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FROM a considerable experience with both very elementary
and more advanced classes, the author has been led to certain con-
clusions in regard to the teaching of elementary physiology and
hygiene. It is not proposed to enter here into a discussion of
the correctness of these conclusions, but a brief statement of a
few principles that seem fundamental may perhaps be allowable.
The chief object of teaching physiology in the public schools
is to train the pupils to keep their bodies in health. The mere
teaching of anatomy and physiology will not accomplish this, for
the pupil cannot master the structure and workings of the body
in a way that will enable him to frame the laws of health and
apply them. Neither can the desired end be reached by teach-
ing rules of health without an anatomical and physiological
basis ; for without such a basis, hygiene is an intangible and an
elusive subject. The author has therefore concluded that a
conservative middle course is wiser than either of the extremes
of method mentioned above. An elementary text in physiology
should be a balanced text, containing sufficient anatomy to make
clear the broader outlines of the structure of the human body,
enough physiology to make plain the great laws according to
which the body lives, and a full discussion of how a violation of
these laws may be avoided.
For the introduction of certain new matter, as, for example,
the cell idea, the work of enzymes, and matter relating to germ
diseases, there is little need for explanation. The groundwork
of physiology and pathology has in recent years so shifted and
extended itself, that the subject-matter of an elementary course
must to a considerable extent be altered if it is to furnish a
proper basis for hygiene. The importance of teaching the
known facts in regard to parasitic diseases and of training
American citizens to apply measures for the prevention of these
diseases, is now recognized, and the reason for the rather full
treatment of communicable diseases will be understood.
One other point in connection with the teaching of physiology
has constantly obtruded itself upon the writer. This is the age
of science, but instead of teaching elementary science in our
public schools, we are teaching unrelated fragments from differ-
ent parts of the field of science. Physiology more than any
other subject is the people's science, and it should be related to
the nature study and the agriculture of the public school course.
In a few places in this book an attempt has been made to lead
the pupil into some of the byways that connect his physiology
and nature study, and special emphasis has been given to cer-
tain facts that are necessary to an understanding not only of
physiology, but of other subjects in the public school curriculum.
For counsel and very great assistance during the preparation
of this text, the author must thank his friend, Professor J. S.
Caldwell of Peabody College for Teachers. He is also under
obligation to Mr. J. C. Freeman, who made the calculations for
the table on pages 350-351 ; and for many suggestions and cor-
rections he is indebted to the following persons: Dr. William H.
Park, Research Laboratory of New York City ; Dr. F. H. Pike,
University of Chicago ; Dr. O. P. Jenkins, Stanford Univer-
sity ; Dr. C. M. Hazen, Medical College of Virginia ; Dr. E. G.
Williams, Virginia State Board of Health; Dr. S. O. Mast,
Johns Hopkins University ; Dr. J. A. C. Chandler, Virginia
Journal of Education ; Professor C. W. Hetherington, Univer-
sity of Missouri ; Miss Virginia Jones, Williamsburg, Virginia,
Public Schools ; Edward Hughes, Stockton, California, Public
Schools; and W. I. Chapman, Natick, Massachusetts, Public
INTRODUCTORY . i
I. THE HUMAN BODY A COLONY OF CELLS . . . 3
II. THE PLAN OF THE HUMAN BODY . '. 16
III. THE RULER OF THE BODY . . 23
IV. THE SKELETON . . 3 1
V. THE SKELETON (continued} ... . - 45
VI. THE MUSCLES . . .' . 59
VII. FOODS AND ENERGY . '7%
VIII. THE DIGESTIVE ORGANS ....
IX. DIGESTION, ABSORPTION, AND OXIDATION OF FOODS . 110
X. DIETETICS .... .120
XI. THE CIRCULATORY SYSTEM . . . 135
XII. RESPIRATION . . . . . 160
XIII. VENTILATION .... .178
XIV. THE KIDNEYS AND THE BODY WASTES . . . . 186
XV. THE SKIN AND THE BODY HEAT . , 19*
XVI. THE NERVOUS SYSTEM . .. ... 210
XVII. THE NERVOUS SYSTEM (continued} . * 225
XVIII. THE EFFECTS OF ALCOHOL ON THE HUMAN BODY . 238
XIX. THE SPECIAL SENSES . . ... . -245
XX. THE SPECIAL SENSES (continued} . . . . . 259
XXI. ACCIDENTS . . .' . , . . . . 274
XXII. DISEASE GERMS . . . . ;. . , * . 285
XXIII. DISEASES CAUSED BY PROTOZOA . . . . 292
XXIV. DISEASES CAUSED BY BACTERIA . . . . . 303
XXV. PREVENTING THE SPREAD OF DISEASE GERMS . . 320
XXVI. TUBERCULOSIS . .. .. ., . ... 340
APPENDIX ., . . . < . , . . . . 347
GLOSSARY i . . . . . . . -355
INDEX . . . . . . - . i i.. > . -357
DID you ever get up in the morning and find that all the
world seemed bright ? And did you ever get up on another
morning and find that all the world was dull ? Do you
remember how on the one morning you sang over your work
and ran on your way to school ? And how on the other
morning you blundered and fretted over j'our work ana did
not care to play ? On the one day you were so happy that
every one was pleased to see you. , Oii : t!ie pther, cl^y^yoiv
were not a pleasant companion for any one. On the one
day the world seemed a beautiful place, and work was easy.
