malaria, yellow fever, the sleeping sickness, and
the hookworm disease. Animals also _carry_ disease, especially the flies
and mosquitoes; rats and other animals are also well known as spreaders of
disease.
From a money standpoint, animals called insects do much harm. It is
estimated that in this country alone they are annually responsible for
$800,000,000 worth of damage by eating crops, forest trees, stored food,
and other material wealth.
The Uses of Animals to Man.--We all know the uses man has made of the
domesticated animals for food and as beasts of burden. But many other uses
are found for animal products, and materials made from animals. Wool, furs,
leather, hides, feathers, and silk are examples. The arts make use of
ivory, tortoise shell, corals, and mother-of-pearl; from animals come
perfumes and oils, glue, lard, and butter; animals produce honey, wax,
milk, eggs, and various other commodities.
The Conservation of our Natural Resources.--Still another reason why we
should study biology is that we may work understandingly for the
conservation of our natural resources, especially of our forests. The
forest, aside from its beauty and its health-giving properties, holds
water in the earth. It keeps the water from drying out of the earth on hot
days and from running off on rainy days. Thus a more even supply of water
is given to our rivers, and thus freshets are prevented. Countries that
have been deforested, such as China, Italy, and parts of France, are now
subject to floods, and are in many places barren. On the forests depend our
supply of timber, our future water power, and the future commercial
importance of cities which, like New York, are located at the mouths of our
navigable rivers.
Plants and Animals mutually Helpful.--Most plants and animals stand in an
attitude of mutual helpfulness to one another, plants providing food and
shelter for animals; animals giving off waste materials useful to plants in
the making of food. We also learn that plants and animals need the same
conditions in their surroundings in order to live: water, air, food, a
favorable temperature, and usually light. The life processes of both plants
and animals are essentially the same, and the living matter of a tree is as
much alive as is the living matter in a fish, a dog, or a man.
Biology in its Relation to Society.--Again, the study of biology should be
part of the education of every boy and girl, because society itself is
founded upon the principles which biology teaches. Plants and animals are
living things, taking what they can from their surroundings; they enter
into competition with one another, and those which are the best fitted for
life outstrip the others. Animals and plants tend to vary each from its
nearest relative in all details of structure. The strong may thus hand down
to their offspring the characteristics which make them the winners. Health
and strength of body and mind are factors which tell in winning.
Man has made use of this message of nature, and has developed improved
breeds of horses, cattle, and other domestic animals. Plant breeders have
likewise selected the plants or seeds that have varied toward better
plants, and thus have stocked the earth with hardier and more fruitful
domesticated plants. Man's dominion over the living things of the earth is
tremendous. This is due to his understanding the principles which underlie
the science of biology.
Finally the study of biology ought to make us better men and women by
teaching us that unselfishness exists in the natural world as well as among
the highest members of society. Animals, lowly and complex, sacrifice their
comfort and their very lives for their young. In the insect communities the
welfare of the individual is given up for the best interests of the
community. The law of mutual give and take, of sacrifice for the common
good, is seen everywhere. This should teach us, as we come to take our
places in society, to be willing to give up our individual pleasure or
selfish gain for the good of the community in which we live. Thus the
application of biological principles will benefit society.
II. THE ENVIRONMENT OF PLANTS AND ANIMALS
_Problem.--To discover some of the factors of the environment of plants and
animals._
_(a) Environment of a plant._
_(b) Environment of an animal._
_(c) Home environment of a girl or boy._
LABORATORY SUGGESTIONS
_Laboratory demonstrations._--Factors of the environment of
a living plant or animal in the vivarium.
_Home exercise._--The study of the factors making up my own
environment and how I can aid in their control.
Environment.--Each one of us, no matter where he lives, comes in contact
with certain surroundings. Air is everywhere around us; light is necessary
to us, so much so that we use artificial light at night. The city street,
with its dirty and hard paving stones, has come to take the place of the
soil of the village or farm. Water and food are a necessary part of our
surroundings. Our clothing, useful to maintain a certain temperature, must
also be included. All these things--air, light, heat, water, food--together
make up our _environment_.
[Illustration: An unfavorable city environment.]
All other animals, and all plants as well, are surrounded by and use
practically the same things from their environment as we do. The potted
plant in the window, the goldfish in the aquarium, your pet dog at home,
all use, as we will later prove, the factors of their environment in the
same manner. Air, water, light, a certain amount of heat, soil to live in
or on, and food form parts of the surroundings of _every_ living thing.
[Illustration: An experiment that shows the air contains about four fifths
nitrogen.]
[Illustration: Apparatus for separating water by means of an electric
current into the two elements, hydrogen and oxygen.]
The Same Elements found in Plants and Animals as in their Environment.--It
has been found by chemists that the plants and animals as well as their
environment may be reduced to about eighty very simple substances known as
_chemical elements_. For example, the air is made up largely of two
elements, _oxygen_ and _nitrogen_. Water, by means of an electric current,
may be broken up into two elements, _oxygen_ and _hydrogen_. The elements
in water are combined to make a _chemical compound_. The oxygen and
nitrogen of the air are not so united, but exist as separate gases. If we
were to study the chemistry of the bodies of plants and animals and of
their foods, we would find them to be made up of certain chemical elements
combined in various complex compounds. These elements are principally
_carbon_, _hydrogen_, _oxygen_, _nitrogen_, and perhaps a dozen others in
very minute proportions. But the same elements present in the living things
might also be found in the environment, for example, water, food, the air,
and the soil. It is logical to believe that living things use the chemical
elements in their surroundings and in some wonderful manner build up their
own bodies from the materials found in their environment. How this is done
we will learn in later chapters.
[Illustration: Chart to show the percentage of chemical elements in the
human body.]
What Plants and Animals take from their Environment. Air.--It is a
self-evident fact that animals need air. Even those living in the water use
the air dissolved in the water. A fish placed in an air-tight jar will soon
die. It will be proven later that plants also need air in order to live.
[Illustration: The effect of water upon the growth of trees. These trees
were all planted at the same time in soil that is sandy and uniform. They
are watered by a small stream which runs from left to right in the picture.
Most of the water soaks into the ground before reaching the last trees.]
Water.--We all know that water must form part of the environment of plants
and animals. It is a matter of common knowledge that pets need water to
drink; so do other animals. Every one knows we must water a potted plant if
we expect it to grow. Water is of so much importance to man that from the
time of the Caesars until now he has spent enormous sums of money to bring
pure water to his cities. The United States government is spending millions
of dollars at the present time to bring by irrigation the water needed to
support life in the western desert lands.
[Illustration: The effect of light upon a growing plant.]
Light as Condition of the Environment.--Light is another important factor
of the environment. A study of the leaves on any green plant growing near a
window will convince one that such plants grow toward the light. All green
plants are thus influenced by the sun. Other plants which are not green
seem either indifferent or are negatively influenced (move away from) the
source of light. Animals may or may not be attracted by light. A moth, for
example, will fly toward a flame, an earthworm will move away from light.
Some animals prefer a moderate or weak intensity of light and live in shady
forests or jungles, prowling about at night. Others seem to need much and
strong light. And man himself enjoys only moderate intensity of light and
heat. Look at the shady side of a city street on any hot day to prove this
statement.
Heat.--Animals and plants are both affected by heat or the absence of it.
In cold weather green plants either die or their life activities are
temporarily suspended,--the plant becomes _dormant_. Likewise small
animals, such as insects, may be killed by cold or they may _hibernate_
under stones or boards. Their life activities are stilled until the coming
of warm weather. Bears and other large animals go to sleep during the
winter and awake thin and active at the approach of warm weather. Animals
or plants used to certain temperatures are killed if removed from those
temperatures. Even man, the most adaptable of all animals, cannot stand
great changes without discomfort and sometimes death. He heats his houses
in winter and cools them in summer so as to have the amount of heat most
acceptable to him, _i.e._ about 70° Fahrenheit.
[Illustration: Vegetation in Northern Russia. The trees in this picture are
nearly one hundred years old. They live under conditions of extreme cold
most of the year.]
The Environment determines the Kind of Animals and Plants within It.--In
our study of geography we learned that certain luxuriant growths of trees
and climbing plants were characteristic of the tropics with its moist, warm
climate. No one would expect to find living there the hardy stunted plants
of the arctic region. Nor would we expect to find the same kinds of animal
life in warm regions as in cold. The surroundings determine the kind of
living things there. Plants or animals _fitted to live_ in a given locality
will probably be found there if they have had an opportunity to reach that
locality. If, for example, temperate forms of life were introduced by man
into the tropics, they would either die or they would gradually change so
as to become fitted to live in their new environment. Sheep with long wool
fitted to live in England, when removed to Cuba, where conditions of
greater heat exist, soon died because they were not fitted or _adapted_ to
live in their changed environment.
[Illustration: Plant life in a moist tropical forest. Notice the air plants
to the left and the resurrection ferns on the tree trunk.]
Adaptations.--Plants and animals are not only fitted to live under certain
conditions, but each part of the body may be fitted to do certain work. I
notice that as I write these words the fingers of my right hand grasp the
pen firmly and the hand and arm execute some very complicated movements.
This they are able to do because of the free movement given through the
arrangement of the delicate bones of the wrist and fingers, their
attachment to the bones of the arm, a wonderful complex of muscles which
move the bones, and a directing nervous system which plans the work.
Because of the peculiar fitness in the structure of the hand for this work
we say it is adapted to its function of grasping objects. Each part of a
plant or animal is usually fitted for some particular work. The root of a
green plant, for example, is fitted to take in water by having tiny
absorbing organs growing from it, the stems have pipes or tubes to convey
liquids up and down and are strong enough to support the leafy part of the
plant. Each part of a plant does work, and is fitted, by means of certain
structures, to do that work. It is because of these adaptations that living
things are able to do their work within their particular environment.
Plants and Animals and their Natural Environment.--Those of us who have
tried to keep potted plants in the schoolroom know how difficult it is to
keep them healthy. Dust, foreign gases in the air, lack of moisture, and
other causes make the artificial environment in which they are placed
unsuitable for them.
A goldfish placed in a small glass jar with no food or no green water
plants soon seeks the surface of the water, and if the water is not changed
frequently so as to supply air the fish will die. Again the artificial
environment lacks something that the fish needs. Each plant and animal is
limited to a certain environment because of certain individual needs which
make the surroundings fit for it to live in.
[Illustration: A natural barrier on a stream. No trout would be found above
this fall. Why not?]
Changes in Environment.--Most plants and animals do not change their
environment. Trees, green plants of all kinds, and some animals remain
fixed in one spot practically all their lives. Certain tiny plants and most
animals move from place to place, either in air, water, on the earth or in
the earth, but they maintain relatively the same conditions in environment.
Birds are perhaps the most striking exception, for some may fly thousands
of miles from their summer homes to winter in the south. Other animals,
too, migrate from place to place, but not usually where there are great
changes in the surroundings. A high mountain chain with intense cold at the
upper altitudes would be a barrier over which, for example, a bear, a deer,
or a snail could not travel. Fish like trout will migrate up a stream until
they come to a fall too high for them to jump. There they must stop because
their environment limits them.
[Illustration: A new apartment house, with out-of-door sleeping porch.]
Man in his Environment.--Man, while he is like other animals in requiring
heat, light, water, and food, differs from them in that he has come to live
in a more or less artificial environment. Men who lived on the earth
thousands of year ago did not wear clothes or have elaborate homes of wood
or brick or stone. They did not use fire, nor did they eat cooked foods. In
short, by slow degrees, civilized man has come to live in a changed
environment from that of other animals. The living together of men in
communities has caused certain needs to develop. Many things can be
supplied in common, as water, milk, foods. Wastes of all kinds have to be
disposed of in a town or city. Houses have come to be placed close
together, or piled on top of each other, as in the modern apartment. Fields
and trees, all outdoor life, has practically disappeared. Man has come to
live in an artificial environment.
Care and Improvement of One's Environment.--Man can modify or change his
surroundings by making this artificial environment favorable to live in. He
may heat his dwellings in winter and cool them in summer so as to maintain
a moderate and nearly constant temperature. He may see that his dwellings
have windows so as to let light and air pass in and out. He may have light
at night and shade by day from intense light. He may have a system of pure
water supply and may see that drains or sewers carry away his wastes. He
may see to it that people ill with "catching" or _infectious_ diseases are
isolated or _quarantined_ from others. This care of the artificial
environment is known as _sanitation_, while the care of the _individual_
for himself within the environment is known as _hygiene_. It will be the
chief end of this book to show girls and boys how they may become good
citizens through the proper control of personal hygiene and sanitation.
REFERENCE BOOKS
ELEMENTARY
Hunter, _Laboratory Problems in Civic Biology_. American
Book Company.
Hough and Sedgwick, _Elements of Hygiene and Sanitation_.
Ginn and Company.
Jordan and Kellogg, _Animal Life_. Appleton.
Sharpe, _A Laboratory Manual for the Solution of Problems in
Biology_, _p. 95_. American Book Company.
Tolman, _Hygiene for the Worker_. American Book Company.
ADVANCED
Allen, _Civics and Health_. Ginn and Company.
III. THE INTERRELATIONS OF PLANTS AND ANIMALS
_Problem.--To discover the general interrelations of green plants and
animals._
_(a) Plants as homes for insects._
_(b) Plants as food for insects._
_(c) Insects as pollinating agents._
LABORATORY SUGGESTIONS
_A field trip_:--Object: to collect common insects and study
their general characteristics; to study the food and shelter
relation of plant and insects. The pollination of flowers
should also be carefully studied so as to give the pupil a
general viewpoint as an introduction to the study of
biology.
_Laboratory exercise._--Examination of simple insect,
identification of parts--drawing. Examination and
identification of some orders of insects.
_Laboratory demonstration._--Life history of monarch and
some other butterflies or moths.
_Laboratory exercise._--Study of simple flower--emphasis on
work of essential organs, drawing.
_Laboratory exercise._--Study of mutual adaptations in a
given insect and a given flower, _e.g._ butter and eggs and
bumble bee.
_Demonstration of examples of insect pollination._
The Object of a Field Trip.--Many of us live in the city, where the crowded
streets, the closely packed apartments, and the city playgrounds form our
environment. It is very artificial at best. To understand better the
_normal environment_ of plants or animals we should go into the country.
Failing in this, an overgrown city lot or a park will give us much more
closely the environment as it touches some animals lower than man. We must
then remember that in learning something of the natural environment of
other living creatures we may better understand our own environment and our
relation to it.
On any bright warm day in the fall we will find insects swarming everywhere
in any vacant lot or the less cultivated parts of a city park.
Grasshoppers, butterflies alighting now and then on the flowers, brightly
marked hornets, bees busily working over the purple asters or golden rod,
and many other forms hidden away on the leaves or stems of plants may be
seen. If we were to select for observation some partially decayed tree, we
would find it also inhabited. Beetles would be found boring through its
bark and wood, while caterpillars (the young stages of butterflies or
moths) are feeding on its leaves or building homes in its branches.
Everywhere above, on, and under ground may be noticed small forms of life,
many of them insects. Let us first see how we would go to work to identify
some of the common forms we would be likely to find on plants. Then a
little later we will find out what they are doing on these plants.
[Illustration: An insect viewed from the side. Notice the head, thorax, and
abdomen. What other characters do you find?]
How to tell an Insect.--A bee is a good example of the group of animals we
call _insects_. If we examine its body carefully, we notice that it has
three regions, a front part or _head_, a middle part called the _thorax_,
and a hind portion, jointed and hairy, the _abdomen_. We cannot escape
noting the fact that this insect has wings with which it flies and that it
also has legs. The three pairs of legs, which are jointed and provided with
tiny hooks at the end, are attached to the thorax. Two pairs of delicate
wings are attached to the upper or _dorsal_ side of the thorax. The thorax
and indeed the entire body, is covered with a hard shell of material
similar to a cow's horn, there being no skeleton inside for the attachment
of muscles. If we carefully watch the abdomen of a living bee, we notice it
move up and down quite regularly. The animal is breathing through tiny
breathing holes called _spiracles_, placed along the side of the thorax and
abdomen. Bees also have compound eyes. Wings are not found on all insects,
but all the other characters just given are marks of the great group of
animals we call _insects_.
[Illustration: Part of the compound eye of an insect (highly magnified).]
Forms to be looked for on a Field Trip.--Inasmuch as there are over 360,000
different species or kinds of insects, it is evident that it would be a
hopeless task for us even to think of recognizing all of them. But we can
learn to recognize a few examples of the common forms that might be met on
a field trip. In the fields, on grass, or on flowering plants we may count
on finding members from six groups or _orders_ of insects. These may be
known by the following characters.
The order _Hymenoptera_ (membrane wing) to which the bees, wasps, and ants
belong is the only insect group the members of which are provided with true
stings. This sting is placed in a sheath at the extreme hind end of the
abdomen. Other characteristics, which show them to be insects, have been
given above.
Butterflies or moths will be found hovering over flowers. They belong to
the order _Lepidoptera_ (scale wings). This name is given to them because
their wings are covered with tiny scales, which fit into little sockets on
the wing much as shingles are placed on a roof. The dust which comes off on
the fingers when one catches a butterfly is composed of these scales. The
wings are always large and usually brightly colored, the legs small, and
one pair is often inconspicuous. These insects may be seen to take liquid
food through a long tubelike organ, called the _proboscis_, which they keep
rolled up under the head when not in use. The young of the butterfly or
moth are known as _caterpillars_ and feed on plants by means of a pair of
hard jaws.
Grasshoppers, found almost everywhere, and crickets, black grasshopper-like
insects often found under stones, belong to the order _Orthoptera_
(straight wings). Members of this group may usually be distinguished by
their strong, jumping hind legs, by their chewing or biting mouth parts,
and by the fact that the hind wings are folded up under the somewhat
stiffer front wings.
[Illustration: Forms of life to be met on a field trip. _A_, The red-legged
locust, one of the _Orthoptera_; _o_, the egg-layer, about natural size.
_B_, the honey bee, one of the _Hymenoptera_, about natural size. _C_, a
bug, one of the _Hemiptera_, about natural size. _D_, a butterfly, an
example of the _Lepidoptera_, slightly reduced. _E_, a house fly, an
example of the _Diptera_, about twice natural size. _F_, an orb-weaving
spider, about half natural size. (This is not an insect, note the number of
legs.) _G_, a beetle, slightly reduced, one of the _Coleoptera_.]
Another group of insects sometimes found on flowers in the fall are flies.
They belong to the order _Diptera_ (two wings). These insects are usually
rather small and have a single pair of gauzy wings. Flies are of much
importance to man because certain of their number are disease carriers.
Bugs, members of the order _Hemiptera_ (half wings), have a jointed
proboscis which points backward between the front legs. They are usually
small and may or may not have wings.
The beetles or _Coleoptera_ (sheath wings), often mistaken for bugs by the
uneducated, have the first pair of hardened wings meeting in a straight
line in the middle of the back, the second pair of wings being covered by
them. Beetles are frequently found on goldenrod blossoms in the fall.
Other forms of life, especially _spiders_, which have four pairs of walking
legs, _centipedes_ and _millepedes_, both of which are wormlike and have
many pairs of legs, may be found.
Try to discover members of the six different orders named above. Collect
specimens and bring them to the laboratory for identification.
Why do Insects live on Plants?--We have found insect life abundant on
living green plants, some visiting flowers, others hidden away on the
stalks or leaves of the plants. Let us next try to find out _why_ insects
live among and upon flowering green plants.
The Life History of the Milkweed Butterfly.--If it is possible to find on
our trip some growing milkweed, we are quite likely to find hovering near,
a golden brown and black butterfly, the monarch or milkweed butterfly
(_Anosia plexippus_). Its body, as in all insects, is composed of three
regions. The monarch frequents the milkweed in order to lay eggs there.
This she may be found doing at almost any time from June until September.
Egg and Larva.--The eggs, tiny hat-shaped dots a twentieth of an inch in
length, are fastened singly to the underside of milkweed leaves. Some
wonderful instinct leads the animal to deposit the eggs on the milkweed,
for the young feed upon no other plant. The eggs hatch out in four or five
days into rapid-growing wormlike caterpillars, each of which will shed its
skin several times before it becomes full size. These caterpillars possess,
in addition to the three pairs of true legs, additional pairs of _prolegs_
or caterpillar legs. The animal at this stage is known as a _larva_.
Formation of Pupa.--After a life of a few weeks at most, the caterpillar
stops eating and begins to spin a tiny mat of silk upon a leaf or stem. It
attaches itself to this web by the last pair of prolegs, and there hangs in
the dormant stage known as the _chrysalis_ or _pupa_. This is a resting
stage during which the body changes from a caterpillar to a butterfly.
[Illustration: Monarch butterfly: adults, larvæ, and pupa on their food
plant, the milkweed. (From a photograph loaned by the American Museum of
Natural History.)]
The Adult.--After a week or more of inactivity in the pupa state, the outer
skin is split along the back, and the adult butterfly emerges. At first the
wings are soft and much smaller than in the adult. Within fifteen minutes
to half an hour after the butterfly emerges, however, the wings are
full-sized, having been pumped full of blood and air, and the little insect
is ready after her wedding flight to follow her instinct to deposit her
eggs on a milkweed plant.
Plants furnish Insects with Food.--Food is the most important factor of any
animal's environment. The insects which we have seen on our field trip feed
on the green plants among which they live. Each insect has its own
particular favorite food plant or plants, and in many cases the eggs of the
insect are laid on the food plant so that the young may have food close at
hand. Some insects prefer the rotted wood of trees. An American zoölogist,
Packard, has estimated that over 450 kinds of insects live upon oak trees
alone. Everywhere animals are engaged in taking their nourishment from
plants, and millions of dollars of damage is done every year to gardens,
fruits, and cereal crops by insects.
[Illustration: Damage done by insects. These trees have been killed by
boring insects.]
All Animals depend on Green Plants.--But insects in their turn are the food
of birds; cats and dogs may kill birds; lions or tigers live on still
larger defenseless animals as deer or cattle. And finally comes man, who
eats the bodies of both plants and animals. But if we reduce this search
after food to its final limit, we see that green plants provide _all_ the
food for animals. For the lion or tiger eats the deer which feeds upon
grass or green shoots of young trees, or the cat eats the bird that lives
on weed seeds. Green plants supply the food of the world. Later by
experiment we will prove this.
Homes and Shelter.--After a field trip no one can escape the knowledge that
plants often give animals a home. The grass shelters millions of
grasshoppers and countless hordes of other small insects which can be
obtained by sweeping through the grass with an insect net. Some insects
build their homes in the trees or bushes on which they feed, while others
tunnel through the wood, making homes there. Spiders build webs on plants,
often using the leaves for shelter. Birds nest in trees, and many other
wild animals use the forest as their home. Man has come to use all kinds of
plant products to aid him in making his home, wood and various fibers being
the most important of these.
What do Animals do for Plants?--So far it has seemed that green plants
benefit animals and receive nothing in return. We will later see that
plants and animals _together_ form a balance of life on the earth and that
one is necessary for the other. Certain substances found in the body wastes
from animals are necessary to the life of a green plant.
Insects and Flowers.--Certain other problems can be worked out in the fall
of the year. One of these is the biological interrelations between insects
and flowers. It is easy on a field trip to find insects lighting upon
flowers. They evidently have a reason for doing this. To find out why they
go there and what they do when there, it will be first necessary for us to
study flowers with the idea of finding out what the insects get from them,
and what the flowers get from the insects.
[Illustration: A section of a flower, cut lengthwise. In the center find
the pistil with the ovary containing a number of ovules. Around this organ
notice a circle of stalked structures, the stamens; the knobs at the end
contain pollen. The outer circles of parts are called the petals and
sepals, as we go from the inside outward.]
The Use and Structure of a Flower.--It is a matter of common knowledge that
flowers form fruits and that fruits contain seeds. They are, then, very
important parts of certain plants. Our field trip shows us that flowers are
of various shapes, colors, and sizes. It will now be our problem first to
learn to know the parts of a flower, and then find out how they are fitted
to attract and receive insect visitors.
The Floral Envelope.--In a flower the expanded portion of the flower stalk,
which holds the parts of the flower, is called the _receptacle_. _The green
leaflike parts covering the unopened flower are called the sepals._
Together they form the _calyx_.
_The more brightly colored structures are the petals._ Together they form
the _corolla_. The corolla is of importance, as we shall see later, in
making the flower conspicuous. Frequently the petals or corolla have bright
marks or dots which lead down to the base of the cup of the flower, where a
sweet fluid called _nectar_ is made and secreted. It is principally this
food substance, later made into honey by bees, that makes flowers
attractive to insects.
The Essential Organs.--A flower, however, could live without sepals or
petals and still do the work for which it exists. Certain _essential
organs_ of the flower are within the so-called floral envelope. They
consist of the _stamens_ and _pistil_, the latter being in the center of
the flower. The structures with the knobbed ends are called _stamens_. In a
single stamen the boxlike part at the end is the _anther_; the stalk which
holds the anther is called the _filament_. The anther is in reality a
hollow box which produces a large number of little grains called _pollen_.
Each pistil is composed of a rather stout base called the _ovary_, and a
more or less lengthened portion rising from the ovary called the _style_.
The upper end of the style, which in some cases is somewhat broadened, is
called the _stigma_. The free end of the stigma usually secretes a sweet
fluid in which grains of pollen from flowers of the same kind can grow.
Insects as Pollinating Agents.--Insects often visit flowers to obtain
pollen as well as nectar. In so doing they may transfer some of the pollen
from one flower to another of the same kind. This transfer of pollen,
called _pollination_, is of the greatest use to the plant, as we will later
prove. No one who sees a hive of bees with their wonderful communal life
can fail to see that these insects play a great part in the life of the
flowers near the hive. A famous observer named Sir John Lubbock tested bees
and wasps to see how many trips they made daily from their homes to the
flowers, and found that the wasp went out on 116 visits during a working
day of 16 hours, while the bee made but a few less visits, and worked only
a little less time than the wasp worked. It is evident that in the course
of so many trips to the fields a bee must light on hundreds of flowers.
[Illustration: Bumblebees. _a_, queen; _b_, worker; _c_, drone.]
Adaptations in a Bee.--If we look closely at the bee, we find the body and
legs more or less covered with tiny hairs; especially are these hairs found
on the legs. _When a plant or animal structure is fitted to do a certain
kind of work, we say it is adapted to do that work._ The joints in the leg
of the bee adapt it for complicated movements; the arrangement of stiff
hairs along the edge of a concavity in one of the joints of the leg forms a
structure well adapted to hold pollen. In this way pollen is collected by
the bee and taken to the hive to be used as food. But while gathering
pollen for itself, the dust is caught on the hairs and other projections on
the body or legs and is thus carried from flower to flower. The value of
this to a flower we will see later.
Field Work.--Is Color or Odor in a Flower an Attraction to an Insect?--Sir
John Lubbock tried an experiment which it would pay a number of careful
pupils to repeat. He placed a few drops of honey on glass slips and placed
them over papers of various colors. In this way he found that the honeybee,
for example, could evidently distinguish different colors. Bees seemed to
prefer blue to any other color. Flowers of a yellow or flesh color were
preferred by flies. It would be of considerable interest for some student
to work out this problem with our native bees and with other insects by
using paper flowers and honey or sirup. Test the keenness of sight in
insects by placing a white object (a white golf ball will do) in the grass
and see how many insects will alight on it. Try to work out some method by
which you can decide whether a given insect is attracted to a flower by
odor alone.
The Sight of the Bumblebee.--The large eyes located on the sides of the
head are made up of a large number of little units, each of which is
considered to be a very simple eye. The large eyes are therefore called the
_compound eyes_. All insects are provided with compound eyes, with simple
eyes, or in most cases with both. The simple eyes of the bee may be found
by a careful observer between and above the compound eyes.
Insects can, as we have already learned, distinguish differences in color
at some distance; they can see _moving_ objects, but they do not seem to be
able to make out form well. To make up for this, they appear to have an
extremely well-developed sense of smell. Insects can distinguish at a great
distance odors which to the human nose are indistinguishable. Night-flying
insects, especially, find the flowers by the odor rather than by color.
[Illustration: The head of a bee. _A_, antennæ or "feelers"; _E_, compound
eye; _S_, simple eye; _M_, mouth parts; _T_, tongue.]
Mouth Parts of the Bee.--The mouth of the bee is adapted to take in the
foods we have mentioned, and is used for the purposes for which man would
use the hands and fingers. The honeybee laps or sucks nectar from flowers,
it chews the pollen, and it uses part of the mouth as a trowel in making
the honeycomb. The uses of the mouth parts may be made out by watching a
bee on a well-opened flower.
Suggestions for Field Work.--In any locality where flowers are abundant,
try to answer the following questions: How many bees visit the
locality in ten minutes? How many other insects alight on the flowers?
Do bees visit flowers of the same kinds in succession, or fly from one
flower on a given plant to another on a plant of a different kind? If the
bee lights on a flower cluster, does it visit more than one flower in the
same cluster? How does a bee alight? Exactly what does the bee do
when it alights?
[Illustration: Flower cluster of "butter and eggs."]
Butter and Eggs (_Linaria vulgaris_).--From July to October this very
abundant weed may be found especially along roadsides and in sunny fields.
The flower cluster forms a tall and conspicuous cluster of orange and
yellow flowers.
The corolla projects into a spur on the lower side; an upper two-parted lip
shuts down upon a lower three-parted lip. The four stamens are in pairs,
two long and two short.
[Illustration: Diagram to show how the bee pollinates "butter and eggs."
The bumblebee, upon entering the flower, rubs its head against the long
pair of anthers (_a_), then continuing to press into the flower so as to
reach the nectar at (_N_) it brushes against the stigma (_S_), thus
pollinating the flower. Inasmuch as bees visit other flowers in the same
cluster, cross-pollination would also be likely. Why?]
Certain parts of the corolla are more brightly colored than the rest of the
flower. This color is a guide to insects. Butter and eggs is visited most
by bumblebees, which are guided by the orange lip to alight just where they
can push their way into the flower. The bee, seeking the nectar secreted in
the spur, brushes his head and shoulders against the stamens. He may then,
as he pushes down after nectar, leave some pollen upon the pistil, thus
assisting in _self-pollination_. Visiting another flower of the cluster, it
would be an easy matter accidentally to transfer this pollen to the stigma
of another flower. In this way pollen is carried by the insect to another
flower of the same kind. This is known as _cross-pollination_. _By
pollination we mean the transfer of pollen from an anther to the stigma of
a flower. Self-pollination is the transfer of pollen from the anther to the
stigma of the same flower; cross-pollination is the transfer of pollen from
the anthers of one flower to the stigma of another flower on the same or
another plant of the same kind._
[Illustration: A wild orchid, a flower of the type from which Charles
Darwin worked out his theory of cross-pollination by insects.]
History of the Discoveries regarding Pollination of Flowers.--Although the
ancient Greek and Roman naturalists had some vague ideas on the subject of
pollination, it was not until the first part of the nineteenth century that
a book appeared in which a German named Conrad Sprengel worked out the
facts that the structure of certain flowers seemed to be adapted to the
visits of insects. Certain facilities were offered to an insect in the way
of easy foothold, sweet odor, and especially food in the shape of pollen
and nectar, the latter a sweet-tasting substance manufactured by certain
parts of the flower known as the nectar glands. Sprengel further discovered
the fact that pollen could be and was carried by the insect visitors from
the anthers of the flower to its stigma. It was not until the middle of the
nineteenth century, however, that an Englishman, Charles Darwin, applied
Sprengel's discoveries on the relation of insects to flowers by his
investigations upon cross-pollination. The growth of the pollen on the
stigma of the flower results eventually in the production of seeds, and
thus new plants. Many species of flowers are self-pollinated and do not do
so well in seed production if cross-pollinated, but Charles Darwin found
that some flowers which were self-pollinated did not produce so many seeds,
and that the plants which grew from their seeds were smaller and weaker
than plants from seeds produced by cross-pollinated flowers of the same
kind. He also found that plants grown from cross-pollinated seeds tended to
_vary_ more than those grown from self-pollinated seed. This has an
important bearing, as we shall see later, in the production of new
varieties of plants. Microscopic examination of the stigma at the time of
pollination also shows that the pollen from another flower usually
germinates before the pollen which has fallen from the anthers of the same
flower. This latter fact alone in most cases renders it unlikely for a
flower to produce seeds by its own pollen. Darwin worked for years on the
pollination of many insect-visited flowers, and discovered in almost every
case that showy, sweet-scented, or otherwise attractive flowers were
adapted or fitted to be cross-pollinated by insects. He also found that, in
the case of flowers that were inconspicuous in appearance, often a
compensation appeared in the odor which rendered them attractive to certain
insects. The so-called carrion flowers, pollinated by flies, are examples,
the odor in this case being like decayed flesh. Other flowers open at
night, are white, and provided with a powerful scent. Thus they attract
night-flying moths and other insects.
Other Examples of Mutual Aid between Flowers and Insects.--Many other
examples of adaptations to secure cross-pollination by means of the visits
of insects might be given. The mountain laurel, which makes our hillsides
so beautiful in late spring, shows a remarkable adaptation in having the
anthers of the stamens caught in little pockets of the corolla. The weight
of the visiting insect on the corolla releases the anther from the pocket
in which it rests so that it springs up, dusting the body of the visitor
with pollen.
[Illustration: The condition of stamens and pistils on the spiked
loosestrife (_Lythrum salicaria_).]
In some flowers, as shown by the primroses or primula of our hothouses, the
stamens and pistils are of different lengths in different flowers. Short
styles and long or high-placed filaments are found in one flower, and long
styles with short or low-placed filaments in the other. Pollination will be
effected only when some of the pollen from a low-placed anther reaches the
stigma of a short-styled flower, or when the pollen from a high anther is
placed upon a long-styled pistil. There are, as in the case of the
loosestrife, flowers having pistils and stamens of three lengths. Pollen
only grows on pistils of the same length as the stamens from which it came.
The milkweed or butterfly weed already mentioned is another example of a
flower adapted to insect pollination.[1]
Footnote 1: For an excellent account of cross-pollination of this
flower, the reader is referred to W. C. Stevens, _Introduction to
Botany_. Orchids are well known to botanists as showing some very
wonderful adaptations. A classic easily read is Darwin, _On the
Fertilization of Orchids_.
[Illustration: The pronuba moth within the yucca flower.]
A very remarkable instance of insect help is found in the pollination of
the yucca, a semitropical lily which lives in deserts (to be seen in most
botanic gardens). In this flower the stigmatic surface is above the anther,
and the pollen is sticky and cannot be transferred except by insect aid.
This is accomplished in a remarkable manner. A little moth, called the
_pronuba_, after gathering pollen from an anther, deposits an egg in the
ovary of the pistil, and then rubs its load of pollen over the stigma of
the flower. The young hatch out and feed on the young seeds which have
grown because of the pollen placed on the stigma by the mother. The baby
caterpillars eat some of the developing seeds and later bore out of the
seed pod and escape to the ground, leaving the plant to develop the
remaining seeds without further molestation.
[Illustration: The pronuba pollinating the pistil of the yucca.]
The fig insect (_Blastophaga grossorum_) is another member of the insect
tribe that is of considerable economic importance. It is only in recent
years that the fruit growers of California have discovered that the
fertilization of the female flowers is brought about by a gallfly which
bores into the young fruit. By importing the gallflies it has been possible
to grow figs where for many years it was believed that the climate
prevented figs from ripening.
[Illustration: Pod of yucca showing where the young pronubas escaped.]
Other Flower Visitors.--Other insects besides those already mentioned are
pollen carriers for flowers. Among the most useful are moths and
butterflies. Projecting from each side of the head of a butterfly is a
fluffy structure, the palp. This collects and carries a large amount of
pollen, which is deposited upon the stigmas of other flowers when the
butterfly pushes its head down into the flower tube after nectar. The
scales and hairs on the wings, legs, and body also carry pollen.
[Illustration: A humming bird about to cross-pollinate a lily.]
Flies and some other insects are agents in cross-pollination. Humming birds
are also active agents in some flowers. Snails are said in rare instances
to carry pollen. Man and the domesticated animals undoubtedly frequently
pollinate flowers by brushing past them through the fields.
[Illustration: A cornfield showing staminate and pistillate flowers, the
latter having become grains of corn. An ear of corn is a bunch of ripened
fruits.]
Pollination by the Wind.--Not all flowers are dependent upon insects or
other animals for cross-pollination. Many of the earliest of spring flowers
appear almost before the insects do. Such flowers are dependent upon the
wind for carrying pollen from the stamens of one flower to the pistil of
another. Most of our common trees, oak, poplar, maple, and others, are
cross-pollinated almost entirely by the wind.
Flowers pollinated by the wind are generally inconspicuous and often lack a
corolla. The anthers are exposed to the wind and provided with much pollen,
while the surface of the stigma may be long and feathery. Such flowers may
also lack odor, nectar, and bright color. Can you tell why?
Imperfect Flowers.--Some flowers, the wind-pollinated ones in particular,
are imperfect; that is, they lack either stamens or pistils. Again, in some
cases, imperfect flowers having stamens only are alone found on one plant,
while those flowers having pistils only are found on another plant of the
same kind. In such flowers, cross-pollination must of necessity follow.
Many of our common trees are examples.
[Illustration: The flower of "Lady Washington" geranium, in which stamens
and pistil ripen at different times, thus insuring cross-pollination. _A_,
flower with ripe stamens; _B_, flower with stamens withered and ripe
pistil.]
Other Cases.--The stamens and pistil ripen at different times in some
flowers. The "Lady Washington" geranium, a common house plant, shows this
condition. Here also cross-pollination must take place if seeds are to be
formed.
Summary.--If we now collect our observations upon flowers with a view to
making a summary of the different devices flowers have assumed to prevent
self-pollination and to secure cross-pollination, we find that they are as
follows:--
_(1) The stamens and pistils may be found in separate flowers, either on
the same or on different plants._
_(2) The stamens may produce pollen before the pistil is ready to receive
it, or vice versa._
_(3) The stamens and pistils may be so placed with reference to each other
that pollination can be brought about only by outside assistance._
Artificial Cross-pollination and its Practical Benefits to Man.--Artificial
cross-pollination is practiced by plant breeders and can easily be tried in
the laboratory or at home. First the anthers must be carefully removed from
the bud of the flower so as to eliminate all possibility of
self-pollination. The flower must then be covered so as to prevent access
of pollen from without; when the ovary is sufficiently developed, pollen
from another flower, having the characters desired, is placed on the stigma
and the flower again covered to prevent any other pollen reaching the
flower. The seeds from this flower when planted _may_ give rise to plants
with the best characters of each of the plants which contributed to the
making of the seeds.
REFERENCE BOOKS
ELEMENTARY
Hunter, _Laboratory Problems in Civic Biology_. American
Book Company.
Andrews, _A Practical Course in Botany_, pages 214-249.
American Book Company.
Atkinson, _First Studies of Plant Life_, Chaps. XXV-XXVI.
Ginn and Company.
Coulter, _Plant Life and Plant Uses_, pages 301-322.
American Book Company.
Dana, _Plants and their Children_, pages 187-255. American
Book Company.
Lubbock, _Flowers, Fruits, and Leaves_, Part I. The
Macmillan Company.
Needham, _General Biology_, pages 1-50. The Comstalk
Publishing Company.
Newell, _A Reader in Botany_, Part II, pages 1-96. Ginn and
Company.
Sharpe, _A Laboratory Manual in Biology_, pages 43-48.
American Book Company.
ADVANCED
Bailey, _Plant Breeding_. The Macmillan Company.
Campbell, _Lectures on the Evolution of Plants_. The
Macmillan Company.
Coulter, Barnes, and Cowles, _A Textbook of Botany_, Part
II. American Book Company.
Darwin, _Different Forms of Flowers on Plants of the Same
Species_, D. Appleton and Company.
Darwin, _Fertilization in the Vegetable Kingdom_, Chaps. I
and II. D. Appleton and Company.
Darwin, _Orchids Fertilized by Insects_, D. Appleton and
Company.
Lubbock, _British Wild Flowers_. The Macmillan Company.
Müller, _The Fertilization of Flowers_. The Macmillan
Company.
IV. THE FUNCTIONS AND COMPOSITION OF LIVING THINGS
_Problems.--To discover the functions of living matter._
_(a) In a living plant._
_(b) In a living animal._
LABORATORY SUGGESTIONS
_Laboratory study of a living plant._--Any whole plant may
be used; a weed is preferable.
_Laboratory demonstration or home study._--The functions of
a living animal.
_Demonstration._--The growth of pollen tubes.
_Laboratory exercise._--The growth of the mature ovary into
the fruit, _e.g._ bean or pea pod.
A Living Plant and a Living Animal Compared.--A walk into the fields or any
vacant lot on a day in the early fall will give us first-hand acquaintance
with many common plants which, because of their ability to grow under
somewhat unfavorable conditions, are called _weeds_. Such plants--the
dandelion, butter and eggs, the shepherd's purse--are particularly well
fitted by nature to produce many of their kind, and by this means drive out
other plants which cannot do this so well. On these or other plants we find
feeding several kinds of animals, usually insects.
If we attempt to compare, for example, a grasshopper with the plant on
which it feeds, we see several points of likeness and difference at once.
Both plant and insect are made up of parts, each of which, as the stem of
the plant or the leg of the insect, appears to be distinct, but which is a
part of the whole living plant or animal. Each part of the living plant or
animal which has a separate work to do is called an _organ_. Thus plants
and animals are spoken of as living _organisms_.
[Illustration: A weed--notice the unfavorable environment.]
Functions of the Parts of a Plant.--We are all familiar with the parts of a
plant,--the root, stem, leaves, flowers, and fruit. But we may not know so
much about their uses to the plant. Each of these structures differs from
every other part, and each has a separate work or function to perform for
the plant. _The root holds the plant firmly in the ground and takes in
water and mineral matter from the soil; the stem holds the leaves up to the
light and acts as a pathway for fluids between the root and leaves; the
leaves, under certain conditions, manufacture food for the plant and
breathe; the flowers form the fruits; the fruits hold the seeds, which in
turn hold young plants which are capable of reproducing adult plants of the
same kind._
The Functions of an Animal.--As we have already seen, the grasshopper has a
head, a jointed body composed of a middle and a hind part, three pairs of
jointed legs, and two pairs of wings. Obviously, the wings and legs are
used for movement; a careful watching of the hind part of the animal shows
us that breathing movements are taking place; a bit of grass placed before
it may be eaten, the tiny black jaws biting little pieces out of the grass.
If disturbed, the insect hops away, and if we try to get it, it jumps or
flies away, evidently seeing us before we can grasp it. Hundreds of little
grasshoppers on the grass indicate that the grasshopper can reproduce its
own kind, but in other respects the animal seems quite unlike the plant.
The animal moves, breathes, feeds, and has sensation, while _apparently_
the plant does none of these. It will be the purpose of later chapters to
prove that the functions of plants and animals are in many respects similar
and that _both plants_ and _animals breathe_, _feed_, and _reproduce_.
[Illustration: Section through the blade of a leaf. _e_, cells of the upper
surface; _d_, cells of the lower surface; _i_, air spaces in the leaf; _v_,
vein in cross sections; _p_, green cells.]
Organs.--If we look carefully at the organ of a plant called a leaf, we
find that the materials of which it is composed do not appear to be
everywhere the same. The leaf is much thinner and more delicate in some
parts than in others. Holding the flat, expanded blade away from the branch
is a little stalk, which extends into the blade of the leaf. Here it splits
up into a network of tiny "veins" which evidently form a framework for the
flat blade somewhat as the sticks of a kite hold the paper in place. If we
examine under the compound microscope a thin section cut across the leaf,
we shall find that the veins as well as the other parts are made up of many
tiny boxlike units of various sizes and shapes. These smallest units of
building material of the plant or animal disclosed by the compound
microscope are called _cells_. The organs of a plant or animal are built of
these tiny structures.
[Illustration: Several cells of _Elodea_, a water plant. _chl._,
chlorophyll bodies; _c.s._, cell sap; _c.w._, cell wall; _n._, nucleus;
_p._, protoplasm. The arrows show the direction of the protoplasmic
movement.]
Tissues.[2]--The cells which form certain parts of the veins, the flat
blade, or other portions of the plant, are often found in groups or
collections, the cells of which are more or less alike in size and shape.
Such a collection of cells is called a _tissue_. Examples of tissues are
the cells covering the outside of the human body, the muscle cells, which
collectively allow of movement, bony tissues which form the framework to
which the muscles are attached, and many others.
Footnote 2: _To the Teacher._--Any simple plant or animal
tissue can be used to demonstrate the cell. Epidermal cells
may be stripped from the body of the frog or obtained by
scraping the inside of one's mouth. The thin skin from an
onion stained with tincture of iodine shows well, as do thin
sections of a young stem, as the bean or pea. One of the
best places to study a tissue and the cells of which it is
composed is in the leaf of a green water plant, _Elodea_. In
this plant the cells are large, and not only their outline,
but the movement of the living matter within the cells, may
easily be seen, and the parts described in the next
paragraph can be demonstrated.
[Illustration: A cell. _ch._, chromosomes; _c.w._, cell wall; _n._,
nucleus; _p._, protoplasm.]
Cells.--_A cell may be defined as a tiny mass of living matter containing a
nucleus, either living alone or forming a unit of the building material of
a living thing._ The living matter of which all cells are formed is known
as _protoplasm_ (formed from two Greek words meaning _first form_). If we
examine under a compound microscope a small bit of the water plant
_Elodea_, we see a number of structures resembling bricks in a wall. Each
"brick," however, is really a plant cell bounded by a thin wall. If we look
carefully, we can see that the material inside of this wall is slowly
moving and is carrying around in its substance a number of little green
bodies. This moving substance is living matter, the protoplasm of the cell.
The green bodies (the _chlorophyll_ bodies) we shall learn more about
later; they are found only in plant cells. All plant and animal cells
appear to be alike in the fact that every living cell possesses a structure
known as the _nucleus_ (pl. _nuclei_), which is found within the body of
the cell. This nucleus is not easy to find in the cells of _Elodea_. Within
the nucleus of all cells are found certain bodies called _chromosomes_.
These chromosomes in a given plant or animal are always constant in number.
These chromosomes are supposed to be the bearers of the qualities which we
believe can be handed down from plant to plant and from animal to animal,
in other words, the inheritable qualities which make the offspring like its
parents.
How Cells form Others.--Cells grow to a certain size and then split into
two new cells. In this process, which is of very great importance in the
growth of both plants and animals, the nucleus divides first. The
chromosomes also divide, each splitting lengthwise and the parts going in
equal numbers to each of the two cells formed from the old cell. In this
way the matter in the chromosomes is divided equally between the two new
cells. Then the rest of the protoplasm separates, and two new cells are
formed. This process is known as _fission_. It is the usual method of
growth found in the tissues of plants and animals.
[Illustration: Stages in the division of one cell to form two. Which part
of the cell divides first? What seems to become of the chromosomes?]
Cells of Various Sizes and Shapes.--Plant cells and animal cells are of
very diverse shapes and sizes. There are cells so large that they can
easily be seen with the unaided eye; for example, the root hairs of plants
and eggs of some animals. On the other hand, cells may be so minute, as in
the case of the plant cells named bacteria, that several million might be
present in a few drops of milk. The forms of cells may be extremely varied
in different tissues; they may assume the form of cubes, columns, spheres,
flat plates, or may be extremely irregular in shape. One kind of tissue
cell, found in man, has a body so small as to be quite invisible to the
naked eye, although it has a prolongation several feet in length. Such are
some of the cells of the nervous system of man and other large animals, as
the ox, elephant, and whale.
Varying Sizes of Living Things.--Plant cells and animal cells may live
alone, or they may form collections of cells. Some plants are so simple in
structure as to be formed of only one kind of cells. Usually living
organisms are composed of several groups of different kinds of cells. It is
only necessary to call attention to the fact that such collections of cells
may form organisms so tiny as to be barely visible to the eye; as, for
instance, some of the small flowerless plants or many of the tiny animals
living in fresh water or salt water. On the other hand, among animals, the
bulk of the elephant and whale, and among plants the big trees of
California, stand out as notable examples. The large plants and animals are
made up of _more_, not necessarily larger, cells.
What Protoplasm can Do.--It responds to influences or stimulation from
without its own substance. Both plants and animals are sensitive to touch
or stimulation by light, heat or cold, certain chemical substances,
gravity, and electricity. Green plants turn toward the source of light.
Some animals are attracted to light and others repelled by it; the
earthworm is an example of the latter. _Protoplasm is thus said to be
irritable._
_Protoplasm has the power to contract and to move._ Muscular movement is a
familiar instance of this power. Movement may also take place in plants.
Some plants fold up their leaves at night; others, like the sensitive
plant, fold their leaflets when touched.
_Protoplasm can form new living matter out of food._ To do this, food
materials must be absorbed into the cells of the living organism. To make
protoplasm, it is evident that the same chemical elements must enter into
the composition of the food substances as are found in living matter. The
simplest plants and animals have this wonderful power as certainly
developed as the most complex forms of life.
_Protoplasm, be it in plant or animal, breathes and throws off waste
materials._ When a living thing does work oxygen unites with food in the
body; the food is burned or _oxidized_ and work is done by means of the
energy released from the food. The waste materials are _excreted_ or passed
out. Plants and animals alike pass off the carbon dioxide which results
from the oxidation of food and of parts of their own bodies. Animals
eliminate wastes containing nitrogen through the skin and the kidneys.
_Protoplasm can reproduce, that is, form other matter like itself._ New
plants are constantly appearing to take the places of those that die. The
supply of living things upon the earth is not decreasing; reproduction is
constantly taking place. In a general way it is possible to say that plants
and animals reproduce in a very similar manner.
The Importance of Reproduction.--Reproduction is the final process that
plants and animals are called upon to perform. Without the formation of
_new_ living things no progress would be possible on the earth. We have
found that insects help flowering plants in this process. Let us now see
exactly what happens when pollen is placed by the bee on the stigma of
another flower of the same kind. To understand this process of reproduction
in flowers, we must first study carefully pollen grains from the anther of
some growing flower.
[Illustration: Pollen grains of different shapes and sizes.]
Pollen.--Pollen grains of various flowers, when seen under the microscope,
differ greatly in form and appearance. Some are relatively large, some
small, some rough, others smooth, some spherical, and others angular. They
all agree, however, in having a thick wall, with a thin membrane under it,
the whole inclosing a mass of protoplasm. At an early stage the pollen
grain contains but a single cell. A little later, however, two nuclei may
be found in the protoplasm. Hence we know that at least two cells exist
there, one of which is called the sperm cell; its nucleus is the sperm
nucleus.
[Illustration: A pollen grain greatly magnified. Two nuclei are found (_n_,
_n'_) at this stage of its growth.]
[Illustration: Three stages in the germination of the pollen grain. The
nuclei in the tube in (3) are the sperm nuclei. Drawn under the compound
microscope.]
Growth of Pollen Grains.--Under certain conditions a pollen grain will grow
or germinate. This growth can be artificially produced in the laboratory by
sprinkling pollen from well-opened flowers of sweet pea or nasturtium on a
solution of 15 parts of sugar to 100 of water. Left for a few hours in a
warm and moist place and then examined under the microscope, the grains of
pollen will be found to have germinated, a long, threadlike mass of
protoplasm growing from it into the sugar solution. The presence of this
sugar solution was sufficient to induce growth. When the pollen grain
germinates, the nuclei enter the threadlike growth (this growth is called
the pollen tube; see Figure). One of the nuclei which grows into the pollen
tube is known as the _sperm nucleus_.
[Illustration: Fertilization of the ovule. A flower cut down lengthwise
(only one side shown). The pollen tube is seen entering the ovule. _a_,
anther; _f_, filament; _pg_, pollen grain; _s_, stigmatic surface; _pt_,
pollen tube; _st_, style; _o_, ovary; _m_, micropyle; _sp_, space within
ovary; _e_, egg cell; _P_, petal; _S_, sepal.]
Fertilization of the Flower.--If we cut the pistil of a large flower (as a
lily) lengthwise, we notice that the style appears to be composed of rather
spongy material in the interior; the ovary is hollow and is seen to contain
a number of rounded structures which appear to grow out from the wall of
the ovary. These are the _ovules_. The ovules, under certain conditions,
will become _seeds_. An explanation of these conditions may be had if we
examine, under the microscope, a very thin section of a pistil, on which
pollen has begun to germinate. The central part of the style is found to be
either hollow or composed of a soft tissue through which the pollen tube
can easily grow. Upon germination, the pollen tube grows downward through
the spongy center of the style, follows the path of least resistance to the
space within the ovary, and there enters the ovule. It is believed that
some chemical influence thus attracts the pollen tube. When it reaches the
ovary, the sperm cell penetrates an ovule by making its way through a
little hole called the _micropyle_. It then grows toward a clear bit of
protoplasm known as the _embryo sac_. The embryo sac is an ovoid space,
microscopic in size, filled with semifluid protoplasm containing several
nuclei. (See Figure.) _One of the nuclei, with the protoplasm immediately
surrounding it, is called the egg cell._ It is this cell that the sperm
nucleus of the pollen tube grows toward; ultimately the sperm nucleus
reaches the egg nucleus and unites with it. _The two nuclei, after coming
together, unite to form a single cell. This process is known as
fertilization._ This single cell formed by the union of the pollen tube
cell or sperm and the egg cell is now called a _fertilized egg_.
Development of Ovule into Seed.--_The primary reason for the existence of a
flower is that it may produce seeds from which future plants will grow.
After fertilization the ovule grows into a seed._ The first beginning of
the growth of the seed takes place at the moment of fertilization. From
that time on there is a growth of the fertilized egg within the ovule which
makes a baby plant called the _embryo_. _The embryo will give rise to the
adult plant._
[Illustration: The fruit of the locust, a bean-like fruit. _p_, the
attachment to the placenta; _s_, the stigma.]
A Typical Fruit,--the Pea or Bean Pod.--If a withered flower of any one of
the pea or bean family is examined carefully, it will be found that the
pistil of the flower continues to grow after the rest of the flower
withers. If we remove the pistil from such a flower and examine it
carefully, we find that it is the ovary that has enlarged. The space within
the ovary has become nearly filled with a number of nearly ovoid bodies,
attached along one edge of the inner wall. These we recognize as the young
seeds.
The pod of a bean, pea, or locust illustrates well the growth from the
flower. The pod, which is in reality a ripened ovary with other parts of
the pistil attached to it, is considered as a _fruit_. By definition, _a
fruit is a ripened ovary and its contents together with any parts of the
flower that may be attached to it_. The chief use of the fruit to the
flower is to hold and to protect the seeds; it may ultimately distribute
them where they can reproduce young plants.
[Illustration: The development of an apple. Notice that in this fruit
additional parts besides the ovary (_o_) become part of the fruit. Certain
outer parts of the flower, the sepals (_s_) and receptacle, become the
fleshy part of the fruit, while the ovary becomes the core. Stages numbered
1 to 7 are in the order of development.]
The Necessity of Fruit and Seed Dispersal to a Plant.--We have seen that
the chief reason for flowers, from the plant's standpoint, is to produce
fruits which contain seeds. Reproduction and the ultimate scattering of
fruits and seeds are absolutely necessary in order that colonies of plants
may reach new localities. It is evident that plants best fitted to scatter
their seeds, or place fruits containing the seeds some little distance from
the parent plants, are the ones which will spread most rapidly. A plant, if
it is to advance into new territory, must get its seeds there first. Plants
which are best fitted to do this are the most widely distributed on the
earth.
How Seeds and Fruits are Scattered.--Seed dispersal is accomplished in many
different ways. Some plants produce enormous numbers of seeds which may or
may not have special devices to aid in their scattering. Most weeds are
thus started "in pastures new." Some prolific plants, like the milkweed,
have _seeds_ with a little tuft of hairlike down which allows them to be
carried by the wind. Others, as the omnipresent dandelion, have their
_fruits_ provided with a similar structure, the pappus. Some plants, as the
burdock and clotbur, have fruits provided with tiny hooks which stick to
the hair of animals, thus proving a means of transportation. Most fleshy
fruits contain indigestible seeds, so that when the fruits are eaten by
animals the seeds are passed off from the body unharmed and may, if
favorably placed, grow. Nuts of various kinds are often carried off by
animals, buried, and forgotten, to grow later. Such are a few of the ways
in which seeds are scattered. All other things being equal, the plants best
equipped to scatter seeds or fruits are those which will drive out other
plants in a given locality. Because of their adaptations they are likely to
be very numerous, and when unfavorable conditions come, for that reason, if
for no other, are likely to survive. Such plants are best exemplified in
the weeds of the grassplots and gardens.
REFERENCE BOOKS
ELEMENTARY
Hunter, _Laboratory Problems in Civic Biology_. American
Book Company.
Andrews, _A Practical Course in Botany_, pages 250-270.
American Book Company.
Atkinson, _First Studies of Plant Life_, Chaps. XXV-XXVI.
Ginn and Company.
Bailey, _Lessons with Plants_, Part III, pages 131-250. The
Macmillan Company.
Coulter, _Plant Life and Plant Uses_. American Book Company.
Dana, _Plants and their Children_, pages 187-255. American
Book Company.
Lubbock, _Flowers, Fruit, and Leaves_, Part I. The Macmillan
Company.
Newell, _A Reader in Botany_, Part II, pages 1-96. Ginn and
Company.
ADVANCED
Bailey, _Plant Breeding_. The Macmillan Company.
Campbell, _Lectures on the Evolution of Plants_. The
Macmillan Company.
Coulter, Barnes, and Cowles, _A Textbook of Botany_, Part
II. American Book Company.
Darwin, _Different Forms of Flowers on Plants of the Same
Species_. Appleton.
Darwin, _Fertilization in the Vegetable Kingdom_, Chaps. I
and II. Appleton.
Darwin, _Orchids Fertilized by Insects_. D. Appleton and
Company.
Müller, _The Fertilization of Flowers_. The Macmillan
Company.
V. PLANT GROWTH AND NUTRITION. CAUSES OF GROWTH
_Problem.--What causes a young plant to grow?_
_(a) The relation of the young plant to its food supply._
_(b) The outside conditions necessary for germination._
_(c) What the young plant does with its food supply._
_(d) How a plant or animal is able to use its food supply._
_(e) How a plant or animal prepares food to use in various parts
of the body._
LABORATORY SUGGESTIONS
_Laboratory exercise._--Examination of bean in pod.
Examination and identification of parts of bean seed.
_Laboratory demonstration._--Tests for the nutrients:
starch, fats or oils, protein.
_Laboratory demonstration._--Proof that such foods exist in
bean.
_Home work._--Test of various common foods for nutrients.
Tabulate results.
_Extra home work by selected pupils._--Factors necessary for
germination of bean. Demonstration of experiments to class.
_Demonstration._--Oxidation of candle in closed jar. Test
with lime water for products of oxidation.
_Demonstration._--Proof that materials are oxidized within
the human body.
_Demonstration._--Oxidation takes place in growing seeds.
Test for oxidation products. Oxygen necessary for
germination.
_Laboratory exercise._--Examination of corn on cob, the corn
grain, longitudinal sections of corn grain stained with
iodine to show that embryo is distinct from food supply.
_Demonstration._--Test for grape sugar.
_Demonstration._--Grape sugar present in growing corn grain.
_Demonstration._--The action of diastase on starch.
Conditions necessary for action of diastase.
What makes a Seed Grow.--The general problem of the pages that follow will
be to explain how the baby plant, or _embryo_, formed in the seed as the
result of the fertilization of the egg cell, is able to grow into an adult
plant. Two sets of factors are necessary for its growth: first, the
presence of food to give the young plant a start; second, certain
stimulating factors outside the young plant, such as water and heat.
[Illustration: Three views of a kidney bean, the lower one having one
cotyledon removed to show the hypocotyl and plumule.]
If we open a bean pod, we find the seeds lying along one edge of the pod,
each attached by a little stalk to the inner wall of the ovary. If we pull
a single bean from its attachment, we find that the stalk leaves a scar on
the coat of the bean; this scar is called the _hilum_. The tiny hole near
the hilum is called the _micropyle_. Turn back to the figure (page 54)
showing the ovule in the ovary. Find there the little hole through which
the pollen tube reached the embryo sac. This hole is identical with the
micropyle in the seed. The thick outer coat (the _testa_) is easily removed
from a soaked bean, the delicate coat under it easily escaping notice. The
seed separates into two parts; these are called the _cotyledons_. If you
pull apart the cotyledons very carefully, you find certain other structures
between them. The rodlike part is called the _hypocotyl_ (meaning _under
the cotyledons_). This will later form the root (and part of the stem) of
the young bean plant. The first true leaves, very tiny structures, are
folded together between the cotyledons. That part of the plant above the
cotyledons is known as the _plumule_ or _epicotyl_ (meaning _above the
cotyledons_). All the parts of the seed within the seed coats together form
the _embryo_ or young plant. A bean seed contains, then, a tiny _plant_
protected by a tough coat.
Food in the Cotyledons.--The problem now before us is to find out how the
embryo of the bean is adapted to grow into an adult plant. Up to this stage
of its existence it has had the advantage of food and protection from the
parent plant. Now it must begin the battle of life alone. We shall find in
all our work with plants and animals that the problem of food supply is
always the most important problem to be solved by the growing organism. Let
us see if the embryo is able to get a start in life (which many animals get
in the egg) from food provided for it within its own body.
Organic Nutrients.--Organic foods (those which come from living sources)
are made up of two kinds of substances, the _nutrients_ or food substances
and _wastes_ or _refuse_. An egg, for example, contains the white and the
yolk, composed of nutrients, and the shell, which is waste. The organic
nutrients are classed in three groups.
_Carbohydrates_, foods which contain carbon, hydrogen, and oxygen in a
certain fixed proportion (C{6}H{10}O{5} is an example). They are the
simplest of these very complex chemical compounds we call organic
nutrients. Starch and sugar are common examples of carbohydrates.
_Fats and Oils._--These foods are also composed of carbon, hydrogen, and
oxygen in a proportion which enables them to unite readily with oxygen.
_Proteins._--A third group of organic foods, proteins, are the most complex
of all in their composition, and have, besides carbon, oxygen, and
hydrogen, the element nitrogen and minute quantities of other elements.
[Illustration: Starch grains in the cells of a potato tuber.]
Test for Starch.--If we boil water with a piece of laundry starch in a test
tube, then cool it and add to the mixture two or three drops of iodine
solution,[3] we find that the mixture in the test tube turns purple or deep
blue. It has been discovered by experiment that starch, and no _other known
substance_, will be turned purple or dark blue by iodine. Therefore, iodine
solution has come to be used as a test for the presence of starch.
Footnote 3: Iodine solution is made by simply adding a few
crystals of the element iodine to 95 per cent alcohol; or,
better, take by weight 1 gram of iodine crystals, 2/3 gram
of iodide of potassium, and dilute to a dark brown color in
weak alcohol (35 per cent) or distilled water.
[Illustration: Test for Starch.]
Starch in the Bean.--If we mash up a little piece of a bean cotyledon which
has been previously soaked in water, and test for starch with iodine
solution, the characteristic blue-black color appears, showing the presence
of the starch. If a little of the stained material is mounted in water on a
glass slide under the compound microscope, you will find that the starch is
in the form of little ovoid bodies called _starch grains_. The starch
grains and other food products are made use of by the growing plant.
Test for Oils.--If the substance believed to contain oil is rubbed on brown
paper or is placed on paper and then heated in an oven, the presence of oil
will be known by a translucent spot on the paper.
[Illustration: Test for protein.]
Protein in the Bean.--Another nutrient present in the bean cotyledon is
_protein_. Several tests are used to detect the presence of this nutrient.
The following is one of the best known:--
Place in a test tube the substance to be tested; for example, a bit of
hard-boiled egg. Pour over it a little strong (60 per cent) nitric acid and
heat gently. Note the color that appears--a lemon yellow. If the egg is
washed in water and a little ammonium hydrate added, the color changes to a
deep orange, showing that a protein is present.
If the protein is in a liquid state, its presence may be proved by heating,
for when it coagulates or thickens, as does the white of an egg when
boiled, protein in the form of an _albumin_ is present.
Another characteristic protein test easily made at home is burning the
substance. If it burns with the odor of burning feathers or leather, then
protein forms part of its composition.[4]
Footnote 4: Other tests somewhat more reliable, but much
more delicate, are the biuret test and test with Millon's
reagent.
A test of the cotyledon of a bean for protein food with nitric acid and
ammonium hydrate shows us the presence of this food. Beans are found by
actual test to contain about 23 per cent of protein, 59 per cent of
carbohydrates, and about 2 per cent oils. The young plant within a pea or
bean is thus shown to be well supplied with nourishment until it is able to
take care of itself. In this respect it is somewhat like a young animal
within the egg, a bird or fish, for example.
Beans and Peas as Food for Man.--So much food is stored in legumes (as
beans and peas) that man has come to consider them a very valuable and
cheap source of food. Study carefully the following table:--
NUTRIENTS FURNISHED FOR TEN CENTS IN BEANS AND PEAS AT
CERTAIN PRICES PER POUND
=========================================================================
| | TEN CENTS WILL PAY FOR
| PRICES |------------------------------------------
FOOD MATERIALS | PER | TOTAL | | |
AS PURCHASED | POUND | FOOD | PROTEIN | FAT |CARBOHYDRATES
| |MATERIAL | | |
---------------------|--------|---------|---------|--------|-------------
| _Cents_| _Pounds_| _Pounds_|_Pounds_| _Pounds_
Kidney beans, dried | 5 | 2.00 | 0.45 | 0.04 | 1.19
Lima beans, fresh, | | | | |
shelled | 8 | 1.25 | .04 | -- | .12
Lima beans, dried | 6 | 1.67 | .30 | .03 | 1.10
String beans, fresh, | | | | |
30 cents per peck | 3 | 3.33 | .07 | .01 | .23
Beans, baked, canned | 5 | 2.00 | .14 | .05 | .39
Lentils, dried | 10 | 1.00 | .26 | .01 | .59
Peas, green, in pod, | | | | |
30 cents per peck | 3 | 3.33 | .12 | .01 | .33
Peas, dried | 4 | 2.50 | .62 | .03 | 1.55
=========================================================================
[Illustration: A series of early stages in the germination of the kidney
bean.]
Germination of the Bean.--If dry seeds are planted in sawdust or earth,
they will not grow. A moderate supply of water must be given to them. If
seeds were to be kept in a freezing temperature or at a very high
temperature, no growth would take place. A moderate temperature and a
moderate water supply are most favorable for their development.
[Illustration: Bean seedlings. The older seedlings at the left have used up
all of the food supply in the cotyledons.]
If some beans were planted so that we might make a record of their growth,
we would find the first signs of germination to be the breaking of the
testa and the pushing outward of the hypocotyl to form the first root. A
little later the hypocotyl begins to curve downward. A later stage shows
the hypocotyl lifting the cotyledon upward. In consequence the hypocotyl
forms an arch, dragging after it the bulky cotyledons. The stem, as soon as
it is released from the ground, straightens out. From between the
cotyledons the budlike plumule or epicotyl grows upward, forming the first
true leaves and all of the stem above the cotyledons. As growth continues,
we notice that the cotyledons become smaller and smaller, until their food
contents are completely absorbed into the young plant. The young plant is
now able to care for itself and may be said to have passed through the
stages of germination.
What makes an Engine Go.--If we examine the sawdust or soil in which the
seeds are growing, we find it forced up by the growing seed. Evidently work
was done; in other words, _energy_ was released by the seeds. A familiar
example of release of energy is seen in an engine. Coal is placed in the
firebox and lighted, the lower door of the furnace is then opened so as to
make a draft of air which will reach the coal. You know the result. The
coal burns, heat is given off, causing the water in the boiler to make
steam, the engine wheels to turn, and work to be done. Let us see what
happens from the chemical standpoint.
Coal, Organic Matter.--Coal is made largely from dead plants, long since
pressed into its present hard form. It contains a large amount of a
chemical element called carbon, the presence of which is characteristic of
all organic material.
[Illustration: The limewater test. The tube at the right shows the effect
of the carbon dioxide.]
Oxidation, its Results.--When things containing carbon are lighted, they
burn. If we place a lighted candle which contains carbon in a closed glass
jar, the candle soon goes out. If we then carefully test the air in the jar
with a substance known as _limewater_,[5] the latter, when shaken up with
the air in the jar, turns milky. This test proves the presence in the jar
of a gas, known as _carbon dioxide_. This gas is formed by the carbon of
the candle uniting with the oxygen in the air. When the oxygen of the air
in the jar was used up, the flame went out, showing that oxygen is
necessary to make a thing burn. This uniting of oxygen with some other
substance is called _oxidation_.
Footnote 5: Limewater can be made by shaking up a piece of
quicklime the size of your fist in about two quarts of
water. Filter or strain the limewater into bottles and it is
ready for use.
[Illustration: Diagram to show that when a piece of wood is burned it forms
water and carbon dioxide.]
Oxidation possible without a Flame.--But a flame is not necessary for
oxidation. Iron, if left in a damp place, becomes rusty. A union between
the oxygen in the water or air and the iron makes what is known as iron
oxide or rust. This is an example of _slow oxidation_.
Oxidation in our Bodies.--If we expel the air from our lungs through a tube
into a bottle of limewater, we notice the limewater becomes milky.
Evidently carbon dioxide is formed in our own bodies and oxidation takes
place there. Is it fair to believe that the heat of our body (for example,
98.6° Fahrenheit under the tongue) is due to oxidation within the body, and
that the work we do results from this chemical process. If so, what is
oxidized?
Energy comes from Foods.--From the foregoing experiment it is evident that
food is oxidized within the human body to release energy for our daily
work. Is it not logical to suppose that all living things, both plant and
animal, release energy as the result of oxidation of foods within their
cells? Let us see if this is true in the case of the pea.
Food oxidized in Germinating Seeds.--If we take equal numbers of soaked
peas, placed in two bottles, one tightly stoppered, the other having no
stopper, both bottles being exposed to identical conditions of light,
temperature, and moisture, we find that the seeds in both bottles start to
germinate, but that those in the closed bottle soon stop, while those in
the open jar continue to grow almost as well as similar seeds placed in an
open dish would.
[Illustration: Experiment that shows the necessity for air in germination.]
Why did not the seeds in the covered jar germinate? To answer this
question, let us carefully remove the stopper from the stoppered jar and
insert a lighted candle. The candle goes out at once. The surer test of
limewater shows the presence of carbon dioxide in the jar. The carbon of
the foodstuffs of the pea united with the oxygen of the air, forming carbon
dioxide. Growth stopped as soon as the oxygen was exhausted. The presence
of carbon dioxide in the jar is an indication that a very important process
which we associate with animals rather than plants, that of _respiration_,
is taking place. The seed, in order to release the energy locked up in its
food supply, must have oxygen, so that the oxidation of the food may take
place. _Hence a constant supply of fresh air is an important factor in
germination._ It is important that air should penetrate between the grains
of soil around a seed. The frequent stirring of the soil enables the air to
reach the seed. Air also acts upon some materials in the soil and puts them
in a form that the germinating seed can use. This necessity for oxygen
shows us at least one reason why the farmer plows and harrows a field and
one important use of the earthworm. Explain.
[Illustration: A grain of corn cut lengthwise. _C_, cotyledon; _E_,
endosperm; _H_, hypocotyl; _P_, plumule.]
Structure of a Grain of Corn.--Examination of a well-soaked grain of corn
discloses a difference in the two flat sides of the grain. A light-colored
area found on one surface marks the position of the embryo; the rest of the
grain contains the food supply. The interesting thing to remember here is
that the food supply is _outside_ of the embryo.
A grain cut lengthwise perpendicular to the flat side and then dipped in
weak iodine shows two distinct parts, an area containing considerable
starch, the _endosperm_, and the embryo or young plant. Careful inspection
shows the hypocotyl and plumule (the latter pointing toward the free end of
the grain) and a part surrounding them, the _single_ cotyledon (see
Figure). Here again we have an example of a fitting for future needs, for
in this fruit the one seed has at hand all the food material necessary for
rapid growth, although the food is here outside the embryo.
[Illustration: Longitudinal section of young ear of corn. _O_, the fruits;
_S_, the stigmas; _SH_, the sheath-like leaves; _ST_, the flower stalk.
(After Sargent.)]
Endosperm the Food Supply of Corn.--We find that the one cotyledon of the
corn grain does not serve the same purpose to the young plant as do the two
cotyledons of the bean. Although we find a little starch in the corn
cotyledon, still it is evident from our tests that the endosperm is the
chief source of food supply. The study of a thin section of the corn grain
under the compound microscope shows us that the starch grains in the
endosperm are large and regular in size. When the grain has begun to grow,
examination shows that the starch grains near the edge of the cotyledon are
much smaller and quite irregular, having large holes in them. We know that
the germinating grain has a much sweeter taste than that which is not
growing. This is noticed in sprouting barley or malt. We shall later find
that, in order to make use of starchy food, a plant or animal must in some
manner change it over to sugar. This change is necessary, because starch
will not dissolve in water, while sugar will; in this form substances can
pass from cell to cell in the plant and thus distribute the food where it
is needed.
[Illustration: Test for grape sugar.]
A Test for Grape Sugar.--Place in a test tube the substance to be tested
and heat it in a little water so as to dissolve the sugar. Add to the fluid
twice its bulk of Fehling's solution,[6] which has been previously
prepared. Heat the mixture, which should now have a blue color, in the test
tube. If grape sugar is present in considerable quantity, the contents of
the tube will turn first a greenish, then yellow, and finally a brick-red
color. Smaller amounts will show less decided red. No other substance than
sugar will give this reaction. If Benedict's test[7] is used, a colored
precipitate will appear in the test tube after boiling.
Footnotes 6 and 7: Directions for making these solutions
will be found in Hunter's _Laboratory Problems in Civic
Biology_.
Starch changed to Grape Sugar in the Corn.--That starch is being changed to
grape sugar in the germinating corn grain can easily be shown if we cut
lengthwise through the embryos of half a dozen grains of corn that have
just begun to germinate, place them in a test tube with some Fehling's
solution, and heat almost to the boiling point. They will be found to give
a reaction showing the presence of sugar along the edge of the cotyledon
and between it and the endosperm.
Digestion.--This change of starch to grape sugar in the corn is a process
of _digestion_. If you chew a bit of unsweetened cracker in the mouth for a
little time, it will begin to taste sweet, and if the chewed cracker, which
we know contains starch, is tested with Fehling's solution, some of the
starch will be found to have changed to grape sugar. Here, again, a process
of digestion has taken place. In both the corn and in the mouth, the change
is brought about by the action of peculiar substances known as digestive
ferments, or _enzymes_. Such substances have the power under certain
conditions to change insoluble foods--solids--into soluble
substances--liquids. The result is that substances which before digestion
would not dissolve in water now will dissolve.
[Illustration: A germinating corn grain. _C_, cotyledon; _H_, growing root
(_hypocotyl_); _P_, growing stem (_plumule_); _S_, endosperm; _d.s._,
digested starch; _p.r._, primary root; _s.r._, secondary root; _r.h._, root
hairs.]
The Action of Diastase on Starch.--The enzyme found in the cotyledon of the
corn, which changes starch to grape sugar, is called _diastase_. It may be
separated from the cotyledon and used in the form of a powder.
To a little starch in half a cup of water we add a very little (1 gram) of
diastase and put the vessel containing the mixture in a warm place, where
the temperature will remain nearly constant at about 98° Fahrenheit. On
testing part of the contents at the end of half an hour, and the remainder
the next morning, for starch and for grape sugar, we find from the morning
test that the starch has been almost completely changed to grape sugar.
Starch and warm water alone under similar conditions will not react to the
test for grape sugar.
Digestion has the Same Purpose in Plants and Animals.--In our own bodies we
know that solid foods taken into the mouth are broken up by the teeth and
moistened by saliva. If we could follow that food, we would find that
eventually it became part of the blood. It was made soluble by digestion,
and in a liquid form was able to reach the blood. Once a part of the body,
the food is used either to release energy or to build up the body.
Summary.--We have seen:
1. That seeds, in order to grow, must possess a food supply either in or
around their bodies.
2. That this food supply must be oxidized before energy is released.
3. That in cases where the food is not stored at the point where it is to
be oxidized the food must be digested so that it may be transported from
one part to another in the same plant.
The life processes of plants and animals, so far, may be considered as
alike; they both feed, breathe (oxidize their food), do work, and grow.
REFERENCE BOOKS
ELEMENTARY
Hunter, _Laboratory Problems in Civic Biology_. American
Book Company.
Andrews, _A Practical Course in Botany_, pages 1-21.
American Book Company.
Atkinson, _First Studies of Plant Life_, Chap. XXX. Ginn and
Company.
Bailey, _Botany_, Chaps. XX, XXX. The Macmillan Company.
Beal, _Seed Dispersal_. Ginn and Company.
Bergen and Davis, _Principles of Botany_, Chaps. XX, XXX.
Ginn and Company.
Coulter, _Plant Life and Plant Uses_. American Book Company.
Dana, _Plants and their Children_. American Book Company.
Mayne and Hatch, _High School Agriculture_. American Book
Company.
Lubbock, _Flowers, Fruits, and Leaves_. The Macmillan
Company.
Newell, _Reader in Botany_, pages 24-49. Ginn and Company.
Sharpe, _A Laboratory Manual in Biology_, pages 55-65.
American Book Company.
ADVANCED
Bailey, _The Evolution of our Native Fruits_. The Macmillan
Company.
Bailey, _Plant Breeding_. The Macmillan Company.
Coulter, Barnes, and Cowles, _A Textbook of Botany_, Vol. I.
American Book Company.
De Candolle, _Origin of Cultivated Plants_. D. Appleton and
Company.
Duggar, _Plant Physiology_. The Macmillan Company.
Farmers' Bulletins, Nos. 78, 86, 225, 344. U. S. Department
of Agriculture.
Hodge, _Nature Study and Life_, Chaps. X, XX. Ginn and Company.
Kerner (translated by Oliver), _Natural History of Plants_.
Henry Holt and Company, 4 vols. Vol. II, Part 2.
Sargent, _Corn Plants_. Houghton, Mifflin, and Company.
VI. THE ORGANS OF NUTRITION IN PLANTS--THE SOIL AND ITS RELATION TO THE
ROOTS
_Problem.--What a plant takes from the soil and how it gets it._
_(a) What determines the direction of growth of roots?_
_(b) How is the root built?_
_(d) What is in the soil that a root might take out?_
_(e) Why is nitrogen necessary, and how is it obtained?_
LABORATORY SUGGESTIONS
_Demonstration_.--Roots of bean or pea.
_Demonstration or home experiment_.--Response of root to
gravity and to water. What part of root is most responsive?
_Laboratory work_.--Root hairs, radish or corn, position on
root, gross structure only. Drawing.
_Demonstration._--Root hair under compound microscope.
_Demonstration._--Apparatus illustrating osmosis.
_Demonstration or a home experiment._--Organic matter
present in soil.
_Demonstration._--Root tubercles of legume.
_Demonstration._--Nutrients present in some roots.
Uses of the Root.--If one of the seedlings of the bean spoken of in the
last chapter is allowed to grow in sawdust and is given light, air, and
water, sooner or later it will die. Soil is part of its natural
environment, and the roots which come in contact with the soil are very
important. It is the purpose of this chapter to find out just how the young
plant is fitted to get what it needs from this part of its environment;
namely, the soil.
The development of a bean seedling has shown us that the root grows first.
_One of the most important functions of the root to a young seed plant is
that of a holdfast, an anchor to fasten it in the place where it is to
develop._ It has many other uses, as the taking in of water with the
mineral and organic matter dissolved therein, the storage of food,
climbing, etc. All functions other than the first one stated arise after
the young plant has begun to develop.
