First book in physiology

Front matter

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Preface

This book is intended for beginners in the study of Physiology, of whatever age they may be. It is a " First Book" for the adult as well as for the child. There is more in common between young and adult minds, in regard to a subject which is new to them, than is commonly supposed. There is for both the same need of simple, clear, and precise statement, with familiar illustration. A book intended to instruct a child in any science should be so written, that it will be just as instructive to an adult unacquainted with the subject. Not only so, but it should be so written, that it will interest and please a mind that has a full knowledge of the subject, by its logical and clear development of simple fundamental facts and principles.

It is a common error to suppose, that there need not to be as logical a presentation of a subject in teaching children as in teaching adults. A correct logic, in the true sense of that word, is necessary in either case. In teaching any science, no matter what the age of the scholar may be, a natural, that is, a logical, arrangement of the facts and principles, is essential to success. Indeed, it is more essential at the outset than it is subsequently, for the beginner lays the very foundations of his knowledge, upon which in his course of learning afterwards he builds up the superstructure. It is the simple facts and principles of science, such as should be taught to the beginner, that are fundamental. In order that he may begin right, he must acquire a clear idea of these.

PREFACE

This, it is obvious, cannot be done by a loose, partial, and illarranged presentation of them, but only by a presentation that is strictly logical. Commonly, this foundation- work, as it may be termed, has to be done over and over again, bringing much unnecessary labor to both teacher and scholar, simply because it is not done right at the outset.

There is another consideration bearing upon this point, which is of great importance. It is essential to the successful study of science that good habits of mind be formed, and the earlier they are formed the better. I need not stop to show that clear logical presentations of facts and principles tend to form such habits, and that a loose, confused mode of presenting them tends to form habits of an opposite character.

Let me not be understood to advocate that prominence of logical framework, as it may be called, which is so common in books for instruction. With all this show of logical arrangement, there is often much that is really very illogical. With the beginner, at least, the less there is of the formalities of arrangement the better. And yet there should in reality be a strict regard to the proper logical order in introducing facts and principles to the mind of the learner. If this natural order be observed, every page that the student learns serves to prepare his mind for what comes after. There is no point in which books for instruction so often fail as in this.

Most books for the instruction of beginners in science, present a strange mixture of child's talk, and language that the child cannot understand, but can only learn by rote. Even the hard technical terms of science often enter abundantly into the compound. It seems to be forgotten that great simplicity of language may be the vehicle of even a deep philosophy, and is consistent with an elevated style. Clear, precise statement, logical order of arrangement, and felicitous illustration, are the elements of such a style. And these elements cannot exist, unless there be an appreciation in the writer's mind of the attitude of the minds that he addresses. He must not only see clearly the facts and principles of science himself, but he must know how to make others see them clearly also.

PREFACE.

It is obvious that in a " First Book " there must be a less number of points introduced than in a book intended for instruction afterward. The field of vision should be gradually enlarged as the»learner advances. At first there must be a selection of such points as he can most readily understand, reserving the more difficult ones for another book. And while the second book should be much more complete than that which is designed for beginners, yet m the latter the really essential and fundamental parts of the science should be clearly presented.

The principles thus advanced I have endeavored to follow in the construction of this little work. It is intended principally for the use of common schools, and yet, like my larger work on Physiology, it is adapted for general reading. It will prepare the reader and the scholar for the more full examination of the subject in the larger work.

I need hardly say, that in order to teach from this book satisfactorily, it is necessary for the teacher to read both books. By doing so, he will see clearly in every case the reason of the selection that I have made in this work from the facts that are presented so fully in the other, and will therefore be better prepared to teach according to the plan that I have in view. The questions that I have placed at the bottom of each page can be altered as the teacher thinks best, to suit the different capacities of his scholars. For certain general directions in teaching Physiology, I refer him to the Appendix of my larger work.

Chapter I. The Machinery Of The Body

1. When you look at any machine made by man, you inquire what it is intended to do. You find, commonly, that it is for some one purpose. Thus, a nailmachine makes nails, and does nothing else ; a papermachine makes paper ; a locomotive draws cars on a track ; and so of other machines.