On the other day all the world was dull, and every task was
hard and disagreeable.
Why were you happy and joyous one morning and misera-
ble and unhappy the next ? Why did you cheerfully do your
work one day and hate the same work the next day ? Was
it money, clothes, or education that made you happy ? Was
it a lack of them that made you unhappy ? All these things
are important, but there is something else much more im-
portant than all of them, something that causes happiness to
bubble up within you no matter what the world is like ; some-
thing that keeps the heart beating strong with hope, and
makes you laugh at hard work ; something without which all
the wealth of the world cannot make you happy, and with
which any sound-minded person can lead a useful and a
successful life. This something that can so change all the
world for you is the healtJi of your oivn body.
We cannot always be in perfect health. Sickness is bound
to come to us all, for there are many things about the human
body that we do not understand, and it has many ailments
that we cannot escape or cure. It is possible, however, for
us to learn many things that will help us to avoid the ill-
health that is so common in the world. In this -book we
shall, therefore, study the human body and how to keep it in
THE HUMAN BODY A COLONY OF CELLS
WHEN you view a brick house from a distance you do not
see the bricks of which the house is built ; but if you look at
the house through a telescope or come close to it, you see
clearly the bricks in the walls of the house. The house which
from a distance appears to be one object is seen to be com-
FlG. i. Cells. A is a single cell as it appears under the microscope, B is a cell
showing that it has length, breadth, and thickness, and C is a group of cells. A cell
found alone usually has a somewhat spherical shape, as shown in A. When cells grow
in groups they press against each other and usually have an irregular shape, as shown
posed of a great number of smaller objects built together to
form one whole.
The human body is composed of many small parts called
cells. When we look at the body we cannot see the cells;
but when a small portion of flesh or skin or other part of the
body is examined under the microscope, the little parts which
4 HUMAN PHYSIOLOGY
make up the body can be distinctly seen. As the walls of the
house are built of bricks, so the human body is built of cells.
The Cell. A cell is a small portion of a transparent,
jelly-like material called protoplasm}- Usually a cell has a
thin wall about it, so that it is like a little sac filled with a
clear, half -liquid substance. In each cell is a nucleus, which
is a denser portion of the protoplasm. Both the nucleus
and the less dense material 2 around it take in food and
grow ; both of them are alive. Taken together they are the
protoplasm, the living substance of the cell.
Living Things Composed of Cells. As a heap of sand is
composed of small grains, so are living things composed of
very tiny cells. 3 Every blade of grass, every weed, every
flower, and every tree is made of cells. Every animal,
whether it be large or small, whether it live in the water, on
the land, or in the air, is composed of cells. Dead materials,
like earth, stones, water, and air, are not made of cells, but
there is nothing living that is not composed of cells.
How Cells are Formed. The ancient Egyptians thought
that crocodiles and frogs came from the mud of the river
Nile, and a great Grecian philosopher believed that insects
sprang from the dew. A wise old German once told the
people how mice could be created from wheat and stagnant
water. Two hundred years ago, it was commonly believed
that maggots came from meat and cheese, and that worms,
insects, snails, and eels came out of decaying matter and
1 In the back of the book the pupil will find a glossary that gives the pronun-
ciations and meanings of many of the more difficult words.
2 The lighter portion of the protoplasm is called cytoplasm.
8 A few cells, for example, a frog's egg, are large enough to be seen with the
naked eye. In general, however, cells are very small; so small that it would
require twenty-five hundred cells from the human body to make a row an inch
THE HUMAN" BODY A COLONY OF CELLS
mud. Fifty years ago, many physicians and other scientific
men believed that disease germs and other little microbes
were formed from unclean and decaying matter, and many
persons still think that this is true.
We know now that all these ideas are incorrect. All living
things, from the smallest germ to the greatest whale, are
made of cells, and a cell can come, not from dead matter,
but only from another living cell.