[Illustration: A root system, showing primary and secondary roots.]
Root System.--If you dig up a young bean seedling and carefully wash the
dirt from the roots, you will see that a long root is developed as a
continuation of the hypocotyl. This root is called the _primary_ root.
Other smaller roots which grow from the primary root are called
_secondary_, or _tertiary_, depending on their relation to the first root
developed.
Downward Growth of Root. Influence of Gravity.--Most of the roots examined
take a more or less downward direction. We are all familiar with the fact
that the force we call gravity influences life upon this earth to a great
degree. Does gravity act on the growing root? This question may be answered
by a simple experiment.
[Illustration: Revolve this figure in the direction of the arrows to see if
the roots of the radish respond to gravity.]
Plant mustard or radish seeds in a pocket garden, place it on one edge and
allow the seeds to germinate until the root has grown to a length of about
half an inch. Then turn it at right angles to the first position and allow
it to remain for one day undisturbed. The roots now will be found to have
turned in response to the change in position, that part of the root near
the growing point being the most sensitive to the change. This experiment
seems to indicate that the roots are influenced to grow downward by the
force of gravity.
Experiments to determine the Influence of Moisture on a Growing Root.--The
objection might well be interposed that possibly the roots in the pocket
garden[8] grew downward after water. That moisture has an influence on the
growing root is easily proved.
Footnote 8: _The Pocket Garden._--A very convenient form of
pocket germinator may be made as follows. Obtain two cleaned
four by five negatives (window glass will do); place one
flat on the table and place on this half a dozen pieces of
colored blotting paper cut to a size a little less than the
glass. Now cut four thin strips of wood to fit on the glass
just outside of the paper. Next moisten the blotter, place
on it some well-soaked radish, mustard seeds or barley
grains, and cover with the other glass. The whole box thus
made should be bound together with bicycle tape. Seeds will
germinate in this box and with care may live for two weeks
or more.
Plant bird seed, mustard or radish seed in the underside of a sponge, which
should be kept wet, and may be suspended by a string under a bell jar in
the schoolroom window. Note whether the roots leave the sponge to grow
downward, or if the moisture in the sponge is sufficient to counterbalance
the force of gravity.
Water a Factor which determines the Course taken by Roots.--_Water, as well
as the force of gravity, has much to do with the direction taken by roots._
Water is always found below the surface of the ground, but sometimes at a
great depth. Most trees, and all grasses, have a greater area of surface
exposed by the roots than by the branches. The roots of alfalfa, a
cloverlike plant used for hay in the Western states, often penetrate the
soil after water for a distance of ten to twenty feet below the surface of
the ground.
Fine Structure of a Root.[9]--When we examine a delicate root in thin
longitudinal section under the compound microscope, we find the entire root
to be made up of cells, the walls of which are uniformly rather thin. Over
the lower end of the root is found a collection of cells, most of which are
dead, loosely arranged so as to form a cap over the growing tip. This is
evidently an adaptation which protects the young and actively growing cells
just under the root cap. In the body of the root a central cylinder can
easily be distinguished from the surrounding cells. In a longitudinal
section a series of tubelike structures may be found within the central
cylinder. These structures are cells which have grown together at the small
end, the long axis of the cells running the length of the main root. In
their development the cells mentioned have grown together in such a manner
as to lose their small ends, and now form continuous hollow tubes with
rather strong walls. Other cells have come to develop greatly thickened
walls; these cells give mechanical support to the tubelike cells.
Collections of such tubes and supporting woody cells together make up what
are known as _fibrovascular bundles_.
Footnote 9: Sections of tradescantia roots are excellent for
demonstration of these structures.
[Illustration: Cross section of a young taproot; _a_, _a_, root hairs; _b_,
outer layer of bark; _c_, inner layer of bark; _d_, wood or central
cylinder.]
Root Hairs.--Careful examination of the root of one of the seedlings of
mustard, radish, or barley grown in the pocket germinator shows a covering
of tiny fuzzy structures. These structures are very minute, at most 3 to 4
millimeters in length. They vary in length according to their position on
the root, the most and the longest root hairs being found near the point
marked _R. H._ in the figure. These structures are outgrowths of the outer
layer of the root (the _epidermis_), and are of very great importance to
the living plant.
[Illustration: Young embryo of corn, showing root hairs (_R. H._) and
growing stem (_P._).]
Structure of a Root Hair.--A single root hair examined under a compound
microscope will be found to be a long, round structure, almost colorless in
appearance. The wall, which is very flexible and thin, is made up of
cellulose, a substance somewhat like wood in chemical composition, through
which fluids may easily pass. Clinging close to the cell wall is the
protoplasm of the cell. The interior of the root hair is more or less
filled with a fluid called _cell sap_. Forming a part of the living
protoplasm of the root hair, sometimes in the hairlike prolongation and
sometimes in that part of the cell which forms the epidermis, is found a
_nucleus_. The protoplasm and nucleus are alive; the cell wall formed by
the living matter in the cell is dead. _The root hair is a living plant
cell_ with a wall so delicate that water and mineral substances from the
soil can pass through it into the interior of the root.
[Illustration: Diagram of a root hair; _CS_, cell sap; _CW_, cell wall;
_P_, protoplasm; _N_, nucleus; _S_, particles of soil.]
How the Root absorbs Water.--The process by which the root hair takes up
soil water can better be understood if we make an artificial root hair
large enough to be easily seen. An egg with part of the outer shell removed
so as to expose the soft skinlike membrane underneath is an example.
Better, an artificial root hair may be _made_ in the following way. Pour
some soft celloidin into a test tube; carefully revolve the test tube so
that an even film of celloidin dries on the inside. This membrane is
removed, filled with white of egg, and tied over the end of a rubber cork
in which a glass tube has previously been inserted. When placed in water,
it gives a very accurate picture of the root hair at work. After a short
time water begins to rise in the tube, having passed through the film of
celloidin. If grape sugar, salt, or some other substance which will
dissolve in water were placed in the water outside the artificial root
hair, it could soon be proved by test to pass through the wall and into the
liquid inside.
Osmosis.--To explain this process we must remember that gases and liquids
of different densities, when separated by a membrane, tend to flow toward
each other and mingle, the greater flow always being in the direction of
the denser medium. _The process by which two gases or fluids, separated by
a membrane, tend to pass through the membrane and mingle with each other,
is called osmosis._ The method by which the root hairs take up soil water
is exactly the same process. It is by osmosis. The white of the egg is the
best possible substitute for living matter; the celloidin membrane
separating the egg from the water is much like the delicate membrane-like
wall which separates the protoplasm of the root hair from the water in the
soil surrounding it. The fluid in the root hair is denser than the soil
water; hence the greater flow is toward the interior of the root hair.[10]
Footnote 10: For an excellent elementary discussion of
osmosis see Moore, _Physiology of Man and Other Animals_.
Henry Holt and Company.
[Illustration: The soil particles are each surrounded with a delicate film
of water. How might the root hairs take up this water?]
Passage of Soil Water within the Root.--We have already seen that in an
exchange of fluids by osmosis the greater flow is always toward the denser
fluid. Thus it is that the root hairs take in more fluid than they give up.
The cell sap, which partly fills the interior of the root hair, is a fluid
of greater density than the water outside in the soil. When the root hairs
become filled with water, the density of the cell sap is lessened, and the
cells of the epidermis are thus in a position to pass along their supply of
water to the cells next to them and nearer to the center of the root. These
cells, in turn, become less dense than their inside neighbors, and so the
transfer of water goes on until the water at last reaches the central
cylinder. Here it is passed over to the tubes of the woody bundles and
started up the stem. The pressure created by this process of osmosis is
sufficient to send water up the stem to a distance, in some plants, of 25
to 30 feet. Cases are on record of water having been raised in the birch a
distance of 85 feet.
Physiological Importance of Osmosis.--It is not an exaggeration to say that
osmosis is a process not only of great importance to a plant, but to an
animal as well. Foods are digested in the food tube of an animal; that is,
they are changed into a soluble form so that they may pass through the
walls of the food tube and become part of the blood. The inner lining of
part of the food tube is thrown into millions of little fingerlike
projections which look somewhat, in size at least, like root hairs. These
fingerlike processes are (unlike a root hair) made up of many cells. But
they serve the same purpose as the root hairs, for they absorb liquid food
into the blood. This process of absorption is largely by osmosis. Without
the process of osmosis we should be unable to use much of the food we eat.
Composition of Soil.--If we examine a mass of ordinary loam carefully, we
find that it is composed of numerous particles of varying size and weight.
Between these particles, if the soil is not caked and hard packed, we can
find tiny spaces. In well-tilled soil these spaces are constantly being
formed and enlarged. They allow air and water to penetrate the soil. If we
examine soil under the microscope, we find considerable water clinging to
the soil particles and forming a delicate film around each particle. In
this manner most of the water is held in the soil.
[Illustration: Inorganic soil is being formed by weathering.]
How Water is held in Soil.--To understand what comes in with the soil
water, it will be necessary to find out a little more about soil.
Scientists who have made the subject of the composition of the earth a
study, tell us that once upon a time at least a part of the earth was
molten. Later, it cooled into solid rock. Soil making began when the ice
and frost, working alternately with the heat, chipped off pieces of rock.
These pieces in time became ground into fragments by action of ice,
glaciers, running water, or the atmosphere. This process is called
weathering. Weathering is aided by oxidation. A glance at almost any
crumbling stones will convince you of this, because of the yellow oxide of
iron (rust) disclosed. So by slow degrees this earth became covered with a
coating of what we call inorganic soil. Later, generation after generation
of tiny plants and animals which lived in the soil died, and their remains
formed the first organic materials of the soil.
[Illustration: This picture shows how the forests help to cover the
inorganic soil with an organic coating. Explain how.]
You are all familiar with the difference between the so-called rich soil
and poor soil. The dark soil contains more dead plant and animal matter,
which forms the portion called _humus_.
[Illustration: Apparatus for testing the capacity of soils to take in and
retain moisture.]
Humus contains Organic Matter.--It is an easy matter to prove that black
soil contains organic matter, for if an equal weight of carefully dried
humus and soil from a sandy road is heated red-hot for some time and then
reweighed, the humus will be found to have lost considerably in weight, and
the sandy soil to have lost very little. The material left after heating
is inorganic material, the organic matter having been burned out.
Soil containing organic materials holds water much more readily than
inorganic soil, as a glance at the accompanying figure shows. If we fill
each of the vessels with a given weight (say 100 grams each) of gravel,
sand, barren soil, rich loam, leaf mold, and 25 grams of dry, pulverized
leaves, then pour equal amounts of water (100 c.c.) on each and measure all
that runs through, the water that has been retained will represent the
water supply that plants could draw on from such soil.
[Illustration: Soil particles cling to root hairs. Why?]
The Root Hairs take more than Water out of the Soil.--If a root containing
a fringe of root hairs is washed carefully, it will be found to have little
particles of soil still clinging to it. Examined under the microscope,
these particles of soil seem to be cemented to the sticky surface of the
root hair. The soil contains, besides a number of chemical compounds of
various mineral substances,--lime, potash, iron, silica, and many
others,--a considerable amount of organic material. Acids of various kinds
are present in the soil. These acids so act upon certain of the mineral
substances that they become dissolved in the water which is absorbed by the
root hairs. Root hairs also give off small amounts of acid. An interesting
experiment may be shown (see Figure on page 80) to prove this. A solution
of _phenolphthalein_ loses its color when an acid is added to it. If a
growing pea be placed in a tube containing some of this solution the latter
will quickly change from a rose pink to a colorless solution.
A Plant needs Mineral Matter to Make Living Matter.--Living matter
(protoplasm), besides containing the chemical elements carbon, hydrogen,
oxygen, and nitrogen, contains a very minute proportion of various elements
which make up the basis of certain minerals. These are calcium (lime),
sulphur, iron, potassium, magnesium, phosphorus, sodium, and chlorine.
That plants will not grow well without certain of these mineral substances
can be proved by the growth of seedlings in a so-called nutrient
solution.[11] Such a solution contains all the mineral matter that a plant
uses for food. If certain ingredients are left out of this solution, the
plants placed in it will not live.
Footnote 11: See Hunter's _Laboratory Problems in Civic
Biology_ for list of ingredients.
[Illustration: Effect of root hairs on phenolphthalein solution. The change
of color indicates the presence of acid.]
Nitrogen in a Usable Form necessary for Growth of Plants.--A chemical
element needed by the plant to make protoplasm is nitrogen. The air can be
proven by experiment to be made up of about four fifths nitrogen, but this
element cannot be taken from either soil, water, or air in a pure state,
but is usually obtained from the organic matter in the soil, where it
exists with other substances in the form of _nitrates_. Ammonia and other
organic compounds which contain nitrogen are changed by two groups of
little plants called _bacteria_, first into nitrites and then nitrates.[12]
Footnote 12: It has recently been discovered that under some
conditions these bacteria are preyed upon by tiny one-celled
animals (_protozoa_) living in the soil and are so reduced
in numbers that they cannot do their work effectively. If,
then, the soil is heated artificially or treated with
antiseptics so as to kill the protozoa, the bacteria which
escape multiply so rapidly as to make the land much richer
than before.
[Illustration: Diagram to show how the nitrogen-fixing bacteria prepare
nitrogen for use by plants; _t_, tubercles.]
Relation of Bacteria to Free Nitrogen.--It has been known since the time of
the Romans that the growth of clover, peas, beans, and other legumes in
soil causes it to become more favorable for growth of other plants. The
reason for this has been discovered in late years. On the roots of the
plants mentioned are found little swellings or nodules; in the nodules
exist millions of bacteria, which take nitrogen from the atmosphere and fix
it so that it can be used by the plant; that is, they assist in forming
nitrates for the plants to use. Only these bacteria, of all the living
plants, have the power to take the free nitrogen from the air and make it
over into a form that can be used by the roots. As all the compounds of
nitrogen are used over and over again, first by plants, then as food for
animals, eventually returning to the soil again, or in part being turned
into free nitrogen, it is evident that any _new_ supply of usable nitrogen
must come by means of these nitrogen-fixing bacteria.
Rotation of Crops.--The facts mentioned above are made use of by careful
farmers who wish to make as much as possible from a given area of ground in
a given time. Such plants as are hosts for the nitrogen-fixing bacteria are
planted early in the season. Later these plants are plowed in and a second
crop is planted. The latter grows quickly and luxuriantly because of the
nitrates left in the soil by the bacteria which lived with the first crop.
For this reason, clover is often grown on land in which it is proposed to
plant corn, the nitrogen left in the soil thus giving nourishment to the
young corn plants. In scientifically managed farms, different crops are
planted in a given field on different years so that one crop may replace
some of the elements taken from the soil by the previous crop. This is
known as rotation of crops.[13] The annual yield of the average farm may
thus be greatly increased.
Footnote 13: That crop rotation is not primarily a process
to conserve the fertility of the soil, but is a sanitary
measure to prevent infection of the soil, is the latest
belief of the scientist.
[Illustration: Nitrogen in the soil is necessary for plants. Explain from
this diagram how nitrogen is put into the soil by some plants and taken out
by others.]
Five of the elements necessary to the life of the plant which may be taken
out of the soil by constant use are calcium, nitrogen, phosphorus,
potassium, and sulphur. Several methods are used by the farmer to prevent
the exhaustion of these and other raw food materials from the soil. One
method known as _fallowing_ is to allow the soil to remain idle until
bacteria and oxidation have renewed the chemical materials used by the
plants. This is an expensive method, if land is dear. The most common
method of enriching soil is by means of fertilizing material rich in plant
food. Manure is most frequently used, but many artificial fertilizers, most
of which contain nitrogen in the form of some nitrate, are used, because
they can be more easily transported and sold. Such are ground bone, guano
(bird manure), nitrate of soda, and many others. These also contain other
important raw food materials for plants, especially potash and phosphoric
acid. Both of these substances are made soluble so as to be taken into the
roots by the action of the carbon dioxide in the soil.
The Indirect Relation of this to the City Dweller.--All of us living in the
city are aware of the importance of fresh vegetables, brought in from the
neighboring market gardens. But we sometimes forget that our great staple
crops, wheat and other cereals, potatoes, fruits of all kinds, our cotton
crop, and all plants we make use of grow directly in proportion to the
amount of raw food materials they take in through the roots. When we also
remember that many industries within the cities, as mills, bakeries, and
the like, as well as the earnings of our railways and steamship lines, are
largely dependent on the abundance of the crops, we may recognize the
importance of what we have read in this chapter.
Food Storage in Roots of Commercial Importance.--Some plants, as the
parsnip, carrot, and radish, produce no seed until the second year, storing
food in the roots the first year and using it to get an early start the
following spring, so as to be better able to produce seeds when the time
comes. This food storage in roots is of much practical value to mankind.
Many of our commonest garden vegetables, as those mentioned above, and the
beet, turnip, oyster plant, sweet potato and many others, are of value
because of the food stored. The sugar beet has, in Europe especially,
become the basis of a great industry.
REFERENCE BOOKS
ELEMENTARY
Hunter, _Laboratory Problems in Civic Biology_. American
Book Company.
Bigelow, _Applied Biology_. The Macmillan Company.
Coulter, _Plant Life and Plant Uses_, Chaps. III, IV.
American Book Company.
Mayne and Hatch, _High School Agriculture_. American Book
Company.
Moore, _The Physiology of Man and Other Animals_. Henry Holt
and Company.
Sharpe, _Laboratory Manual in Biology_, pp. 73-87. American
Book Company.
ADVANCED
Coulter, Barnes, and Cowles, _A Textbook of Botany_, Part
II. Amer. Book Co.
Duggar, _Plant Physiology_. The Macmillan Company.
Goodale, _Physiological Botany_. American Book Company.
Green, _Vegetable Physiology_, Chaps. V, VI. J. and A.
Churchill.
Kerner-Oliver, _Natural History of Plants_. Henry Holt and
Company.
MacDougal, _Plant Physiology_. Longmans, Green, and Company.
VII. PLANT GROWTH AND NUTRITION--PLANTS MAKE FOOD
_Problem.--Where, when, and how do green plants make food?_
_(a) How and why is moisture given off from leaves?_
_(b) What is the reaction of leaves to light?_
_(c) What is made in green leaves in the sunlight?_
_(d) What by-products are given off in the above process?_
_(e) Other functions of leaves._
LABORATORY SUGGESTIONS
_Demonstration._--Water given off by plant in sunlight. Loss
of weight due to transpiration measured.
_Laboratory exercise._--
(_a_) Gross structure of a leaf.
(_b_) Study of stoma and lower epidermis under microscope.
(_c_) Study of cross section to show cells and air spaces.
_Demonstration._--Reaction of leaves to light.
_Demonstration._--Light necessary to starch making.
_Demonstration._--Air necessary to starch making.
_Demonstration._--Oxygen a by-product of starch making.
What becomes of the Water taken in by the Roots?--We have seen that more
than pure water has been absorbed through the root hairs into the roots.
What becomes of this water and the other substances that have been
absorbed? This question may be partly answered by the following
experiments.
[Illustration: Apple twigs split to show the course of colored water up the
stem.]
Passage of Fluids up the Stem.--If any young growing shoots (young
seedlings of corn or pea, or the older stems of garden balsam,
touch-me-not, or sunflower) are placed in red ink (eosin), and left in the
sun for a few hours, the red ink will be found to have passed up the stem.
If such stems were examined carefully, it would be seen that the colored
fluid is confined to collections of woody tubes immediately under the inner
bark. Water evidently rises in that part of the stem we call the wood.
[Illustration: Experiment to prove that water is given off through the
leaves of a green plant.]
Water given off by Evaporation from Leaves.--Take some well-watered potted
green plant, as a geranium or hydrangea, cover the pot with sheet rubber,
fastening the rubber close to the stem of the plant. Next weigh the plant
with the pot. Then cover it with a tall bell jar and place the apparatus in
the sun. In a few minutes drops of moisture are seen to gather on the
_inside_ of the jar. If we now weigh the potted plant, we find it weighs
less than before. Obviously the loss comes from the water lost, and
evidently this water escapes as vapor from either the stem or leaves.
[Illustration: The skeleton of a leaf. _M.R._, the midrib; _P._, the
leafstalk; _V._, the veins.]
The Structure of a Leaf.--In the experiment with the red ink mentioned
above we will find that the fluid has gone out into the skeleton or
framework of the leaf. Let us now examine a leaf more carefully. It shows
usually (1) a flat, broad _blade_, which may take almost any conceivable
shape; (2) a _stem_ which spreads out in the blade (3) in a number of
_veins_.
[Illustration: Section through the blade of a leaf as seen under the
compound microscope. _S_, air spaces, which communicate with the outside
air; _V_, vein in cross section; _S.T._, breathing hole (stoma); _E_, outer
layer of cells; _P_, green cells.]
The Cell Structure of a Leaf.--The under surface of a leaf seen under the
microscope usually shows numbers of tiny oval openings. These are called
_stomata_ (singular _stoma_). Two cells, usually kidney-shaped, are found,
one on each side of the opening. These are the _guard cells_. By change in
shape of these cells the opening of the stoma is made larger or smaller.
Larger irregular cells form the _epidermis_, or outer covering of the leaf.
Study of the leaf in cross section shows that these stomata open directly
into air chambers which penetrate between and around the loosely arranged
cells composing the underpart of the leaf. The upper surface of leaves
sometimes contains stomata, but more often they are lacking. The under
surface of an oak leaf of ordinary size contains about 2,000,000 stomata.
Under the upper epidermis is a layer of green cells closely packed together
(called collectively the _palisade layer_). These cells are more or less
columnar in shape. Under these are several rows of rather loosely placed
cells just mentioned. These are called collectively the _spongy tissue_. If
we happen to have a section cut through a vein, we find this composed of a
number of tubes made up of, and strengthened by, thick-walled cells. The
veins are evidently a continuation of the tubes of the stem out into the
blade of the leaf.
Evaporation of Water.--During the day an enormous amount of water is taken
up by the roots and passed out through the leaves. So great is this excess
at times that a small grass plant on a summer's day evaporates more than
its own weight in water. This would make nearly half a ton of water
delivered to the air during twenty-four hours by a grass plot twenty-five
by one hundred feet, the size of the average city lot. According to Ward,
an oak tree may pass off two hundred and twenty-six times its own weight in
water during the season from June to October.
From which Surface of the Leaf is Water Lost?--In order to find out whether
water is passed out from any particular part of the leaf, we may remove two
leaves of the same size and weight from some large-leaved plant[14]--a
mullein was used for the illustrations given below--and cover the upper
surface of one leaf and the lower surface of the other with vaseline. The
leaf stalks of each should be covered with wax or vaseline, and the two
leaves exactly balanced on the pans of a balance which has previously been
placed in a warm and sunny place. Within an hour the leaf which has the
upper surface covered with vaseline will show a loss of weight. Examination
of the surface of a mullein leaf shows us that the _lower surface of the
leaf is provided with stomata_. It is through these organs, then, that
water is passed out from the tissues of the leaf.
Footnote 14: The "rubber plant" leaf is an easily obtainable
and excellent demonstration.
[Illustration: Experiment to show through which surface of a leaf water
passes off.]
Factors in Transpiration.--The amount of water lost from a plant varies
greatly under different conditions. The humidity of the air, its
temperature, and the temperature of the plant all affect the rate of
transpiration. The stomata also tend to close under some conditions, thus
helping to prevent evaporation. But there seems to be no certain regulation
of this water loss. Consequently plants droop or wilt on hot dry days
because they cannot obtain water rapidly enough from the soil to make up
for the loss through the leaves.
[Illustration: Diagrams of a stoma. _a_, surface view of a closed stoma;
_b_, the same stoma opened. (After Hanson.) _c_, diagrams of a transverse
section through a stoma, dotted lines indicate the closed position of the
guard cells, the heavy lines the open condition. (After Schwendener.)]
Green Plants Food Makers.--We have previously stated that green plants are
the great food makers for themselves and for animals. We are now ready to
attack the problem of how green plants _make_ food.
The Sun a Source of Energy.--We all know the sun is a source of most of the
energy that is released on this earth in the form of heat or light. Every
boy knows the power of a "burning glass." Solar engines have not come into
any great use as yet, because fuel is cheaper, but some day we undoubtedly
will directly harness the energy of the sun in everyday work. Actual
experiments have shown that vast amounts of energy are given to the earth.
When the sun is highest in the sky, energy equivalent to one hundred horse
power is received by a plot of land twenty-five by one hundred feet, the
size of a city lot. Plants receive and use much of this energy by means of
their leaves.
Effect of Light on Plants.--In young plants which have been grown in total
darkness, no green color is found in either stems or leaves, the latter
often being reduced to mere scales. The stems are long and more or less
reclining. We can explain the changed condition of the seedling grown in
the dark only by assuming that light has some effect on the protoplasm of
the seedling and induces the growth of the green part of the plant. If
seedlings have been growing on a window sill, or where the light comes in
from one side, you have doubtless noticed that the stem and leaves of the
seedlings incline in the direction from which the light comes. The
experiment pictured shows this effect of light very plainly. A hole was cut
in one end of a cigar box and barriers were erected in the interior of the
box so that the seeds planted in the sawdust received their light by an
indirect course. The young seedling in this case responded to the influence
of the stimulus of light so as to grow out finally through the hole in the
box into the open air. This growth of the stem to the light is of very
great importance to a growing plant, because, as we shall see later, food
making depends largely on the amount of sunlight the leaves receive.
[Illustration: Two stages in an experiment to show that green plants grow
toward the light.]
Effect of Light on Leaf Arrangement.--It is a matter of common knowledge
that green leaves turn toward the light. Place growing pea seedlings,
oxalis, or any other plants of rapid growth near a window which receives
full sunlight. Within a short time the leaves are found to be in positions
to receive the most sunlight possible. Careful observation of any plant
growing outdoors shows us that in almost every case the leaves are so
disposed as to get much sunlight. The ivy climbing up the wall, the
morning-glory, the dandelion, and the burdock all show different
arrangements of leaves, each presenting a large surface to the light.
Leaves are often definitely arranged, fitting in between one another so as
to present their upper surface to the sun. Such an arrangement is known as
a _leaf mosaic_. In the case of the dandelion, a _rosette_ or whorled
cluster of leaves is found. In the horse-chestnut, where the leaves come
out opposite each other, the older leaves have longer petioles than the
young ones. In the mullein the entire plant forms a cone. The old leaves
near the bottom have long stalks, and the little ones near the apex come
out close to the main stalk. In every case each leaf receives a large
amount of light. Other modifications of these forms may easily be found on
any field trip.
[Illustration: A lily, showing long narrow leaves.]
[Illustration: The dandelion, showing a whorled arrangement of long
irregular leaves.]
Starch made by a Green Leaf.--If we examine the palisade layer of the leaf,
we find cells which are almost cylindrical in form. In the protoplasm of
such cells are found a number of little green-colored bodies, which are
known as _chloroplasts_ or _chlorophyll bodies_. If we place the leaf in
wood alcohol, we find that the bodies still remain, but that the color is
extracted, going into the alcohol and giving to it a beautiful green color.
The chloroplasts are, indeed, simply part of the protoplasm of the cell
colored green. These bodies are of the greatest importance directly to
plants and indirectly to animals. _The chloroplasts, by means of the energy
received from the sun, manufacture starch out of certain raw materials._
These raw materials are soil water, which is passed up through the bundles
of tubes into the veins of the leaf from the roots, and carbon dioxide,
which is taken in through the stomata or pores, which dot the under surface
of the leaf. A plant with variegated leaves, as the coleus, makes starch
only in the green part of the leaf, even though these raw materials reach
all parts of the leaf.
[Illustration: An experiment to show the effect of excluding light (but not
air) from the leaves of a green plant. The result of this experiment is
seen in the next picture. (Experiment performed by C. Dobbins and A.
Schwartz.)]
[Illustration: Starchless area in a leaf caused by excluding sunlight by
means of a strip of black cloth.]
Light and Air necessary for Starch Making.--If we pin strips of black
cloth, such as alpaca, over some of the leaves of a growing hydrangea which
has previously been placed in a dark room for a few hours, and then put the
plant in direct sunlight for an hour or two, we are ready to test for
starch. We then remove some of the covered leaves and extract the
chlorophyll with wood alcohol (because the green color of the chlorophyll
interferes with the blue color of the starch test). A test then shows that
starch is present only in the portions of the leaves exposed to sunlight.
From this experiment we infer that the sun has something to do with starch
making in a leaf. The necessity of a part of the air (carbon dioxide) for
starch making may also easily be proved, for the parts of leaves covered
with vaseline will be found to contain no starch, while parts of the leaf
without vaseline, but exposed to the sun and air, do contain starch.
[Illustration: Diagram to show starch making. Read the text carefully and
then explain this diagram.]
Air is necessary for the process of starch making in a leaf, not only
because carbon dioxide gas is absorbed (there are from three to four parts
in ten thousand present in the atmosphere), but also because the leaf is
alive and must have oxygen in order to do work. This oxygen it takes from
the air around it.
[Illustration: Diagram to illustrate the formation of starch in a leaf.]
Comparison of Starch Making and Milling.--The manufacture of starch by the
green leaf is not easily understood. The process has been compared to the
milling of grain. In this case the mill is the green part of the leaf. The
sun furnishes the motive power, the chloroplasts constitute the machinery,
and soil water and carbon dioxide are the raw products taken into the mill.
The manufactured product is starch, and a certain by-product (corresponding
to the waste in a mill) is also given out. This by-product is oxygen. To
understand the process fully, we must refer to a small portion of the leaf
shown below. Here we find that the cells of the green layer of the leaf,
under the upper epidermis, perform most of the work. The carbon dioxide is
taken in through the stomata and reaches the green cells by way of the
intercellular spaces and by osmosis from cell to cell. Water reaches the
green cells through the veins. It then passes into the cells by osmosis,
and there becomes part of the cell sap. The light of the sun easily
penetrates to the cells of the palisade layer, giving the energy needed to
make the starch. This whole process is a very delicate one, and will take
place only when external conditions are favorable. For example, too much
heat or too little heat stops starch making in the leaf. This building up
of food and the release of oxygen by the plant in the presence of sunlight
is called _photosynthesis_.
[Illustration: Diagram (after Stevens) to illustrate the processes of
breathing and food making in the cells of a green leaf in the sunlight.]
Manufacture of Fats.--Inasmuch as tiny droplets of oil are found _inside_
the chlorophyll bodies in the leaf, we believe that fats, too, are made
there, probably by a transformation of the starch already manufactured.
Protein Making and its Relation to the Making of Living Matter.--Protein
material is a food which is necessary to form protoplasm. Protein food is
present in the leaf, and is found in the stem or root as well. Proteins can
apparently be manufactured in any of the cells of green plants, the
presence of light not seeming to be a necessary factor. How it is
manufactured is a matter of conjecture. The minerals brought up in the soil
water form part of its composition, and starch or grape sugar give three
elements (C, H, and O). The element nitrogen is taken up by the roots as a
nitrate (nitrogen in combination with lime or potash). Proteins are
probably not made directly into protoplasm in the leaf, but are stored by
the cells of the plant and used when needed, either to form new cells in
growth or to repair waste. While plants and animals obtain their food in
different ways, they probably make it into living substance (_assimilate_
it) in exactly the same manner.
[Illustration: An example of how a tree may exert energy. This rock has
been split by the growing tree.]
Foods serve exactly the same purposes in plants and in animals; they either
build living matter or they are burned (oxidized) to furnish energy (power
to do work). If you doubt that a plant exerts energy, note how the roots of
a tree bore their way through the hardest soil, and how stems or roots of
trees often split open the hardest rocks, as illustrated in the figure
above.
Starch-Making and its Relation to Human Welfare.--Leaves which have been in
darkness show starch to be present soon after exposure to light. A corn
plant sends 10 to 15 grams of reserve material into the ears in a single
day. The formation of fruit, and especially the growth of the grain fields,
show the economic importance of this fact. Not only do plants make their
own food and store it away, but they make food for animals as well. And the
food is stored in such a stable form that it may be sent to all parts of
the world in the form of grain or other fruits. Animals, herbivorous and
flesh-eating, man himself, all are dependent upon the starch-making
processes of the green plant for the ultimate source of their food. When we
remember that in 1913 in the United States the total value of all farm
crops was over $6,000,000,000, and when we realize that these products came
from the air and soil through the energy of the sun, we may begin to
realize why as city boys and girls the study of plant biology is of
importance to us.
[Illustration: Experiment to show that oxygen is given off by green plants
in the sunlight.]
Green Plants give off Oxygen in Sunlight.--In still another way green
plants are of direct use to us in the city. During this process of
starch-making oxygen is given off as a by-product. This may easily be
proven by the following experiment.[15] Place any green water plant in a
battery jar partly filled with water, cover the plants with a glass funnel
and mount a test tube full of water over the mouth of the funnel. Then
place the apparatus in a warm sunny window. Bubbles of gas are seen to rise
from the plant. After two or three hours of hot sun, enough of the gas can
be obtained by displacement of the water to make the oxygen test.
Footnote 15: Immediate success with this experiment will be
obtained if the water has been previously charged with
carbon dioxide.
That oxygen is given off as a by-product by green plants is a fact of
far-reaching importance. City parks are true "breathing spaces." The green
covering of the earth is giving to animals an element that they must have,
while the animals in their turn are supplying to the plants carbon dioxide,
a compound used in food-making. Thus a widespread relation of mutual
helpfulness exists between plants and animals.
Respiration by Leaves.--All living things require oxygen. It is by means of
the oxidation of food materials within the plant's body that the energy
used in growth and movement is released. A plant takes in oxygen largely
through the stomata of the leaves, to a less extent through the _lenticels_
or breathing holes in the stem, and through the roots. Thus rapidly growing
tissues receive the oxygen necessary for them to perform their work. The
products of oxidation in the form of carbon dioxide are also passed off
through these same organs. It can be shown by experiment that a plant uses
up oxygen in the darkness; in the light the amount of oxygen given off as a
by-product in the process of starch-making is, of course, much greater than
the amount used by the plant.
Summary.--From the above paragraphs it is seen that a leaf performs the
following functions: (1) breathing, or the taking in of oxygen and passing
off of carbon dioxide; (2) starch-making, with the incidental passing out
of oxygen; (3) formation of proteins, with their digestion and assimilation
to form new tissues; and (4) the transpiration of water.
REFERENCE BOOKS
ELEMENTARY
Hunter, _Laboratory Problems in Civic Biology_. American
Book Company.
Andrews, _A Practical Course in Botany_, pages 160-177.
American Book Company.
Coulter, _A Textbook of Botany_, pages 5-40. D. Appleton and
Company.
Coulter, _Plant Life and Plant Uses_. American Book Company.
Dana, _Plants and their Children_, pages 135-185. American
Book Company.
Sharpe, _A Laboratory Manual in Biology_, pages 90-102.
American Book Company.
Stevens, _Introduction to Botany_, pages 81-99. D. C. Heath
and Company.
ADVANCED
Clement, _Plant Physiology and Ecology_. Henry Holt and
Company.
Coulter, Barnes, and Cowles, _A Textbook of Botany_, Part
II, and Vol. II. American Book Company.
Darwin, _Insectivorous Plants_. D. Appleton and Company.
Duggar, _Plant Physiology_. The Macmillan Company.
Goodale, _Physiological Botany_, pages 337-353 and 409-424.
American Book Company.
Green, _Vegetable Physiology_. J. and A. Churchill.
Lubbock, _Flowers, Fruits, and Leaves_, last part. The
Macmillan Company.
MacDougal, _Practical Textbook of Plant Physiology_.
Longmans, Green, and Company.
Report of the Division of Forestry, U.S. Department of
Agriculture, 1899.
Ward, _The Oak_. D. Appleton and Company.
VIII. PLANT GROWTH AND NUTRITION--THE CIRCULATION AND FINAL USES OF FOOD BY
PLANTS
_Problem.--How green plants store and use the food they make._
_(a) What are the organs of circulation?_
_(b) How and where does food circulate?_
_(c) How does the plant assimilate its food?_
LABORATORY SUGGESTIONS
_Laboratory exercise._--The structure (cross section) of a
woody stem.
_Demonstration._--To show that food passes downward in the
bark.
_Demonstration._--To show the condition of food passing
through the stem.
_Demonstration._--Plants with special digestive organs.
The Circulation and Final Uses of Foods in Green Plants.--We have seen that
cells of green plants make food and that such cells are mostly in the
leaves. But _all_ parts of the bodies of plants grow. Roots, stems, leaves,
flowers, and fruits grow. Seeds are storehouses of food. We must now
examine the stem of some plant in order to see how food is distributed,
stored, and finally used in the various parts of the plant.
The Structure of a Woody Stem.--If we cut a cross section through a young
willow or apple stem, we find it shows three distinct regions. The center
is occupied by the spongy, soft _pith_; surrounding this is found the
rather tough _wood_, while the outermost area is _bark_. More careful study
of the bark reveals the presence of three layers--an outer layer, a middle
green layer, and an inner fibrous layer, the latter usually brown in color.
This layer is made up largely of tough fiberlike cells known as _bast_
fibers. The most important parts of this inner bark, so far as the plant is
concerned, are many tubelike structures known as _sieve tubes_. These are
long rows of living cells, having perforated sievelike ends. Through these
cells food materials pass downward from the upper part of the plant, where
they are manufactured.
[Illustration: Section of a twig of box elder three years old, showing
three annual growth rings. The radiating lines (_m_) which cross the wood
(_w_) represent the pith rays, the principal ones extending from the pith
in the center to the cortex or bark. (From Coulter's _Plant Relations_.)]
In the wood will be noticed (see Figure) a number of lines radiating
outward from the pith toward the bark. These are thin plates of pith which
separate the wood into a number of wedge-shaped masses. These masses of
wood are composed of many elongated cells, which, placed end to end, form
thousands of little tubes connecting the leaves with the roots. In addition
to these are many thick-walled cells, which give strength to the mass of
wood. The bundles of tubes with their surrounding hard walled cells are the
continuation of the bundles of tubes which are found in the root. In
sections of wood which have taken several years to grow, we find so-called
_annual rings_. The distance between one ring and the next (see Figure)
usually represents the amount of growth in one year. Growth takes place
from an actively dividing layer of cells, known as the _cambium layer_.
This layer forms wood cells from its inner surface and bark from its outer
surface. Thus new wood is formed as a distinct ring around the old wood.
Use of the Outer Bark.--The outer bark of a tree is protective. The cells
are dead, the heavy woody skeletons serving to keep out cold and dryness,
as well as prevent the evaporation of fluids from within. The bark also
protects the tree from attack of other plants or animals which might harm
it. Most trees are provided with a layer of corky cells. This layer in the
cork oak is thick enough to be of commercial importance. The function of
the corky layer in preventing evaporation is well seen in the case of the
potato, which is a true stem, though found underground. If two potatoes of
equal weight are balanced on the scales, the skin having been peeled from
one, the peeled potato will be found to lose weight rapidly. This is due to
loss of water, which is held in by the skin of the unpeeled potato (see
right hand figure below).
There are also small breathing holes known as _lenticels_ scattered through
the surface of the bark. These can easily be seen in a young woody stem of
apple, beech, or horse-chestnut.
[Illustration: Experiment to show that the skin of the potato (a stem)
retards evaporation.]
Proof that Food passes down the Stem.--If freshly cut willow twigs are
placed in water, roots soon begin to develop from that part of the stem
which is under water. If now the stem is girdled by removing the bark in a
ring just above where the roots are growing, the latter will eventually
die, and new roots will appear above the girdled area. The food material
necessary for the outgrowth of roots evidently comes from above, and the
passage of food materials takes place in a downward direction just outside
the wood in the layer of bark which contains the bast fibers and sieve
tubes. This experiment with the willow explains why it is that trees die
when girdled so as to cut the sieve tubes of the inner bark. The food
supply is cut off from the protoplasm of the cells in the part of the tree
below the cut area. Many of the canoe birches of our Adirondack forest are
thus killed, girdled by thoughtless visitors. In the same manner mice and
other gnawing animals kill fruit trees. Food substances are also conducted
to a much less extent in the wood itself, and food passes from the inner
bark to the center of the tree by way of the pith plates. This can be
proved by testing for starch in the pith plates of young stems. It is found
that much starch is stored in this part of the tree trunk.
[Illustration: Experiment to show that food material passes down in the
inner bark.]
In what Form does Food pass through the Stem?--We have already seen that
materials in solution (those substances which will dissolve in the water)
will pass from cell to cell by the process of osmosis. This is shown in the
experiment illustrated in the figure. Two thistle tubes are partly filled,
one with starch and water, the other with sugar and water, and a piece of
parchment paper is tied over the end of each. The lower ends of both tubes
are placed in a glass dish under water. After twenty-four hours, the water
in the dish is tested for starch, and then for sugar. We find that only the
sugar, which has been dissolved by the water, can pass through the
membrane.
[Illustration: Experiment to show osmosis of sugar (right hand tube) and
non-osmosis of starch (left hand tube).]
Digestion.--Much of the food made in the leaves is stored in the form of
starch. But starch, being insoluble, cannot be passed from cell to cell in
a plant. It must be changed to a soluble form, for otherwise it could not
pass through the delicate cell membranes. This is accomplished by the
process of _digestion_. We have already seen that starch is changed to
grape sugar in the corn by the action of a substance (an enzyme) called
_diastase_. This process of digestion seemingly may take place in all
living parts of the plant, although most of it is done in the leaves. In
the bodies of all animals, including man, starchy foods are changed in a
similar manner, but by other enzymes, into soluble grape sugar.
The food material may be passed in a soluble form until it comes to a place
where food storage is to take place, then it can be transformed to an
insoluble form (starch, for example); later, when needed by the plant in
growth, it may again be transformed and sent in a soluble form through the
stem to the place where it will be used.
In a similar manner, protein seems to be changed and transferred to various
parts of the plant. Some forms of protein substance are _soluble_ and
others _insoluble_ in water. White of egg, for example, is slightly
soluble, but can be rendered insoluble by heating it so that it coagulates.
Insoluble proteins are digested within the plant; how and where is but
slightly understood. In a plant, soluble proteins pass down the sieve tubes
in the bast and then may be stored in the bast or medullary rays of the
wood in an insoluble form, or they may pass into the fruit or seeds of a
plant, and be stored there.
[Illustration: Diagram to show the areas in a plant through which the raw
food materials pass up the stem and food materials pass down.]
What forces Water up the Stem.--We have seen that the process of osmosis is
responsible for taking in soil water, and that the enormous absorbing
surface exposed by the root hairs makes possible the absorption of a large
amount of water. Frequently this is more than the weight of the plant in
every twenty-four hours.
Experiments have been made which show that at certain times in the year
this water is in some way forced up the tiny tubes of the stem. During the
spring season, in young and rapidly growing trees, water has been proved to
rise to a height of nearly ninety feet. The force that causes this rise of
water in stems is known as _root pressure_.
The greatest factor, however, is transpiration of water from leaves. This
evaporation of water in the form of vapor seems to result in a kind of
suction on the column of water in the stem. In the fall, after the leaves
have gone, much less water is taken in by roots, showing that an intimate
relation exists between the leaves and the root.
Summary of the Functions of Green Plants.--The processes which we have just
described (with the exception of food making) are those which occur in the
lives of any plant or animal. All plants and animals breathe, they oxidize
their foods to release energy, carbon dioxide being given off as the result
of the union of the carbon in the foods with the oxygen of the air. Both
plants and animals digest their food; plants may do this in the cells of
the root, stem, and leaf. Digestion must always occur so that food can be
moved in a soluble condition from cell to cell in the plant's body.
[Illustration: Leaf of sundew closing over a captured insect.]
[Illustration: The Venus fly trap, showing open and closed leaves.]
Plants with Special Digestive Organs.--Some plants have special organs of
digestion. One of these, the sundew, has leaves which are covered on one
side with tiny glandular hairs. These attract insects and later serve to
catch and digest the nitrogenous matter of these insects by means of
enzymes poured out by the same hairs. Another plant, the Venus fly trap,
catches insects in a sensitive leaf which folds up and holds the insect
fast until enzymes poured out by the leaf slowly digest it. Still others,
called pitcher plants, use as food the decayed bodies of insects which fall
into their cuplike leaves and die there. In this respect plants are like
those animals which have certain organs in the body set apart for the
digestion of food.
Assimilation.--The assimilation of foods, or making of foods into living
matter, is a process we know very little about. We know it takes place in
the living cells of plants and animals. But how foods are changed into
living matter is one of the mysteries of life which we have not yet solved.
Excretion.--The waste and repair of living matter seems to take place in
both plants and animals. When living plants breathe, they give off carbon
dioxide. In the process of starch-making, oxygen might be considered the
waste product. Water is evaporated from leaves and stems. The leaves fall
and carry away waste mineral substances which they contain.
[Illustration: The embryos of (_a_) the morning glory, (_b_) the barberry,
(_c_) the potato, (_d_) the four o'clock, showing the position of their
food supply. (After Gray.)]
Reproduction.--Finally, both plants and animals have organs of
reproduction. We have seen that the flower gives rise, after pollination,
to a fruit which holds the seeds. These seeds hold the _embryo_. Thus the
young plant is doubly protected for a time and is finally thrown off in the
seed with enough food to give it a start in life. In much the same way we
will find that animals reproduce, either by laying eggs which contain an
_embryo_ and food to start it in life or, as in the higher animals, by
holding and protecting the embryo within the body of the mother until it is
born, a helpless little creature, to be tenderly nourished by the mother
until able to care for itself.
The Life Cycle.--Ultimately both plants and animals grow old and die. Some
plants, for example the pea or bean, live but a season; others, such as the
big trees of California, live for hundreds of years. Some insects exist as
adults but a day, while the elephant is said to live almost two hundred
years. The span of life from the time the plant or animal begins to grow
until it dies is known as the _life cycle_.
REFERENCE BOOKS
ELEMENTARY
Hunter, _Laboratory Problems in Civic Biology_. American
Book Company.
Andrews, _A Practical Course in Botany_, pages 112-127.
American Book Company.
Atkinson, _First Studies of Plant Life_, Chaps. IV, V, VI,
VIII, XXI. Ginn.
Coulter, _Plant Life and Plant Uses_, Chap. V. American Book
Company.
Dana, _Plants and their Children_, pages 99-129. American
Book Company.
Mayne and Hatch, _High School Agriculture_. American Book
Company.
Hodge, _Nature Study and Life_, Chaps. IX, X, XI. Ginn and
Company.
MacDougal, _The Nature and Work of Plants_. The Macmillan
Company.
ADVANCED
Apgar, _Trees of the United States_, Chaps. II, V, VI.
American Book Company.
Coulter, Barnes, and Cowles, _A Textbook of Botany_, Vol. I.
American Book Company.
Duggar, _Plant Physiology_. The Macmillan Company.
Ganong, _The Teaching Botanist_. The Macmillan Company.
Goebel, _Organography of Plants_, Part V. Clarendon Press.
Goodale, _Physiological Botany_. American Book Company.
Gray, _Structural Botany_, Chap. V. American Book Company.
Kerner-Oliver, _Natural History of Plants_. Henry Holt and
Company.
Strasburger, Noll, Schenck, and Karston, _A Textbook of
Botany_. The Macmillan Company.
Ward, _The Oak_. D. Appleton and Company.
Yearbook, U. S. Department of Agriculture, 1894, 1895,
1898-1910.
IX. OUR FORESTS, THEIR USES AND THE NECESSITY FOR THEIR PROTECTION
_Problem.--Man's relations to forests._
_(a) What is the value of forests to man?_
_(b) What can man do to prevent forest destruction?_
LABORATORY SUGGESTIONS
Demonstration of some uses of wood. Optional exercise on
structure of wood. Method of cutting determined by
examination. Home work on study of furniture trim, etc.
Visit to Museum to study some economic uses of wood.
Visit to Museum or field trip to learn some common trees.
[Illustration: A forest in North Carolina. (U. S. G. S.)]
The Economic Value of Trees. Protection and Regulation of Water
Supply.--Trees form a protective covering for parts of the earth's surface.
They prevent soil from being washed away, and they hold moisture in the
ground. The devastation of immense areas in China and considerable damage
by floods in parts of Switzerland, France, and in Pennsylvania has resulted
where the forest covering has been removed. No one who has tramped through
our Adirondack forest can escape noticing the differences in the condition
of streams surrounded by forest and those which flow through areas from
which trees have been cut. The latter streams often dry up entirely in hot
weather, while the forest-shaded stream has a never failing supply of
crystal water.
[Illustration: Working to prevent erosion after the removal of the forest
in the French Alps.]
[Illustration: Erosion at Sayre, Pennsylvania, by the Chemung River.
(Photograph by W. C. Barbour.)]
The city of New York owes much of its importance to its position at the
mouth of a great river with a harbor large enough to float the navies of
the world. This river is supplied with water largely from the Adirondack
and Catskill forests. Should these forests be destroyed, it is not
impossible that the frequent freshets which would follow would so fill the
Hudson River with silt and débris that the ship channels in the bay,
already costing the government hundreds of thousands of dollars a year to
keep dredged, would become too shallow for ships. If this _should_ occur,
the greatest city in this country would soon lose its place and become of
second-rate importance.
The story of how this very thing happened to the old Greek
city of Poseidonia is graphically told in the following lines:--
"It was such a strange, tremendous story, that of the Greek
Poseidonia, later the Roman Pæstum. Long ago those
adventuring mariners from Greece had seized the fertile
plain, which at that time was covered with forests of great
oak and watered by two clear and shining rivers. They drove
the Italian natives back into the distant hills, for the
white man's burden even then included the taking of all the
desirable things that were being wasted by incompetent
natives, and they brought over colonists--whom the
philosophers and moralists at home maligned, no doubt, in
the same pleasant fashion of our own day. And the colonists
cut down the oaks, and plowed the land, and built cities,
and made harbors, and finally dusted their busy hands and
busy souls of the grime of labor and wrought splendid
temples in honor of the benign gods who had given them the
possessions of the Italians and filled them with power and
fatness.
"Every once in so often the natives looked lustfully down
from the hills upon this fatness, made an armed snatch at
it, were driven back with bloody contumely, and the heaping
of riches upon riches went on. And more and more the oaks
were cut down--mark that! for the stories of nations are so
inextricably bound up with the stories of trees--until all
the plain was cleared and tilled; and then the foothills
were denuded, and the wave of destruction crept up the
mountain sides, and they, too, were left naked to the sun
and the rains.
"At first these rains, sweeping down torrentially,
unhindered by the lost forests, only enriched the plain with
the long-hoarded sweetness of the trees; but by and by the
living rivers grew heavy and thick, vomiting mud into the
ever shallowing harbors, and the land soured with the
undrained stagnant water. Commerce turned more and more to
deeper ports, and mosquitoes began to breed in the brackish
soil that was making fast between the city and the sea.
"Who of all those powerful landowners and rich merchants
could ever have dreamed that little buzzing insects could
sting a great city to death? But they did. Fevers grew more
and more prevalent. The malaria haunted population went more
and more languidly about their business. The natives, hardy
and vigorous in the hills, were but feebly repulsed.
Carthage demanded tribute, and Rome took it, and changed the
city's name from Poseidonia to Pæstum. After Rome grew weak,
Saracen corsairs came in by sea and grasped the slackly
defended riches, and the little winged poisoners of the
night struck again and again, until grass grew in the
streets, and the wharves crumbled where they stood. Finally,
the wretched remnant of a great people wandered away into
the more wholesome hills, the marshes rotted in the heat and
grew up in coarse reeds where corn and vine had flourished,
and the city melted back into the wasted earth."[16]
Footnote 16: Elizabeth Bisland and Anne Hoyt, _Seekers in
Sicily_. John Lane Company.
[Illustration: Result of deforestation in China. This land has been ruined
by erosion. (Carnegie Institution Research in China.)]
Prevention of Erosion by Covering of Organic Soil.--We have shown how
ungoverned streams might dig out soil and carry it far from its original
source. Examples of what streams have done may be seen in the deltas formed
at the mouths of great rivers. The forest prevents this by holding the
water supply and letting it out gradually. This it does by covering the
inorganic soil with humus or decayed organic material. In this way the
forest floor becomes like a sponge, holding water through long periods of
drought. The roots of the trees, too, help hold the soil in place. The
gradual evaporation of water through the stomata of the leaves cools the
atmosphere, and this tends to precipitate the moisture in the air.
Eventually the dead bodies of the trees themselves are added to the organic
covering, and new trees take their place.
[Illustration: The forest regions of the United States.]
Other Uses of the Forest.--In some localities forests are used as
windbreaks and to protect mountain towns against avalanches. In winter they
moderate the cold, and in summer reduce the heat and lessen the danger from
storms. Birds nesting in the woods protect many valuable plants which
otherwise might be destroyed by insects.
Forests have great commercial importance. Pyrogallic and other acids are
obtained from trees, as are tar, creosote, resin, turpentine, and many
useful oils. The making of maple sirup and sugar forms a profitable
industry in several states.
The Forest Regions of the United States.--The combined area of all the
forests in the United States, exclusive of Alaska, is about 500,000,000
acres. This seemingly immense area is rapidly decreasing in acreage and in
quality, thanks to the demands of an increasing population, a woeful
ignorance on the part of the owners of the land, and wastefulness on the
part of cutters and users alike.
A glance at the map on page 109 shows the distribution of our principal
forests. Washington ranks first in the production of lumber. Here the great
Douglas fir, one of the "evergreens," forms the chief source of supply. In
the Southern states, especially Louisiana and Mississippi, yellow pine and
cypress are the trees most lumbered.
Which states produce the most hardwoods? From which states do we get most
of our yellow pine, spruce, red fir, redwood? Where are the heaviest
forests of the United States?
[Illustration: Transportation of lumber in the West. A logging train.]
[Illustration: Transportation of lumber in the East. Logs are mostly
floated down rivers to the mills.]
Uses of Wood.--Even in this day of coal, wood is still by far the most used
fuel. It is useful in building. It outlasts iron under water, in addition
to being durable and light. It is cheap and, with care of the forests,
inexhaustible, while our mineral wealth may some day be used up. Distilled
wood gives wood alcohol. Partially burned wood is charcoal. In our forests
much of the soft wood (the cone-bearing trees, spruce, balsam, hemlock, and
pine), and poplars, aspens, basswood, with some other species, make paper
pulp. The daily newspaper and cheap books are responsible for inroads on
our forests which cannot well be repaired. It is not necessary to take the
largest trees to make pulp wood. Hence many young trees of not more than
six inches in diameter are sacrificed. Of the hundreds of species of trees
in our forests, the conifers are probably most sought after for lumber.
Pine, especially, is probably used more extensively than any other wood. It
is used in all heavy construction work, frames of houses, bridges, masts,
spars and timber of ships, floors, railway ties, and many other purposes.
Cedar is used for shingles, cabinetwork, lead pencils, etc.; hemlock and
spruce for heavy timbers and, as we have seen, for paper pulp. Another use
for our lumber, especially odds and ends of all kinds, is in the
packing-box industry. It is estimated that nearly 50 per cent of all lumber
cut ultimately finds its way into the construction of boxes. Hemlock bark
is used for tanning.
The hard woods--ash, basswood, beech, birch, cherry, chestnut, elm, maple,
oak, and walnut--are used largely for the "trim" of our houses, for
manufacture of furniture, wagon or car work, and endless other purposes.
[Illustration: Diagrams of sections of timber. _a_, cross section; _b_,
radial; _c_, tangential. (From Pinchot, U. S. Dept. of Agriculture.)]
Methods of cutting Timber.--A glance at the diagram of the sections of
timber shows us that a tree may be cut radially through the middle of the
trunk or tangentially to the middle portion. Most lumber is cut
tangentially. In wood cut in this manner the yearly rings take a more or
less irregular course. The grain in wood is caused by the fibers not taking
straight lines in their course in the tree trunk. In many cases the fibers
of the wood take a spiral course up the trunk, or they may wave outward to
form little projections. Boards cut out of such a piece of wood will show
the effect seen in many of the school desks, where the annual rings appear
to form elliptical markings. Quite a difference in color and structure is
often seen between the heartwood, composed of the dead walls of cells
occupying the central part of the tree trunk, and the sapwood, the living
part of the stem.
[Illustration: Section of a tree trunk showing knot.]
Knots.--Knots, as can be seen from the diagram, are branches which at one
time started in their outward growth and were for some reason killed.
Later, the tree, continuing in its outward growth, surrounded them and
covered them up. A dead limb should be pruned before such growth occurs.
The markings in bird's-eye maple are caused by buds which have not
developed, and have been overgrown with the wood of the tree.
Destruction of the Forest.--_By Waste in Cutting._--Man is responsible for
the destruction of one of this nation's most valuable assets. This is
primarily due to wrong and wasteful lumbering. Hundreds of thousands of
dollars' worth of lumber is left to rot annually because the lumbermen do
not cut the trees close enough to the ground, or because through careless
felling of trees many other smaller trees are injured. There is great waste
in the mills. In fact, man wastes in every step from the forest to the
finished product.
[Illustration: A forest in the far west totally destroyed by fire and
wasteful lumbering.]
_By Fire._--Indirectly, man is responsible for fire, one of the greatest
enemies of the forest. Most of the great forest fires of recent years, the
losses from which total in the hundreds of millions, have been due either
to railroads or to carelessness in making fires in the woods. It is
estimated that in forest lands traversed by railroads from 25 per cent to
90 per cent of the fires are caused by coal-burning locomotives. For this
reason laws have been made in New York State requiring locomotives passing
through the Adirondack forest preserve to burn oil instead of coal. This
has resulted in a considerable reduction in the number of fires. In
addition to the loss in timber, the fires often burn out the organic matter
in the soil (the "duff") forming the forest floor, thus preventing the
growth of forest there for many years to come. In New York and other states
fires are fought by an organized corps of fire wardens, whose duty it is to
watch the forest and to fight forest fires.
Other Enemies.--Other enemies of the forest are numerous fungus plants,
insect parasites which bore into the wood or destroy the leaves, and
grazing animals, particularly sheep. Wind and snow also annually kill many
trees.
Forestry.--In some parts of central Europe, the value of the forests was
seen as early as the year 1300 A.D., and many towns consequently bought up
the surrounding forests. The city of Zurich has owned forests in its
vicinity for at least 600 years and has found them a profitable investment.
In this country only recently has the importance of preserving and caring
for our forests been noted by our government. Now, however, we have a
Forest Survey of the Department of Agriculture and numerous state and
university schools of forestry which are rapidly teaching the people of
this country the best methods for the preservation of our forests. The
Federal government has set aside a number of tracts of mountain forest in
some of the Western states, making a total area of over 167,000,000 acres.
New York has established for the same purpose the Adirondack Park, with
nearly 1,500,000 acres of timberland. Pennsylvania has one of 700,000
acres, and many other states have followed their example.
[Illustration: The forest primeval. Trees are killing each other in the
struggle for light and air.]
[Illustration: A German beech forest. The trees are kept thinned out so as
to allow the young trees to get a start. Contrast this with the picture
above.]
Methods for Keeping and Protecting the Forests.--Forests should be kept
thinned. Too many trees are as bad as too few. They struggle with one
another for foothold and light, which only a few can enjoy. In cutting the
forest, it should be considered as a harvest. The oldest trees are the
"ripe grain," the younger trees being left to grow to maturity. Several
methods of renewing the forest are in use in this country. (1) Trees may be
cut down and young ones allowed to sprout from cut stumps. This is called
coppice growth. This growth is well seen in parts of New Jersey. (2) Areas
or strips may be cut out so that seeds from neighboring trees are carried
there to start new growth. (3) Forests may be artificially planted. Two
seedlings planted for every tree cut is a rule followed in Europe. (4) The
most economical method is that shown in the lower picture on page 114,
where the largest trees are thinned out over a large area so as to make
room for the younger ones to grow up. The greatest dangers to the forests
are from fire and from careless cutting, and these dangers may be kept in
check by the efficient work of our national and state foresters.
[Illustration: We must protect our city trees. This tree was badly wounded
by being gnawed by a horse.]
A City's Need for Trees.--The city of Paris, well known as one of the most
beautiful of European capitals, spends over $100,000 annually in caring for
and replacing some of the 90,000 trees owned by the city. All over the
United States the city governments are beginning to realize what European
cities have long known, that trees are of great value to a city. They are
now following the example of European cities by planting trees and by
protecting the trees after they are planted. Thousands of city trees are
annually killed by horses which gnaw the bark. This may be prevented by
proper protection of the trunk by means of screens or wire guards. Chicago
has appointed a city forester, who has given the following excellent
reasons why trees should be planted in the city:--
(1) Trees are beautiful in form and color, inspiring a constant
appreciation of nature.
(2) Trees enhance the beauty of architecture.
(3) Trees create sentiment, love of country, state, city, and home.
(4) Trees have an educational influence upon citizens of all ages,
especially children.
(5) Trees encourage outdoor life.
(6) Trees purify the air.
(7) Trees cool the air in summer and radiate warmth in winter.
(8) Trees improve climate and conserve soil and moisture.
(9) Trees furnish resting places and shelter for birds.
(10) Trees increase the value of real estate.
(11) Trees protect the pavement from the heat of the sun.
(12) Trees counteract adverse conditions of city life.
Let us all try to make Arbor Day what it should be, a day for
caring for and planting trees, for thus we may preserve this most
important heritage of our nation.
REFERENCE BOOKS
ELEMENTARY
Hunter, _Laboratory Problems in Civic Biology_. American
Book Company.
Mayne and Hatch, _High School Agriculture_. American Book
Company.
Murrill, _Shade Trees_, Bul. 205, Cornell University
Agricultural Experiment Station.
Pinchot, _A Primer of Forestry_, Division of Forestry, U. S.
Department of Agriculture.
ADVANCED
Apgar, _Trees of the United States_, Chaps. II, V, VI.
American Book Company.
Coulter, Barnes, and Cowles, _A Textbook of Botany_, Part I
and Vol. II. American Book Company.
Goebel, _Organography of Plants_, Part V. Clarendon Press.
Strasburger, Noll, Schenck, and Karston, _A Textbook of
Botany_. The Macmillan Company.
Ward, _Timber and Some of its Diseases_. The Macmillan
Company.
Yearbook, U. S. Department of Agriculture, Division of
Forestry, Buls. 7, 10, 13, 16, 17, 18, 20, 26, 27.
X. THE ECONOMIC RELATION OF GREEN PLANTS TO MAN
_Problems.--How green plants are useful to man._
_(a) As food._
_(b) For clothing._
_(c) Other uses._
_How green plants are harmful to man._
SUGGESTED LABORATORY WORK
If a commercial museum is available, a trip should be planned to work
over the topics in this chapter. The school collection may well
include most of the examples mentioned, both of useful and harmful
plants.
A study of weeds and poisonous plants should be taken up in actual
laboratory work, either by collection and identification or by
demonstration.
Green Plants have a "Dollar and Cents" Value.--To the girl or boy living in
the city green plants seem to have little direct value. Although we see
vegetables for sale in stores and we know that fruits have a money value,
we are apt to forget that the wealth of our nation depends more upon its
crops than it does on its manufactories and business houses. The economic
or "dollars and cents" value of plants is enormous and far too great for us
to comprehend in terms of figures.
We have already seen some of the uses to mankind of the products of the
forest; let us now consider some other plant products.
[Illustration:
Cabbage Onions Lettuce
Leaves used as food.]
Leaves as Food.--Grazing animals feed almost entirely on tender shoots or
leaves, blades of grass, and other herbage. Certain leaves and buds are
used by man as food. Lettuce, beet tops, kale, spinach, broccoli, are
examples. A cabbage head is nothing but a big bud which has been cultivated
by man. An onion is a compact budlike mass of thickened leaves which
contain stored food.
[Illustration:
Celery Kohl-rabi Potato Sugar cane
Stems used as food.]
Stems as Food.--A city child would, if asked to name some stem used as
food, probably mention asparagus. We sometimes forget that one of our
greatest necessities, cane sugar, comes from the stem of sugar cane. Over
seventy pounds of sugar is used each year by every person in the United
States. To supply the growing demand beets are now being raised for their
sugar in many parts of the world, so that nearly half the total supply of
sugar comes from this source. Maple sugar is a well-known commodity which
is obtained by boiling the sap of sugar maple until it crystallizes. Over
16,000 tons of maple sugar is obtained every spring, Vermont producing
about 40 per cent of the total output. The sago palm is another stem which
supports the life of many natives in Africa. Another stem, living
underground, forms one of man's staple articles of diet. This is the
potato.
Roots as Food.--Roots which store food for plants form important parts of
man's vegetable diet. Beets, radishes, carrots, parsnips, sweet potatoes,
and many others might be mentioned.
The following table shows the proportion of foods in some of the commoner
roots and stems:--
--------------------------------------------------------------------
| WATER| PROTEINS| CARBOHYDRATES| FAT | MINERAL MATTER
-------------+------+---------+--------------+-----+----------------
Potato | 75 | 1.2 | 18 | 0.3 | 1.0
Carrot | 89 | 0.5 | 5 | 0.2 | 1.0
Parsnip | 81 | 1.2 | 8.7 | 1.5 | 1.0
Turnip | 92.8 | 0.5 | 4. | 0.1 | 0.8
Onion | 91 | 1.5 | 4.8 | 0.2 | 0.5
Sweet potato | 74 | 1.5 | 20.2 | 0.1 | 1.5
Beet | 82.2 | 0.4 | 13.4 | 0.1 | 0.9
--------------------------------------------------------------------
[Illustration:
Wheat Nuts Pear Melon
Seeds and fruits used for food.]
Fruits and Seeds as Foods.--Our cereal crops, corn, wheat, etc., have
played a very great part in the civilization of man and are now of so much
importance to him as food products that bread made from flour from the
wheat has been called the "staff of life." Our grains are the cultivated
progeny of wild grasses. Domestication of plants and animals marks epochs
in the advance of civilization. The man of the stone age hunted wild beasts
for food, and lived like one of them in a cave or wherever he happened to
be; he was a nomad, a wanderer, with no fixed home. He may have discovered
that wild roots or grains were good to eat; perhaps he stored some away for
future use. Then came the idea of growing things at home instead of digging
or gathering the wild fruits from the forest and plain. The tribes which
first cultivated the soil made a great step in advance, for they had as a
result a fixed place for habitation. The cultivation of grains and cereals
gave them a store of food which could be used at times when other food was
scarce. The word "cereal" (derived from Ceres, the Roman Goddess of
Agriculture) shows the importance of this crop to Roman civilization. From
earliest times the growing of grain and the progress of civilization have
gone hand in hand. As nations have advanced in power, their dependence upon
the cereal crops has been greater and greater.
"Indian corn," says John Fiske, in _The Discovery of America_, "has played
a most important part in the history of the New World. It could be planted
without clearing or plowing the soil. There was no need of threshing or
winnowing. Sown in tilled land, it yields more than twice as much food per
acre as any other kind of grain. This was of incalculable advantage to the
English settlers in New England, who would have found it much harder to
gain a secure foothold upon the soil if they had had to begin by preparing
it for wheat or rye."
To-day, in spite of the great wealth which comes from our mineral
resources, live stock, and manufactured products, the surest index of our
country's prosperity is the size of the corn and wheat crop. According to
the last census, the amount of capital invested in agriculture was over
$20,000,000,000, while that invested in manufacture was less than one half
that amount.
Corn.--About three billion bushels of corn were raised in the United States
during the year 1910. This figure is so enormous that it has but little
meaning to us. In the past half century our corn crop has increased over
350 per cent. Illinois and Iowa are the greatest corn-producing states,
each having a yearly record of over four hundred million bushels. The
figure on this page shows the principal corn-producing areas in the United
States.
[Illustration: Indian Corn Production--Percentage]
Indian corn is put to many uses. It is a valuable food. It contains a large
proportion of starch, from which glucose (grape sugar) and alcohol are
made. Machine oil and soap are made from it. The leaves and stalk are an
excellent fodder; they can be made into paper and packing material.
Mattresses can be stuffed with the husks. The pith is used as a protective
belt placed below the water line of our huge battleships. Corn cobs are
used for fuel, one hundred bushels having the fuel value of a ton of coal.
[Illustration: Wheat Crop in United States--Percentage Source]
Wheat.--Wheat is the crop of next greatest importance in size. Nearly seven
hundred millions of bushels were raised in this country in 1910,
representing a total money value of over $700,000,000. Seventy-two per cent
of all the wheat raised comes from the North Central states and California.
About three fourths of the wheat crop is exported, nearly one half of it to
Great Britain, thus indirectly giving employment to thousands of people on
railways and steamships. Wheat has its chief use in its manufacture into
flour. The germ, or young wheat plant, is sifted out during this process
and made into breakfast foods. Flour making forms the chief industry of
Minneapolis, Minnesota, and of several other large and wealthy cities in
this country.
[Illustration: A field of rice, showing the conditions of culture.]
Other Grains.--Of the other grain and cereals raised in this country, oats
are the most important crop, over one billion bushels having been produced
in 1910. Barley is another grain, a staple of some of the northern
countries of Europe and Asia. In this country, it is largely used in making
malt for the manufacture of beer. Rye is the most important cereal crop of
northern Europe, Russia, Germany, and Austro-Hungary producing over 50 per
cent of the world's supply. One of the most important grain crops for the
world (although relatively unimportant in the United States) is rice. The
fruit of this grasslike plant, after thrashing, screening, and milling,
forms the principal food of one third of the human race. Moreover, its
stems furnish straw, its husks make a bran used as food for cattle, and the
grain, when fermented and distilled, yields alcohol.
Garden Fruits.--Green plants and especially vegetables have
come to play an important part in the dietary of man. The
diseases known as scurvy and beri-beri, the latter the curse of the
far Eastern navies, have been largely prevented by adding vegetables
and fruit juices to the dietary of the sailors. People in
this country are beginning to find that more vegetables and less
meat are better than the meat diet so often used. Market gardening
forms the lucrative business of many thousands of people
near our great cities. Some of the more important fruits are
squash, cucumbers, pumpkins, melons, tomatoes, peppers, strawberries,
raspberries, and blackberries. The latter fruits bring in
an annual income of $25,000,000 to our market gardeners. Beans
and peas are important as foods because of their relatively large
amount of protein. Canning green corn, peas, beans, and tomatoes
has become an important industry.
[Illustration: Picking apples, an important crop in some parts of the
United States.]
Orchard and Other Fruits.--In the United States over one hundred and
seventy-five million bushels of apples are grown every year. Pears, plums,
apricots, peaches, and nectarines also form large orchards, especially in
California. Nuts form one of our important articles of food, largely
because of the large amount of protein contained in them.
The grape crop of the world is commercially valuable, because of the
raisins and wine produced. The culture of lemons, oranges, and grapefruit
has come in recent years to give a living to many people in this country as
well as in other parts of the world. Figs, olives, and dates are staple
foods in the Mediterranean countries and are sources of wealth to the
people there, as are coconuts, bananas, and many other fruits in tropical
countries.
Beverages and Condiments.--The coffee and cacao beans, and leaves of the
tea plant, products of tropical regions, form the basis of very important
beverages of civilized man. Pepper, black and red, mustard, allspice,
nutmegs, cloves, and vanilla are all products manufactured from various
fruits or seeds of tropical plants.
Alcoholic liquors are produced from various plants in different parts of
the world, the dried fruit of the hop vine being an important product of
New York State used in the making of beer.
Raw Materials.--Besides use as food, green plants have many other uses.
Many of our city industries would not be in existence, were it not for
certain plant products which furnish the raw materials for many
manufacturing industries. Many cities of the east and south, for example,
depend upon cotton to give employment to thousands of factory hands.
[Illustration: Cotton Crop in United States--Percentage Source
Cotton Crop in United States--Percentage Consumption]
Cotton.--Of our native plant products cotton is probably of the most
importance to the outside world. Over eleven million bales of five hundred
pounds each are raised annually.
The cotton plant thrives in warm regions. Its commercial importance is
gained because the seeds of the fruit have long filaments attached to them.
Bunches of these filaments, after treatment, are easily twisted into
threads from which are manufactured cotton cloth, muslin, calico, and
cambric. In addition to the fiber, cottonseed oil, a substitute for olive
oil, is made from the seeds, and the refuse remaining makes an excellent
cattle fodder.
[Illustration: Map showing the spread of the cotton boll weevil. It was
introduced from Mexico about 1894. What proportion of the cotton raising
belt was infected in 1908?]
Cotton Boll Weevil.--The cotton crop of the United States has rather
recently been threatened with destruction by a beetle called the cotton
boll weevil. This insect, which bores into the young pod of the cotton,
develops there, stunting the growth of the fruit to such an extent that
seeds are not produced. The loss in Texas alone is estimated at over
$10,000,000 a year. The boll weevil, because of the protection offered by
the cotton boll, is very difficult to exterminate. The weevils are
destroyed by birds, the infected bolls and stalks are burnt, millions are
killed each winter by cold, other insects prey on them, but at the present
time they are one of the greatest pests the south knows.
[Illustration: Mexican cotton boll weevil. Much enlarged, above; natural
size, below. (Herrick.)]
The control of this pest seems to depend upon early planting so that the
crop has an opportunity to ripen before the insects in the boll grow large
enough to do harm. Ultimately the boll weevil may do more good than harm by
bringing into the market a type of cotton plant that ripens very early.
Vegetable Fibers.--Among the most important are Manila hemp, which comes
from the leaf-stalks of a plant of the banana family and true hemp, which
is the bast or woody fiber of a plant cultivated in most warm parts of the
earth. Flax is also an important fiber plant, grown largely in Russia and
other parts of Europe (see picture on next page). From the bast fibers of
the stem of this herb linen cloth is made.
[Illustration: Flax grown for fiber.]
Vegetable Oils.--Some of the same plants which give fiber also produce oil.
Cotton seed oil pressed from the seeds, linseed oil from the seeds of the
flax plant, and coconut oil (the covering of the nut here producing the
fiber) are examples.
[Illustration: Poison ivy, a climbing plant which is poisonous to touch.
Notice the leaves in threes.]
Some Harmful Green Plants.--We have seen that on the whole green plants are
useful to man. There are, however, some that are harmful. For example, the
poison ivy is extremely poisonous to touch. The poison ivy is a climbing
plant which attaches itself to the trees or walls by means of tiny air
roots which grow out from the stem. It is distinguished from its harmless
climbing neighbor, the Virginia Creeper, by the fact that its leaves are
notched in _threes_ instead of _fives_. Every boy and girl should know
poison ivy.
Numerous other poisonous common plants are found, but one other deserves
special notice because of its presence in vacant city lots. The Jimson Weed
(_Datura_) is a bushy plant, from two to five feet high, bearing large
leaves. It has white or purplish flowers, and later bears a four-valved
seed pod containing several hundred seeds. These plants contain a powerful
poison, and people are often made seriously ill by eating the roots or
other parts by mistake.
Weeds.--From the economic standpoint the green plants which do the greatest
damage are weeds. Those plants which provide best for their young are
usually the most successful in life's race. Plants which combine with the
ability to scatter many seeds over a wide territory the additional
characteristics of rapid growth, resistance to dangers of extreme cold or
heat, attacks of enemies, inedibility, and peculiar adaptations to
cross-pollination or self-pollination, are usually spoken of as weeds. They
flourish in the sterile soil of the roadside and in the fertile soil of the
garden. By means of rapid growth they kill other plants of slower growth by
usurping their territory. Slow-growing plants are thus actually
exterminated. Many of our common weeds have been introduced from other
countries and have, through their numerous adaptations, driven out other
plants which stood in their way. Such is the Russian Thistle. A single
plant of this kind will give rise to over 20,000 seeds. First introduced
from Russia in 1873, it spread so rapidly that in twenty years it had
appeared as a common weed over an area of some twenty-five thousand square
miles. It is now one of the greatest pests in our Northwest.
REFERENCE BOOKS
ELEMENTARY
Hunter, _Laboratory Problems in Civic Biology_. American
Book Company.
Gannet, _Commercial Geography_. American Book Company.
Sargent, _Plants and their Uses_. Henry Holt and Company.
Toothaker, _Commercial Raw Materials_. Ginn and Company.
U. S. Dept. of Agriculture, Farmers' Bulletin 86, _Thirty
Poisonous Plants of the United States_, V. K. Chestnut.
Bulletin 17. _Two Hundred Weeds, How to Know Them and How to
Kill Them_, L. H. Dewey.
ADVANCED
Bailey, _Cyclopedia of American Agriculture_. The Macmillan
Company.
XI. PLANTS WITHOUT CHLOROPHYLL IN THEIR RELATION TO MAN
_Problems.--(a) How molds and other saprophytic fungi do harm to man._
_(b) What yeasts do for mankind._
_(c) A study of bacteria with reference to_
_(1) Conditions favorable and unfavorable to growth._
_(2) Their relations to mankind._
_(3) Some methods of fighting harmful bacteria and diseases
caused by them._
LABORATORY SUGGESTIONS
_Field work._--Presence of bracket fungi and chestnut
canker.
_Home experiment._--Conditions favorable to growth of mold.
_Laboratory demonstration._--Growth of mold, structure,
drawing.
_Home experiment or laboratory demonstration._--Conditions
unfavorable for growth of molds.
_Demonstration._--Process of fermentation.
_Microscopic demonstration._--Growing yeast cells. Drawing.
_Home experiment._--Conditions favorable for growth of
yeast.
_Home experiment._--Conditions favorable for growth of yeast
in bread.
_Demonstration and experiment._--Where bacteria may be
found.
_Demonstration._--Methods of growth of bacteria, pure
cultures and colonies shown.
_Demonstration._--Foods preferred by bacteria.
_Demonstration._--Conditions favorable for growth of
bacteria.
_Demonstration._--Conditions unfavorable for growth of
bacteria.
_Demonstration by charts, diagrams, etc._--The relation of
bacteria to disease in a large city.
COLORLESS PLANTS ARE USEFUL AND HARMFUL TO MAN
The Fungi.--We have found that green plants on the whole are useful to
mankind. But not all plants are green. Most of us are familiar with the
edible mushroom sold in the markets or the so-called "toadstools" found in
parks or lawns. These plants contain no chlorophyll and hence do not make
their own food. They are members of the plant group called _fungi_. Such
plants are almost as much dependent upon the green plants for food as are
animals. But the fungi require for the most part dead organic matter for
their food. This may be obtained from decayed vegetable or animal material
in soil, from the bodies of dead plants and animals, or even from foods
prepared for man. Fungi which feed upon _dead_ organic material are known
as _saprophytes_. Examples are the mushrooms, the yeasts, molds, and some
bacteria, of which more will be learned later.
[Illustration: Chestnut trees in a New York City park; killed by a
parasite, the chestnut canker.]
Some Parasitic Fungi.--Other fungi (and we will find this applies to some
animals as well) prefer _living_ plants or animals for their food. Thus a
tiny plant, recently introduced into this country, known as the chestnut
canker, is killing our chestnut trees by the thousands in the eastern part
of the United States. It produces millions of tiny reproductive cells known
as _spores_; these spores, blown about by the wind, light on the trees,
sprout, and send in under the bark a threadlike structure which sucks in
the food circulating in the living cells, eventually causing the death of
the tree. _A plant or animal which lives at the expense of another living
plant or animal is called a parasite._ The chestnut canker is a dangerous
parasite. Later we shall see that animal and plant parasites destroy yearly
crops and trees valued at hundreds of millions of dollars and cause untold
misery and suffering to humanity.
[Illustration: Shelf fungi. (Photographed by W. C. Barbour.)]