2. But the human body is not a single machine for a single purpose. It is a complicated machine, and serves many purposes. It differs very much in this respect from the machines that man makes. While for example, it is a machine that walks, walking is not the only thing that it does. It is not like the locomotive, that does nothing but draw cars. It can perform a great variety of motions besides walking. It can run, jump, leap, climb, &c.

3. You see the same difference, if instead of looking at the body as a whole, you look at any particular part of it. Look, for example, at the hand, and com-

What is said of machines made by man ? How does the machinery of the body differ from these ? 1* pare it with the most ingenious machinery that man has ever made. The variety of things that it can do is almost endless. So, too, if you open your mouth before a looking-glass, and move about that busy little machine, the tongue, you will get some idea of the great variety of motion that it can perform.

4. But besides being a locomotive machine, capable of all this variety of motion, the human body is also a machine in which many things are made. Blood is made in it. This red fluid is made out of the food which this machine puts into its mouth and eats. And then from the blood are made all the various parts of the body.

5. In order that the blood may be used to construct all parts of the body, it must be carried everywhere. There is a wonderful set of machinery to do this. The heart is pumping night and day, sending out the blood through the pipes that branch out from it all over the body.

6. Then the blood, when it has been used, is not fit to be used again until it is changed. There is, therefore, a set of machinery in the chest for the purpose' of changing the blood. The blood is carried to the lungs, and there it is exposed to the air that we breathe into the lungs every time that we draw a breath. By being aired in this way, it is fitted to be used again, and it goes back to the heart that it may be pumped out again all over the body.

7. But the most wonderful machinery in the body

Mention some particular parts of the body in which this difference is seen. What is made by the machinery of the body ? By what machinery is the blood circulated ? How is the blood changed after it has been used ?

MACHINERY OF THE BODY. 11

is that which we find in the nervous system. The brain is the great central organ of this system. From it branch out white cords, called nerves, which are found in every part of the body. This nervous system is somewhat like a telegraph, though it is much more perfect and mysterious. The brain may be considered as the central office, where the mind has its seat. The neTrves may be called the wires, by which messages are sent forth and received by the mind.

8. Messages are sent by means of the nerves to the muscles, whenever the mind wills that any part of the body move. Thus, when you wish to move your hand, messages are sent from the brain to the muscles that move this part. When the mind wills that the whole body shall move, a great number of these messages are sent in all directions at once.

9. The mind too receives messages through the nerves. It receives them from the senses. When we see, something is sent by means of the nerves of the eyes to the brain, and thus reaches the mind, just as electricity goes along the wires of a telegraph. And the same may be said of the other senses.

10. Observe now how great a variety of machinery there is in the body. The digestive machinery grinds up the food with its teeth and mixes it with juices in such a way that blood is made out of it. Then the machinery of the circulation moves the blood about everywhere in the body, so that all the parts may be made out of it and be kept in repair. The breathing

What is the most wonderful machinery in the body ? What is it like ? And how ? Describe what is done when the muscles act. How and from what does the mind receive messages ? Give what is stated in *lf 10 about the variety of the machinery in the body.

machinery continually purifies the blood after it has been used, and so fits it again for use. Then by means of the nervous machinery the mind uses the parts that are thus constructed from the blood — viz., the muscles, the bones, and the organs of the senses.

11. You see that some of the machinery of the body is for the purpose of making other machinery. This is the business of the machinery of the digestion, the circulation, and the respiration. This machinery makes nerves, and muscles, and bones, and the brain, and the eye, and the other organs of the senses. The object then of eating and drinking and breathing and having the blood circulate, is to make machinery for the mind to use.

12. There is one difference between the machinery of the body and the machines constructed by man, that I have not yet mentioned. AVhen man makes a machine he cannot use it till it is completed. If he wishes to alter it or repair it, he cannot use it at all while he is doing this. But the machinery of the body is constantly altered while it is in use. I will illustrate this difference.