FIG. 2. Cell division. The nucleus of the cell divides and part goes to each end
of- the cell. A wall is formed across the cell, dividing it into two parts, each of which
is a cell. All new cells are formed in this way.
The nucleus of a cell divides, and part of it goes to each
end of the cell. Then a wall forms across the cell, and
divides it into two parts. Each part is a new cell with its
own nucleus, and each part grows as large as the parent
cell. All new cells are formed in this way. " Every cell
comes from a cell."
One-Celled and Many-Celled Animals. In a drop of stag-
nant water many hundreds of little animals may sometimes
be found, animals so small that you can see them only
with a microscope. One of these little animals has only one
cell in its body. The animal is a single cell that swims
about alone and lives by itself. When this cell divides, the
two new cells separate, and each one forms a new animal.
6 HUMAN PHYSIOLOGY
The bodies of all the larger animals (for example, the
body of the chick in an egg) begin with a single cell, but
when this cell divides, the new cells do not separate, like
those of the one-celled animals. The cells remain together
and keep on dividing and dividing until, in the body of a
large animal, like a man, there are millions and millions of
cells, more than you could count in many years. The
FIG. 3. A one-celled animal dividing. This cell swims about in the water by
means of small hair-like cilia which beat the water. When it divides, the new cells
separate instead of remaining together as they do in the many-celled animals.
difference between the little one-celled animals and the larger
many-celled animals is therefore this : in one-celled animals,
the cells separate after they divide and each cell lives alone.
In the many-celled animals, the cells remain together after
division, and live in a great colony.
Your body, therefore, is a great colony of cells, and each
cell in it corresponds to an entire one-celled animal. You
might almost think of yourself as made up of a great com-
munity of little animals, yet this idea would not be wholly
correct. The cells of our bodies have learned to live to-
gether. They would die if separated, and it takes them all
to make one complete animal.
THE HUMAN BODY A COLONY OF CELLS 7
Different Kinds of Cells do Different Kinds of Work. The
single cell of a one-celled animal must do many different
kinds of work to live. It has no hands to get foo'd for it,
no teeth to chew the food, and no stomach to digest it. It
has no lungs to breathe in oxygen, and no kidneys to throw
off its poisonous wastes. It lives all alone, with no other
cells to help it, and it must do everything for itself. Each
cell in the human body has the same needs as the little
animal cell which lives alone. Each must have food, must
get oxygen from the air, and must get rid of its poison-
ous wastes. Many of our cells are shut up in the center
of the body, where they can get neither food nor oxygen for
themselves, and their waste matter would poison both them-
selves and their neighbors if there were not some way of
getting it entirely out of the body. Each cell cannot
take care of itself, as does the little animal in the drop of
You can easily see how much it would be to the advantage
of all the cells in the body for each one to give up trying
to do everything for itself, and for all of them to unite and
work for the good of the whole community. This they have
done. They have divided the work, and
each cell has taken for its own some special
task. The cells of the stomach digest the
food ; the bone cells build up a strong frame-
work to support the body ; the muscle cells
, , . . .., FIG. 4. Cells from
move the body ; the kidney cells throw out aglandof the stom .
wastes ; the lung cells take in oxygen from ach. The function
the air ; and the cells of the blood (red blood f work j
is to digest the food.
corpuscles) carry oxygen through all the
body to the cells. Each cell is a skilled workman doing
some particular work for the body as a whole, and not
Connective tissue. In its first stage
connective tissue is a group of cells
which build around themselves a mass
of jelly-like material, as shown in A.
This material hardens into the fibers
that are seen between the cells in D.
All through the body a framework of
connective tissue runs, holding the cells,
organs, and tissues in place.
One of the
cells are asso-
Cells of the outer
layer of the skin.
These cells form a
for the body. The
outer cells die and
dry up until they are
A muscle cell from the stomach. The
muscle cells have the work of moving the
Bone cells. These much-branched cells
deposit around themselves bone material
(b), thus building bones to support the body.
The bone cells build a network of fibers like
dense connective tissue and then fill the
spaces between the fibers with hard mineral
matter. a is a cavity from which the bone
cell has been removed.
Fat cells. Food for the body is stored in
these cells. Large quantities of fat collect
in the cell, and crowd the protoplasm (a
and b} to one side. A fat cell is little
more than a bag of oil.
FIG. 5. Cells from the human body. Each kind of cell in the body has a
particular work to do for the body as a whole.
THE HUMAN BODY A COLONY OF CELLS
an unskilled laborer trying to do all the many different kinds
of work necessary to provide for its own wants.
