Physiology

by Sir M. Foster

What does this teach us? It teaches us that the power which a muscle has of contracting when called upon to do so, may be lost and regained, and that it is lost when the blood is prevented from getting to it. When a cord is tied round the whole arm, the power of the whole arm is lost. This loss of power is the beginning of death, and indeed if the cord were not unloosed the arm would quite die—would mortify, as it is said. When only those blood-vessels which go to the biceps are tied, the biceps alone begins to die, all the rest of the arm remaining alive, and the first sign of death in the biceps is the loss of the power to contract when called upon to do so.

In order that you may bend your arm, then, you must not only have a biceps muscle with its nerves, its tendons, and all its arrangements of bones and joints, but the muscle must be supplied with blood.

[19.] We can now go a step further and ask the question, What is there in the blood that thus gives to the muscle the power of contracting, that in other words keeps the muscle alive? The answer is very easily found. What is the name commonly given to this power of a muscle to contract? We generally call it strength. Lay your arm straight out on the table, put a heavy weight in your hand, and try to bend your arm. If you could do it, one would say you were strong; if you could not, one would say you were weak—all the stronger or weaker, the heavier or lighter the weight. In the one case your biceps had great power of contracting; in the other, little power. Try and find out the heaviest weight you can raise in this way by bending your arm, some morning, not too long after breakfast, when you are fresh and in good condition. Go without any dinner, and in the afternoon or evening, when you are tired and hungry, try to raise the same weight in the same way. You will not be able to do it. Your biceps will have lost some of its power of contracting, will be weaker than it was in the morning. What makes it weak? The want of food. But how can the food affect the muscle? You do not place the food in the muscle; you put it into your mouth, and from thence it goes into your stomach and into the rest of your alimentary canal, and there seems to disappear. How does the food get at the muscle? By means of the blood. The food becomes blood. The things which you eat as food become changed into other things which form part of the blood. Those things going to the muscle give it strength and enable it to contract. And that is why food makes you strong.

[20.] But you are always wanting food day by day, from time to time. Why is that? Because the muscle in getting strength out of the food changes it, uses it up, and so is always wanting fresh blood and new food. We have seen in Art. 1 that food is fuel. We have also seen that muscle (and other parts of the body do the same) is always burning, burning without flame but with heat, burning slowly but burning all the same, and doing the more work the more it burns. The fuel it burns is not dry wood or coal, but wet, watery blood, a special kind of fuel prepared for its private use, in the workshop of the stomach or elsewhere, out of the food eaten by the mouth. This it is always using up; of this it must always have a proper supply, if it is to go on working. Hence there must always be fresh blood preparing; hence there must from time to time be fresh supplies of food out of which to manufacture fresh blood.

To understand then fully what happens when you bend your arm, we have to learn not only what we have learnt about the bones and the joint and the muscle and the nerves, about the machinery and the engine, we have to study also how the food is changed into blood, how the blood is brought to the muscle, what it is in the blood on which the muscle lives, what it is which the muscle burns, and how the things which result from the burning, the ashes and the smoke or carbonic acid and the rest of them, are carried away from the muscle and out of the body.

Meanwhile let me remind you that for the sake of being simple I have been all this while speaking of one muscle only, the biceps in the arm. But there are a multitude of muscles in the body besides the biceps, as there are many bones besides those of the arm, and many joints besides the elbow. But what I have said of the one is in a general way true of all the rest. The muscles have various forms, they pull upon the bones in various ways, they work on levers of various kinds. The joints differ much in the way in which they work. All manner of movements are produced by muscles pulling sometimes with and sometimes against each other. But you will find when you come to examine them that all the movements of which your body is capable depend at bottom on this—that certain muscular fibres, in obedience to a something reaching them through their nerves, contract, shorten, and grow thick, and so pull their one end towards the other, and that to do this they must be continually supplied with pure blood.

Moreover, what I have said of the relations of muscle to blood is also true of all other parts of the body. Just as the muscle cannot work without a due supply of blood, so also the brain and the spinal cord and the nerves have even a more pressing need of pure blood. The weakness and faintness which we feel from want of food is quite as much a weakness of the brain and of the nerves as of the muscles,—perhaps rather more so. And other parts of the body of which we shall have to speak later on need blood too.

The whole history of our daily life is shortly this. The food we eat becomes blood, the blood is carried all over the body, round and round in the torrent of the circulation; as it sweeps past them, or rather through them, the muscle, the brain, the nerve, the skin pick out new food for their work and give back the things they have used or no longer want. As they all have different works, some use up what others have thrown away. There are, besides, scavengers and cleaners to pick up things no longer wanted anywhere and to throw them out of the body. Thus the blood is kept pure as well as fresh. Through the blood thus ever brought to them, each part does its work: the muscle contracts, the brain feels and wills, the nerves carry the feeling and the willing, and the other organs of the body do their work too, and thus the whole body is kept alive and well.

THE NATURE OF BLOOD. § IV.

[21.] What, then, is this blood which does so much?