Another fungus which does much harm to the few trees found in large towns
and cities is the shelf or bracket fungus. The part of the body visible on
the tree looks like a shelf or bracket, hence the name. This bracket is in
reality the reproductive part of the plant; on its lower surface are formed
millions of little bodies called _spores_. These spores are capable, under
favorable conditions, of reproducing new plants. The true body of the
plant, a network of threads, is found under the bark. This fungus begins
its life as a spore in some part of the tree which has become _diseased_ or
_broken_. Once established, it spreads rapidly. There is no remedy except
to kill the tree and burn it, so as to destroy the spores. Many fine trees,
sound except for a slight bruise or other injury, are annually infected and
eventually killed. In cities thousands of trees become infected through
careless hitching of horses so that the horse may gnaw the tree, thus
exposing a fresh surface on which spores may obtain lodgment and grow (see
page 115).
Suggestions for Field Work.--A field trip to a park or grove near home may
show the great destruction of timber by this means. Count the number of
perfect trees in a given area. Compare it with the number of trees attacked
by the fungus. Does the fungus appear to be transmitted from one tree to
another near at hand? In how many instances can you discover the point
where the fungus first attacked the tree?
Fungi of our Homes.--But not all fungi are wild. Some have become
introduced into our homes and these live on food or other materials. _These
plants are very important because of their relation to life in a town or
crowded city._[17]
Footnote 17: Experiments on conditions favorable to growth
of mold should be introduced here.
[Illustration: Bread mold; _r_, rhizoids; _s_, fruiting bodies containing
spores.]
The Growth of Bread Mold.--If a piece of moist bread is exposed to the air
of the schoolroom, or in your own kitchen for a few minutes and then
covered with a glass tumbler and kept in a warm place, in a day or two a
fuzzy whitish growth will appear on the surface of the bread. This growth
shortly turns black. If we now examine a little piece of the bread with a
lens or low-powered microscope, we find a tangled mass of threads (the
_mycelium_) covering the surface of the bread. From this mass of threads
project tiny upright stalks bearing round black bodies, the fruit. Little
rootlike structures known as _rhizoids_ dip down into the bread, and absorb
food for its threadlike body. The upright threads with the balls at the end
contain many tiny bodies called _spores_. These spores have been formed by
the division of the protoplasm making up the fruiting bodies into many
separate cells. When grown under favorable conditions, the spores will
produce more mycelia, which in turn bear fruiting bodies.
Physiology of the Growth of Mold.--Molds, in order to grow rapidly, need
oxygen, moisture, and moderate heat. They seem to prefer dark, damp places
where there is not a free circulation of air, for if the bell jar is
removed from growing mold for even a short time, the mold wilts. Too great
or very little heat will prevent growth and kill everything except the
spores. They obtain their food from the material on which they live. This
they are able to do by means of digestive enzymes given out by the rootlike
parts, by means of which the molds cling to the bread. These digestive
enzymes change the starch of the bread to sugar and the protein to a
soluble form which will pass by osmosis into cells of the mold. Thus the
mold is able to absorb food material. These foods are then used to supply
energy and make protoplasm. This seems to be the usual method by which
saprophytes make use of the materials on which they live.
What can Molds live On?--We have seen that black mold lives upon bread. We
would find that it or some other mold (_e.g._ green or blue mold) live upon
decaying or overripe fruit,--apples, peaches, and plums being especially
susceptible to their growth. Molds feed upon all cakes or breads, upon
meat, cheese, and many raw vegetables. They are almost sure to grow upon
flour if it is allowed to get damp. Moisture seems necessary for their
growth. Jelly is a substance particularly favorable to molds for this
reason. Shoes, leather, cloth, paper, or even moist wood will give food
enough to support their growth. At least one troublesome disease,
_ringworm_, is due to the growth of molds in the skin.
What Mold does to Foods.--Mold usually changes the taste of the material it
grows upon, rendering it "musty" and sometimes unfit to eat. Eventually it
will spoil food completely because decay sets in. Decay, as we will see
later, is not entirely due to mold growth, but is usually caused by another
group of organisms, the _bacteria_. Molds, however, in feeding _do_ cause
chemical changes which result in decay or putrefaction. Some molds are
useful. They give the flavor to Roquefort, Gorgonzola, Camembert, and Brie
cheeses. But on the whole molds are pests which the housekeeper wishes to
get rid of.
How to prevent Molds.[18]--As we have seen, moisture is favorable for mold
growth; conversely, dryness is unfavorable. Inasmuch as the spores of mold
abound in the air, materials which cannot be kept dry should be covered.
Jelly after it is made should at once be tightly covered with a thin layer
of paraffin, which excludes the air and possible mold spores. Or waxed
paper may be fastened over the surface of the jelly so as to exclude the
spores. To prevent molds from attacking fresh fruit, the surface of the
fruit should be kept dry and, if possible, each piece of fruit should be
wrapped in paper. Why? Heating with dry heat to 212° for a few moments will
kill any mold spores that happen to be in food. Moldy food, if heated after
removing surface on which the mold grew, is perfectly good to eat.
Footnote 18: An experiment to show conditions unfavorable
for growth of molds should be shown at this point.
Dry dusting or sweeping will raise dust, which usually contains mold
spores. Use a dampened broom or dust cloth frequently in the kitchen if you
wish to preserve foods from molds.
Other Moldlike Fungi.--Mildews are near relatives of the molds found in our
homes. They may attack leather, cloth, etc., in a damp house. Other allied
forms may do damage to living plants. Some of these live upon the lilac,
rose, or willow. These fungi do not penetrate the host plant to any depth,
for they obtain their food from the outer layer of cells in the leaf of
their host and cover the leaves with the whitish threads of the mycelium.
Hence they may be killed by means of applications of some fungus-killing
fluid, as Bordeaux mixture.[19] Among the useful plants preyed upon by
mildews are the plum, cherry, and peach trees. (The diseases known as black
knot and peach curl are thus caused.) Another important member of this
group is the tiny parasite found on rye and other grains, which gives us
the drug ergot.
Footnote 19: See Goff and Mayne, _First Principles of
Agriculture_, page 59, for formula of Bordeaux mixture.
Among other parasitic fungi are rusts and smuts. Wheat rust is probably the
most destructive parasitic fungus. Indirectly this parasite is of
considerable importance to the citizen of a great city because of its
effect upon the price of wheat.
YEASTS IN THEIR RELATION TO MAN
Fermentation.--It is of common knowledge to country boys or girls that the
juice of fresh apples, grapes, and some other fruits, if allowed to stand
exposed to the air for a short time will _ferment_. That is, the sweet
juice will begin to taste sour and to have a peculiar odor, which we
recognize as that of alcohol. The fermenting juice appears to be full of
bubbles which rise to the surface. If we collect enough of these bubbles of
gas to make a test, we find it to be carbon dioxide.
Evidently something changed some part of the apple or grape, the sugar,
(C{6}H{12}O{6}), into alcohol, 2(C{2}H{6}O), and carbon dioxide, 2(CO{2}).
This chemical process is known as _fermentation_.
[Illustration: Apparatus to show effect of fermentation. _N_, molasses,
water and yeast plants; _C_, bubbles of carbon dioxide.]
Yeast causes Fermentation.--Let us now take a compressed yeast cake, shake
up a small portion of it in a solution of molasses and water, and fill a
fermentation tube with the mixture. Leave the tube in a warm place
overnight. In the morning a gas will be found to have been collected in the
closed end of the tube (see Figure on page 138). The taste and
odor of the liquid shows alcohol to be present, and the gas, if tested, is
proven carbon dioxide. Evidently yeast causes fermentation.
What are Yeasts?--If now part of the liquid from the fermentation tube
which contains the settlings be drawn off, a drop placed on a slide and a
little weak iodine added and the mixture examined under the compound
microscope, two kinds of structures will be found (see Figure below),
starch grains which are stained deep blue, and other smaller ovoid
structures of a brownish yellow color. The latter are yeast plants.
[Illustration: Yeast and starch grains. Notice that the starch grains
around which are clustered yeast cells have been rounded off by the yeast
plants. How do you account for this?]
Size and Shape, Manner of Growth, etc.--The common compressed yeast cake
contains millions of these tiny plants. In its simplest form a yeast plant
is a single cell. The shape of such a plant is ovoid, each cell showing
under the microscope the granular appearance of the protoplasm of which it
is formed. Look for tiny clear areas in the cells; these are vacuoles, or
spaces filled with fluid. The nucleus is hard to find in a yeast cell. Many
of the cells seem to have others attached to them, sometimes there being
several in a row. Yeast cells reproduce very rapidly by a process of
budding, a part of the parent cell forming one or more smaller daughter
cells which eventually become free from the parent.
Conditions favorable to growth of Yeast.--_Experiment._--Label three pint
fruit jars A, B, and C. Add one fourth of a compressed yeast cake to two
cups of water containing two tablespoonfuls of molasses or sugar. Stir the
mixture well and divide it into three equal parts and pour them into the
jars. Place covers on the jars. Put jar A in the ice box on the ice, and
jar B over the kitchen stove or near a radiator; pour the contents of jar C
into a small pan and boil for a few minutes. Pour back into C, cover and
place it next to B. After forty-eight hours, look to see if any bubbles
have made their appearance in any of the jars. If the experiment has been
successful, only jar B will show bubbles. After bubbles have begun to
appear at the surface, the fluid in jar B will be found to have a sour
taste and will smell unpleasantly. The gas which rises to the surface, if
collected and tested, will be found to be carbon dioxide. The contents of
jar B have fermented. Evidently, the growth of yeast will take place only
under conditions of moderate warmth and moisture.
Carbohydrates necessary to Fermentation.--Sugar must be present in order
for fermentation to take place. The wild yeasts cause fermentation of the
apple or grape juice because they live on the skin of the apple or grape.
Various peoples recognize this when they collect the juice of certain
fruits and, exposing it to the air, allow it to ferment. Such is the _saki_
or rice wine of the Japanese, the _tuba_ or sap of the coconut palm of the
Filipinos and the _pulqué_ of the Mexicans.
Beer and Wine Making.--Brewers' yeasts are cultivated with the greatest
care; for the different flavors of beer seem to depend largely upon the
condition of the yeast plants. Beer is made in the following manner.
Sprouted barley, called malt, in which the starch of the grain has been
changed to grape sugar by digestion, is killed by drying in a hot kiln. The
malt is dissolved in water, and hops are added to give the mixture a bitter
taste. Now comes the addition of the yeast plants, which multiply rapidly
under the favorable conditions of food and heat. Fermentation results on a
large scale from the breaking down of the grape sugar, the alcohol
remaining in the fluid, and the carbon dioxide passing off into the air. At
the right time the beer is stored either in bottles or casks, but
fermentation slowly continues, forming carbon dioxide in the bottles. This
gives the sparkle to beer when it is poured from the bottle.
In wine making the wild yeasts growing on the skin of the grapes set up a
slow fermentation. It takes several weeks before the wine is ready to
bottle. In sparkling wines a second fermentation in the bottles gives rise
to carbon dioxide in such quantity as to cause a decided frothing when the
bottle is opened.
Commercial Yeast.--Cultivated yeasts are now supplied in the home as
compressed or dried yeast cakes. In both cases the yeast plants are mixed
with starch and other substances and pressed into a cake. But the
compressed yeast cake must be used fresh, as the yeast plants begin to die
rapidly after two or three days. The dried yeast cake, while it contains a
much smaller number of yeast plants, is nevertheless probably more reliable
if the yeast cannot be obtained fresh.
[Illustration: _a_ _b_ _c_]
The cut illustrates an experiment that shows how yeast plants depend upon
food in order to grow. In each of three fermentation tubes were placed an
equal amount of a compressed yeast cake. Then tube _a_ was filled with
distilled water, tube _b_ with a solution of glucose and water, and tube
_c_ with a nutrient solution containing nitrogenous matter as well as
glucose. The quantity of gas (CO{2}) in each tube is an index of the amount
of growth of the yeast cells. In which tube did the greatest growth take
place?
Bread Making.--Most of us are familiar with the process of bread making.
The materials used are flour, milk or water or both, salt, a little sugar
to hasten the process of fermentation, or "_rising_," as it is called, some
butter or lard, and yeast.
After mixing the materials thoroughly by a process called "kneading," the
bread is put aside in a warm place (about 75° Fahrenheit) to "rise." If we
examine the dough at this time, we find it filled with holes, which give
the mass a spongy appearance. The yeast plants, owing to favorable
conditions, have grown rapidly and filled the cavities with carbon dioxide.
Alcohol is present, too, but this is evaporated when the dough is baked.
The baking cooks the starch of the bread, drives off the carbon dioxide and
alcohol, and kills the yeast plants, besides forming a protective crust on
the loaf.
Sour Bread.--If yeast cakes are not fresh, sour bread may result from their
use. In such yeast cakes there are apt to be present other tiny one-celled
plants, known as _bacteria_. Certain of these plants form acids after
fermentation takes place. The sour taste of the bread is usually due to
this cause. The remedy would be to have fresh yeast, to have good and fresh
flour, and to have clean vessels with which to work.
Importance of Yeasts.--Yeasts in their relation to man are thus seen to be
for the most part useful. They may get into canned substances put up in
sugar and cause them to "work," giving them a peculiar flavor. But they can
be easily killed by heating to the temperature of boiling. On the other
hand, yeast plants are necessary for the existence of all the great
industries which depend upon fermentation. And best of all they give us
leavened bread, which has become a necessity to most of mankind.
BACTERIA IN THEIR RELATION TO MAN
What Bacteria do and Where They May be Found.--A walk through a crowded
city street on any warm day makes one fully alive to odors which pervade
the atmosphere. Some of these unpleasant odors, if traced, are found to
come from garbage pails, from piles of decaying fruit or vegetables, or
from some butcher shop in which decayed meat is allowed to stand. This
characteristic phenomena of decay is one of the numerous ways in which we
can detect the presence of bacteria. These tiny plants, "man's invisible
friends and foes," are to be found "anywhere, but not everywhere," in
nature. They swarm in stale milk, in impure water, in soil, in the living
bodies of plants and animals and in their dead bodies as well. Most
"catching" diseases we know to be caused directly by them; the processes of
decay, souring of milk, acid fermentation, the manufacture of nitrogen for
plants are directly or indirectly due to their presence. It will be the
purpose of the next paragraphs to find some of the places where bacteria
may be found and how we may know of their presence.
[Illustration: A steam sterilizer.]
How we catch Bacteria to Study Them.--To study bacteria it is first
necessary to find some material in which they will grow, then kill all
living matter in this food material by heating to boiling point (212°) for
half an hour or more (this is called _sterilization_), and finally protect
the _culture medium_, as this food is called, from other living things that
might grow upon it.
One material in which bacteria seem to thrive is a mixture of beef extract,
digested protein and gelatine or agar-agar, the latter a preparation
derived from seaweed. This mixture, after sterilization, is poured into
flat dishes with loose-fitting covers. These _petri_ dishes, so called
after their inventor, are the traps in which we collect and study bacteria.
Where Bacteria might Grow.--Expose a number of these sterilized dishes,
each for the same length of time, to some of the following conditions:
(_a_) exposed to the air of the schoolroom.
(_b_) exposed in the halls of the school while pupils are passing.
(_c_) exposed in the halls of the school when pupils are not moving.
(_d_) exposed at the level of a dirty and much-used city street.
(_e_) exposed at the level of a well-swept and little-used city street.
(_f_) exposed in a city park.
(_g_) exposed in a factory building.
(_h_) dirt from hands placed in dish.
(_i_) rub interior of mouth with finger and touch surface of dish.
(_j_) touch surface of dish with decayed vegetable or meat.
(_k_) touch surface of dish with dirty coin or bill.
(_l_) place in dish two or three hairs from boy's head.
This list might be prolonged indefinitely.
[Illustration: Colonies of bacteria growing in a petri dish.]
Now let us place all of the dishes together in a moderately warm place (a
closet in the schoolroom will do) and watch for results. After a day or two
little spots, brown, yellow, white, or red, will begin to appear. These
spots, which grow larger day by day, are _colonies_ made up of millions of
bacteria. But probably each colony arose from a single bacterium which got
into the dish when it was exposed to the air.
How we may isolate Bacteria of Certain Kinds from Others.--In order to get
a number of bacteria of a given kind to study, it becomes necessary to grow
them in what is known as a pure culture. This is done by first growing the
bacteria in some medium such as beef broth, gelatin, or on potato.[20] Then
as growth follows the colonies of bacteria appear in the culture media or
the beef broth becomes cloudy. If now we wish to study one given form, it
becomes necessary to isolate them from the others. This is done by the
following process: a platinum needle is first passed through a flame to
_sterilize_ it; that is, to kill all living things that may be on the
needle point. Then the needle, which cools very quickly, is dipped in a
colony containing the bacteria we wish to study. This mass of bacteria is
quickly transferred to another sterilized plate, and this plate is
immediately covered to prevent any other forms of bacteria from entering.
When we have succeeded in isolating a certain kind of bacterium in a given
dish, we are said to have a _pure culture_. Having obtained a pure culture
of bacteria, they may easily be studied under the compound microscope.
Footnote 20: For directions for making a culture medium, see
Hunter, _Laboratory Problems in Civic Biology_. Culture
tubes may be obtained, already prepared, from Parke, Davis,
and Company or other good chemists.
[Illustration: A pure culture of bacteria. Notice that the bacteria are all
the same size and shape.]
Size and Form.--In size, bacteria are the most minute plants known. A
bacterium of average size is about 1/10000 of an inch in length, and
perhaps 1/50000 of an inch in diameter. Some species are much larger,
others smaller. A common spherical form is 1/50000 of an inch in diameter.
They are so small that several million are often found in a single drop of
impure water or sour milk. Three well-defined forms of bacteria are
recognized: a spherical form called a _coccus_, a rod-shaped bacterium, the
_bacillus_, and a spiral form, the _spirillum_. Some bacteria are capable
of movement when living in a fluid. Such movement is caused by tiny
lashlike threads of protoplasm called _flagella_. The flagella project from
the body, and by a rapid movement cause locomotion to take place. Bacteria
reproduce with almost incredible rapidity. It is estimated that a single
bacterium, by a process of division called _fission_, will give rise to
over 16,700,000 others in twenty-four hours. Under unfavorable conditions
they stop dividing and form rounded bodies called spores. This spore is
usually protected by a wall and may withstand very unfavorable conditions
of dryness or heat; even boiling for several minutes will not kill some
forms.
[Illustration: A figure to show the relative size and shape of (1) a green
mold, (2) yeast cells, and (3) different forms of bacteria; _B_, bacillus;
_C_, coccus; _S_, spirillum forms. The yeast and bacteria are drawn to
scale, they are much enlarged in proportion to the green mold, being
actually much smaller than the mold spores seen at the top of the picture.]
Where Bacteria are most Numerous.--As the result of our experiments, we can
make some generalizations concerning the presence of bacteria in our own
environment. They are evidently present in the air, and in greater quantity
in air that is moving than quiet air. Why? That they stick to particles of
dust can be proven by placing a little dust from the schoolroom in a
culture dish. Bacteria are present in greater numbers where crowds of
people live and move, the air from dusty streets of a populous city
contains many more bacteria than does the air of a village street. The air
of a city park contains relatively few bacteria as compared with the
near-by street. The air of the woods or high mountains fewer still. Why?
Our previous experiment has shown that dirt on our hands, the mouth and
teeth, decayed meat and vegetables, dirty money, the very hairs of our head
are all carriers of bacteria.
Fluids the Favorite Home of Bacteria.--Tap water, standing water, milk,
vinegar, wine, cider all can be proven to contain bacteria by experiments
similar to those quoted above. Spring or artesian well water would have
very few, if any, bacteria, while the same quantity of river water, if it
held any sewage, might contain untold millions of these little organisms.
Foods preferred by Bacteria.--If bacteria are living and contain no
chlorophyll, we should expect them to obtain protein food in order to grow.
Such is not always the case, for some bacteria seem to be able to build up
protein out of simple inorganic nitrogenous substances. If, however, we
take several food substances, some containing much protein and others not
so much, we will find that the bacteria cause decay in the proteins almost
at once, while other food substances are not always attacked by them.
[Illustration: Growth of bacteria in a drop of impure water allowed to run
down a sterilized culture in a dish.]
What Bacteria do to Foods.--When bacteria feed upon a protein they use part
of the materials in the food so that it falls to pieces and eventually
rots. The material left behind after the bacteria have finished their meal
is quite different from its original form. It is broken down by the action
of the bacteria into gases, fluids, and some solids. It has a
characteristic "rotten" odor and it has in it poisons which come as a
result of the work of the bacteria. These poisonous wastes, called
_ptomaines_, we shall learn more about later.
Conditions Favorable and Unfavorable to the Growth of Bacteria.--Moisture
and Dryness.--_Experiment_.--Take two beans, remove the skins, crush one,
soak the second bean overnight and then crush it. Place in test tubes, one
dry, the second with water. Leave in a warm place two or three days, then
smell each tube. In which is decay taking place? In which tube are bacteria
at work? How do you know?
Moisture.--Moisture is an absolute need for bacterial growth, consequently
keeping material dry will prevent the growth of germs upon its surface.
Foods, in order to decay, must contain enough water to make them moist.
Bacteria grow most freely in fluids.
Light.--If we cover one half of a petri dish in which bacteria are growing
with black paper and then place the dish in a light warm place for a few
days, the growth of bacteria in the light part of the dish will be found to
be checked, while growth continues in the covered part. It is a matter of
common knowledge that disease germs thrive where dirt and darkness exist
and are killed by any long exposure to sunlight. This shows us the need of
light in our homes, especially in our bedrooms.
Air.--We have seen that plants need oxygen in order to perform the work
that they do. This is equally true of all animals. But not all bacteria
need _air_ to live; in fact, some are killed by the presence of air. Just
how these organisms get the oxygen necessary to oxidize their food is not
well understood. The fact that some bacteria grow without air makes it
necessary for us to use the one sure weapon we have for their
extermination, and that is heat.
Heat.--_Experiment._--Take four cultures containing bouillon, inoculate
each tube with bacteria and plug each tube with absorbent cotton. Place one
tube in the ice box, a second tube in a dark closet at a moderate
temperature, a third in a warm place (about 100° Fahrenheit), and boil the
contents of the fourth tube for ten minutes, then place it with tube number
two. In which tubes does growth take place most rapidly? Why?
Bacteria grow very slowly if at all in the temperature of an ice box, very
rapidly at the room temperature of from 70° to 90° and much less rapidly at
a higher temperature. All bacteria except those which have formed spores
can be instantly killed as soon as boiling point is reached, and most
spores are killed by a few minutes boiling.
Sterilization.--The practical lessons drawn from _sterilization_ are many.
We know enough now to boil our drinking water if we are uncertain of its
purity; we sterilize any foods that we believe might harbor bacteria, and
thus keep them from spoiling. The industry of canning is built upon the
principle of sterilization.
Canning.--Canning is simply a method by which first the bacteria in a
substance are killed by heating and then the substance is put into vessels
into which no more bacteria may gain entrance. This is usually done at home
by boiling the fruit or vegetable to be canned either in salt and water or
with sugar and water, either of which substances aids in preventing the
growth of bacteria. The time of boiling will be long or short, depending
upon the materials to be canned. Some vegetables, as peas, beans, and corn,
are very difficult to can, probably because of spores of bacteria which may
be attached to them. Fruits, on the other hand, are usually much easier to
preserve. After boiling for the proper time, the food, now free from all
bacteria, must be put into jars or cans that are themselves absolutely
_sterile_ or free from germs. This is done by first boiling the jars, then
pouring the boiling hot material into the hot jars and sealing them so as
to prevent the entrance of bacteria later.
Uses of Canning.--Canning as an industry is of immense importance to
mankind. Not only does it provide him with fruits and vegetables at times
when he could not otherwise get them, but it also cheapens the cost of such
things. It prevents the waste of nature's products at a time when she is
most lavish with them, enabling man to store them and utilize them later.
Canning has completely changed the life of the sailor and the soldier, who
in former times used to suffer from various diseases caused by lack of a
proper balance of food.
[Illustration: Pasteurizing milk. Why should this be done?]
Pasteurization.--Milk is one of the most important food supplies of a great
city. It is also one of the most difficult supplies to get in good
condition. This is in part due to the fact that milk is produced at long
distances from the city and must be brought first from farms to the
railroads, then shipped by train, again taken to the milk supply depot by
wagon, there bottled, and again shipped by delivery wagons to the
consumers. When we remember that much of the milk used in New York City is
forty-eight hours old and when we realize that bacteria grow _very_ rapidly
in milk, we see the need of finding some way to protect the supply so as to
make it safe, particularly for babies and young children.
This is done by _pasteurization_, a method named after the French
bacteriologist Louis Pasteur. To pasteurize milk we heat it to a
temperature of not over 170° Fahrenheit for from ten minutes to half an
hour. By such a process all harmful germs will be killed and the keeping
qualities of the milk greatly lengthened. Most large milk companies
pasteurize their city supply by a rapid pasteurization at a much higher
temperature, but this method slightly changes the flavor of the milk.
Cold Storage.--Man has also come to use cold to keep bacteria from growing
in foods. The ice box at home and cold storage on a larger scale enables
one to keep foods for a more or less lengthy period. If food is frozen, as
in cold storage, it might keep without growth of bacteria for years. But
fruits and vegetables cannot be frozen without spoiling their flavor. And
all foods after freezing seem particularly susceptible to the bacteria of
decay. For that reason products taken from cold storage must be used at
once.
Ptomaines.--Many foods get their flavor from the growth of molds or
bacteria in them. Cheese, butter, the gamey taste of certain meats, the
flavor of sauerkraut, are all due to the work of bacteria. But if bacteria
are allowed to grow so as to become very numerous, the ptomaines which
result from their growth in foods may poison the person eating such foods.
Frequently ptomaine poisoning occurs in the summer time because of the
rapid growth of bacteria. Much of the indigestion and diarrhoea which
attack people during the summer is doubtless due to this kind of poisoning.
Preservatives.[21]--This leads us to ask if we may not preserve food in
ways other than those mentioned so as to protect ourselves from danger of
ptomaine poisoning. Many substances check the development of bacteria and
in this way they _preserve_ the food. Preservatives are of two kinds, those
harmless to man and those that are poisonous. Of the former, salt and sugar
are examples; of the latter, formaldehyde and possibly benzoic acid.
Footnote 21: Perform experiment here to determine the value
of different preservatives. Use sugar, salt, vinegar,
boracic acid, benzoic acid, formaldehyde, and alcohol.
Sugar.--We have noted the use of sugar in canning. Small amounts of sugar
will be readily attacked by yeasts, molds, and bacteria, but a 40 to 50 per
cent solution will effectually keep out bacteria. Preserves are fruits
boiled in about their own weight of sugar. Condensed milk is preserved by
the sugar added to it; so are candied and, in part, dried fruits.
Salt.--Salt has been used for centuries to keep foods. Meats are smoked,
dried, and salted; some are put down in strong salt solutions. Fish,
especially cod and herring, are dried and salted. The keeping of butter is
also due to the salt mixed with it. Vinegar is another preservative. It,
like salt, changes the flavor of materials kept in it and so cannot come
into wide use. Spices are also used as preservatives.
Harmful Preservatives.--Certain chemicals and drugs, used as preservatives,
seem to be on the border line of harmfulness. Such are benzoic acid, borax,
or boracic acid. Such drugs _may_ be harmless in small quantities, but
unfortunately in canned goods we do not always know the amount used. The
national government in 1906 passed what is known as the Pure Food Law,
which makes it illegal to use any of these preservatives (excepting benzoic
acid in very small amounts). Food which contains this preservative will be
so labeled and should not be given to children or people with weak
digestion. Unfortunately people do not always read the labels and thus the
pure food law is ineffective in its working. Infrequently formaldehyde or
other preservatives are used in milk. Such treatment renders milk unfit for
ordinary use and is an illegal process.
Disinfectants.[22]--Frequently it becomes necessary to destroy bacteria
which cause diseases of various kinds. This process is called
_disinfecting_. The substances commonly used are carbolic acid, formalin or
formaldehyde, lysol, and bichloride of mercury. Of these, the last named is
the most powerful as well as the most dangerous to use. As it attacks
metal, it should not be used in a metal pail or dish. It is commonly put up
in tablets which are mixed to form a 1 to 1000 solution. Such tablets
should be carefully safeguarded because of possible accidental poisoning.
Footnote 22: Experiment to determine the most effective
disinfectants. Use tubes of bouillon containing different
strength solutions of formaldehyde, lysol, iodine, carbolic
acid, and bichloride of mercury. Results. Conclusions.
Formaldehyde used in liquid form is an excellent disinfectant. When burned
in a formalin candle, it sets free an intensely pungent gas which is often
used for disinfecting sick rooms after the patient has been removed.
Carbolic acid is perhaps the best disinfectant of all. If used in a
solution of about 1 part to 25 of water, it will not burn the skin. It is
of particular value to disinfect skin wounds, as it heals as well as
cleanses when used in a weak solution. Its rather pleasant odor makes it
useful to cover up unpleasant smells of the sick room.
The fumes of burning sulphur, which are so often used for disinfecting, are
of little real value.
[Illustration: This shows how organic matter is broken down by bacteria so
it may be used again by green plants.]
Bacteria cause Decay.--Let us next see in what ways the bacteria directly
influence man upon the earth. Have you ever stopped to consider what life
would be like on the earth if things did not decay? The sea would soon be
filled and the land covered with dead bodies of plants and animals.
Conditions of life would become impossible and living things on the earth
would cease to exist.
Fortunately, bacteria cause decay. All organic matter, in whatever form, is
sooner or later decomposed by the action of untold millions of bacteria
which live in the air, water, and soil. These soil bacteria are most
numerous in rich damp soils containing large amounts of organic material.
They are very numerous around and in the dead bodies of plants and animals.
To a considerable degree, then, these bacteria are useful in feeding upon
these dead bodies, which otherwise would soon cover the surface of the
earth to the exclusion of everything else. Bacteria may thus be scavengers.
They oxidize organic materials, changing them to compounds that can be
absorbed by plants and used in building protoplasm. Without bacteria and
fungi it would be impossible for life to exist on the earth, for green
plants would be unable to get the raw food materials in forms that could be
used in making food and living matter. In this respect bacteria are of the
greatest service to mankind.
[Illustration: Microscopic appearance of ordinary milk, showing fat
globules and bacteria which cause the souring of milk.]
Relation to Fermentation.--They may incidentally, as a result of this
process of decay, continue the process of fermentation begun by the yeasts.
In making vinegar the yeasts first make alcohol (see page 135) which the
bacteria change to acetic acid. The lactic acid bacteria, which sour milk,
changing the milk sugar to an acid, grow very rapidly in a warm
temperature; hence milk which is cooled immediately and kept cool or which
is pasteurized and kept in a cool place will not sour readily. Why? These
same lactic acid bacteria may be useful when they sour the milk for the
cheese maker.
Other Useful Bacteria.--Certain bacteria give flavor to cheese and butter,
while still other bacteria aid in the "curing" of tobacco, in the
production of the dye indigo, in the preparation of certain fibers of
plants for the market, as hemp, flax, etc., in the rotting of animal matter
from the skeletons of sponges, and in the process of tanning hides to make
leather.
[Illustration: A field of alfalfa, a plant which harbors the
nitrogen-fixing bacteria.]
Nitrogen-fixing Bacteria.--Still other bacteria, as we have seen before,
"change over" nitrogen in organic material in the soil and even the free
nitrogen of the air so that it can be used by plants in the form of a
compound of nitrogen. The bacteria living in tubercles on the roots of
clover, beans, peas, etc., have the power of thus "fixing" the free
nitrogen in the air found between particles of soil. This fact is made use
of by farmers who rotate their crops, growing first a crop of clover or
other plants having root tubercles, which produce the bacteria, then
plowing these in and planting another crop, as wheat or corn, on the same
area. The latter plants, making use of the nitrogen compounds there,
produce a larger crop than when grown in ground containing less nitrogenous
material.
Bacteria cause Disease.--The most harmful bacteria are those which cause
diseases of plants and animals. Certain diseases of plants--blights, rots,
and wilts--are of bacterial nature. These do much annual damage to fruits
and other parts of growing plants useful to man as food. But by far the
most important are the bacteria which cause disease in man. They accomplish
this by becoming parasites in the human body. Millions upon millions of
bacteria exist in the human body at all times--in the mouth, on the teeth,
in the blood, and especially in the lower part of the food tube. Some in
the food tube are believed to be useful, some harmless, and some harmful;
others in the mouth cause decay of the teeth, while a few kinds, if present
in the body, may cause disease.
[Illustration: Tubercles on the roots of the soy bean. They contain the
nitrogen-fixing bacteria. (Fletcher's Soils.) Copyright by Doubleday, Page
and Company.]
It is known that bacteria, like other living things, feed and give off
organic waste from _their own_ bodies. This waste, called a _toxin_, is
poison to the host on which the bacteria live, and it is usually the
production of this toxin that causes the symptoms of disease. Some forms,
however, break down tissues and plug up the small blood vessels, thus
causing disease.
Diseases caused by Bacteria.--It is estimated that bacteria cause annually
over 50 per cent of the deaths of the human race. As we will later see, a
very large proportion of these diseases might be prevented if people were
educated sufficiently to take the proper precautions to prevent their
spread. These precautions might save the lives of some 3,000,000 of people
yearly in Europe and America. Tuberculosis, typhoid fever, diphtheria,
pneumonia, blood poisoning, syphilis, and a score of other germ diseases
ought not to exist. A good deal more than half of the present misery of
this world might be prevented and this earth made cleaner and better by the
coöperation of the young people now growing up to be our future home
makers.
[Illustration: A single cell scraped from the roof of the mouth and highly
magnified. The little dots are bacteria, most of which are harmless. Notice
the comparative size of bacteria and cell.]
How we take Germ Diseases.--Germ or contagious diseases either enter the
body by way of the mouth, nose, or other body openings, or through a break
in the skin. They may be carried by means of air, food, or water, but are
usually _transmitted directly_ from the person who has the disease to a
well person. This may be done through personal contact or by handling
articles used by the sick person or by drinking or eating foods which have
received some of the germs. From this it follows that if we know the
methods by which a given disease is communicated, we may protect ourselves
from it and aid the civic authorities in preventing its spread.
[Illustration: Deaths from tuberculosis compared with other contagious
diseases in the city of New York in 1908.]
Tuberculosis.--The one disease responsible for the greatest number of
deaths--perhaps one seventh of the total on the globe--is tuberculosis. It
is estimated that of all people alive in the United States to-day,
5,000,000 will die of this disease. But this disease is slowly but surely
being overcome. It is believed that within perhaps one hundred years, with
the aid of good laws and sanitary living, it will be almost extinct.
[Illustration: This curve shows a decreasing death rate from tuberculosis.
Explain.]
Tuberculosis is caused by the growth of bacteria, called the _tubercle
bacilli_, within the lungs or other tissues of the human body. Here they
form little tubers full of germs, which close up the delicate air passages
in the lungs, while in other tissues they give rise to hip-joint disease,
scrofula, lupus, and other diseases, depending on the part of the body they
attack. Tuberculosis may be contracted by taking the bacteria into the
throat or lungs or possibly by eating meat or drinking milk from tubercular
cattle. Especially is it communicated from a consumptive to a well person
by kissing, by drinking or eating from the same cup or plate, using the
same towels, or in coming in direct contact with the person having the
germs in his body. Although there are always some of the germs in the air
of an ordinary city street, and though we may take some of these germs into
our bodies at any time, yet the bacteria seem able to gain a foothold only
under certain conditions. It is only when the tissues are in a worn-out
condition, when we are "run down," as we say, that the parasite may obtain
a foothold in the lungs. Even if the disease gets a foothold, it is quite
possible to cure it if it is taken in time. The germ of tuberculosis is
killed by exposure to bright sunlight and fresh air. Thus the course of the
disease may be arrested, and a permanent cure brought about, by a life in
the open air, the patient sleeping out of doors, taking plenty of
nourishing food and very little exercise. See also Chapter XXIV.
[Illustration: This figure shows how sewage from a cesspool (_c_) might get
into the water supply: _lm_, layer of rock; _w_, wash water.]
Typhoid Fever.--One of the most common germ diseases in this country and
Europe is typhoid fever. This is a disease which is conveyed by means of
water and food, especially milk, oysters, and uncooked vegetables. Typhoid
fever germs live in the intestine and from there get into the blood and are
carried to all parts of the body. A poison which they give off causes the
fever so characteristic of the disease. The germs multiply very rapidly in
the intestine and are passed off from the body with the excreta from the
food tube. If these germs get into the water supply of a town, an epidemic
of typhoid will result. Among the recent epidemics caused by the use of
water containing typhoid germs have been those in Butler, Pa., where 1364
persons were made ill; Ithaca, N. Y., with 1350 cases; and Watertown, N.
Y., where over 5000 cases occurred. Another source of infection is milk.
Frequently epidemics have occurred which were confined to users of milk
from a certain dairy. Upon investigation it was found that a case of
typhoid had occurred on the farm where the milk came from, that the germs
had washed into the well, and that this water was used to wash the milk
cans. Once in the milk, the bacteria multiplied rapidly, so that the
milkman gave out cultures of typhoid in his milk bottles. Proper
safeguarding of our water and milk supply is necessary if we are to keep
typhoid away.
Blood Poisoning.--The bacterium causing blood poisoning is another
toxin-forming germ. It lives in dust and dirt and is often found on the
skin. It enters the body through cuts or bruises. It seems to thrive best
in less oxygen than is found in the air. It is therefore important not to
close up with court-plaster wounds which such germs may have entered. It,
with typhoid, is responsible for four times as many deaths as bullets and
shells in time of battle. The wonderfully small death rate of the Japanese
army in their war with Russia was due to the fact that the Japanese
soldiers always boiled their drinking water before using it, and their
surgeons always dressed all wounds on the battlefield, using powerful
antiseptics in order to kill any bacteria that might have lodged in the
exposed wounds.
[Illustration: This figure shows how a milk route might be instrumental in
spreading diphtheria. _X_ is a farm on which a case of diphtheria occurred
that was responsible for all the cases along milk routes _A_ and _F_ in
Hyde Park, Dorchester, and Milton. How would you explain this?]
Other Diseases.--Many other diseases have been traced to bacteria.
Diphtheria is one of the best known. As it is a throat disease, it may
easily be conveyed from one person to another by kissing, putting into the
mouth objects which have come in contact with the mouth of the patient, or
by food into which the germs have been carried. Another disease which
probably causes more misery in the world than any other germ disease is
syphilis. Hundreds of thousands of new-born babies die annually or grow up
handicapped by deformities from this dread scourge. Syphilis and gonorrhea,
both diseases of the same sort and contracted in the same manner, hand down
to innocent wives and still more innocent children a heritage of disease
"even unto the third and fourth generation." Grippe, pneumonia, whooping
cough, and colds are believed to be caused by bacteria. Other diseases, as
malaria, yellow fever, sleeping sickness, and probably smallpox, scarlet
fever, and measles, are due to the attack of one-celled animal parasites.
Of these we shall learn later in Chapter XV.
Immunity.--It has been found that after an attack of a germ disease the
body will not soon be again attacked by the same disease. This immunity, of
which we will learn more later, seems to be due to a manufacture in the
blood of substances which fight the bacteria or their poisons. If a person
keeps his body in good physical condition and lives carefully, he will do
much toward acquiring this natural immunity.
Acquired Immunity.--Modern medicine has discovered means of protecting the
body from some contagious diseases. Vaccination as protection against
smallpox, the use of antitoxins (of which more later) against diphtheria,
and inoculation against typhoid are all ways in which we may be protected
against diseases.
Methods of fighting Germ Diseases.--As we have seen, diseases produced by
bacteria may be caused by the bacteria being _directly_ transferred from
one person to another, or the disease may obtain a foothold in the body
from food, water, or by taking them into the blood through a cut or a wound
or a body opening.
It is evident that as individuals we may each do something to prevent the
spread of germ diseases, especially in our homes. We may keep our bodies,
especially our hands and faces, clean. Sweeping and dusting may be done
with damp cloths so as not to raise a dust; our milk and water, when from a
suspicious supply, may be _sterilized_ or pasteurized. Wounds through which
bacteria might obtain foothold in the body should be washed with some
_antiseptic_ such as carbolic acid (1 part to 25 water), which kills the
germs. In a later chapter we shall learn more of how we may coöperate with
the authorities to combat disease and make our city or town a better place
in which to live.[23]
Footnote 23: Teachers may take up parts or all of Chapter
XXIV at this point. I have found it advisable to repeat much
of the work on bacteria _after_ the students have taken up
the study of the human organism.
REFERENCE BOOKS
ELEMENTARY
Hunter, _Laboratory Problems in Civic Biology_. American
Book Company.
Bigelow, _Introduction to Biology_. The Macmillan Company.
Conn, _Bacteria, Yeasts, and Molds in the Home_. Ginn and
Company.
Conn, _Story of Germ Life_. D. Appleton and Company.
Davison, _The Human Body and Health_. American Book Company.
Frankland, _Bacteria in Daily Life_. Longmans, Green, and
Company.
Overton, _General Hygiene_. American Book Company.
Prudden, _Dust and its Dangers_. G. P. Putnam's Sons.
Prudden, _The Story of the Bacteria_. G. P. Putnam's Sons.
Ritchie, _Primer of Sanitation_. World Book Company.
Sharpe, _Laboratory Manual in Biology_, pages 123-132.
American Book Company.
ADVANCED
Conn, _Agricultural Bacteriology_. P. Blakiston's Sons and
Company.
Coulter, Barnes, and Cowles, _A Textbook of Botany_, Vol. I.
American Book Company.
De Bary, _Comparative Morphology and Biology of the Fungi,
Mycetozoa, and Bacteria_. Clarendon Press.
Duggar, _Fungous Diseases of Plants_. Ginn and Company.
Hough and Sedgwick, _The Human Mechanism_. Ginn and Company.
Hutchinson, _Preventable Diseases_. Houghton, Mifflin and
Company.
Lee, _Scientific Features of Modern Medicine_. Columbia
University Press.
Muir and Ritchie, _Manual of Bacteriology_. The Macmillan
Company.
Newman, _The Bacteria_. G. P. Putnam's Sons.
Sedgwick, _Principles of Sanitary Science and Public
Health_. The Macmillan Company.
XII. THE RELATIONS OF PLANTS TO ANIMALS
_Problems.--To determine the general biological relations existing between
plants and animals._
_(a) As shown in a balanced aquarium._
_(b) As shown in hay infusion._
SUGGESTIONS FOR LABORATORY WORK
_Demonstration of life in a "balanced" and "unbalanced"
aquarium._--Determination of factors causing balance.
_Demonstration of hay infusion._--Examination to show forms of animal
and plant life.
Tabular comparison between balanced aquarium and hay infusion.
Some Ways in which Plants affect Animals.--We have been studying the life
of plants in order better to understand the life of animals and men. We
have seen first that green plants play indirectly a tremendous part in
man's welfare by supplying him with food. We have found that the colorless
plants directly affected his welfare by causing disease, and by causing
decay, thus making usable the nitrogen locked up in dead bodies of plants
and animals, and by some even supplying nitrogen from the atmosphere. The
dependence of animals upon plants has been shown and the interdependence of
plants on animals has also been seen in cross-pollination and in the supply
of raw food materials to plants by animals.
Study of a Balanced Aquarium.--Perhaps the best way for us to understand
the interrelation between plants and animals is to study an aquarium in
which plants and animals live and in which a balance has been established
between the plant life on one side and animal life on the other. Aquaria
containing green pond weeds, either floating or rooted, a few snails, some
tiny animals known as water fleas, and a fish or two will, if kept near a
light window, show this relation.
[Illustration: A balanced aquarium. Explain the term "balanced."]
We have seen that green plants under favorable conditions of sunlight,
heat, moisture, and with a supply of raw food materials, give off oxygen as
a by-product while manufacturing food in their green cells. We know the
necessary raw materials for starch manufacture are carbon dioxide and
water, while nitrogenous material is necessary for the making of proteins
within the plant. In previous experiments we have proved that carbon
dioxide is given off by any living thing when oxidation occurs in the body.
The crawling snails and the swimming fish give off carbon dioxide, which is
dissolved in the water; the plants themselves, at all times, oxidize food
within their bodies, and so must _pass off_ some carbon dioxide. The green
plants in the daytime _use up_ the carbon dioxide obtained from the various
sources and, with the water taken in, manufacture starch. While this
process is going on, oxygen is given off to the water of the aquarium, and
this free oxygen is used by the animals there.
[Illustration: This diagram shows that plants and animals on the earth hold
the same relation to each other as plants and animals in a balanced
aquarium. Explain the diagram in your notebook.]
[Illustration: The carbon and oxygen cycle in the balanced aquarium. Trace
by means of the arrows the carbon from the time plants take it in as CO{2}
until animals give it off. Show what happens to the oxygen.]
But the plants are continually growing larger. The snails and fish, too,
eat parts of the plants. Thus the plant life gives food to the animals
within the aquarium. The animals give off certain nitrogenous wastes of
which we shall learn more later. These materials, with other nitrogenous
matter from the dead parts of the plants or animals, form part of the raw
material used for protein manufacture in the plant. This nitrogenous matter
is prepared for use by several different kinds of bacteria which first
break the dead bodies down and then give it to the plants in the form of
soluble nitrates. The green plants manufacture food, the animals eat the
plants and give off organic waste, from which the plants in turn make their
food and living matter. The plants give off oxygen to the animals, and the
animals give carbon dioxide to the plants. Thus a balance exists between
the plants and animals in the aquarium. Make a table to show this balance.
[Illustration: The relations between green plants and animals.]
Relations between Green Plants and Animals.--What goes on in the aquarium
is an example of the relation existing between all green plants and all
animals. Everywhere in the world green plants are making food which
becomes, sooner or later, the food of animals. Man does not feed to a great
extent upon leaves, but he eats roots, stems, fruits, and seeds. When he
does not feed directly upon plants, he eats the flesh of plant eating
animals, which in turn feed directly upon plants. And so it is the world
over; the plants are the food makers and supply the animals. Green plants
also give a very considerable amount of oxygen to the atmosphere every day,
which the animals may use.
[Illustration: The nitrogen cycle. Trace the nitrogen from its source in
the air until it gets back again into the air.]
The Nitrogen Cycle.--The animals in their turn supply much of the carbon
dioxide that the plant uses in starch making. They also supply some of the
nitrogenous matter used by the plants, part being given the plants from the
dead bodies of their own relatives and part being prepared from the
nitrogen of the air through the agency of bacteria, which live upon the
roots of certain plants. These bacteria are the only organisms that can
take nitrogen from the air. Thus, in spite of all the nitrogen of the
atmosphere, plants and animals are limited in the amount available. And the
available supply is used over and over again, perhaps in nitrogenous food
by an animal, then it may be given off as organic waste, get into the soil,
and be taken up by a plant through the roots. Eventually the nitrogen forms
part of the food supply in the body of the plant, and then may become part
of its living matter. When the plant dies, the nitrogen is returned to the
soil. Thus the usable nitrogen is kept in circulation.[24]
Footnote 24: A small amount of nitrogen gas is returned to
the atmosphere by the action of the decomposing bacteria on
the ammonia compounds in the soil. (See figure of nitrogen
cycle.)
Symbiosis.--We have seen that in the balanced aquarium the animals and
plants, in a wide sense, form a sort of unconscious partnership. _This
process of living together for mutual advantage is called symbiosis._ Some
animals thus combine with plants; for example, the tiny animal known as the
hydra with certain of the one-celled algæ, and, if we accept the term in a
wide sense, all green plants and animals live in this relation of mutual
give and take. Animals also frequently live in this relation to each other,
as the crab, which lives within the shell of the oyster; the sea anemones,
which are carried around on the backs of some hermit crabs, aiding the crab
in protecting it from its enemies, and being carried about by the crab to
places where food is plentiful.
[Illustration: Life in the late stage of a hay infusion. _B_, bacteria,
swimming or forming masses of food upon which the one-celled animals, the
paramoecia, are feeding; _G_, gullet; _F.V._, food vacuole; _C.V._,
contractile vacuole; _P_, pleurococcus; _P.D._, pleurococcus dividing.
(Drawn from nature by J. W. Teitz.)]
A Hay Infusion.--Still another example of the close relation between plants
and animals may be seen in the study of a hay infusion. If we place a wisp
of hay or straw in a small glass jar nearly full of water, and leave it for
a few days in a warm room, certain changes are seen to take place in the
contents of the jar; after a little while the water gets cloudy and darker
in color, and a scum appears on the surface. If some of this scum is
examined under the compound microscope, it will be found to consist almost
entirely of bacteria. These bacteria evidently aid in the decay which (as
the unpleasant odor from the jar testifies) is beginning to take place. As
we have learned, bacteria flourish wherever the food supply is abundant.
The water within the jar has come to contain much of the food material
which was once within the leaves of the grass,--organic nutrients, starch,
sugar, and proteins, formed in the leaf by the action of the sun on the
chlorophyll of the leaf, and now released into the water by the breaking
down of the walls of the cells of the leaves. The bacteria themselves
release this food from the hay by causing it to decay. After a few days
small one-celled animals appear; these multiply with wonderful rapidity, so
that in some cases the surface of the water seems to be almost white with
active one-celled forms of life. If we ask ourselves where these animals
come from, we are forced to the conclusion that they must have been in the
water, in the air, or on the hay. Hay is dried grass and may have been cut
in a field near a pool containing these creatures. When the pool dried up,
the wind may have scattered some of these little organisms in the dried mud
or dust. Some may have existed in a dormant state on the hay and the water
awakened them to active life. In the water, too, there may have been some
living cells, plants and animals.
At first the multiplication of the tiny animals within the hay infusion is
extremely rapid; there is food in abundance and near at hand. After a few
days more, however, several kinds of one-celled animals may appear, some of
which prey upon others. Consequently a struggle for life takes place, which
becomes more and more intense as the food from the hay is used up.
Eventually the end comes for all the animals unless some green plants
obtain a foothold within the jar. If such a thing happens, food will be
manufactured within their bodies, a new food supply arises for the animals
within the jar, and a balance of life may result.
REFERENCE BOOKS
ELEMENTARY
Hunter, _Laboratory Problems in Civic Biology_. American
Book Company.
Sharpe, _A Laboratory Manual for the Solution of Problems in
Biology_, pp. 133-138. American Book Company.
ADVANCED
Eggerlin and Ehrenberg, _The Fresh Water Aquarium and its
Inhabitants_. Henry Holt and Company.
Furneaux, _Life in Ponds and Streams_. Longmans, Green, and
Company.
Parker, _Biology_. The Macmillan Company.
Sedgwick and Wilson, _Biology_. Henry Holt and Company.
XIII. SINGLE-CELLED ANIMALS CONSIDERED AS ORGANISMS
_Problems.--To determine:_
_(a) How a one-celled animal is influenced by its environment._
_(b) How a single cell performs its functions._
_(c) The structure of a single-celled animal._
LABORATORY SUGGESTIONS
_Laboratory study._--Study of paramoecium under compound
microscope in its relation to food, oxygen, etc.
Determination of method of movement, turning, avoiding
obstructions, sensitiveness to stimuli. Drawings to
illustrate above points.
_Laboratory demonstration._--Living paramoecium to show
structure of cell. Demonstration with carmine to show food
vacuoles, and action of cilia. Use of charts and stained
specimens to show other points of cell structure. Laboratory
demonstration of fission.
[Illustration: Pleurococcus. A very simple plant cell.]
The Simplest Plants.--We have seen that perhaps the simplest plant would be
exemplified by one of the tiny bacteria we have just read about. A typical
one-celled plant, however, would contain green coloring matter or
chlorophyll, and would have the power to manufacture its own food under
conditions giving it a moderate temperature, a supply of water, oxygen,
carbon dioxide, and sunlight. Such a simple plant is the _pleurococcus_,
the "green slime" seen on the shady sides of trees, stones, or city houses.
This plant would meet one definition of a cell, as it is a minute mass of
protoplasm containing a nucleus. It is surrounded by a wall of a woody
material formed by the activity of the living matter within the cell. It
also contains a little mass of protoplasm colored green. Of the work of the
chlorophyll in the manufacture of organic food we have already learned.
Such is a simple plant cell. Let us now examine a simple animal cell in
order to compare it with that of a plant.
Where to find Paramoecium.--If we examine very carefully the surface of a
hay infusion, we are likely to notice in addition to the scum formed of
bacteria, a mass of whitish tiny dots collected along the edge of the jar
close to the surface of the water. More attentive observation shows us that
these objects move, and that they are never found far from the surface.
The Life Habits of Paramoecium.--If we place on a slide a drop of water
containing some of these moving objects and examine it under the compound
microscope, we find each minute whitish dot is a cell, elongated, oval, or
elliptical in outline and somewhat flattened. This is a one-celled animal
known as the _paramoecium_ or the slipper animalcule (because of its
shape).
Seen under the low power of the microscope, it appears to be extremely
active, rushing about now rapidly, now more slowly, but seemingly always
taking a definite course. The narrower end of the body (the _anterior_)
usually goes first. If it pushes its way past any dense substance in the
water, the cell body is seen to change its shape temporarily as it squeezes
through.
Response to Stimuli.--Many of these little creatures may be found collected
around masses of food, showing that they are attracted by it. In another
part of the slide we may find a number of the paramoecia lying close to the
edge of an air bubble with the greatest possible amount of their surface
exposed to its surface. These animals are evidently taking in oxygen by
osmosis. They are breathing. A careful inspection of the jar containing
paramoecia shows thousands of tiny whitish bodies collected near the
surface of the jar. In the paramoecium, as in the one-celled plants, the
protoplasm composing the cell responds to certain agencies acting upon it,
coming from without; these agencies we call _stimuli_. Such stimuli may be
light, differences of temperature, presence of food, electricity, or other
factors of its surroundings. Plant and animal cells may react differently
to the same stimulus. In general, however, we know that protoplasm is
_irritable_ to some of these factors. To severe stimuli, protoplasm usually
responds by _contracting_, another power which it possesses. We know, too,
that plant and animal cells take in food and change the food to protoplasm,
that is, that they _assimilate_ food; and that they may waste away and
repair themselves. Finally, we know that new plant and animal cells are
_reproduced_ from the original bit of protoplasm, a single cell.
[Illustration: A paramoecium. _c.v._, contractile vacuole; _f.v._, food
vacuole; _m_, mouth; _ma.n._, macronucleus; _mi.n._, micronucleus; _w.v._,
water vacuole.]
The Structure of Paramoecium.--The cell body is almost transparent, and
consists of semifluid protoplasm which has a granular grayish appearance
under the microscope. This protoplasm appears to be bounded by a very
delicate membrane through which project numerous delicate threads of
protoplasm called _cilia_. (These are usually invisible under the
microscope).
The locomotion of the paramoecium is caused by the movement of these cilia,
which lash the water like a multitude of tiny oars. The cilia also send
particles of food into a funnel-like opening, the _gullet_, on one side of
the cell. Once inside the cell body, the particles of food materials are
gathered into little balls within the almost transparent protoplasm. These
masses of food seem to be inclosed within a little area containing fluid,
called a _vacuole_. Other vacuoles appear to be clear; these are spaces in
which food has been digested. One or two larger vacuoles may be found;
these are the _contractile vacuoles_; their purpose seems to be to pass off
waste material from the cell body. This is done by pulsation of the
vacuole, which ultimately bursts, passing fluid waste to the outside. Solid
wastes are passed out of the cell in somewhat the same manner. No breathing
organs are seen, because osmosis of oxygen and carbon dioxide may take
place anywhere through the cell membrane. The nucleus of the cell is not
easily visible in living specimens. In a cell that has been stained it has
been found to be a double structure, consisting of one large and one small
portion, called, respectively, the _macronucleus_ and the _micronucleus_.
[Illustration: Paramoecium dividing by fission. _M_, mouth; _MAC._,
macronucleus; _MIC._, micronucleus. (After Sedgwick and Wilson.)]
Reproduction of Paramoecium.--Sometimes a paramoecium may be found in the
act of dividing by the process known as _fission_, to form two new cells,
each of which contains half of the original cell. This is a method of
_asexual_ reproduction. The original cell may thus form in succession many
hundreds of cells in every respect like the original parent cell.
[Illustration: Amoeba, with pseudopodia (_P._) extended; _EC_, ectoplasm;
_END_, endoplasm; the dark area (_N._) is the nucleus. (From a photograph
loaned by Professor G. N. Calkins.)]
Amoeba.[25]--In order to understand more fully the life of a simple bit of
protoplasm, let us take up the study of the _amoeba_, a type of the
simplest form of animal life. Unlike the plant and animal cells we have
examined, the amoeba has no fixed form. Viewed under the compound
microscope, it has the appearance of an irregular mass of granular
protoplasm. Its form is constantly changing as it moves about. This is due
to the pushing out of tiny projections of the protoplasm of the cell,
called _pseudopodia_ (false feet). The locomotion is accomplished by a
streaming or flowing of the semifluid protoplasm. The pseudopodia are
pushed forward in the direction which the animal is to go, the rest of the
body following. In the central part of the cell is the nucleus. This
important organ is difficult to see except in cells that have been stained.
Footnote 25: Amoebæ _may_ be obtained from the hay infusion,
from the dead leaves in the bottom of small pools, from the
same source in fresh-water aquaria, from the roots of
duckweed or other small water plants, or from green algæ
growing in quiet localities. No _sure_ method of obtaining
them can be given.
Although but a single cell, still the amoeba appears to be aware of the
existence of food when it is near at hand. Food may be taken into the body
at any point, the semifluid protoplasm simply rolling over and engulfing
the food material. Within the body, as in the paramoecium, the food becomes
inclosed within a fluid space or vacuole. The protoplasm has the power to
take out such material as it can use to form new protoplasm or give energy.
Circulation of food material is accomplished by the constant streaming of
the protoplasm within the cell.
[Illustration: Amoeba, showing the changes which take place during division
of the cell. The dark body in each figure is the nucleus; the transparent
circle, the contractile vacuole; the large granular masses, the food
vacuoles. Much magnified.]
The cell absorbs oxygen from the water by osmosis through its delicate
membrane, giving up carbon dioxide in return. Thus the cell "breathes"
through any part of its body covering.
Waste nitrogenous products formed within the cell when work is done are
passed out by means of the contractile vacuole.
The amoeba, like other one-celled organisms, reproduces by the process of
fission. A single cell divides by splitting into two others, each of which
resembles the parent cell, except that they are of less bulk. When these
become the size of the parent amoeba, they each in turn divide. This is a
kind of asexual reproduction.
When conditions unfavorable for life come, the amoeba, like some one-celled
plants, encysts itself within a membranous wall. In this condition it may
become dried and be blown through the air. Upon return to a favorable
environment, it begins life again, as before. In this respect it resembles
the spore of a plant.
[Illustration: Vorticella. _e_, gullet; _n_, nucleus; _cv_, contractile
vacuole; _a_, axis; _s_, sheath; _fv_, food vacuole. (From Herrick'_s
General Zoölogy_.)]
The Cell as a Unit.--In the daily life of a one-celled animal we find the
single cell performing all the general activities which we shall later find
the many-celled animal is able to perform. In the amoeba no definite parts
of the cell appear to be set off to perform certain functions; but any part
of the cell can take in food, can absorb oxygen, can change the food into
protoplasm, and excrete the waste material. The single cell is, in fact, an
organism able to carry on the business of living almost as effectually as a
very complex animal.
Complex One-celled Animals.--In the paramoecium we find a single cell, but
we find certain parts of the cell having certain definite functions: the
cilia are used for locomotion; a definite part of the cell takes in food,
while the waste passes out at another definite spot. In another one-celled
animal called _vorticella_, part of the cell has become elongated and is
contractile. By this stalk the little animal is fastened to a water plant
or other object. The stalk may be said to act like a muscle fiber, as its
sole function seems to be movement; the cilia are located at one end of the
cell and serve to create a current of water which will bring food particles
to the mouth. Here we have several parts of the cell, each doing a
different kind of work. This is known as _physiological division of labor_.
Habitat of Protozoa.--Protozoa are found almost everywhere in shallow
water, especially close to the surface. They appear to be attracted near to
the surface by the supply of oxygen. Every fresh-water lake swarms with
them; the ocean contains countless myriads of many different forms.
Use as Food.--They are so numerous in lakes, rivers, and the ocean as to
form the food for many animals higher in the scale of life. Almost all fish
that do not take the hook and that travel in schools, or companies,
migrating from one place to another, live partly on such food. Many feed on
slightly larger animals, which in turn eat the Protozoa. Such fish have on
each side of the mouth attached to the gills a series of small structures
looking like tiny rakes. These are called the _gill rakers_, and aid in
collecting tiny organisms from the water as it passes over the gills. The
whale, the largest of all mammals, strains protozoans and other small
animals and plants out of the water by means of hanging plates of whalebone
or baleen, the slender filaments of which form a sieve from the top to the
bottom of the mouth.
Protozoa cause Disease.--Protozoa of certain kinds play an important part
in causing malaria, yellow fever, and other diseases, as we shall see
later.[26] (See page 217.)
Footnote 26: Teachers may find it expedient to take up the
study of protozoan diseases at this point.
REFERENCE BOOKS
ELEMENTARY
Hunter, _Laboratory Problems in Civic Biology_. American
Book Company.
Davison, _Human Body and Health_. American Book Company.
Jordan, Kellogg and Heath, _Animal Studies_. D. Appleton and
Company.
Sharpe, _Laboratory Manual_, pp. 140-143. American Book
Company.
ADVANCED
Calkins, _The Protozoa_. Macmillan Company.
Jennings, _Study of the Lower Organisms_. Carnegie
Institution Report.
Parker, _Lessons in Elementary Biology_. The Macmillan
Company.
Wilson, _The Cell in Development and Inheritance_. The
Macmillan Company.
XIV. DIVISION OF LABOR. THE VARIOUS FORMS OF PLANTS AND ANIMALS
_Problems.--The development and forms of plants._
_The development of a simple animal._
_What is division of labor? In what does it result?_
_How to know the chief characters of some great animal groups._
LABORATORY SUGGESTIONS
_A visit to a botanical garden or laboratory
demonstration._--Some of the forms of plant life. Review of
essential facts in development of bean or corn embryo.
_Demonstration._--Charts or models showing the development
of a many-celled animal from egg through gastrula stage.
_Demonstration._--Types which illustrate increasing
complexity of body form and division of labor.
_Museum trip._--To afford pupil a means of identification of
examples of principal phyla. This should be preceded by
objective demonstration work in school laboratory.
Reproduction in Plants.--Although there are very many plants and animals so
small and so simple as to be composed of but a single cell, by far the
greater part of the animal and plant world is made up of individuals which
are collections of cells living together.
[Illustration: A cell of pond scum. How might it divide to form a long
thread made up of cells?]
In a simple plant like the pond scum, a string or filament of cells is
formed by a single cell dividing crosswise, the two cells formed each
dividing into two more. Eventually a long thread of cells is thus formed.
At times, however, a cell is formed by the union of two cells, one from
each of two adjoining filaments of the plant. At length a hard coat forms
around this cell, which has now become a _spore_. The tough covering
protects it from unfavorable changes in the surroundings. Later, when
conditions become favorable for its germination, the spore may form a new
filament of pond scum. In molds, in yeasts, and in the bacteria we also
found spores could be formed by the protoplasm of the plant cutting up into
a number of tiny spores. These spores are called _asexual_ (without sex)
because they are not formed by the union of two cells, and may give rise to
other tiny plants like themselves. Still other plants, mosses and ferns,
give rise to two kinds of spores, sexual and asexual. All of these
collectively are called _spore plants_.
[Illustration: The formation of spores in pond scum. _zs_, zygospore; _f_,
fusion in progress.]
Reproduction in Seed Plants.--Another great group of plants we have
studied, plants of varied shapes and sizes, produce seeds. They bear
flowers and fruits.
[Illustration: The formation and growth of a plant embryo. 1, the sperm and
egg cell uniting; 2, a fertilized egg; 3, two cells formed by division; 4,
four cells formed from two; 5, a many-celled embryo; 6, young plant; _H_,
hypocotyl; _P_, plumule; _C_, cotyledons.]
The embryo develops from a single fertilized "egg," growing by cell
division into two, four, eight, and a constantly increasing number of cells
until after a time a baby plant is formed, which as in the bean, either
contains some stored food to give it a start in life, or, as in the corn,
is surrounded with food which it can digest and absorb into its own tiny
body. We have seen that these young plants in the seed are able to develop
when conditions are favorable. Furthermore, the young of each kind of plant
will eventually develop into the kind of plant its parent was and into no
other kind. Thus the plant world is divided into many tribes or groups.
Plants are placed in Groups.--If we plant a number of peas so that they
will all germinate under the same conditions of soil, temperature, and
sunlight, the seedlings that develop will each differ one from another in a
slight degree.[27] But in a general way they will have many characters in
common, as the shape of the leaves, the possession of tendrils, form of the
flower and fruit. A _species_ of plants or animals is a group of
individuals so much alike in their characters that they might have had the
same parents. Individuals of such species differ slightly; for no two
individuals are exactly alike.
Footnote 27: NOTE TO TEACHERS.--A trip to the Botanical
Garden or to a Museum should be taken at this time.
[Illustration: A colony of trilliums, a flowering plant. (Photograph by W.
C. Barbour.)]
[Illustration: Rock fern, _polypody_. Notice the underground stem giving
off roots from its lower surface, and leaves (_C_), (_S_), from its upper
surface.]
Species are grouped together in a larger group called a genus. For example,
many kinds of peas--the wild beach peas, the sweet peas, and many
others--are all grouped in one genus (called _Lathyrus_, or vetchling)
because they have certain structural characteristics in common.
Plant and animal genera are brought together in still larger groups, the
classification based on general likenesses in structure. Such groups are
called, as they become successively larger, _Family_, _Order_, and _Class_.
Thus both the plant and animal kingdoms are grouped into divisions, the
smallest of which contains individuals very much alike; and the largest of
which contains very many groups of individuals, the groups having some
characters in common. This is called a system of classification.
Classification of the Plant Kingdom.--The entire plant kingdom has been
divided into four sub-kingdoms by botanists:--
1. _Spermatophytes._ { _Angiosperms_, true flowering plants.
{ _Gymnosperms_, the pines and their allies.
2. _Pteridophytes._ The fern plants and their allies.
3. _Bryophytes._ The moss plants and their allies
4. _Thallophytes._ The Thallophytes form two groups: the Algæ and the
Fungi; the algæ being green, while the fungi have
no chlorophyll.
[Illustration: Rockweed, a brown algæ, showing its distribution on rocks
below highwater mark.]
The extent of the plant kingdom can only be hinted at; each year new
species are added to the lists. There are about 110,000 species of
flowering plants and nearly as many flowerless plants. The latter consist
of over 3500 species of fernlike plants, some 16,500 species of mosses,
over 5600 lichens (plants consisting of a partnership between algæ and
fungi), approximately 55,000 species of fungi, and about 16,000 species of
algæ.
[Illustration: A moss plant. _G_, the moss body; _S_, the spore-bearing
stalk (fruiting body).]
Development of a Simple Animal.--Many-celled animals are formed in much the
same way as are many-celled seed plants. A common bath sponge, an
earthworm, a fish, or a dog,--each and all of them begin life in the same
manner. In a many-celled animal the life history begins with a single cell,
the fertilized egg. As in the flowering plant, this cell has been formed by
the union of two other cells, a tiny (usually motile) cell; the _sperm_,
and a large cell, the _egg_. After the egg is fertilized by a sperm cell,
it splits into two, four, eight, and sixteen cells; as the number of cells
increases, a hollow ball of cells called the _blastula_ is formed; later
this ball sinks in on one side, and a double-walled cup of cells, now
called a _gastrula_, results. Practically all animals pass through the
above stages in their development from the egg, although these stages are
often not plain to see because of the presence of food material (yolk) in
the egg.
In animals the body consists of three layers of cells: those of the
outside, developed from the outer layer of the gastrula, are called
_ectoderm_, which later gives rise to the skin, nervous system, etc.; an
inner layer, developed from the inner layer of the gastrula, the
_endoderm_, which forms the lining of the digestive organs, etc.; a middle
layer, called the _mesoderm_, lying between the ectoderm and the endoderm,
is also found. In higher animals this layer gives rise to muscles, the
skeleton, and parts of other internal structures.
[Illustration: Stages in the development of a fertilized egg into the
gastrula stage. Read your text, then draw these stages and name each
stage.]
Physiological Division of Labor.--If we compare the amoeba and the
paramoecium, we find the latter a more complex organism than the former. An
amoeba may take in food through any part of the body; the paramoecium has a
definite gullet; the amoeba may use any part of the body for locomotion;
the paramoecium has definite parts of the cell, the cilia, fitted for this
work. Since the structure of the paramoecium is more complex, we say that
it is a "higher" animal. In the vorticella, a still more complex cell, part
of the cell has grown out like a stalk, has become contractile, and acts
like muscle.
[Illustration: Photograph of a living _vorticella_, showing the contractile
stalk and the cilia around the mouth. Compare this figure with that of the
paramoecium. Which cell shows greater division of labor?]
As we look higher in the scale of life, we invariably find that certain
parts of a plant or animal are set apart to do certain work, and only that
work. Just as in a community of people, there are some men who do rough
manual work, others who are skilled workmen, some who are shopkeepers, and
still others who are professional men, so among plants and animals,
wherever _collections_ of cells live together to form an organism, there is
division of labor, some cells being fitted to do one kind of work, while
others are fitted to do work of another sort. This is called physiological
division of labor.
[Illustration: Enlarged lengthwise section of the hydra, a very simple
animal which shows slight division of labor. _ba_, base; _b_, bud; _m_,
mouth; _ov_, ovary; _sp_, spermary.]
[Illustration: Different forms of tissue cells. _C_, bone making cells;
_E_, epithelial cells; _F_, fat cells; _L_, liver cells; _M_, muscle cell;
_i_, involuntary; _v_, voluntary; _N_, nerve cell; _C B_, cell body;
_N.F._, nerve fiber; _T.B._, nerve endings; _W_, colorless blood cells.]
As we have seen, the higher plants are made up of a vast number of cells of
many kinds. Collections of cells alike in structure and performing the same
function we have called a _tissue_. Examples of animal tissues are the
highly contractile cells set apart for movement, _muscles_; those which
cover the body or line the inner parts of organs, the skin, or
_epithelium_; the cells which form secretions or _glands_ and the sensitive
cells forming the _nervous_ tissues.
Frequently several tissues have certain functions to perform in conjunction
with one another. The arm of the human body performs movement. To do this,
several tissues, as muscles, nerves, and bones, must act together. A
collection of tissues performing certain work we call an _organ_.
[Illustration: Part of a sponge, showing how cells perform division of
labor. _ect_, ectoderm; _mes_, mesoderm; _end_, endoderm; _c.c._, ciliated
cells, which take in food by means of their flagellæ or large cilia
(_fla_).]
In a simple animal like a sponge, division of labor occurs between the
cells; some cells which line the pores leading inward create a current of
water, and feed upon the minute organisms which come within reach, other
cells build the skeleton of the sponge, and still others become eggs or
sperms. In higher animals more complicated in structure and in which the
tissues are found working together to form organs, division of labor is
much more highly specialized. In the human arm, an organ fitted for certain
movements, think of the number of tissues and the complicated actions which
are possible. The most extreme division of labor is seen in the organism
which has the most complex actions to perform and whose organs are fitted
for such work, for there the cells or tissues which do the particular work
do it quickly and very well.
In our daily life in a town or city we see division of labor between
individuals. Such division of labor may occur among other animals, as, for
example, bees or ants. But it is seen at its highest in a great city or in
a large business or industry. In the stockyards of Chicago, division of
labor has resulted in certain men performing but a single movement during
their entire day's work, but this movement repeated so many times in a day
has resulted in wonderful accuracy and speed. Thus division of labor
obtains its end.
Organs and Functions Common to All Animals.--The same general functions
performed by a single cell are performed by a many-celled animal. But in
the many-celled animals the various functions of the single cell are taken
up by the organs. In a complex organism, like man, the organs and the
functions they perform may be briefly given as follows:--
(1) The organs of _food taking_: food may be taken in by individual cells,
as those lining the pores of the sponge, or definite parts of a food tube
may be set apart for this purpose, as the mouth and parts which place food
in the mouth.
(2) The organs of _digestion_: the food tube and collections of cells which
form the glands connected with it. The enzymes in the fluids secreted by
the latter change the foods from a solid form (usually insoluble) to that
of a _fluid_. Such fluid may then pass by osmosis, through the walls of the
food tube into the blood.
(3) The organs of _circulation_: the tubes through which the blood, bearing
its organic foods and oxygen, reaches the tissues of the body. In simple
animals, as the sponge and hydra, no such organs are needed, the fluid food
passing from cell to cell by osmosis.
(4) The organs of _respiration_: the organs in which the blood receives
oxygen and gives up carbon dioxide. The outer layer of the body serves this
purpose in very simple animals; gills or lungs are developed in more
complex animals.
(5) The organs of _excretion_: such as the kidneys and skin, which pass off
nitrogenous and other waste matters from the body.
(6) The organs of _locomotion_: muscles and their attachments and
connectives; namely, tendons, ligaments, and bones.
(7) The organs of _nervous control_: the central nervous system, which has
control of coördinated movement. This consists of scattered cells in low
forms of life; such cells are collected into groups and connected with each
other in higher animals.
(8) The organs of _sense_: collections of cells having to do with the
reception and transmission of sight, hearing, smell, taste, touch,
pressure, and temperature sensations.
(9) The organs of _reproduction_: the sperm and egg-forming organs.
Almost all animals have the functions mentioned above. In most, the various
organs mentioned are more or less developed, although in the simpler forms
of animal life some of the organs mentioned above are either very poorly
developed or entirely lacking. But in the so-called "higher" animals each
of the above-named functions is assigned to a certain organ or group of
organs. The work is done better and more quickly than in the "lower"
animals. Division of labor is thus a guide in helping us to determine the
place of animals in the groups that exist on the earth.
The Animal Series.--We have found that a one-celled animal can perform
certain functions in a rather crude manner. Man can perform these same
functions in an extremely efficient manner. Division of labor is well
worked out, extreme complexity of structure is seen. Between these two
extremes are a great many groups of animals which can be arranged more or
less as a series, showing the gradual evolution or development of life on
the earth. It will be the purpose of the following pages to show the chief
characteristics of the great groups of the animal kingdom.
[Illustration: The glasslike skeleton of a _radiolarian_, a protozoan.
(From model at American Museum of Natural History.)]
I. Protozoa.--Animals composed of a single cell, reproducing by cell
division.
The following are the principal classes of Protozoa, examples of which we
may have seen or read about:--
CLASS I. _Rhizopoda_ (Greek for _root-footed_). Having no fixed form, with
pseudopodia. Either naked as _Amoeba_ or building limy (_Foraminifera_) or
glasslike skeletons (_Radiolaria_).
CLASS II. _Infusoria (in infusions)._ Usually active ciliated Protozoa.
Examples, _Paramoecium_, _Vorticella_.
CLASS III. _Sporozoa (spore animals)._ Parasitic and usually nonactive.
Example, _Plasmodium malariæ_.
[Illustration: A horny fiber sponge. Notice that it is a
colony. One fourth natural size.]
II. Sponges.--Because the body contains many pores through which water
bearing food particles enters, these animals are called _Porifera_. They
are classed according to the skeleton they possess into limy, glasslike,
and horny fiber sponges. The latter are the sponges of commerce. With but
few exceptions sponges live in salt water and are never free swimming.
[Illustration: Sea anemones. One half natural size. The right hand specimen
is expanded and shows the mouth surrounded by the tentacles. The left hand
specimen is contracted. (From model at the American Museum of Natural
History.)]
III. Coelenterates.--The hydra and its salt-water allies, the jellyfish,
hydroids, and corals, belong to a group of animals known as the
_Coelenterata_. The word "coelenterate" (_coelom_ = body cavity, _enteron_
= food tube) explains the structure of the group. They are animals in which
the real body cavity is lacking, the animal in its simplest form being
little more than a bag. Some examples are the hydra, shown on page 179,
salt-water forms known as hydroids, colonial forms which have part of their
life free swimming as jellyfish; sea anemones and coral polyps, tiny
colonial hydra like forms which build a living or secreted covering.
IV. Worms.--The wormlike animals are grouped into _flatworms_,
_roundworms_, and segmented or _jointed_ worms.
(_a_) Flatworms are sometimes parasitic, examples being the tapeworm and
liver fluke. They are usually small, ribbon- or leaf-like and flat and live
in water.
(_b_) Roundworms, minute threadlike creatures, are not often seen by the
city girl or boy. Vinegar eels, the horsehair worm, the pork worm or
trichina and the dread hookworm are examples.
(_c_) Segmented worms are long, jointed creatures composed of body rings or
segments. Examples are the earthworm, the sandworm (known to New York boys
as the fishworm), and the leeches or bloodsuckers.
[Illustration: A jointed worm. The sandworm. Slightly reduced.]
[Illustration: The common starfish seen from below to show the tube feet.
About one half natural size.]
[Illustration: The crayfish, a crustacean. _A_, antenna; _M_, mouth; _E_,
compound stalked eye; _Ch_, pincher claw; _C.P._, cephalothorax; _Ab_,
abdomen; _C.F._, caudal fin. A little reduced.]
V. Echinoderms.--These are spiny-skinned animals, which live in salt water.
They are still more complicated in structure than the worms and may be
known by the spines in their skin. They show radial symmetry. Starfish or
sea urchins are examples.
VI. Arthropods.--These animals are distinguished by having jointed body and
legs. They form two great groups. The higher forms of the _Crustacea_ have
only two regions in the body, a fused head and thorax, called the
_cephalothorax_, and an abdominal region. A second group is the _Insecta_,
of which we know something already. Crustacea breathe by means of _gills_,
which are structures for taking oxygen out of the water, while adult
insects breathe through air tubes called _trachea_.
Two smaller groups of arthropods also exist, the _Arachnida_, consisting of
spiders, scorpions, ticks, and mites, and the _Myriapoda_, examples being
the "thousand leggers" found in some city houses.
[Illustration: A common snail, a mollusk. (From a photograph by Davison.)]
VII. Mollusca.--Another large group is the Mollusca. This phylum gets its
name from the soft, unsegmented body (_mollis_ = soft). Mollusks usually
have a shell, which may be of one piece, as a snail, or two pieces or
_valves_, as the clam or oyster.
[Illustration: The skeleton of a dog; a typical vertebrate.]
VIII. The Vertebrates.--All of the animals we have studied thus far agree
in having whatever skeleton or hard parts they possess on the outside of
the body. Collectively, they are called _Invertebrates_. This exoskeleton
differs from the main or axial skeleton of the higher animals, the latter
being inside of the body. The exoskeleton is dead, being secreted by the
cells lining the body, while the endoskeleton is, in part at least, alive
and is capable of growth, _e.g._ a broken arm or leg bone will grow
together. But a man has certain parts of the skeleton, as nails or hair,
formed by the skin and in addition possesses inside bones to which the
muscles are attached. Some of the bones are arranged in a flexible column
in the _dorsal_ (the back) side of the body. This _vertebral column_, as it
is called, is distinctive of all _vertebrates_. Within its bony protection
lies the delicate central nervous system, and to this column are attached
the big bones of the legs and arms. The vertebrate animals deserve more of
our attention than other forms of life because man himself is a vertebrate.
[Illustration: The sand shark, an elasmobranch. Note the slits leading from
the gills. (From a photograph loaned by the American Museum of Natural
History.)]