13. The machinery of the child's body is small machinery, but every part of it gradually becomes larger, and in manhood it is of its full size. But no machine made by man can grow to be a larger one. Now, the machinery of the body not only grows, but it is kept in use while it is growing. A small telescope never grows to be a large one, but the little eye of the infant

Can the machinery that man makes be kept in use while he is altering or repairing it? How is it with the machinery of the body ? What is said of the growing of the machinery of the body ?

MACHINERY OF THE BODY. 13

grows to be the large eye of a man, and is used every day while this is done. A cord does not grow to be a rope, but the muscles grow as we use them.

14. The machines that man constructs cannot be repaired while they are in use ; they have to lie by for repair, as it is expressed. It is not so with the machinery of the body ; repairing is going on while it is in use. In the machinery made by man it is done only now and then, but in the machinery of the body it is done all the time, every day, every hour, every moment.

15. One thing is to be noticed, however, about this repairing of the body. Some of its machinery must have seasons of rest, in order that the repairing may be thoroughly done. This is the case with the brain, the nerves, and the muscles. When the mind has worked these parts of the machinery during the day, the rest of night is needed to repair fully the wear and tear. Though- the business of repairing them is going on all the time, more of it is done while they are at rest in the hours of sleep than when we are awake.

16. Another thing to be remarked is, that when the machinery is much deranged by disease, more rest than is commonly taken at night is needed. There must be some lying by for repair now. Thus, if a limb be inflamed, it must be kept still. An inflamed eye needs to have the light shut out from it. If the brain be diseased, the mind must be kept from using

Does the machinery of the body lie by for repair ? What parts of the machinery of the body must have seasons of rest to have the repairing well done ? What is said of the need of rest for repairing in disease ?

it as much as is possible ; that is, it must be kept from thinking. And what is true of particular parts of the machinery is true of it as a whole. When the whole body is disordered, as in fever, all the machinery must be kept as- quiet as possible.

17. There is some of the machinery that never stops, either when we are sick or when we are asleep ; it is the breathing and the circulating machinery. The heart is always beating, and the chest is always heaving ; they never rest from their work, and they are stopped only by death.

18. In this chapter I have given you some general views of the machinery of the body. In the following chapters I shall describe particular parts of it, and shall explain to you how they operate. I shall speak of the machinery of digestion, of circulation, of respiration, the nervous machinery, &c, each of them separately.

Chapter II. The Different Structures Of The Body

1. Before considering each subject particularly, let us look in this chapter at some of the various things or structures that make up the machinery of the body. By doing this, these subjects will be more clear to you. For, as I shall mention different parts of the body, as I proceed, you will understand me better, if you have some knowledge of these parts at the beginning.

What parts of the machinery of the body never rest?

DIFFERENT STRUCTURES OF THE BODY. 15

2. Notice first, the hard bones which are the framework of the body. These are very different in their shapes in different parts of the frame. For example, in the leg and arm they are long and slender, while in the head they make a box to hold the brain. They vary much in size also.

3. The bones are composed partly of mineral and partly of animal substance. When you see a pile of bones near a slaughter-house, which have been a longtime exposed to the air, you see only the mineral part of them. The animal or soft part has been taken away by the heat of the sun and the washing of the rain. The same thing can be done, very quickly, by exposing a bone to a very hot fire. A bone thus deprived of its animal part is very brittle, and breaks easily.

4. The animal part of a bone can be obtained also separate from the mineral part. This can be done by putting it into a mixture of

Fig. 1.

an acid, called muriatic acid, and water. The acid takes the mineral part away, and leaves the animal part in perfect shape. While the mineral part is brittle, this soft animal part can be bent so as

What is said of the shapes of the bones, and of their size? Of whal two parts is bone composed ? How can the mineral part be obtained separate from the other part ? How can the animal part be obtained by itself?

to be tied into a knot, if the bone be one of the longones. Fig. 1 represents a thigh-bone thus tied, after being deprived of its mineral part.

5. In the child, -when the bones are growing, they do not have as much of the mineral part as the bones of old persons do. It is well that they do not ; for if they did, the frequent falls of the child would often give him a broken bone. If an old person should have as many falls as children commonly do, his brittle bones would very often snap asunder. A fall down stairs, which in the child is generally followed only by a momentary fright, a short crying-spell, and perhaps a bruise, is apt to break some bone in the old, and may even destroy life.