The Cells Dependent on Each Other. You will now under-
stand that the cells in the body must depend on each other for
many things. If the stomach fails to digest the food, there
will be a lack of food in all the cells. If the kidneys do not
throw off the wastes, all the cells will be poisoned. If the
lungs stop taking in oxygen, all the cells must die for lack
of oxygen. If part of the cells fail in their work, all the
cells must suffer, and death usually comes to the body because
part of the cells have ceased to work.
The Body compared to a Community. The resemblance
between the body and a community of people must now
be very clear to you. In both the body and the com-
munity we have individuals, each leading his own life and
yet making a part of a greater whole. In
the community we have individuals of dif-
ferent occupations, doctors, teachers, car-
penters, blacksmiths, grocers, and milkmen.
In the body we have, as we have seen, cells
of different kinds, muscle cells, bone cells,
digestive cells, and many others. In both
the body and the community the individual
does not provide everything that he uses,
but depends on others for many things.
The carpenter builds houses for the milk-
man and the grocer, and these persons
bring the carpenter his food. The stom-
ach cells digest food for the cells of the
lungs, and the lung cells take in oxygen
for the stomach cells.
Communities are prosperous and the body is healthy only
FIG. 6. Cells from
the lining of the tra-
chea, a is a cell that
mucus (b) in which dust
and germs from the air
are caught. The cilia
(c) on the other cells
beat upward and sweep
the mucus, dust, and
germs up out of the
air passages and lungs.
10 HUMAN PHYSIOLOGY
when the individuals do their work faithfully and well ; for
no person in a community lives to
himself, and no cell in the body lives
to itself, but each has a share in the
life of all. New individuals from time
to time are born into the community
FIG. 7. Cells from the blood. and other individuals die> New cdls
A is a white corpuscle whose
function is to kill disease germs; are constantly being formed in the
B is an edge view and cis a side body, and every day millions of cells
view of the red corpuscles that ^. , , . _
carry oxygen through the body. m the b d y are destroyed. Com-
munities increase in size when the
number of births in them exceeds the number of deaths, and
the body grows when the number of new cells formed in it is
greater than is the number of the cells that die. Thus in
many ways the body resembles a community of people where
each individual is doing something for the good of all.
Tissues. If you have now in mind what has been said
about cells and their work, you will have no difficulty in
understanding what is meant by tissties. In a factory we
usually find the workmen who do the same kind of work all
collected in one part of the factory. So in the body we
usually find grouped together the cells which do the same
kind of work. The great group of nerve cells is in the brain.
The muscle cells are collected in the muscles, and the kidney
cells in the kidneys. Where cells of one kind are grouped,
a tissue is formed, so we may say that a tissue is a group of
cells which do the same kind of work. Muscle tissue is
made of muscle cells, fatty tissue of fat cells, and nerve
tissue of nerve cells. Each tissue is a group of cells which
do some particular work for the body as a whole, and in
return have many things done for them by the cells of other
THE HUMAN BODY A COLONY OF CELLS \\
Organs. An organ is a part of the body that does a special
work. The kidney is an organ for throwing out wastes, the
lungs are organs for taking in oxygen, the eye is an organ
for seeing, and the stomach is an organ for storing and digest-
ing food. Some organs, like the liver, the kidneys, and the
heart, are chiefly of one kind of tissue. Other organs have
in them many kinds of tissues. The hand is an example
of an organ of this kind, bone, connective tissue, muscle, and
skin all being united in it to form an organ for grasping.
Why you should understand the Cell. It is very impor-
tant for you to understand the cell, because a clear idea of
the cell will give yon a new way of thinking about all
living things. Having an understanding of it, you will
not only think of an animal as a living thing, but you will
also think of the millions of cells in its body, each filled
with living protoplasm. When you see a plant cut down,
or an insect, or a frog, or a bird killed, you will not only
think of how the plant or animal dies, but you will think
of how all the little cells in its body also die ; and from
thinking of the living objects about you in this new way,
you will become interested in many things which you do not
now notice, and will understand much that now seems strange
to you. When you see a rose living for several days after it
has been cut from the bush and placed in water, or when
you see a branch of a plant living and growing when placed
in the soil, you will know that when a part of a plant is cut
off from the body of the plant, its cells need not always
die. If you read that when a starfish, or certain kinds of
worms, are cut into pieces, each piece grows into a complete
animal, you will see that in these animals, as in plants,
the cells are more independent than in the human body,
and that a group of them is able to live without the rest of
12 HUMAN PHYSIOLOGY
the body. Also, when you learn to think of animals as groups
of cells, you will not wonder that a frog's legs should twitch
and jerk in the skillet; or that after the head has been cut
off, a snake's tail can live and move, and a turtle can walk
about. For you will understand that in these animals, as
in the rose, part of the cells can live for a time without the
others, and that the muscle cells are living and moving after
the brain cells are dead. All these things and many others