This Primer is an attempt to explain in the most simple manner possible some of the most important and most general facts of Physiology, and may be looked upon as an introduction to the Elementary Lessons of Professor Huxley.
In my descriptions and explanations I have supposed the reader to be willing to handle and examine such things as a dead rabbit and a sheep’s heart; and written accordingly, I have done this purposely, from an increasing conviction that actual observation of structures is as necessary for the sound learning of even elementary physiology, as are actual experiments for chemistry. At the same time I have tried to make my text intelligible to those who think reading verbal descriptions less tiresome than observing things for themselves.
It seemed more desirable in so elementary a work to insist, even with repetition, on some few fundamental truths, than to attempt to skim over the whole wide field of Physiology. I have therefore omitted all that relates to the Senses and to the functions of the Nervous System, merely just referring to them in the concluding article. These the reader must study in the “Elementary Lessons.”
M. Foster.
1. Did you ever on a winter’s day, when the ground was as hard as a stone, the ponds all frozen, and everything cold and still, stop for a moment, as you were running in play along the road or skating over the ice, to wonder at yourself and ask these two questions:—“Why am I so warm when all things around me, the ground, the trees, the water, and the air, are so cold? How is it that I am moving about, running, walking, jumping, when nothing else that I can see is stirring at all, except perhaps a stray bird seeking in vain for food?”
These two questions neither you nor anyone else can answer fully; but we may answer them in part, and the knowledge which helps us to the answer is called Physiology.
2. You can move of your own accord. You do not need to wait, like the boughs or the leaves, till the wind blows upon you, or, like the stones, till somebody stirs you. The bird, too, can move of its own accord, so can a dog, so can any animal as long as it is alive. If you leave a stone in any particular spot, you expect to find the stone there when you come to it again a long time afterwards; if you do not, you say somebody or something has moved it. But if you put a sparrow or mouse on the grass plot, you know that directly your back is turned it will be off.
All animals move of themselves. But only so long as they are alive. When you find the body of a snake on the road, the first thing you do is to stir it with a stick. If it moves only as you move it, and as far as you move it, just as a bit of rope might do, you say it is dead. But if, when you touch it, it stirs of itself, wriggles about, and perhaps at last glides away, you know it is alive. Every living animal, of whatever kind, from yourself down to the tiniest creature that swims about in a little pool of water and cannot be seen without a microscope, moves of itself. Left to itself, it moves and rests, rests and moves; stirred by anything, away it goes, running, flying, creeping, crawling, or swimming.
Something of the kind sometimes happens with lifeless things. When a stone is carefully balanced on the top of a high wall, a mere touch will send it toppling down to the ground. But when it has reached the ground it stops there, and if you want to repeat the trick you must carry the stone up to the top of the wall again. You know the toy made like a mouse, which, when you touch it in a particular place, runs away apparently of its own accord, as if it were alive. But it soon stops, and when it has stopped you may touch it again and again without making it go on. Not until you have wound it up will it go on again as it did before. And every time you want it to run you must wind it up afresh. Living animals move again and again, and yet need no winding up, for they are always winding themselves up. Indeed, as we go on in our studies we shall come to look upon our own bodies and those of all animals as pieces of delicate machinery with all manner of springs, which are always running down but always winding themselves up again.
3. You are warm; beautifully warm, even on the coldest winter day, if you have been running hard; very warm if you are well wrapped up with clothing, which, as you say, keeps the cold out, but really keeps the warmth in. The bed you go to at night may be cold, but it is warm when you leave it in the morning. Your body is as good as a fire, warming itself and everything near it.
The bird too is warm, so is the dog and the horse, and every four-footed beast you know. Some animals however, such as reptiles, frogs, fish, snails, insects, and the like do not seem warm when you touch them. Yet really they are always a little warm, and some times they get quite warm. If you were to put a thermometer into a hive of bees when they are busy you would find that they are very warm indeed. All animals are more or less warm as long as they are alive, some of them, such as birds and four-footed beasts, being very warm. But only so long as they are alive; after death they quickly become cold. When you find a bird lying on the grass quite still, not stirring when it is touched, to make quite sure of its being dead you feel it. If it is quite cold, you say it has been dead some time; if it is still warm, you say it is only just dead—perhaps hardly dead, and may yet revive.
4. You are warm, and you move about of yourself. You are able to move because you are warm; you are warm in order that you may move. How does this come about? Just think for a moment of something which is not an animal, but which is warm and moves about, which only moves when it is warm, and which is warm in order that it may move. I mean a locomotive steam-engine. What makes the engine move? The burning coke or coal, whose heat turns the water into steam, and so works the piston, while at the same time the whole engine becomes warm. You know that for the engine to do so much work, to run so many miles, so much coal must be burnt; to keep it working it must be “stoked” with fresh coal, and all the while it is working it is warm: when its stock of coal is burnt out it stops, and, like a dead animal, grows cold.