Five groups or classes of vertebrates exist. _Fishes_, _Amphibians_,
_Reptiles_, _Birds_, and _Mammals_. Let us see how to distinguish one class
from another.
[Illustration: The sturgeon, a ganoid fish.]
Fishes.--Fishes are familiar animals to most of us. We know that they live
in the water, have a backbone, and that they have fins. They breathe by
means of gills, delicate organs fitted for taking oxygen out of the water.
The heart has two chambers, an auricle and a ventricle. They have a skin in
which are glands secreting mucus, a slimy substance which helps them go
through the water easily. They usually lay very many eggs.
CLASSIFICATION OF FISHES
ORDER I. _The Elasmobranchs._ Fishes which have a soft skeleton made
of cartilage and exposed gill slits. Examples: sharks, skates, and
rays.
ORDER II. _The Ganoids._ Fishes which once were very numerous on the
earth, but which are now almost extinct. They are protected by
platelike scales. Examples: gars, sturgeon, and bowfin.
[Illustration: A bony fish.]
ORDER III. _The Teleosts, or Bony Fishes._ They compose 95 per cent of
all living fishes. In this group the skeleton is bony, the gills are
protected by an operculum, and the eggs are numerous. Most of our
common food fishes belong to this class.
ORDER IV. _The Dipnoi, or Lung Fishes._ This is a very small group. In
many respects they are more like amphibians than fishes, the swim
bladder being used as a lung. They live in tropical Africa, South
America, and Australia, inhabiting the rivers and lakes there.
Characteristics of Amphibia.--The frog belongs to the class of vertebrates
known as Amphibia. As the name indicates (_amphi_, both, and _bia_, life),
members of this group live both in water and on land. In the earlier stages
of their development they take oxygen into the blood by means of gills.
When adult, however, they breathe by means of lungs. At all times, but
especially during the winter, the skin serves as a breathing organ. The
skin is soft and unprotected by bony plates or scales. The heart has three
chambers, two auricles and one ventricle. Most amphibians undergo a
complete metamorphosis, or change of form, the young being unlike the
adults.
[Illustration: Newt. (From a photograph loaned by the American Museum of
Natural History.) About natural size.]
[Illustration: The leopard frog, an amphibian.]
CLASSIFICATION OF AMPHIBIA
ORDER I. _Urodela._ Amphibia having usually poorly developed
appendages. Tail persistent through life. Examples: mud puppy, newt,
salamander.
ORDER II. _Anura._ Tailless Amphibia, which undergo a metamorphosis,
breathing by gills in larval state, by lungs in adult state.
Examples: toad and frog.
Characteristics of Reptilia.--These animals are characterized by having
scales developed from the skin. In the turtle they have become bony and are
connected with the internal skeleton. Reptiles always breathe by means of
lungs, differing in this respect from the amphibians. They show their
distant relationship to birds in that their large eggs are incased in a
leathery, limy shell.
[Illustration: Box tortoise, a land reptile. (From photograph loaned by the
American Museum of Natural History.) About one fourth natural size.]
[Illustration: The gila monster, a poisonous lizard. About one twelfth
natural size.]
CLASSIFICATION OF REPTILES
ORDER I. _Chelonia_ (turtles and tortoises). Flattened reptiles with
body inclosed in bony case. No teeth or sternum (breastbone).
Examples: snapping turtle, box tortoise.
ORDER II. _Lacertilia_ (lizards). Body covered with scales, usually
having two-paired appendages. Breathe by lungs. Examples: fence
lizard, horned toad.
[Illustration: The common garter snake. Reduced to about one tenth natural
size.]
ORDER III. _Ophidia_ (snakes). Body elongated, covered with scales. No
limbs present. Examples: garter snake, rattlesnake.
ORDER IV. _Crocodilia._ Fresh-water reptiles with elongated body and
bony scales on skin. Two-paired limbs. Examples: alligator, crocodile.
Birds.--Birds among all other animals are known by their covering of
feathers and the presence of wings. The feathers are developed from the
skin. These aid in flight, and protect the body from the cold.
[Illustration: Adaptations in the bills of birds. Could we tell anything
about the food of a bird from its bill? Do these birds all get their food
in the same manner? Do they all eat the same kind of food?]
The form of the bill in particular shows adaptation to a wonderful degree.
A duck has a flat bill for pushing through the mud and straining out the
food; a bird of prey has a curved or hooked beak for tearing; the
woodpecker has a sharp, straight bill for piercing the bark of trees in
search of the insect larvæ which are hidden underneath. Birds do not have
teeth.
[Illustration: Common tern and young, showing nesting and feeding habits.
(From group at American Museum of Natural History.)]
The rate of respiration, of heartbeat, and the body temperature are all
higher in the bird than in man. Man breathes from twelve to fourteen times
per minute. Birds breathe from twenty to sixty times a minute. Because of
the increased activity of a bird, there comes a necessity for a greater and
more rapid supply of oxygen, an increased blood supply to carry the
material to be used up in the release of energy, and a means of rapid
excretion of the wastes resulting from the process of oxidation. Birds are
large eaters, and the digestive tract is fitted to digest the food quickly,
by having a large crop in which food may be stored in a much softened
condition. As soon as the food is part of the blood, it may be sent rapidly
to the places where it is needed, by means of the large four-chambered
heart and large blood vessels.
The high temperature of the bird is a direct result of this rapid
oxidation; furthermore, the feathers and the oily skin form an insulation
which does not readily permit of the escape of heat. This insulating cover
is of much use to the bird in its flights at high altitudes, where the
temperature is often very low. Birds lay eggs and usually care for their
young.
[Illustration: African ostrich, one of the largest living birds.]
CLASSIFICATION OF BIRDS
ORDER I. _Cursores._ Running birds with no keeled breastbone. Examples:
ostrich, cassowary.
ORDER II. _Passeres._ Perching birds; three toes in front, one behind. Over
one half of all species of birds are included in this order. Examples:
sparrow, thrush, swallow.
ORDER III. _Gallinæ._ Strong legs; feet adapted to scratching. Beak stout.
Examples: jungle fowl, grouse, quail, domestic fowl.
ORDER IV. _Raptores._ Birds of prey. Hooked beak. Strong claws. Examples:
eagle, hawk, owl.
ORDER V. _Grallatores._ Waders. Long neck, beak, and legs. Examples: snipe,
crane, heron.
ORDER VI. _Natatores._ Divers and swimmers. Legs short, toes webbed.
Examples: gull, duck, albatross.
ORDER VII. _Columbinæ._ Like Gallinæ, but with weaker legs. Examples: dove,
pigeon.
ORDER VIII. _Pici._ Woodpeckers. Two toes point forward, two backward, and
adaptation for climbing. Long, strong bill.
ORDER IX. _Psittaci._ Parrots, hooked beak and fleshy tongue.
ORDER X. _Coccyges._ Climbing birds, with powerful beak. Examples:
kingfisher, toucan, and cuckoo.
ORDER XI. _Macrochires._ Birds having long-pointed wings, without scales on
metatarsus. Examples: swift, humming bird, and goatsucker.
Mammals.--Dogs and cats, sheep and pigs, horses and cows, all of our
domestic animals (and man himself) have characters of structure which cause
them to be classed as mammals. They, like some other vertebrates, have
lungs and warm blood. They also have a hairy covering and bear young
developed to a form similar to their own,[28] and nurse them with milk
secreted by glands known as the _mammary glands_; hence the term "mammal."
Footnote 28: With the exception of the monotremes.
[Illustration: The bison, an almost extinct mammal.]
Adaptations in Mammalia.--Of the thirty-five hundred species, most inhabit
continents; a few species are found on different islands, and some, as the
whale, inhabit the ocean. They vary in size from the whale and the elephant
to tiny shrew mice and moles. Adaptations to different habitat and methods
of life abound; the seal and whale have the limbs modified into flippers,
the sloth and squirrel have limbs peculiarly adapted to climbing, while the
bats have the fore limbs modeled for flight.
Lowest Mammals.--The lowest are the monotremes, animals which lay eggs like
the birds, although they are provided with hairy covering like other
mammals. Such are the Australian spiny anteater and the duck mole.
All other mammals bring forth their young developed to a form similar to
their own. The kangaroo and opossum, however, are provided with a pouch on
the under side of the body in which the very immature, blind, and helpless
young are nourished until they are able to care for themselves. These
pouched animals are called _marsupials_.
The other mammals may be briefly classified as follows:--
CLASSIFICATION OF HIGHER MAMMALS
ORDER I. _Edentata._ Toothless or with very simple teeth. Examples:
anteater, sloth, armadillo.
ORDER II. _Rodentia._ Incisor teeth chisel-shaped, usually two above and
two below. Examples: beaver, rat, porcupine, rabbit, squirrel.
ORDER III. _Cetacea._ Adapted to marine life. Examples: whale, porpoise.
ORDER IV. _Ungulata._ Hoofs, teeth adapted for grinding. Examples: (_a_)
odd-toed, horse, rhinoceros, tapir; (_b_) even-toed, ox, pig, sheep, deer.
ORDER V. _Carnivora._ Long canine teeth, sharp and long claws. Examples:
dog, cat, lion, bear, seal, and sea lion.
ORDER VI. _Insectivora._ Example: mole.
ORDER VII. _Cheiroptera._ Fore limbs adapted to flight, teeth pointed.
Example: bat.
ORDER VIII. _Primates._ Erect or nearly so, fore appendage provided with
hand. Examples: monkey, ape, man.
[Illustration: The geological history of the horse. (After Mathews, in the
American Museum of Natural History.) Ask your teacher to explain this
diagram.]
Increasing Complexity of Structure and of Habits in Plants and Animals.--In
our study of biology so far we have attempted to get some notion of the
various factors which act upon living things. We have seen how plants and
animals interact upon each other. We have learned something about the
various physiological processes of plants and animals, and have found them
to be in many respects identical. We have found grades of complexity in
plants from the one-celled plant, bacterium or pleurococcus, to the
complicated flowering plants of considerable size and with many organs. So
in animal life, from the Protozoa upward, there is constant change, and the
change is toward greater complexity of structure and functions. An insect
is a higher type of life than a protozoan, because its structure is more
complex and it can perform its work with more ease and accuracy. A fish is
a higher type of animal than the insect for these same reasons, and also
for another. The fish has an internal skeleton which forms a pointed column
of bones on the _dorsal_ side (the back) of the animal. It is a vertebrate
animal.
[Illustration: The evolutionary tree. Modified from Galloway. Copy this
diagram in your notebook. Explain it as well as you can.]
The Doctrine of Evolution.--We have now learned that animal forms may be
arranged so as to begin with very simple one-celled forms and culminate
with a group which contains man himself. This arrangement is called the
_evolutionary series_. Evolution means change, and these groups are
believed by scientists to represent stages in complexity of development of
life on the earth. Geology teaches that millions of years ago, life upon
the earth was very simple, and that gradually more and more complex forms
of life appeared, as the rocks formed latest in time show the most highly
developed forms of animal life. The great English scientist, Charles
Darwin, from this and other evidence, explained the theory of evolution.
This is the belief that simple forms of life on the earth slowly and
gradually gave rise to those more complex and that thus ultimately the most
complex forms came into existence.
The Number of Animal Species.--Over 500,000 species of animals are known to
exist to-day, as the following table shows.
Protozoa 8,000 Arachnids 16,000
Sponges 2,500 Crustaceans 16,000
Coelenterates 4,500 Mollusks 61,000
Echinoderms 4,000 Fishes 13,000
Flat-worms 5,000 Amphibians 1,400
Roundworms 1,500 Reptiles 3,500
Annelids 4,000 Birds 13,000
Insects 360,000 Mammals 3,500
Myriapods 2,000 -------
Total 518,900
Man's Place in Nature.--Although we know that man is separated mentally by
a wide gap from all other animals, in our study of physiology we must ask
where we are to place man. If we attempt to classify man, we see at once he
must be placed with the vertebrate animals because of his possession of a
vertebral column. Evidently, too, he is a mammal, because the young are
nourished by milk secreted by the mother and because his body has at least
a partial covering of hair. Anatomically we find that we must place man
with the apelike mammals, because of these numerous points of structural
likeness. The group of mammals which includes the monkeys, apes, and man we
call the _primates_.
Although anatomically there is a greater difference between the lowest type
of monkey and the highest type of ape than there is between the highest
type of ape and the lowest savage, yet there is an immense mental gap
between monkey and man.
Instincts.--Mammals are considered the highest of vertebrate animals, not
only because of their complicated structure, but because their instincts
are so well developed. Monkeys certainly seem to have many of the mental
attributes of man.
Professor Thorndike of Columbia University sums up their habits of learning
as follows:--
"In their method of learning, although monkeys do not reach the human
stage of a rich life of ideas, yet they carry the animal method of
learning, by the selection of impulses and association of them with
different sense-impressions, to a point beyond that reached by any
other of the lower animals. In this, too, they resemble man; for he
differs from the lower animals not only in the possession of a new
sort of intelligence, but also in the tremendous extension of that
sort which he has in common with them. A fish learns slowly a few
simple habits. Man learns quickly an infinitude of habits that may be
highly complex. Dogs and cats learn more than the fish, while monkeys
learn more than they. In the number of things he learns, the complex
habits he can form, the variety of lines along which he can learn
them, and in their permanence when once formed, the monkey justifies
his inclusion with man in a separate mental genus."
Evolution of Man.--Undoubtedly there once lived upon the earth races of men
who were much lower in their mental organization than the present
inhabitants. If we follow the early history of man upon the earth, we find
that at first he must have been little better than one of the lower
animals. He was a nomad, wandering from place to place, feeding upon
whatever living things he could kill with his hands. Gradually he must have
learned to use weapons, and thus kill his prey, first using rough stone
implements for this purpose. As man became more civilized, implements of
bronze and of iron were used. About this time the subjugation and
domestication of animals began to take place. Man then began to cultivate
the fields, and to have a fixed place of abode other than a cave. The
beginnings of civilization were long ago, but even to-day the earth is not
entirely civilized.
The Races of Man.--At the present time there exist upon the earth five
races or varieties of man, each very different from the other in instincts,
social customs, and, to an extent, in structure. These are the Ethiopian or
negro type, originating in Africa; the Malay or brown race, from the
islands of the Pacific; the American Indian; the Mongolian or yellow race,
including the natives of China, Japan, and the Eskimos; and finally, the
highest type of all, the Caucasians, represented by the civilized white
inhabitants of Europe and America.
REFERENCE BOOKS
ELEMENTARY
Hunter, _Laboratory Problems in Civic Biology_, American
Book Company.
Bulletin of U. S. Department of Agriculture, _Division of
Biological Survey_, Nos. 1, 6, 13, 17.
Davison, _Practical Zoölogy_. American Book Company.
Ditmars, _The Reptiles of New York_. Guide Leaflet 20. Amer.
Mus. of Nat. History.
Sharpe, _A Laboratory Manual in Biology_, pp. 140-150,
American Book Company.
Walker, _Our Birds and Their Nestlings_. American Book
Company.
Walter, H. E. and H. A., _Wild Birds in City Parks_.
Published by authors.
ADVANCED
Apgar, _Birds of the United States_. American Book Company.
Beebe, _The Bird_. Henry Holt and Company.
Ditmars, _The Reptile Book_. Doubleday, Page and Company.
Hegner, _Zoölogy_. The Macmillan Company.
Hornaday, _American Natural History_.
Jordan and Evermann, _Food and Game Fishes_. Doubleday, Page
and Company.
Parker and Haswell, _Textbook of Zoölogy_. The Macmillan
Company.
_Riverside Natural History._ Houghton, Mifflin and Company.
Weed and Dearborn, _Relation of Birds to Man_. Lippincott.
XV. THE ECONOMIC IMPORTANCE OF ANIMALS
_Problems.--I. To determine the uses of animals._
_(a) Indirectly as food._
_(b) Directly as food._
_(c) As domesticated animals._
_(d) For clothing._
_(e) Other direct economic uses._
_(f) Destruction of harmful plants and animals._
_--II. To determine the harm done by animals._
_(a) Animals destructive to those used for food._
_(b) Animals harmful to crops and gardens._
_(c) Animals harmful to fruit and forest trees._
_(d) Animals destructive to stored food or clothing._
_(e) Animals indirectly or directly responsible for disease._
LABORATORY SUGGESTIONS
Inasmuch as this work is planned for the winter months the
laboratory side must be largely museum and reference work.
It is to be expected that the teacher will wish to refer to
much of this work at the time work is done on a given group.
But it is pedagogically desirable that the work as planned
should be _varied_. Interest is thus held. Outlines prepared
by the teacher to be filled in by the student are desirable
because they lead the pupil to individual selection of what
seems to _him_ as important material. Opportunity should be
given for laboratory exercises based on original sources.
The pupils should be made to use reports of the U. S.
Department of Agriculture, the Biological Survey, various
States Reports, and others.
Special home laboratory reports may be well made at this
time, for example: determination at a local fish market of
the fish that are cheap and fresh at a given time. Have the
students give reasons for this. Study conditions in the meat
market in a similar manner. Other local food conditions may
also be studied first hand.
USES OF ANIMALS
Indirect Use as Food.--Just as plants form the food of animals, so some
animals are food for others. Man may make use of such food directly or
indirectly. Many mollusks, as the barnacle and mussel, are eaten by fishes.
Other fish live upon tiny organisms, water fleas and other small
crustaceans. These in turn feed upon still smaller animals, and we may go
back and back until finally we come to the Protozoa and one-celled water
plants as an ultimate source of food.
Direct Use as Food. Lower Forms.--The forms of life lower than the
Crustacea are of little use directly as food, although the Chinese are very
fond of one of the Echinoderms, a holothurian.
[Illustration: North American lobster. This specimen, preserved at the U.
S. Fish Commission at Woods Hole, was of unusual size and weighed over
twenty pounds.]
Crustacea as Food.--Crustaceans, however, are of considerable value for
food, the lobster fisheries in particular being of importance. The lobster
is highly esteemed as food, and is rapidly disappearing from our coasts as
the result of overfishing. Between twenty and thirty million are yearly
taken on the North Atlantic coast. This means a value at present prices of
about $15,000,000. Laws have been enacted in New York and other states
against overfishing. Egg-carrying lobsters must be returned to the water;
all smaller than six to nine inches in length (the law varies in different
states) must be put back; other restrictions are placed upon the taking of
the animals, in hope of saving the race from extinction. Some states now
hatch and care for the young for a period of time; the United States Bureau
of Fisheries is also doing much good work, in the hope of restocking to
some extent the now almost depleted waters.
Several other common crustaceans are near relatives of the crayfish. Among
them are the shrimp and prawn, thin-shelled, active crustaceans common
along our eastern coast. In spite of the fact that they form a large part
of the food supply of many marine animals, especially fish, they do not
appear to be decreasing in numbers. They are also used as food by man, the
shrimp fisheries in this country aggregating over $1,000,000 yearly.
[Illustration: The edible blue crab. (From a photograph loaned by the
American Museum of Natural History.)]
Another edible crustacean of considerable economic importance is the blue
crab. Crabs are found inhabiting muddy bottoms; in such localities they are
caught in great numbers in nets or traps baited with decaying meat. They
are, indeed, among our most valuable sea scavengers, although they are
carnivorous hunters as well. The young crabs differ considerably in form
from the adult. They undergo a complete _metamorphosis_ (change of form).
Immediately after molting or shedding of the outer shell in order to grow
larger, crabs are greatly desired by man as an article of food. They are
then known as "shedders," or soft-shelled crabs.
[Illustration: The oyster.]
Mollusks as Food.--Oysters are never found in muddy localities, for in such
places they would be quickly smothered by the sediment in the water. They
are found in nature clinging to stones or on shells or other objects which
project a little above the bottom. Here food is abundant and oxygen is
obtained from the water surrounding them. Hence oyster raisers throw oyster
shells into the water and the young oysters attach themselves.
In some parts of Europe and this country where oysters are raised
artificially, stakes or brush are sunk in shallow water so that the young
oyster, which is at first free-swimming, may escape the danger of
smothering on the bottom. After the oysters are a year or two old, they are
taken up and put down in deeper water as seed oysters. At the age of three
and four years they are ready for the market.
The oyster industry is one of the most profitable of our fisheries. Nearly
$15,000,000 a year has been derived during the last decade from such
sources. Hundreds of boats and thousands of men are engaged in dredging for
oysters. Three of the most important of our oyster grounds are Long Island
Sound, Narragansett Bay, and Chesapeake Bay.
[Illustration: This diagram shows how cases of intestinal disease (typhoid
and diarrhoea) have been traced to oysters from a locality where they were
"fattened" in water contaminated with sewage. (Loaned by American Museum of
Natural History.)]
Sometimes oysters are artificially "fattened" by placing them on beds near
the mouths of fresh-water streams. Too often these streams are the bearers
of much sewage, and the oyster, which lives on microscopic organisms, takes
in a number of bacteria with other food. Thus a person might become
infected with the typhoid bacillus by eating raw oysters. State and city
supervision of the oyster industry makes this possibility very much less
than it was a few years ago, as careful bacteriological analysis of the
surrounding water is constantly made by competent experts.
Clams.--Other bivalve mollusks used for food are clams and scallops. Two
species of the former are known to New Yorkers, one as the "round," another
as the "long" or "soft-shelled" clams. The former (_Venus mercenaria_) was
called by the Indians "quahog," and is still so called in the Eastern
states. The blue area of its shell was used by the Indians to make wampum,
or money. The quahog is now extensively used as food. The "long" clam (_Mya
arenaria_) is considered better eating by the inhabitants of Massachusetts
and Rhode Island. This clam was highly prized as food by the Indians. The
clam industries of the eastern coast aggregate nearly $1,000,000 a year.
The dredging for scallops, another molluscan delicacy, forms an important
industry along certain parts of the eastern coast.
[Illustration: Salmon leaping a fall on their way to their spawning beds.
(Photographed by Dr. John A. Sampson.)]
Fish as Food.--Fish are used as food the world over. From very early times
the herring were pursued by the Norsemen. Fresh-water fish, such as
whitefish, perch, pickerel, pike, and the various members of the trout
family, are esteemed food and, especially in the Great Lake region, form
important fisheries. But by far the most important food fishes are those
which are taken in salt water. Here we have two types of fisheries, those
where the fish comes up a river to spawn, as the salmon, sturgeon, or shad,
and those in which fishes are taken on their feeding grounds in the open
ocean. Herring are the world's most important catch, though not in this
country. Here the salmon of the western coast is taken to the value of over
$13,000,000 a year. Cod fishing also forms an important industry; over 7000
men being employed and over $2,000,000 of codfish being taken each year in
this country.
[Illustration: Globe Fisheries.]
Hundreds of other species of fish are used as food, the fish that is
nearest at hand being often the cheapest and best. Why, for example, is the
flounder so cheap in the New York markets? In what waters are the cod and
herring fisheries, sardine, oyster, sponge, pearl oyster? (See chart on
page 201.)
Amphibia and Reptiles as Food.--Frogs' legs are esteemed a delicacy.
Certain reptiles are used as food by people of other nationalities, the
Iguana, a Mexican lizard, being an example. Many of the sea-water turtles
are of large size, the leatherback and the green turtle often weighing six
hundred to seven hundred pounds each. The flesh of the green turtle and
especially of the diamond-back terrapin, an animal found in the salt
marshes along our southeastern coast, is highly esteemed as food.
Unfortunately for the preservation of the species, these animals are
usually taken during the breeding season when they go to sandy beaches to
lay their eggs.
Birds as Food.--Birds, both wild and domesticated, form part of our food
supply. Unfortunately our wild game birds are disappearing so fast that we
should not consider them as a source of food. Our domestic fowls, turkey,
ducks, etc., form an important food supply and poultry farms give lucrative
employment to many people. Eggs of domesticated birds are of great
importance as food, and egg albumin is used for other purposes,--clarifying
sugars, coating photographic papers, etc.
Mammals as Food.--When we consider the amount of wealth invested in cattle
and other domesticated animals bred and used for food in the United States,
we see the great economic importance of mammals. The United States,
Argentina, and Australia are the greatest producers of cattle. In this
country hogs are largely raised for food. They are used fresh, salted,
smoked as ham and bacon, and pickled. Sheep, which are raised in great
quantities in Australia, Argentina, Russia, Uruguay, and this country, are
one of the world's greatest meat supplies.
Goats, deer, many larger game animals, seals, walruses, etc., give food to
people who live in parts of the earth that are less densely populated.
Domesticated Animals.-- When man emerged from his savage state on the
earth, one of the first signs of the beginning of civilization was the
domestication of animals. The dog, the cow, sheep, and especially the
horse, mark epochs in the advance of civilization. Beasts of burden are
used the world over, horses almost all over the world, certain cattle, as
the water buffalo, in tropical Malaysia; camels, goats, and the llama are
also used as draft animals in some other countries.
[Illustration: Feeding silkworms. The caterpillars are the white objects in
the trays.]
Man's wealth in many parts of the world is estimated in terms of his cattle
or herds of sheep. So many products come from these sources that a long
list might be given, such as meats, milk, butter, cheese, wool, or other
body coverings, leather, skins, and hides used for other purposes. Great
industries are directly dependent upon our domesticated animals, as the
making of shoes, the manufacture of woolen cloth, the tanning industry, and
many others.
Uses for Clothing.--The manufacture of silk is due to the production of raw
silk by the silkworm, the caterpillar of a moth. It lives upon the mulberry
and makes a cocoon from which the silk is wound. The Chinese silkworm is
now raised to a slight extent in southern California. China, Japan, Italy,
and France, because of cheaper labor, are the most successful silk-raising
countries.
The use of wool gives rise to many great industries. After the wool is cut
from the sheep, it has to be washed and scoured to get out the dirt and
grease. This wool fat or lanoline is used in making soap and ointments. The
wool is next "carded," the fibers being interwoven by the fine teeth of the
carding machine or "combed," the fibers here being pulled out parallel to
each other. Carded wool becomes woolen goods; combed wool, worsted goods.
The wastes are also utilized, being mixed with "shoddy" (wool from cloth
cuttings or rags) to make woolen goods of a cheap grade.
Goat hair, especially that of the Angora and the Cashmere goat, has much
use in the clothing industries. Camel's hair and alpaca are also used.
[Illustration: Polar bear, a fur-bearing mammal which is rapidly being
exterminated. Why?]
Fur.--The furs of many domesticated and wild animals are of importance. The
Carnivora as a group are of much economic importance as the source of most
of our fur. The fur seal fisheries alone amount to many millions of dollars
annually. Otters, skunks, sables, weasels, foxes, and minks are of
considerable importance as fur producers. Even cats are now used for fur,
usually masquerading under some other name. The fur of the beaver, one of
the largest of the rodents or gnawing mammals, is of considerable value, as
are the coats of the chinchilla, muskrats, squirrels, and other rodents.
The fur of the rabbit and nutria are used in the manufacture of felt hats.
The quills of the porcupines (greatly developed and stiffened hairs) have a
slight commercial value.
Conservation of Fur-bearing Animals Needed.--As time goes on and the furs
of wild animals become scarcer and scarcer through overkilling, we find the
need for protection and conservation of many of these fast-vanishing wild
forms more and more imperative. Already breeding of some fur-bearing
animals has been tried with success, and cheap substitutes for wild animal
skins are coming more and more into the markets. Black-fox breeding has
been tried successfully in Prince Edward Island, Canada, $2500 to $3000
being given for a single skin. Skunk, marten, and mink are also being bred
for the market. Game preserves in this country and Canada are also helping
to preserve our wild fur-bearing animals.
Animal Oils.--Whale oil, obtained from the fat or "blubber" of whales, is
used extensively for lubricating. Neat's-foot oil comes from the feet of
cattle and is also used in lubrication. Tallow and lard, two fats from
cattle, sheep, and pigs, have so many well-known uses that comment is
unnecessary. Cod-liver oil is used medically and is well known. But it is
not so widely known that a fish called the menhaden or "moss bunkers" of
the Atlantic coast produces over 3,000,000 gallons of oil every year and is
being rapidly exterminated in consequence.
Hides, Horns, Hoofs, etc.--Leathers, from cattle, horses, sheep, and goats,
are used everywhere. Leather manufacture is one of the great industries of
the Eastern states, hundreds of millions of dollars being invested in its
manufacturing plants. Horns and bones are utilized for making combs,
buttons, handles for brushes, etc. Glue is made from the animal matter in
bones. Ivory, obtained from elephant, walrus, and other tusks, forms a
valuable commercial product. It is largely used for knife handles, piano
keys, combs, etc.
Perfumes.--The musk deer, musk ox, and muskrat furnish a valuable perfume
called musk. Civet cats also give us a somewhat similar perfume. Ambergris,
a basis for delicate perfumes, comes from the intestines of the sperm
whale.
Protozoa.--The Protozoa have played an important part in rock building. The
chalk beds of Kansas and other chalk formations are made up to a large
extent of the tiny skeletons of _Protozoa_, called _Foraminifera_. Some
limestone rocks are also composed in large part of such skeletons. The
skeletons of some species are used to make a polishing powder.
Sponges.--The sponges of commerce have the skeleton composed of tough
fibers of material somewhat like that of cow's horn. This fiber is elastic
and has the power of absorbing water. In a living state, the horny fiber
sponge is a dark-colored fleshy mass, usually found attached to rocks. The
warm waters of the Mediterranean Sea and the West Indies furnish most of
our sponges. The sponges are pulled up from their resting place on the
bottom, by means of long-handled rakes operated by men in boats or are
secured by divers. They are then spread out on the shore in the sun, and
the living tissues allowed to decay; then after treatment consisting of
beating, bleaching, and trimming, the bath sponge is ready for the market.
Some forms of coral are of commercial value. The red coral of the
Mediterranean Sea is the best example.
[Illustration: In some countries little metal images of Buddha are placed
within the shells of living pearl oysters or clams. Over these the mantle
of the animal secretes a layer of mother of pearl as is shown in the
picture.]
Pearls and Mother of Pearl.--Pearls are prized the world over. It is a
well-known fact that even in this country pearls of some value are
sometimes found within the shells of the fresh-water mussel and the oyster.
Most of the finest, however, come from the waters around Ceylon. If a pearl
is cut open and examined carefully, it is found to be a deposit of the
mother-of-pearl layer of the shell around some central structure. It has
been believed that any foreign substance, as a grain of sand, might
irritate the mantle at a given point, thus stimulating it to secrete around
the substance. It now seems likely that most perfect pearls are due to the
growth within the mantle of the clam or oyster of certain parasites, stages
in the development of a flukeworm. The irritation thus set up in the tissue
causes mother of pearl to be deposited around the source of irritation,
with the subsequent formation of a pearl.
The pearl-button industry in this country is largely dependent upon the
fresh-water mussel, the shells of which are used. This mussel is being so
rapidly depleted that the national government is working out a means of
artificial propagation of these animals.
Honey and Wax.--Honeybees[29] are kept in hives. A colony consists of a
queen, a female who lays the eggs for the colony, the drones, whose duty it
is to fertilize the eggs, and the workers.
Footnote 29: Their daily life may be easily watched in the
schoolroom, by means of one of the many good and cheap
observation hives now made to be placed in a window frame.
Directions for making a small observation hive for school
work can be found in Hodge, _Nature Study and Life_, Chap.
XIV. Bulletin No. 1, U. S. Department of Agriculture,
entitled _The Honey Bee_, by Frank Benton, is valuable for
the amateur beekeeper. It may be obtained for twenty-five
cents from the Superintendent of Documents, Union Building,
Washington, D.C.
[Illustration: Cells of honeycomb, queen cell on right at bottom.]
The cells of the comb are built by the workers out of wax secreted from the
under surface of their bodies. The wax is cut off in thin plates by means
of the wax shears between the two last joints of the hind legs. These cells
are used to place the eggs of the queen in, one egg to each cell, and the
young are hatched after three days, to begin life as footless white grubs.
The young are fed for several days, then shut up in the cells and allowed
to form pupæ. Eventually they break their cells and take their place as
workers in the hive, first as nurses for the young and later as pollen
gatherers and honey makers.
We have already seen (pages 37 to 39) that the honeybee gathers nectar,
which she swallows, keeping the fluid in her crop until her return to the
hive. Here it is forced out into cells of the comb. It is now thinner than
what we call honey. To thicken it, the bees swarm over the open cells,
moving their wings very rapidly, thus evaporating some of the water. A hive
of bees have been known to make over thirty-one pounds of honey in a single
day, although the average is very much less than this. It is estimated from
twenty to thirty millions of dollars' worth of honey and wax are produced
each year in this country.
Cochineal and Lac.--Among other products of insect origin is cochineal, a
red coloring matter, which consists of the dried bodies of a tiny insect,
one of the plant lice which lives on the cactus plants in Mexico and
Central America. The lac insect, another one of the plant lice, feeds on
the juices of certain trees in India and pours out a substance from its
body which after treatment forms shellac. Shellac is of much use as a basis
for varnish.
Gall Insects.--Oak galls, growths caused by the sting of wasp-like insects,
give us products used in ink making, in tanning, and in making pyrogallic
acid which is much used in developing photographs.
Insects destroy Harmful Plants or Animals.--Some forms of animal life are
of great importance because of their destruction of harmful plants or
animals.
[Illustration: An insect friend of man. An ichneumon fly boring in a tree
to lay its eggs in the burrow of a boring insect harmful to that tree.]
A near relative of the bee, called the ichneumon fly, does man indirectly
considerable good because of its habit of laying its eggs and rearing the
young in the bodies of caterpillars which are harmful to vegetation. Some
of the ichneumons even bore into trees in order to deposit their eggs in
the larvæ of wood-boring insects. It is safe to say that the ichneumons
save millions of dollars yearly to this country.
Several beetles are of value to man. Most important of these is the natural
enemy of the orange-tree scale, the ladybug, or ladybird beetle. In New
York state it may often be found feeding upon the plant lice, or aphids,
which live on rosebushes. The carrion beetles and many water beetles act as
scavengers. The sexton beetles bury dead carcasses of animals. Ants in
tropical countries are particularly useful as scavengers.
Insects, besides pollinating flowers, often do a service by eating harmful
weeds. Thus many harmful plants are kept in check. We have noted that they
spin silk, thus forming clothing; that in many cases they are preyed upon,
and that they supply an enormous multitude of birds, fishes, and other
animals with food.
[Illustration: The common toad, an insect eater.]
Use of the Toad.--The toad is of great economic importance to man because
of its diet. No less than eighty-three species of insects, mostly
injurious, have been proved to enter into the dietary. A toad has been
observed to snap up one hundred and twenty-eight flies in half an hour.
Thus at a low estimate it could easily destroy one hundred insects during a
day and do an immense service to the garden during the summer. It has been
estimated by Kirkland that a single toad may, on account of the cutworms
which it kills, be worth $19.88 each season it lives, if the damage done by
each cutworm be estimated at only one cent. Toads also feed upon slugs and
other garden pests.
Birds eat Insects.--The food of birds makes them of the greatest economic
importance to our country. This is because of the relation of insects to
agriculture. A large part of the diet of most of our native birds includes
insects harmful to vegetation. Investigations undertaken by the United
States Department of Agriculture (Division of Biological Survey) show that
a surprisingly large number of birds once believed to harm crops really
perform a service by killing injurious insects. Even the much maligned crow
lives to some extent upon insects. Swallows in the Southern states kill the
cotton-boll weevil, one of our worst insect pests. Our earliest visitor,
the bluebird, subsists largely on injurious insects, as do woodpeckers,
cuckoos, kingbirds, and many others. The robin, whose presence in the
cherry tree we resent, during the rest of the summer does much good by
feeding upon noxious insects. Birds use the food substances which are most
abundant around them at the time.[30]
Footnote 30: The following quotation from I. P. Trimble, _A
Treatise on the Insect Enemies of Fruit and Shade Trees_,
bears out this statement: "On the fifth of May, 1864, ...
seven different birds ... had been feeding freely upon small
beetles.... There was a great flight of beetles that day;
the atmosphere was teeming with them. A few days after, the
air was filled with Ephemera flies, and the same species of
birds were then feeding upon them."
During the outbreak of Rocky Mountain locusts in Nebraska in
1874-1877, Professor Samuel Aughey saw a long-billed marsh
wren carry thirty locusts to her young in an hour. At this
rate, for seven hours a day, a brood would consume 210
locusts per day, and the passerine birds of the eastern half
of Nebraska, allowing only twenty broods to the square mile,
would destroy daily 162,771,000 of the pests. The average
locust weighs about fifteen grains, and is capable each day
of consuming its own weight of standing forage crops, which
at $10 per ton would be worth $1743.26. This case may serve
as an illustration of the vast good that is done every year
by the destruction of insect pests fed to nestling birds.
And it should be remembered that the nesting season is also
that when the destruction of injurious insects is most
needed; that is, at the period of greatest agricultural
activity and before the parasitic insects can be depended on
to reduce the pests. The encouragement of birds to nest on
the farm and the discouragement of nest robbing are
therefore more than mere matters of sentiment; they return
an actual cash equivalent, and have a definite bearing on
the success or failure of the crops.--_Year Book of the
Department of Agriculture._
[Illustration: Food of some common birds. Which of the above birds should
be protected by man and why?]
Birds eat Weed Seeds.--Not only do birds aid man in his battles with
destructive insects, but seed-eating birds eat the seeds of weeds. Our
native sparrows (not the English sparrow), the mourning dove, bobwhite, and
other birds feed largely upon the seeds of many of our common weeds. This
fact alone is sufficient to make birds of vast economic importance.
Not all birds are seed or insect feeders. Some, as the cormorants, ospreys,
gulls, and terns, are active fishers. Near large cities gulls especially
act as scavengers, destroying much floating garbage that otherwise might be
washed ashore to become a menace to health. The vultures of India and
semitropical countries are of immense value as scavengers. Birds of prey
(owls) eat living mammals, including many rodents; for example, field mice,
rats, and other pests.
Extermination of our Native Birds.--Within our own times we have witnessed
the almost total extermination of some species of our native birds. The
American passenger pigeon, once very abundant in the Middle West, is now
extinct. Audubon, the greatest of all American bird lovers, gives a graphic
account of the migration of a flock of these birds. So numerous were they
that when the flock rose in the air the sun was darkened, and at night the
weight of the roosting birds broke down large branches of the trees in
which they rested. To-day not a single wild specimen of this pigeon can be
found, because they were slaughtered by the hundreds of thousands during
the breeding season. The wholesale killing of the snowy egret to furnish
ornaments for ladies' headwear is another example of the improvidence of
our fellow-countrymen. Charles Dudley Warner said, "Feathers do not improve
the appearance of an ugly woman, and a pretty woman needs no such aid."
Wholesale killing for plumage, eggs, and food, and, alas, often for mere
sport, has reduced the number of our birds more than one half in thirty
states and territories within the past fifteen years. Every crusade against
indiscriminate killing of our native birds should be welcomed by all
thinking Americans. The recent McLane bill which aims at the protection of
migrating birds and the bird-protecting clause of the recently passed
tariff bill shows that this country is awaking to the value of her bird
life. Without the birds the farmer would have a hopeless fight against
insect pests. The effect of killing native birds is now well seen in Italy
and Japan, where insects are increasing and do greater damage each year to
crops and trees.
Of the eight hundred or more species of birds in the United States, only
six species of hawks (Cooper's and the sharp-shinned hawk in particular),
and the great horned owl, which prey upon useful birds; the sapsucker,
which kills or injures many trees because of its fondness for the growing
layer of the tree; the bobolink, which destroys yearly $2,000,000 worth of
rice in the South; the crow, which feeds on crops as well as insects; and
the English sparrow, may be considered as enemies of man.
The English Sparrow.--The English sparrow is an example of a bird
introduced for the purpose of insect destruction, that has done great harm
because of its relation to our native birds. Introduced at Brooklyn in 1850
for the purpose of exterminating the cankerworm, it soon abandoned an
insect diet and has driven out most of our native insect feeders.
Investigations by the United States Department of Agriculture have shown
that in the country these birds and their young feed to a large extent upon
grain, thus showing them to be injurious to agriculture. Dirty and very
prolific, it already has worked its way from the East as far as the Pacific
coast. In this area the bluebird, song sparrow, and yellowbird have all
been forced to give way, as well as many larger birds of great economic
value and beauty. The English sparrow has become a pest especially in our
cities, and should be exterminated in order to save our native birds. It is
feared in some quarters that the English starling which has recently been
introduced into this country may in time prove a pest as formidable as the
English sparrow.
[Illustration: This shows how some snakes (constrictors) kill and eat their
prey. (Series photographed by C. W. Beebe and Clarence Halter.)]
Food of Snakes.--Probably the most disliked and feared of all animals are
the snakes. This feeling, however, is rarely deserved, for, on the whole,
our common snakes are beneficial to man. The black snake and the milk snake
feed largely on injurious rodents (rats, mice, etc.), the pretty green
snake eats injurious insects, and the little DeKay snake feeds partially on
slugs. If it were not that the rattlesnake and the copperhead are venomous,
they also could be said to be useful, for they live on English sparrows,
rats, mice, moles, and rabbits.
Food of Herbivorous Animals.--We must not forget that other animals besides
insects and birds help to keep down the rapidly growing weeds. Herbivorous
animals the world over destroy, besides the grass which they eat, untold
multitudes of weeds, which, if unchecked, would drive out the useful
occupants of the pasture, the grasses and grains.
HARM DONE BY ANIMALS
Economic Loss from Insects.--The money value of crops, forest trees, stored
foods, and other material destroyed annually by insects is beyond belief.
It is estimated that they get one tenth of the country's crops, at the
lowest estimate a matter of some $300,000,000 yearly. "The common schools
of the country cost in 1902 the sum of $235,000,000, and all higher
institutions of learning cost less than $50,000,000, making the total cost
of education in the United States considerably less than the farmers lost
from insect ravages.
"Furthermore, the yearly losses from insect ravages
aggregate nearly twice as much as it costs to maintain our
army and navy; more than twice the loss by fire; twice the
capital invested in manufacturing agricultural implements;
and nearly three times the estimated value of the products
of all the fruit orchards, vineyards, and small fruit farms
in the country."--SLINGERLAND.
The total yearly value of all farm and forest products in New York is
perhaps $150,000,000, and the one tenth that the insects get is worth
$15,000,000.
Insects which damage Garden and Other Crops.--The grasshoppers and the
larvæ of various moths do considerable harm here, especially the "cabbage
worm," the cutworm, a feeder on all kinds of garden truck, and the corn
worm, a pest on corn, cotton, tomatoes, peas, and beans.
Among the beetles which are found in gardens is the potato beetle, which
destroys the potato plant. This beetle formerly lived in Mexico upon a wild
plant of the same family as the potato, and came north upon the
introduction of the potato into Colorado, evidently preferring cultivated
forms to wild forms of this family.
[Illustration: Cotton-boll weevil. _a_, larva; _b_, pupa; _c_, adult.
Enlarged about four times. (Photographed by Davison.)]
The one beetle doing by far the greatest harm in this country is the
cotton-boll weevil. Imported from Mexico, since 1892 it has spread over
eastern Texas and into Louisiana. The beetle lays its eggs in the young
cotton fruit or boll, and the larvæ feed upon the substance within the
boll. It is estimated that if unchecked this pest would destroy yearly one
half of the cotton crop, causing a loss of $250,000,000. Fortunately, the
United States Department of Agriculture is at work on the problem, and,
while it has not found any way of exterminating the beetle as yet, it has
been found that, by planting more hardy varieties of cotton, the crop
matures earlier and ripens before the weevils have increased in sufficient
numbers to destroy the crop (see page 126).
The bugs are among our most destructive insects. The most familiar examples
of our garden pests are the squash bug; the chinch bug, which yearly does
damage estimated at $20,000,000, by sucking the juice from the leaves of
grain; and the plant lice, or aphids. One, living on the grape, yearly
destroys immense numbers of vines in the vineyards of France, Germany, and
California.
[Illustration: Female tussock moth which has just emerged from the cocoon
at the left, upon which it has deposited over two hundred eggs. (Photograph
by Davison.)]
[Illustration: Caterpillar of tussock moth. (Photograph by Davison.)]
Insects which harm Fruit and Forest Trees.--Great damage is annually done
trees by the larvæ of moths. Massachusetts has already spent over
$3,000,000 in trying to exterminate the imported gypsy moth. The codling
moth, which bores into apples and pears, is estimated to ruin yearly
$3,000,000 worth of fruit in New York alone, which is by no means the most
important apple region of the United States. Among these pests, the most
important to the dweller in a large city is the tussock moth, which
destroys our shade trees. The caterpillar may easily be recognized by its
hairy, tufted red head. The eggs are laid on the bark of shade trees in
what look like masses of foam. (See figure on page 215.) By collecting and
burning the egg masses in the fall, we may save many shade trees the
following year.
The larvæ of some moths damage the trees by boring into the wood of the
tree on which they live. Such are the peach, apple, and other fruit-tree
borers common in our orchards. Many beetle larvæ also live in trees and
kill annually thousands of forest and shade trees. The hickory borer
threatens to kill all the hickory trees in the Eastern states.
Among the bugs most destructive to trees are the scale insect and the plant
lice. The San José scale, a native of China, was introduced into the fruit
groves of California about 1870 and has spread all over the country. A
ladybird beetle, which has also been imported, is the most effective agent
in keeping this pest in check.
Insects of the House or Storehouse.--Weevils are the greatest pests,
frequently ruining tons of stored corn, wheat, and other cereals. Roaches
will eat almost anything, even clothing; they are especially fond of all
kinds of breadstuffs. The carpet beetle is a recognized foe of the
housekeeper, the larvæ feeding upon all sorts of woolen material. The larvæ
of the clothes moth do an immense amount of damage, especially to stored
clothing. Fleas, lice, and particularly bedbugs are among man's personal
foes. Besides being unpleasant they are believed to be disease carriers and
as such should be exterminated.[31]
Footnote 31: Directions for the treatment of these pests may
be found in pamphlets issued by the U. S. Department of
Agriculture.
Food of Starfish.--Starfish are enormously destructive to young clams and
oysters, as the following evidence, collected by Professor A. D. Mead, of
Brown University, shows. A single starfish was confined in an aquarium with
fifty-six young clams. The largest clam was about the length of one arm of
the starfish, the smallest about ten millimeters in length. In six days
every clam in the aquarium was devoured. Hundreds of thousands of dollars'
damage is done annually to the oysters in Connecticut alone by the ravages
of starfish. During the breeding season of the clam and oyster the boats
dredge up tons of starfish which are thrown on shore to die or to be used
as fertilizer.
THE RELATIONS OF ANIMALS TO DISEASE
[Illustration: The life history of the malarial parasite. This cut of the
malarial parasite shows parts of the body of the mosquito and of man. To
understand the life history begin at the point where the mosquito injects
the crescent-shaped bodies into the blood of man. Notice that after the
spores are released from the corpuscles of man two kinds of cells _may be
formed_. These are probably a sexual stage. Development within the body of
the mosquito will only take place when the parasite is taken into its body
at this sexual stage.]
The Cause of Malaria.--The study of the life history and habits of the
Protozoa has resulted in the finding of many parasitic forms, and the
consequent explanation of some kinds of disease. One parasitic protozoan
like an amoeba is called _Plasmodium malariæ_. It causes the disease known
as malaria. When a mosquito (the _anopheles_) sucks the blood from a person
having malaria this parasite passes into the stomach of the mosquito. After
completing a part of its life history within the mosquito's body the
parasite establishes itself within the glands which secrete the saliva of
the mosquito. After about eight days, if the infected mosquito bites a
person, some of the parasites are introduced into the blood along with the
saliva. These parasites enter the corpuscles of the blood, increase in
size, and then form spores. The rapid process of spore formation results in
the breaking down of the blood corpuscles and the release of the spores,
and the poisons they manufacture, into the blood. This causes the chill
followed by the fever so characteristic of malaria. The spores may again
enter the blood corpuscles and in forty-eight or seventy-two hours repeat
the process thus described, depending on the kind of malaria they cause.
The only cure for the disease is _quinine_ in rather large doses. This
kills the parasites in the blood. But quinine should not be taken except
under a physician's directions.
[Illustration: How to distinguish the harmless mosquito (_culex_), _a_,
from the malarial mosquito (_anopheles_), _b_, when at rest. Notice the
position of legs and body.]
The Malarial Mosquito.--Fortunately for mankind, not all mosquitoes harbor
the parasite which causes malaria. The harmless mosquito (_culex_) may be
usually distinguished from the mosquito which carries malaria (_anopheles_)
by the position taken when at rest. Culex lays eggs in tiny rafts of one
hundred or more eggs in any standing water; thus the eggs are distinguished
from those of anopheles, which are not in rafts. Rain barrels, gutters, or
old cans may breed in a short time enough mosquitoes to stock a
neighborhood. The larvæ are known as wigglers. They breathe through a tube
in the posterior end of the body, and may be recognized by their peculiar
movement when on their way to the surface to breathe. The pupa,
distinguished by a large thoracic region, breathes through a pair of tubes
on the thorax. The fact that both larvæ and pupæ take air from the surface
of the water makes it possible to kill the mosquito during these stages by
pouring oil on the surface of the water where they breed. The introduction
of minnows, gold fish, or other small fish which feed upon the larvæ in the
water where the mosquitoes breed will do much to free a neighborhood from
this pest. Draining swamps or low land which holds water after a rain is
another method of extermination. Some of the mosquito-infested districts
around New York City have been almost freed from mosquitoes by draining the
salt marshes where they breed. Long shallow trenches are so built as to tap
and drain off any standing water in which the eggs might be laid. In this
way the mosquito has been almost exterminated along some parts of our New
England coast.
[Illustration: Swamps are drained and all standing water covered with a
film of oil in order to exterminate mosquitoes. Why is the oil placed on
the surface of the water?]
Since the beginning of historical times, malaria has been prevalent in
regions infested by mosquitoes. The ancient city of Rome was so greatly
troubled by periodic outbreaks of malarial fever that a goddess of fever
came to be worshiped in order to lessen the severity of what the
inhabitants believed to be a divine visitation. At the present time the
malaria of Italy is being successfully fought and conquered by the draining
of the mosquito-breeding marshes. By a little carefully directed oiling of
water a few boys may make an almost uninhabitable region absolutely safe to
live in. Why not try it if there are mosquitoes in your neighborhood?
Yellow Fever and Mosquitoes.--Another disease carried by mosquitoes is
yellow fever. In the year 1878 there were 125,000 cases and 12,000 deaths
in the United States, mostly in Alabama, Louisiana, and Mississippi. During
the French occupation of the Panama Canal zone the work was at a standstill
part of the time because of the ravages of yellow fever. Before the war
with Spain thousands of people were ill in Cuba. But to-day this is
changed, and yellow fever is under almost complete control, both here and
in the Canal zone, where the mosquito (_stegomyia_) which carries yellow
fever exists.
[Illustration: Notice the difference in the number of yearly deaths from
yellow fever before and _after_ the American occupation of Havana.]
This is due to the experiments during the summer of 1900 of a Commission of
United States army officers, headed by Dr. Walter Reed. Of these men one,
Dr. Jesse Lazear, gave up his life to prove experimentally that yellow
fever was caused by mosquitoes. He allowed himself to be bitten by a
mosquito that was known to have bitten a yellow fever patient, contracted
the disease, and died a martyr to science. Others, soldiers, volunteered to
further test by experiment how the disease was spread, so that in the end
Dr. Reed was able to prove to the world that if mosquitoes could be
prevented from biting people who had yellow fever the disease could not be
spread. The accompanying illustration shows the result of this knowledge
for the city of Havana. For years Havana was considered one of the pest
spots of the West Indies. Visitors shunned this port and commerce was much
affected by the constant menace of yellow fever. At the time of the
American occupation after the war with Spain, the experiments referred to
above were undertaken. The city was cleaned up, proper sanitation
introduced, screens placed in most buildings, and the breeding places of
the mosquitoes were so nearly destroyed that the city was practically free
from mosquitoes. The result, so far as yellow fever was concerned, was
startling, as you can see by reference to the chart. Notice also the rise
in the death rate when the young Cuban Republic took control. How do you
account for that? We all know what American scientific medicine and
sanitation is doing in Panama and in the Philippines.
[Illustration: Stegomyia, the carrier of yellow fever. (After Howard.)]
Other Protozoan Diseases.--Many other diseases of man are probably caused
by parasitic protozoans. Dysentery of one kind appears to be caused by the
presence of an amoeba-like animal in the digestive tract which comes
usually through an impure water supply. Smallpox, rabies, and possibly
other diseases are caused by protozoans. Smallpox, which was once the most
dreaded disease known to man, because of its spread in epidemics, has been
conquered by _vaccination_, of which we shall learn more later. The death
rate from rabies or hydrophobia has in a like manner been greatly reduced
by a treatment founded on the same principles as vaccination and invented
by Louis Pasteur.
Another group of protozoan parasites are called _trypanosomes_. These are
parasitic in insects, fish, reptiles, birds, and mammals in various parts
of the world. They cause various diseases of cattle and other domestic
animals, being carried to the animal in most cases by flies. One of this
family is believed to live in the blood of native African zebras and
antelopes; seemingly it does them no harm. But if one of these parasites is
transferred by the dreaded tsetse fly to one of the domesticated horses or
cattle of the colonist of that region, death of the animal results.
Another fly carries a species of trypanosome to the natives of Central
Africa, which causes "the dreaded and incurable sleeping sickness." This
disease carries off more than fifty thousand natives yearly, and many
Europeans have succumbed to it. Its ravages are now largely confined to an
area near the large Central African lakes and the Upper Nile, for the fly
which carries the disease lives near water, seldom going more than 150 feet
from the banks of streams or lakes. The British government is now trying to
control the disease in Uganda by moving all the villages at least two miles
from the lakes and rivers. Among other diseases that may be due to
protozoans is kala-agar, a fever in hot Asiatic countries which is probably
carried by the bedbug, and African tick fever, probably carried by a small
insect called the tick. Bubonic plague, one of the most dreaded of all
infectious diseases, is carried to man by fleas from rats. In this country
many fatal diseases of cattle, as "tick," or Texas cattle fever, are
probably caused by protozoans.
[Illustration: Life history of house flies, showing from left to right the
eggs, larvæ, pupæ, and adult flies. (Photograph, about natural size, by
Overton.)]
The Fly a Disease Carrier.--We have already seen that mosquitoes of
different species carry malaria and yellow fever. Another rather recent
addition to the black list is the house fly or typhoid fly. We shall see
later with what reason this name is given. The development of the typhoid
fly is extremely rapid. A female may lay from one hundred to two hundred
eggs. These are usually deposited in filth or manure. Dung heaps about
stables, privy vaults, ash heaps, uncared-for garbage cans, and fermenting
vegetable refuse form the best breeding places for flies. In warm weather,
the eggs hatch a day or so after they are laid and become larvæ, called
maggots. After about one week of active feeding, these wormlike maggots
become quiet and go into the pupal stage, whence under favorable conditions
they emerge within less than another week as adult flies. The adults breed
at once, and in a short summer there may be over ten generations of flies.
This accounts for the great number. Fortunately relatively few flies
survive the winter. The membranous wings of the adult fly appear to be two
in number, a second pair being reduced to tiny knobbed hairs called
balancers. The head is freely movable, with large compound eyes. The mouth
parts form a proboscis, which is tonguelike, the animal obtaining its food
by lapping and sucking. The foot shows a wonderful adaptation for clinging
to smooth surfaces. Two or three pads, each of which bears tubelike hairs
that secrete a sticky fluid, are found on its under surface. It is by this
means that the fly is able to walk upside down, and carry bacteria on its
feet.
[Illustration: The foot of a fly, showing the hooks, hairs, and pads which
collect and carry bacteria. The fly doesn't wipe his feet.]
[Illustration: Colonies of bacteria which have developed in a culture
medium upon which a fly was allowed to walk.]
The Typhoid Fly a Pest.--The common fly is recognized as a pest the world
over. Flies have long been known to spoil food through their filthy habits,
but it is more recently that the very serious charge of spread of diseases,
caused by bacteria, has been laid at their door. In a recent experiment two
young men from the Connecticut Agricultural Station found that a single fly
might carry on its feet anywhere from 500 to 6,600,000 bacteria, the
average number being over 1,200,000. Not all of these germs are harmful,
but they might easily include those of typhoid fever, tuberculosis, summer
complaint, and possibly other diseases. A recent pamphlet published by the
Merchants' Association in New York City shows that the rapid increase of
flies during the summer months has a definite correlation with the increase
in the number of cases of summer complaint. Observations in other cities
seem to show the increase in number of typhoid cases in the early fall is
due, in part at least, to the same cause. A terrible toll of disease and
death may be laid at the door of the typhoid fly.
[Illustration: Showing how flies may spread disease by means of
contaminating food.]
Recently the stable fly has been found to carry the dread disease known as
infantile paralysis.
[Illustration: There were 329 typhoid cases in Jacksonville, Florida, in
1910, 158 in 1911, 87 in first 10 months of 1912. 80 to 85 per cent of
outdoor toilets were made fly proof during winter of 1910. Account for the
decrease in typhoid after the flies were kept out of the toilets.]
Remedies.--Cleanliness which destroys the breeding place of flies, the
frequent removal and destruction of garbage, rubbish, and manure, covering
of all food when not in use and especially the _careful_ screening of
windows and doors during the breeding season, will all play a part in the
reduction of flies. To the motto "swat the fly" should be added, "remove
their breeding places!"
[Illustration: Flea which transmits Bubonic plague from rat to man.]
Other Insect Disease Carriers.--Fleas and bedbugs have been recently added
to those insects proven to carry disease to man. Bubonic plague, which is
primarily a disease of rats, is undoubtedly transmitted from the infected
rats to man by the fleas. Fleas are also believed to transmit leprosy
although this is not proven.
To rid a house of fleas we must first find their breeding places. Old
carpets, the sleeping places of cats or dogs or any dirty unswept corner
may hold the eggs of the flea. The young breed in cracks and crevices,
feeding upon organic matter there. Eventually they come to live as adults
on their warm-blooded hosts, cats, dogs, or man. Evidently destruction of
the breeding places, careful washing of all infected areas, the use of
benzine or gasoline in crevices where the larvæ may be hid are the most
effective methods of extermination. Pets which might harbor fleas should be
washed frequently with a weak (two to three per cent) solution of creolin.
Bedbugs are difficult to prove as an agent in the transmission of disease
but their disgusting habits are sufficient reason for their extermination.
It has been proven by experiment that they may spread typhoid and relapsing
fevers. They prefer human blood to other food and have come to live in
bedrooms and beds because this food can be obtained there. They are
extremely difficult to exterminate because their flat body allows them to
hide in cracks out of sight. Wooden beds are thus better protection for
them than iron or brass beds. Boiling water poured over the cracks when
they breed or a mixture of strong corrosive sublimate four parts, alcohol
four parts and spirits of turpentine one part, are effective remedies.
How the Harm done by Insects is Controlled.--The combating of insects is
directed by several bodies of men, all of which have the same end in view.
These are the Bureau of Entomology of the United States Department of
Agriculture, the various state experiment stations, and medical and civic
organizations.
The Bureau of Entomology works in harmony with the other divisions of the
Department of Agriculture, giving the time of its experts to the problems
of controlling insects which, for good or ill, influence man's welfare in
this country. The destruction of the malarial mosquito and control of the
typhoid fly; the destruction of harmful insects by the introduction of
their natural enemies, plant or animal; the perfecting of the honeybee (see
Hodge, _Nature Study and Life_, page 240), and the introduction of new
species of insects to pollinate flowers not native to this country (see
_Blastophaga_, page 43), are some of the problems to which these men are
now devoting their time.
All the states and territories have, since 1888, established state
experiment stations, which work in coöperation with the government in the
war upon injurious insects. These stations are often connected with
colleges, so that young men who are interested in this kind of natural
science may have opportunity to learn and to help.
The good done by these means directly and indirectly is very great.
Bulletins are published by the various state stations and by the Department
of Agriculture, most of which may be obtained free. The most interesting of
these from the high school standpoint are the Farmers' Bulletins, issued by
the Department of Agriculture, and the Nature Study pamphlets issued by the
Cornell University in New York state.
[Illustration: This diagram shows how bubonic plague is carried to man.
Explain the diagram.]
Animals Other than Insects may be Disease Carriers.--The common brown rat
is an example of a mammal, harmful to civilized man, which has followed in
his footsteps all over the world. Starting from China, it spread to eastern
Europe, thence to western Europe, and in 1775 it had obtained a lodgment in
this country. In seventy-five years it reached the Pacific coast, and is
now fairly common all over the United States, being one of the most
prolific of all mammals. Rats are believed to carry bubonic plague, the
"Black Death" of the Middle Ages, a disease estimated to have killed
25,000,000 people during the fourteenth century. The rat, like man, is
susceptible to plague; fleas bite the rat and then biting man transmit the
disease to him. A determined effort is now being made to exterminate the
rat because of its connection with bubonic plague.
Other Parasitic Animals cause Disease.--Besides parasitic protozoans other
forms of animals have been found that _cause_ disease. Chief among these
are certain round and flat worms, which have come to live as parasites on
man and other animals. A one-sided relationship has thus come into
existence where the worm receives its living from the host, as the animal
is called on which the parasite lives. Consequently the parasite frequently
becomes fastened to its host during adult life and often is reduced to a
mere bag through which the fluid food prepared by its host is absorbed.
Sometimes a complicated life history has arisen from their parasitic
habits. Such is seen in the life history of the liver fluke, a flatworm
which kills sheep, and in the tapeworm.
[Illustration: The life cycle of a tapeworm. (1) The eggs are taken in with
filthy food by the pig; (2) man eats undercooked pork by means of which the
bladder worm (3) is transferred to his own intestine (4).]
Cestodes or Tapeworms.--These parasites infest man and many other
vertebrate animals. The tapeworm (_Tænia solium_) passes through two stages
in its life history, the first within a pig, the second within the
intestine of man. The developing eggs are passed off with wastes from the
intestine of man. The pig, an animal with dirty habits, may take in the
worm embryos with its food. The worm develops within the intestine of the
pig, but soon makes its way into the muscle or other tissues. It is here
known as a bladderworm. If man eats raw or undercooked pork containing
these worms, _he_ may become a host for the tapeworm. Thus during its
complete life history it has two hosts. Another common tapeworm parasitic
on man lives part of its life as an embryo within the muscles of cattle.
The adult worm consists of a round headlike part provided with hooks, by
means of which it fastens itself to the wall of the intestine. This head
now buds off a series of segmentlike structures, which are practically bags
full of sperms and eggs. These structures, called _proglottids_, break off
from time to time, thus allowing the developing eggs to escape. The
proglottids have no separate digestive systems, but the whole body surface,
bathed in digested food, absorbs it and is thus enabled to grow rapidly.
[Illustration: _Trichinella spiralis_ imbedded in human muscle. (After
Leuckart.)]
Roundworms.--Still other wormlike creatures called roundworms are of
importance to man. Some, as the vinegar eel found in vinegar, or the
pinworms parasitic in the lower intestine, particularly of children, do
little or no harm. The pork worm or _trichina_, however, is a parasite
which may cause serious injury. It passes through the first part of its
existence as a parasite in a pig or other vertebrate (cat, rat, or rabbit),
where it lies, covered within a tiny sac or _cyst_, in the muscles of its
hosts. If raw pork containing these worms is eaten by man, the cyst is
dissolved off by the action of the digestive fluids, and the living
trichina becomes free in the intestine of man. Here it reproduces and the
young bore their way through the intestine walls and enter the muscles,
causing inflammation there. This causes a painful and often fatal disease
known as _trichinosis_.
The Hookworm.--The discovery by Dr. C. W. Stiles of the Bureau of Animal
Industry, that the laziness and shiftlessness of the "poor whites" of the
South is partly due to a parasite called the _hookworm_, reads like a fairy
tale.
The people, largely farmers, become infected with a larval stage of the
hookworm, which develops in moist earth. It enters the body usually through
the skin of the feet, for children and adults alike, in certain localities
where the disease is common, go barefoot to a considerable extent.
A complicated journey from the skin to the intestine now follows, the larvæ
passing through the veins to the heart, from there to the lungs; here they
bore into the air passages and eventually work their way by way of the
windpipe into the intestine. One result of the injury of the lungs is that
many thus infected are subject to tuberculosis. The adult worms, once in
the food tube, fasten themselves and feed upon the blood of their host by
puncturing the intestine wall. The loss of blood from this cause is not
sufficient to account for the bloodlessness of the person infected, but it
has been discovered that the hookworm pours out a poison into the wound
which prevents the blood from clotting rapidly (see page 315); hence a
considerable loss of blood occurs from the wound after the worm has
finished its meal and gone to another part of the intestine.
[Illustration: A family suffering from hookworm.]
The cure of the disease is very easy; thymol is given, which weakens the
hold of the worm, this being followed by Epsom salts. For years a large
area in the South undoubtedly has been retarded in its development by this
parasite; hundreds of millions of dollars and thousands of lives have been
needlessly sacrificed.
"The hookworm is not a bit spectacular: it doesn't get itself
discussed in legislative halls or furiously debated in political
campaigns. Modest and unassuming, it does not aspire to such dignity.
It is satisfied simply with (1) lowering the working efficiency and
the pleasure of living in something like two hundred thousand persons
in Georgia and all other Southern states in proportion; with (2)
amassing a death rate higher than tuberculosis, pneumonia, or typhoid
fever; with (3) stubbornly and quite effectually retarding the
agricultural and industrial development of the section; with (4)
nullifying the benefit of thousands of dollars spent upon education;
with (5) costing the South, in the course of a few decades, several
hundred millions of dollars. More serious and closer at hand than the
tariff; more costly, threatening, and tangible than the Negro problem;
making the menace of the boll weevil laughable in comparison--it is
preëminently the problem of the South."--_Atlanta Constitution._
Animals that prey upon Man.--The toll of death from animals which prey upon
or harm man directly is relatively small. Snakes in tropical countries kill
many cattle and not a few people.
The bite of the rattlesnake of our own country, although dangerous, seldom
kills. The dreaded cobra of India has a record of over two hundred and
fifty thousand persons killed in the last thirty-five years. The Indian
government yearly pays out large sums for the extermination of venomous
snakes, over two hundred thousand of which have been killed during a single
year.
[Illustration: A flesh-eating reptile, the alligator.]
Alligators and Crocodiles.--These feed on fishes, but often attack large
animals, as horses, cows, and even man. They seek their prey chiefly at
night, and spend the day basking in the sun. The crocodiles of the Ganges
River in India levy a yearly tribute of many hundred lives from the
natives.
Carnivorous animals such as lions and tigers still inflict damage in
certain parts of the world, but as the tide of civilization advances, their
numbers are slowly but surely decreasing so that as important factors in
man's welfare they may be considered almost negligible.
REFERENCE BOOKS
ELEMENTARY
Hunter, _Laboratory Problems in Civic Biology_. American
Book Company.
Beebe, _The Bird_. Henry Holt and Company.
Bigelow, _Applied Biology_. Macmillan and Company.
Davison, _Practical Zoölogy_. American Book Company.
Herrick, _Household Insects and Methods of Control_. Cornell
Reading Courses.
Hornaday, _Our Vanishing Wild Life_. New York Zoölogical
Society.
Hodge, _Nature Study and Life_. Ginn and Company.
Kipling, _Captains Courageous_. Charles Scribner's Sons.
Sharpe, _Laboratory Manual_, pp. 157-158, 182-203, 320-341.
American Book Company.
Stone and Cram, _American Animals_. Doubleday, Page and
Company.
Toothaker, _Commercial Raw Materials_. Ginn and Company.
ADVANCED
Flower, _The Horse_. D. Appleton and Company.
Hornaday, _The American Natural History_. Macmillan and
Company.
Jordan, _Fishes_. Henry Holt and Company.
Jordan and Evermann, _American Food and Game Fishes_.
Doubleday, Page and Company.
Schaler, _Domesticated Animals, their Relations to Man and
to His Advancement in Civilization_. Charles Scribner's
Sons.
XVI. THE FISH AND FROG, AN INTRODUCTORY STUDY OF VERTEBRATES
_Problems._--_To determine how a fish and a frog are fitted for the life
they lead._
_To determine some methods of development in vertebrate animals._
_(a) Fishes._
_(b) Frogs._
_(c) Other animals._
LABORATORY SUGGESTIONS
_Laboratory exercise._--Study of a living fish--adaptations
for protection, locomotion, food getting, etc.
_Laboratory demonstration._--The development of the fish or
frog egg.
_Visit to the aquarium._--Study of adaptations, economic
uses of fishes, artificial propagation of fishes.
Two Methods of Breathing in Vertebrates.--Vertebrate animals have at least
two methods of getting their oxygen. In other respects their life processes
are nearly similar. Of all vertebrates fishes are the only ones fitted to
breathe all their lives under water. Other vertebrates are provided with
lungs and take their oxygen directly from the air.[32] We will next take up
the study of a fish to see how it is fitted for its life in the water.
Footnote 32: With the exception of a few lungless
salamanders. Most salamanders get much of their supply of
oxygen through their moist skins.
STUDY OF A FISH
The Body.--One of our common fresh-water fish is the bream, or golden
shiner. The body of the bream runs insensibly into the head, the neck being
absent. The long, narrow body with its smooth surface fits the fish
admirably for its life in the water. Certain cells in the skin secrete
mucus or slime, another adaptation. The position of the scales, overlapping
in a backward direction, is yet another adaptation which aids in passing
through the water. Its color, olive above and bright silver and gold below,
is protective. Can you see how?
[Illustration: The bream. _A_, dorsal fin; _B_, caudal fin; _C_, anal fin;
_D_, pelvic fin; _E_, pectoral fin.]
The Appendages and their Uses.--The appendages of the fish consist of
paired and unpaired fins. The paired fins are four in number, and are
believed to correspond in position and structure with the paired limbs of a
man. Note the illustration above and locate the paired _pectoral_ and
_pelvic_ fins. (These are so called because they are attached to the bones
forming the pectoral and pelvic girdles. See page 268.) Find, by
comparison with the Figure, the _dorsal_, _anal_, and _caudal_ fins. How
many unpaired fins are there?
The flattened, muscular body of the fish, tapering toward the caudal fin,
is moved from side to side with an undulating motion which results in the
forward movement of the fish. This movement is almost identical with that
of an oar in sculling a boat. Turning movements are brought about by use of
the lateral fins in much the same way as a boat is turned. We notice the
dorsal and other single fins are evidently useful in balancing and
steering.
The Senses.--The position of the eyes at the side of the head is an evident
advantage to the fish. Why? The eye is globular in shape. Such an eye has
been found to be very nearsighted. Thus it is unlikely that a fish is able
to perceive objects at any great distance from it. The eyes are unprotected
by eyelids, but the tough outer covering and their position afford some
protection.
Feeding experiments with fishes show that a fish becomes aware of the
presence of food by smelling it as well as by seeing it. The nostrils of a
fish can be proved to end in little pits, one under each nostril hole. Thus
they differ from our own, which are connected with the mouth cavity. In the
catfish, for example, the _barbels_, or horns, receive sensations of smell
and taste. They do not perceive odors as we do for a fish perceives only
substances that are dissolved in the water in which it lives. The senses of
taste and touch appear to be less developed than the other senses.
Along each side of most fishes is a line of tiny pits, provided with sense
organs and connected with the central nervous system of the fish. This
area, called the _lateral line_, is believed to be sensitive to mechanical
stimuli of certain sorts. The "ear" of the fish is under the skin and
serves partly as a balancing organ.
Food Getting.--A fish must go after its food and seize it, but has no
structures for grasping except the teeth. Consequently we find the teeth
small, sharp, and numerous, well adapted for holding living prey. The
tongue in most fishes is wanting or very slightly developed.
Breathing.--A fish, when swimming quietly or when at rest, seems to be
biting when no food is present. A reason for this act is to be seen when we
introduce a little finely powdered carmine into the water near the head of
the fish. It will be found that a current of water enters the mouth at each
of these biting movements and passes out through two slits found on each
side of the head of the fish. Investigation shows us that under the broad,
flat plate, or _operculum_, forming each side of the head, lie several
long, feathery, red structures, the _gills_.
[Illustration: Diagram of the gills of a fish. (_H_), the heart which
forces the blood into the tubes (_V_), which run out into the gill
filaments. A gill bar (_G_) supports each gill. The blood after exchanging
its carbon dioxide for oxygen is sent out to the cells of the body through
the artery (_A_).]
Gills.--If we examine the gills of any large fish, we find that a single
gill is held in place by a bony arch, made of several pieces of bone which
are hinged in such a way as to give great flexibility to the gill arch, as
the support is called. Covering the bony framework, and extending from it,
are numerous delicate filaments covered with a very thin membrane or skin.
Into each of these filaments pass two blood vessels; in one blood flows
downward and in the other upward. Blood reaches the gills and is carried
away from these organs by means of two large vessels which pass along the
bony arch previously mentioned. In the gill filament the blood comes into
contact with the free oxygen of the water bathing the gills. An exchange of
gases through the walls of the gill filaments results in the loss of carbon
dioxide and a gain of oxygen by the blood. The blood carries oxygen to the
cells of the body and (as work is done by the cells as a result of the
oxidation of food) brings carbon dioxide back to the gills.
Gill Rakers.--If we open wide the mouth of any large fish and look inward,
we find that the mouth cavity leads to a funnel-like opening, the gullet.
On each side of the gullet we can see the gill arches, guarded on the inner
side by a series of sharp-pointed structures, the _gill rakers_. In some
fishes in which the teeth are not well developed, there seems to be a
greater development of the gill rakers, which in this case are used to
strain out small organisms from the water which passes over the gills. Many
fishes make such use of the gill rakers. Such are the shad and menhaden,
which feed almost entirely on _plankton_, a name given to the small plants
and animals found by millions in the water.
Digestive System.--The gullet leads directly into a baglike stomach. There
are no salivary glands in the fishes. There is, however, a large liver,
which appears to be used as a digestive gland. This organ, because of the
oil it contains, is in some fishes, as the cod, of considerable economic
importance. Many fishes have outgrowths like a series of pockets from the
intestine. These structures, called the _pyloric cæca_, are believed to
secrete a digestive fluid. The intestine ends at the vent, which is usually
located on the under side of the fish, immediately in front of the anal
fin.
[Illustration: A fish opened to show _H_, the heart; _G_, the gills; _L_,
the liver; _S_, the stomach; _I_, the intestine; _O_, the ovary; _K_, the
kidney, and _B_, the air bladder.]
Swim Bladder.--An organ of unusual significance, called the _swim bladder_,
occupies the region just dorsal to the food tube. In young fishes of many
species this is connected by a tube with the anterior end of the digestive
tract. In some forms this tube persists throughout life, but in other
fishes it becomes closed, a thin, fibrous cord taking its place. The swim
bladder aids in giving the fish nearly the same weight as the water it
displaces, thus buoying it up. The walls of the organ are richly supplied
with blood vessels, and it thus undoubtedly serves as an organ for
supplying oxygen to the blood when all other sources fail. In some fishes
(the _dipnoi_, page 187) it has come to be used as a lung.
Circulation of the Blood.--In the vertebrate animals the blood is said to
circulate in the body, because it passes through a more or less closed
system of tubes in its course around the body. In the fishes the heart is a
two-chambered muscular organ, a thin-walled _auricle_, the receiving
chamber, leading into a thick-walled muscular _ventricle_ from which the
blood is forced out. The blood is pumped from the heart to the gills; there
it loses some of its carbon dioxide; it then passes on to other parts of
the body, eventually breaking up into very tiny tubes called _capillaries_.
From the capillaries the blood returns, in tubes of gradually increasing
diameter, toward the heart again. The body cells lie between the smallest
branches of the capillaries. Thus they get from the blood food and oxygen
and return to the blood the wastes resulting from oxidation within the cell
body. During its course some of the blood passes through the kidneys and is
there relieved of part of its nitrogenous waste. Circulation of blood in
the body of the fish is rather slow. The temperature of the blood being
nearly that of the surrounding media in which the fish lives, the animal
has incorrectly been given the term "cold-blooded."
Nervous System.--As in all other vertebrate animals, the brain and spinal
cord of the fish are partially inclosed in bone. The central nervous system
consists of a _brain_, with nerves connecting the organs of sight, taste,
smell, and hearing, and such parts of the body as possess the sense of
touch; a _spinal cord_; and _spinal nerves_. Nerve cells located near the
outside of the body send in messages to the central system, which are there
received as sensations. Cells of the central nervous system, in turn, send
out messages which result in the movement of muscles.
Skeleton.--In the vertebrates, of which the bony fish is an example, the
skeleton is under the skin, and is hence called an _endoskeleton_. It
consists of a bony framework, the vertebral column which protects the
spinal cord and certain attached bones, the ribs, with other spiny bones to
which the unpaired fins are attached. The paired fins are attached to the
spinal column by two collections of bones, known respectively as the
_pectoral_ and _pelvic girdles_. The bones in the main skeleton serve in
the fish for the attachment of powerful muscles, by means of which
locomotion is accomplished. In most fishes, the _exoskeleton_, too, is well
developed, consisting usually of scales, but sometimes of bony plates.
Food of Fishes.--We have already seen that in a balanced aquarium the
balance of food was preserved by the plants, which furnished food for the
tiny animals or were eaten by larger ones,--for example, snails or fish.
The smaller animals in turn became food of larger ones. The nitrogen
balance was maintained through the excretions of the animals and their
death and decay.
The marine world is a great balanced aquarium. The upper layer of water is
crowded with all kinds of little organisms, both plant and animal. Some of
these are microscopic in size; others, as the tiny crustaceans, are visible
to the eye. On these little organisms some fish feed entirely, others in
part. Such are the menhaden[33] (bony, bunker, mossbunker of our coast),
the shad, and others. Other fishes are bottom feeders, as the blackfish and
the sea bass, living almost entirely upon mollusks and crustaceans. Still
others are hunters, feeding upon smaller species of fish, or even upon
their weaker brothers. Such are the bluefish, squeteague or weakfish, and
others.
Footnote 33: It has been discovered by Professor Mead of
Brown University that the increase in starfish along certain
parts of the New England coast was in part due to
overfishing of menhaden, which at certain times in the year
feed almost entirely on the young starfish.
What is true of salt-water fish is equally true of those inhabiting our
fresh-water streams and lakes. It is one of the greatest problems of our
Bureau of Fisheries to discover this relation of various fishes to their
food supplies so as to aid in the conservation and balance of life in our
lakes, rivers, and seas.
Migration of Fishes.--Some fishes change their habitat at different times
during the year, moving in vast schools northward in summer and southward
in the winter. In a general way such migrations follow the coast lines.
Examples of such migratory fish are the cod, menhaden, herring, and
bluefish. The migrations are due to temperature changes, to the seeking
after food, and to the spawning instinct. Some fish migrate to shallower
water in the summer and to deeper water in the winter; here the reason for
the migration is doubtless the change in temperature.
[Illustration: Development of a trout. 1, the embryo within the egg; 2, the
young fish just hatched with the yoke sac still attached; 3, the young
fish.]
The Egg-laying Habits of the Bony Fishes.--The eggs of most bony fishes are
laid in great numbers, varying from a few thousand in the trout to many
hundreds of thousands in the shad and several millions in the cod. The time
of egg-laying is usually spring or early summer. At the time of spawning
the male usually deposits milt, consisting of millions of sperm cells, in
the water just over the eggs, thus accomplishing fertilization. Some
fishes, as sticklebacks, sunfish, toadfish, etc., make nests, but usually
the eggs are left to develop by themselves, sometimes attached to some
submerged object, but more frequently free in the water. In some eggs a
tiny oil drop buoys up the egg to the surface, where the heat of the sun
aids development. They are exposed to many dangers, and both eggs and
developing fish are eaten, not only by birds, fish of other species, and
other water inhabitants, but also by their own relatives, and even parents.