6. The bones are bound together by firm ligaments, so that while they move on each other at the joints, they are held in their places. The bones are moved by muscles. The muscles make up the bulk of the fleshy part of the body. Their color is red. The tendons are white and shining cords, by which the muscles pull the bones, in moving them.

7. As I must refer occasionally to the action of muscles before I come to the chapter on the muscles, I will explain to you now the manner in which they act. A muscle is composed of a great number of very small fibres or threads. When it acts, each one of these fibres shortens itself.

What is the difference between tbe bones of the old and those of the young in regard to these two parts ? What would happen to the child if there were not this difference ? By what are the bones bound together ? By what are they moved ? What are the tendons ? What is a muscle composed of?

a

DIFFERENT STRUCTURES OF THE BODY. 17

8. I will show how this FlG . 2 . shortening of the fibres moves the bones, by means of some figures. Suppose #, in Fig. 2, is a bone that is fixed so that it cannot be moved, and that b can be moved. Let e be a fibre that extends from the one bone to the other. If the fibre c shorten itself, it will draw the bone b towards a, as represented in the lower figure.

The same thing is true of a number of fibres, as represented in Fig. 3. You see, then, how ^ it is true of a multitude of fibres, as they are bound together in a muscle.

9. Let d, in Fig. 4, represent a bone that is fixed, and e a bone that moves on d, with a hinge-like joint. If the fibres are relaxed, the bone e will be as in Fig. 4 ; but if the fibres contract, the bone will be as in Fig. 5. These two figures show the action of the lower jaw, as it is moved up and down by the muscles, in eating. In Fig. 4, e is like the lower jaw when it is down ; and in Fig. 5 it is like it when it is up, so that its teeth press against those of the fixed upper jaw.

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Explain by figures 2 and 3, how the fibres of a muscle act. Illustrate the manner in which the muscles move the lower jaw in eating.

10. Figs. 6 and 7 show you how the muscle that bends the elbow acts. In Fig. 6 the bones a and b are represented as they are when the arm is extended out straight. The muscle which is represented by the line d, is relaxed.

When it contracts or shortens itself, the bone b will

be bent upon a, as seen in Fig. 7.

11. These two examples of muscular action will be sufficient for the present. In some of the succeeding chapters you will see examples of other ways in which the muscles operate ; and, in the chapter on the muscles, the many various ways in which they act will be fully illustrated.

12. I have thus spoken of the bones with their ligaments, and the muscles with their tendons. The limbs of the body are made up of these four structures. They compose also all the outer parts or walls of the trunk of the body and of the head. Within these walls are the three great cavities of the body, containing its most important organs.

13. In the cavity of the head is the brain. This delicate and soft organ is shut in very securely by that round box of bones, called the cranium or skull. The cavity of the chest contains the heart and the lungs. The walls of this cavity are the spinal column, or back-bone, as it called, the ribs, and the breastniustrate the manner in which the muscles bend the arm at the elbow. Of what four structures are the limbs of the body composed? What other parts do they compose?

DIFFERENT STRUCTURES OF THE BODY. 19.

bone. These are strongly bound together by muscles and ligaments. In the cavity of the abdomen are the stomach, liver, &c. Its walls are the spine behind, and at the sides and in front, broad flat muscles and tendons. The organs contained in these three cavities I shall speak of in other parts of this book.

14. In all the different structures of the body of which I have spoken, there are blood-vessels, large and small, circulating the blood everywhere. Nerves too go everywhere, branching out from the brain and spinal marrow. They are whitish cords, which by dividing continually are distributed to all parts of the body. The blood-vessels and nerves are everywhere mingled together. For if you prick any part, the nerves feel the pain, and the blood-vessels at the same time let out their blood.

15. All the parts and organs of the body are well packed together. They are so arranged that there is no loss of room. And there is a kind of packing material made use of everywhere between all the parts. It is a very fine and nice material. You can see it if you look at a piece of meat from any animal. If you pull the fibres of the meat a little apart, you will see a delicate white substance between them. You will also see different portions of the meat separated from each other by considerable layers of this substance. These are the different muscles with the packing material between them.