Well, your body too, just like the steam-engine, moves about and is warm, because a fire is always burning in your body. That fire, like the furnace of the engine, needs fresh fuel from time to time, only your fuel is not coal, but food. In three points your body differs from the steam-engine. In the first place, you do not use your fire to change water into steam, but in quite a different way, as we shall see further on. Secondly, your fire is a burning not of dry coal, but of wet food, a burning which although an oxidation (Chemistry Primer, Art. 5) takes place in the midst of water, and goes on without any light being given out. Thirdly, the food you take is not burnt in a separate part of your body, in a furnace like that of the engine set apart for the purpose. The food becomes part and parcel of your body, and it is your whole body which is burnt, bit by bit.
Thus it is the food burning or being oxidized within your body, or as part of your body, which enables you to move and keeps you warm. If you try to do without food, you grow chilly and cold, feeble, faint, and too weak to move. If you take the right quantity of proper food, you will be able to get the best work out of the engine, your body; and if you work your body aright, you can keep yourself warm on the coldest winter day, without any need of artificial fire.
5. But if this be so, in order to oxidize your food, you have need of oxygen. The fire of the engine goes out if it is not fed with air as well as fuel. So will your fire too. If you were shut up in an air-tight room, the oxygen in the room would get less and less, from the moment you entered the room, being used up by you; the oxidation of your body would after a while flag, and you would soon die for want of fresh oxygen (see Chemistry Primer, p. 14).
You have, throughout your whole life, a need of fresh oxygen, you must always be breathing fresh air to carry on in your body the oxidation which gives you strength and warmth.
6. When a candle is burnt (Chemistry Primer, p. 6) it turns into carbonic acid, and water. When wood or coal is burnt, we get ashes as well. If you were to take all your daily food and dry it, it too would burn into ashes, carbonic acid, and water (with one or two other things of which we shall speak afterwards).
Your body is always giving out carbonic acid (Chemistry Primer, Exp. 7). Your body is always giving out water by the lungs, as seen when you breathe on a glass, by the skin, and by the kidneys; and we shall see that we always give out more water than we take in as food or drink. Your body too is daily giving out by the kidneys and bowels, matters which are not exactly ashes, but very like them. We do not oxidize our food quite into ashes, but very nearly; we burn it into substances which are no longer useful for oxidation in the body, and which, being useless, are cast out of the body as waste matters.
The tale then is complete. By the help of the oxygen of the air which you take in as you breathe, you oxidize the food which is in your body. You get rid of the water, the carbonic acid, and other waste matters which are left after the oxidation, and out of the oxidation you get the heat which keeps you warm and the power which enables you to move.
Thus all your life long you are in constant need of oxygen and food. The oxygen you take in at every breath, the food at every meal. How you get rid of the waste matters we shall see further on.
If you were to live, as one philosopher of old did, in a large pair of delicate scales, you would find that the scale in which you were would sink down at every meal, and gradually rise between as you got lighter and hungry. If the food you took were more than you wanted, so that it could not all be oxidized, it would remain in your body as part of your flesh, and you would grow heavier and stouter from day to day; if it were less, you would grow thinner and lighter; if it were just as much as and no more than you needed, you would remain day after day of exactly the same weight, the scale in which you sat rising as much between meals as it sank at the meal time.
What we have to learn in this Primer is—How the food becomes part and parcel of your body; how it gets oxidized; how the oxidation gives you power to move; how it is that you are able to move in all manner of ways, when you like, how you like, and as much as you like.
First of all we must learn something about the build of your body, of what parts it is made, and how the parts are put together.
7. When you want to make a snow man, you take one great roll of snow to make the body or trunk. This you rest on two thinner rolls which serve as legs. Near the top of the trunk you stick in another thin roll on either side—these you call the two arms: and lastly, on quite the top of the trunk you place a round ball for a head. Head, trunk, and limbs, i.e. legs and arms—these together make up a complete body.
In your snow man these are all alike, all balls of snow differing only in size and form; but in your own body, head, trunk, and limbs are quite unlike, as you might easily tell on taking them to pieces. Now you cannot very well take your own body to pieces, but you easily can that of a dead rabbit. Suppose you take one of the limbs, say a leg, to begin with.
First of all there is the skin with the hair on the outside. If you carefully cut this through with a knife or pair of scissors and strip it off, you will find it smooth and shiny inside. Underneath the skin you see what you call flesh, rather paler, not so red as the flesh of beef or mutton, but still quite like it. Covering the flesh there may be a little fat. In a sheep’s leg as you see it at the butcher’s there is a good deal of fat, in the rabbit’s there is very little.
This reddish flesh you must henceforward learn to speak of as muscle. If you pull it about a little, you will find that you can separate it easily into parcels or slips running lengthways down the leg, each slip being fastened tight at either end, but loose between. Each slip is what is called a muscle. You will notice that many of these muscles are joined, sometimes at one end only, sometimes at both, to white or bluish white glistening cords or bands; made evidently of different material from the muscle itself. They are not soft and fleshy like the muscle, but firm and stiff. These are tendons. Sometimes they are broad and short, sometimes thin and long.