Consequently a very small percentage of eggs ever produce mature fish.
The Relation of the Spawning Habits to Economic Importance of Fish.--The
spawning habits of fish are of great importance to us because of the
economic value of fish to mankind, not only directly as a food, but
indirectly as food for other animals in turn valuable to man. Many of our
most desirable food fishes, notably the salmon, shad, sturgeon, and smelt,
pass up rivers from the ocean to deposit their eggs, swimming against
strong currents much of the way, some species leaping rapids and falls, in
order to deposit their eggs in localities where the conditions of water and
food are suitable, and the water shallow enough to allow the sun's rays to
warm it sufficiently to cause the eggs to develop. The Chinook salmon of
the Pacific coast, the salmon used in the Western canning industry, travels
over a thousand miles up the Columbia and other rivers, where it spawns.
The salmon begin to pass up the rivers in early spring, and reach the
spawning beds, shallow deposits of gravel in cool mountain streams, before
late summer. Here the fish, both males and females, remain until the
temperature of the water falls to about 54° Fahrenheit. The eggs and milt
are then deposited, and the old fish die, leaving the eggs to be hatched
out later by the heat of the sun's rays.
Need of Conservation.--The instinct of this and other species of fish to go
into shallow rivers to deposit their eggs has been made use of by man. At
the time of the spawning migration the salmon are taken in vast numbers,
for the salmon fisheries net over $16,000,000 annually.
But the need for conservation of this important national asset is great.
The shad have within recent time abandoned their breeding places in the
Connecticut River, and the salmon have been exterminated along our eastern
coast within the past few decades. It is only a matter of a few years when
the Western salmon will be extinct if fishing is continued at the present
rate. More fish must be allowed to reach their breeding places. To do this
a closed season on the rivers of two or three days out of each seven while
the shad or the salmon run would do much good.
The sturgeon, the eggs of which are used in the manufacture of the delicacy
known as _caviar_, is an example of a fish that is almost extinct in this
part of the world. Other food fish taken at the breeding season are also in
danger.
[Illustration: Artificial fertilization of fish eggs.]
Artificial Propagation of Fishes.--Fortunately, the government through the
Bureau of Fisheries, and various states by wise protective laws and by
artificial propagation of fishes, are beginning to turn the tide. Certain
days of the week the salmon are allowed to pass up the Columbia unmolested.
Closed breeding seasons protect our trout, bass, and other game fish, also
the catching of fish under a certain size is prohibited.
[Illustration: Early development of salmon. Natural size.]
Many fish hatcheries, both government and state, are engaged in
artificially fertilizing millions of fish eggs of various species and
protecting the young fry until they are of such size that they can take
care of themselves, when they are placed in ponds or streams. This
artificial fertilization is usually accomplished by first squeezing out the
ripe eggs from a female into a pan of water; in a similar manner the milt
or sperm cells are obtained, and poured over the eggs. The eggs are thus
fertilized. They are then placed in receptacles supplied with running water
and left to develop under favorable conditions. Shortly after the egg has
segmented (divided into many cells) the embryo may be seen developing on
one side of the egg. The rest of the egg is made up of food or yolk, and
when the baby fish hatches it has for some time the yolk attached to its
ventral surface. Eventually the food is absorbed into the body of the fish.
The development of the fish is direct, the young fish becoming an adult
without any great change in form. The young fry are kept under ideal
conditions until later, when they are shipped, sometimes thousands of
miles, to their new homes.
NOTE TO TEACHER.--It is suggested that in the spring term the frog be
studied, but if animal biology be taken up during the fall term the fish
only might be used.
THE FROG
Adaptations for Life.--The most common frog in the eastern part of the
United States is the leopard frog. It is recognized by its greenish brown
body with dark spots, each spot being outlined in a lighter-colored
background. In spite of the apparent lack of harmony with their
surroundings, their color appears to give almost perfect protection. In
some species of frogs the color of the skin changes with the surroundings
of the frog, another means of protection.
Adaptations for life in the water are numerous. The ovoid body, the head
merging into the trunk, the slimy covering (for the frog is provided, like
the fish, with mucus cells in the skin), and the powerful legs with webbed
feet, are all evidences of the life which the frog leads.
Locomotion.--You will notice that the appendages have the same general
position on the body and same number of parts as do your own (upper arm,
forearm, and hand; thigh, shank, and foot, the latter much longer
relatively than your own). Note that while the hand has four fingers, the
foot has five toes, the latter connected by a web. In swimming the frog
uses the stroke we all aim to make when we are learning to swim. Most of
the energy is liberated from the powerful backward push of the hind legs,
which in a resting position are held doubled up close to the body. On land,
locomotion may be by hopping or crawling.
[Illustration: This diagram shows how the frog uses its tongue to catch
insects.]
Sense Organs.--The frog is well provided with sense organs. The eyes are
large, globular, and placed at the side of the head. When they are closed,
a delicate fold, or third eyelid, called the _nictitating membrane_, is
drawn over each eye. Frogs probably see best moving objects at a few feet
from them. Their vision is much keener than that of the fish. The external
ear (_tympanum_) is located just behind the eye on the side of the body.
Frogs hear sounds and distinguish various calls of their own kind, as is
proved by the fact that frogs recognize the warning notes of their mates
when any one is approaching. The inner ear also has to do with balancing
the body as it has in fishes and other vertebrates. Taste and smell are
probably not strong sensations in a frog or toad. They bite at moving
objects of almost any kind when hungry. The long flexible tongue, which is
fastened at the front, is used to catch insects. Experience has taught
these animals that moving things, insects, worms, and the like, make good
food. These they swallow whole, the tiny teeth being used to hold the food.
Touch is a well-developed sense. They also respond to changes in
temperature under water, remaining there in a dormant state for the winter
when the temperature of the air becomes colder than that of the water.
Breathing.--The frog breathes by raising and lowering the floor of the
mouth, pulling in air through the two nostril holes. Then the little flaps
over the holes are closed, and the frog swallows this air, forcing it down
into the baglike lungs. The skin is provided with many tiny blood vessels,
and in winter, while the frogs are dormant at the bottom of the ponds, it
serves as the only organ of respiration.
[Illustration: Internal organs of a frog: M, mouth; T, tongue; Lu, lungs;
H, heart; St, stomach; I, small intestine; L, liver; G, gall bladder; P,
pancreas; C, cloaca; B, urinary bladder; S, spleen; K, kidney; Od, oviduct;
O, ovary; Br, brain; Sc, spinal cord; Ba, back bone.]
The Food Tube and its Glands.--The mouth leads like a funnel into a short
tube, the _gullet_. On the lower floor of the mouth can be seen the
slitlike _glottis_ leading to the lungs. The gullet widens almost at once
into a long _stomach_, which in turn leads into a much coiled intestine.
This widens abruptly at the lower end to form the _large intestine_. The
latter leads into the _cloaca_ (Latin, _sewer_), into which open the
_kidneys_, _urinary bladder_, and reproductive organs (_ovaries_ or
_spermaries_). Several _glands_, the function of which is to produce
digestive fluids, open into the food tube. These digestive fluids, by means
of the ferments or enzymes contained in them, change insoluble food
materials into a soluble form. This allows of the absorption of food
material through the walls of the food tube into the blood. The glands
(having the same names and uses as those in man) are the _salivary glands_,
which pour their juices into the mouth, the _gastric glands_ in the walls
of the stomach, and the _liver_ and _pancreas_, which open into the
intestine.
Circulation.--The frog has a well-developed heart, composed of a
thick-walled muscular ventricle and two thin-walled auricles. The heart
pumps the blood through a system of closed tubes to all parts of the body.
Blood enters the right auricle from all parts of the body; it then contains
considerable carbon dioxide; the blood entering the left auricle comes from
the lungs, hence it contains a considerable amount of oxygen. Blood leaves
the heart through the ventricle, which thus pumps some blood containing
much and some containing little oxygen. Before the blood from the tissues
and lungs has time to mix, however, it leaves the ventricle and by a
delicate adjustment in the vessels leaving the heart most of the blood
containing much oxygen is passed to all the various organs of the body,
while the blood deficient in oxygen, but containing a large amount of
carbon dioxide, is pumped to the lungs, where an exchange of oxygen and
carbon dioxide takes place by osmosis.
In the tissues of the body wherever work is done the process of burning or
oxidation must take place, for by such means only is the energy necessary
to do the work released. Food in the blood is taken to the muscle cells or
other cells of the body and there oxidized. The products of the
burning--carbon dioxide--and any other organic wastes given off from the
tissues must be eliminated from the body. As we know, the carbon dioxide
passes off through the lungs and to some extent through the skin of the
frog, while the nitrogenous wastes, poisons which must be taken from the
blood, are eliminated from it in the kidneys.
Change of Form in Development of the Frog.--Not all vertebrates develop
directly into an adult. The frog, for example, changes its form completely
before it becomes an adult. This change in form is known as a
_metamorphosis_. Let us examine the development of the common leopard frog.
[Illustration: Development of a frog. 1, two cell stage; 2, four cell
stage; 3, 8 cells are formed, notice the upper cells are smaller; in (4)
the lower cells are seen to be much larger because of the yolk; 5, the egg
has continued to divide and has formed a gastrula; 6, 7, the body is
lengthening, head is seen at the right hand end; 8, the young tadpole with
external gills; 9, 10, the gills are internal, hind legs beginning to form;
11, the hind legs show plainly; 12, 13, 14, later stages in development;
15, the adult frog. Figures 1, 2, 3, 4, 5, 6, and 7 are very much enlarged.
(Drawn after Leukart and Kny by Frank M. Wheat.)]
The eggs of this frog are laid in shallow water in the early spring. Masses
of several hundred, which may be found attached to twigs or other supports
under water, are deposited at a single laying. Immediately before leaving
the body of the female they receive a coating of jellylike material, which
swells up after the eggs are laid. Thus they are protected from the attack
of fish or other animals which might use them as food. The upper side of
the egg is dark, the light-colored side being weighted down with a supply
of yolk (food). The fertilized egg soon segments (divides into many cells),
and in a few days, if the weather is warm, these eggs have each grown into
an oblong body which shows the form of a tadpole. Shortly after the tadpole
wriggles out of the jellylike case and begins life outside the egg. At
first it remains attached to some water weed by means of a pair of
suckerlike projections; later a mouth is formed, and the tadpole begins to
feed upon algæ or other tiny water plants. At this time, about two weeks
after the eggs were laid, gills are present on the outside of the body.
Soon after, the external gills are replaced by gills which grow out under a
fold of the skin which forms an operculum somewhat as in the fish. Water
reaches the gills through the mouth and passes out through a hole on the
left side of the body. As the tadpole grows larger, legs appear, the hind
legs first, although for a time locomotion is performed by means of the
tail. In the leopard frog the change from the egg to adult is completed in
one summer. In late July or early August, the tadpole begins to eat less,
the tail becomes smaller (being absorbed into other parts of the body), and
before long the transformation from the tadpole to the young frog is
complete. In the green frog and bullfrog the metamorphosis is not completed
until the beginning of the second summer. The large tadpoles of such forms
bury themselves in the soft mud of the pond bottom during the winter.
Shortly after the legs appear, the gills begin to be absorbed, and lungs
take their place. At this time the young animal may be seen coming to the
surface of the water for air. Changes in the diet of the animal also occur;
the long, coiled intestine is transformed into a much shorter one. The
animal, now insectivorous in its diet, becomes provided with tiny teeth and
a mobile tongue, instead of keeping the horny jaws used in scraping off
algæ. After the tail has been completely absorbed and the legs have become
full grown, there is no further structural change, and the metamorphosis is
complete.
[Illustration: At the left is a hen's egg, opened to show the embryo at the
center (the spot surrounded by a lighter area). At the right is an English
sparrow one day after hatching.]
Development of Birds.--The white of the hen's egg is put on during the
passage of the real egg (which is in the yolk or yellow portion) to the
outside of the body. Before the egg is laid a shell is secreted over its
surface. If the fertilized egg of a hen be broken and carefully examined,
on the surface of the yolk will be found a little circular disk. This is
the beginning of the growth of an _embryo_ chick. If a series of eggs taken
from an incubator at periods of twenty-four hours or less apart were
examined, this spot would be found at first to increase in size; later the
little embryo would be found lying on the surface. Still later small blood
vessels could be made out reaching into the yolk for food, the tiny heart
beating as early as the second day of incubation. After about three weeks
of incubation the little chick hatches; that is, breaks the shell, and
emerges in almost the same form as the adult.
[Illustration: The embryo (_e_) of a mammal, showing the absorbing organ in
black, the branch-like processes which absorb blood from the mother being
shown at (_v_); _ct_, the tube connecting the embryo with the absorbing
organ or placenta.]
Development of a Mammal.--In mammals after fertilization the egg undergoes
development within the body of the mother. Instead of blood vessels
connecting the embryo with the yolk as in the chick, here the blood vessels
are attached to an absorbing organ, known as the _placenta_. This structure
sends branch-like processes into the wall of the _uterus_ (the organ which
holds the embryo) and absorbs nourishment and oxygen by osmosis from the
blood of the mother. After a length of time which varies in different
species of mammals (from about three weeks in a guinea pig to twenty-two
months in an elephant), the young animal is expelled by muscular
contraction of the uterus, or is born. The young, usually, are born in a
helpless condition, then nourished by milk furnished by the mother until
they are able to take other food. Thus we see as we go higher in the scale
of life fewer eggs formed, but those few eggs are more carefully protected
and cared for by the parents. The chances of their growth into adults are
much greater than in the cases when many eggs are produced.
REFERENCE BOOKS
ELEMENTARY
Hunter, _Laboratory Problems in Civic Biology_. American
Book Company.
Bigelow, _Introduction to Biology_. The Macmillan Company.
Cornell _Nature Study Leaflets_. Bulletins XVI, XVII.
Davison, _Practical Zoölogy_, pages 185-199. American Book
Company.
Hodge, _Nature Study and Life_, Chaps. XVI, XVII. Ginn and
Company.
Sharpe, _Laboratory Manual_, pp. 195, 204-209. American Book
Company.
ADVANCED
Dickerson, _The Frog Book_. Doubleday, Page and Company.
Holmes, _The Biology of the Frog_. The Macmillan Company.
Jordan, _Fishes_. Henry Holt and Company.
Morgan, _The Development of the Frog's Egg_. The Macmillan
Company.
Needham, _General Biology_. Comstock Publishing Company.
XVII. HEREDITY, VARIATION, PLANT AND ANIMAL BREEDING
_Problems.--To determine what makes the offspring of animals or plants
tend to be like their parents._
_To determine what makes the offspring of animals and plants
differ from their parents._
_To learn about some methods of plant and animal breeding._
_(a) By selection._
_(b) By hybridizing._
_(c) By other methods._
_To learn about some methods of improving the human race._
_(a) By eugenics._
_(b) By euthenics._
SUGGESTIONS FOR LABORATORY WORK
_Laboratory exercise._--On variation and heredity among members of a
class in the schoolroom.
_Laboratory exercise._--On construction of curve of variation in
measurements from given plants or animals.
_Laboratory demonstration._--Stained egg cells (_ascaris_) to show
chromosomes.
_Laboratory demonstrations._--To illustrate the part played in plant
or animal breeding by
(_a_) selection.
(_b_) hybridizing.
(_c_) budding and grafting.
_Laboratory demonstration._--From charts to illustrate how human
characteristics may be inherited.
HEREDITY AND EUGENICS
Heredity and what it Means.--As I look over the faces of the boys in my
class I notice that each boy seems to be more or less like each other boy
in the class; he has a head, body, arms, and legs, and even in minor ways
he resembles each of the other boys in the room. Moreover, if I should ask
him I have no doubt but that he would tell me that he resembled in many
respects his mother or father. Likewise if I should ask his _parents_ whom
he resembled, they would say, "I can see his grandmother or his grandfather
in him."
This wonderful force which causes the likeness of the child to its parents
and to _their_ parents we call _heredity_. Heredity causes the plants as
well as animals to be like their parents. If we trace the workings of
heredity in our own individual case, we will probably find that we are
molded like our ancestors not only in physical characteristics but in
mental qualities as well. The ability to play the piano or to paint is
probably as much a case of inheritance as the color of our eyes or the
shape of our nose. We are a complex of physical and mental characters,
received in part from all our ancestors.
[Illustration: Variations in the Catalpa caterpillar. (Photographed,
natural size, by Davison.)]
Variation.--But I notice another thing; no boy in the class before me is
_exactly_ like any other boy, even twins having minute differences. In this
wonderful mold of nature each one of us tends to be slightly different from
his or her parents. Each plant, each animal, varies to a greater or lesser
degree from its immediate ancestors and may vary to a very great degree.
This factor in the lives of plants and animals is called _variation_.
Heredity and variation are the cornerstones on which all the work in the
improvement of plants and animals, including man himself, are built.
The Bearers of Heredity.--We have seen that somewhere in every living cell
is a structure known as a nucleus. In this nucleus, which is a part of the
living matter of the cell, are certain very minute structures always
present, known as _chromosomes_. These chromosomes (so called because they
take up color when stained) are believed to be the structures which contain
the _determiners_ of the qualities which may be passed from parent plant to
offspring or from animal to animal; in other words, the qualities that are
inheritable (see page 252).
The Germ Cells.--But it has been found that certain cells of the body, the
egg and the sperm cells, before uniting contain only half as many
chromosomes as do the body cells. In preparing for the process of
fertilization, half of these elements have been eliminated, so that when
the egg and sperm cell are united they will have the full number of
chromosomes that the other cells have.
If the chromosomes carry the determiners of the characters which are
inheritable, then it is easy to see that a fertilized egg must contain an
equal number of chromosomes from the bodies of each parent. Consequently
characteristics from each parent are handed down to the new individual.
This seems to be the way in which nature succeeds in obtaining variation,
by providing cell material from two different individuals.
Offspring are Part of their Ancestors.--We can see that if you or I receive
characteristics from our parents and they received characteristics from
their parents, then we too must have some of the characteristics of the
grandparents, and it is a matter of common knowledge that each of us does
have some trait or lineament which can be traced back to our grandfather or
grandmother. Indeed, as far back as we are able to go, ancestors have added
something.
[Illustration: COMPARISON OF SEXUAL AND ASEXUAL CELL REPRODUCTION]
Charles Darwin and Natural Selection.--The great Englishman Charles Darwin
was one of the first scientists to realize how this great force of heredity
applied to the development or evolution of plants and animals. He knew that
although animals and plants were like their ancestors, they also tended to
vary. In nature, the variations which best fitted a plant or animal for
life in its own environment were the ones which were handed down because
those having variations which were not fitted for life in that particular
environment would die. Thus nature seized upon favorable variations and
after a time, as the descendants of each of these individuals also tended
to vary, a new species of plant or animal, fitted for the place it had to
live in, would be gradually evolved.
Mutations.--Recently a new method of variation has been discovered by a
Dutch naturalist, named Hugo de Vries. He found that new species of plants
and animals arise suddenly by "mutations" or steps. This means that new
species instead of arising from very slight variations, continuing during
long periods of years (as Darwin believed), might arise very suddenly as a
very great variation which would at once breed true. It is easily seen that
such a condition would be of immense value to breeders, as new plants or
animals quite unlike their parents might thus be formed and perpetuated. It
will be one of the future problems of plant and animal breeders to isolate
and breed "mutants," as such organisms are called.
[Illustration: Improvement in corn by selection. To the left, the corn
improved by selection from the original type at the right.]
Artificial Selection.--Darwin reasoned that if nature seized upon favorable
variants, then man, by selecting the variations he wanted, could form new
varieties of plants or animals much more quickly than nature. And so to-day
plant or animal breeders _select_ the forms having the characters they wish
to perpetuate and breed them together. This method used by plant and animal
breeders is known as _selection_.
Selective Planting.--_By selective planting we mean choosing the best
plants and planting the seed from these plants with a view of improving the
yield._ In doing this we must not necessarily select the most perfect
fruits or grains, but must select seeds from the _best plants_. A wheat
plant should be selected not from its yield alone, but from its ability to
stand disease and other unfavorable conditions. In 1862 a Mr. Fultz, of
Pennsylvania, found three heads of beardless or bald wheat while passing
through a large field of bearded wheat. These were probably _mutants_ which
had lost the chaff surrounding the kernel. Mr. Fultz picked them out, sowed
them by themselves, and produced a quantity of wheat now known favorably
all over the world as the Fultz wheat. In selecting wheat, for example, we
might breed for a number of different characters, such as more starch, or
more protein in the grain, a larger yield per acre, ability to stand cold
or drought or to resist plant disease. Each of these characters would have
to be sought for separately and could only be obtained after long and
careful breeding. The work of Mendel (see page 257) when applied to plant
breeding will greatly shorten the time required to produce better plants of
a given kind. By careful seed selection, some Western farmers have
increased their wheat production by 25 per cent. This, if kept up all over
the United States, would mean over $100,000,000 a year in the pockets of
the farmers.
Hybridizing.--We have already seen that pollen from one flower may be
carried to another of the same species, thus producing seeds. If pollen
from one plant be placed on the pistil of another of an _allied_ species or
variety, fertilization _may_ take place and new plants be eventually
produced from the seeds. This process is known as _hybridizing_, and the
plants produced by this process known as _hybrids_.
[Illustration: In hybridizing, all of the flower is removed at the line
(_W_) except the pistil (_P_). Then pollen from another flower of a nearly
related kind is placed on the pistil and the pollinated flower covered up
with a paper bag. Can you explain why?]
Hybrids are extremely variable, rarely breed from seeds, and often are
apparently quite unlike either parent plant. They must be grown for several
years, and all plants that do not resemble the desired variety must be
killed off, if we expect to produce a hybrid that will breed more plants
like itself. Luther Burbank, the great hybridizer of California, destroys
tens of thousands of plants in order to get one or two with the characters
which he wishes to preserve. Thus he is yearly adding to the wealth of this
country by producing new plants or fruits of commercial value. A number of
years ago he succeeded in growing a new variety of potato, which has
already enriched the farmers of this country about $20,000,000. One of his
varieties of black walnut trees, a very valuable hard wood, grows ten to
twelve times as rapidly as ordinary black walnuts. With lumber yearly
increasing in price, a quick growing tree becomes a very valuable
commercial product. Among his famous hybrids are the plumcot, a cross
between an apricot and a plum, his numerous varieties of berries and his
splendid "Climax" plum, the result of a cross between a bitter Chinese plum
and an edible Japanese plum. But none of Burbank's products grow from
seeds; they are all produced _asexually_, from hybrids by some of the
processes described in the next paragraph.
The Department of Agriculture and its Methods.--The Department of
Agriculture is also doing splendid work in producing new varieties of
oranges and lemons, of grain and various garden vegetables. The greatest
possibilities have been shown by department workers to be open to the
farmer or fruit grower through hybridizing, and by budding, grafting, or
slipping.
[Illustration: Steps in budding. _a_, twig having suitable buds to use;
_b_, method of cutting out bud; _c_, how the bark is cut; _d_, how the bark
is opened; _e_, inserting the bud; _f_, the bud in place; _g_, the bud
properly bound in place.]
_Budding._--If a given tree, for example, produces a kind of fruit which is
of excellent quality, it is possible sometimes to attach parts of the tree
to another strong tree of the same species that may not bear good fruit.
This is done by _budding_. A T-shaped incision is cut in the bark; a bud
from the tree bearing the desired fruit is placed in the cut and bound in
place. When a shoot from the embedded bud grows out the following spring,
it is found to have all the characters of the tree from which it was taken.
[Illustration: Steps in tongue grafting. _a_, the two branches to be
formed; _b_, a tongue cut in each; _c_, fitted together; _d_, method of
wrapping.]
Grafting.--Of much the same nature is grafting. Here, however, a small
portion of the stem of the closely allied tree is fastened into the trunk
of the growing tree in such a manner that the two cut layers just under the
bark will coincide. This will allow of the passage of food into the grafted
part and insure the ultimate growth of the twig. Grafting and budding are
of considerable economic value to the fruit grower, as it enables him to
produce at will, trees bearing choice varieties of fruit.[34]
Footnote 34: For full directions for budding and grafting,
see Goff and Mayne, _First Principles of Agriculture_, Chap.
XIX, Mayne and Hatch, _High School Agriculture_, pp.
159-165, or Hodge, _Nature Study and Life_, pages 169-179.
Other Methods.--Other methods of plant propagation are by means of runners,
as when strawberry plants strike root from long stems that run along the
ground; layering, where roots may develop on covered up branches of
blackberry or raspberry plants; slips, roots developing from stems which
are cut off and placed in moist sand; from tubers, as in planting potatoes;
and by means of bulbs, as the tulip or hyacinth. All of the above means of
propagation are asexual and are of importance in our problem of plant
breeding.
[Illustration: Plant breeding plots. (Minnesota Experiment Station.)]
The Work of Gregor Mendel.--Fifty years ago, an Austrian monk, Gregor
Mendel, found in breeding garden peas that these plants passed on certain
_fixed characters_, as the shape of the seed, the color of the pod when
ripe, and others, and that when two pea plants of different characters were
crossed, one of these characters would be likely to appear in the offspring
of the second generation in the ratio of three to one. Such characters as
would appear to the exclusion of others in the first crossing of the plants
were called _dominant_, the ones not appearing, _recessive_
characteristics. When these seeds were again sown the ones bearing a
recessive characteristic would produce only peas with this recessive
characteristic, but the ones with a dominant characteristic might give rise
to a pure dominant or to offspring having partly a dominant and partly a
recessive character; pure dominants being to the mixed offspring in the
ratio of 1 to 2. The pure dominants if bred with others like themselves
would produce only pure dominants, but the cross breeds would again produce
mixed offspring of three kinds in the ratio of one dominant to two cross
breeds and one recessive. The feature of this work that interests us is
that _unit_ characters are passed along by heredity in the germ cells
_pure_, that is, unchanged, from one generation to another, and
independently of each other.
[Illustration: Illustration of Mendel's Law.]
Determiners of Character.--A child then resembles his parents in some
definite particulars because certain _determiners_ of characters have been
present in the germ cells of one of the parents. If the determiner of a
certain character is _absent_ from the germ cells of both parents, it will
be _absent_ in _all_ of their offspring.
These discoveries of Mendel are of the greatest importance in plant and
animal breeding because they enable the breeder to isolate certain
characters and by proper selection to breed varieties which have these
desired characters, instead of waiting for a _chance_ union of the desired
characters by nature.
Animal Breeding.--It has been pointed out that the domestication of wild
animals, the horse, cattle, sheep, goats, and the dog, marked a great
advance in civilization in the history of the earth's peoples. As the young
of these animals came to be bred in captivity the peoples owning them would
undoubtedly pick out the strongest and best of the offspring, killing off
the others for food. Thus they came unconsciously to select and aid nature
in producing a stronger and better stock. Later man began to recognize
certain characters that he wished to have in horses, dogs, or cattle, and
so by slow processes of breeding and "crossing" or hybridizing one nearly
allied form with another the numerous groups of domesticated animals began
to appear.
[Illustration: What has resulted from artificial selection among dogs.
(After Romanes.)]
In Darwin's time animal breeding was so far advanced that he got his ideas
of selection by nature in evolution from the artificial selection practiced
by animal breeders. A glance at the pictures will give some idea of the
changes that have taken place in the form of some animals since man began
to breed them a few thousand years ago.
[Illustration: The four-toed ancestor of the present horse, restored from a
study of its fossil skeleton. (After Knight in American Museum of Natural
History.)]
Some Domesticated Animals.--Our domesticated dogs are descended from a
number of wolflike forms in various parts of the world. All the present
races of cats, on the other hand, seem to be traced back to Egypt. Modern
horses are first noted in Europe and Asia, but far older forms flourished
on the earth in former geologic periods. It is interesting to note that
America was the original home of the horse, although at the time of the
earliest explorers the horse was unknown here, the wild horse of the
Western plains having arisen from horses introduced by the Spaniards. Long
ages ago, the first ancestors of the horse were probably little animals
about the size of a fox. The earliest horse we have knowledge of had four
toes on the fore and three toes on the hind foot. Thousands of years later
we find a larger horse, the size of a sheep, with a three-toed foot. By
gradual changes, caused by the tendency of the animals to vary and by the
action of the surroundings upon the animal in preserving these variations,
there was eventually produced our present horse, an animal with legs
adapted for rapid locomotion, with feet particularly fitted for the life in
open fields, and with teeth which serve well to seize and grind herbage.
Knowledge of this sort was also used by Darwin to show that constant
changes in the form of animals have been taking place since life began on
the earth.
The horse, which for some reason disappeared in this country, continued to
exist in Europe, and man, emerging from his early savage condition, began
to make use of the animal. We know the horse was domesticated in early
Biblical times, and that he soon became one of man's most valued servants.
In more recent times, man has begun to change the horse by breeding for
certain desired characteristics. In this manner have been established and
improved the various types of horses familiar to us as draft horses, coach
horses, hackneys, and the trotters.
It is needless to say that all the various domesticated animals have been
tremendously changed in a similar manner since civilized man has come to
live on the earth. When we realize the very great amount of money invested
in domesticated animals; that there are over 60,000,000 each of sheep,
cattle, and swine and over 20,000,000 horses owned in this country, then we
may see how very important a part the domestic animals play in our lives.
Improvement of Man.--If the stock of domesticated animals can be improved,
it is not unfair to ask if the health and vigor of the future generations
of men and women on the earth might not be improved by applying to them the
laws of selection. This improvement of the future race has a number of
factors in which we as individuals may play a part. These are personal
hygiene, selection of healthy mates, and the betterment of the environment.
Personal Hygiene.--In the first place, good health is the one greatest
asset in life. We may be born with a poor bodily machine, but if we learn
to recognize its defects and care for it properly, we may make it do its
required work effectively. If certain muscles are poorly developed, then by
proper exercise we may make them stronger. If our eyes have some defect, we
can have it remedied by wearing glasses. If certain drugs or alcohol lower
the efficiency of the machine, we can avoid their use. With proper _care_ a
poorly developed body may be improved and do effective work.
Eugenics.--When people marry there are certain things that the individual
as well as the race should demand. The most important of these is freedom
from germ diseases which might be handed down to the offspring.
Tuberculosis, syphilis, that dread disease which cripples and kills
hundreds of thousands of innocent children, epilepsy, and feeble-mindedness
are handicaps which it is not only unfair but criminal to hand down to
posterity. The science of being well born is called _eugenics_.
[Illustration: In this and the following diagrams the circle represents a
female, the square a male. N means normal; F means feeble-minded; A,
alcoholic; T, tubercular; _Sx_, sexually immoral; _Sy_, having syphilis.
This chart shows the record of a certain family for three generations. A
normal woman married an alcoholic and tubercular man. He must have been
feeble-minded also as two of his children were born feeble-minded. One of
these children married another feeble-minded woman, and of their five
children two died in infancy and three were feeble-minded. (After
Davenport.)]
[Illustration: This chart shows that feeble-mindedness is a characteristic
sure to be handed down in a family where it exists. The feeble-minded woman
at the top left of the chart married twice. The first children from a
normal father are all normal, but the other children from an alcoholic
father are all feeble-minded. The right-hand side of the chart shows a
terrible record of feeble-mindedness. Should feeble-minded people be
allowed to marry? (After Davenport.)]
The Jukes.--Studies have been made on a number of different families in
this country, in which mental and moral defects were present in one or both
of the original parents. The "Jukes" family is a notorious example. The
first mother is known as "Margaret, the mother of criminals." In
seventy-five years the progeny of the original generation has cost the
state of New York over a million and a quarter of dollars, besides giving
over to the care of prisons and asylums considerably over a hundred
feeble-minded, alcoholic, immoral, or criminal persons. Another case
recently studied is the "Kallikak" family.[35] This family has been traced
back to the War of the Revolution, when a young soldier named Martin
Kallikak seduced a feeble-minded girl. She had a feeble-minded son from
whom there have been to the present time 480 descendants. Of these 33 were
sexually immoral, 24 confirmed drunkards, 3 epileptics, and 143
_feeble-minded_. The man who started this terrible line of immorality and
feeble-mindedness later married a normal Quaker girl. From this couple a
line of 496 descendants have come, with _no_ cases of feeble-mindedness.
The evidence and the moral speak for themselves!
Footnote 35: The name Kallikak is fictitious.
Parasitism and its Cost to Society.--Hundreds of families
such as those described above exist to-day, spreading disease,
immorality, and crime to all parts of this country. The cost to
society of such families is very severe. Just as certain animals
or plants become parasitic on other plants or animals, these families
have become parasitic on society. They not only do harm to others
by corrupting, stealing, or spreading disease, but they are actually
protected and cared for by the state out of public money. Largely
for them the poorhouse and the asylum exist. They take from
society, but they give nothing in return. They are true parasites.
The Remedy.--If such people were lower animals, we would
probably kill them off to prevent them from spreading. Humanity
will not allow this, but we do have the remedy of separating the
sexes in asylums or other places and in various ways preventing
intermarriage and the possibilities of perpetuating such a low and
degenerate race. Remedies of this sort have been tried successfully
in Europe and are now meeting with success in this country.
Blood Tells.--Eugenics show us, on the other hand, in a study
of the families in which are brilliant men and women, the fact that
the descendants have received the _good_ inheritance from their
ancestors. The following, taken from Davenport's _Heredity in
Relation to Eugenics_, illustrates how one family has been famous
in American History.
In 1667 Elizabeth Tuttle, "of strong will, and of extreme intellectual
vigor, married Richard Edwards of Hartford, Conn., a man of high repute and
great erudition. From their one son descended another son, Jonathan
Edwards, a noted divine, and president of Princeton College. Of the
descendants of Jonathan Edwards much has been written; a brief catalogue
must suffice: Jonathan Edwards, Jr., president of Union College; Timothy
Dwight, president of Yale; Sereno Edwards Dwight, president of Hamilton
College; Theodore Dwight Woolsey, for twenty-five years president of Yale
College; Sarah, wife of Tapping Reeve, founder of Litchfield Law School,
herself no mean lawyer; Daniel Tyler, a general in the Civil War and
founder of the iron industries of North Alabama; Timothy Dwight, second,
president of Yale University from 1886 to 1898; Theodore William Dwight,
founder and for thirty-three years warden of Columbia Law School; Henrietta
Frances, wife of Eli Whitney, inventor of the cotton gin, who, burning the
midnight oil by the side of her ingenious husband, helped him to his
enduring fame; Merrill Edwards Gates, president of Amherst College;
Catherine Maria Sedgwick of graceful pen; Charles Sedgwick Minot, authority
on biology and embryology in the Harvard Medical School; Edith Kermit
Carow, wife of Theodore Roosevelt; and Winston Churchill, the author of
_Coniston_ and other well-known novels."
[Illustration: This record shows the inheritance of artistic ability (black
circles and squares). (After Davenport.)]
Of the daughters of Elizabeth Tuttle distinguished descendants also came.
Robert Treat Paine, signer of the Declaration of Independence; Chief
Justice of the United States Morrison R. Waite; Ulysses S. Grant and Grover
Cleveland, presidents of the United States. These and many other prominent
men and women can trace the characters which enabled them to occupy the
positions of culture and learning they held back to Elizabeth Tuttle.
Euthenics.--Euthenics, the betterment of the environment, is another
important factor in the production of a stronger race. The strongest
physical characteristics may be ruined if the surroundings are unwholesome
and unsanitary. The slums of a city are "at once symptom, effect, and cause
of evil." A city which allows foul tenements, narrow streets, and crowded
slums to exist will spend too much for police protection, for charity, and
for hospitals.
Every improvement in surroundings means improvement of the chances of
survival of the race. In the spring of 1913 the health department and
street-cleaning department of the city of New York coöperated to bring
about a "clean up" of all filth, dirt, and rubbish from the houses,
streets, and vacant lots in that city. During the summer of 1913 the health
department reported a smaller percentage of deaths of babies than ever
before. We must draw our own conclusions. Clean streets and houses, clean
milk and pure water, sanitary housing, and careful medical inspection all
do their part in maintaining a low rate of illness and death, thus reacting
upon the health of the citizens of the future. It will be the purpose of
the following pages to show how we may best care for our own bodies and how
we may better the environment in which we are placed.
REFERENCE BOOKS
ELEMENTARY
Hunter, _Laboratory Problems in Civic Biology_. American
Book Company.
Bailey, _Plant Breeding_. Macmillan and Company.
Harwood, _New Creations in Plant Life_. The Macmillan
Company.
Jordan, _The Heredity of Richard Roe_. American Unitarian
Association.
Sharpe, _Laboratory Manual_, pp. 64-72, 345-347. American
Book Company.
ADVANCED
Allen, _Civics and Health_. Ginn and Company.
Coulter, Castle, East, Tower, and Davenport, _Heredity and
Eugenics_. University of Chicago Press.
Davenport, _Heredity in Relation to Eugenics_. Henry Holt
and Company.
De Vries, _Plant Breeding_. Open Court Publishing Company.
Goddard, _The Kallikak Family_. The Macmillan Company.
Kellicott, _The Social Direction of Human Evolution_.
Appleton Company.
Punnet, _Mendelism_. The Macmillan Company.
Richards, Helen M., _Euthenics, the Science of Controllable
Environment_.
Walter, _Genetics_. The Macmillan Company.
XVIII. THE HUMAN MACHINE AND ITS NEEDS
_Problem.--To obtain a general understanding of the parts and uses of the
bodily machine._
LABORATORY SUGGESTIONS
_Demonstration._--Review to show that the human body is a
complex of cells.
_Laboratory demonstration_ by means of (_a_) human skeleton
and (_b_) manikin to show the position and gross structure
of the chief organs of man.
Man and his Environment.--In the last chapter we saw that one factor in the
improvement of man lies in giving him better surroundings. It will be the
purpose of the following chapters to show how man is fitted to live in the
environment in which he is placed. He comes in contact with air, light,
water, soil, food, and shelter which make his somewhat artificial
environment; he must adapt himself to get the best he can out of this
environment.
The Needs of Living Things.--We have already found that the primary needs
of plants and animals are the same. They both need food, they both need to
digest their food and to have it circulate in a fluid form to the cells
where it will be used. They both need oxygen so as to release the energy
locked up in their food. And they both need to reproduce so that their kind
may be continued on the earth. What is true of plants and other animals is
true of man.
The Needs of Simple and Complex Animals the Same.--The simplest animal, a
single cell, has the same needs as the most complex. The _cell_ paramoecium
feeds, digests, oxidizes its food, and releases energy. The _cells_ of the
human body built up into tissues have the same needs and perform the same
functions as the paramoecium. It is the _cells_ of the body working
together in groups as tissues and organs that make the complicated actions
of man possible. Division of labor has arisen because of the complex needs
and work of the organism.
[Illustration: The human body seen from the side in longitudinal section.]
The Human Body a Machine.--In all animals, and the human animal is no
exception, the body has been likened to a machine in that it turns over the
_latent_ or potential energy stored up in food into _kinetic_ energy
(mechanical work and heat), which is manifested when we perform work. One
great difference exists between an engine and the human body. The engine
uses fuel unlike the substance out of which it is made. The human body, on
the other hand, uses for fuel the same substances out of which it is
formed; it may, indeed, use part of its own substance for food. It must as
well do more than purely mechanical work. The human organism must be so
delicately adjusted to its surroundings that it will react in a ready
manner to stimuli from without; it must be able to utilize its fuel (food)
in the most economical manner; it must be fitted with machinery for
transforming the energy received from food into various kinds of work; it
must properly provide the machine with oxygen so that the fuel will be
oxidized, and the products of oxidation must be carried away, as well as
other waste materials which might harm the effectiveness of the machine.
Most important of all, the human machine must be able to repair itself.
In order to understand better this complicated machine, the human body, let
us briefly examine the structure of its parts and thus get a better idea of
the interrelation of these parts and of their functions.
The Skin.--Covering the body is a protective structure called the skin.
Covered on the outside with dead cells, yet it is provided with delicate
sense organs, which give us perception of touch, taste, smell, pressure,
and temperature. It also aids in getting wastes out of the body by means of
its sweat glands and plays an important part in equalizing the temperature
of the body.
[Illustration: Skeleton of a man. _CR._, cranium; _CL._, clavicle; _ST._,
sternum; _H._, humerus; _V.C._, vertebral column; _R._, radius; _U._, ulna;
_P._, pelvic girdle; _C._, carpals; _M._, metacarpals; _Ph._, phalanges;
_F._, femur; _Fi._, fibula; _T._, tibia; _Tar._, tarsals; _MT._,
metatarsals.]
Bones and Muscles.--The body is built around a framework of bones. These
bones, which are bound together by tough _ligaments_, fall naturally into
two great groups, the bones of the body proper, vertebral column, ribs,
breast bone, and skull, which form the _axial_ skeleton, and the
appendages, two sets of bones which form the framework of the arms and
legs, which with the bones which attach them to the axial skeleton form the
_appendicular_ skeleton.
To the bones are attached the muscles of the body. Movement is accomplished
by contraction of muscles, which are attached so as to cause the bones to
act as levers. Bones also protect the nervous system and other delicate
organs. They also help to give form and rigidity to the body.
[Illustration: Diagram showing action of biceps muscle. _a_, contracted;
_b_, extended; _h_, humerus; _s_, scapula.]
Hygiene of Muscles and Bones.--Young people especially need to know how to
prevent certain defects which are largely the result of bad habits of
posture. Standing erect is an example of a good habit, round shoulders a
bad habit of this sort. The habit of a wrong position of bones and muscles
once formed is very hard to correct. This can best be done by certain
corrective exercises at home or in the gymnasium.
Round shoulders is most common among people whose occupation causes them to
stoop. Drawing, writing, and a wrong position when at one's desk are among
the causes. Exercises which strengthen the back muscles and cause the head
to be kept erect are helpful in forming the habit of erect carriage.
Slight curvature of the spine either backward or forward is helped most by
exercises which tend to straighten the body, such as stretching up with the
hands above the head. Lateral curvature of the spine, too often caused by a
"hunched-up" position at the school desk, may also be corrected by
exercises which tend to lengthen the spinal column.
[Illustration: Three classes of levers in the human body; bones and muscles
act together. _A_, a lever of the first class; _B_, a lever of the second
class; _C_, a lever of the third class.]
It is the duty of every girl and boy to have good posture and erect
carriage, not only because of the better state of health which comes with
it, but also because one's self-respect demands that each one of us makes
the best of the gifts that nature has given us. An erect head, straight
shoulders, and elastic carriage go far toward making their owner both liked
and respected.
[Illustration: Bad posture in the schoolroom may cause permanent injury to
the spine.]
Other Body Structures.--In spaces between the muscles are found various
other structures,--blood vessels, which carry blood to and from the great
pumping station, the heart, and thence to all parts of the body; connective
tissue, which holds groups of muscle or other cells together; fat cells,
scattered in various parts of the body; various gland cells, which
manufacture enzymes; and the cells of the nervous system, which aid in
directing the body parts.
Body Cavity.--Within the body is a cavity, which in life is almost
completely filled with various organs. A thin wall of muscle called the
_diaphragm_ divides the body cavity into two unequal spaces. In the upper
space are found the _heart_ and _lungs_, in the lower, the digestive tract
with its glands, the _liver_, _kidneys_, and other structures (see page 267).
Digestion, Absorption, and Excretion.--Running through the body is a food
tube in which undigested food is placed and from which digested or liquid
food is absorbed into the blood so that the cells of the various organs
which do the work may receive food. Emptying into this food tube are
various groups of gland cells, which pour digestive fluids over the solid
foods, thus aiding in changing them to liquids. Solid wastes are passed out
through the posterior end of the food tube, while liquid wastes are
excreted by means of glands called _kidneys_.
Work done by Cells.--Food, prepared in the digestive tract, and oxygen from
the lungs are taken by the blood to the cells. Bathed in liquid food, the
cells do their work; they promote the oxidization of food and the exchange
of carbon dioxide for oxygen in the blood, while other wastes of the cells
are given off, to pass eventually through the kidneys and out of the body.
The Nervous System.--The smooth working of the bodily machine is due to
another set of structures which direct the working of the parts so that
they will act in unison. This director is the nervous system. We have seen
that, in the simplest of animals, one cell performs the functions necessary
to its existence. In the more complex animals, where groups of cells form
tissues, each having a different function, a nervous system is developed.
_The functions of the human nervous system are:_ (1) _the providing of man
with sensation, by means of which he gets in touch with the world about
him;_ (2) _the connecting of organs in different parts of the body so that
they act as a united and harmonious whole;_ (3) _the giving to the human
being a will, a provision for thought._ Coöperation in word and deed is the
end attained. We are all familiar with examples of the coöperation of
organs. You see food; the thought comes that it is good to eat; you reach
out, take it, raise it to the mouth; the jaws move in response to your
will; the food is chewed and swallowed. While digestion and absorption of
the food are taking place, the nervous system is still in control. The
nervous system also regulates pumping of blood over the body, respiration,
secretion of glands, and, indeed, every bodily function. Man is the highest
of all animals because of the extreme development of the nervous system.
Man is the thinking animal, and as such is master of the earth.
REFERENCE READING FOR THIS AND SUCCEEDING CHAPTERS ON HUMAN BIOLOGY
ELEMENTARY
Hunter, _Laboratory Problems in Civic Biology_. American
Book Company.
Davison, _The Human Body and Health_. American Book Company.
Gulick, _The Gulick Hygiene Series_. Ginn and Company.
Overton, _General Hygiene_. American Book Company.
Ritchie, _Human Physiology_. World Book Company.
Sharpe, _Laboratory Manual in Botany_, pages 218-225.
American Book Company.
ADVANCED
Halliburton, _Kirk's Handbook of Physiology_. P. Blakiston's
Son and Company.
Hough and Sedgwick, _The Human Mechanism_. Ginn and Company.
Howell, _Physiology_, 3d edition. W. B. Saunders Company.
Schafer, _Textbook of Physiology_. The Macmillan Company.
Stiles, _Nutritional Physiology_. W. B. Saunders Company.
Verworn, _General Physiology_. The Macmillan Company.
XIX. FOODS AND DIETARIES
_Problems.--A study of foods to determine:--_
_(a) Their nutritive value._
_(b) The relation of work, environment, age, sex, and
digestibility of foods to diet._
_(c) Their relative cheapness._
_(d) The daily Calorie requirement._
_(e) Food adulteration._
_(f) The relation of alcohol to the human system._
LABORATORY SUGGESTIONS
_Laboratory exercise._--Composition of common foods. The
series of food charts supplied by the United States
Department of Agriculture makes an excellent basis for a
laboratory exercise to determine common foods rich in (_a_)
water, (_b_) starch, (_c_) sugar, (_d_) fats or oils, (_e_)
protein, (_f_) salts, (_g_) refuse.
_Demonstration._--Method of using bomb calorimeter.
_Laboratory and home exercise._--To determine the best
individual balanced dietary (using standard of Atwater,
Chittenden, or Voit) as determined by the use of the
100-Calorie portion.
_Demonstration._--Tests for some common adulterants.
_Demonstration._--Effect of alcohol on protein, _e.g._ white
of egg.
_Demonstration._--Alcohol in some patent medicines.
_Demonstration._--Patent medicines containing acetanilid.
Determination of acetanilid.
Why we Need Food.--A locomotive engine takes coal, water, oxygen, from its
environment. A living plant or animal takes organic food, water, and oxygen
from its environment. Both the living and nonliving machine do the same
thing with this fuel or food. They oxidize it and release the energy in it.
But the living organism in addition may use the food to repair parts that
have broken down or even build new parts. _Thus food may be defined as
something that releases energy or that forms material for the growth or
repair of the body of a plant or animal._ The millions of cells of which
the body is composed must be given material which will form more living
matter or material which can be oxidized to release energy when muscle
cells move, or gland cells secrete, or brain cells think.
[Illustration: The composition of milk. Why is it considered a good food?]
Nutrients.--Certain nutrient materials form the basis of food of both
plants and animals. These have been stated to be _proteins_ (such as lean
meat, eggs, the gluten of bread), _carbohydrates_ (starches, sugars, gums,
etc.), _fats_ and _oils_ (both animal and vegetable), _mineral matter_ and
_water_.
Proteins.--Protein substances contain the element nitrogen. Hence such
foods are called nitrogenous foods. Man must form the protoplasm of his
body (that is, the muscles, tendons, nervous system, blood corpuscles, the
living parts of the bone and the skin, etc.) in part at least from
nitrogenous food. Some of this he obtains by eating the flesh of animals,
and some he obtains directly from plants (for example, peas and beans).
Proteins are the only foods available for tissue building. They may be
oxidized to release energy if occasion requires it.
Fats and Oils.--Fats and oils, both animal and vegetable, are the materials
from which the body derives part of its energy. The chemical formula of a
fat shows that, compared with other food substances, there is very little
oxygen present; hence the greater capacity of this substance for uniting
with oxygen. The rapid burning of fat compared with the slower combustion
of a piece of meat or a piece of bread illustrates this. A pound of butter
releases over twice as much energy to the body as does a pound of sugar or
a pound of steak. Human fatty tissue is formed in part from fat eaten, but
carbohydrate or even protein food may be changed and stored in the body as
fat.
Carbohydrates.--We see that the carbohydrates, like the fats, contain
carbon, hydrogen, and oxygen. _Carbohydrates are essentially
energy-producing foods._ They are, however, of use in building up or
repairing tissue. It is certainly true that in both plants and animals such
foods pass directly, together with foods containing nitrogen, to repair
waste in tissues, thus giving the needed proportion of carbon, oxygen, and
hydrogen to unite with the nitrogen in forming the protoplasm of the body.
[Illustration: Three portions of foods, each of which furnishes about the
same amount of nourishment.]
Inorganic Foods.--Water forms a large part of almost every food substance.
It forms about five sixths of a normal daily diet. The human body, by
weight, is about two thirds water. About 90 per cent of the blood is water.
Water is absolutely essential in passing off waste of the body. When we
drink water, we take with it some of the inorganic salts used by the body
in the making of bone and in the formation of protoplasm. Sodium chloride
(table salt), an important part of the blood, is taken in as a flavoring
upon our meats and vegetables. Phosphate of lime and potash are important
factors in the formation of bone.
Phosphorus is a necessary substance for the making of living matter, milk,
eggs, meat, whole wheat, and dried peas and beans containing small amounts
of it. Iron also is an extremely important mineral, for it is used in the
building of red blood cells. Meats, eggs, peas and beans, spinach, and
prunes, are foods containing some iron.
Some other salts, compounds of calcium, magnesium, potassium, and
phosphorus, have been recently found to aid the body in many of its most
important functions. The beating of the heart, the contraction of muscles,
and the ability of the nerves to do their work appear to be due to the
presence of minute quantities of these salts in the body.
Uses of Nutrients.--The following table sums up the uses of nutrients to
man:[36]--
Protein Forms tissue \
White of eggs (albumen), (muscles, tendon, }
curd of milk (casein), lean and probably } All serve as
meat, gluten of wheat, etc. fat) } _fuel_ and yield
} _energy_ in form
Fats Form fatty tissue. } of heat and muscular
Fat of meat, butter, olive oil, } strength.
oils of corn and wheat, etc. }
}
Carbohydrates Transformed into }
Sugar, starch, etc. fat. /
Mineral matters (ash) Aid in forming bone,
Phosphates of lime, potash, assist in digestion,
soda, etc. aid in absorption
and in other ways
help the body parts
do their work.
Water used as a vehicle to carry nutrients, and enters into the
composition of living matter.
Footnote 36: Adapted from Atwater, _Principles of Nutrition
and Nutritive Value of Food_, U. S. Department of
Agriculture, 1902.
Common Foods contain the Nutrients.--We have already found in our plant
study that various plant foods are rich in different nutrients,
carbohydrates forming the chief nutrient in the foods we call cereals,
breads, cake, fleshy fruits, sugars, jellies, and the like. Fats and oils
are most largely found in nuts and some grains. Animal foods are our chief
supply of protein. White of egg and lean meat are almost pure protein and
water. Proteins are most abundant, as we should expect, in those plants
which are richly supplied with nitrogen; peas and beans, and in grains and
nuts. Fats, which are melted into oils at the temperature of the body, are
represented by the fat in meats, bacon, pork, lard, butter, and vegetable
oils.
Water.--Water is, as we have seen, a valuable part of food. It makes up a
very high percentage of fresh fruits and vegetables; it is also present in
milk and eggs, less abundant in meats and fish, and is lowest in dried
foods and nuts. The amount of water in a given food is often a decided
factor in the cost of the given food, as can easily be seen by reference to
the chart on page 283.
Refuse.--Some foods bought in the market may contain a certain unusable
portion. This we call refuse. Examples of refuse are bones in meat, shells
of eggs or of shellfish, the covering of plant cells which form the skins
of potatoes or other vegetables. The amount of refuse present also plays an
important part in the values of foods for the table. The table[37] on page
276 gives the percentages of organic nutrients, water, and refuse present
in some common foods.
[Illustration: Table of food values. Determine the percentage of water in
codfish, loin of beef, milk, potatoes. Percentage of refuse in leg of
mutton, codfish, eggs, and potatoes. What _is_ the refuse in each case?
Find three foods containing a high percentage of protein; of fat; of
carbohydrate. Find some food in which the proportions of protein, fat, and
carbohydrate are combined in a good proportion.]
Fuel Values of Nutrients.--In experiments performed by Professor Atwater
and others, and in the appended tables, the value of food as a source of
energy is stated in heat units called _Calories_. _A Calorie is the amount
of heat required to raise the temperature of one kilogram of water from
zero to one degree Centigrade._ This is about equivalent to raising one
pound four degrees Fahrenheit. The fuel value of different foods may be
computed in a definite manner. This is done by burning a given portion of a
food (say one gram) in the apparatus known as a _calorimeter_. By this
means may be determined the number of degrees the temperature of a given
amount of water is raised during the process of burning. It has thus been
found that a gram of fat will liberate 9.3 Calories of heat, while a gram
of starch or sugar only about 4 Calories. The burning value of fat is,
therefore, over twice that of carbohydrates. In a similar manner protein
has been shown to have about the same fuel value as carbohydrates, _i.e._ 4
Calories to a gram.[38]
Footnote 37 and 38: W. O. Atwater, _Principles of Nutrition
and Nutritive Value of Food_, U. S. Department of
Agriculture, 1902.
The Relation of Work to Diet.--It has been shown experimentally that a man
doing hard, muscular work needs more food than a person doing light work.
The mere exercise gives the individual a hearty appetite; he eats more and
needs more of all kinds of food than a man or boy doing light work.
Especially is it true that the person of sedentary habits, who does brain
work, should be careful to eat less food and food that will digest easily.
His protein food should also be reduced. Rich or hearty foods may be left
for the man who is doing hard manual labor out of doors, for any extra work
put on the digestive organs takes away just so much from the ability of the
brain to do its work.
[Illustration: Foods of plant origin. Select 5 foods containing a high
percentage of protein, 5 with a high percentage of carbohydrates, 5 with a
high percentage of water. Do vegetable foods contain much fat? Which of the
above-mentioned foods have the highest burning value?]
[Illustration: Foods largely of animal origin. Compare with the previous
chart with reference to amount of protein, carbohydrate, and fat in foods.
Compare the burning value of plant and animal foods. Compare the relative
percentage of water in both kinds of foods.]
[Illustration: The composition of milk.]
The Relation of Environment to Diet.--We are all aware of the fact that the
body seems to crave more food in winter than in summer. The temperature of
the body is maintained at 98.6° in winter as in summer, but much more heat
is lost from the body in cold weather. Hence feeding in winter should be
for the purpose of maintaining our fuel supply. We need heat-producing
food, and we need _more_ food in winter than in summer. We may use
carbohydrates for this purpose, as they are economical and digestible. The
inhabitants of cold countries get their heat-releasing foods largely from
fats. In tropical countries and in hot weather little protein should be
eaten and a considerable amount of fresh fruit used.
The Relation of Age to Diet.--As we will see a little later, age is a
factor not only in determining the kind but the amount of food to be used.
Young children require far less food than do those of older growth or
adults. The body constantly increases in weight until young manhood, or
womanhood, then its weight remains nearly stationary, varying with health
or illness. It is evident that food in adults simply repairs the waste of
cells and is used to supply energy. Elderly people need much less protein
than do younger persons. But inasmuch as the amount of food to be taken
into the body should be in proportion to the body weight, it is also
evident that growing children do not, as is popularly supposed, need as
much food as grown-ups.
The Relation of Sex to Diet.--As a rule boys need more food than girls, and
men than women. This seems to be due to, first, the more active muscular
life of the man and, secondly, to the greater amount of fat in the tissues
of the woman, making loss of heat less. Larger bodies, because of greater
surface, give off more heat than smaller ones. Men are usually larger in
bulk than are women,--another reason for more food in their case.
The Relation of Digestibility to Diet.--Animal foods in general may be said
to be more completely digested within the body than plant foods. This is
largely due to the fact that plant cells have woody walls that the
digestive juices cannot act upon. Cereals and legumes are less digestible
foods than are dairy products, meat, or fish. This does not mean
necessarily that these foods would not agree with you or me but that in
general the body would get less nourishment out of the total amount
available.
The agreement or disagreement of food with an individual is largely a
personal matter. I, for example, cannot eat raw tomatoes without suffering
from indigestion, while some one else can digest tomatoes but not
strawberries. Each individual should learn early in life the foods that
disagree with him personally and leave such foods out of his dietary. For
"what is one man's meat may be another man's poison."
The Relation of Cost of Food to Diet.--It is a mistaken notion that the
best foods are always the most expensive. A glance at the table (page 283)
will show us that both fuel value and tissue-building value is present in
some foods from vegetable sources, as well as in those from animal sources,
and that the vegetable foods are much cheaper. The American people are far
less economical in their purchase of food than most other nations. Nearly
one half of the total income of the average workingman is spent on food.
Not only does he spend a large amount on food, but he wastes money in
purchasing the wrong kinds of food. A comparison of the daily diets of
persons in various occupations in this and other countries shows that as a
rule we eat more than is necessary to supply the necessary fuel and repair,
and that our workingmen eat more than those of other countries. Another
waste of money by the American is in the false notion that a large
proportion of the daily dietary should be meat. Many people think that the
most expensive cuts of meat are the most nutritious. The falsity of this
idea may be seen by a careful study of the tables on pages 283 and 286.
The Best Dietary.--Inasmuch as all living substance contains nitrogen, it
is evident that protein food must form a part of the dietary; but protein
alone is not usable. If more protein is eaten than the body requires, then
immediately the liver and kidneys have to work overtime to get rid of the
excess of protein which forms a poisonous waste harmful to the body. We
must take foods that will give us, as nearly as possible, the proportion of
the different chemical elements as they are contained in protoplasm. It has
been found, as a result of studies of Atwater and others, that a man who
does muscular work requires a little less than one quarter of a pound of
protein, the same amount of fat, and about one pound of carbohydrate to
provide for the growth, waste, and repair of the body and the energy used
up in one day.
The Daily Calorie Requirement.--Put in another way, Atwater's standard for
a man at light exercise is food enough to yield 2816 Calories; of these,
410 Calories are from protein, 930 Calories from fat, and 1476 Calories
from carbohydrate. That is, for every 100 Calories furnished by the food,
14 are from protein, 32 from fat, and 54 from carbohydrate. In exact
numbers, the day's ration as advocated by Atwater would contain about 100
grams or 3.7 ounces protein, 100 grams or 3.7 ounces fat, and 360 grams or
13 ounces carbohydrate. Professor Chittenden of Yale University, another
food expert, thinks we need proteins, fats, and carbohydrates in about the
proportion of 1 to 3 to 6, thus differing from Atwater in giving less
protein in proportion. Chittenden's standard for the same man is food to
yield a total of 2360 Calories, of which protein furnishes 236 Calories,
fat 708 Calories, and carbohydrates 1416 Calories. For every 100 Calories
furnished by the food, 10 are from protein, 30 from fat, 60 from
carbohydrate. In actual amount the Chittenden diet would contain 2.16
ounces protein, 2.83 ounces fat, and 13 ounces carbohydrate. A German named
Voit gives as ideal 25 Calories from proteins, 20 from fat, and 55 from
carbohydrate, out of every 100 Calories; this is nearer our actual daily
ration. In addition, an ounce of salt and nearly one hundred ounces of
water are used in a day.
[Illustration: Table showing the cost of various foods. Using this table,
make up an economical dietary for one day, three meals, for a man doing
moderate work. Give reasons for the amount of food used and for your choice
of foods. Make up another dietary in the same manner, using expensive
foods. What is the difference in your bill for the day?]
A Mixed Diet Best.--Knowing the proportion of the different food substances
required by man, it will be an easy matter to determine from the tables and
charts shown you the best foods for use in a mixed diet. Meats contain too
much nitrogen in proportion to the other substances. In milk, the
proportion of proteins, carbohydrates, and fats is nearly right to make
protoplasm; a considerable amount of mineral matter being also present. For
these reasons, milk is extensively used as a food for children, as it
combines food material for the forming of protoplasm with mineral matter
for the building of bone. Some vegetables (for example, peas and beans)
contain a large amount of nitrogenous material but in a less digestible
form than is found in some other foods. Vegetarians, then, are correct in
theory when they state that a diet of vegetables may contain everything
necessary to sustain life. But a mixed diet containing meat is healthier. A
purely vegetable diet contains much waste material, such as the cellulose
forming the walls of plant cells, which is indigestible. It has been
recently discovered that the outer coats of some grains, as rice, contain
certain substances (enzymes) which aid in digestion. In the case of
polished rice, when this outer coat is removed the grain has much less food
value.
Daily Fuel Needs of the Body.--It has been pointed out that the daily diet
should differ widely according to age, occupation, time of year, etc. The
following table shows the daily fuel needs for several ages and
occupations:--
DAILY CALORIE NEEDS (APPROXIMATELY)
1. For child under 2 years 900 Calories
2. For child from 2-5 years 1200 Calories
3. For child from 6-9 years 1500 Calories
4. For child from 10-12 years 1800 Calories
5. For child from 12-14 (woman, light work, also) 2100 Calories
6. For boy (12-14), girl (15-16), man, sedentary 2400 Calories
7. For boy (15-16) (man, light muscular work) 2700 Calories
8. For man, moderately active muscular work 3000 Calories
9. For farmer (busy season) 3200 to 4000 Calories
10. For ditchers, excavators, etc. 4000 to 5000 Calories
11. For lumbermen, etc. 5000 and more Calories
Normal Heat Output.--The following table gives the result of some
experiments made to determine the hourly and daily expenditure of energy of
the average normal grown person when asleep and awake, at work or at
rest:--
AVERAGE NORMAL OUTPUT OF HEAT FROM THE BODY
==========================================================
| AVERAGE
CONDITIONS OF MUSCULAR ACTIVITY | CALORIES
| PER HOUR
-------------------------------------------+--------------
Man at rest, sleeping | 65 Calories
Man at rest, awake, sitting up | 100 Calories
Man at light muscular exercise | 170 Calories
Man at moderately active muscular exercise | 290 Calories
Man at severe muscular exercise | 450 Calories
Man at very severe muscular exercise | 600 Calories
==========================================================
It is very simple to use such a table in calculating the number of Calories
which are spent in twenty-four hours under different bodily conditions. For
example, suppose the case of a clerk or school teacher leading a relatively
inactive life, who
sleeps for 9 hours × 65 Calories = 585
works at desk 9 hours × 100 Calories = 900
reads, writes, or studies 4 hours × 100 Calories = 400
walks or does light exercise 2 hours × 170 Calories = 340
----
2225
This comes out, as we see, very close to example 6 of the table[39] on page
284.
Footnote 39: The above tables have been taken from the
excellent pamphlet of the Cornell Reading Course, No. 6,
_Human Nutrition_.
How we may Find whether we are Eating a properly Balanced Diet.--We already
know approximately our daily Calorie needs and about the proportion of
protein, fat, and carbohydrate needed. Dr. Irving Fisher of Yale University
has worked out a very easy method of determining whether one is living on a
proper diet. He has made up a number of tables, in which he has designated
portions of food, each of which furnishes 100 Calories of energy. The
tables show the proportion of protein, fat, and carbohydrate in each food,
so that it is a simple matter by using such a table to estimate the
proportions of the various nutrients in our dietary. We may depend upon
taking somewhere near the proper amount of food if we take a diet based
upon either Atwater's, Chittenden's, or Voit's standard. One of the most
interesting and useful pieces of home work that you can do is to estimate
your own personal dietary, using the tables giving the 100-Calorie portion
to see if you have a properly balanced diet. From the table on page 286
make out a simple dietary for yourself for one day, estimating your own
needs in Calories and then picking out 100-Calorie portions of food which
will give you the proper proportions of protein, fat, and carbohydrate.
TABLE OF 100 CALORIE PORTIONS--MODIFIED FROM FISHER
============================================================================
| |WT. IN| CAL. FURNISHED| PRICE
| | OZ. |----+----+-----+--------+------
|PORT. CONTAINING | 100 | | |CAR- | | 100
FOOD | 100 CALORIES | CAL.|PRO-| FAT|BOHY-| 1 LB. | CAL.
| | PORT.|TEIN| |DRATE| | POR.
------------------+------------------+------+----+----+-----+--------+------
Oysters |1 doz. | 6.8 | 49 |22 | 29 | .175 | .07
Bean soup |1/2 small serving | 2.6 | 24 |12 | 64 | | .007
Cream of corn |2/3 ordin. serv. | 3.1 | 11 |58 | 31 | | .02
Vegetable soup |1/2 ordin. serv. | 2.4 | 8 |89 | 3 | | .01
Cod fish (fresh) |ordin. serv. | 5 | 95 | 5 | 0 | .12 | .04
Salmon (canned) |small serv. | 1.75 | 45 |55 | 0 | .22 | .03
Chicken |1/2 large serv. | 1.75 | 39 |56 | 5 | .22 | .05
Veal cutlet |2/3 large serv. | 2.4 | 54 |46 | 0 | .28 | .045
Beef, corned |1/2 large serv. | 1.0 | 15 |85 | 0 | .16 | .01
Beef, sirloin | small serv. | 1.6 | 33 |67 | 0 | .34 | .04
Beef, round | small serv. | 1.8 | 39 |61 | 0 | .24 | .025
Ham, lean | ordin. serv. | 1.1 | 28 |72 | 0 | .22 | .015
Lamb chops |1/2 ordin. serv. | 1.0 | 24 |76 | 0 | .20 | .013
Mutton, leg | ordin. serv. | 1.2 | 35 |65 | 0 | .20 | .015
Eggs, boiled |1 large egg | 2.1 | 32 |68 | 0 |.30 doz.| .025
Eggs, scrambled |1-1/3 ordin. serv.| 2.5 | 37 |58 | 5 |.30 doz.| .03
Beans, baked | side dish | 2.66 | 21 |18 | 61 | .08 | .013
Potatoes, mashed | ordin. serv. | 3.2 | 10 |25 | 65 | .02 | .005
Macaroni |1/3 large serv. | .95 | 15 | 3 | 82 | .10 | .01
Potato salad | ordin. serv. | 2.25 | 10 |57 | 33 | .20 | .025
Tomatoes, sliced |4 large serv. |15. | 15 |16 | 69 | .10 | .10
Rolls, plain |1 large roll | 1.2 | 12 | 7 | 81 |.10 doz.| .01
Butter | ordin. pat | .44 | 5 |99.5| | .35 | .01
Wheat bread |1 small slice | .96 | 15 | 5 | 80 | .07 | .005
Chocolate cake |1/2 ord. sq. piece| .98 | 7 |22 | 71 | .32 | .02
Gingerbread |1/2 ord. sq. piece| .96 | 6 |23 | 71 | .16 | .01
Custard pudding | ordin. serv. | 3.25 | 18 |42 | 40 | .15 | .03
Rice pudding | very small serv.| 2.65 | 8 |13 | 79 | .13 | .02
Apple pie |1/3 piece | 1.3 | 5 |32 | 63 | | .013
Cheese, American |1-1/2 cu. in. | .77 | 25 |73 | 2 | .19 | .01
Crackers (soda) |2 crackers | .9 | 10 |20 | 70 | .10 | .007
Currant jelly |2 heap. spoons | 1.1 | 2 | 0 | 98 | .40 | .025
Sugar |3 teaspoons | .86 | 0 | 0 | 100 | .06 | .003
Milk as bought | small glass | 4.9 | 19 |52 | 29 | .05 | .015
Milk, cond., sweet|4 teaspoons | 1.06 | 10 |23 | 67 | | .01
Oranges |1 large one | 9.4 | 6 | 3 | 91 | | .025
Peanuts |13 double ones | .62 | 20 |63 | 17 | | .004
Almonds, shelled |8-15 | .53 | 13 |77 | 10 | | .025
============================================================================
From the preceding table plan a well-balanced and cheap dietary for one day
for a family of five, two adults and three children. Make a second dietary
for the same time and same number of people which shall give approximately
the same amount of tissue and energy producing food from more expensive
materials.
Food Waste in the Kitchen.--Much loss occurs in the improper cooking of
foods. Meats especially, when overdone, lose much of their flavor and are
far less easily digested than when they are cooked rare. The chief reasons
for cooking meats are that the muscle fibers may be loosened and softened,
and that the bacteria or other parasites in the meat may be killed by the
heat. The common method of frying makes foods less digestible. Stewing is
an economical as well as healthful method. A good way to prepare meat,
either for stew or soup, is to place the meat, cut in small pieces, in cold
water, and allow it to simmer for several hours. Rapid boiling toughens the
muscle fibers by the too rapid coagulation of the albuminous matter in
them, just as the white of egg becomes tough when boiled too long. Boiling
and roasting are excellent methods of cooking meat. In order to prevent the
loss of the nutrients in roasting, it is well to baste the meat frequently;
thus a crust is formed on the outer surface of the meat, which prevents the
escape of the juices from the inside.
Vegetables are cooked in order that the cells containing starch grains may
be burst open, thus allowing the starch to be more easily attacked by the
digestive fluids. Inasmuch as water may dissolve out nutrients from
vegetable tissues, it is best to boil them rapidly in a small amount of
water. This gives less time for the solvent action to take place.
Vegetables should be cooked with the outer skin left on when it is
possible.
Adulterations in Foods.--The addition of some cheaper substance to a food,
or the subtraction of some valuable substance from a food, with the view to
cheating the purchaser, is known as _adulteration_. Many foods which are
artificially manufactured have been adulterated to such an extent as to be
almost unfit for food, or even harmful. One of the commonest adulterations
is the substitution of grape sugar (glucose) for cane sugar. Glucose,
however, is not a harmful adulterant. It is used largely in candy making.
Flour and other cereal foods are sometimes adulterated with some cheap
substitutes, as bran or sawdust. Alum is sometimes added to make flour
whiter. Probably the food which suffers most from adulteration is milk, as
water can be added without the average person being the wiser. By means of
an inexpensive instrument known as a _lactometer_, this cheat may easily be
detected. In most cities, the milk supply is carefully safeguarded, because
of the danger of spreading typhoid fever from impure milk (see Chapter
XX). Before the pure food law was passed in 1906, milk was
frequently adulterated with substances like formalin to make it keep sweet
longer. Such preservatives are harmful, and it is now against the law to
add anything whatever to milk.
Coffee, cocoa, and spices are subject to great adulteration; cottonseed oil
is often substituted for olive oil; butter is too frequently artificial;
while honey, sirups of various kinds, cider and vinegar, have all been
found to be either artificially made from cheaper substitutes or to contain
such substitutes.
Pure Food Laws.--Thanks to the National Pure Food and Drug Law passed by
Congress in 1906, and to the activity of various city and state boards of
health, the opportunity to pass adulterated foods on the public is greatly
lessened. This law compels manufacturers of foods or medicines to state the
composition of their products on the labels placed on the jars or bottles.
So if a person reads the label he can determine exactly what he is getting
for his money.
Impure Water.--Great danger comes from drinking impure water. This subject
has already been discussed under Bacteria, where it was seen that the
spread of typhoid fever in particular is due to a contaminated water
supply. As citizens, we must aid all legislation that will safeguard the
water used by our towns and cities. Boiling water for ten minutes or longer
will render it safe from all organic impurities.
Stimulants.--We have learned that food is anything that supplies building
material or releases energy in the body; but some materials used by man,
presumably as food, do not come under this head. Such are tea and coffee.
When taken in moderate quantities, _they produce a temporary increase in
the vital activities_ of the person taking them. This is said to be a
stimulation; and material taken into the digestive tract, producing this,
is called a _stimulant_. In moderation, tea and coffee appear to be
harmless. Some people, however, cannot use either without ill effects, even
in small quantity. It is the _habit_ formed of relying upon the stimulus
given by tea or coffee that makes them a danger to man. Cocoa and
chocolate, although both contain a stimulant, are in addition good foods,
having from 12 per cent to 21 per cent of protein, from 29 per cent to 48
per cent fat, and over 30 per cent carbohydrate in their composition.
Is Alcohol a Food?--The question of the use of alcohol has been of late
years a matter of absorbing interest and importance among physiologists. A
few years ago Dr. Atwater performed a series of very careful experiments by
means of the respiration calorimeter, to ascertain whether alcohol is of
use to the body as food.[40] In these experiments the subjects were given,
instead of their daily allotment of carbohydrates and fats, enough alcohol
to supply the same amount of energy that these foods would have given. The
amount was calculated to be about two and one half ounces per day, about as
much as would be contained in a bottle of light wine.[41] This alcohol was
administered in small doses six times during the day. Professor Atwater's
results may be summed up briefly as follows:--
1. The alcohol administered was almost all oxidized in the body.
2. The potential energy in the alcohol was transformed into heat or
muscular work.
3. The body did about as well with the rations including alcohol as it did
without it.
Footnote 40: Alcohol is made up of carbon, oxygen, and
hydrogen. It is very easily oxidized, but it cannot, as is
shown by the chemical formula, be of use to the body in
tissue building, because of its lack of nitrogen.
Footnote 41: Alcoholic beverages contain the following
proportions of alcohol: beer, from 2 to 5 per cent; wine,
from 10 to 20 per cent; liquors, from 30 to 70 per cent.
Patent medicines frequently contain as high as 60 per cent
alcohol. (See page 294.)
The committee of fifty eminent men appointed to report on the physiological
aspects of the drink problem reported that a large number of scientific men
state that they are in the habit of taking alcoholic liquor in small
quantities, and many report that they do not _feel_ harm thereby. A number
of scientists seem to agree that within limits alcohol may be a kind of
food, although a very _poor_ food.
On the other hand, we know that although alcohol may technically be
considered as a food, it is a very unsatisfactory food and, as the
following statements show, it has an effect on the body tissues which foods
do not have.
Professor Chittenden of Yale College, in discussing the food problem of
alcohol, writes as follows:
"It is true that alcohol in moderate quantities may serve as a food,
_i.e._ it can be oxidized with the liberation of heat. It may to some
extent take the place of fat and carbohydrates, but it is not a
perfect substitute for them, and for this reason alcohol has an action
that cannot be ignored. It reduces liver oxidation. It therefore
presents a dangerous side wholly wanting in carbohydrates and fat. The
latter are simply burned up to carbonic acid and water or are
transformed to glycogen and fat, but alcohol, although more easily
oxidized, is at all times liable to obstruct, in a measure at least,
the oxidative processes of the liver and probably of other tissues
also, thereby throwing into the circulation bodies, such as uric acid,
which are harmful to health, a fact which at once tends to draw a
distinct line of demarcation between alcohol and the two
non-nitrogenous foods, fat and carbohydrates. Another matter must be
emphasized, and it is that the form in which alcohol is taken is of
importance. Port wine, for instance, has more influence on the amount
of uric acid secreted than an equivalent amount of alcohol has in some
other form. To conclude: as an adjunct to the ordinary daily diet of
the healthy man alcohol cannot be considered as playing the part of a
true non-nitrogenous food."--Quoted in _American Journal of
Inebriety_, Winter, 1906.
Effect of Alcohol on Living Matter.--If we examine raw white of egg, we
find a protein which closely resembles protoplasm in its chemical
composition; it is called albumen. Add to a little albumen in a test tube
some 95 per cent alcohol and notice what happens. As soon as the alcohol
touches the albumen the latter coagulates and becomes hard like boiled
white of egg. Shake the alcohol with the albumen and the entire mass soon
becomes a solid. This is because the alcohol draws the water out of the
albumen. It has been shown that albumen is somewhat like protoplasm in
structure and chemical composition. Strong alcohol acts in a similar manner
on living matter when it is absorbed by the living body cells. It draws
water from them and hardens them. It has a chemical and physical action
upon living matter.
Alcohol a Poison.--But alcohol is also in certain quantities a poison. _A
commonly accepted definition of a poison is that it is any substance which,
when taken into the body, tends to cause serious detriment to health, or
the death of the organism._ That alcohol may do this is well known by
scientists.
It is a matter of common knowledge that alcohol taken in small quantities
does not do any _apparent_ harm. But if we examine the vital records of
life insurance companies, we find a large number of deaths directly due to
alcohol and a still greater number due in part to its use. In the United
States every year there are a third more deaths from alcoholism and
cirrhosis of the liver (a disease _directly_ caused by alcohol) than there
are from typhoid fever. The poisonous effect is not found in small doses,
but it ultimately shows its harmful effect. Hardening of the arteries, an
old-age disease, is rapidly becoming in this country a disease of the
middle aged. From it there is no escape. It is chiefly caused by the
cumulative effect of alcohol. The diagram following, compiled by two
English life insurance companies that insure moderate drinkers and
abstainers, shows the death rate to be considerably higher among those who
use alcohol.
[Illustration: Abstainers live longer than moderate drinkers.]
Dr. Kellogg, the founder of the famous Battle Creek Sanitarium, points out
that strychnine, quinine, and many other drugs are oxidized in the body but
surely cannot be called foods. The following reasons for not considering
alcohol a food are taken from his writings:--
"1. A habitual user of alcohol has an intense craving for
his accustomed dram. Without it he is entirely unfitted for
business. One never experiences such an insane craving for
bread, potatoes, or any other particular article of food.
"2. By continuous use the body acquires a tolerance for
alcohol. That is, the amount which may be imbibed and the
amount required to produce the characteristic effects first
experienced gradually increase until very great quantities
are sometimes required to satisfy the craving which its
habitual use often produces. This is never the case with
true foods.... Alcohol behaves in this regard just as does
opium or any other drug. It has no resemblance to a food.
"3. When alcohol is withdrawn from a person who has been
accustomed to its daily use, most distressing effects are
experienced.... Who ever saw a man's hand trembling or his
nervous system unstrung because he could not get a potato or
a piece of cornbread for breakfast? In this respect, also,
alcohol behaves like opium, cocaine, or any other enslaving
drug.
"4. Alcohol lessens the appreciation and the value of brain
and nerve activity, while food reënforces nervous and mental
energy.
"5. Alcohol as a protoplasmic poison lessens muscular power,
whereas food increases energy and endurance.
"6. Alcohol lessens the power to endure cold. This is true
to such a marked degree that its use by persons accompanying
Arctic expeditions is absolutely prohibited. Food, on the
other hand, increases ability to endure cold. The
temperature after taking food is raised. After taking
alcohol, the temperature, as shown by the thermometer, is
lowered.
"7. Alcohol cannot be stored in the body for future use,
whereas all food substances can be so stored.
"8. Food burns slowly in the body, as it is required to
satisfy the body's needs. Alcohol is readily oxidized and
eliminated, the same as any other oxidizable drug."
[Illustration: Experiment (by Davison) to show how the nicotine in six
cigarettes was sufficient to kill this fish. The smoke from the cigarettes
was passed through the water in which the fish is swimming.]