16. This packing material, which is called the cel-

What are the three great cavities of the body ? What are their walls ? What do they contain ? What is said of blood-vessels and nerves in the different structures of the body ? What is said of the packing of the parts of the body ?

hilar membrane, is not only around all the muscles and between their fibres, but it is around everything and in almost everything in the body. It is full of little cells or spaces ; and hence comes its name. In some parts these cells are larger than in others. The fat of the body is in cells of this substance, mostly just under the skin. When the cells contain fat they are larger than they usually are.

IT. This cellular substance is very yielding, so that the motions of the body are not made less free by their being thus bound together by this packing material. When the. muscles are performing some of their motions this substance is very much moved and stretched, but it always yields easily and is not torn.

18. The cells of this substance are kept moist by a very little watery fluid. When this fluid is in greater quantity than it should be, the disease called dropsy is present ; and it is because the cells everywhere open into each other, that the water in this disease is so apt to accumulate in the lowest parts of the lower limbs.

19. Over all the parts of the body is the skin covering them up from our view. It also defends them from injury. While for this purpose it is very firm, it is at the same time quite yielding, so that it may not restrain the motions of the body. Underneath the skin the cellular substance is very abundant, connecting the skin with the muscles and other parts.

20. There is a kind of skin, called the mucous

Describe the appearance of the common packing material. What is said of the fat ? What is said of the yielding character of the cellular membrane ? What is said of its cells ? What is said of the skin ?

DIFFERENT STRUCTURES OF THE BODY. 21

membrane, that begins in the mouth and nose, and lines all the passages to the lungs, the stomach, and other organs. It may be called the interior skin of the body. It is termed the mucous membrane, because it is moistened by mucus, a glairy fluid which constantly oozes from it. The red covering of the lips does not seem to be either skin or mucous membrane, but a texture somewhat like both of them.

21. The serous membranes are so called because they are moistened with a watery fluid called serum. They line the outside of some of the great organs of the body, and also the inside of the walls of the cavities that hold them. Thus the lungs are covered with a serous membrane, and the inside of the walls of the chest is lined with it. You can see what the object of this is : as the chest moves in breathing, the lungs rub a little . against the walls of the chest ; but the smooth shining serous membrane that lines them prevents the rubbing from doing any harm. The same thing is true of the organs in the abdomen. The rubbing of the stomach and the intestines against each other and against the walls of the abdomen, would make them sore and inflamed, if they were not all lined with, this smooth and moistened membrane.

22. I have not described to you all the structures in the body, but only those that it is well for you to understand in the beginning. You will know more in relation to these as I proceed, and I shall also describe to you in the succeeding chapters some other structures.

What is said of the mucous membrane ? What is said of the red skin of the lips ? What are the serous membranes ? What do they line ? Of what use are they in the chest, and in the abdomen ?

Chapter III. Digestion

1. I have already told you in the first chapter that the blood, which is the common building material of the body, is made out of the food that we eat. That this may be done, the food must be digested, as it is termed.

2. Digestion is not a single and simple process; several things are done. First, the food is cut and ground by a sort of mill in the mouth ; and while this is going on the food is thoroughly moistened by a liquid called the saliva. As fast as it is ground and moistened it is passed through a tube that extends from the back part of the throat down into the stomach. There the food is mixed with another liquid called the gastric juice. It is then passed on into the intestines. There all that part of the food that can be used to make blood is sucked up by a multitude of little vessels. These vessels join together to form a tube which empties itself into the blood. Having thus described in a general way the manner in which the nourishing part of our food is separated and extracted from it, let us look at the different parts of the process more particularly.

3. First, the food is cut and ground up by the teeth. The teeth, in order to be fitted for this work,

From what is the blood made ? Is digestion one simple process ? What is first done to the food ? By what is the food moistened ? What is done with it after it is ground and moistened ? What is mixed with the food in the stomach ? Into what does it pass from the stomach ? What is doue with it in the intestines ?