Human physiology; an elementary text-book with special emphasis on hygiene and sanitation

Front matter

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Preface

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

iii

IV

PREFACE 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, Dr. J. S. Caldwell of the Bureau of Plant Industry, United States Department of Agriculture. 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 corrections he is indebted to the fol¬ lowing persons: Dr. William H. Park, Dr. F. H. Pike, Dr. O. P. Jenkins, Dr. C. M. Hazen, Dr. E. G. Williams, Dr. S. O. Mast, Dr. J. A. C. Chandler, Professor C. W. Hetherington, Miss Virginia Jones, Edward Hughes, and W. I. Chapman.

Contents

PAGE

Introductory . » i

CHAPTER

Chapter I 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 Cis 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 in C.

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 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 1 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 scholar 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.

3 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 long.

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.

FlG. 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.

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 J

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 food 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 water.

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 move the body; the kidney cells throw out wastes; the lung cells take in oxygen from the air; and the cells of the blood (red blood 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

FIG. 4. Cells from a gland of the stom¬ ach. The function (work) of these cells is to digest the food.

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 B.

All through the body a framework of connective tissue runs, holding the cells, organs, and tissues in place.

One of the nerve cells from the brain. These cells are asso¬ ciated with thought.

layer of the skin.

These cells form a protective covering for the body. The outer cells die and dry up until they are mere scales.

A muscle cell from the stomach. The muscle cells have the work of moving the body.

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 OP 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 tracnea. a is a cell that manufactures sticky mucus ( b ) in which dust and germs from the air are caught. The cilia (t) on the other cells beat upward and sweep the mucus, dust, and germs up out of the air passages and lungs.

EO 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 and other individuals die. New cells are constantly being formed in the body, and every day millions of cells in the body 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 tissues. 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 ceils 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 tissues.

Fig. 7. Cells from the blood.

A is a white corpuscle whose function is to kill disease germs; 2? is an edge view and Cis a side view of the red corpuscles that carry oxygen through the body.

THE HUMAN BODY A COLONY OF CELLS n

Organs. An organ is a part of the body that docs 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 you 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 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 you can clear up for yourself, if you will think about the cell instead of about the body as a whole.

A second very important reason why you should under¬ stand the cell is that you may intelligently care for your own bodies. Each of the great multitude cf cells in your body is following out its own little life, and each is industriously work¬ ing for the good of the community in which it lives. We hope that you will understand that your cells must have proper food, oxygen, exercise, and rest, and that they must get rid of their waste matter. You should realize that any medicine you take can act on the body only by being carried by the blood through the body and entering the living proto¬ plasm of the cells. If it helps the cells, it is beneficial to the body, and if it injures the cells, it injures the body. You should understand how reckless it is to take in among all these delicate cells patent medicines, headache remedies, alcohol, or tobacco, unless you are perfectly certain that these things will not harm the cells. For the cells of your body are the most important things in all the world to you. If they become diseased, you will fall sick; and if they fail in their work, your life must cease. When the bricks crumble, the house falls; and when the cells are dead, the body is dead, for the life is in the cell.

There is a third reason why you should understand the

THE HUMAN BODY A COLONY OF CELLS cell, and that is because in physiology we constantly study the work of the different kinds of cells . If you did not under¬ stand the figures 1 , 2 , 3 , and 4 , you would get very little pleasure or profit from trying to solve problems in arith¬ metic; and if you do not understand what a cell is and how the body is made up of cells, you will think that physi¬ ology is a dull subject indeed, and it will never J mean much to you. But understanding the cell, you can study the differ¬ ent parts of the body intelligently, and in all the world you will find nothing more wonderful or interesting than your own body.

Anatomy, Physiology, and Hygiene. Anatomy is the study of the structure of the body , — the study of the way all its organs are composed of tissues and its tissues made of cells, and of how all the organs and tissues are joined together to make one body. Physiology is the study of the function of the different cells , tissues , and organs , — the study of the work which all the different parts of the body do. Hygiene is the study of how to keep the body in health . These three subjects we must study in this book.

Summary. The human body, like all other living things, is composed of cells. Each cell is a little piece of protoplasm that takes in food and grows and is alive. Cells are formed only by the division of other cells, and living things can come only from other living things of the same kind. They can¬ not come from dead matter, although this has often been believed.

When a one-celled animal divides, the new cells separate. In many-celled animals the cells remain together after divi¬ sion, and the bodies of the larger animals are great colonies of cells. Each cell of the human body corresponds to an entire one-celled animal. Each cell in the body, like a one-celled animal, must have food and oxygen and must get rid of its wastes.