The Use of Tobacco.--A well-known authority defines a narcotic as a
substance "_which directly induces sleep, blunts the senses, and, in large
amounts, produces complete insensibility_." Tobacco, opium, chloral, and
cocaine are examples of narcotics. Tobacco owes its narcotic influence to a
strong poison known as nicotine. Its use in killing insect parasites on
plants is well known. In experiments with jellyfish and other lowly
organized animals, the author has found as small a per cent as one part of
nicotine to one hundred thousand parts of sea water to be sufficient to
profoundly affect an animal placed within it. The illustration here given
shows the effect of nicotine upon a fish, one of the vertebrate animals.
Nicotine in a pure form is so powerful a poison that two or three drops
would be sufficient to cause the death of a man by its action upon the
nervous system, especially the nerves controlling the beating of the heart.
This action is well known among boys training for athletic contests. The
heart is affected; boys become "short-winded" as a result of the action on
the heart. It has been demonstrated that tobacco has, too, an important
effect on muscular development. The stunted appearance of the young smoker
is well known.
[Illustration: The amounts of alcohol in some liquors and in some patent
medicines. _a_, beer, 5 %; _b_, claret, 8 %; _c_, champagne, 9 %; _d_,
whisky, 50 %; _e_, well-known sarsaparilla, 18 %; _f_, _g_, _h_,
much-advertised nerve tonics, 20 %, 21 %, 25 %; _i_, another
much-advertised sarsaparilla, 27 %; _j_, a well-known tonic, 28 %; _k_,
_l_, bitters, 37 %, 44 % alcohol.]
Use and Abuse of Drugs.--The American people are addicted to the use of
drugs, and especially patent medicines. A glance at the street-car
advertisements shows this. Most of the medicines advertised contain alcohol
in greater quantity than beer or wine, and many of them have opium,
morphine, or cocaine in their composition. Paregoric and laudanum,
medicines sometimes given to young children, are examples of dangerous
drugs that contain opium. Dr. George D. Haggard of Minneapolis has shown by
many analyses that a large number of the so-called "malts," "malt
extracts," and "tonics," including several of the best known and most
advertised on the market, are simply disguised beers and, frequently, very
poor beers at that. These drugs, in addition to being harmful, affect the
person using them in such a manner that he soon feels the need for the
drug. Thus the drug habit is formed,--a condition which has wrecked
thousands of lives. A number of articles on patent medicines recently
appeared in a leading magazine and have been collected and published under
the title of _The Great American Fraud_. In this booklet the author points
out a number of different kinds of "cures" and patent medicines. The most
dangerous are those headache or neuralgia cures containing _acetanilid_.
This drug is a heart depresser and should not be used without medical
advice. Another drug which is responsible for habit formation is _cocaine_.
This is often found in catarrh or other cures. Alcohol is the basis of all
tonics or "bracers." Every boy and girl should read this booklet so as to
be forearmed against evils of the sort just described.
REFERENCE READING ON FOODS
Hunter, _Laboratory Problems in Civic Biology._ American Book
Company.
Allen, _Civics and Health._ Ginn and Company.
Bulletin 13, American School of Home Economics, Chicago.
Cornell University Reading Course, Buls. 6 and 7, _Human
Nutrition._
Davison, _The Human Body and Health._ American Book Company.
Jordan, _The Principles of Human Nutrition._ The Macmillan
Company.
Kehler, L. F., _Habit-forming Agents._ Farmers' Bulletin 393,
U. S. Dept. of Agri.
Lusk, _Science and Nutrition._ W. B. Saunders Company.
Norton, _Foods and Dietetics._ American School of Home Economics.
Olsen, _Pure Foods._ Ginn and Company.
Sharpe, _A Laboratory Manual for the Solution of Problems in
Biology,_ pp. 226-240. American Book Company.
Stiles, _Nutritional Physiology._ W. B. Saunders Company.
_The Great American Fraud._ American Medical Association, Chicago.
_The Propaganda for Reform in Proprietary Medicines._ Am.
Medical Association.
Farmers' Bulletin: numbers 23, 34, 42, 85, 93, 121, 128, 132,
142, 182, 249, 295, 298.
Reprint from Yearbook, 1901, Atwater, _Dietaries in Public
Institutions._
Reprint from Yearbook, 1902, Milner, _Cost of Food related to
its Nutritive Value._
Experiment Station, Circular 46, Langworthy, _Functions and
Uses of Food._
XX. DIGESTION AND ABSORPTION
_Problems.--To determine where digestion takes place by examining_:--
_(a) The functions of glands._
-(b) The work done in the mouth._
-(c) The work done in the stomach._
-(d) The work done in the small intestine._
-(e) The function of the liver._
_To discover the absorbing apparatus and how it is used._
LABORATORY SUGGESTIONS
_Demonstration of food tube of man_ (manikin).--Comparison
with food tube of frog. Drawing (comparative) of food tube
and digestive glands of frog and man.
_Demonstration of simple gland._--(Microscopic preparation.)
_Home experiment and laboratory demonstration._--The
digestion of starch by saliva. Conditions favorable and
unfavorable.
_Demonstration experiment._--The digestion of proteins with
artificial gastric juice. Conditions favorable and
unfavorable.
_Demonstration._--An emulsion as seen under the compound
microscope.
_Demonstration._--Emulsification of fats with artificial
pancreatic fluid. Digestion of starch and protein with
artificial pancreatic fluid.
_Demonstration_ of "tripe" to show increase of surface of
digestive tube.
_Laboratory or home exercise._--Make a table showing the
changes produced upon food substances by each digestive
fluid, the reaction (acid or alkaline) of the fluid, when
the fluid acts, and what results from its action.
Purpose of Digestion.--We have learned that starch and protein food of
plants are formed in the leaves. A plant, however, is unable to make use of
the food in this condition. Before it can be transported from one part of
the plant body to another, it is changed into a soluble form. In this state
it can be passed from cell to cell by the process of osmosis. Much the same
condition exists in animals. In order that food may be of use to man, it
must be changed into a state that will allow of its passage in a soluble
form through the walls of the alimentary canal, or food tube. This is done
by the enzymes which cause digestion. It will be the purpose of this
chapter to discover where and how digestion takes place in our own body.
Alimentary Canal.--In all vertebrate animals, including man, food is taken
in the mouth and passed through a _food tube_ in which it is digested. This
tube is composed of different portions, named, respectively, as we pass
from the _mouth_ downward, the _gullet_, _stomach_, _small_ and _large
intestine_, and _rectum_.
[Illustration: The digestive tract of the frog and man. _Gul_, gullet; _S_,
stomach; _L_, liver; _G_, gall bladder; _P_, pancreas; _Sp_, spleen; _SI_,
small intestine; _LI_, large intestine; _V_, appendix; _A_, anus.]
Comparison of Food Tube of a Frog and Man.--If we compare the food tube of
a dissected frog with the food tube of man (as shown by a manikin or
chart), we find part for part they are much the same. But we notice that
the intestines of man, both small and large, are relatively longer than in
the frog. We also notice in man the body cavity or space in which the
internal organs rest is divided in two parts by a wall of muscle, the
_diaphragm_, which separates the heart and lungs from the other internal
organs. In the frog no muscular diaphragm exists. In the frog we can see
plainly the silvery transparent _mesentery_ or double fold of the lining of
the body cavity in which the organs of digestion are suspended. Numerous
blood vessels can be found especially in the walls of the food tube.
Glands.--In addition to the alimentary canal proper, we find a number of
_digestive glands_, varying in size and position, connected with the canal.
[Illustration: Diagram of a gland. _i_, the common tube which carries off
the secretions formed in the cells lining the cavity _c_; _a_, arteries
carrying blood to the glands; _v_, veins taking blood away from the
glands.]
What a Gland Does. Enzymes.--In man there are the saliva gland of the
mouth, the gastric glands of the stomach, the pancreas and liver, the two
latter connected with the small intestine, and the intestinal glands in the
walls of the intestine. Besides glands which aid in digestion there are
several others of which we will speak later. As we have already learned, a
gland is a collection of cells which takes up material from within the body
and manufactures from it something which is later poured out as a
secretion. An example of a gland in plants is found in the nectar-secreting
cells of a flower.
Certain substances, called _enzymes_, formed by glands cause the digestion
of food. The enzymes secreted by the cells of the glands and poured out
into the food tube act upon insoluble foods so as to change them to a
soluble form. They are the product of the activity of the cell, although
they are not themselves alive. We do not know much about enzymes
themselves, but we can observe what they do. Some enzymes render soluble
different foods, others work in the blood, still others probably act within
any cell of the body as an aid to oxidation, when work is done. Enzymes are
very sensitive to changes in temperature and to the degree of _acidity_ or
_alkalinity_[42] of the material in which they act. We will find that the
enzymes found in glands in the mouth will not act long in the stomach
because of the change from an alkaline surrounding in the mouth to that of
an acid in the stomach. Enzymes seem to be able to work indefinitely,
providing the surroundings are favorable. A small amount of digestive
fluid, if it had long enough to work, could therefore digest an indefinite
amount of food.
Footnote 42: The teacher should explain the meaning of these
terms.
Gland Structure.--The entire inner surface of the food tube is covered with
a soft lining of _mucous membrane_. This is always moist because certain
cells, called _mucus cells_, empty out their contents into the food tube,
thus lubricating its inner surface. When a large number of cells which have
the power to secrete fluids are collected together, the surface of the food
tube may become indented at this point to form a pitlike _gland_. Often
such depressions are branched, thus giving a greater secreting surface, as
is seen in the figure on page 298. The cells of the gland are always
supplied with blood vessels and nerves, for the secretions of the glands
are under the control of the nervous system.
How a Gland Secretes.--We must therefore imagine that as the blood goes to
the cells of a gland it there loses some substances which the gland cells
take out and make over into the particular enzyme that they are called upon
to manufacture. Under certain conditions, such as the sight or smell of
food, or even the desire for it, the activity of the gland is stimulated.
It then pours out its secretion containing the digestive enzyme. Thus a
gland does its work.
Salivary Glands.--We are all familiar with the substance called _saliva_
which acts as a lubricant in the mouth. Saliva is manufactured in the cells
of three pairs of glands which empty into the mouth, and which are called,
according to their position, the _parotid_ (beside the ear), the
_submaxillary_ (under the jawbone), and the _sublingual_ (under the
tongue).
[Illustration: Experiment showing non-osmosis of starch in tube _A_, and
osmosis of sugar in tube _B_.]
Digestion of Starch.--If we collect some saliva in a test tube, add to it a
little starch paste, place the tube containing the mixture for a few
minutes in tepid water, and then test with Fehling's solution, we shall
find grape sugar present. Careful tests of the starch paste and of the
saliva made separately will usually show no grape sugar in either.
If another test be made for grape sugar, in a test tube containing starch
paste, saliva, and a few drops of any weak acid, the starch will be found
not to have changed. The digestion or change of starch to grape sugar is
caused by the presence in the saliva of an _enzyme_, or _digestive
ferment_. You will remember that starch in the growing corn grain was
changed to grape sugar by an enzyme called _diastase_. Here a similar
action is caused by an enzyme called _ptyalin_. This ferment acts _only_ in
an alkaline medium at about the temperature of the body.
[Illustration: The mouth cavity of man. _e_, Eustachian tube; _hp_, hard
palate; _sp_, soft palate; _ut_, upper teeth; _bc_, buccal cavity; _lt_,
lower teeth; _t_, tongue; _ph_, pharynx; _ep_, epiglottis; _lx_, voice box;
_oe_, gullet; _tr_, trachea.]
Mouth Cavity in Man.--In our study of a frog we find that the mouth cavity
has two unpaired and four paired tubes leading from it. These are (_a_) the
_gullet_ or food tube, (_b_) the _windpipe_ (in the frog opening through
the _glottis_), (_c_) the paired nostril holes (_posterior nares_), (_d_)
the paired _Eustachian tubes_, leading to the ear. All of these openings
are found in man.
In man the mouth cavity, and all internal surfaces of the food tube, are
lined with a _mucous membrane_. The _mucus_ secreted from gland cells in
this lining makes a slippery surface so that the food may slip down easily.
The roof of the mouth is formed in front by a plate of bone called the
_hard palate_, and a softer continuation to the back of the mouth, the
_soft palate_. These separate the nose cavity from that of the mouth
proper. The part of the space back of the soft palate is called the
_pharynx_, or throat cavity. From the pharynx lead off the _gullet_ and
_windpipe_, the former back of the latter. The lower part of the mouth
cavity is occupied by a muscular tongue. Examination of its surface with a
looking-glass shows it to be almost covered in places by tiny projections
called _papillæ_. These papillæ contain organs known as _taste buds_, the
sensory endings of which determine the taste of substances. The tongue is
used in moving food about in the mouth, and in starting it on its way to
the gullet; it also plays an important part in speaking.
[Illustration: I. Teeth of the upper jaw, from below. _1, 2_, incisors;
_3_, canine; _4, 5_, premolars; _6, 7, 8_, molars. II. longitudinal section
of a tooth. _E_, enamel; _D_, dentine; _C_, cement; _P_, pulp cavity.]
The Teeth.--In man the teeth, unlike those of the frog, are used in the
mechanical preparation of the food for digestion. Instead of holding prey,
they crush, grind, or tear food so that more surface may be given for the
action of the digestive fluids. The teeth of man are divided, according to
their functions, into four groups. In the center of both the upper and
lower jaw in front are found eight teeth with chisel-like edges, four in
each jaw; these are the _incisors_, or cutting teeth. Next is found a
single tooth on each side (four in all); these have rather sharp points and
are called the _canines_. Then come two teeth on each side, eight in all,
called _premolars_. Lastly, the _flat-top molars_, or grinding teeth, of
which there are six in each jaw. Food is caught between irregular
projections on the surface of the molars and crushed to a pulpy mass.
Hygiene of the Mouth.--Food should simply be chewed and relished, with no
thought of swallowing. There should be no more effort to prevent than to
force swallowing. It will be found that if you attend only to the agreeable
task of extracting the flavors of your food, Nature will take care of the
swallowing, and this will become, like breathing, involuntary. The instinct
by which most people eat is perverted through the "hurry habit" and the use
of abnormal foods. Thorough mastication takes time, and therefore one must
not feel hurried at meals if the best results are to be secured. The
stopping point for eating should be at the _earliest_ moment after one is
really satisfied.
Care of the Teeth.--It has been recently found that fruit acids are very
beneficial to the teeth. Vinegar diluted to about half strength with water
makes an excellent dental wash. Clean your teeth carefully each morning and
before going to bed. Use dental silk after meals. We must remember that the
bacteria which cause decay of the teeth are washed down into the stomach
and may do even more harm there than in the mouth.
How Food is Swallowed.--After food has been chewed and mixed with saliva,
it is rolled into little balls and pushed by the tongue into such position
that the muscles of the throat cavity may seize it and force it downward.
Food, in order to reach the gullet from the mouth cavity, must pass over
the opening into the windpipe. When food is in the course of being
swallowed, the upper part of this tube forms a trapdoor over the opening.
When this trapdoor is not closed, and food "goes down the wrong way," we
choke, and the food is expelled by coughing.
[Illustration: Peristaltic waves on the gullet of man. (A bolus means
little ball.)]
The Gullet, or Esophagus.--Like the rest of the food tube the gullet is
lined by soft and moist mucous membrane. The wall is made up of two sets of
muscles,--the inside ones running around the tube; the outer layer of
muscle taking a longitudinal course. After food leaves the mouth cavity, it
gets beyond our direct control, and the muscles of the gullet, stimulated
to activity by the presence of food in the tube, push the food down to the
stomach by a series of contractions until it reaches the stomach. These
wavelike movements (called _peristaltic_ movements) are characteristic of
other parts of the food tube, food being pushed along in the stomach and
the small intestine by a series of slow-moving muscular waves. Peristaltic
movement is caused by muscles which are not under voluntary nervous
control, although anger, fear, or other unpleasant emotions have the effect
of slowing them up or even stopping them entirely.
Stomach of Man.--The stomach is a pear-shaped organ capable of holding
about three pints. The end opposite to the gullet, which empties into the
small intestine, is provided with a ring of muscle forming a valve called
the _pylorus_. There is also another ring of muscle guarding the entrance
to the stomach.
Gastric Glands.--If we open the stomach of the frog, and remove its
contents by carefully washing, its wall is seen to be thrown into folds
internally. Between the folds in the stomach of man, as well as in the
frog, are located a number of tiny pits. These form the mouths of the
_gastric glands_, which pour into the stomach a secretion known as the
_gastric juice_. The gastric glands are little tubes, the lining of which
secretes the fluid. When we think of or see appetizing food, this secretion
is given out in considerable quantity. The stomach, like the mouth,
"waters" at the sight of food. Gastric juice is slightly acid in its
chemical reaction, containing about .2 per cent free _hydrochloric acid_.
It also contains two very important enzymes, one called _pepsin_, and
another less important one called _rennin_.
Action of Gastric Juice.--If protein is treated with artificial gastric
juice at the temperature of the body, it will be found to become swollen
and then gradually to change to a substance which is soluble in water. This
is like the action of the gastric juice upon proteins in the stomach.
The other enzyme of gastric juice, called _rennin_, curdles or coagulates a
protein found in milk; after the milk is curdled, the pepsin is able to act
upon it. "Junket" tablets, which contain rennin, are used in the kitchen to
cause this change.
[Illustration: A peptic gland, from the stomach, very much magnified. _A_,
central or chief cell, which makes pepsin; _B_, border cells, which make
acid. (From Miller's _Histology_.)]
The hydrochloric acid found in the gastric juice acts upon lime and some
other salts taken into the stomach with food, changing them so that they
may pass into the blood and eventually form the mineral part of bone or
other tissue. The acid also has a decided antiseptic influence in
preventing growth of bacteria which cause decay, and some of which might
cause disease.
Movement of Walls of Stomach.--The stomach walls, provided with three
layers of muscle which run in an oblique, circular, and longitudinal
direction (taken from the inside outward), are well fitted for the constant
churning of the food in that organ. Here, as elsewhere in the digestive
tract, the muscles are involuntary, muscular action being under the control
of the so-called _sympathetic nervous system_. Food material in the stomach
makes several complete circuits during the process of digestion in that
organ. Contrary to common belief, the greatest amount of food is digested
_after_ it leaves the stomach. But this organ keeps the food in it in
almost constant motion for a considerable time, a meal of meat and
vegetables remaining in the stomach for three or four hours. While movement
is taking place, the gastric juice acts upon proteins, softening them,
while the constant churning movement tends to separate the bits of food
into finer particles. Ultimately the semifluid food, much of it still
undigested, is allowed to pass in small amounts through the pyloric valve,
into the small intestine. This is allowed by the relaxation of the ringlike
muscles of the pylorus.
Experiments on Digestion in the Stomach.--Some very interesting experiments
have recently been made by Professor Cannon of Harvard with reference to
movements of the stomach contents. Cats were fed with material having in it
bismuth, a harmless chemical that would be visible under the X-ray. It was
found that shortly after food reached the stomach a series of waves began
which sent the food toward the pyloric end of the stomach. If the cat was
feeling happy and well, these contractions continued regularly, but if the
cat was cross or bad tempered, the movements would stop. This shows the
importance of _cheerfulness_ at meals. Other experiments showed that food
which was churned into a soft mass was only permitted to leave the stomach
when it became thoroughly permeated by the gastric juice. It is the _acid_
in the partly digested food that causes the stomach valve to open and allow
its contents to escape little by little into the small intestine.
The partly digested food in the small intestine almost immediately comes in
contact with fluids from two glands, the liver and pancreas. We shall first
consider the function of the pancreas.
Position and Structure of the Pancreas.--The most important digestive gland
in the human body is the pancreas. The gland is a rather diffuse structure;
its duct empties by a common opening with the bile duct into the small
intestine, a short distance below the pylorus. In internal structure, the
pancreas resembles the salivary glands.
[Illustration: Appearance of milk under the microscope, showing the natural
grouping of the fat globules. In the circle a single group is highly
magnified. Milk is one form of an emulsion. (S. M. Babcock, Wis. Bul. No.
61.)]
Work done by the Pancreas.--Starch paste added to artificial pancreatic
fluid and kept at blood heat is soon changed to sugar. Protein, under the
same conditions, is changed to a peptone. Fats, which so far have been
unchanged except to be melted by the heat of the body, are changed by the
action of the pancreas into a form which can pass through the walls of the
food tube. If we test pancreatic fluid, we find it strongly _alkaline_ in
its reaction. If two test tubes, one containing olive oil and water, the
other olive oil and a weak solution of caustic soda, an _alkali_, be shaken
violently and then allowed to stand, the oil and water will quickly
separate, while the oil, caustic soda, and water will remain for some time
in a milky _emulsion_. If this emulsion be examined under the microscope,
it will be found to be made of millions of little droplets of fat, floating
in the liquid. The presence of the caustic soda helped the forming of the
emulsion. Pancreatic fluid similarly emulsifies fats and changes them into
soft soaps and fatty acids. Fat in this form may be absorbed. The process
of this transformation is not well understood.
Conditions under which the Pancreas does its Work.--The secretion from this
gland seems to be influenced by the overflow of acid material from the
stomach. This acid, on striking the lining of the small intestine, causes
the formation in its walls of a substance known as _secretin_. This
secretin reaches the blood and seems to stimulate all the glands pouring
fluid into the intestine to do more work. A pint or more of pancreatic
fluid is secreted every day.
The Intestinal Fluid.--Three different pancreatic enzymes do the work of
digestion, one acting on starch, another on protein, and a third on fats.
It has been found that some of these enzymes will not do their work unless
aided by the _intestinal_ fluid, a secretion formed in glands in the walls
of the small intestine. This fluid, though not much is known about it, is
believed to play an important part in the digestion of all kinds of foods
left undigested in the small intestine.
Liver.--The liver is the largest gland in the body. In man, it hangs just
below the diaphragm, a little to the right side of the body. During life,
its color is deep red. It is divided into three lobes, between two of which
is found the _gall bladder_, a thin-walled sac which holds the _bile_, a
secretion of the liver. Bile is a strongly alkaline fluid of greenish
color. It reaches the intestine through the same opening as the pancreatic
fluid. Almost one quart of bile is passed daily into the digestive canal.
The color of bile is due to certain waste substances which come from the
destruction of worn-out red corpuscles of the blood. This destruction takes
place in the liver.
[Illustration: Diagram of a bit of the wall of the small intestine, greatly
magnified, _a_, mouths of intestinal glands; _b_, villus cut lengthwise to
show blood vessels and lacteal (in center); _e_, lacteal sending branches
to other villi; _i_, intestinal glands; _m_, artery; _v_, vein; _l_, _t_,
muscular coats of intestine wall.]
Functions of Bile.--The action of bile is not very well known. It has the
very important faculty of aiding the pancreatic fluid in digestion, though
alone it has slight if any digestive power. Certain substances in the bile
aid especially in the absorption of fats. Bile seems to be mostly a waste
product from the blood and as such incidentally serves to keep the contents
of the intestine in a more or less soft condition, thus preventing extreme
constipation.
The Liver a Storehouse.--Perhaps the most important function of the liver
is the formation within it of a material called _glycogen_, or animal
starch. The liver is supplied by blood from two sources. The greater amount
of blood received by the liver comes directly from the walls of the stomach
and intestine to this organ. It normally contains about one fifth of all
the blood in the body. This blood is very rich in food materials, and from
it the cells of the liver take out sugars to form glycogen.[43] Glycogen is
stored in the liver until such a time as a food is needed that can be
quickly oxidized; then it is changed to sugar and carried off by the blood
to the tissue which requires it, and there used for this purpose. Glycogen
is also stored in the muscles, where it is oxidized to release energy when
the muscles are exercised.
Footnote 43: It is known that glycogen _may_ be formed in
the body from protein, and possibly from fatty foods.
The Absorption of Digested Food into the Blood.--The object of digestion is
to change foods from an insoluble to a soluble form. This has been seen in
the study of the action of the various digestive fluids in the body, each
of which is seen to aid in dissolving solid foods, changing them to a
fluid, and, in case of the bile, actually assisting them to pass through
the wall of the intestine. A small amount of digested food may be absorbed
by the blood in the blood vessels of the walls of the stomach. Most of the
absorption, however, takes place through the walls of the small intestine.
Structure of the Small Intestine.--The small intestine in man is a slender
tube nearly twenty feet in length and about one inch in diameter. If the
chief function of the small intestine is that of absorption, we must look
for adaptations which increase the absorbing surface of the tube. This is
gained in part by the inner surface of the tube being thrown into
transverse folds which not only retard the rapidity with which food passes
down the intestine, but also give more absorbing surface. But far more
important for absorption are millions of little projections which cover the
inner surface of the small intestine.
The Villi.--So numerous are these projections that the whole surface
presents a velvety appearance. Collectively, these structures are called
the _villi_ (singular _villus_). They form the chief organs of absorption
in the intestine, several thousand being distributed over every square inch
of surface. By means of the folds and villi the small intestine is
estimated to have an absorbing surface equal to twice that of the surface
of the body. Between the villi are found the openings of the _intestinal
glands_.
Internal Structure of a Villus.--The internal structure of a villus is best
seen in a longitudinal section. We find the outer wall made up of a thin
layer of cells, the _epithelial_ layer. It is the duty of these cells to
absorb the semifluid food from within the intestine. Underneath these cells
lies a network of very tiny blood vessels, while inside of these, occupying
the core of the villus, are found spaces which, because of their white
appearance after absorption of fats, have been called _lacteals_. (See
figure, page 307.)
[Illustration: Diagram to show how the nutrients reach the blood.]
Absorption of Foods.--Let us now attempt to find out exactly how foods are
passed from the intestines into the blood. Food substances in solution may
be soaked up as a sponge would take up water, or they may pass by osmosis
into the cells lining the villus. These cells break down the peptones into
a substance that will pass into and become part of the blood. Once within
the villus, the sugars and digested proteins pass through tiny blood
vessels into the larger vessels comprising the _portal circulation_. These
pass through the liver, where, as we have seen, sugar is taken from the
blood and stored as glycogen. From the liver, the food within the blood is
sent to the heart, from there is pumped to the lungs, from there returns to
the heart, and is pumped to the tissues of the body. A large amount of
water and some salts are also absorbed through the walls of the stomach and
intestine as the food passes on its course. The fats in the form of soaps
and fatty acids pass into the space in the center of the villus. Later they
are changed into fats again, probably in certain groups of gland cells
known as _mesenteric_ glands, and eventually reach the blood by way of the
thoracic duct without passing through the liver.
Large Intestine.--The large intestine has somewhat the same structure as
the small intestine, except that it lacks the villi and has a greater
diameter. Considerable absorption, however, takes place through its walls
as the mass of food and refuse material is slowly pushed along by the
muscles within its walls.
Vermiform Appendix.--At the point where the small intestine widens to form
the large intestine, a baglike pouch is formed. From one side of this pouch
is given off a small tube about four inches long, closed at the lower end.
This tube, the rudiment of what is an important part of the food tube in
the lower vertebrates, is called the _vermiform appendix_. It has come to
have unpleasant notoriety in late years, as the site of serious
inflammation.
Constipation.--In the large intestine live millions of bacteria, some of
which make and give off poisonous substances known as toxins. These
substances are easily absorbed through the walls of the large intestine,
and, when they pass into the blood, cause headaches or sometimes serious
trouble. Hence it follows that the lower bowel should be emptied of this
matter as frequently as possible, at least once a day. Constipation is one
of the most serious evils the American people have to deal with, and it is
largely brought about by the artificial life which we lead, with its lack
of exercise, fresh air, and sleep. Fruit with meals, especially at
breakfast, plenty of water between meals and before breakfast, exercise,
particularly of the abdominal muscles, and regular habits will all help to
correct this evil.
Hygienic Habits of Eating; the Causes and Prevention of Dyspepsia.--From
the contents of the foregoing chapter it is evident that the object of the
process of digestion is to break up solid food so that it may be absorbed
to form part of the blood. Any habits we may form of thoroughly chewing our
food will evidently aid in this process. Undoubtedly much of the distress
known as dyspepsia is due to too hasty meals with consequent lack of proper
mastication of food. The message of Mr. Horace Fletcher in bringing before
us the need of proper mastication of food and the attendant evils of
overeating is one which we cannot afford to ignore. It is a good rule to go
away from the table feeling a little hungry. Eating too much overtaxes the
digestive organs and prevents their working to the best advantage. Still
another cause of dyspepsia is eating when in a _fatigued_ condition. It is
always a good plan to rest a short time before eating, especially after any
hard manual work. We have seen how great a part unpleasant emotions play in
preventing peristaltic movements of the food tube. Conversely, pleasant
conversation, laughter, and fun will help you to digest your meal. Eating
between meals is condemned by physicians because it calls the blood to the
digestive organs at a time when it should be more active in other parts of
the body.
Effect of Alcohol on Digestion.--It is a well-known fact that alcohol
extracts water from tissues with which it is in contact. This fact works
much harm to the interior surface of the food tube, especially the walls of
the stomach, which in the case of a hard drinker are likely to become
irritated and much toughened. In very small amounts alcohol stimulates the
secretion of the salivary and gastric glands, and thus appears to aid in
digestion.
The following results of experiments on dogs, published in the _American
Journal of Physiology_, Vol. I, Professor Chittenden of Yale University
gives as "strictly comparable," because "they were carried out in
succession on the same day." They show that alcohol retards rather than
aids in digestion:--
==========================================================================
NUMBER OF EXPERIMENT |1/16 LB. MEAT WITH WATER| 1/16 LB. MEAT WITH
| | DILUTE ALCOHOL
------------------------+------------------------+------------------------
XVII [alpha] 9:15 A.M. | Digested in 3 hours |
XVII [beta] 3:00 P.M. | | Digested in 3:15 hours
XVIII [alpha] 8:30 A.M. | Digested in 2:30 hours |
XVIII [beta] 2:10 P.M. | | Digested in 3:00 hours
XIX [alpha] 9:00 A.M. | Digested in 2:30 hours |
XIX [beta] 2:30 P.M. | | Digested in 3:00 hours
XX [alpha] 9:15 A.M. | | Digested in 2:45 hours
XX [beta] 2:30 P.M. | Digested in 2:15 hours |
VI [alpha] 9:15 A.M. | | Digested in 3:45 hours
VI [beta] 1:00 P.M. | Digested in 3:15 hours |
------------------------+------------------------+------------------------
Average | 2:42 hours | 3:09 hours
------------------------+------------------------+------------------------
As a result of his experiments, Professor Chittenden remarks: "We believe
that the results obtained justify the conclusion that gastric digestion as
a whole is not materially modified by the introduction of alcoholic fluids
with the food. In other words, the unquestionable acceleration of gastric
secretion which follows the ingestion of alcoholic beverages is, as a rule,
counterbalanced by the inhibitory effect of the alcoholic fluids upon the
chemical process of gastric digestion, with perhaps at times a tendency
towards preponderance of inhibitory action." Others have come to the same
or stronger conclusions as to the undesirable action of alcohol on
digestion, as a result of their own experiments.
Effect of Alcohol on the Liver.--The effect of heavy drinking upon the
liver is graphically shown in the following table prepared by the
Scientific Temperance Federation of Boston, Mass.:--
[Illustration: Proportion of deaths from disease in a certain area due to
alcohol. The black area shows deaths due to alcohol.[44]]
Footnote 44: Does not include deaths from general alcoholic
paralysis or other organic diseases due to alcohol. Liver
cirrhosis due to alcohol conservatively estimated at 75 per
cent of total cases.
"Alcoholic indulgence stands almost if not altogether in the
front rank of the enemies to be combated in the battle for
health."--PROFESSOR WILLIAM T. SEDGWICK.
XXI. THE BLOOD AND ITS CIRCULATION
_Problems.--To discover the composition and uses of the different parts of
the blood._
_To find out the means by which the blood is circulated about the
body._
LABORATORY SUGGESTIONS
_Demonstration._--Structure of blood, fresh frog's blood and
human blood. Drawings.
_Demonstration._--Clotting of blood.
_Demonstration._--Use of models to demonstrate that the
heart is a force pump.
_Demonstration._--Capillary circulation in web of frog's
foot or tadpole's tail. Drawing.
_Home or laboratory exercise._--On relation of exercise on
rate of heart beat.
Function of the Blood.--The chief function of the digestive tract is to
change foods to such form that they can be absorbed through the walls of
the food tube and become part of the blood.[45]
Footnote 45: This change is due to the action of certain
enzymes upon the nutrients in various foods. But we also
find that peptones are changed back again to proteins when
once in the blood. This appears to be due to the
_reversible_ action of the enzymes acting upon them. (See
page 307.)
If we examine under the microscope a drop of blood taken from the frog or
man, we find it made up of a fluid called _plasma_ and two kinds of bodies,
the so-called _red corpuscles_ and _colorless corpuscles_, floating in this
plasma.
Composition of Plasma.--The plasma of blood is found to be largely (about
90 per cent) water. It also contains a considerable amount of protein, some
sugar, fat, and mineral material. It is, then, the medium which holds the
fluid food that has been absorbed from within the intestine. This food is
pumped to the body cells where, as work is performed, oxidation takes place
and heat is given off as a form of energy. The almost constant temperature
of the body is also due to the blood, which brings to the surface of the
body much of the heat given off by oxidation of food in the muscles and
other tissues. When the blood returns from the tissues where the food is
oxidized, the plasma brings back with it to the lungs part of the carbon
dioxide liberated where oxidation has taken place. Some waste products, to
be spoken of later, are also found in the plasma.
[Illustration: Human blood as seen under the high power of the compound
microscope; at the extreme right is a colorless corpuscle.]
The Red Blood Corpuscle; its Structure and Functions.--The red corpuscle in
the blood of the frog is a true cell of disklike form, containing a
nucleus. The red corpuscle of man is made in the red marrow of bones and in
its young stages has a nucleus. In its adult form, however, it lacks a
nucleus. Its form is that of a biconcave disk. So small and so numerous are
these corpuscles that over five million are found in a cubic centimeter of
normal blood. They make up almost one half the total volume of the blood.
The color, which is found to be a dirty yellow when separate corpuscles are
viewed under the microscope, is due to a protein material called
_hæmoglobin_. Hæmoglobin contains a large amount of iron. It has the power
of uniting very readily with oxygen whenever that gas is abundant, and,
after having absorbed it, of giving it up to the surrounding media, when
oxygen is there present in smaller amounts than in the corpuscle. This
function of carrying oxygen is the most important function of the red
corpuscle, although the red corpuscle also removes part of the carbon
dioxide from the tissues on their return to the lungs. The taking up of
oxygen is accompanied by a change in color of the mass of corpuscles from a
dull red to a bright scarlet.
Clotting of Blood.--If fresh beef blood is allowed to stand overnight,
it will be found to have separated into two parts, a dark red, almost solid
_clot_ and a thin, straw-colored liquid called _serum_. Serum is found to
be made up of about 90 per cent water, 8 per cent protein, 1 per cent
other organic foods, and 1 per cent mineral substances. In these respects
it very closely resembles the fluid food that is absorbed from the
intestines.
If another jar of fresh beef blood is poured into a pan and briskly whipped
with a bundle of little rods (or with an egg beater), a stringy substance
will be found to stick to the rods. This, if washed carefully, is seen to
be almost colorless. Tested with nitric acid and ammonia, it is found to
contain a protein substance which is called _fibrin_.
Blood plasma, then, is made up of a fluid portion of serum, and fibrin,
which, although in a fluid state in the blood vessels within the body,
coagulates when blood is removed from the blood vessels. This coagulation
aids in making a blood clot. A clot is simply a mass of fibrin threads with
a large number of corpuscles tangled within. The clotting of blood is of
great physiological importance, for otherwise we might bleed to death even
from a small wound.
Blood Plates.--In blood within the circulatory system of the body, the
fibrin is held in a fluid state called _fibrinogen_. An enzyme, acting upon
this fibrinogen, the soluble protein in the blood, causes it to change to
an insoluble form, the fibrin of the clot. This change seems to be due to
the action of minute bodies in the blood known as _blood plates_. Under
abnormal conditions these blood plates break down, releasing some
substances which eventually cause this enzyme to do its work.
[Illustration: A small artery (_A_) breaking up into capillaries (_c_)
which unite to form a vein (_V_). Note at (_P_) several colorless
corpuscles, which are fighting bacteria at that point.]
The Colorless Corpuscle; Structure and Functions.--A colorless corpuscle is
a cell irregular in outline, the shape of which is constantly changing.
These corpuscles are somewhat larger than the red corpuscles, but less
numerous, there being about one colorless corpuscle to every three hundred
red ones. They have the power of movement, for they are found not only
inside but outside the blood vessels, showing that they have worked their
way between the cells that form the walls of the blood tubes.
[Illustration: A colorless corpuscle catching and eating germs.]
A Russian zoölogist, Metchnikoff, after studying a number of simple
animals, such as medusæ and sponges, found that in such animals some of the
cells lining the inside of the food cavity take up or engulf minute bits of
food. Later, this food is changed into the protoplasm of the cell.
Metchnikoff believed that the colorless corpuscles of the blood have
somewhat the same function. This he later proved to be true. Like the
amoeba, they feed by engulfing their prey. This fact has a very important
bearing on the relation of colorless corpuscles to certain diseases caused
by bacteria within the body. If, for example, a cut becomes infected by
bacteria, inflammation may set in. Colorless corpuscles at once surround
the spot and attack the bacteria which cause the inflammation. If the
bacteria are few in number, they are quickly eaten by certain of the
colorless corpuscles, which are known as _phagocytes_. If bacteria are
present in great quantities, they may prevail and kill the phagocytes by
poisoning them. The dead bodies of the phagocytes thus killed are found in
the pus, or matter, which accumulates in infected wounds. In such an event,
we must come to the aid of nature by washing the wound with some
antiseptic, as weak carbolic acid or hydrogen peroxide.
Antibodies and their Uses.--In case of disease where, for example, fever is
caused by poison given off from bacteria we find the cells of the body
manufacture and pour into the blood a substance known as an _antibody_.
This substance does not of necessity kill the harmful germs or even stop
their growth. It does, however, unite with the toxin or poison given off by
the germs and renders it entirely harmless.
Function of Lymph.--The tissues and organs of the body are traversed by a
network of tubes which carry the blood. Inside these tubes is the blood
proper, consisting of a fluid plasma, the colorless corpuscles, and the red
corpuscles. Outside the blood tubes, in spaces between the cells which form
tissues, is found another fluid, which is in chemical composition very much
like plasma of the blood. This is the _lymph_. It is, in fact, fluid food
in which some colorless amoeboid corpuscles are found. Blood gives up its
food material to the lymph. This it does by passing it through the walls of
the capillaries. The food is in turn given up to the tissue cells, which
are bathed by the lymph.
[Illustration: The exchange between blood and the cells of the body.]
Some of the amoeboid corpuscles from the blood make their way between the
cells forming the walls of the capillaries. _Lymph, then, is practically
blood plasma plus some colorless corpuscles. It acts as the medium of
exchange between the blood proper and the cells in the tissues of the
body._ By means of the food supply thus brought, the cells of the body are
able to grow, the fluid food being changed to the protoplasm of the cells.
By means of the oxygen passed over by the lymph, oxidation may take place
within the cells. Lymph not only gives food to the cells of the body, but
also takes away carbon dioxide and other waste materials, which are
ultimately passed out of the body by means of the lungs, skin, and kidneys.
Internal Secretions.--In addition to all the functions given above, the
blood has recently been shown to carry the secretions of a number of glands
through which it passes, although these glands have no ducts to carry off
their secretions. These internal secretions seem _absolutely necessary_ for
the health of the body. Several glands, the thyroid, adrenal bodies, the
testes, and ovaries, as well as the pancreas, give off these remarkable
substances.
The Amount of Blood and its Distribution.--Blood forms, by weight, about
one sixteenth of the body. This would be about four quarts to a body weight
of 130 pounds. Normally, about one half of the blood of the body is found
in or near the organs lying in the body cavity below the diaphragm, about
one fourth in the muscles, and the rest in the head, heart, lungs, large
arteries, and veins.
Blood Temperature.--The temperature of blood in the human body is normally
about 98.6° Fahrenheit when tested under the tongue by a thermometer,
although the temperature drops almost two degrees after we have gone to
sleep at night. It is highest about 5 P.M. and lowest about 4 A.M. In
fevers, the temperature of the body sometimes rises to 107°; but unless
this temperature is soon reduced, death follows. Any considerable drop in
temperature below the normal also means death. Body heat results from the
oxidation of food, and the circulation of blood keeps the temperature
nearly uniform in all parts of the body.
Cold-blooded Animals.--In animals which are called cold-blooded, the blood
has no fixed temperature, but varies with the temperature of the medium in
which the animal lives. Frogs, in the summer, may sit for hours in water
with a temperature of almost 100°. In winter, they often endure freezing so
that the blood and lymph within the spaces under the loose skin are frozen
into ice crystals. This change in body temperature is evidently an
adaptation to the mode of life.
Circulation of the Blood in Man.--The blood is the carrying agent of the
body. Like a railroad or express company, it takes materials from one part
of the human organism to another. This it does by means of the organs of
circulation,--the heart and blood vessels. These blood vessels are called
_arteries_ where they carry blood away from the heart, _veins_ where they
bring blood back to the heart, and _capillaries_ where they connect the
larger blood vessels. The organs of circulation thus form a system of
connected tubes through which the blood flows.
The Heart; Position, Size, Protection.--The heart is a cone-shaped muscular
organ about the size of a man's fist. It is located immediately above the
diaphragm, and lies so that the muscular apex, which points downward, moves
while beating against the fifth and sixth ribs, just a little to the left
of the midline of the body. This fact gives rise to the notion that the
heart is on the left side of the body. The heart is surrounded by a loose
membranous bag called the _pericardium_, the inner lining of which secretes
a fluid in which the heart lies. When, for any reason, the pericardial
fluid is not secreted, inflammation arises in that region.
[Illustration: Diagram showing the front half of the heart cut away: _a_,
aorta; _l_, arteries to the lungs; _la_, left auricle; _lv_, left
ventricle; _m_, tricuspid valve open; _n_, bicuspid or mitral valve closed;
_p_ and _r_, veins from the lungs; _ra_, right auricle; _rv_, right
ventricle; _v_, vena cava. Arrows show direction of circulation.]
Internal Structure of Heart.--If we should cut open the heart of a mammal
down the midline, we could divide it into a right and a left side, _each of
which would have no internal connection with the other_. Each side is made
up of an upper thin-walled portion with a rather large internal cavity, the
_auricle_, which opens into a lower smaller portion with heavy muscular
walls, the _ventricle_. Communication between auricles and ventricles is
guarded by little flaps or _valves_. The auricles receive blood from the
veins. The ventricles pump the blood into the arteries.
The Heart in Action.--The heart is constructed on the same plan as a force
pump, the valves preventing the reflux of blood into the auricle when it is
forced out of the ventricle. Blood enters the auricles from the veins
because the muscles of that part of the heart relax; this allows the space
within the auricles to fill. Almost immediately the muscles of the
ventricles relax, thus allowing blood to pass into the chambers within the
ventricles. Then, after a short pause, during which time the muscles of the
heart are resting, a wave of muscular contraction begins in the auricles
and ends in the ventricles, with a sudden strong contraction which forces
the blood out into the arteries. Blood is kept on its course by the valves,
which act in the same manner as do the valves in a pump. The blood is thus
made to pass into the arteries upon the contraction of the ventricle walls.
[Illustration: The heart is a force pump; prove it from these diagrams.]
[Illustration:
I. Circulation in a fish. _G_, gills; _C_, capillaries of the body. Notice
the two-chambered heart.
II. The circulation in a frog. _L_, the lungs; _C_, the capillaries. Notice
the heart has three chambers. What is the condition of blood leaving the
ventricle to go to the cells of the body?
III. The circulation in man. _H_, head; _A_, arms; _L_, lungs; _S_,
stomach; _Li_, liver; _K_, kidney; _S.I._, small intestine; _L.I._, large
intestine; _Le_, legs; _1_, right auricle; _2_, right ventricle; _3_, left
ventricle; _4_, left auricle; _5_, dorsal aorta; _6_, vein to lungs. ]
The Course of the Blood in the Body.--Although the two sides of the heart
are separate and distinct from each other, yet every drop of blood that
passes through the right heart likewise passes later through the left
heart. There are two distinct systems of circulation in the body. The
_pulmonary circulation_ takes the blood through the right auricle and
ventricle, to the lungs, and passes it back to the left auricle. This is a
relatively short circulation, the blood receiving in the lungs its supply
of oxygen, and there giving up some of its carbon dioxide. The greater
circulation is known as the _systemic circulation_; in this system, the
blood leaves the left ventricle through the great dorsal _aorta_. A large
part of the blood passes directly to the muscles; some of it goes to the
nervous system, kidneys, skin, and other organs of the body. It gives up
its supply of food and oxygen in these tissues, receives the waste products
of oxidation while passing through the capillaries, and returns to the
right auricle through two large vessels known as the _venæ cavæ_. It
requires only from twenty to thirty seconds for the blood to make the
complete circulation from the ventricle back again to the starting point.
This means that the entire volume of blood in the human body passes three
or four thousand times a day through the various organs of the body.[46]
Footnote 46: See Hough and Sedgwick, _The Human Mechanism_,
page 136.
Portal Circulation.--Some of the blood, on its way back to the heart,
passes to the walls of the food tube and to its glands. From there it is
sent with its load of absorbed food to the liver. Here the vein which
carries the blood (called the portal vein) breaks up into capillaries
around the cells of the liver, when it gives up sugar to be stored as
glycogen. From the liver, blood passes directly to the right auricle. The
_portal circulation_, as it is called, is the only part of the circulation
where the blood passes through two sets of capillaries on its way from
auricle to auricle.
[Illustration: Capillary circulation in the web of a frog's foot, as seen
under the compound microscope. _a_, _b_, small veins; _c_, pigment cells in
the skin; _d_, capillaries in which the oval corpuscles are seen to follow
one another in single series.]
Circulation in the Web of a Frog's Foot.--If the web of the foot of a live
frog or the tail of a tadpole is examined under the compound microscope, a
network of blood vessels will be seen. In some of the larger vessels the
corpuscles are moving rapidly and in spurts; these are _arteries_. The
arteries lead into smaller vessels hardly greater in diameter than the
width of a single corpuscle. This network of _capillaries_ may be followed
into larger _veins_ in which the blood moves regularly. This illustrates
the condition in any tissue of man where the arteries break up into
capillaries, and these in turn unite to form veins.
Structure of the Arteries.--A distinct difference in structure exists
between the arteries and the veins in the human body. The arteries, because
of the greater strain received from the blood which is pumped from the
heart, have thicker muscular walls, and in addition are very elastic.
Cause of the Pulse.--The _pulse_, which can easily be detected by pressing
the large artery in the wrist or the small one in front of and above the
external ear, is caused by the gushing of blood through the arteries after
each pulsation of the heart. As the large arteries pass away from the
heart, the diameter of each individual artery becomes smaller. At the very
end of their course, these arteries are so small as to be almost
microscopic in size and are very numerous. There are so many that if they
were placed together, side by side, their united diameter would be much
greater than the diameter of the large artery (_aorta_) which passes blood
from the left side of the heart. This fact is of very great importance, for
the force of the blood as it gushes through the arteries becomes very much
less when it reaches the smaller vessels. This gushing movement is quite
lost when the capillaries are reached, first, because there is so much more
space for the blood to fill, and second, because there is considerable
friction caused by the very tiny diameter of the capillaries.
Capillaries.--The capillaries form a network of minute tubes everywhere in
the body, but especially near the surface and in the lungs. It is through
their walls that the food and oxygen pass to the tissues, and carbon
dioxide is given up to the plasma. They form the connection that completes
the system of circulation of blood in the body.
Function and Structure of the Veins.--If the arteries are supply pipes
which convey fluid food to the tissues, then the veins may be likened to
drain pipes which carry away waste material from the tissues. Extremely
numerous in the extremities and in the muscles and among other tissues of
the body, they, like the branches of a tree, become larger and unite with
each other as they approach the heart.
[Illustration: Valves in a vein. Notice the thin walls of the vein.]
If the wall of a vein is carefully examined, it will be found to be neither
so thick nor so tough as an artery wall. When empty, a vein collapses; the
wall of an artery holds its shape. If you hold your hand downward for a
little time and then examine it, you will find that the veins, which are
relatively much nearer the surface than are the arteries, appear to be very
much knotted. This appearance is due to the presence of tiny valves within.
These valves open in the direction of the blood current, but would close if
the direction of the blood flow should be reversed (as in case a deep cut
severed a vein). As the pressure of blood in the veins is much less than in
the arteries, the valves thus aid in keeping the flow of blood in the veins
toward the heart. The higher pressure in arteries and the suction in the
veins (caused by the enlargement of the chest cavity in breathing) are the
chief factors which cause a steady flow of blood through the veins in the
body.
Lymph Vessels.--The lymph is collected from the various tissues of the body
by means of a number of very thin-walled tubes, which are at first very
tiny, but after repeated connection with other tubes ultimately unite to
form large ducts. These lymph ducts are provided, like the veins, with
valves. The pressure of the blood within the blood vessels forces
continually more plasma into the lymph; thus a slow current is maintained.
On its course the lymph passes through many collections of gland cells, the
_lymph glands_. In these glands some impurities appear to be removed and
colorless corpuscles made. The lymph ultimately passes into a large tube,
the _thoracic duct_, which flows upward near the ventral side of the spinal
column, and empties into the large subclavian vein in the left side of the
neck. Another smaller lymph duct enters the right subclavian vein.
[Illustration: The lymph vessels; the dark spots are lymph glands: _lac_,
lacteals; _rc_, thoracic duct.]
The Lacteals.--We have already found that part of the digested food
(chiefly carbohydrates, proteins, salts, and water) is absorbed directly
into the blood through the walls of the villi and carried to the liver.
Fat, however, is passed into the spaces in the central part of the villi,
and from there into other spaces between the tissues, known as the
_lacteals_. The lacteals carry the fats into the blood by way of the
thoracic duct. The lacteals and lymph vessels have in part the same course.
It will be thus seen that lymph at different parts of its course would
have a very different composition.
The Nervous Control of the Heart and Blood Vessels.--Although the muscles
of the heart contract and relax without our being able to stop them or
force them to go faster, yet in cases of sudden fright, or after a sudden
blow, the heart may stop beating for a short interval. This shows that the
heart is under the control of the nervous system. Two sets of nerve fibers,
both of which are connected with the central nervous system, pass to the
heart. One set of fibers accelerates, the other slows or inhibits, the
heart beat. The arteries and veins are also under the control of the
sympathetic nervous system. This allows of a change in the diameter of the
blood vessels. Thus, blushing is due to a sudden rush of blood to the
surface of the body caused by an expansion of the blood vessels at the
surface. The blood vessels of the body are always full of blood. This
results from an automatic regulation of the diameter of the blood tubes by
a part of the nervous system called the _vasomotor nerves_. These nerves
act upon the muscles in the walls of the blood vessels. In this way, each
vessel adapts itself to the amount of blood in it at a given time. After a
hearty meal, a large supply of blood is needed in the walls of the stomach
and intestines. At this time, the arteries going to this region are dilated
so as to receive an extra supply. When the brain performs hard work, blood
is supplied in the same manner to that region. Hence, one should not study
or do mental work immediately after a hearty meal, for blood will be drawn
away to the brain, leaving the digestive tract with an insufficient supply.
Indigestion may follow as a result.
The Effect of Exercise on the Circulation.--It is a fact familiar to all
that the heart beats more violently and quickly when we are doing hard work
than when we are resting. Count your own pulse when sitting quietly, and
then again after some brisk exercise in the gymnasium. Exercise in
moderation is of undoubted value, because it sends the increased amount of
blood to such parts of the body where increased oxidation has been taking
place as the result of the exercise. The best forms of exercise are those
which give as many muscles as possible work--walking, out-of-door sports,
any exercise that is not violent. Exercise should not be attempted
immediately after eating, as this causes a withdrawal of blood from the
digestive tract to the muscles of the body. Neither should exercise be
continued after becoming tired, as poisons are then formed in the muscles,
which cause the feeling we call _fatigue_. Remember that extra work given
to the heart by extreme exercise may injure it, causing possible trouble
with the valves.
[Illustration: Stopping flow of blood from an artery by applying a tight
bandage (ligature) between the cut and the heart.]
Treatment of Cuts and Bruises.--Blood which oozes slowly from a cut will
usually stop flowing by the natural means of the formation of a clot. A cut
or bruise should, however, be washed in a weak solution of carbolic acid or
some other antiseptic in order to prevent bacteria from obtaining a
foothold on the exposed flesh. If blood, issuing from a wound, gushes in
distinct pulsations, then we know that an artery has been severed. To
prevent the flow of blood, a tight bandage known as a _tourniquet_ must be
tied between the cut and the heart. A handkerchief with a knot placed over
the artery may stop bleeding if the cut is on one of the limbs. If this
does not serve, then insert a stick in the handkerchief and twist it so as
to make the pressure around the limb still greater. Thus we may close the
artery until the doctor is called, who may sew up the injured blood vessel.
The Effect of Alcohol upon the Blood.--It has recently been discovered that
alcohol has an extremely injurious effect upon the colorless corpuscles of
the blood, lowering their ability to fight disease germs to a marked
degree. This is well seen in a comparison of deaths from certain infectious
diseases in drinkers and abstainers, the percentage of mortality being much
greater in the former.
Dr. T. Alexander MacNichol, in a recent address, said:--
"Massart and Bordet, Metchnikoff and Sims Woodhead, have
proved that alcohol, even in very dilute solution, prevents
the white blood corpuscles from attacking invading germs,
thus depriving the system of the coöperation of these
important defenders, and reducing the powers of resisting
disease. The experiments of Richardson, Harley, Kales, and
others have demonstrated the fact that one to five per cent
of alcohol in the blood of the living human body in a
notable degree alters the appearance of the corpuscular
elements, reduces the oxygen bearing elements, and prevents
their reoxygenation."
Alcohol weakens Resistance to Disease.--In acute illnesses, grippe, fevers,
blood poisoning, etc., substances formed in the blood termed "antibodies"
antagonize the action of bacteria, facilitating their destruction by the
white blood cells and neutralizing their poisonous influence. In a person
with good "resistance" this protective machinery, which we do not yet
thoroughly understand, works with beautiful precision, and the patient
"gets well." Experiments by scientific experts have demonstrated that
alcohol restrains the formation of these marvelous antibodies. Alcohol puts
to sleep the sentinels that guard your body from disease.
The Effect of Alcohol on the Circulation.--Alcoholic drinks affect the very
delicate adjustment of the nervous center's controlling the blood vessels
and heart. Even very dilute alcohol acts upon the muscles of the tiny blood
vessels; consequently, more blood is allowed to enter them, and, as the
small vessels are usually near the surface of the body, the habitual
redness seen in the face of hard drinkers is the ultimate result.
"The first effect of diluted alcohol is to make the heart
beat faster. This fills the small vessels near the surface.
A feeling of warmth is produced which causes the drinker to
feel that he was warmed by the drink. This feeling, however,
soon passes away, and is succeeded by one of chilliness. The
body temperature, at first raised by the rather rapid
oxidation of the alcohol, is soon lowered by the increased
radiation from the surface.
"The immediate stimulation to the heart's action soon passes
away and, like other muscles, the muscles of the heart lose
power and contract with less force after having been excited
by alcohol."--MACY, _Physiology_.
Alcohol, when brought to act directly on heart muscle, lessens the force of
the beat. It may even cause changes in the tissues, which eventually result
in the breaking of the walls of a blood vessel or the plugging of a vessel
with a blood clot. This condition may cause the disease known as
_apoplexy_.
Effects of Tobacco upon the Circulation.--"The frequent use of cigars or
cigarettes by the young seriously affects the quality of the blood.
The red blood corpuscles are not fully developed and charged with
their normal supply of life-giving oxygen. This causes paleness of the
skin, often noticed in the face of the young smoker. Palpitation of
the heart is also a common result, followed by permanent weakness, so
that the whole system is enfeebled, and mental vigor is impaired as
well as physical strength."--MACY, _Physiology_.
XXII. RESPIRATION AND EXCRETION
_Problems.--A study of respiration to find out:--
(a) What changes in blood and air take place within the
lungs.
(b) The mechanics of respiration.
A study of ventilation to discover:--
(a) The reason for ventilation.
(b) The best method of ventilation.
A study of the organs of excretion._
LABORATORY SUGGESTIONS
_Demonstration._--Comparison of lungs of frog with those of
bird or mammal.
_Experiment._--The changes of blood within the lungs.
_Experiment._--Changes taking place in air in the lungs.
_Experiment._--The use of the ribs in respiration.
_Demonstration experiment._--What causes the filling of air
sacs of the lungs?
_Demonstration experiment._--What are the best methods of
ventilating a room?
_Demonstration._--Best methods of dusting and cleaning.
_Demonstration._--Beef or sheep's kidney to show areas.
Necessity for Respiration.--We have seen that plants and animals need
oxygen in order that the life processes may go on. Food is oxidized to
release energy, just as coal is burned to give heat to run an engine. As a
draft of air is required to make fire under the boiler, so, in the human
body, oxygen must be given so that food in tissues may be oxidized to
release energy used in work. This oxidation takes place in the cells of the
body, be they part of a muscle, a gland, or the brain. _Blood, in its
circulation to all parts of the body, is the medium which conveys the
oxygen to that place in the body where it will be used._
[Illustration: Air passages in the human lungs. _a_, larynx; _b_, trachea
(or windpipe); _c_, _d_, bronchi; _e_, bronchial tubes; _f_, cluster of air
cells.]
The Organs of Respiration in Man.--We have alluded to the fact that the
lungs are the organs which give oxygen to the blood and take from it carbon
dioxide. The course of the air passing to the lungs in man is much the same
as in the frog. Air passes through the nose, and into the windpipe. This
cartilaginous tube, the top of which may easily be felt as the Adam's apple
of the throat, divides into two _bronchi_. The bronchi within the lungs
break up into a great number of smaller tubes, the _bronchial tubes_, which
divide somewhat like the small branches of a tree. The bronchial tubes,
indeed all the air passages, are lined with ciliated cells. The cilia of
these cells are constantly in motion, beating with a quick stroke toward
the outer end of the tube, that is, toward the mouth. Hence any foreign
material will be raised from the throat first by the action of the cilia
and then by coughing or "clearing the throat." The bronchi end in very
minute air sacs, little pouches having elastic walls, into which air is
taken when we inspire, or take a deep breath. In the walls of these pouches
are numerous capillaries, the ends of arteries which pass from the heart
into the lung. _It is through the very thin walls of the air sacs that an
interchange of gases takes place which results in the blood giving up part
of its load of carbon dioxide, and taking up oxygen in its place._ This
exchange appears to be aided by the presence of an enzyme in the lung
tissues. This is another example of the various kinds of work done by the
enzymes of the body.
[Illustration: Diagram to show what the blood loses and gains in one of the
air sacs of the lungs.]
Changes in the Blood within the Lungs.--Blood, after leaving the lungs, is
much brighter red than just before entering them. The change in color is
due to a taking up of oxygen by the _hæmoglobin_ of the red corpuscles.
Changes taking place in blood are obviously the reverse of those which take
place in air in the lungs. Every hundred cubic centimeters of blood going
into the lungs contains 8 to 12 c.c. of oxygen, 45 to 50 c.c. of carbon
dioxide, and 1 to 2 c.c. of nitrogen. The same amount of blood passing out
of the lungs contains 20 c.c. of oxygen, 38 c.c. of carbon dioxide, and 1
to 2 c.c. of nitrogen. The water, of which about half a pint is given off
daily, is mostly lost from the blood.
Changes in Air in the Lungs.--Air is much warmer after leaving the lungs
than before it enters them. Breathe on the bulb of a thermometer to prove
this. Expired air contains a considerable amount of moisture, as may be
proved by breathing on a cold polished surface. This it has taken up in the
air sacs of the lungs. The presence of carbon dioxide in expired air may
easily be detected by the limewater test. Air such as we breathe out of
doors contains, by volume:--
Nitrogen 76.95
Oxygen 20.61
Carbon dioxide .03
Argon 1.00
Water vapor (average) 1.40
Air expired from the lungs contains:--
Nitrogen 76.95
Oxygen 15.67
Carbon dioxide 4.38
Water vapor 2
Argon 1
In other words, there is a loss between 4 and 5 per cent oxygen, and nearly
a corresponding gain in carbon dioxide, in expired air. There are also some
other organic substances present.
[Illustration: The respiration of cells.]
Cell Respiration.--It has been shown, in the case of very simple animals,
such as the _amoeba_, that when oxidation takes place in a cell, work
results from this oxidation. The oxygen taken into the lungs is not used
there, but is carried by the blood to such parts of the body as need oxygen
to oxidize food materials in the cells. Since work is done in the cells of
the body, food and oxygen are therefore required. The quantity of oxygen
used by the body is nearly dependent on the amount of work performed.
Oxygen is constantly taken from the blood by tissues in a state of rest and
is used up when the body is at work. This is suggested by the fact that in
a given time a man, when working, gives off more oxygen (in carbon dioxide)
than he takes in during that time.
While work is being done certain wastes are formed in the cell. Carbon
dioxide is given off when carbon is burned. But when proteins are burned,
another waste product containing nitrogen is formed. This must be passed
off from the cells, as it is a poison. Here again the lymph and blood, the
common carriers, take the waste material to points where it may be
_excreted_ or passed out of the body.
The Mechanics of Respiration. The Pleura.--The lungs are covered with a
thin elastic membrane, the _pleura_. This forms a bag in which the lungs
are hung. Between the walls of the bag and the lungs is a space filled with
lymph. By this means the lungs are prevented from rubbing against the walls
of the chest.
[Illustration: The chest cavity (_a_) at the time of a full breath; (_b_),
after an expiration. Explain how the cavity for lungs is made larger.]
Breathing.--In every full breath there are two distinct movements,
inspiration (taking air in) and expiration (forcing air out). In man an
inspiration is produced by the contraction of the muscles between the ribs,
together with the contraction of the diaphragm, the muscular wall just
below the heart and lungs; this results in pulling down the diaphragm and
pulling upward and outward of the ribs, thus making the space within the
chest cavity larger. The lungs, which lie within this cavity, are filled by
the air rushing into the larger space thus made. That this cavity is larger
than it was at first may be demonstrated by a glance at the accompanying
figure. An expiration is simpler than an inspiration, for it requires no
muscular effort; the muscles relax, the breastbone and ribs sink into
place, while the diaphragm returns to its original position.
[Illustration: Apparatus to show the mechanics of breathing.]
A piece of apparatus which illustrates to a degree the mechanics of
breathing may be made as follows: Attach a string to the middle of a piece
of sheet rubber. Tie the rubber over the large end of a bell jar. Pass a
glass Y-tube through a rubber stopper. Fasten two small toy balloons to the
branches of the tube. Close the small end of the jar with the stopper.
Adjust the tube so that the balloons shall hang free in the jar. If now the
rubber sheet is pulled down by means of the string, the air pressure in the
jar is reduced and the toy balloons within expand, owing to the air
pressure down the tube. When the rubber is allowed to go back to its former
position, the balloons collapse.
[Illustration: Diagram showing the relative amounts of tidal, complemental,
reserve, and residual air. The brace shows the average lung capacity for
the adult man.]
Rate of Breathing and Amount of Air Breathed.--During quiet breathing, the
rate of inspiration is from fifteen to eighteen times per minute; this rate
largely depends on the amount of physical work performed. About 30 cubic
inches of air are taken in and expelled during the ordinary quiet
respiration. The air so breathed is called _tidal air_. In a "long" breath,
we take in about 100 cubic inches in addition to the tidal air. This is
called _complemental air_. By means of a forced expiration, it is possible
to expel from 75 to 100 cubic inches more than tidal air; this air is
called _reserve air_. What remains in the lungs, amounting to about 100
cubic inches, is called the _residual air_. The value of deep breathing is
seen by a glance at the diagram. It is only by this means that we clear the
lungs of the reserve air with its accompanying load of carbon dioxide.
Respiration under Nervous Control.--The muscular movements which cause an
inspiration are partly under the control of the will, but in part the
movement is beyond our control. The nerve centers which govern inspiration
are part of the sympathetic nervous system. Anything of an irritating
nature in the trachea or larynx will cause a sudden expiration or cough.
When a boy runs, the quickened respiration is due to the fact that oxygen
is used up rapidly and a larger quantity of carbon dioxide is formed. The
carbon dioxide in the blood stimulates the nervous center which has control
of respiration to greater activity, and quickened inspiration follows.
Need of Ventilation.--During the course of a day the lungs lose to the
surrounding air nearly two pounds of carbon dioxide. This means that about
three fifths of a cubic foot is given off by each person during an hour.
When we are confined for some time in a room, it becomes necessary to get
rid of this carbon dioxide. This can be done only by means of proper
ventilation. A considerable amount of moisture is given off from the body,
and this moisture in a crowded room is responsible for much of the
discomfort. The air becomes humid and uncomfortable. It has been found that
by keeping the air in motion in such a room (as through the use of electric
fans) much of this discomfort is obviated.
The presence of impurities in the air of a room may easily be determined by
its odor. The odor of a poorly ventilated room is due to organic impurities
given off with the carbon dioxide. This, fortunately, gives us an index of
the amount of waste material in the air. Among the factors which take
oxygen from the air in a closed room and produce carbon dioxide are burning
gas or oil lamps and stoves, and the presence of a number of people.
[Illustration: Three ways of ventilating a room. _i_, inlet for air; _o_,
outlet for air. Which is the best method of ventilation? Explain.]
Proper Ventilation.--Ventilation consists in the removal of air that has
been used, and the introduction of a fresh supply to take its place. Heated
air rises, carrying with it much of the carbon dioxide and other
impurities. A good method of ventilation for the home is to place a board
two or three inches high between the lower sash and the frame of a window
or to have the window open an inch or so at the top and the bottom. An open
fireplace in a room aids in ventilation because of the constant draft up
the flue.
Sweeping and Dusting.--It is very easy to demonstrate the amount of dust in
the air by following the course of a beam of light in a darkened room. We
have already proved that spores of mold and yeast exist in the air. That
bacteria are also present can be proved by exposing a sterilized gelatin
plate to the air in a schoolroom for a few moments.[47]
Footnote 47: Expose two sterilized dishes containing culture
media; one in a room being swept with a damp broom, and the
other in a room which is being swept in the usual manner.
Note the formation of colonies of bacteria in each dish. In
which dish does the more abundant growth take place?
Many of the bacteria present in the air are active in causing diseases of
the respiratory tract, such as diphtheria, membranous croup, and
tuberculosis. Other diseases, as colds, bronchitis (inflammation of the
bronchial tubes), and pneumonia (inflammation of the tiny air sacs of the
lungs), are also caused by bacteria.
[Illustration: Plate culture exposed for five minutes in a school hall
where pupils were passing to recitations. Each spot is a colony of bacteria
or mold.]
Dust, with its load of bacteria, will settle on any horizontal surface in a
room not used for three or four hours. Dusting and sweeping should always
be done with a damp cloth or broom, otherwise the bacteria are simply
stirred up and sent into the air again. The proper watering of streets
before they are swept is also an important factor in health. Much dust is
composed largely of dried excreta of animals. Soft-coal smoke does its
share to add to the impurities of the air, while sewer gas and illuminating
gas are frequently found in sufficient quantities to poison people. Pure
air is, as can be seen, almost an impossibility in a great city.
[Illustration: A sleeping porch, an ideal way to get fresh air at night.]
How to get Fresh Air.--As we know, green plants give off in the sunlight
considerable more oxygen than they use, and they use up carbon dioxide. The
air in the country is naturally purer than in the city, as smoke and
bacteria are not so prevalent there, and the plants in abundance give off
oxygen. In the city the night air is purer than day air, because the
factories have stopped work, the dust has settled, and fewer people are on
the streets. The old myth of "night air" being injurious has long since
been exploded, and thousands of people of delicate health, especially those
who have weak throat or lungs, are regaining health by sleeping out of
doors or with the windows wide open. The only essential in sleeping out of
doors or in a room with a low temperature is that the body be kept warm and
the head be protected from strong drafts by a nightcap or hood. Proper
ventilation at _all_ times is one of the greatest factors in good health.
Change of Air.--Persons in poor health, especially those having
tuberculosis, are often cured by a change of air. This is not always so
much due to the composition of the air as to change of occupation, rest,
and good food. Mountain air is dry, and relatively free from dust and
bacteria, and often helps a person having tuberculosis. Air at the seaside
is beneficial for some forms of disease, especially hay fever and bone
tuberculosis. Many sanitariums have been established for this latter
disease near the ocean, and thousands of lives are being annually saved in
this way.
[Illustration: Unfavorable sleeping conditions. Explain why unfavorable.]
Ventilation of Sleeping Rooms.--Sleeping in close rooms is the cause of
much illness. Beds ought to be placed so that a constant supply of fresh
air is given without a direct draft. This may often be managed with the use
of screens. Bedroom windows should be thrown open in the morning to allow
free entrance of the sun and air, bedclothes should be washed frequently,
and sheets and pillow covers often changed. Bedroom furniture should be
simple, and but little drapery allowed in the room.
Hygienic Habits of Breathing.--Every one ought to accustom himself upon
going into the open air to inspire slowly and deeply to the full capacity
of the lungs. A slow expiration should follow. Take care to force the air
out. Breathe through the nose, thus warming the air you inspire before it
enters the lungs and chills the blood. Repeat this exercise several times
every day. You will thus prevent certain of the air sacs which are not
often used from becoming hardened and permanently closed.
Relation of Proper Exercise to Health.--We are all aware that exercise in
moderation has a beneficial effect upon the human organism. The pale face,
drooping shoulders, and narrow chest of the boy or girl who takes no
regular exercise is too well known. Exercise, besides giving direct use of
the muscles, increases the work of the heart and lungs, causing deeper
breathing and giving the heart muscles increased work; it liberates heat
and carbon dioxide from the tissues where the work is taking place, thus
increasing the respiration of the tissues themselves, and aids mechanically
in the removal of wastes from tissues. It is well known that exercise, when
taken some little time after eating, has a very beneficial effect upon
digestion. Exercise and especially games are of immense importance to the
nervous system as a means of rest. The increasing number of playgrounds in
this country is due to this acknowledged need of exercise, especially for
growing children.
Proper exercise should be moderate and varied. Walking in itself is a
valuable means of exercising certain muscles, so is bicycling, but neither
is ideal as the _only_ form to be used. _Vary_ your exercise so as to bring
different muscles into play, take exercise that will allow free breathing
out of doors if possible, and the natural fatigue which follows will lead
you to take the rest and sleep that every normal body requires.
Exercise should always be limited by fatigue, which brings with it fatigue
poisons. This is nature's signal when to rest. If one's use of diet and air
is proper, the fatigue point will be much further off than otherwise. One
should learn to _relax_ when not in activity. The habit produces rest, even
between exertions very close together, and enables one to continue to
repeat those exertions for a much longer time than otherwise. The habit of
lying down when tired is a good one.
The Relation of Tight Clothing to Correct Breathing.--It is impossible to
breathe correctly unless the clothing is worn loosely over the chest and
abdomen. Tight corsets and tight belts prevent the walls of the chest and
the abdomen from pushing outward and interfere with the drawing of air into
the lungs. They may also result in permanent distortion of parts of the
skeleton directly under the pressure. Other organs of the body cavity, as
the stomach and intestines, may be forced downward, out of place, and in
consequence cannot perform their work properly.
Suffocation and Artificial Respiration.--Suffocation results from the
shutting off of the supply of oxygen from the lungs. It may be brought
about by an obstruction in the windpipe, by a lack of oxygen in the air,
by inhaling some other gas in quantity, or by drowning. A severe electric
shock may paralyze the nervous centers which control respiration, thus
causing a kind of suffocation. In the above cases, death often may be
prevented by prompt recourse to artificial respiration. To accomplish
this, place the patient on his back with the head lower than the body;
grasp the arms near the elbows and draw them _upward_ and _outward_ until
they are stretched above the head, on a line with the body. By this means
the chest cavity is enlarged and an inspiration produced. To produce
an expiration, carry the arms downward, and press them against the chest,
thus forcing the air out of the lungs. This exercise, regularly repeated
every few seconds, if necessary for hours, has been the source of saving
many lives.
Common Diseases of the Nose and Throat.--Catarrh is a disease to
which people with sensitive mucous membrane of the nose and throat are
subject. It is indicated by the constant secretion of mucus from these
membranes. Frequent spraying of the nose and throat with some mild
antiseptic solutions is found helpful. Chronic catarrh should be attended
to by a physician. Often we find children breathing entirely through the
mouth, the nose being seemingly stopped up. When this goes on for
some time the nose and throat should be examined by a physician for
_adenoids_, or growths of soft masses of tissue which fill up the nose cavity,
thus causing a shortage of the air supply for the body. Many a child,
backward at school, thin and irritable, has been changed to a healthy,
normal, bright scholar by the removal of adenoids. Sometimes the
tonsils at the back of the mouth cavity may become enlarged, thus shutting
off the air supply and causing the same trouble as we see in a case of
adenoids. The simple removal of the obstacle by a doctor soon cures
this condition. (See page 395.)
Organs of Excretion.--All the life processes which take place in a living
thing result ultimately, in addition to giving off of carbon dioxide, in
the formation of organic wastes within the body. The retention of these
wastes which contain nitrogen, is harmful to animals. In man, the skin and
kidneys remove this waste from the body, hence they are called the organs
of excretion.
[Illustration: Longitudinal section through a kidney.]
The Human Kidney.--The human kidney is about four inches long, two and one
half inches wide, and one inch in thickness. Its color is dark red. If the
structure of the medulla and cortex (see figure above) is examined under
the compound microscope, you will find these regions to be composed of a
vast number of tiny branched and twisted tubules. The outer end of each of
these tubules opens into the _pelvis_, the space within the kidney; the
inner end, in the cortex, forms a tiny closed sac. In each sac, the outer
wall of the tube has grown inward and carried with it a very tiny artery.
This artery breaks up into a mass of capillaries. These capillaries, in
turn, unite to form a small vein as they leave the little sac. Each of
these sacs with its contained blood vessels is called a _glomerulus_.
[Illustration: Diagram of kidney circulation, showing a glomerulus and
tubule: _a_, artery bringing blood to part; _b_, capillary bringing blood
to glomerulus; _b'_, vessel continuing with blood to vein; _c_, vein; _t_,
tubule; _G_, glomerulus.]
Wastes given off by the Blood in the Kidney.--In the glomerulus the blood
loses by osmosis, through the very thin walls of the capillaries, first, a
considerable amount of water (amounting to nearly three pints daily);
second, a nitrogenous waste material known as urea; third, salts and other
waste organic substances, uric acid among them.
These waste products, together with the water containing them, are known as
_urine_. The total amount of nitrogenous waste leaving the body each day is
about twenty grams. It is passed through the _ureter_ to the _urinary
bladder_; from this reservoir it is passed out of the body, through a tube
called the _urethra_. After the blood has passed through the glomeruli of
the kidneys it is purer than in any other place in the body, because,
before coming there, it lost a large part of its burden of carbon dioxide
in the lungs. After leaving the kidney it has lost much of its nitrogenous
waste. So dependent is the body upon the excretion of its poisonous
material that, in cases where the kidneys do not do their work properly,
death may ensue within a few hours.
[Illustration: Diagram of a section of the skin. (Highly magnified.)]
Structure and Use of Sweat Glands.--If you examine the palm of your hand
with a lens, you will notice the surface is thrown into little ridges. In
these ridges may be found a large number of very tiny pits; these are the
pores or openings of the sweat-secreting glands. From each opening a little
tube penetrates deep within the epidermis; there, coiling around upon
itself several times, it forms the sweat gland. Close around this coiled
tube are found many capillaries. From the blood in these capillaries, cells
lining the wall of the gland take water, and with it a little carbon
dioxide, urea, and some salts (common salt among others). This forms the
excretion known as _sweat_. The combined secretions from these glands
amount normally to a little over a pint during twenty-four hours. At all
times, a small amount of sweat is given off, but this is evaporated or is
absorbed by the underwear; as this passes off unnoticed, it is called
_insensible perspiration_. In hot weather or after hard manual labor the
amount of perspiration is greatly increased.
Regulation of Heat of the Body.--The bodily temperature of a person engaged
in manual labor will be found to be but little higher than the temperature
of the same person at rest. We know from our previous experiments that heat
is released. Muscles, nearly one half the weight of the body, release about
five sixths of their energy as heat. At all times they are giving up some
heat. How is it that the bodily temperature does not differ greatly at such
times? The temperature of the body is largely regulated by means of the
activity of the sweat glands. The blood carries much of the heat, liberated
in the various parts of the body by the oxidation of food, to the surface
of the body, where it is lost in the evaporation of sweat. In hot weather
the blood vessels of the skin are dilated; in cold weather they are made
smaller by the action of the nervous system. The blood thus loses water in
the skin, the water evaporates, and we are cooled off. _The object of
increased perspiration, then, is to remove heat from the body._ With a
large amount of blood present in the skin, perspiration is increased; with
a small amount, it is diminished. Hence, we have in the skin an automatic
regulator of bodily temperature.
Sweat Glands under Nervous Control.--The sweat glands, like the other
glands in the body, are under the control of the sympathetic nervous
system. Frequently the nerves dilate the blood vessels of the skin, thus
helping the sweat glands to secrete, by giving them more blood.
"Thus regulation is carried out by the nervous system
determining, on the one hand, the _loss_ by governing the
supply of blood to the skin and the action of the sweat
glands; and on the other, the _production_ by diminishing or
increasing the oxidation of the tissues."--FOSTER AND SHORE,
_Physiology_.
Colds and Fevers.--The regulation of blood passing through the blood
vessels is under control of the nervous system. If this mechanism is
interfered with in any way, the sweat glands may not do their work,
perspiration may be stopped, and the heat from oxidation held within the
body. The body temperature goes up, and a fever results.
[Illustration: _A_, blood vessels in skin normal; _B_, when congested.]
If the blood vessels in the skin are suddenly cooled when full of blood,
they contract and send the blood elsewhere. As a result a congestion or
cold may follow. Colds are, in reality, a congestion of membranes lining
certain parts of the body, as the nose, throat, windpipe, or lungs.
When suffering from a cold, it is therefore important not to chill the
skin, as a full blood supply should be kept in it and so kept from the seat
of the congestion. For this reason hot baths (which call the blood to the
skin), the avoiding of drafts (which chill the skin), and warm clothing are
useful factors in the care of colds.
Hygiene of the Skin.--The skin is of importance both as an organ of
excretion and as a regulator of bodily temperature. The skin of the entire
body should be bathed frequently so that this function of excretion may be
properly performed. Pride in one's own appearance forbids a dirty skin. For
those who can stand it, a cold sponge bath is best. Soap should be used
daily on parts exposed to dirt. Exercise in the open air is important to
all who desire a good complexion. The body should be kept at an even
temperature by the use of proper underclothing. Wool, a poor conductor of
heat, should be used in winter, and cotton, which allows of a free escape
of heat, in summer.
Cuts, Bruises, and Burns.--In case the skin is badly broken, it is
necessary to prevent the entrance and growth of bacteria. This may be done
by washing the wound with weak antiseptic solutions such as 3 per cent
_carbolic acid_, 3 per cent _lysol_, or _peroxide of hydrogen_ (full
strength). These solutions should be applied immediately. A burn or scald
should be covered at once with a paste of baking soda, with olive oil, or
with a mixture of limewater and linseed oil. These tend to lessen the pain
by keeping out the air and reducing the inflammation.