As you are separating these muscles from each other you will see (running down the leg between them) little white soft threads, very often branching out and getting too small to be seen. These are nerves. Between the muscles too are other little cords, red, or reddish black, and if you prick them, a drop or several drops of blood will ooze out. These are veins, and are not really cords or threads, but hollow tubes, filled with blood. Lying alongside the veins are similar small tubes, containing very little blood, or none at all. These are arteries. The veins and arteries together are called blood-vessels, and it will be easy for you to make out that the larger ones you see are really hollow tubes. Lastly, if you separate the muscles still more, you will come upon the hard bone in the middle of the leg, and if you look closely you will find that many of the muscles are fastened to this bone.
Now try to put back everything in its place, and you will find that though you have neither cut nor torn nor broken either muscle or blood-vessel or bone, you cannot get things back into their place again. Everything looks “messy.” This is partly because, though you have torn neither muscle nor blood-vessel, you have torn something which binds skin and muscle and fat and blood-vessels and bone all together; and if you look again you will see that between them there is a delicate stringy substance which binds and packs them all together, just as cotton-wool is used to pack up delicate toys and instruments. This stringy packing material which you have torn and spoilt is called connective because it connects all the parts together.
Well, then, in the leg (and it is just the same in the arm) we have skin, fat, muscle, tendons, blood-vessels, nerves, and bone all packed together with connective and covered with skin. These together form the solid leg. We may speak of them as the tissues of the leg.
8. If now you turn to the trunk and cut through the skin of the belly, you will first of all see muscles again, with nerves and blood-vessels as before. But when you carefully cut through the muscles (for you cannot easily separate them from each other here), you come upon something which you did not find in
Fig. 1.—The Viscera of a Rabbit as seen upon simply opening the Cavities of the Thorax and Abdomen without any further Dissection.
A, cavity of the thorax, pleural cavity of either side; B, diaphragm; C, ventricles of the heart; D, auricles; E, pulmonary artery; F, aorta; G, lungs, collapsed, and occupying only the back part of the chest; H, lateral portions of pleural membranes; I, cartilage at the end of sternum; K, portion of the wall of body left between thorax and abdomen; a, cut ends of the ribs; L, the liver, in this case lying more to the left than the right of the body; M, the stomach; N, duodenum; O, small intestine; P, the cæcum, so largely developed in this and other herbivorous animals; Q, the large intestine.
the leg, a great cavity. This is something quite new—there is nothing like it in the leg—a great cavity, quite filled with something, but still a great cavity; and if you slit the rabbit right up the front of its trunk and turn down or cut away the sides as has been done in Fig. 1, you will see that the whole trunk is hollow from top to bottom, from the neck to the legs.
If you look carefully you will see that the cavity is divided into two by a cross partition (Fig. 1, B) called the diaphragm. The part below the diaphragm is the larger of the two, and is called the abdomen or belly; in it you will see a large dark red mass, which is the liver (L). Near the liver is the smooth pale stomach (M), and filling up the rest of the abdomen you will see the coils of the intestine or bowel, very narrow in some parts (O), very broad (P Q), broader even than the stomach, in others. If you pull the bowels on one side as you easily can do, you will find lying underneath them two small brownish red lumps, one on each side. These are the kidneys.
In the smaller cavity above the diaphragm, called the thorax or chest, you will see in the middle the heart (C), and on each side of the heart two pink bodies, which when you squeeze them feel spongy. These are the two lungs (G). You will notice that the heart and lungs do not fill up the cavity of the chest nearly so much as the liver, stomach, bowels, &c. fill up the cavity of the belly. In fact, in the chest there seems to be a large empty space. But as we shall see further on, the lungs did quite fill the chest before you opened it, but shrank up very much directly you cut into it, and so left the great space you see.
9. The trunk then is really a great chamber containing what are called the viscera, and divided into an upper and lower half, the upper half being filled with the heart and lungs, the lower with the liver, stomach, bowels, and some other organs. In front the abdomen is covered by skin and muscle only. But if all the sides of the trunk were made of such soft material it would be then a mere bag which could never keep its shape unless it were stuffed quite full. Some part of it must be strengthened and stiffened. And indeed the trunk is not a bag with soft yielding sides, but a box with walls which are in part firm and hard. You noticed that when you were cutting through the front of the chest you had to cut through several hard places. These were the ribs (Fig. 1, a), made either of hard bone or of a softer gristly substance called cartilage. And if you take away all the viscera from the cavity of the trunk and pass your finger along the back of the cavity, you will feel all the way down from the neck to the legs a hard part. This is the backbone or vertebral column. When you want to make a straw man stand upright you run a pole right through him to give him support. Such a support is the backbone to your own body, keeping the trunk from falling together.
In the abdomen nothing more is wanted than this backbone, the sides and front of the cavity being covered in with skin and muscle only. In the chest the sides are strengthened by the ribs, long thin hoops of bone which are fastened to the backbone behind and meet in front in a firm hard part, partly bone, partly cartilage, called the sternum.
But this backbone is not made of one long straight piece of bone. If it were you would never be able to bend your body. To enable you to do this it is made up of ever so many little flat round pieces of bone, laid one a-top of the other, with their flat sides carefully joined together, like so many bungs stuck together. Each of these little round flat pieces of the backbone is called a vertebrabodyarchFrontispieceFig. 2spinal canalFig. 2C.S.