It would not be possible for a cell in the body to supply all of its own wants, so each cell spends all its time in one kind of work, and depends on other cells for many things that are necessary to its life. It follows, therefore, that when part of the cells in the body fail in their work the whole body must die. The division of labor among the cells causes the body in a striking way to resemble a community where the people have different occupations and each one has many of his wants supplied by others.

As the workmen who do the same kind of work in a fac¬ tory are often found together, so the cells that do the same kind of work in the body are found in groups. Such a group of cells — cells that do the same kind of work — is called a tissue. An organ is a part of the body that, like the hand or the eye, is fitted for some special work. It may be composed chiefly of one or of many kinds of tissues.

A clear idea of the cell is a very great help in understand¬ ing all living things, in caring for our own bodies, and in the study of physiology. Anatomy is the study of the structure of the body, Physiology is the study of the function of the different organs of the body, and Hygiene is the study of how to keep the body in health.

Of what is the human body composed ? Describe or draw a Cell. What kind of objects are composed of cells? How are new cells formed? Where do living things come from? Give some of the beliefs that have been held by different people in regard to the ori¬ gin of animals and plants. Describe the process of cell division.

THE HUMAH BODY A COLONY OF CELLS

In a one-celled animal what do the cells do after division? What do the cells do after division in a many-celled animal ? What in the human body corresponds to an entire one-celled animal? What are some of the needs of a cell?

Explain why a cell in the body could not provide for all its own wants. Name some of the different kinds of cells )in the body and explain the function (work) of each. What happens to the body if part of the cells fail in their work? Give examples of cells that must do their work to keep the body alive. Mention some ways in which the body corresponds to a community of people.

What is a tissue? Name some of the body tissues. What is an organ? Name some organs of the body and give their functions.

Give three reasons why it is important to understand the cell.

What is Anatomy? Physiology? Hygiene?

If a cell and a peach were compared, what part of the cell would correspond to the seed of the peach? to the flesh of the peach? to the skin of the peach ?

In an egg there is one living cell lying on the side of the yolk. What is necessary to make this cell grow and divide ? Of what use are the yolk and white of the egg to the cell within the egg? Into what have the yolk and the white been changed by the time the egg hatches ?

Does the cell in a duck’s egg grow into a duck and the cell in a hen’s egg into a chick because the food supply in the eggs is different, or because the living cells in the eggs are different? Are the cells of your body always composed of the same materials, no matter what kind of food you eat?

Can a branch be transferred from one tree to another and still live? Can a piece of tissue be transferred from one person to an¬ other? Ask a physician if cells from the body of an animal can be transplanted to the human body.

What happens in a wound when it heals? Ask a physician how the cells in a scar differ from the cells in other parts of the skin.

Chapter II The Plan Of The Human Body

The human body is com¬ posed of a head, a trunk, and two pairs of limbs. It is sup¬ ported by a skeleton, the most important part of which is the spinal column , or backbone.

In the head are eyes, ears, a nose, and a mouth. The body has in it two cavities, a dorsal or back cavity, and a ventral or front cavity. In these two cavities are found most of the organs of the body.

The Dorsal Cavity. In the head is a great cavity, and opening out of this cavity at the base is a long passage¬ way that runs through the spinal column from top to bottom. The cavity in the

Fig. 8. The cavities of the body. The head and the canal in the

dorsal cavity is in the head and the spinal backbone, taken together, are column. The ventral cavity is in the front

of the trunk and is divided by the diaphragm the dorsal Cavity. In tnis into an upper and a lower part. cavity lie the great centers of

the nervous system, the brain and the spinal cord .

1 The name dorsal comes from dor 1 sum, the Latin word for back. In the lower animals it is easy to see that the cavity in the head and the canal in the spinal

THE PLAN OF THE HUMAN BODY

The Ventral Cavity. The ven¬ tral cavity is a great hollow in the front part of the trunk.

Stretched across it is a thin sheet of muscle, called the dia¬ phragm, which divides it into an upper and a lower part. The trachea upper part is the chest or thoracic ES0PHAQUS cavity. It contains the heart and lungs and many of the great blood vessels. The lower part is th z abdominal cavity. In.the heart left side of this cavity, its outer 0,APHF end close up under the dia- L phragm, lies the stomach. On s the right side of the body and partly covering the stomach is the liver. The intestine is very long and is coiled again „ and again in the abdominal cav¬ ity, filling most of it. Attached to the back walls of the cavity are the two kidneys, which fig. 9. Section of the body showtake waste matter out of the ing the positions of the organs in the