Summary of Changes in Blood within the Body.--We have already seen that red
corpuscles in the lungs lose part of their load of carbon dioxide that they
have taken from the tissues, replacing it with oxygen. This is accompanied
by a change of color from purple (in blood which is poor in oxygen) to that
of bright red (in richly oxygenated blood). Other changes take place in
other parts of the body. In the walls of the food tube, especially in the
small intestine, the blood receives its load of fluid food. In the muscles
and other working tissues the blood gives up food and oxygen, receiving
carbon dioxide and organic waste in return. In the liver, the blood gives
up its sugar, and the worn-out red corpuscles which break down are removed
(as they are in the spleen) from the circulation. In glands, it gives up
materials used by the gland cells in their manufacture of secretions. In
the kidneys, it loses water and nitrogenous wastes (_urea_). In the skin,
it also loses some waste materials, salts, and water.
"The Effect of Alcohol on Body Heat.--It is usually believed
that 'taking a drink' when cold makes one warmer. But such
is not the case. In reality alcohol lowers the temperature
of the body by dilating the blood vessels of the skin. It
does this by means of its influence on the nervous system.
It is, therefore, a mistake to drink alcoholic beverages
when one is extremely cold, because by means of this more
bodily heat is allowed to escape.
"Because alcohol is quickly oxidized, and because heat is
produced in the process, it was long believed to be of value
in maintaining the heat of the body. A different view now
prevails as the result of much observation and experiment.
Physiologists show by careful experiments that though the
temperature of the body rises during digestion of food, it
is lowered for some hours when alcohol is taken. The flush
which is felt upon the skin after a drink of wine or spirits
is due in part to an increase of heat in the body, but also
to the paralyzing effect of the alcohol upon the capillary
walls, allowing them to dilate, and so permitting more of
the warm blood of the interior of the body to reach the
surface. There it is cooled by radiation, and the general
temperature is lowered."--MACY, _Physiology_.
Effect of Alcohol on Respiration.--Alcohol tends to congest the membrane of
the throat and lungs. It does this by paralyzing the nerves which take care
of the tiny blood vessels in the walls of the air tubes and air sacs. The
capillaries become full of blood, the air spaces are lessened, and
breathing is interfered with. The use of alcohol is believed by many
physicians to predispose a person to tuberculosis. Certainly this disease
attacks drinkers more readily than those who do not drink. Alcohol
interferes with the respiration of the cells because it is oxidized very
quickly within the body as it is quickly absorbed and sent to the cells. So
rapid is this oxidation that it interferes with the oxidation of other
substances. Using alcohol has been likened to burning kerosene in a stove;
the operation is a dangerous one.
Effects of Tobacco on Respiration.--Tobacco smoke contains the same kind of
poisons as the tobacco, with other irritating substances added. It is
extremely irritating to the throat; it often causes a cough, and renders it
more liable to inflammation. If the smoke is inhaled more deeply, the
vaporized nicotine is still more readily absorbed and may thus produce
greater irritation in the bronchi and lungs. Cigarettes are worse than
other forms of tobacco, for they contain the same poisons with others in
addition.
Effect of Alcohol on the Kidneys.--It is said that alcohol is one of the
greatest causes of disease in the kidneys. The forms of disease known as
"fatty degeneration of the kidney" and "Bright's disease" are both
frequently due to this cause. The kidneys are the most important organs for
the removal of nitrogenous waste.
Alcohol unites more easily with oxygen than most other food materials,
hence it takes away oxygen that would otherwise be used in oxidizing these
foods. Imperfect oxidation of foods causes the development and retention of
poisons in the blood which it becomes the work of the kidneys to remove. If
the kidneys become overworked, disease will occur. Such disease is likely
to make itself felt as rheumatism or gout, both of which are believed to be
due to waste products (poisons) in the blood.
Poisons produced by Alcohol.--When too little oxygen enters the draft of
the stove, the wood is burned imperfectly, and there are clouds of smoke
and irritating gases. So, if oxygen unites with the alcohol and too little
reaches the cells, instead of carbon dioxide, water, and urea being formed,
there are other products, some of which are exceedingly poisonous and which
the kidneys handle with difficulty. The poisons retained in the circulation
never fail to produce their poisonous effects, as shown by headaches,
clouded brain, pain, and weakness of the body. The word "intoxication"
means "in a state of poisoning." These poisons gradually accumulate as the
alcohol takes oxygen from the cells. The worst effects come last, when the
brain is too benumbed to judge fairly of their harm.
REFERENCE BOOKS
ELEMENTARY
Hunter, _Laboratory Problems in Civic Biology_. American
Book Company.
Davison, _Human Body and Health_. American Book Company.
Gulick, _Hygiene Series, Emergencies, Good Health_. Ginn
and Company.
Hough and Sedgwick, _The Human Mechanism_. Ginn and Company.
Macy, _General Physiology_. American Book Company.
Ritchie, _Human Physiology_. World Book Company.
XXIII. BODY CONTROL AND HABIT FORMATION
_Problems.--How is body control maintained?
(a) What is the mechanism of direction and control?
(b) What is the method of direction and control?
(c) What are habits? How are they formed and how broken?
(d) What are the organs of sense? What are their uses?
(e) How does alcohol affect the nervous system?_
LABORATORY SUGGESTIONS
_Demonstration._--Sensory motor reactions.
_Demonstration._--Nervous system. Models and frog
dissections.
_Demonstration._--Neurones under compound microscope
(optional).
_Demonstration._--Reflex acts are unconscious acts: show how
conscious acts may become habitual.
_Home exercise_ in habit forming.
_The senses.--Home exercises._--(1) To determine areas most
sensitive to touch. (2) To determine or map out hot and cold
spots on an area on the wrist. (3) To determine functions of
different areas on tongue.
_Demonstration._--Show how eye defects are tested.
_Laboratory summary._--The effects of alcohol on the nervous
system.
The Body a Self-directed Machine.--Throughout the preceding chapters the
body has been likened to an engine, which, while burning its fuel, food,
has done work. If we were to carry our comparison further, however, the
simile ceases. For the engineer runs the engine, while the bodily machine
is self-directive.
Moreover, most of the acts we perform during a day's work are results of
the automatic working of this bodily machine. The heart pumps; the blood
circulates its load of food, oxygen, and wastes; the movements of breathing
are performed; the thousand and one complicated acts that go on every day
within the body are _seemingly_ undirected.
[Illustration: The central nervous system.]
Automatic Activity.--In addition to this, numbers of other of our daily
acts are not thought about. If we are well-regulated body machines, we get
up in the morning, automatically wash, clean our teeth, dress, go to the
toilet, get our breakfast, walk to school, even perform such complicated
processes as that of writing, without _thinking_ about or _directing_ the
machine. In these respects we have become creatures of habit. Certain acts
which once we might have learned consciously, have become automatic.
But once at school, if we are really making good in our work in the
classroom, we begin a higher control of our bodily functions. Automatic
control acts no longer, and sensation is not the only guide--for we now
begin to make _conscious choice_; we weigh this matter against another,--in
short, we _think_.
Parts of the Nervous System.--This wonderful self-directive apparatus
placed within us, which is in part under control of our will, is known as
the nervous system. In the vertebrate animals, including man, it consists
of two divisions. One includes the brain, spinal cord, the cranial and
spinal nerves, which together make up the _cerebro-spinal nervous system_.
The other division is called the _sympathetic nervous system_ and has to do
with those bodily functions which are beyond our control. Every group of
cells in the body that has work to do (excepting the floating cells of the
blood) is directly influenced by these nerves. Our bodily comfort is
dependent upon their directive work. The organs which put us in touch with
our surroundings are naturally at the _surface_ of the body. Small
collections of nerve cells, called _ganglia_, are found in all parts of the
body. These nerve centers are connected, to a greater or less degree, with
the surface of the body by the nerves, which serve as pathways between the
end organs of touch, sight, taste, etc., and the centers in the brain or
spinal cord. Thus sensation is obtained.
Sensations and Reactions.--We have already seen that simpler forms of life
perform certain acts because certain outside forces acting upon them cause
them to _react_ to the stimulus from without. The one-celled animal
responds to the presence of food, to heat, to oxygen, to other conditions
in its surroundings. An earthworm is repelled by light, is attracted by
food. All animals, including man, are put in touch with their surroundings
by what we call the organs of sensation. The senses of man, besides those
we commonly know as those of sight, hearing, taste, smell, and touch, are
those of temperature, pressure, and pain. It is obvious that such organs,
if they are to be of use to an animal, must be at the outside of the body.
Thus we find eyes and ears in the head, and taste cells in the mouth, while
other cells in the nose perceive odors, and still others in the skin are
sensitive to heat or cold, pressure or pain.
But this is not all. Strangely enough, we do not see with our eyes or taste
with our taste cells. These organs receive the sensations, and by means of
a complicated system of greatly elongated cell structures, the message is
sent inward, relayed by other elongated cells until the sensory message
reaches an inner station, in the central nervous system. We see and hear
and smell in our brain. Let us next examine the structure of the nerve
cells or _neurons_ part of which serve as pathways for these messages.
[Illustration: Diagram of a neuron or nerve unit.]
Neurones.--A nerve cell, like other cells in the body, is a mass of
protoplasm containing a nucleus. But the body of the nerve cell is usually
rather irregular in shape, and distinguished from most other cells by
possessing several delicate, branched protoplasmic projections called
_dendrites_. One of these processes, the axon, is much longer than the
others and ends in a muscle or organ of sensation. The axon forms the
pathway over which nervous impulses travel to and from the nerve centers.
A nerve consists of a bundle of such tiny axons, bound together by
connective tissue. As a nerve ganglia is a center of activity in the
nervous system, so a cell body is a center of activity which may send an
impulse over this thin strand of protoplasm (the axon) prolonged many
hundreds of thousands of times the length of the cell. Some neurones in the
human body, although visible only under the compound microscope, give rise
to axons several feet in length.
Because some bundles of axons originate in organs that receive sensations
and send those sensations to the central nervous system, they are called
_sensory nerves_. Other axons originate in the central nervous system and
pass outward as nerves producing movement of muscles. These are called
_motor nerves_.
The Brain of Man.--In man, the central nervous system consists of a brain
and spinal cord inclosed in a bony case. From the brain, twelve pairs of
nerves are given off; thirty-one pairs more leave the spinal cord. The
brain has three divisions. The _cerebrum_ makes up the largest part. In
this respect it differs from the cerebrum of the frog and other
vertebrates. It is divided into two lobes, the _hemispheres_, which are
connected with each other by a broad band of nerve fibers. The outer
surface of the cerebrum is thrown into folds or _convolutions_ which give a
large surface, the cell bodies of the neurons being found in this part of
the cerebrum. Holding the cell bodies and fibers in place is a kind of
connective tissue. The inner part (white in color) is composed largely of
fibers which pass to other parts of the brain and down into the spinal
cord. Under the cerebrum, and dorsal to it, lies the little brain, or
_cerebellum_. The two sides of the cerebellum are connected by a band of
nerve fibers which run around into the lower hindbrain or _medulla_. This
band of fibers is called the _pons_. The medulla is, in structure, part of
the spinal cord, and is made up largely of fibers running longitudinally.
The Sympathetic Nervous System.--Connected with the central nervous system
is that part of the nervous apparatus that controls the muscles of the
digestive tract and blood vessels, the secretions of gland cells, and all
functions which have to do with life processes in the body. This is called
the sympathetic nervous system.
Functions of the Parts of the Central Nervous System of the Frog.--From
careful study of living frogs, birds, and some mammals we have learned much
of what we know of the functions of the parts of the central nervous system
in man.
It has been found that if the entire brain of a frog is destroyed and
separated from the spinal cord, "the frog will continue to live, but with a
very peculiarly modified activity." It does not appear to breathe, nor does
it swallow. It will not move or croak, but if acid is placed upon the skin
so as to irritate it, the legs make movements to push away and to clean off
the irritating substance. The spinal cord is thus shown to be a center for
defensive movements. If the cerebrum is separated from the rest of the
nervous system, the frog seems to act a little differently from the normal
animal. It jumps when touched, and swims when placed in water. It will
croak when stroked, or swallow if food be placed in its mouth. But it
manifests no hunger or fear, and is in every sense a machine which will
perform certain actions after certain stimulations. Its movements are
automatic. If now we watch the movements of a frog which has the brain
uninjured in any way, we find that it acts _spontaneously_. It tries to
escape when caught. It feels hungry and seeks food. It is capable of
voluntary action. It acts like a normal individual.
[Illustration: Diagram to show the parts of the brain and action of the
different parts of the brain.]
Functions of the Cerebrum.--In general, the functions of the different
parts of the brain in man agree with those functions we have already
observed in the frog. The cerebrum has to do with conscious activity; that
is, thought. It presides over what we call our thoughts, our will, and our
sensations. A large part of the area of the outer layer of the cerebrum
seems to be given over to some one of the different functions of speech,
hearing, sight, touch, movements of bodily parts. The movement of the
smallest part of the body appears to have its definite localized center in
the cerebrum. Experiments have been performed on monkeys, and these,
together with observations made on persons who had lost the power of
movement of certain parts of the body, and who, after death, were found to
have had diseases localized in certain parts of the cerebrum, have given to
us our knowledge on this subject.
[Illustration: Diagram of the nerve path of a simple reflex action.]
Reflex Actions; their Meaning.--If through disease or for other reasons the
cerebrum does not function, no will power is exerted, nor are intelligent
acts performed. All acts performed in such a state are known as _reflex
actions_. The involuntary brushing of a fly from the face, or the attempt
to move away from the source of annoyance when tickled with a feather, are
examples of reflexes. In a reflex act, a person does not think before
acting. The nervous impulse comes from the outside to cells that are not in
the cerebrum. The message is short-circuited back to the surface by motor
nerves, without ever having reached the thinking centers. The nerve cells
which take charge of such acts are located in the cerebellum or spinal
cord.
Automatic Acts.--Some acts, however, are learned by conscious thought, as
writing, walking, running, or swimming. Later in life, however, these
activities become automatic. The actual performance of the action is then
taken up by the cerebellum, medulla, and spinal ganglia. Thus the thinking
portion of the brain is relieved of part of its work.
Bundles of Habits.--It is surprising how little real thinking we do during
a day, for most of our acts are habitual. Habit takes care of our dressing,
our bathing, our care of the body organs, our methods of eating; even our
movements in walking and the kind of hand we write are matters of habit
forming. We are bundles of habits, be they good ones or bad ones.
Habit Formation.--The training of the different areas in the cerebrum to do
their work well is the object of education. When we learned to write, we
exerted conscious effort in order to make the letters. Now the act of
forming the letters is done without thought. By training, the act has
become automatic. In the beginning, a process may take much thought and
many trials before we are able to complete it. After a little practice, the
same process may become almost automatic. We have formed a habit. Habits
are really acquired reflex actions. They are the result of nature's method
of training. The conscious part of the brain has trained the cerebellum or
spinal cord to do certain things that, at first, were taken charge of by
the cerebrum.
Importance of Forming Right Habits.--Among the habits early to be acquired
are the habits of studying properly, of concentrating the mind, of learning
self-control, and, above all, of contentment. Get the most out of the world
about you. Remember that the immediate effect in the study of some subjects
in school may not be great, but the cultivation of correct methods of
thinking may be of the greatest importance later in life. The man or woman
who has learned how to concentrate on a problem, how to weigh all sides
with an unbiased mind, and then to decide on what they believe to be best
and right are the efficient and happy ones of their generation.
"The hell to be endured hereafter, of which theology tells,
is no worse than the hell we make for ourselves in this
world by habitually fashioning our characters in the wrong
way. Could the young but realize how soon they will become
mere walking bundles of habits, they would give more heed to
their conduct while in the plastic state. We are spinning
our own fates, good or evil, and never to be undone. Every
smallest stroke of virtue or of vice leaves its
never-so-little scar. The drunken Rip Van Winkle, in
Jefferson's play, excuses himself for every fresh
dereliction by saying, 'I won't count this time!' Well! he
may not count it, and a kind Heaven may not count it; but it
is being counted none the less. Down among his nerve cells
and fibers the molecules are counting it, registering and
storing it up to be used against him when the next
temptation comes. Nothing we ever do is, in strict
scientific literalness, wiped out. Of course this has its
good side as well as its bad one. As we become permanent
drunkards by so many separate drinks, so we become saints in
the moral, and authorities in the practical and scientific,
spheres by so many separate acts and hours of work. Let no
youth have any anxiety about the upshot of his education,
whatever the line of it may be. If he keep faithfully busy
each hour of the working day, he may safely leave the final
result to itself. He can with perfect certainty count on
waking up some fine morning, to find himself one of the
competent ones of his generation, in whatever pursuit he may
have singled out."--JAMES, _Psychology_.
Some Rules for Forming Good Habits.--Professor Horne gives several rules
for making good or breaking bad habits. They are: "First, _act on every
opportunity_. Second, _make a strong start_. Third, _allow no exception_.
Fourth, _for the bad habit establish a good one_. Fifth, summoning all the
man within, _use effort of will_." Why not try these out in forming some
good habit? You will find them effective.
[Illustration: The effect of fatigue on nerve cells. _a_, healthy brain
cell; _b_, fatigued brain cell.]
Necessity of Food, Fresh Air, and Rest.--The nerve cells, like all other
cells in the body, are continually wasting away and being rebuilt.
Oxidation of food material is more rapid when we do mental work. The cells
of the brain, like muscle cells, are not only capable of fatigue, but show
this in changes of form and of contents. _Food_ brought to them in the
blood, plenty of _fresh air_, especially when engaged in active brain work,
and _rest_ at proper times, are essential in keeping the nervous system in
condition. One of the best methods of resting the brain cells is a change
of occupation. Tennis, golf, baseball, and other outdoor sports combine
muscular exercise with brain activity of a different sort from that of
business or school work. But change of occupation will not rest exhausted
neurones. For this, sleep is necessary. Especially is sleep an important
factor in the health of the nervous system of growing children.
Necessity of Sleep.--Most brain cells attain their growth early in life.
Changes occur, however, until some time after the school age. Ten hours of
sleep should be allowed for a child, and at least eight hours for an adult.
At this time, only, do the brain cells have opportunity to rest and store
food and energy for their working period.
Sleep is one way in which all cells in the body, and particularly those of
the nervous system, get their rest. The nervous system, by far the most
delicate and hardest-worked set of tissues in the body, needs rest more
than do other tissues, for its work directing the body only ends with sleep
or unconsciousness. The afternoon nap, snatched by the brain worker, gives
him renewed energy for his evening's work. It is not hard application to a
task that wearies the brain; it is _continuous_ work without rest.
THE SENSES
Touch.--In animals having a hard outside covering, such as certain worms,
insects, and crustaceans, minute hairs, which are sensitive to touch, are
found growing out from the body covering. At the base of these hairs are
found neurones which send axons inward to the central nervous system.
[Illustration: Nerves in the skin: _a_, nerve fiber; _b_, tactile papillæ,
containing a tactile corpuscle; _c_, papillæ containing blood vessels.
(After Benda.)]
Organs of Touch.--In man, the nervous mechanism which governs touch is
located in the folds of the dermis or in the skin. Special nerve endings,
called the _tactile corpuscles_, are found there, each inclosed in a sheath
or capsule of connective tissue. Inside is a complicated nerve ending, and
axons pass inward to the central nervous system. The number of tactile
corpuscles present in a given area of the skin determines the accuracy and
ease with which objects may be known by touch.
If you test the different parts of the body, as the back of the hand, the
neck, the skin of the arm, of the back, or the tip of the tongue, with a
pair of open dividers, a vast difference in the accuracy with which the two
points may be distinguished is noticed. On the tip of the tongue, the two
points need only be separated by 1/24 of an inch to be so distinguished. In
the small of the back, a distance of 2 inches may be reached before the
dividers feel like two points.
Temperature, Pressure, Pain.--The feeling of temperature, pressure, and
pain is determined by different end organs in the skin. Two kinds of nerve
fibers exist in the skin, which give distinct sensations of heat and cold.
These nerve endings can be located by careful experimentation. There are
also areas of nerve endings which are sensitive to pressure, and still
others, most numerous of all, sensitive to pain.
Taste Organs.--The surface of the tongue is folded into a number of little
projections known as papillæ. These may be more easily found on your own
tongue if a drop of vinegar is placed on its broad surface. In the folds,
between these projections on the top and back part of the tongue, are
located the organs of taste. These organs are called _taste buds_.
[Illustration: _A_, isolated taste bud, from whose upper free end project
the ends of the taste cells; _B_, supporting or protecting cell; _C_,
sensory cell.]
Each taste bud consists of a collection of spindle-shaped neurones, each
cell tipped at its outer end with a hairlike projection. These cells send
inward fibers to other cells, the fibers from which ultimately reach the
brain. The sensory cells are surrounded by a number of projecting cells
which are arranged in layers about them. Thus the organ in longitudinal
section looks somewhat like an onion cut lengthwise.
How we Taste.--Four kinds of substances may be distinguished by the sense
of taste. These are sweet, sour, bitter, and salt. Certain taste cells
located near the back of the tongue are stimulated only by a bitter taste.
Sweet substances are perceived by cells near the tip of the tongue, sour
substances along the sides, and salt about equally all over the surface. A
substance must be dissolved in fluid in order to be tasted. Many things
which we believe we taste are in reality perceived by the sense of smell.
Such are spicy sauces and flavors of meats and vegetables. This may easily
be proved by holding the nose and chewing, with closed eyes, several
different substances, such as an apple, an onion, and a raw potato.
Smell.--The sense of smell is located in the membrane lining the upper
part of the nose. Here are found a large number of rod-shaped cells which
are connected with the brain by means of the olfactory nerve. In order
to perceive odors, it is necessary to have them diffused in the air; hence
we sniff so as to draw in more air over the olfactory cells.
The Organ of Hearing.--The organ of hearing is the ear. The outer
ear consists of a funnel-like organ composed largely of cartilage which is
of use in collecting sound waves. This part of the ear incloses the auditory
canal, which is closed at the inner end by a tightly stretched membrane,
the _tympanic membrane_ or ear drum. The function of the tympanic
membrane is to receive sound waves, for all sound is caused by
vibrations in the air, these vibrations being transmitted, by the means
of a complicated apparatus found in the middle ear, to the real organ of
hearing located in the inner ear.
[Illustration: Section of ear: _E.M._, auditory canal; _Ty.M._, tympanic
membrane; _Eu._, Eustachian tube; _Ty_, middle ear; _Coc._, _A.S.C._,
_E.S.C._, etc., internal ear.]
Middle Ear.--The middle ear in man is a cavity inclosed by the temporal
bone, and separated from the outer ear by the tympanic membrane. A little
tube called the _Eustachian tube_ connects the inner ear with the mouth
cavity. By allowing air to enter from the mouth, the air pressure is
equalized on the ear drum. For this reason, we open the mouth at the time
of a heavy concussion and thus prevent the rupture of the delicate tympanic
membrane. Placed directly against the tympanic membrane and connecting it
with the inner ear is a chain of three tiny bones, the smallest bones of
the body. The outermost is called the _hammer_; the next the _anvil_; the
third the _stirrup_. All three bones are so called from their resemblances
in shape to the articles for which they are named. These bones are held in
place by very small muscles which are delicately adjusted so as to tighten
or relax the membranes guarding the middle and inner ear.
The Inner Ear.--The inner ear is one of the most complicated, as well as
one of the most delicate, organs of the body. Deep within the temporal bone
there are found two parts, one of which is called, collectively, the
_semicircular canal region_, the other the _cochlea_, or organ of hearing.
It has been discovered by experimenting with fish, in which the
semicircular canal region forms the chief part of the ear, that this region
has to do with the equilibrium or balancing of the body. We gain in part
our knowledge of our position and movements in space by means of the
_semicircular canals_.
That part of the ear which receives sound waves is known as the _cochlea_,
or snail shell, because of its shape. This very complicated organ is lined
with sensory cells provided with cilia. The cavity of the cochlea is filled
with a fluid. It is believed that somewhat as a stone thrown into water
causes ripples to emanate from the spot where it strikes, so sound waves
are transmitted by means of the fluid filling the cavity to the sensory
cells of the cochlea (collectively known as the _organ of Corti_) and
thence to the brain by means of the auditory nerve.
The Character of Sound.--When vibrations which are received by the ear
follow each other at regular intervals, the sound is said to be musical. If
the vibrations come irregularly, we call the sound a noise. If the
vibrations come slowly, the pitch of the sound is low; if they come
rapidly, the pitch is high. The ear is able to perceive as low as thirty
vibrations per second and as high as almost thirty thousand. The ear can be
trained to recognize sounds which are unnoticed in untrained ears.
[Illustration: Longitudinal section through the eye.]
The Eye.--The eye or organ of vision is an almost spherical body which fits
into a socket of bone, the _orbit_. A stalklike structure, the _optic
nerve_, connects the eye with the brain. Free movement is obtained by means
of six little muscles which are attached to the outer coat, the _eyeball_,
and to the bony socket around the eye.
The wall of the eyeball is made up of three coats. An outer tough white
coat, of connective tissue, is called the _sclerotic coat_. Under the
sclerotic coat, in front, the eye bulges outward a little. Here the outer
coat is continuous with a transparent tough layer called the _cornea_. A
second coat, the _choroid_, is supplied with blood vessels and cells which
bear pigments. It is a part of this coat which we see through the cornea as
the colored part of the eye (the _iris_). In the center of the iris is a
small circular hole (the _pupil_). The iris is under the control of
muscles, and may be adjusted to varying amounts of light, the hole becoming
larger in dim light, and smaller in bright light. The inmost layer of the
eye is called the _retina_. This is, perhaps, the most delicate layer in
the entire body. Despite the fact that the retina is less than 1/80 of an
inch in thickness, there are several layers of cells in its composition.
The optic nerve enters the eye from behind and spreads out to form the
surface of the retina. Its finest fibers are ultimately connected with
numerous elongated cells which are stimulated by light. The retina is dark
purple in color, this color being caused by a layer of cells next to the
choroid coat. This accounts for the black appearance of the pupil of the
eye, when we look through the pupil into the darkened space within the
eyeball. The retina acts as the sensitized plate in the camera, for on it
are received the impressions which are transformed and sent to the brain as
sensations of sight. The eye, like the camera, has a lens. This lens is
formed of transparent, elastic material. It is found directly behind the
iris and is attached to the choroid coat by means of delicate ligaments. In
front of the lens is a small cavity filled with a watery fluid, the
_aqueous humor_, while behind it is the main cavity of the eye, filled with
a transparent, almost jellylike, _vitreous humor_. The lens itself is
elastic. This circumstance permits of a change of form and, in consequence,
a change of focus upon the retina of the lens. By means of this change in
form, or _accommodation_, we are able to distinguish between near and
distant objects.
[Illustration: How far away can you read these letters? Measure the
distance. Twenty feet is a test for the normal eye.]
Defects in the Eye.--In some eyes, the lens is in focus for near objects,
but is not easily focused upon distant objects; such an eye is said to be
nearsighted. Other eyes which do not focus clearly on objects near at hand
are said to be farsighted. Still another eye defect is astigmatism, which
causes images of lines in a certain direction to be indistinct, while
images of lines transverse to the former are distinct. Many nervous
troubles, especially headaches, may be due to eye strain. We should have
our eyes examined from time to time, especially if we are subject to
headaches.
The Alcohol Question.--It is agreed by investigators that in large or
continued amounts alcohol has a narcotic effect; that it first dulls or
paralyzes the nerve centers which control our judgment, and later acts upon
the so-called motor centers, those which control our muscular activities.
The reason, then, that a man in the first stages of intoxication talks
rapidly and sometimes wittily, is because the centers of judgment are
paralyzed. This frees the speech centers from control exercised by our
judgment, with the resultant rapid and free flow of speech.
In small amounts alcohol is believed by some physiologists to have always
this same narcotic effect, while other physiologists think that alcohol
does stimulate the brain centers, especially the higher centers, to
increased activity. Some scientific and professional men use alcohol in
small amounts for this stimulation and report no seeming harm from the
indulgence. Others, and by far the larger number, agree that this
stimulation from alcohol is only apparent and that even in the smallest
amounts alcohol has a narcotic effect.
The Paralyzing Effects of Alcohol on the Nervous System.--Alcohol has the
effect of temporarily paralyzing the nerve centers. The first effect is
that of exhilaration. A man may do more work for a time under the
stimulation of alcohol. This stimulation, however, is of short duration and
is invariably followed by a period of depression and inertia. In this
latter state, a man will do less work than before. In larger quantities,
alcohol has the effect of completely paralyzing the nerve centers. This is
seen in the case of a man "dead drunk." He falls in a stupor because all of
the centers governing speech, sight, locomotion, etc., have been
temporarily paralyzed. If a man takes a very large amount of alcohol, even
the nerve centers governing respiration and circulation may become
poisoned, and the victim will die.
Effect on the Organs of Special Sense.--Professor Forel, one of the
foremost European experts on the question of the effect of alcohol on the
nervous system, says: "Through all parts of nervous activity from the
innervation of the muscles and the simplest sensation to the highest
activity of the soul the paralyzing effect of alcohol can be demonstrated."
Several experimenters of undoubted ability have noted the paralyzing effect
of alcohol even in small doses. By the use of delicate instruments of
precision, Ridge tested the effect of alcohol on the senses of smell,
vision, and muscular sense of weight. He found that two drams of absolute
alcohol produced a positive decrease in the sensitiveness of the nerves of
feeling, that so small a quantity as one half dram of absolute alcohol
diminished the power of vision and the muscular sense of weight. Kraepelin
and Kurz by experiment determined that the acuteness of the special senses
of sight, hearing, touch, taste, and smell was diminished by an ounce of
alcohol, the power of vision being lost to one third of its extent and a
similar effect being produced on the other special senses. Other
investigators have reached like conclusions. There is no doubt but that
alcohol, even in small quantities, renders the organs of sense less
sensitive and therefore less accurate.
[Illustration: Table to show a comparison of chances of illness and death
in drinkers and non-drinkers. Solid black, drinkers. (From German
sources.)]
Effect of Alcohol on the Ability to Resist Disease.--Among certain classes
of people the belief exists that alcohol in the form of brandy or some
other drink or in patent medicines, malt tonics, and the like is of great
importance in building up the body so as to resist disease or to cure it
after disease has attacked it. Nothing is further from the truth. In
experiments on a large number of animals, including dogs, rabbits, guinea
pigs, fowls, and pigeons, Laitenen, of the University of Helsingsfors,
found that alcohol, without exception, made these animals more susceptible
to disease than were the controls.
One of the most serious effects of alcohol is the lowered resistance of the
body to disease. It has been proved that a much larger proportion of hard
drinkers die from infectious or contagious diseases than from special
diseased conditions due to the direct action of alcohol on the organs of
the body. This lowered resistance is shown in increased liability to
contract disease and increased severity of the disease. We have already
alluded to the findings of insurance companies with reference to the length
of life--the abstainers from alcohol have a much better chance of a longer
life and much less likelihood of infection by disease germs.
Use of Alcohol in the Treatment of Disease.--In the London Temperance
Hospital alcohol was prescribed seventy-five times in thirty-three years.
The death rate in this hospital has been lower than that of most general
hospitals. Sir William Collins, after serving nineteen years as surgeon in
this hospital, said:--
"In my experience, speaking as a surgeon, the use of alcohol
is not essential for successful surgery.... At the London
Temperance Hospital, where alcohol is very rarely
prescribed, the mortality in amputation cases and in
operation cases generally is remarkably low. Total
abstainers are better subjects for operation, and recover
more rapidly from accidents, than those who habitually take
stimulants."
In a paper read at the International Congress on Tuberculosis, in New York,
1906, Dr. Crothers remarked that alcohol as a remedy or a preventive
medicine in the treatment of tuberculosis is a most dangerous drug, and
that all preparations of sirups containing spirits increase, rather than
diminish, the disease.
Dr. Kellogg says: "The paralyzing influence of alcohol upon the white cells
of the blood--a fact which is attested by all investigators--is alone
sufficient to condemn the use of this drug in acute or chronic infections
of any sort."
[Illustration: Effect of use of alcohol on memory.]
The Effect of Alcohol upon Intellectual Ability.--With regard to the
supposed quickening of the mental processes Horsley and Sturge, in their
recent book, _Alcohol and the Human Body_, say:
"Kraepelin found that the simple reaction period, by which
is meant the time occupied in making a mere response to a
signal, as, for instance, to the sudden appearance of a
flag, was, after the ingestion of a small quantity of
alcohol (1/4 to 1/2 ounce), slightly accelerated; that there
was, in fact, a slight shortening of the time, as though the
brain were enabled to operate more quickly than before. But
he found that after a few minutes, in most cases, a slowing
of mental action began, becoming more and more marked, and
enduring as long as the alcohol was in active operation in
the body, _i.e._ four to five hours.... Kraepelin found that
it was only more or less automatic work, such as reading
aloud, which was quickened by alcohol, though even this was
rendered less trustworthy and accurate." Again: "Kraepelin
had always shared the popular belief that a small quantity
of alcohol (one to two teaspoonfuls) had an accelerating
effect on the activity of his mind, enabling him to perform
test operations, as the adding and subtracting and learning
of figures more quickly. But when he came to measure with
his instruments the exact period and time occupied, he
found, to his astonishment, that he had accomplished these
mental operations, not more, but less, quickly than
before.... Numerous further experiments were carried out in
order to test this matter, and these proved that _alcohol
lengthens the time taken to perform complex mental
processes_, while by a singular illusion the person
experimented upon imagines that his psychical actions are
rendered more rapid."
[Illustration: The effect of alcohol upon ability to do mental work.]
_Attention_--that is, the power of the mind to grasp and consider
impressions obtained through the senses--is weakened by drink. The ability
of the mind to associate or combine ideas, the faculty involved in sound
_judgment_, showed that when the persons had taken the amounts of alcohol
mentioned, the combinations of ideas or judgments expressed by them were
confused, foggy, sentimental, and general. When the persons had taken no
alcohol, their judgments were rational, specific, keen, showing closer
observation.
"The words of Professor Helmholtz at the celebration of his
seventieth birthday are very interesting in this connection.
He spoke of the ideas flashing up from the depths of the
unknown soul, that lies at the foundation of every truly
creative intellectual production, and closed his account of
their origin with these words: 'The smallest quantity of an
alcoholic beverage seemed to frighten these ideas
away.'"--DR. G. SIMS WOODHEAD, Professor of Pathology,
Cambridge University, England.
Professor Von Bunge (_Textbook of Physiological and Pathological
Chemistry_) of Switzerland says that:
"The stimulating action which alcohol appears to exert on
the brain functions is only a paralytic action. The cerebral
functions which are first interfered with are _the power of
clear judgment and reason_. No man ever became witty by aid
of spirituous drinks. The lively gesticulations and useless
exertions of intoxicated people are due to paralysis,--the
restraining influences, which prevent a sober man from
uselessly expending his strength, being removed."
The Drink Habit.--The harmful effects of alcohol (aside from the purely
physiological effect upon the tissues and organs of the body) are most
terribly seen in the formation of the alcohol habit. The first effect of
drinking alcoholic liquors is that of exhilaration. After the feeling of
exhilaration is gone, for this is a temporary state, the subject feels
depressed and less able to work than before he took the drink. To overcome
this feeling, he takes another drink. The result is that before long he
finds a habit formed from which he cannot escape. With body and mind
weakened, he attempts to break off the habit. But meanwhile his will, too,
has suffered from overindulgence. He has become a victim of the drink
habit!
"The capital argument against alcohol, that which must
eventually condemn its use, is this, that _it takes away all
the reserved control, the power of mastership, and therefore
offends against the splendid pride in himself or herself,
which is fundamental in every man or woman worth
anything_."--DR. JOHN JOHNSON, quoting Walt Whitman.
Self-indulgence, be it in gratification of such a simple desire as that for
candy or the more harmful indulgence in tobacco or alcoholic beverages, is
dangerous--not only in its immediate effects on the tissues and organs, but
in its more far-reaching effects on habit formation. Each one of us is a
bundle of appetites. If we gratify appetites of the wrong kind, we are
surely laying the foundation for the habit of excess. Self-denial is a good
thing for each of us to practice at one time or another, if for no other
purpose than to be ready to fight temptation when it comes.
The Economic Effect of Alcoholic Poisoning.--In the struggle for existence,
it is evident that the man whose intellect is the quickest and keenest,
whose judgment is most sound, is the man who is most likely to succeed. The
paralyzing effect of alcohol upon the nerve centers must place the drinker
at a disadvantage. In a hundred ways, the drinker sooner or later feels the
handicap that the habit of drink has imposed upon him. Many corporations,
notably several of our greatest railroads (the Pennsylvania and the New
York Central Railroad among them), refuse to employ any but abstainers in
positions of trust. Few persons know the number of railway accidents due to
the uncertain eye of some engineer who mistook his signal, or the hazy
inactivity of the brain of some train dispatcher who, because of drink,
forgot to send the telegram that was to hold the train from wreck. In
business and in the professions, the story is the same. The abstainer wins
out over the drinking man.
Effect of Alcohol on Ability to do Work.--In _Physiological Aspects of the
Liquor Problem_, Professor Hodge, formerly of Clark University, describes
many of his own experiments showing the effect of alcohol on animals. He
trained four selected puppies to recover a ball thrown across a gymnasium.
To two of the dogs he gave food mixed with doses of alcohol, while the
others were fed normally. The ball was thrown 100 feet as rapidly as
recovered. This was repeated 100 times each day for fourteen successive
days. Out of 1400 times the dogs to which alcohol had been given brought
back the ball only 478 times, while the others secured it 922 times.
Dr. Parkes experimented with two gangs of men, selected to be as nearly
similar as possible, in mowing. He found that with one gang abstaining from
alcoholic drinks and the other not, the abstaining gang could accomplish
more. On transposing the gangs, the same results were repeatedly obtained.
Similar results were obtained by Professor Aschaffenburg of Heidelberg
University, who found experimentally that men "were able to do 15 per cent
less work after taking alcohol."
Recently many experiments along the same lines have been made. In
typewriting, in typesetting, in bricklaying, or in the highest type of
mental work the result is the same. The quality and quantity of work done
on days when alcohol is taken is less than on days when no alcohol is
taken.
The Relation of Alcohol to Efficiency.--We have already seen that work is
neither so well done nor is as much accomplished by drinkers as by
non-drinkers.
A Massachusetts shoe manufacturer told a recent writer on temperance that
in one year his firm lost over $5000 in shoes spoiled by drinking men, and
that he had himself traced these spoiled shoes to the workmen who, through
their use of alcoholic liquors, had thus rendered themselves incapable.
This is a serious handicap to our modern factory system, and explains why
so many factory towns and cities are strongly favoring a policy of "No
license" in opposition to the saloons.
"It is believed that the largest number of accidents in shops and mills
takes place on Monday, because the alcohol that is drunk on Sunday takes
away the skill and attentive care of the workman. To prove the truth of
this opinion, the accidents of the building trades in Zurich were studied
during a period of six years, with the result shown by this table":--
[Illustration: Shaded, non-alcoholic; black, alcoholic, accidents. (From
Tolman, _Hygiene for the Worker_.)]
Another relation to efficiency is shown by the following chart. During the
week the curve of working efficiency is highest on Friday and lowest on
Monday. The number of accidents were also least on Friday and greatest on
Monday. Lastly the assaults were fewest in number on Friday and greatest on
Sunday and Monday. The moral is plain. Workingmen are apt to spend their
week's wages freely on Saturday. Much of this goes into drink, and as a
result comes crime on Sunday because of the deadened moral and mental
condition of the drinker, and loss of efficiency on Monday, because of the
poisonous effects of the drug.
[Illustration: Notice that the curve of efficiency is lowest on Monday and
that crimes and accidents are most frequent on Sunday and Monday. Account
for this.]
Effect of Alcohol upon Duration of Life.--Still more serious is the
relation of alcohol as a direct cause of disease (see table).
It is as yet quite impossible, in the United States at least, to tell just
how many deaths are brought about, directly or indirectly, by alcohol.
Especially is this true in trying to determine the number of cases of
deaths from disease promoted by alcohol. In Switzerland provision is made
for learning these facts, and the records of that country throw some light
on the subject.
Dr. Rudolph Pfister made a study of the records of the city of Basle for
the years 1892-1906, finding the percentage of deaths in which alcohol had
been reported by the attending physician as one cause of death. He found
that 18.1 per cent of all deaths of men between 40 and 50 years of age were
caused, in part at least, by alcohol, and this at what should be the most
active period in a man's life, the time when he is most needed by his
family and community. Taking all ages between 20 and 80, he found that
alcohol was one cause of death in one man in every ten who died.
[Illustration]
Another study was made by a certain doctor in Sweden, from records of 1082
deaths occurring in his own practice and the local hospital. No case was
counted as alcoholic of which there was the slightest doubt. Of deaths of
adult men, 18 in every 100 were due, directly or indirectly, to alcoholism.
In middle life, between the ages of 40 and 50, 29; and between 50 and 60
years of age, 25.6 out of every 100 deaths had alcohol as one cause, thus
agreeing with other statistics we have been quoting.--From the
_Metropolitan_, Vol. XXV, Number 11.
[Illustration: The proportion of crime due to alcohol is shown in black.]
The Relation of Alcohol to Crime.--A recent study of more than 2500
habitual users of alcohol showed that over 66 per cent had committed crime.
Usually the crimes had been done in saloons or as a result of quarrels
after drinking. Of another lot of 23,581 criminals questioned, 20,070 said
that alcohol had led them to commit crime.
The Relation of Alcohol to Pauperism.--We have already spoken of the Jukes
family. These and many other families of a similar sort are more or less
directly a burden upon the state. Alcohol is in part at least responsible
for the condition of such families. Alcohol weakens the efficiency and
moral courage, and thus leads to begging, pauperism, petty stealing or
worse, and ultimately to life in some public institution. In Massachusetts,
of 3230 inmates of such institutions, 66 per cent were alcoholics.
The Relation of Alcohol to Heredity.--Perhaps the gravest side of the
alcohol question lies here. If each one of us had only himself to think of,
the question of alcohol might not be so serious. But drinkers may hand down
to their unfortunate children tendencies toward drink as well as nervous
diseases of various sorts; an alcoholic parent may beget children who are
epileptic, neurotic, or even insane.
In the State of New York there are at the present time some 30,000 insane
persons in public and private hospitals. It is believed that about one
fifth of them, or 6000 patients, owe their insanity to alcohol used either
by themselves or by their parents. In the asylums of the United States
there are 150,000 insane people. Taking the same proportions as before,
there are 30,000 persons in this country whom alcohol has made or has
helped to make insane. This is the most terrible side of the alcohol
problem.
REFERENCE READING
ELEMENTARY
Hunter, _Laboratory Problems in Civic Biology_. American
Book Company.
Overton, _General Hygiene_. American Book Company.
The Gulick Hygiene Series, _Emergencies, Good Health, The
Body at Work, Control of Body and Mind_. Ginn and Company.
Ritchie, _Human Physiology_. World Book Company.
Hough and Sedgwick, _The Human Mechanism_. Ginn and Company.
XXIV. MAN'S IMPROVEMENT OF HIS ENVIRONMENT
_Problems.--How may we improve our home conditions of living?_
_How may we help improve our conditions at school?_
_How does the city care for the improvement of our environment?_
_(a) In inspection of buildings, etc._
_(b) In inspection of food supplies._
_(c) In inspection of milk._
_(d) In care of water supplies._
_(e) In disposal of wastes._
_(f) In care of public health._
LABORATORY SUGGESTIONS
_Home exercise._--How to ventilate my bedroom.
_Demonstration._--Effect of use of duster and damp cloth
upon bacteria in schoolroom.
_Home exercise._--Luncheon dietaries.
_Home exercise._--Sanitary map of my own block.
_Demonstration._--The bacterial content of milk of various
grades and from different sources.
_Demonstration._--Bacterial content of distilled water, rain
water, tap water, dilute sewage.
_Laboratory exercise._--Study of board of health tables to
plot curves of mortality from certain diseases during
certain times of year.
The Purpose of this Chapter.--In the preceding chapters we have traced the
lives of both plants and animals within their own environment. We have seen
that man, as well as plants and other animals, needs a favorable
environment in order to live in comfort and health. It will be the purpose
of the following pages first to show how we as individuals may better our
home environment, and secondly, to see how we may aid the civic authorities
in the betterment of conditions in the city in which we live.
[Illustration: How I should ventilate my bedroom.]
Home Conditions.--The Bedroom.--We spend about one third of our total time
in our bedroom. This room, therefore, deserves more than passing attention.
First of all, it should have good ventilation. Two windows make an ideal
condition, especially if the windows receive some sun. Such a condition as
this is manifestly impossible in a crowded city, where too often the
apartment bedrooms open upon narrow and ill-ventilated courts. Until
comparatively recent time, tenement houses were built so that the bedrooms
had practically no light or air; now, thanks to good tenement-house laws,
wide airshafts and larger windows are required by statute.
Care of the Bedroom.--Since sunlight cannot always be obtained for a
bedroom, we must so care for and furnish the room that it will be difficult
for germs to grow there. Bedroom furniture should be light and easy to
clean, the bedstead of iron, the floors painted or of hardwood. No hangings
should be allowed at the windows to collect dust, nor should carpets be
allowed for the same reason. Rugs on the floor may easily be removed when
cleaning is done. The furniture and woodwork should be wiped with a damp
cloth every day. Why a _damp_ cloth? In certain tenements in New York City,
tuberculosis is believed to have been spread by people occupying rooms in
which a previous tenant has had tuberculosis. A new tenant should insist on
a thorough cleaning of the bedrooms and removal of old wall paper before
occupancy.
Sunlight Important.--In choosing a house in the country we would take a
location in which the sunlight was abundant. A shaded location might be too
damp for health. Sunlight should enter at least some of the rooms. In
choosing an apartment we should have this matter in mind, for, as we know,
germs cannot long exist in sunlight.
[Illustration: This map shows how cases of tuberculosis are found recurring
in the same locality and in the same houses year after year. Each black dot
is one case of tuberculosis.]
Heating.--Houses in the country are often heated by open fires, stoves or
hot-air furnaces, all of which make use of heated currents of air to warm
the rooms. But in the city apartments, usually pipes conduct steam or hot
water from a central plant to our rooms. The difficulty with this system is
that it does not give us fresh air, but warms over the stale air in a room.
Steam causes our rooms to be too warm part of the time, and not warm enough
part of the time. Thus we become overheated and then take cold by becoming
chilled. Steam heat is thus responsible for much sickness.
Lighting.--Lighting our rooms is a matter of much importance. A student
lamp, or shaded incandescent light, should be used for reading. Shades must
be provided so that the eyes are protected from direct light. Gas is a
dangerous servant, because it contains a very poisonous substance, carbon
monoxide. "It is estimated that 14 per cent of the total product of the gas
plant leaks into the streets and houses of the cities supplied." This forms
an unseen menace to the health in cities. Gas pipes, and especially gas
cocks, should be watched carefully for escaping gas. Rubber tubing should
not be used to conduct gas to movable gas lamps, because it becomes worn
and allows gas to escape.
[Illustration: During the summer all food should be protected from flies.
Why?]
Insects and Foods.--In the summer our houses should be provided with
screens. All food should be carefully protected from flies. Dirty dishes,
scraps of food, and such garbage should be quickly cleaned up and disposed
of after a meal. Insect powder (pyrethrum) will help keep out "croton bugs"
and other undesirable household pests, but cleanliness will do far more.
Most kitchen pests, as the roach, simply stay with us because they find
dirt and food abundant.
Use of Ice.--Food should be properly cared for at all times, but especially
during the summer. Iceboxes are a necessity, especially where children
live, in order to keep milk fresh. A dirty icebox is almost as bad as none
at all, because food will decay or take on unpleasant odors from other
foods.
[Illustration: The wrong and the right kind of garbage cans.]
Disposal of Wastes.--In city houses the disposal of human wastes is
provided for by a city system of sewers. The wastes from the kitchen, the
garbage, should be disposed of each day. The garbage pail should be
frequently sterilized by rinsing it with boiling water. Plenty of lye or
soap should be used. Remember that flies frequent the uncovered garbage
pail, and that they may next walk on your food. Collection and disposal of
garbage is the work of the municipality.
[Illustration: The culture (_A_) was exposed to the air of a dirty street
in the crowded part of Manhattan. (_B_) was exposed to the air of a
well-cleaned and watered street in the uptown residence portion. Which
culture has the more colonies of bacteria? How do you account for this?]
School Surroundings.--How to Improve Them.--From five to six hours a day
for forty weeks is spent by the average boy or girl in the schoolroom. It
is part of our environment and should therefore be considered as worthy of
our care. Not only should a schoolroom be attractive, but it should be
clean and sanitary. City schools, because of their locations, of the
sometimes poor janitorial service, and especially because of the
selfishness and carelessness of children who use them, may be very dirty
and unsanitary. Dirt and dust breed and carry bacteria. Plate cultures show
greatly increased numbers of bacteria to be in the air when pupils are
moving about, for then dust, bearing bacteria, is stirred up and circulated
through the air. Sweeping and dusting with dry brooms or feather dusters
only stirs up the dust, leaving it to settle in some other place with its
load of bacteria. Professor Hodge tells of an experience in a school in
Worcester, Mass. A health brigade was formed among the children, whose duty
was to clean the rooms every morning by wiping all exposed surface with a
damp cloth. In a school of 425 pupils not a single case of contagious
diseases appeared during the entire year. Why not try this in your own
school?
Unselfishness the Motto.--Pupils should be unselfish in the care of a
school building. Papers and scraps dropped by some careless boy or girl
make unpleasant the surroundings for hundreds of others. Chalk thrown by
some mischievous boy and then tramped underfoot may irritate the lungs of a
hundred innocent schoolmates. Colds or worse diseases may be spread through
the filthy habits of some boys who spit in the halls or on the stairways.
Lunch Time and Lunches.--If you bring your own lunch to school, it should
be clean, tasty, and well balanced as a ration. In most large schools
well-managed lunch rooms are part of the school equipment, and balanced
lunches can be obtained at low cost. Do not make a lunch entirely from cold
food, if hot can be obtained. Do not eat only sweets. Ice cream is a good
food, if taken with something else, but be sure of your ice cream. "Hokey
pokey" cream, tested in a New York school laboratory, showed the presence
of many more colonies of bacteria than _good_ milk would show. Above all,
be sure the food you buy is clean. Stands on the street, exposed to dust
and germs, often sell food far from fit for human consumption.
[Illustration: A sensible lunch box, sanitary and compact.]
If you eat your lunch on the street near your school, remember not to
scatter refuse. Paper, bits of lunch, and the like scattered on the streets
around your school show lack of school spirit and lack of civic pride. Let
us learn above all other things to be good citizens.
[Illustration: Dust exhausts on grinding wheels protect lungs of the
workmen.]
Inspection of Factories, Public Buildings, etc.--It is the duty of a city
to inspect the condition of all public buildings and especially of
factories. Inspection should include, first, the supervision of the work
undertaken. Certain trades where grit, dirt, or poison fumes are given off
are dangerous to human health, hence care for the workers becomes a
necessity. Factories should also be inspected as to cleanliness, the amount
of air space per person employed, ventilation, toilet facilities, and
proper fire protection. Tenement inspection should be thorough and should
aim to provide safe and sanitary homes.
Inspection of Food Supplies.--In a city certain regulations for the care of
public supplies are necessary. Foods, both fresh and preserved, must be
inspected and rendered safe for the thousands of people who are to use
them. All raw foods exposed on stands should be covered so as to prevent
insects or dust laden with bacteria from coming in contact with them. Meats
must be inspected for diseases, such as tuberculosis in beef, or
trichinosis in pork. Cold storage plants must be inspected to prevent the
keeping of food until it becomes unfit for use. Inspection of sanitary
conditions of factories where products are canned, or bakeries where foods
are prepared, must be part of the work of a city in caring for its
citizens.
Care of Raw Foods.--Each one of us may coöperate with the city government
by remembering that fruits and vegetables can be carriers of disease,
especially if they are sold from exposed stalls or carts and handled by the
passers-by. All vegetables, fruits, or raw foods should be carefully washed
before using. Spoiled or overripe fruit, as well as meat which is decayed,
is swarming with bacteria and should not be used.
An interesting exercise would be the inspection of conditions in your own
home block. Make a map showing the houses on the block. Locate all stores,
saloons, factories, etc. Notice any cases of contagious disease, marking
this fact on the map. Mark all heaps of refuse in the street, all uncovered
garbage pails, any street stands that sell uncovered fruit, and any stores
with an excessive number of flies.
In addition to food inspection, two very important supplies must be
rendered safe by a city for its citizens. These are milk and water.
[Illustration: Clean cows in clean barns with clean milkers and clean milk
pails means clean milk in the city.]
Care in Production of Milk.--Milk when drawn from a healthy cow should be
free from bacteria. But immediately on reaching the air it may receive
bacteria from the air, from the hands of the person who milks the cows,
from the pail, or from the cow herself. Cows should, therefore, be milked
in surroundings that are sanitary, the milkers should wear clean garments,
put on over their ordinary clothes at milking time, while pails and all
utensils used should be kept clean. Especially the surface exposed on the
udder from which the milk is drawn should be cleansed before milking.
Most large cities now send inspectors to the farms from which milk is
supplied. Farms that do not accept certain standards of cleanliness are not
allowed to have their milk become part of the city supply.
Tuberculosis and Milk.--It is recognized that in some European countries
from 30 to 40 per cent of all cattle have tuberculosis. Many dairy herds in
this country are also infected. It is also known that the tubercle bacillus
of cattle and man are much alike in form and action and that _probably_ the
germ from cattle would cause tuberculosis in man. Fortunately, the
tuberculosis germ does not _grow_ in milk, so that even if milk from
tubercular cattle should get into our supply, it would be diluted with the
milk of healthy cattle. In order to protect our milk supply from these
germs it would be necessary to kill all tubercular cattle (almost an
impossibility) or to pasteurize our milk so as to kill the germs in it.
Other Disease Germs in Milk.--We have already shown how typhoid may be
spread through milk. Usually such outbreaks may be traced to a single case
of typhoid, often a person who is a "typhoid carrier," _i.e._ one who may
not suffer from the effects of the disease, but who carries the germs in
his body, spreading them by contact. A recent epidemic of typhoid in New
York City was traced to a single typhoid carrier on a farm far from the
city. Sometimes the milk cans may be washed in contaminated water or the
cows may even get the germs on their udders by wading in a polluted stream.
Diphtheria, scarlet fever, and Asiatic cholera are also undoubtedly spread
through milk supplies. Milk also plays a very important part in the high
death rate from diarrhoeal diseases among young children in warm weather.
Why?
[Illustration: A diagram to show how typhoid may be spread in a city
through an infected milk supply. The black spots in the blocks mean cases
of typhoid. _A_, a farm where typhoid exists; the dashes in the streets
represent the milk route. _B_ is a second farm which sends part of its milk
to _A_; the milk cans from _B_ are washed at farm _A_ and sent back to _B_.
A few cases of typhoid appear along _B_'s milk route. How do you account
for that?]
Grades of Milk in a City Supply.--Milk which comes to a city may be roughly
placed in three different classes. The best milk, coming from farms where
the highest sanitary standards exist, where the cows are all tubercular
tested, where modern appliances for handling and cooling the milk exist, is
known as certified or, in New York City, grade A milk. Most of the milk
sold, however, is not so pure nor is so much care taken in handling it.
Such milk, known in New York as grade B milk, is pasteurized before
delivery, and is sold only in bottles. A still lower grade of milk (dipped
milk) is sold direct from cans. It is evident that such milk, often exposed
to dust and other dirt, is unfit for any purpose except for cooking. It
should under no circumstances be used for children. A regulation recently
made by the New York City Department of Health states that milk sold
"loose" in restaurants, lunch-rooms, soda fountains, and hotels must be
pasteurized.
Care of a City Milk Supply.--Besides caring for milk in its production on
the farm, proper transportation facilities must be provided. Much of the
milk used in New York City is forty-eight hours old before it reaches the
consumer. During shipment it must be kept in refrigerator cars, and during
transit to customers it should be iced. Why? All but the highest grade milk
should be pasteurized. Why? Milk should be bottled by machinery if possible
so as to insure no personal contact; it should be kept in clean, cool
places; and no milk should be sold by dipping from cans. Why is this a
method of dispensing impure milk?
Care of Milk in the Home.--Finally, milk at home should receive the best of
care. It should be kept on ice and in covered bottles, because it readily
takes up the odors of other foods. If we are not certain of its purity or
keeping qualities, it should be pasteurized at home. Why?
[Illustration: New York City is spending $350,000,000 to have a pure and
abundant water supply. This is the tunnel which will bring the water from
the Catskill Mountains to New York City.]
Water Supplies.--One of the greatest assets to the health of a large city
is pure water. By pure water we mean water free from all _organic_
impurities, including germs. Water from springs and deep driven wells is
the safest water, that from large reservoirs next best, while water that
has drainage in it, river water for example, is very unsafe.
The waters from deep wells or springs if properly protected will contain no
bacteria. Water taken from protected streams into which no sewage flows
will have but few bacteria, and these will be destroyed if exposed to the
action of the sun and the constant aëration (mixing with oxygen) which the
surface water receives in a large lake or reservoir. But water taken from a
river into which the sewage of other towns and cities flows must be
filtered before it is fit for use.
[Illustration: The city of Lowell in 1891 took its water _without
filtering_, _i.e._ from the Merrimack River at the point shown on the map.
Typhoid fever broke out in North Chelmsford and about two weeks later cases
began to appear in Lowell until a great epidemic occurred. Explain this
outbreak. Each black dot is a case of typhoid.]
Typhoid fever germs live in the food tube, hence the excreta of a typhoid
patient will contain large numbers of germs. In a city with a system of
sewage such germs might eventually pass from the sewers into a river. Many
cities take their water supply directly from rivers, sometimes not far
below another large town. Such cities must take many germs into their water
supply. Many cities, as Cleveland and Buffalo, take their water from lakes
into which their sewage flows. Others, as Albany, Pittsburgh, and
Philadelphia, take their drinking water directly from rivers into which
sewage from cities above them on the river has flowed. Filtering such water
by means of passing the water through settling basins and sand filters
removes about 98 per cent of the germs. The result of drinking unfiltered
and filtered water in certain large cities is shown graphically at right.
In cities which drain their sewage into rivers and lakes, the question of
sewage disposal is a large one, and many cities now have means of disposing
of their sewage in some manner as to render it harmless to their neighbors.
[Illustration: Filter beds at Albany, N. Y.]
[Illustration: Cases of typhoid per 100,000 inhabitants before filtering
water supply (solid) and after (shaded) in _A_, Watertown, N. Y.; _B_,
Albany, N. Y.; _C_, Lawrence, Mass.; D, Cincinnati, Ohio. What is the
effect of filtering the water supply?]
Railroads are often responsible for carrying typhoid and spreading it. It
is said that a recent outbreak of typhoid in Scranton, Pa., was due to the
fact that the excreta from a typhoid patient traveling in a sleeping car
was washed by rain into a reservoir near which the train was passing.
Railroads are thus seen to be great open sewers. A sanitary car toilet is
the only remedy.
[Illustration: This chart shows that during a cholera epidemic in 1892
there were hundreds of cases of cholera in Hamburg, which used unfiltered
water from the Elbe, but in adjoining Altona, where filtered water was
used, the cases were very few.]
[Illustration: Stone filter beds in a sewage disposal plant.]
Sewage Disposal.--Sewage disposal is an important sanitary problem for any
city. Some cities, like New York, pour their sewage directly into rivers
which flow into the ocean. Consequently much of the liquid which bathes the
shores of Manhattan Island is dilute sewage. Other cities, like Buffalo or
Cleveland, send their sewage into the lakes from which they obtain their
supply of drinking water. Still other cities which are on rivers are forced
to dispose of their sewage in various ways. Some have a system of filter
beds in which the solid wastes are acted upon by the bacteria of decay, so
that they can be collected and used as fertilizer. Others precipitate or
condense the solid materials in the sewage and then dispose of it. Another
method is to flow the sewage over large areas of land, later using this
land for the cultivation of crops. This method is used by many small
European cities.
[Illustration: Collecting ashes.]
The Work of the Department of Street Cleaning.--In any city a menace to the
health of its citizens exists in the refuse and garbage. The city streets,
when dirty, contain countless millions of germs which have come from
decaying material, or from people ill with disease. In most large cities a
department of street cleaning not only cares for the removal of dust from
the streets, but also has the removal of garbage, ashes, and other waste as
a part of its work. The disposal of solid wastes is a tremendous task. In
Manhattan the dry wastes are estimated to be 1,000,000 tons a year in
addition to about 175,000 tons of garbage. Prior to 1895 in the city of New
York garbage was not separated from ashes; now the law requires that
garbage be placed in separate receptacles from ashes. Do you see why? The
street-cleaning department should be aided by every citizen; rules for the
separation of garbage, papers, and ashes should be kept. Garbage and ash
cans should be _covered_. The practice of upsetting ash or garbage cans is
one which no young citizen should allow in his neighborhood, for sanitary
reasons. The best results in summer street cleaning are obtained by washing
or flushing the streets, for thus the dirt containing germs is prevented
from getting into the air. The garbage is removed in carts, and part of it
is burned in huge furnaces. The animal and plant refuse is cooked in great
tanks; from this material the fats are extracted, and the solid matter is
sold for fertilizer. Ashes are used for filling marsh land. Thus the
removal of waste matter may pay for itself in a large city.
[Illustration: The upper picture shows the stables where millions of flies
were bred; the lower picture, the disinfection of manure so as to prevent
the breeding of flies.]
An Experiment in Civic Hygiene.--During the summer of 1913 an interesting
experiment on the relation of flies and filth to disease was carried on in
New York City by the Bureau of Public Health and Hygiene of the New York
Association for improving the condition of the poor. Two adjoining blocks
were chosen in a thickly populated part of the Bronx near a number of
stables which were the sources of great numbers of flies. In one block all
houses were screened, garbage pails were furnished with covers, refuse was
removed and the surroundings made as sanitary as possible. In the adjoining
block conditions were left unchanged. During the summer as flies began to
breed in the manure heaps near the stables all manure was disinfected. Thus
the breeding of flies was checked. The campaign of education was continued
during the summer by means of moving pictures, nurses, boy scouts, and
school children who became interested.
At the end of the summer it was found that there had been a considerable
decrease in the number of cases of fly-carried diseases and a still greater
decrease in the total days of sickness (especially of children) in the
screened and sanitary block. The table and pictures speak for themselves.
If such a small experiment shows results like this, then what might a
general clean-up of a city show?
[Illustration: In the upper picture a little girl can be seen dumping
garbage from the fire escape. She was a foreigner and knew no better. The
picture below shows the result of such garbage disposal.]
Public Hygiene.--Although it is absolutely necessary for each individual to
obey the laws of health if he or she wishes to keep well, it has also
become necessary, especially in large cities, to have general supervision
over the health of people living in a community. This is done by means of a
department or board of health. It is the function of this department to
care for public health. In addition to such a body in cities, supervision
over the health of its citizens is also exercised by state boards of
health. But as yet the government of the United States has not established
a Bureau of Health, important as such a bureau would be.
The Functions of a City Board of Health.--The administration of the Board
of Health in New York City includes a number of divisions, each of which
has a different work to do. Each is in itself important, and, working
together, the entire machine provides ways and means for making the great
city a safe and sanitary place in which to live. Let us take up the work of
each division of the health board in order to find out how we may coöperate
with them.
[Illustration: Comparison of cases of illness during the summer of 1913 in
two city blocks, one clean and the other dirty. What are your conclusions?]
The Division of Infectious Diseases.--Infectious diseases are chiefly
spread through _personal contact_. It is the duty of a government to
prevent a person having such a disease from spreading it broadcast among
his neighbors. This can be done by _quarantine_ or _isolation_ of the
person having the disease. So the board of health at once isolates any case
of disease which may be communicated from one person to another. No one
save the doctor or nurse should enter the room of the person quarantined.
After the disease has run its course, the clothing, bedding, etc., in the
sick room is fumigated. This is usually done by the board of health.
Formaldehyde in the form of candles for burning or in a liquid form is a
good disinfectant. In disinfecting the room should be tightly closed to
prevent the escape of the gas used, as the object of the disinfection is to
kill all the disease germs left in the room. In some cases of infectious
disease, as scarlet fever, it is found best to isolate the patients in a
hospital used for that purpose. Examples of the most infectious diseases
are measles, scarlet fever, whooping cough, and diphtheria.
Immunity.--In the prevention of germ diseases we must fight the germ by
attacking the parasites directly with poisons that will kill them (such
poisons are called _germicides_ or _disinfectants_), and we must strive to
make the persons coming in contact with the disease unlikely to take it.
This insusceptibility or _immunity_ may be either natural or acquired.
Natural immunity seems to be in the constitution of a person, and may be
inherited. Immunity may be acquired by means of such treatment as the
antitoxin treatment for diphtheria. This treatment, as the name denotes, is
a method of neutralizing the poison (toxin) caused by the bacteria in the
system. It was discovered a few years ago by a German, Von Behring, that
the serum of the blood of an animal immune to diphtheria is capable of
neutralizing the poison produced by the diphtheria-causing bacteria. Horses
are rendered immune by giving them the diphtheria toxin in gradually
increasing doses. The serum of the blood of these horses is then used to
inoculate the patient suffering from or exposed to diphtheria, and thus the
disease is checked or prevented altogether by the antitoxin injected into
the blood. The laboratories of the board of health prepare this antitoxin
and supply it fresh for public use.
[Illustration: Antitoxin for diphtheria prepared by the New York Board of
Health.]
It has been found from experience in hospitals that deaths from diphtheria
are largely preventable by _early use_ of antitoxin. When antitoxin was
used on the first day of the disease no deaths took place. If not used
until the second day, 5 deaths occurred in every hundred cases, on the
third day 11 deaths, on the 4th day 19 deaths, and on the 5th day 20 deaths
out of every hundred cases. It is therefore advisable, in a suspected case
of diphtheria, to have antitoxin used at once to prevent serious results.
Vaccination.--Smallpox was once the most feared disease in this country; 95
per cent of all people suffered from it. As late as 1898, over 50,000
persons lost their lives annually in Russia from this disease. It is
probably not caused by bacteria, but by a tiny animal parasite. Smallpox
has been brought under absolute control by vaccination,--the inoculation of
man with the substance (called _virus_) which causes cowpox in a cow.
Cowpox is like a mild form of smallpox, and the introduction of this virus
gives complete immunity to smallpox for several years after vaccination.
This immunity is caused by the formation of a germicidal substance in the
blood, due to the introduction of the virus. Another function of the board
of health is the preparation and distribution of vaccine (material
containing the virus of cowpox).
Rabies (Hydrophobia).--This disease, which is believed to be caused by a
protozoan parasite, is communicated from one dog to another in the saliva
by biting. In a similar manner it is transferred to man. The great French
bacteriologist, Louis Pasteur, discovered a method of treating this disease
so that when taken early at the time of the entry of the germ into the body
of man, the disease can be prevented. In some large cities (among them New
York) the board of health has established a laboratory where free treatment
is given to all persons bitten by dogs suspected of having rabies.
Vaccination against Typhoid.--Typhoid fever has within the past five years
received a new check from vaccination which has been introduced into our
army and which is being used with good effect by the health departments of
several large cities.
The following figures show the differences between number of cases and
mortality in the army in 1898 during the war with Spain and in 1911 during
the concentration of certain of our troops at San Antonio, Texas.
1898--2nd Division, 7th Army Corps, Jacksonville, Florida.
June-October, 1898
Mean strength, 10,759.
Cases of typhoid certain and probable, 2693.
Death from typhoid, 258.
Death from all diseases, 281.
Manoeuver Division, San Antonio, Texas. March 10-July 11, 1911.
Mean strength, 12,801.
Cases of typhoid, 1.
Death from typhoid, 0.
Deaths all diseases, 11.
[Illustration: Comparison of cases of and death from typhoid in 1898 and
1911. What have we learned about combating typhoid since 1898?]
During this period there were 49 cases of typhoid and 19 deaths in the
near-by city of San Antonio. But in camp, _where vaccination for typhoid
was required_, all were practically immune. In the army at large, since
typhoid vaccination has been practiced, 1908-1909, the death rate from
typhoid has dropped from 2.9 per 1000 to .03 per 1000, a wonderful record
when we remember that during the Spanish-American War 86 per cent of the
deaths in the army were from typhoid fever.
[Illustration: The best cures for tuberculosis are rest, plenty of fresh
out-of-door air, and wholesome food.]
[Illustration: A sanitarium for tuberculosis. Notice the outdoor sleeping
rooms.]
How the Board of Health fights Tuberculosis.--Tuberculosis, which a few
years ago killed fully one seventh of the people who died from disease in
this country, now kills less than one tenth. This decrease has been largely
brought about because of the treatment of the disease. Since it has been
proved that tuberculosis if taken early enough is curable, by quiet living,
good food, and _plenty_ of fresh air and light, we find that numerous
sanitaria have come into existence which are supported by private or public
means. At these sanitaria the patients _live_ out of doors, especially
sleep in the air, while they have plenty of nourishing food and little
exercise. The department of health of New York City maintains a sanitarium
at Otisville in the Catskill Mountains. Here people who are unable to
provide means for getting away from the city are cared for at the city's
expense and a large percentage of them are cured. In this way and by
tenement house laws which require proper air shafts and window ventilation
in dwellings, by laws against spitting in public places, and in other ways,
the boards of health in our towns and cities are waging war on
tuberculosis.
Ex-President Roosevelt said, in one of his latest messages to Congress:--
"There are about 3,000,000 people seriously ill in the
United States, of whom 500,000 are consumptives. _More than
half of this illness is preventable._ If we count the value
of each life lost at only $1700 and reckon the average
earning lost by illness at $700 a year for grown men, we
find that the economic gain from mitigation of preventable
disease in the United States would exceed $1,500,000,000 a
year. This gain can be had through medical investigation and
practice, school and factory hygiene, restriction of labor
by women and children, the education of the people in both
public and private hygiene, and through improving the
efficiency of our health service, municipal, state, and
national."
Work of the Division of School and Infant Hygiene.--Besides the work of the
division of infectious disease, the division of sanitation, which regulates
the general sanitary conditions of houses and their surroundings and the
division of inspection, which looks after the purity and conditions of sale
and delivery of milk and foods, there is another department which most
vitally concerns school children. This is the division of school and infant
hygiene. The work of this department is that of the care of the children of
the city. During the year 1912, 279,776 visits were made to the homes of
school children of the city of New York by inspectors and nurses. Besides
this, thousands of children in school were cared for and aided by the city.
Adenoids.--Many children suffer needlessly from adenoids,--growths in the
back of the nose or mouth which prevent sufficient oxygen being admitted to
the lungs. A child suffering from these growths is known as a "mouth
breather" because the mouth is opened in order to get more air. The result
to the child may be a handicap of deafness, chronic running of the nose,
nervousness, and lack of power to think. His body cells are starving for
oxygen. A very simple operation removes this growth. Coöperation on the
part of the children and parents with the doctors or nurses of the board of
health will do much in removing this handicap from many young lives.
Eyestrain.--Another handicap to a boy or girl is eyestrain. Twenty-two per
cent of the school children of Massachusetts were recently found to have
defects in vision. Tests for defective eyesight may be made at school
easily by competent doctors, and if the child or parent takes the advice
given to correct this by procuring proper glasses, a handicap on future
success will be removed.
Decayed Teeth.--Decayed teeth are another handicap, cared for by this
division. Free dental clinics have been established in many cities, and if
children will do their share, the chances of their success in later life
will be greatly aided. Boys and girls, if handicapped with poor eyes or
teeth, do not have a fair chance in life's competition. In a certain school
in New York City there were 236 pupils marked "C" in their school work.
These children were examined, and 126 were found to have bad teeth, 54
defective vision, and 56 other defects, as poor hearing, adenoids, enlarged
tonsils, etc. Of these children 185 were treated for these various
difficulties, and 51 did not take treatment. During the following year's
work 176 of these pupils _improved_ from "C" to "B" or "A", while 60 did
not improve. If defects _are_ such a handicap in school, then what would be
the chances of success in life outside.
In conclusion: this department of school hygiene deserves the earnest aid
of every young citizen, girl or boy. If each of us would honestly help by
maintaining quarantine in the case of contagious disease, by observing the
rules of the health department in fumigation, by acting upon advice given
in case of eyestrain, bad teeth, or adenoids, and most of all by observing
the rules of personal hygiene as laid down in this book, the city in which
we live would, a generation hence, contain stronger, more prosperous, and
more efficient citizens than it does to-day.
REFERENCE BOOKS
ELEMENTARY
Hunter, _Laboratory Problems in Civic Biology_. American
Book Company.
Davison, _The Human Body and Health_. American Book Company.
Gulick Hygiene Series, _Town and City_. Ginn and Company.
Hough and Sedgwick, _The Human Mechanism_, Part II. Ginn and
Company.
Overton, _General Hygiene_. American Book Company.
Richards, _Sanitation in Daily Life_. Whitcomb and Barrows.
Richmond and Wallach, _Good Citizenship_. American Book
Company.
Ritchie, _Primer of Sanitation_. World Book Company.
Sharpe, _Laboratory Manual of Biology_, pages 320-334.
American Book Company.
ADVANCED
Allen, _Civics and Health_. Ginn and Company.
Chapin, _Municipal Sanitation in the United States_. Snow
and Farnham.
Chapin, _Sources and Modes of Infection_. Wiley and Sons.
Conn, _Practical Dairy Bacteriology_. Orange Judd Company.
Hough and Sedgwick, _The Human Mechanism_. Part II. Ginn and
Company.
Hutchinson, _Preventable Diseases_. The Houghton, Mifflin
Company.
Morse, _The Collection and Disposal of Municipal Waste_.
Municipal Journal and Engineer.
Overlock, _The Working People, Their Health and How to
Protect It_. Mass. Health Book Publishing Co.
Price, _Handbook of Sanitation_. Wiley and Sons.
Tolman, _Hygiene for the Worker_. American Book Company.
REPORTS, ETC.
_American Health Magazine._
Annual Report of Department of Health, City of New York (and
other cities).
Bulletins and Publications of Committee of One Hundred on
National Health.
_School Hygiene_, American School Hygiene Association.
Grinnell, _Our Army versus a Bacillus_. National Geographic
Magazine.
XXV. SOME GREAT NAMES IN BIOLOGY
If we were to attempt to group the names associated with the study of
biology, we would find that in a general way they were connected either
with discoveries of a purely scientific nature or with the benefiting of
man's condition by the _application_ of the purely scientific discoveries.
The first group are necessary in a science in order that the second group
may apply their work. It was necessary for men like Charles Darwin or
Gregor Mendel to prove their theories before men like Luther Burbank or any
of the men now working in the Department of Agriculture could benefit
mankind by growing new varieties of plants. The discovery of scientific
truths must be achieved before the men of modern medicine can apply these
great truths to the cure or prevention of disease. Since we are most
interested in discoveries which touch directly upon human life, the men of
whom this chapter treats will be those who, directly or indirectly, have
benefited mankind.
The Discoverers of Living Matter.--The names of a number of men living at
different periods are associated with our first knowledge of cells. About
the middle of the seventeenth century microscopes came into use. Through
their use plant cells were first described and pictured as hollow boxes or
"cells." But it was not until 1838 that two German friends, Schleiden and
Schwann by name, working on plants and animals, discovered that both of
these forms of life contained a jellylike substance that later came to be
called _protoplasm_. Another German named Max Schultz in 1861 gave the name
protoplasm to _all living matter_, and a little later still Professor
Huxley, a famous Englishman, friend and champion of Charles Darwin, called
attention to the physical and chemical qualities of protoplasm so that it
came to be known as the chemical and physical basis of life.
[Illustration: Prof. Tyndall's experiment to show that if air containing
germs is kept from organic substances, such substances will not decay. The
box is sterilized; likewise the tubes (_t_) containing nutrients. Air is
allowed to enter by the tubes (_u_), which are so made that dust is
prevented from entering. A thermometer (_th_) records the temperature. The
substances in the tubes do not decay, no matter how favorable the
temperature.]
Life comes from Life.--Another group of men, after years of patient
experimentation, worked out the fact that _life comes from other life_. In
ancient times it was thought that life arose _spontaneously_; for example,
that fish or frogs arose out of the mud of the river bottoms, and that
insects came from the dew or rotting meat. It was believed that bacteria
arose spontaneously in water, even as late as 1876, when Professor Tyndall
proved by experiment the contrary to be true.
As early as 1651 William Harvey, the court physician of Charles I of
England, showed that all life came from the egg. It was much later,
however, that the part played by the sperm and egg cell in fertilization
was carefully worked out. It is to Harvey, too, that we owe the beginnings
of our knowledge of the circulation of the blood. He showed that blood
moved through tubes in the body and that the heart pumped it. He might be
called the father of modern physiology as well as the father of embryology.
A long list of names might be added to that of Harvey to show how gradually
our knowledge of the working of the human body has been added to. At the
present time we are far from knowing all the functions of the various parts
of the human engine, as is shown by the number of investigators in
physiology at the present time. Present-day problems have much to do with
the care of the human mechanism and with its surroundings. The solution of
these problems will come from applying the sciences of hygiene, preventive
medicine, and sanitation.
In the preceding chapters of this book we have learned something about our
bodies and their care. We have found that man is able within limitations to
control his environment so as to make it better to live in. All of the
scientific facts that have been of use to man in the control of disease
have been found out by men who have devoted their lives in the hope that
their experiments and their sacrifices of time, energy, and sometimes life
itself might make for the betterment of the human race. Such men were
Harvey, Jenner, Lister, Koch, and Pasteur.
[Illustration: Edward Jenner, the discoverer of vaccination.]
Edward Jenner and Vaccination.--The civilized world owes much to Edward
Jenner, the discoverer of vaccination against smallpox. Born in Berkeley, a
little town of Gloucestershire, England, in 1749, as a boy he showed a
strong liking for natural history. He studied medicine and also gave much
time to the working out of biological problems. As early as 1775 he began
to associate the disease called cowpox with that of smallpox, and gradually
the idea of inoculation against this terrible scourge, which killed or
disfigured hundreds of thousands every year in England alone, was worked
out and applied. He believed that if the two diseases were similar, a
person inoculated with the mild disease (cowpox) would after a slight
attack of this disease be immune against the more deadly and loathsome
smallpox. It was not until 1796 that he was able to prove his theory, as at
first few people would submit to vaccination. War at this time was being
waged between France and England, so that the former country, usually so
quick to appreciate the value of scientific discoveries, was slow to give
this method a trial. In spite of much opposition, however, by the year
1802, vaccination was practiced in most of the civilized countries of the
world. At the present time the death rate in Great Britain, the home of
vaccination, is less than .3 to every 1,000,000 living persons. This shows
that the disease is practically wiped out in England. An interesting
comparison with these figures might be made from the history of the disease
in parts of Russia where vaccination is not practiced. There, thousands of
deaths from smallpox occur annually. During the winter of 1913-1914 an
epidemic of smallpox with more than 250 cases broke out in the city of
Niagara Falls. This epidemic appears to be due to a campaign conducted by
people who do not believe in vaccination. In cities and towns near by,
where vaccination was practiced, no cases of smallpox occurred. Naturally
if opposition to vaccination is found nowadays, Jenner had a much harder
battle to fight in his day. He also had many failures, due to the imperfect
methods of his time. The full worth of his discovery was not fully
appreciated until long after his death, which occurred in 1823.
[Illustration: Louis Pasteur.]
Louis Pasteur.--The one man who, in biological science, did more than any
other to directly benefit mankind was Louis Pasteur. Born in 1822, in the
mountains near the border of northeastern France, he spent the early part
of his life as a normal boy, fond of fishing and not very partial to study.
He inherited from his father, however, a fine character and grim
determination, so that when he became interested in scientific pursuits he
settled down to work with enthusiasm and energy.
At the age of twenty-five he became well known throughout France as a
physicist. Shortly after this he became interested in the tiny plants we
call bacteria, and it was in the field of bacteriology that he became most
famous. First as professor at Strassburg and at Lille, later as director of
scientific studies in the École Normale at Paris, he showed his interest in
the application of his discoveries to human welfare.
In 1857 Pasteur showed that fermentation was due to the presence of
bacteria, it having been thought up to this time that it was a purely
chemical process. This discovery led to very practical ends, for France was
a great wine-producing country, and with a knowledge of the cause of
fermentation many of the diseases which spoiled wine were checked.
In 1865-1868 Pasteur turned his attention to a silkworm disease which
threatened to wipe out the silk industry of France and Italy. He found that
this disease was caused by bacteria. After a careful study of the case he
made certain recommendations which, when carried out, resulted in the
complete overthrow of the disease and the saving of millions of dollars to
the poor people of France and Italy.
The greatest service to mankind came later in his life when he applied
certain of his discoveries to the treatment of disease. First experimenting
upon chickens and later with cattle, he proved that by making a virus
(poison) from the germs which caused certain diseases he could reduce this
virus to any desired strength. He then inoculated the animals with the
virus of reduced strength, giving the inoculated animals a mild attack of
the disease, and found that this made them _immune_ from future attacks.
This discovery, first applied to chicken cholera, laid the foundation for
all future work in the uses of serums, vaccines, and antitoxins.
Pasteur was perhaps the best known through his study of rabies. The great
Pasteur Institute, founded by popular subscriptions from all over the
world, has successfully treated over 22,000 cases of rabies with a death
rate of less than 1 per cent. But more than that it has been the place
where Roux, a fellow worker with Pasteur, discovered the antitoxin for
diphtheria which has resulted in the saving of thousands of human lives.
Here also have been established the principles of inoculation against
bubonic plague, lockjaw, and other germ diseases.
Pasteur died in 1895 at the age of seventy-three, "the most perfect man in
the realm of science," a man beloved by his countrymen and honored by the
entire world.
[Illustration: Robert Koch.]
Robert Koch.--Another name associated with the battle against disease germs
is that of Robert Koch. Born in Klausthal, Hanover, in 1843, he later
became a practicing physician, and about 1880 was called to Berlin to
become a member of the sanitary commission and professor in the school of
medicine. In 1881 he discovered the germ that causes tuberculosis and two
years later the germ that causes Asiatic cholera. His later work has been
directed toward the discovery of a cure for tuberculosis and other germ
diseases. As yet, however, no certain cure seems to have been found.
Lister and Antiseptic Treatment of Wounds.--A third great benefactor of
mankind was Sir Joseph Lister, an Englishman who was born in 1827. As a
professor of surgery he first applied antiseptics in the operating room. By
means of the use of carbolic acid or other antiseptics on the surface of
wounds, on instruments, and on the hands and clothing of the operating
surgeons, disease germs were prevented from taking a foothold in the
wounds. Thus blood poisoning was prevented. This single discovery has done
more to prevent death after operations than any other of recent time.
Modern Workers on the Blood.--At the present time several names stand out
among investigators on the blood. Paul Ehrlich, a German born in 1854, is
justly famous for his work on the blood and its relation to immunity from
certain diseases. His last great research has given to the world a specific
against the dread disease syphilis.
Another name associated with the blood is that of Elias Metchnikoff, a
Russian. He was born in 1845. Metchnikoff first advanced the belief that
the colorless blood corpuscles, or _phagocytes_, did service as the
sanitary police of the body. He has found that there are several different
kinds of colorless corpuscles, each having somewhat different work to do.
Much of the modern work done by physiologists on the blood are directly
founded on the discoveries of Metchnikoff.
[Illustration: Charles Darwin, the grand old man of biology.]
Heredity and Evolution. Charles Darwin.--There is still another important
line of investigation in biology that we have not mentioned. This is the
doctrine of evolution and the allied discoveries along the line of
heredity. The development or evolution of plants and animals from simpler
forms to the many and present complex forms of life have a practical
bearing on the betterment of plants and animals, including man himself. The
one name indelibly associated with the word evolution is that of Charles
Darwin.
Charles Darwin was born on February 12, 1809, a son of well-to-do parents,
in the pretty English village of Shrewsbury. As a boy he was very fond of
out-of-door life, was a collector of birds' eggs, stamps, coins, shells,
and minerals. He was an ardent fisherman, and as a young man became an
expert shot. His studies, those of the English classical school, were not
altogether to his liking. It is not strange, perhaps, that he was thought a
very ordinary boy, because his interest in the out-of-doors led him to
neglect his studies. Later he was sent to Edinburgh University to study
medicine. Here the dull lectures, coupled with his intense dislike for
operations, made him determine never to become a physician. But all this
time he showed his intense interest in natural history and took frequent
part in the discussions at the meetings of one of the student zoölogical
societies.
In 1828 his father sent him to Cambridge to study for the ministry. His
three years at the university were wasted so far as preparation for the
ministry were concerned, but they were invaluable in shaping his future. He
made the acquaintance of one or two professors who were naturalists like
himself, and in their company he spent many happy hours in roaming over the
countryside collecting beetles and other insects. In 1831 an event occurred
which changed his career and made Darwin one of the world's greatest
naturalists. He received word through one of his professional friends that
the position of naturalist on her Majesty's ship _Beagle_ was open for a
trip around the world. Darwin applied for the position, was accepted, and
shortly after started on an eventful five years' trip around the world. He
returned to England a famous naturalist and spent the remainder of his long
and busy life producing books which have done more than those of any other
writer to account in a satisfactory way for the changes of form and habits
of plants and animals on the earth. His theories established a foundation
upon which plant and animal breeders were able to work.
His wonderful discovery of the doctrine of evolution was due not only to
his information and experimental evidence, but also to an iron
determination and undaunted energy. In spite of almost constant illness
brought about by eyestrain, he accomplished more than most well men have
done. His life should mean to us not so much the association of his name
with the _Origin of Species_ or _Plants and Animals under Domestication_,
two of his most famous books, but rather that of a patient, courteous, and
brave gentleman who struggled with true English pluck against the odds of
disease and the attacks of hostile critics. He gave to the world the proofs
of the theory on which we to-day base the progress of the world. Darwin
lived long enough to see many of his critics turn about and come over to
his beliefs. He died on the 19th of April, 1882, at seventy-four years of
age.
Associated with Darwin's name we must place two other co-workers on
heredity and evolution, Alfred Russel Wallace, an Englishman who
independently and at about the same time reached many of the conclusions
that Darwin came to, and August Weissman, a German. The latter showed that
the protoplasm of the germ cells (eggs and sperms) is directly handed down
from generation to generation, they being different from the other body
cells from the very beginning. In 1883 a German named Boveri discovered
that the chromosomes of the egg and the sperm cell were at the time of
fertilization just half in number of the other cells (see page 252) so that
a _fertilized_ egg was really a _whole cell_ made up of _two half cells_,
one from each parent. The chromosomes within the nucleus, we remember, are
believed to be the bearers of the hereditary qualities handed down from
parent to child. This discovery shows us some of the mechanics of heredity.
Applications to Plant and Animal Breeding.--Turning to the practical
applications of the scientific work on the method of heredity, the name of
Gregor Mendel, an Austrian monk, stands out most prominently. Mendel lived
from 1822 until 1884. His work, of which we already have learned something
(see page 258), remained undiscovered until a few years ago. The
application of his methods to plant and animal raising are of the utmost
importance because the breeder is able to separate the qualities he desires
and breed for those qualities only. Another name we have mentioned with
reference to plant breeding is Hugo de Vries, the Dutchman who recently
showed that in some cases plants arise as new species by sudden and great
variations known as _mutations_. And lastly, in our own California, Luther
Burbank, by careful hybridizing, is making lasting fame with his new and
useful hybrid plants.
REFERENCES
Conn, _Biology_. Silver, Burdett & Co.
Darwin, _Life and Letters of Charles Darwin_. Appletons.
Galton, _Hereditary Genius_. London (1892).
Thompson, _Heredity_. John Murray, London England.
Wasmann, _Problem of Evolution_. Kegan Paul, Trench, Trübner and Co.,
London, E. C.
APPENDIX
A SUGGESTED OUTLINE FOR BIOLOGY BEGINNING IN THE FALL
LIST OF TOPICS
FIRST TERM
First week. WHY STUDY BIOLOGY? Relation to human health, hygiene. Relations
existing between plants and animals. Relation of bacteria to man. Uses of
plants and animals. Conservation of plants and animals. Relation to life of
citizen in the city. Plants and animals in relation to their environment.
What is the environment; light, heat, water, soil, food, etc. What plants
take out of the environment. What animals take out of the environment.
Dependence of plants and animals upon the factors of the environment.
_Laboratory_: Study of a plant or an animal in the school or at home to
determine what it takes from its environment.
Second week. SOME RELATIONS EXISTING BETWEEN PLANTS (GREEN) AND ANIMALS.
Field trip planned to show that insects feed upon plants; make their homes
upon plants. That flowers are pollinated by insects. Insects lay eggs upon
certain food plants. Green plants make food for animals. Other relations.
(Time allotment. One day trip, collecting, etc.; two days' discussion of
trip in all its relations.) Make a careful study of the locality you wish
to visit, have a plan that the pupils know about beforehand. Review and
hygiene of pupil's environment, 2 days.
Third week. STUDY OF A FLOWER, PARTS ESSENTIAL TO POLLINATION NAMED.
Adaptations for insect pollination worked out in laboratory. Study of bee
or butterfly as an insect carrier of pollen. Names of parts of insect
learned. Elementary knowledge of groups of insects seen on field trip.
Bees, butterflies, grasshoppers, beetles, possibly flies and bugs. Drawing
of a flower, parts labeled. Drawing of an insect, outline only, parts
labeled. Careful study of some fall flower fitted for insect pollination
with an insect as pollinating agent. Some examples of cross-pollination
explained. Practical value of cross-pollination.
Fourth week. LIVING PLANTS AND ANIMALS COMPARED. Parts of plants,
functions; organs, tissues, cells. Demonstration cells of onion or elodea.
How cells form others. What living matter can do. Reproduction. Growth of
pollen tube, fertilization. Development of ovule into seed. Fruits, how
formed. Uses, to man.
Fifth week. WHAT MAKES A SEED GROW. Bean seed, a baby plant, and food
supply. Food, what is it? Organic nutrients, tests for starch, protein,
oil. Show their presence in seeds.
Sixth week. NEED FOR FOODS. Germination of bean due to (_a_) presence of
foods, (_b_) outside factors. What is done with the food. Release of
energy. Examples of engine, plants, human body. Oxidation in body. Proof by
experiment. Test for presence of CO{2}. Oxidation in growing plant,
experiment. Respiration a general need for both plants and animals.
Seventh week. NEED FOR DIGESTION. The corn grain. Parts, growth, food
supply outside body of plant, how does it get inside. Digestion, need for.
Test for grape sugar. Enzymes, their function. Action of diastase on
starch.
Eighth week. WHAT PLANTS TAKE FROM THE SOIL, HOW THEY DO THIS. Use of root.
Influence of gravity and water. Why? Absorption a function. Root hairs.
Demonstration. Pocket gardens, optional home work, but each pupil must work
on root hairs from actual specimen. How root absorbs. Osmosis; what
substances will osmose. Experiments to demonstrate this.
Ninth week. COMPOSITION OF SOIL. What root hairs take out of soil. Plant
needs mineral matter to make living matter. Why? Nitrogen necessary.
Sources of nitrogen, the nitrogen-fixing bacteria. Relation of this to man.
Rotation of crops.
Tenth week. HOW GREEN PLANTS MAKE FOOD. Passage of liquids up stem.
Demonstration. Structure of a green leaf. Cellular structure demonstrated.
Microscopic demonstration of cells, stoma, air spaces, chlorophyll bodies.
Evaporation of water from green leaf, regulation of transpiration.
Eleventh week. _Midterm Examinations._ Sun a source of energy. Effect of
light on green plants. Experimental proof. Starch made in green leaf. Light
and air necessary for starch making. Proof. Protein making in leaf.
By-products in starch making. Proof. Respiration.
Twelfth week. THE CIRCULATION AND DISTRIBUTION OF FOOD IN GREEN PLANTS.
Uses of bark, wood, what part of stem does food pass down. Willow twig
experiment. Summary of functions of living matter in plant. Forestry
lecture. Economic uses of green plants. Reports.
Thirteenth week. PLANTS WITHOUT CHLOROPHYLL IN THEIR RELATION TO MAN.
Saprophytic fungi. Molds. Growth on bread or other substances. Conditions
most favorable for growth. Favorite foods. Methods of prevention. Economic
importance.
Fourteenth week. YEASTS IN THEIR RELATION TO MAN. Experiments to show
fermentation is caused by yeasts. Experiments to show conditions necessary
for fermentation. The part played by yeasts in bread making, in wine
making, in other industries. Structure of yeast demonstrated. Summary.
Fifteenth week. EXPERIMENTS TO SHOW WHERE BACTERIA MAY BE FOUND AND
CONDITIONS NECESSARY TO GROWTH BEGUN. Have cultures collected and placed in
a warm room during the holidays. Suggested experiments are exposure to air
of quiet room and room with persons moving, dust of floor, knife blade,
etc.
Sixteenth, seventeenth, and eighteenth weeks. THE MONTH OF JANUARY SHOULD
BE DEVOTED TO THE STUDY OF BACTERIA IN THEIR GENERAL RELATIONS TO MAN.
Economically, both directly and indirectly. Especial emphasis placed on the
nature and necessity of decay. Bacteria in relation to disease should also
be emphasized. The experiments to be performed and the topics expected to
be covered follow.
CONDITIONS FAVORABLE AND UNFAVORABLE FOR GROWTH OF BACTERIA. (Use bouillon
cultures.) Effect of intense heat, sterile bouillon exposed to air, effect
of boiling, effect of cold, effect of antiseptics (corrosive sublimate,
carbolic acid, boric acid, formalin, etc.), effect of large amounts of
sugar and salt and the relation of this to preserving, etc. Bring out
practical application of principles demonstrated. Discuss sterilization in
medicine and surgery, cold storage, canning, sterilization, _e.g._
laundries, etc., use of antiseptics, preserving by means of salt and sugar.
Microscopic demonstration of bacteria. Methods of reproduction. Importance
in causing organic decay, fixation of nitrogen, various useful forms in
cheese making, butter ripening, etc. Harmfulness of bacteria as disease
producers. Specific diseases discussed: tuberculosis, typhoid, infective
colds, blood poisoning, etc. Vaccination. Antitoxins begun--continued after
knowledge of human body is gained. Work of Lister and Pasteur.
Nineteenth and twentieth weeks. REVIEW AND EXAMINATIONS.
SECOND TERM
First week. THE BALANCED AQUARIUM. Carbon and nitrogen cycles. Balanced
aquarium and hay infusion compared.
Second week. ONE PROTOZOAN, DEMONSTRATION TO SHOW CHANGES IN SHAPE,
RESPONSE TO STIMULI, SUMMARY OF VITAL PROCESSES IN CELL. Food getting,
digestion, assimilation, oxidation, excretion, growth, reproduction.
Internal structure of protozoan. Protozoa as cause of disease.
Third week. GENERAL SURVEY OF ANIMAL KINGDOM. Survey introduced by museum
trip if possible. Protozoa, worm, insect, fish, mammal. Distinction between
vertebrate and invertebrate. Character of mammalia. Division of labor
emphasized. Man's place in nature.
Fourth week. STUDY OF THE FROG. Relation to habitat, adaptations for
locomotion, food getting, respiration, comparison of frog and fish on
latter point. Osmotic exchange of gases emphasized. Cell respiration.
Fifth week. METAMORPHOSIS OF FROG. Fertilization, cell division, and
differentiation emphasized. Touch on plant and animal breeding. Function of
chromosomes as bearers of heredity. Comparison of bird's egg and mammal
embryo.
Sixth week. FACTORS IN BREEDING. 1. Variation. 2. Selection. 3. Heredity
fixes variation. 4. Hybridizing. 5. Control of environment. Eugenics in
relation to (_a_) crime, (_b_) disease, (_c_) genius. Continuity of germ
plasm. Work of Darwin, Mendel, De Vries, Burbank.
Seventh week. A BRIEF STUDY OF THE GROSS STRUCTURE OF THE HUMAN BODY. Skin,
muscles, bones. Removal of lime from bone by HCl to show other substances
and need for lime. Effect of posture, spinal curvature, fractures, sprains.
Eighth week. NEED FOR FOOD. Nutritive value of food. Use of charts to show
foods rich in carbohydrates, fats, proteins, minerals, water, refuse. The
relation of age, sex, work, and environment to the food requirements. What
is a cheap food. Price list of common foods at present time. Efforts of
government to secure a cheap food supply for the people. Digestibility of
foods.
Ninth week. HOW THE FUEL VALUE OF FOOD HAS BEEN DETERMINED. Meaning of
calorie. The 100-caloric portion, its use in determining a daily or weekly
dietary. Standard dietary as determined by Atwater. Comparison of standards
of Chittenden and Voit with those of Atwater.
Tenth week. STUDY OF PUPIL'S DIETARY. Planning ideal meals. Individual
dietaries for one day required from each pupil. Discussions and
corrections. The family dietary. Relation to cost.
Eleventh week. DIGESTION. The digestive system in the frog and in man
compared. Drawings of each. Glands and enzymes. Internal secretions and
their importance. Demonstration of glandular tissues. Experiment to show
digestion of starch in mouth.
Twelfth week. DIGESTION CONTINUED. Digestion of white of egg by gastric
juice. Digestion of starch with pancreatic fluid. Functions of pancreatic
juice. Microscopic examination of emulsion. Reasons for digestion. Part
played by osmosis. Demonstration of osmosis. Non-osmosis of non-digested
foods, comparison between osmosable qualities of starch and grape sugar.
Thirteenth week. ABSORPTION. Where and how foods are absorbed. The
structure of a villus explained. Course taken by foods after absorption.
Function of liver. Blood making the result of absorption. Composition of
blood, red and colorless corpuscles, plasma, blood plates, antibodies.
Microscopic drawing of corpuscles of frog's and man's blood.
Fourteenth week. CIRCULATION OF BLOOD. The heart and lungs of frog
demonstrated. Heart of man a force pump, explain with use of force pump.
Demonstration of beef's heart. Circulation and changes of blood in various
parts of body. Work of cells with reference to blood made clear. Capillary
circulation (demonstration of circulation in tadpole's tail or web of
frog's foot).
Fifteenth week. RESPIRATION AND EXCRETION. Necessity for taking of oxygen
to cells and removal of wastes from cells. Part played by blood and lymph.
Mechanics of breathing (use of experiments). Changes of air and blood in
lungs (experiments). Best methods of ventilation (experiments). Elimination
of wastes from blood by lungs, skin, and kidneys. Cell respiration.
Sixteenth week. HYGIENE OF ORGANS OF EXCRETION, especially care of skin.
The general structure and functions of the central nervous system. Sensory
and motor nerves. Reflexes, instincts, habits. Habit formation, importance
of right habits. Rules for habit formation. Habit-forming drugs and other
agents. Lecture.
Seventeenth, eighteenth, nineteenth weeks. CIVIC HYGIENE AND SANITATION.
Hygiene of special senses, eye and ear. A well citizen an efficient
citizen. Public health is purchasable. Improvement of environment a means
of obtaining this. Civic hygiene and sanitation. Cleaning up neighborhood,
inquiry into home and street conditions. Fighting the fly. Conditions of
milk and water supply. Relation of above to disease. Work of Board of
Health, etc. Review and Examinations.
SUGGESTED SYLLABUS FOR COURSE BEGINNING FEBRUARY 1
AND ENDING THE FOLLOWING JANUARY
FIRST TERM
First week. WHY STUDY BIOLOGY? Relation to human health, hygiene. Relations
existing between plants and animals. Relation of bacteria to man. Uses of
plants and animals. Conservation of plants and animals. Relation to life of
citizen in this city. Needs of plants and animals: (1) food, (2) water, (3)
air, (4) proper temperature. Study of a single plant or animal in relation
to its environment. Problems of city government: (_a_) storage,
preservation and distribution of foods, (_b_) water supply, (_c_)
overcrowded tenements, (_d_) street cleaning, (_e_) clean schools.
Biological problems in city government.
Second week. INTERRELATIONS BETWEEN PLANTS AND ANIMALS. Plants furnish
food, clothing, shelter, and medicine. Animals use food, shelter. Man's use
of plants as above. Man's use of animals as above. Plant and animal
industries. Use of balanced aquarium as illustrative material.
Third week. DESTRUCTION OF FOOD AND OTHER THINGS BY MOLD. Home experiment.
Conditions favorable to growth of mold. Food, moisture, temperature.
Destruction of commodities by mold: food, leather, clothing.
Fourth week, fifth week. DESTRUCTION OF FOODS BY BACTERIA. Experiment. To
show where bacteria are found. Soil, dust, water, milk, hands, mouth. Use
and harm of decay. Relation to agriculture. Experiment. Conditions
favorable and unfavorable to growth of bacteria: boiling, cold, sugar,
salt. Bacteria in relation to disease briefly mentioned. Bacteria in
industries.
Sixth week. USE OF STORED FOOD BY YOUNG GREEN PLANT: (_a_) for energy,
(_b_) for construction of tissue. Experiment. Structure of bean seed. Draw
to show outer coat, cotyledon, hypocotyl, and plumule. Test for starch and
sugar (grape). Test for oil, protein, water, mineral matter. Use of all
nutrients to seedling.
Seventh week. OTHER NEEDS OF YOUNG PLANTS. Home experiments to show (_a_)
temperature, (_b_) amount of water most favorable to germination.
Experiment. To show need of oxygen. To show that germinating seeds give off
carbon dioxide. Proof of presence of carbon dioxide in breath. The needs of
a young plant compared with those of a boy or girl.
Eighth week. DIGESTION IN SEEDLING. Structure of corn grain. Experiment. To
show that starch is digested in a growing seedling (corn). Experiment. To
show that diastase digests starch. Discussion of experiments.
Ninth week. WHAT PLANTS TAKE FROM THE SOIL AND HOW THEY DO THIS. Use of
roots. Proof that it holds plant in position, takes in water and mineral
matter, and in some cases stores food. Influence of gravity and water.
Labeled drawing of root hair. Root hair as a _cell_ emphasized. Osmosis
demonstrated.
Tenth week. COMPOSITION OF THE SOIL. Demonstration of presence of mineral
and organic substances in the soil. What root hairs take from the soil.
Mineral matter necessary and why. Importance and sources of nitrogen. Soil
exhaustion and its prevention. Nitrogen-fixing bacteria. Review bacteria of
decay. Rotation of crops.
Eleventh week. UPWARD COURSE OF MATERIALS IN THE STEM. Demonstration of pea
seedlings with eosin to show above. Demonstration of evaporation of water
from a leaf. Action of stomata in control of transpiration. Cellular
structure of leaf. Demonstration of elodea to show cell.
Twelfth week. SUN A SOURCE OF ENERGY. Heliotropism. Demonstration.
Necessity of sunlight for starch manufacture. Necessity of air for starch
manufacture. By-products in starch making. Oil manufacture in leaf. Protein
manufacture in plant. Respiration.
Thirteenth week. REPRODUCTION. Necessity for (_a_) perpetuation, (_b_)
regeneration. Study of a typical flower to show sepals, petals, stamens,
pistil. Functions of each part. Cross and longitudinal sections of ovary
shown and drawn. Emphasis on essential organs. Pollination, self and cross.
(NOTE. At least one field trip must be planned for the month of May. This
trip will take up the following topics: The relations between flowers and
insects. The food and shelter relation between plants and animals.
Recognition of 5 to 10 common trees. Need of conservation of forests. An
extra trip could well be taken to give child a little knowledge and love
for spring flowers and awakening nature.)
Fourteenth week. STUDY OF THE BEE OR BUTTERFLY WITH REFERENCE TO
ADAPTATIONS FOR INSECT POLLINATION. Study of an irregular flower to show
adaptations for insect visitors. Fertilization begun. Growth of pollen
tubes.
Fifteenth week. FERTILIZATION COMPLETED. Use of chart to show part played
by egg and sperm cell. Ultimate result the formation of embryo and its
growth under favorable conditions into young plant. Relation of flower and
fruit, pea, or bean used for this purpose. Development of fleshy fruit.
Apple used for this purpose.
Sixteenth week. MATURING OF PARTS AND STORING OF FOOD IN SEED AND FRUIT.
The devices for scattering the seeds and relation to future plants. Résumé
of processes of nutrition to show how materials found in fruit and seed are
obtained by the plant.
Seventeenth week. PLANT BREEDING. Factors: (_a_) selective planting, (_b_)
cross-pollination, (_c_) hybridizing. Heredity and variation begun. Darwin
and Burbank mentioned.
Eighteenth and nineteenth weeks. THE NATURAL RESOURCES OF MAN: SOIL, WATER,
PLANTS, ANIMALS. The relation of plant life to the above factors of the
environment. The relation of insects to plants (forage and other crops) and
the relation of birds to insects. Need for conservation of the helpful
factors in the environment of plants. Attention called to some native birds
as insect and wood destroyers.
Twentieth week. REVIEW AND EXAMINATIONS.
SECOND TERM
First week. THE BALANCED AQUARIUM. Study of conditions producing this. The
rôle of green plants, the rôle of animals. What causes the balance. How the
balance may be upset. The nitrogen cycle. What it means in the world
outside the aquarium. Symbiosis as opposed to parasitism. Examples.
Second week. STUDY OF THE PARAMOECIUM. Study of a hay infusion to show how
environment reacts upon animals. Relation to environment. Study of cell
under microscope to show reactions. Structure of cell. Response to stimuli,
function of cilia, gullet, nucleus, contractile vacuoles, food vacuoles,
asexual reproduction. Drawings to show how locomotion is performed, general
structure. Copy chart for fine structure.
Third week. A BIRD'S-EYE VIEW OF THE ANIMAL KINGDOM. One day. Development
of a multicellular organism. (Use models.) One day. Physiological division
of labor. Tissues, organs. Functions common to all animals. Illustrative
material. Optional trip to museum for use of illustrative material to
illustrate the principal characteristics of (_a_) a simple metazoan,
sponge, or hydrazoan, (_b_) a segmented worm, (_c_) a crustacean (Decapod),
(_d_) an insect, (_e_) a mollusk and echinoderm, (_f_) vertebrates.
(Differences between vertebrates and invertebrates.) The characteristics of
the vertebrates. Distinguish between fishes, amphibia, reptiles, birds,
mammals. Two days for discussion. Man's place in the animal series,
elementary discussion of what evolution means.
Fourth week. THE ECONOMIC IMPORTANCE OF ANIMALS. Uses of animals: (1) As
food. Directly: fish, shellfish, birds, domesticated mammals. (2)
Indirectly as food: protozoa, crustacea. (3) They destroy harmful animals
and plants. Snakes--birds; birds--insects; birds--weed seeds; herbivorous
animals--weeds. (4) Furnish clothing, etc. Pearl buttons, etc. (5) Animal
industries, silkworm culture, etc. (6) Domesticated animals.
Animals do harm: (1) To gardens. (2) To crops. (3) To stored
food; examples, rats, insects, etc. (4) To forest and shade
trees. (5) To human life. Disease: parasitism and its
results,--examples, from worms, etc.; disease carriers fly,
etc. Preventive measures. Methods of extermination.
References to Toothaker's _Commercial Raw Materials_. Use
one day for laboratory work from references.
Fifth week. THE STUDY OF A WATER-BREATHING VERTEBRATE. Two days. The fish,
adaptations in body, fins, for food getting, for breathing. Structure of
gills shown. Laboratory demonstration to show how water gets to the gills.
Drawings. Outline of fish, gills. Required trip to aquarium. Object, to see
fish in environment. One day. Home work at market. Why are some fish more
expensive than others. Economic importance of fish. Relation of habits of
(_a_) food getting, (_b_) spawning to catching and extermination of fish.
Two days. Means of preventing overfishing, stocking, fishing laws,
artificial fertilization of eggs, methods. Development of fish egg.
Comparison with that of frog and bird.
Sixth week. THE FACTORS UNDERLYING PLANT AND ANIMAL BREEDING. Study of
pupils in class to show heredity and variation. Conclusion. Animals tend to
vary and to be like their ancestors. Heredity, rôle of sex cells,
chromosomes. Principles of plant breeding. Selective planting, hybridizing,
work of Darwin, Mendel, De Vries, and Burbank. Methods and results. Animal
breeding, examples given, results. Improvement of man: (1) by control of
environment, (_a_) example of clean-up campaign, 1913; (2) by control of
individual, personal hygiene, and control of heredity. Eugenics. Examples
from Davenport, Goddard, etc.
Seventh week. THE HUMAN MACHINE. Skin, bones and muscles, function of each.
Examples and demonstration with skeleton. Organs of body cavity; show
manikin. Work done by cells in body.
Eighth week. STUDY OF FOODS to determine: (_a_) nutritive value. Exercise
with food charts to determine foods rich in water, starch, sugar, fats,
proteins, mineral salts, refuse. One day. (_b_) Nutritive value of foods as
related to work, age, sex, environment, cost, and digestibility. Foods
compared to determine what is really a cheap food.
Ninth week. HOW THE FUEL VALUE OF FOOD HAS BEEN DETERMINED. The dietaries
of Atwater, Chittenden, and Voit. The 100-calorie portion table and its
use.
Tenth week. THE APPLICATION OF THE 100-CALORIE PORTION TO THE MAKING OF THE
DAILY DIETARIES. Luncheon dietaries. A balanced dietary for pupil for one
day. Family dietaries. Relation to cost. Reasons for this.
Eleventh week. FOOD ADULTERATIONS. Tests. Drugs and the alcohol question.
Twelfth week. DIGESTION. The alimentary canal of frog and of man compared.
Drawings. (One day.) The work of glands. Work of salivary gland. Enzymes,
internal secretions. Experiments to show (_a_) digestion of starch by
saliva, (_b_) digestion of proteins by gastric or pancreatic juice, (_c_)
emulsification of fats in the presence of an alkaline medium. Functions of
other digestive glands. Movements of stomach and intestine discussed and
explained.
Thirteenth week. ABSORPTION. How it takes place, where it takes place.
Passage of foods into blood, function of liver, glycogen.
Fourteenth week. THE BLOOD AND ITS CIRCULATION. Composition and functions
of plasma, red corpuscles, colorless corpuscles, blood plates, antibodies.
The lymph and work of tissues. The blood and its method of distribution.
Heart a force pump. Demonstration. Arteries, capillaries (demonstration),
veins. Hygiene of exercise.
Fifteenth week. WHAT RESPIRATION DOES FOR THE BODY. The apparatus used.
Changes of blood within lungs, changes of air within lungs. Demonstration.
Cell respiration. The mechanics of respiration. Demonstration. Ventilation,
need for, explain proper ventilation. Demonstration. Hygiene of fresh air
and proper breathing. Dusting, sweeping, etc.
Sixteenth week. EXCRETION, ORGANS OF. Skin and kidneys, regulation of body
heat. Colds and fevers. Proper care of skin, hygiene. Summary of blood
changes in body. Explanation of same.
Seventeenth week. BODY CONTROL AND HABIT FORMATION. Nervous system, nerve
control. The neuron theory, brain psychology explained in brief. Habits and
habit formation. Hygiene of sense organs.
Eighteenth and nineteenth weeks. CIVIC HYGIENE AND SANITATION. THE
IMPROVEMENT OF ONE'S ENVIRONMENT. Civic conditions discussed. Water, milk,
food supplies. Relation to disease. How safeguarded. How help improve
conditions in city.
Twentieth week. REVIEW AND EXAMINATIONS.
HYGIENE OUTLINE
(This outline may be introduced with Plant Biology, or,
better, may come as application of the work in Second-term
Biology.)
THE ENVIRONMENT. Changes for betterment under control. How a city boy may
improve his environment: by proper clothing, proper food and preparation of
food, by care in home life; by sanitary conditions in neighborhood and in
home.
REVIEW OF ACTIVITIES OF CELL. Irritability, food taking, assimilation,
oxidation, excretion, reproduction. Similarity of functions of plant and
animal cells. All cells perform these functions. Some cells perform
functions especially well, _e.g._ contracting muscle cells. All cells need
food and oxygen. Some must have this carried to them. A system of tubes
carries blood which carries food and oxygen. Food must be prepared to get
into the blood. Digestive system: mouth, teeth, stomach, intestines,
glands, and digestive juices. Uses of above in preparing food to pass into
the blood. Absorption of food into the blood. How oxygen gets to the cells.
Nose, throat, windpipe, lungs; blood goes to lungs and carries away oxygen.
Excretion. Cells give up wastes to blood and these wastes taken out of
blood by kidneys and other glands and passed out of body. Sweat, urine,
carbon dioxide.
CERTAIN KINDS OF WORK PERFORMED BY CERTAIN KINDS OF CELLS. Advantage of
this. Cells of movement. Muscles, tissues. Bones as levers necessary for
some movements. This especially true for legs and arms. Skeleton also
necessary for protection of internal organs and support of body. Making of
special things in the body, _e.g._ digestive juices given to certain cells
called gland cells. Working together or coördination of different organs
provided for by nervous system. This is composed of cells which are highly
irritable or sensitive. Collections of these nerve cells give us the power
of feeling or sensation and of thinking.
DIETETICS. Diet influenced by age, weight, occupation, temperature or
climate, cheapness of food, digestibility.
NUTRIENTS. List of nutrients found in seeds and fruits, also other common
foods. Need of nutrients for human body. Nitrogenous foods, examples. A
mixed diet best.
DIGESTION AND INDIGESTION. What is digestion? Where does it take place?
_Causes of indigestion._ Eating too rapidly and not chewing food. Eating
foods hard to digest. Overeating. Eating between meals. Hard exercise
immediately before or after eating.
CONSTIPATION. A condition in which the bowels do not move at least once
every day. Dangers of constipation. Poisonous materials may be absorbed,
causing lack of inclination to work, headache. Importance of regular habits
of emptying the bowels. Each one must try to get at the cause of
constipation in his own case. _Causes of constipation._ Lack of exercise,
improper food, not drinking enough water, lack of laxative food, as fruits;
lack of sleep, lack of regular habits. _Remedies._ Avoid use of drugs. Half
hour before breakfast a glass of hot water, exercise of abdominal muscles,
laxative foods, form habit of moving bowels after breakfast.
HYGIENE OF CIRCULATION AND ABSORPTION. How digested foods get to the cells.
Absorption. Definition. The passing of the digested food into the blood.
How accomplished. Blood vessels. In walls of stomach and food tube.
Membrane of cells separating food from blood. Food passes by osmosis
through the membrane and by osmosis through the thin walls of the blood
vessels.
CIRCULATION OF FOODS. Blood contains foods, oxygen, and waste materials.
Heart pumps the blood, blood vessels subdivide until very small and thin,
so food, etc., passes from them to cells. Hygiene of the heart.
TRANSPIRATION AND EXCRETION. Skin, function in excretion. Bathing. Care of
skin. Hot baths. Bathe at least twice a week. Cold baths, how taken.
Bathtub not a necessity. Effect of latter on educating skin to react.
Relation to catching cold.
CARE OF SCALP AND NAILS. Scalp should be washed weekly. If dandruff
present, wash often enough to keep clean. Baldness often results from
dandruff. Finger nails cut even with end of fingers and cleaned daily with
scrub brush.
HYGIENE OF RESPIRATION. Definition of respiration. Object of respiration.
(Connection between circulation and respiration.) Necessity of oxygen.
Organs of respiration. Lungs most important. Deep breath, function.
Ventilation, reasons for. Mouth breathing. Results. Lessened mental power,
nasal catarrh, colds easily caught.
PLANTS HARMFUL TO MAN. Poison ivy and mushrooms. Treatment. Poisoning. Send
for physician. Cause vomiting by (1) finger, (2) mustard and water. (NOTE.
An unconscious person should not be given anything by the mouth unless he
can swallow.) Relation of yeasts and bacteria to man. Fermentation a cause
of indigestion. Relation to candy, sirups, sour stomach, formation of gas
causes pain.
BACTERIA OF MOUTH AND ALIMENTARY CANAL. Entrance of bacteria by mouth and
nose. Nose: "cold in the head," grippe, catarrh. Mouth: decay of teeth,
tonsillitis, diphtheria. Germs pass from one person to another, no one
originates germs in himself. Precautions against receiving and transferring
germs. Common drinking cups, towels, coins, lead pencils, moistening
fingers to turn pages in book or to count roll of bills. Tuberculosis
germs. Entrance by mouth, lungs favorite place, may be any part of body.
Dust of air, sweeping streets, watering a necessity. Spitting in streets
and in public buildings. Germs of typhoid fever. Entrance: water, milk,
fresh uncooked vegetables, oysters. Thrive in small intestines.
Preventable. Typhoid epidemics, methods of prevention of typhoid.
Conditions favorable for growth of specific disease germs. Work of Boards
of Health.
Home sanitary conditions, sunlight, air, curtains and blinds, open windows.
Live out of doors as much as possible. Cleanliness. Bare walls well
scrubbed better than carpets and rugs. Lace curtains, iron bedsteads, one
thickness of paper on walls. Open plumbing, dry cellars, all garbage
promptly removed.
This outline is largely the work of Dr. L. J. Mason and Dr. C. H. Morse of
the department of biology of the De Witt Clinton High School.
WEIGHTS, MEASURES, AND TEMPERATURES
As the metric system of weights and measures and the Centigrade measurement
of temperatures are employed in scientific work, the following tables
showing the English equivalents of those in most frequent use are given for
the convenience of those not already familiar with these standards. The
values given are approximate only, but will answer for all practical
purposes.
WEIGHT
===================================
Kilogram | kg. | 2-1/5 pounds
----------+-----+------------------
| | 15-1/2 grains
| | avoirdupois.
| | 1/28 of an ounce
Gram | gm. | avoirdupois.
-----------------------------------
CAPACITY
-----------------------------------
| | 61 cubic inches,
| | or a little more
| | than 1 quart,
Liter | l. | U. S. measure.
----------+-----+------------------
Cubic | | cc. 1/16 of a
centimeter| | cubic inch.
===================================
MEASURES OF LENGTH
==================================
METRIC |ENGLISH EQUIVALENTS
----------+---+-------------------
Kilometer |km.| 2/3 of a mile.
| |
----------+---+-------------------
Meter | m.| 39 inches.
| |
----------+---+-------------------
Decimeter |dm.| 4 inches.
| |
----------+---+-------------------
Centimeter|cm.| 2/5 of an inch.
| |
----------+---+-------------------
Millimeter|mm.| 1/25 of an inch.
| |
==================================
The next table gives the Fahrenheit equivalent for every tenth degree
Centigrade from absolute zero to the boiling point of water. To find the
corresponding F. for any degree C., multiply the given C. temperature by
nine, divide by five, and add thirty-two. Conversely, to change F. to C.
equivalent, subtract thirty-two, multiply by five, and divide by nine.
CENT. FAHR.
-------------
100 212
90 194
80 176
70 158
60 140
50 122
40 104
30 86
20 68
10 50
0 32
-10 14
-20 -4
-30 -22
-40 -40
-50 -58
-100 -148
-------------
Absolute zero
-273 -459
LABORATORY EQUIPMENT
The following articles comprise a simple equipment for a laboratory class
of ten. The equipment for larger classes is proportionately less in price.
The following articles may be obtained from any reliable dealer in
laboratory supplies, such as the Bausch and Lomb Optical Company of
Rochester, N.Y., or the Kny-Scheerer Company, 404, 410 West 27th Street,
New York City:--
1 balance, Harvard trip style, with weights on carrier.
1 bell jar, about 365 mm. high by 165 mm. in diameter.
10 wide mouth (salt mouth) bottles, with corks to fit.
10 25 c.c. dropping bottles for iodine, etc.
25 250 c.c. glass-stoppered bottles for stock solutions.
100 test tubes, assorted sizes, principally 6" × 3/4".
50 test tubes on base (excellent for demonstrations).
2 graduated cylinders, one to 100 c.c., one to 500 c.c.
1 package filter paper 300 mm. in diameter.
10 flasks, Erlenmeyer form, 500 c.c. capacity.
2 glass funnels, one 50, one 150 mm. in diameter.
30 Petri dishes, 100 mm. in diameter, 10 mm. in depth.
10 feet glass tubing, soft, sizes 2, 3, 4, 5, 6, assorted.
1 aquarium jar, 10 liters capacity.
2 specimen jars, glass tops, of about 1 liter capacity.
10 hand magnifiers, vulcanite or tripod form.
2 compound demonstration microscopes or 1 more expensive compound
microscope.
300 insect pins, Klaeger, 3 sizes assorted.
10 feet rubber tubing to fit glass tubing, size 3/8 inch.
1 chemical thermometer graduated to 100° C.
15 agate ware or tin trays about 350 mm. long by 100 wide.
1 gal. 95 per cent alcohol. (Do not use denatured alcohol.)
1 set gram weights, 1 mg. to 100 g.
1 razor, for cutting sections.
1 box rubber bands, assorted sizes.
1 support stand with rings.
2 books test paper, red and blue.
10 Syracuse watch glasses.
1 steam sterilizer (tin will do).
1 spool fine copper wire.
1 test tube rack.
5 test tube brushes.
10 pairs scissors.
10 pairs forceps.
20 needles in handles.
10 scalpels.
12 mason jars, pints.
12 mason jars, quarts.
1 alcohol lamp.
1 gross slides.
100 cover slips No. 2.
1 mortar and pestle.
2 bulb pipettes.
1 liter formol.
1 oz. iodine cryst.
1 oz. potassium iodide.
6 oz. nitric acid.
6 oz. ammonium hydrate.
6 oz. benzole or xylol.
6 oz. chloroform.
1/2 lb. copper sulphate.
1/2 lb. sodium hydroxide.
1/2 lb. rochelle salts.
6 oz. glycerine.
The materials for Pasteur's solution and Sach's nutrient solution can best
be obtained from a druggist at the time needed and in very small and
accurately measured quantities.
The agar or gelatine cultures in Petri dishes may be obtained from the
local Board of Health or from any good druggist. These cultures are not
difficult to make, but take a number of hours' consecutive work, often
difficult for the average teacher to obtain. Full directions how to prepare
these cultures will be found in Hunter's _Laboratory Problems in Civic
Biology_.
INDEX
(Illustrations are indicated by page numerals in bold-faced type.)
Absorption, definition, 270;
of digested foods, 308, 309.
Accommodation of eye, 361.
Acetanilid, 295.
Action of the heart, 319.
Adaptations, 24;
in bee, 36;
in birds, |189|;
in fish, 232;
in frog, 241;
in mammalia, 192.
Adenoids, 340, 395.
Adulteration in foods, 288.
Air, and bacteria, 145;
composition of, |20|;
fresh, 337;
needed in germination, |66|;
necessary in starch making, 91;
passages in lungs, 330;
use to plants and animals, 21.
Albumin, 62.
Alcohol, a food, 289;
a poison, 291.
and ability to resist disease, 363;
and ability to work, 368;
and body heat, 345;
and crime, 371, |372|;
and digestion, 311;
and duration of life, 370;
and efficiency, 369;
and heredity, 372;
and intellectual ability, 364;
and kidneys, 346;
and living matter, 291;
and memory, |365|;
and mental ability, |366|;
and nervous system, 362;
and organs of special sense, 362;
and pauperism, 371;
and resistance, 327;
and respiration, 346;
and the blood, 327;
and treatment of disease, 364;
effect on circulation, 327;
effect on eye, 361;
effect on liver, 312;
produces poisons, 347.
Algæ, 176.
Alfalfa plant, |151|.
Alimentary canal, 297.
Alkali, 306.
Alkalinity, 298.
Alligator, |230|.
Ambergris, 205.
Ammonium hydrate, 61.
Amoeba, |170|, 182, 332.
Amphibia, 186, 187;
as food, 202.
Anal fin of fish, 233.
Angiosperms, 176.
Animals, as disease carriers, 227;
breeding of, 259;
domesticated, 260;
functions of, 48, 180;
need plants, 34;
oils of, 205;
parasitic, 227;
series, 182;
that prey upon man, 230;
use to man, 17;
use to plants, 34.
Annual rings, 98.
Anopheles, 217, |218|.
Anosia plexippus, 32.
Anther, 36.
Antibodies, uses of, 316.
Antiseptics, 157.
Antitoxin, 157, |391|.
Anura, 188.
Anvil, 359.
Aorta, 320.
Apoplexy, 328.
Appendages of the fish, 233.
Appendicular skeleton, 268.
Appendix, 309.
Apples, 56, |124|.
Aqueous humor, 361.
Arachnida, 185.
Arteries, 318;
structure of, 323.
Arthropods, 185.
Artificial, cross-pollination, 46;
propagation of fishes, 240;
respiration, 340;
selection, 253.
Asexual reproduction, 174.
Assimilation in plants, 103.
Attention, effect of alcohol, 364.
Audubon, 211.
Auricle of human heart, 319;
of fish heart, 236.
Automatic activity, 348, 354.
Axial skeleton, 268.
Bacillus, 142.
Bacteria, 134;
and fermentation, 150;
cause decay, 149;
cause disease, 151;
effect on food, 144;
growth of, 145;
isolating a pure culture, 142;
nitrogen fixing, 80, |81|, 151, |152|;
of decay, 144;
relation to man, 16;
size and form, 142, |143|;
useful, 150;
where found, 139, |141|.
Bacteriology, 16.
Bad posture, |270|.
Balanced, aquarium, 159, |160|;
diet, 285.
Barbels of fish, 234.
Barberry embryo, |103|.
Bark, use of, 98.
Barrier, natural, |25|.
Bast, 97.
Beans, as food, 62.
Beans, peas, 55.
Beans, seedlings, |63|.
Bedroom, care of, 374.
Bee, adaptations, 36;
head of, |38|;
mouth parts, 38.
Beer and wine making, 137.
Benedict's test, 68.
Benzoic acid, 148.
Beverages and condiments, 124.
Biceps, |269|.
Bichloride of mercury, 148.
Bile, functions of, 306, 307.
Biology, definition, 15;
relation to society, 18.
Birds, 189;
as food, 202;
classification, 191;
development, 246;
eat insects, 209;
eat weed seeds, 210;
embryo, |246|, 247.
Bismuth, 304.
Bison, |192|.
Black Death, 227.
Blade of leaf, 85.
Blastula, 177.
Blood, amount and distribution, 318;
changes in lungs, 330;
circulation of man, 318;
clotting, 314;
composition, |314|;
effect of alcohol, 327;
function, 313;
plates, 315;
poisoning, 156;
temperature, 318;
vessel of skin, |344|.
Blubber, 205.
Blue crab, |199|.
Board of health, functions, 389.
Body, a machine, 348;
cavity, 270;
heat and alcohol, 345;
of fish, 232.
Bony fish, |187|.
Boracic acid, 148.
Borax, 148.
Brain, of fish, 237;
of man, 351.
Bread, making, 139;
mold, |133|.
Bream, |233|.
Breathing, |333|;
and tight clothing, 339;
hygienic habits, 338;
in leaf, |93|;
of fish, 234;
of frog, 242;
of vertebrates, 232;
rate of, 334.
Breeding of animals, 259.
Bright's disease, 346.
Bronchi, 330.
Bronchial tubes, 330.
Bruises, 345.
Bryophytes, 176.
Bubonic plague, 227.
Budding, 255, |256|.
Bumblebees, 37.
Burbank, Luther, 406.
Burns, treatment of, 345.
Butter and eggs, 38, |39|.
Calorie, portion, |286|;
requirement, 282.
Calyx, 35.
Cambium layer, 98.
Canning, 145.
Cannon, Prof., 304.
Capillaries, 318, 323;
circulation in, |322|;
of fish, 236.
Carbohydrates, 60, 273.
Carbolic acid, 149.
Carbon and oxygen cycle, |161|.
Carbon dioxide, test for, |64|.
Care of milk supply, 380, 383.
Carnivorous, 230.
Caudal fin of fish, 233.
Cause of dyspepsia, 310.
Cells, |50|;
as units, 171;
division, |51|;
mucous, 299;
of pond scum, |173|;
reproduction of, 50;
respiration, 332;
tissue, |179|;
work of, 270.
Cephalothorax, 185.
Cerebellum, 352.
Cerebro-spinal nervous system, 350.
Cerebrum, 351.
Cestodes, 227.
Changes, of blood in lungs, 330;
of air in lungs, 331.
Characters, determiners of, 258.
Chelonia, 188.
Chemical, compounds, 20;
elements, 20;
of human body, |21|.
Chestnut canker, |131|.
China, deforestation in, |108|.
Chittenden table, |311|.
Chloral, 293.
Chlorophyll bodies, 50, 90.
Chloroplasts, 90.
Chromosomes, 50;
and heredity, 251.
Chrysalis, 33.
Cilia, 171.
Circulation, effect of alcohol, 327;
effect of exercise, 326;
effect of tobacco, 328;
in fish, frog, man, |321|, |322|;
in stem, 99, |100|, |101|;
of blood of man, 318;
of fish, 236;
of frog, 243;
portal, 322;
pulmonary, 320;
systemic, 320.
City's need for trees, 115.
Civic hygiene, 388.
Clams, 200.
Classification, of birds, 191;
of plants, 176.
Cloaca of frog, 243.
Clothing, 203.
Clotting of blood, 314.
Coal, 64.
Cobra, 230.
Cocaine, 293.
Coccus bacteria, 142.
Cochineal and lac, 208.
Cochlea, 359.
Codling moth, 215.
Coelenterates, 183.
Cold-blooded animals, 318;
effect of, |23|.
Cold storage, 147.
Colds and fevers, 343.
Coleoptera, 32.
Collecting ashes, |387|.
Colonies of bacteria, 141;
of trilliums, |175|.
Colorless corpuscles, 313;
structure, 315;
function, |316|.
Common foods contain nutrients, 275.
Comparison, of food tube of frog and man, |297|;
of mold, yeast and bacteria, |143|;
of starch making and milling, 92.
Complemental air, 334.
Complex one-celled animals, 171.
Composition, of milk, |273|, |280|;
of plasma, 313;
of soil, 77.
Compound eyes of bumblebee, 37, |38|.
Conservation, of food fish, 239;
of fur-bearing animals, 204;
of our natural resources, 17.
Constipation, 310.
Constrictor killing a mouse, |213|.
Contagious diseases, 152.
Convolutions, 352.
Corn, 120, |121|;
germinated grain cut lengthwise, |69|;
long section of ear, |67|;
structure of grain, |66|.
Cornfield, |44|.
Corolla, 35.
Corpuscles, colorless and red, 313.
Cost of food and diet, 281, |283|;
of parasitism, 263.
Cotton, 125;
boll weevil, 126, |127|, |214|.
Cotyledons, 59;
food in, 60.
Crab, |199|.
Crayfish, |184|.
Crocodile, 230.
Crocodilia, 189.
Crustacea, 185.
Culex, 218, |218|.
Culture medium, 140.
Cuts and bruises, treatment, 326, 345.
Daily calorie requirement, 282;
fuel needs of body, 284.
Dandelion, whorled leaves, |90|.
Darwin, Charles, 40, 404.
Darwin and natural selection, 253.
Deaths, table, |312|.
Decay caused by bacteria, 149.
Decayed teeth, 396.
Defects in eye, 361.
Deforestation in China, |108|.
Dendrites, 351.
Department of Agriculture, work of, 255.
Department of street cleaning, 387.
Determiners, 251;
of character, 258.
Development, of apple, 56;
of bird, 246;
of egg, |178|;
of trout, |238|;
of mammal, 247;
of salmon, |241|;
of simple animal, 177.
Diagram of frog's tongue, |242|;
of gills of fish, |235|;
of neuron, |351|;
of wall small intestine, |307|.
Diaphragm, 270, 297.
Diastase, 101, 300;
action on starch, 69.
Diet, and cost of food, 281;
and digestibility, 281;
balanced, 285;
relation of age, 280;
relation of environment to, 280;
relation to sex, 280;
relation of work to, 277;
the best, 284.
Dietary, the best, 282.
Digested food, absorption of, 308.
Digestibility and diet, 281.
Digestion, 68, 100, 181;
effect of alcohol, 311;
definition of, 270;
in stem, 99;
in stomach, 304;
of starch, 299;
purpose of, 69, 296.
Digestive system of fish, 235.
Digestive tract of frog and man, |297|.
Diphtheria, 152.
Dipnoi, 187, 236.
Diptera, 31.
Discoverers of living matter, 398.
Disease, and alcohol, |312|;
and bacteria, 151;
carriers, animals, 226;
carriers, flies, 222;
carriers, insects, 225;
caused by bacteria, 152;
caused by protozoa, 172;
effect of alcohol, 327;
of nose and throat, 340;
protozoan, 221.
Disinfectants, 148.
Division of labor, 178, 267.
Dog, skeleton, |185|.
Domesticated animals, 203, 260.
Dominant characters, 258.
Dormant, 22.
Dorsal, 186;
fin, 233.
Drugs, use and abuse, 294.
Duff, 113.
Dyspepsia, cause and prevention, 310.
Ear, section, |359|.
Echinoderms, 184.
Economic value of green plants, 117;
importance of spawning habits of fishes, 239.
Ectoderm, 177.
Effect of light on leaves, 88.
Efficiency of a week, |370|.
Egg, 177, 246.
Egg-laying habits of fishes, 238.
Ehrlich, Paul, 403.
Elasmobranchs, 187.
Elements, chemical, 20, |21|.
Elodea, |49|, 50.
Embryo, 58, 59, |103|;
of bird, 247;
of mammal, |247|.
Emulsion, 306.
Endoderm, 177.
Endoskeleton, definition, 237.
Endosperm, 67.
Enemies of forests, 113, |114|.
Energy, 64;
of a tree, |94|;
source of, 88.
English sparrow, 212.
Environment, |19|, 19;
care and improvement of, 26;
changes in, 25;
determines kind of plants and animals, 23, |23|, |24|;
normal, 28;
of man, 26, 266;
natural, 25;
relation to diet, 280;
what plants and animals take from, 21.
Enzymes, 68, 101, 298.
Epicotyl, 59.
Epidermis, 86.
Epithelial layer, 308.
Epithelium, 179.
Erosion, prevention of, |106|, 108;
at Sayre, Pa., |106|.
Essential organs, 36.
Esophagus, 302.
Eugenics, 261.
Eustachian tubes, 300, 359.
Euthenics, 264.
Evaporation, |99|;
of water, 85, 86, |87|.
Evolution, 194, 195.
Excretion, 181, 270, 332;
organs of, 340;
in plants, 103.
Exercise and circulation, 326;
and health, 339.
Exoskeleton, 185, 237.
Extermination of birds, 211.
Eye, compound, |30|;
defects in, 361;
section of, |360|.
Eyestrain, 395.
Factory inspection, 379.
Fallowing, 82.
Fatigue, 326;
and nerve cells, |356|.
Fats and oils, 60, 273.
Fehling's solution, 68, 299.
Fermentation, 135, |136|, 150.
Fertilization, of fish eggs, |240|;
of flower, 54.
Fibers, vegetable, 127.
Fibrin, 315.
Fibrinogen, 315.
Fig insect, 43.
Filament, 36.
Filter beds at Albany, N. Y., |385|.
Fins, 233.
Fishes, 186;
artificial propagation, 240;
as food, 201;
body of, 232;
breathing, 234;
circulation, 236, |321|;
digestive system, 235;
egg-laying habits, 238;
food getting, 234;
food of, 237;
gills, |234|;
heart, 236;
migration, 238;
nervous system, 237;
skeleton, 237;
senses, 233;
swim bladder, 236.
Fission, 170.
Flagella of bacteria, 142.
Flatworms, 183.
Flax, |128|.
Flea, |225|.
Floral envelope, 35.
Flower, fertilization of, 54;
lengthwise section, |35|;
use and structure, 35.
Fluid, 181.
Fly, a disease carrier, 222;
foot of, |223|;
life history, |222|;
typhoid, 223.
Foods, absorption of, 309;
adulteration, 288;
amphibia as, 202;
birds as, 202;
cost of, |283|;
fish as, 201;
fruits and seeds, 119;
getting of fish, 234;
in cotyledons, 60;
inorganic, 274;
inspection, 380;
is alcohol a food, 289;
leaves, 117, |118|;
making in green leaf, |93|;
mammals as, 202;
of animal origin, |279|;
of bacteria, 144;
of fishes, 237;
of insects, 33;
of plant origin, |278|;
of starfish, 216;
reptiles as, 202;
roots as, 119;
stems as, 118;
taking, 181;
tube of frog, |243|;
values, tables, |276|;
waste in kitchen, 287;
why we need, 272.
Foraminifera, 182.
Forestry, 113.
Forest destruction, 112, |113|;
fires, 112;
of North Carolina, |105|;
other uses, 109;
protecting, 114;
regions of United States, |109|.
Formaldehyde, 148.
Formation of habits, 354.
Four o'clock embryo, |103|.
Fresh air, |337|.
Frog, adaptations for life, 241;
and man, digestive tract, |297|;
breathing, 242;
circulation, 243, 322;
development of, 244;
diagram of tongue, |242|;
food tube, 243;
glands, 243;
locomotion of, 241;
long section, |243|;
metamorphosis, |245|;
nervous system, 352;
sense organs, 242.
Fruit, a typical, 55.
Fruit of locust, |55|.
Fruits and seeds as foods, 119.
Fruits, how scattered, 56.
Fuel, daily needs, 284.
Fuel values of nutrients, 277.
Functions, of all animals, 180;
of an animal, 48;
of bile, 307;
of blood, 313;
of cerebrum, 353;
of colorless corpuscle, |316|;
of lymph, 317;
of parts of plant, 48;
of red corpuscle, 314.
Fungi, 130, 176;
moldlike, 135;
of our homes, 132.
Fur-bearing animals, 204.
Gall bladder, 306;
insects, 208.
Gallflies, 43.
Ganoids, |186|, 187.
Garbage cans, |377|.
Garden fruits, 123.
Gastric glands, 303;
of frog, 243.
Gastric juice, 303.
Gastrula, 177, |178|.
Genus, 175.
Geranium, |45|.
German forest, |114|.
Germ cells, 251.
Germination, of bean, 63;
of pollen, |54|.
Gills of fish, 234;
rakers, 172, 234.
Glands, 297, 298, 299;
gastric, 303;
lymph, 324;
of frog, 243;
salivary, 299.
Glomerulus, |341|.
Glottis of frog, 243.
Glycogen, 307.
Gonorrhea, 156.
Grafting, |256|.
Grains, 122.
Grape sugar, test for, |68|.
Gravity, influence on root, 72.
Green plants, economic value, 117;
give off oxygen, 95;
harmful, 127;
make starch, 90, |92|.
Groups of plants, 174.
Guano, 82.
Guard cells, 88.
Gullet, 297, 300, 301, 302, |303|;
of frog, 243.
Gymnosperms, 176.
Gypsy moth, 215.
Habits, 354.
Habitat of protozoa, 172.
Habit formation, 354.
Hæmoglobin, 314, 330.
Hammer, 359.
Hard palate, 301.
Harm done by insects, |34|, 225.
Harmful green plants, 127;
preservatives, 148.
Hay infusion, 163, |164|.
Head of a bee, |38|.
Heart a force pump, |320|;
diagram, |319|;
in action, 319;
internal structure, 319;
of fish, 236;
size, position, 318.
Heat, and bacteria, 145;
effect of, 22;
output, 285.
Heating the house, 375.
Hemiptera, 32.
Hen's egg, |246|.
Herbivorous animals, 213.
Heredity, and evolution, 404;
bearers of, 251;
definition, 249;
relation of alcohol to, 372.
Hervey, William, 399.
Hibernate, 22.
Hides, 205.
Hilum, 59.
Honey and wax, 207.
Hookworm, 183, 228, |229|.
Horse, ancestor of, |193|, |260|.
How food is swallowed, 302.
Human blood, |314|.
Human body, a machine, 267;
composition of, |21|.
Human physiology, definition, 15.
Humming bird, |43|.
Humus, 79.
Hundred calorie portions, |286|.
Huxley, 398.
Hybridizing, 254.
Hybrids, 254.
Hydra, |179|.
Hydrochloric acid, 303.
Hydrogen of water, |20|, 20.
Hydrophobia, 392.
Hygiene, 27;
of breathing, 338;
of skin, 344;
of mouth, 302;
of muscles and bones, 268;
outline, 415;
personal, 261.
Hypocotyl, 59.
Hymenoptera, 30.
Ichneumon fly, |208|.
Illness of drinkers, |363|.
Imperfect flowers, 44, |45|.
Immunity, 157, 390.
Improvement, by selection, |253|;
of man, 261.
Impure water, 289.
Incisors, |301|.
Infectious diseases, 27, 363, 390.
Infusoria, 182.
Inner ear, 359.
Inoculation, 157.
Inorganic soil, |77|;
foods, 274.
Insects, 185;
and foods, 376;
as disease carriers, 225;
as pollinating agents, 36;
damage done by, |34|, 214;
diagram of, |29|;
food of, 33;
of the house, 216;
orders of, 30.
Inspection, of factories, 379;
of raw food, 380.
Instincts, 195.
Internal secretions, 317.
Intestinal fluid, 306;
glands, 308.
Intestine, large, 309.
Invertebrates, 185.
Iris, 360.
Isolation, 390.
Jenner, Edward, |400|.
Jimson weed, 128.
Jukes, 261.
Kidney bean, |59|, |63|.
Kidneys, 181;
human, |341|;
of frog, 243.
Kinetic energy, 267.
Knots, 112.
Koch, Robert, |403|.
Labor, division of, 178.
Laboratory equipment, 418.
Lacteals, 309, 324.
Lactic acid, 150.
Lactometer, 288.
Ladybug, 209.
Large intestine, 309;
of frog, 243.
Larva of milkweed butterfly, 32.
Latent energy, 267.
Lateral line, 234.
Leaves, as food, 117;
evaporation of water from, 85;
cell structure of, 85;
mosaic, 90;
respiration, 96;
section, |49|;
skeleton of, |85|;
structure, 85, |86|.
Length measures, 417.
Leopard frog, |188|.
Lepidoptera, 30.
Levers, |269|.
Life comes from life, 399.
Life cycle, 104;
of plants, 103.
Life history of malarial parasite, 217.
Ligaments, 268.
Ligature, applying, |326|.
Light, a condition of environment, 21, |22|;
and bacteria, 145;
effect of, |22|;
necessary for starch making, 91.
Lighting the home, 376.
Lily, narrow leaves, |90|.
Limewater test, |64|.
Lister, Sir Joseph, 403.
Liver, 306;
a storehouse, 307;
effect of alcohol on, 312;
of frog, 243.
Living matter and alcohol, 291;
plant and animal compared, 47;
things, needs of, 266;
things, varying sizes of, 51.
Lizard, |188|.
Lobster, |198|.
Locomotion, 181;
of frog, 241.
Lowell, typhoid area, |384|.
Lumber transporting, |110-111|.
Lungs, air passages, 330;
changes of blood in, 330.
Lymph, function, 317;
glands and vessels, 324, |325|.
Lysol, 148.
MacNichol, Dr. T. Alexander, 327.
Macronucleus, 169.
Malaria, cause, 217.
Malarial mosquito, |218|.
Malarial parasite, life history, 217.
Mammal development, 247;
embryo, |247|.
Mammals, 191;
adaptations, 192;
as food, 202;
classification, 192.
Mammary glands, 191.
Man, animals that prey upon, 230;
and his environment, 266;
circulation of blood, 318;
improvement of, 261;
in his environment, 26;
mouth cavity, 300;
place in nature, 195;
races of, 196;
stomach, 303.
Manufacture of fats, 93.
Measures, 417.
Mechanics of respiration, 332, |333|.
Membrane, mucous, 299.
Mendel, Gregor, 257, 406.
Mesenteric glands, 309.
Mesentery, 297.
Mesoderm, 177.
Metamorphosis of frog, 244, |245|.
Metchnikoff, 316.
Methods, of cutting timber, 111;
of breathing in vertebrates, 232.
Micronucleus, 169.
Micropyle, 59.
Middle ear, |359|.
Migration of fishes, 238.
Milk, and tuberculosis, 381;
composition of, |273|, |280|;
germs in, 381;
grades of, 381;
under microscope, |150|, |305|.
Milkweed, butterfly, 32, |33|.
Milling and starch making, 92.
Mink, 205.
Mixed diet, 284.
Moisture, |24|, |78|.
Mollusca, 185.
Mollusk, |185|.
Mold, 133, 134, 135;
yeast and bacteria, |143|.
Morning glory embryo, |103|.
Mosquito, malarial, |218|;
yellow fever, 219.
Moss plant, |177|.
Mother of pearl, |206|.
Motor nerves, 351.
Mouth cavity in man, 300, |300|.
Mouth parts of bee, 38.
Mucous membrane, 299.
Mucus cells, 299.
Muscles and bones, hygiene, 268.
Mutations, 253, 406.
Mutual aid between flowers and insects, 41.
Mycelium, 133.
Myriapoda, 185.
Natural environment, 25;
selection, 253.
Nectar, 35.
Need, of food, 272;
of sleep, 356;
of ventilation, 335.
Needs of living things, 266.
Nerve cells and fatigue, 356;
vasomotor, 325.
Nervous control, 181;
of heart, 325;
of respiration, 334;
of sweat glands, 343.
Nervous system, 271, |349|;
of frog, 352.
Neuron, diagram, |351|.
Newt, |187|.
Nicotine, 293.
Nictitating membrane of frog, 242.
Nitrates, 80.
Nitric acid, 61.
Nitrogen, 80;
cycle, |162|;
fixing bacteria, 80, |81|, 151;
of air, |20|.
Nodules, 81.
Normal heat output, 285.
Nose and throat, diseases, 340.
Nucleus, 50.
Nutrients, 273, 274;
fuel values, 277;
in common foods, 275.
Object of a field trip, 28.
Oils, test for, 61.
Operculum, 234.
Ophidia, 189.
Orbit of eye, 360.
Orchard fruits, 124.
Organic matter, 64.
Organic nutrients, 60.
Organisms, 47.
Organs, 47, 48, 180;
of Corti, 360;
of excretion, 340;
of hearing, 358;
of respiration, 330;
of taste, 358;
of touch, 357.
Orthoptera, 30.
Osmosis, definition, 75;
experiment, |100|;
physiological importance, 77.
Ostrich, |191|.
Outline of courses, 407-414.
Ovaries of frog, 243.
Ovary, 36.
Ovules, 54.
Oxidation, 64;
in our bodies, 65.
Oxygen cycle, |161|;
given off by green plants, 95;
of air, 20;
of water, |20|.
Oyster, |199|, 200.
Packard (zoölogist), 33.
Palate, hard and soft, 301.
Palisade tissue, 86.
Pancreas, 305;
of frog, 243;
work of, 305.
Papillæ, 301.
Pappus, 57.
Paramoecium, 167, |168|, |169|;
needs of, 266;
response to stimuli, 167.
Parasites, 131.
Parasitic animals cause disease, 227.
Parasitism, cost and remedy, 263.
Parotid, 299.
Pasteur, Louis, |401|.
Pasteurization, 146.
Pea pod, 55.
Pearls, 206.
Pectoral fin, 233.
Pelvic fin, 233.
Pepsin, 303.
Peptic gland, |304|.
Perfumes, 205.
Pericardium, 319.
Peristaltic waves, |303|.
Personal hygiene, 261.
Perspiration, 343.
Petals, 35.
Petri dishes, 140.
Phagocytes, 316.
Pharynx, 301.
Phenolphthalein, 80.
Phosphoric acid, 82.
Photosynthesis, |92|, 93.
Physiology of mold, 133.
Pistil, 36.
Pith, 97.
Placentæ of mammal, 247.
Plankton, 235.
Plants, animals depend on, 34;
and animals, mutually helpful, 18;
classification, 176;
food for insects, 33;
as food makers, 88;
function of parts, 48;
groups, 174;
need minerals, 80;
need of nitrogen, 80, |82|;
processes, 103;
reproduction, 173.
Plasma, 313.
Plasmodium malariæ, 182, 217.
Pleura, 332.
Pleurococcus, |166|.
Plumule, 59.
Pneumonia, 336.
Pocket garden, 73.
Poison, alcohol, 291;
ivy, |128|;
produced by alcohol, 347.
Polar bear, |204|.
Pollen, 36;
germination of, 53, |54|.
Pollination, 36, 40;
cross and self, 40;
wind, 44.
Pond scum, |173|.
Pons, 352.
Porifera, 182.
Portal circulation, 309, 322.
Portions, hundred calorie, |286|.
Potato beetle, 214.
Potato beetle, embryo, |103|.
Premolars, 302.
Preservatives, 147.
Prevention of dyspepsia, 310;
of molds, 134.
Proboscis, 30.
Prolegs, 32.
Pronuba, |42|, |43|.
Protecting forests, 114.
Proteins, 60, 273;
making, 93;
test for, |61|.
Protoplasm, 50;
what it can do, 52.
Protozoa, 172, 182, 205.
Protozoan diseases, 221.
Pteridophytes, 176.
Ptomaines, 144, 147.
Ptyalin, 300.
Public hygiene, 389.
Pulmonary circulation, 320.
Pulse, cause, 323.
Pupa of milkweed butterfly, |33|.
Pupil of eye, 360.
Pure food laws, 288.
Purpose of digestion, 69, 296.
Pyloric cæca, 235.
Quarantine, 27, 390.
Rabies, 392.
Races of man, 196.
Radiolaria, 182.
Radiolarian skeleton, |182|.
Recessive characters, 258.
Rectum, 297.
Red corpuscles, 313, 314.
Reflex actions, 353.
Regulation of heat of body, 343.
Relation, of age to diet, 280;
of alcohol to crime, 371;
of alcohol to heredity, 372;
of alcohol to pauperism, 371;
of animals to man, 17;
of bacteria to free nitrogen, 81;
of bacteria to man, 16;
of biology to society, 18;
of cost of food to diet, 281;
of digestibility to diet, 281;
of environment to diet, 280;
of green plants and animals, 15, 161, |162|;
of sex to diet, 280;
of work to diet, 277;
of yeasts to man, 135.
Rennin, 303.
Reproduction, 103, 181;
importance of, 52;
in seed plants, 173, 174;
of cells, 50;
of Paramoecium, 169.
Reptiles, 186.
Reptilia, 188.
Reserve air, 334.
Residual air, 334.
Respiration, 66, 181;
and alcohol, 346;
and nervous control, 334;
and tobacco, 346;
mechanics of, 332, |333|;
necessity for, 329;
organs of, 330;
of cells, |332|;
of leaves, 96.
Retina, 360.
Rhizoids, 133.
Rhizopoda, 182.
Rice field, |123|.
Ringworm, 134.
Roaches, 216.
Rock fern, |175|.
Rockweed, |176|.
Roots as food, 119;
as food storage, 83;
downward growth of, 72;
fine structure, 73;
give out acid, 79, |80|;
hairs, 74, |75|;
influence of gravity, 72;
influence of moisture, 73;
passage of soil water, 76;
pressure, 101;
system, primary, secondary, tertiary roots, 72;
uses of, 71.
Rotation of crops, 81.
Roundworms, 183, 228.
Rules of habit formation, 356.
Russian thistle, 129.
Saliva, 69, 299.
Salivary glands, 299;
glands of frog, 243.
Salmon, |201|, |241|.
Sand shark, |186|.
Sandworm, |184|.
Sanitarium for tuberculosis, |394|.
Sanitation, 27.
Saprophytes, 131.
Scavengers, 150.
Schleiden and Schwann, 398.
Schultz, Max, 398.
Sclerotic coat, 360.
Sea anemones, |183|.
Secretion, 299, 306.
Secretions, internal, 317.
Section, of ear, |359|;
of timber, |111|.
Sedgwick, William T., 312.
Seed, 54;
how scattered, 56;
plants, reproduction, |174|;
why it grows, 58.
Seedlings of bean, |63|.
Segmented worms, 183.
Selection, artificial, 253;
natural, 253.
Selective planting, 254.
Semicircular canal, 359.
Sensations, 350.
Sense organs, 181;
of fish, 233;
of frog, 242.
Senses, 357.
Sensory nerves, 351.
Sepals, 35.
Series, animal, 182.
Serum, 314.
Sewage disposal, |386|.
Sex, relation to diet, 280.
Shelf fungi, |132|.
Sieve tubes, 97.
Simple animal, development, 177.
Simplest plants, 166.
Skeleton, of dog, |185|;
of fish, 237;
of leaf, |85|;
of man, |268|.
Skin, 268;
hygiene of, 344.
Skunk, 205.
Sleep, need of, 356.
Small intestine, |307|, 308.
Smell, sense of, 358.
Snail, |185|.
Snakes, |189|;
food of, 212.
Soft palate, 301.
Soil, composition of, 77;
how water is held in, 77, |78|.
Sound, character of, 360.
Sour bread, 139.
Soy beans, |152|.
Sparrow, |246|.
Spawning habits, economic importance, 239.
Species, 175, 194.
Sperm, 177.
Spermaries of frog, 243.
Spermatophytes, 176.
Spinal cord of fish, 237.
Spiracles, 29.
Spirillum, 142.
Sponge, |180|, 182, |183|, 206.
Spore, 131, 173;
plants, 174.
Sporozoa, 182.
Sprengel, Conrad, 40.
Squash bug, 215.
Stables, clean and filthy, |388|.
Stamens, 36.
Starch, action of diastase, 69;
digestion, 299;
grains, |60|;
in bean, 61;
made by green leaves, 90, |92|;
test for, |61|.
Starch making and milling, 92.
Starfish, |184|;
food of, 216.
Stegomyia, |221|.
Stems, as food, 118;
passage of fluids up, |84|;
structure of, 97.
Sterilization, 145.
Sterilizer, |140|.
Stigma, 36.
Stimulants, 289.
Stirrup, 359.
Stomata, 86, |88|.
Stomach, 297;
digestive experiments, 304;
of frog, 243;
of man, 303.
Street cleaning department, 387.
Structure, colorless corpuscles, 315;
of leaf, 85;
of red corpuscle, 314;
of root, 73;
of root hairs, 74.
Sturgeon, |186|.
Style, 36.
Sublingual glands, 299.
Submaxillary glands, 299.
Suffocation, 340.
Sulphur, 149.
Sun, source of energy, 88.
Sundew, 102.
Sunlight in home, 374.
Sweat glands, |342|.
Sweeping and dusting, 336.
Swim bladder of fish, 236.
Symbiosis, 163.
Sympathetic nerves, 352;
nervous system, 304, 350.
Syphilis, 152, 156.
Systemic circulation, 320.
Table of cost of food, |276|, |283|.
Tactile corpuscles, 357.
Tænia solium, 227.
Tapeworm, |227|.
Taproot, cross section, |74|.
Taste buds, 301, 358.
Teeth, |301|.
Teleosts, 187.
Temperature, 417;
of blood, 318.
Tern, |190|.
Testa, 59.
Test, for carbon dioxide, 64;
nutrients, 61, 68.
Thallophytes, 176.
Thoracic duct, 324.
Tidal air, 334.
Timber, methods of cutting, 111.
Tissue cells, 49, |179|.
Toad, use of, 209.
Tobacco and circulation, 328;
and respiration, 346;
users of, 293.
Tortoise, |188|.
Touch, 357.
Tourniquet, 326.
Toxin, 152, 316.
Trachea, 185.
Transpiration, |85|, 87.
Transportation of lumber, |110|, |111|.
Treatment of cuts and bruises, 326.
Trees, need of city, 115;
preventing erosion, 108;
regulate water supply, 105;
value of, 105.
Trichina, |228|.
Trichinosis, 228.
Trillium, |175|.
Trout, development, |238|.
Trypanosomes, 221.
Tuberculosis, 152, |153|;
and milk, 381;
how to fight, 393, |394|.
Tussock moth, |215|.
Twig, section of, |98|.
Tympanic membrane, 358.
Tympanum of frog, 242.
Tyndall box, |399|.
Typhoid, |224|, |385|;
and diarrhoea, |200|.
Typhoid fever, 152, |155|, |382|.
Unit characters, 258.
Ureter, 342.
Urethra, 342.
Urine, 341.
Urodela, 188.
Uses, of animals, 198;
of antibodies, 316;
of green plants, 117;
of ice, 377;
of nutrients, 274;
of protozoa, 172.
Uterus of a mammal, |247|.
Vaccination, 157, 221, 391.
Vacuoles, contracting, 168.
Value, of insects, 208;
of trees, 105.
Valves, 185, 319;
in vein, |324|.
Variation, 250.
Vasomotor nerves, 325.
Vegetable fibers and oils, 127.
Veins, 318;
function and structure, 323;
valves, |324|.
Venæ cavæ, 322.
Ventilation, 335, 338.
Ventricle, 319;
of fish heart, 236.
Venus fly trap, 102.
Vermiform appendix, 309.
Vertebral column, 186.
Vertebrates, breathing of, 232.
Villi, 308.
Virginia creeper, 128.
Virus, 392.
Vitreous humor, 361.
Vorticella, |171|, 178.
Vries, Hugo de, 253, 406.
Warner, Chas. Dudley, 211.
Waste of food, 287.
Water, 275;
composition of, |20|;
impure, 289;
supply, 383.
Weed, |48|, 128.
Weights, 417.
Wheat crop, 121, |122|.
Wild orchid, |40|.
Windpipe, 300, 301.
Wood, uses of, 110.
Work of cells, 270;
of Department of Agriculture, 255;
relation to diet, 277.
Worms, 183.
Yeasts, 136, 138, 139;
relation to man, 135.
Yellow fever mosquito, 219.
Yucca, 42, |43|.
Zygospore, |174|.
Transcriber's Notes:
Punctuation, use of hyphens, and accent marks were standardized. Obsolete
and alternative spellings were left unchanged. Spelling of 'paramoecium' and
'paramoecia' were left unchanged.
Braces are used to indicate subscripted numbers in chemical formulas, e.g.
CO{2}. Pipes (|) are used to designate bold numbers in the index.
Footnotes were moved to the end of the paragraph in which the anchor
occurs. Footnote anchors [6] and [7] refer to the same footnote, as do
anchors [37] and [38].
Greek letters in the chart in Chapter XX are spelled within brackets: [alpha]
and [beta].
The following changes were made for consistency within the text:
'zoological' to 'zoölogical'
'diarrhea' to 'diarrhoea'
Other changes:
'proteid' to 'protein' in the header of the table in Chapter V
'do' added to header to Chapter VII ... how do green plants make food?...
'S arpe' to 'Sharpe' in the Reference Books list at the end of
Chapter XIV
'yoke' to 'yolk' ... (which is the yolk or yellow portion) ...
'does' to 'do' ... Both ... do the same thing ...
'page 207' to 'page 307,' in reference to lacteals.
'centers' to 'center's' ... the nervous center's controlling the blood ...
'scapels' to 'scalpels' in the appendix list of laboratory equipment
'and' added to '... Pasteur's solution and Sach's nutrient solution ...'
'Scavangers' to 'Scavengers' in the index
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