Part 22

Most of you will probably find yourselves, first eye-minded, then motor-minded. That is, on the Whole, the most useful arrangement. But the best sort of mind is one that can handle all three kinds of ideas; and think about seeing, hearing, and doing all about equally well. So you had better notice which you can’t do, and set about learning to do it.

XXXV

Living Automobiles

If you will think back over what you have already learned in this book, you will see that we began by finding out something about how we men, the animals, and the plants come to have any such things as bodies at all. We learned how the little chick forms inside the egg, and the little plant inside the seed. We learned, too, about the wonderful life-jelly or protoplasm of which all living things are made; how it shapes itself into cells; how it builds these cells into our various members, eyes and bones and hair and muscles; and how the body changes, as we grow from youth to maturity, and from maturity to old age.

Then, after we had learned something about this body of ours, we turned to consider how we use it. We found about something of what animals cannot do, and what they can do, and how they do it. We learned how animals of various sorts, and plants as well, see and feel and act; and we learned also something about how we ourselves do our thinking, which is so very different, and so very much better done, than that of any animal or plant.

Now we turn to a different matter. We have taken up being, and doing, and thinking. Now we shall consider living. We shall learn about how the body of the plant or animal feeds itself and keeps alive, and how the different parts of it, the bones and skin and leaves and bark, manage to get on with one another, and work together like a well-made machine.

For, of course, the body is a machine. It is a vastly complex machine, many, many times more complicated than any machine ever made by hands; but still after all a machine. It has been likened to a steam engine. But that was before we knew as much about the way it works as we know now. It really is a gas engine; like the engine of an automobile, a motorboat, or an airplane.

I don’t suppose that any boy, at least, needs to be told the difference between a gas engine and a steam engine. In the one, we build a fire under the boiler, and turn water to steam. Then the steam goes thru a pipe to the cylinder, where it pushes the piston back and forth, first on one side, then on the other, and so turns the wheels.

In the gas engine, on the other hand, there is no boiler, no steam, and no fire. A mixture of air and gasolene vapor flows into the cylinder, cold. There it explodes, set off by an electric spark, and the push of that explosion moves the piston and makes the wheels go round.

We, I say, are not steam engines. We have neither boiler nor steam nor fire. But each little working cell is like a little cylinder, which takes up from the blood air and food, mixes them together inside itself, waits with everything ready to go off, gets the proper signal thru a nerve, then explodes and does something.

That’s the way a muscle does its work. It is a many-thousand-cylindered engine. Each little fiber of the muscle is a cylinder; and each time you lift your hand or move your foot there is a perfect battery of minute explosions. You cannot hear them, for there is no pop—the muffling is vastly better than any engine-builder ever devised. But you do feel the heat; and if you move fast and hard enough, you have to stop to cool off and get a drink.

The plants also are many-cylindered gas engines. They do not do so much work as animals do, not so much running round and moving things. But they do move, and certainly grow and lift themselves high in the air. This much work they do by exploding their cells, just as animals or automobiles do theirs. The growing plants take their food out of the air thru their leaves; and they take also the air itself in the same way. They mix these together inside their cells; and when there is work to be done, growing, moving, or any other sort, they explode a little of the mixture and do it.

Don’t think then that animals and plants and human beings are merely like automobiles. They are automobiles. Their fuel is their food. They mix it with air. They explode the mixture, and move. Anything that does that is an automobile, and runs with a gas engine.

XXXVI

Air and Fuel

We are, then, gas engines. So we have to have air to mix with our gasoline. The simpler water animals, such as sponges, which are mostly holes, and all minute creatures, both animals and plants, simply take it in directly into their cells where they are going to use it. There is plenty of air in water—you can see it fizzle out from the water in a drinking glass when you draw water from a faucet in cold weather. The water creatures breathe this out of the water, and die of suffocation if you put them in boiled water from which the boiling has driven out the air.

Most animals which have blood, use this to carry the air to their cells. For blood, whatever else it is, is nine-tenths water, and will dissolve air like any other water. The insects, however, though they have blood, do not use it to carry air. Instead, they have a system of branching pipes running all over their bodies, and opening at various points on the surface. You can often make these out easily, a pair of openings for each joint, on the sides of caterpillar’s body. These pipes carry the air everywhere over the insect’s body, even to the feet, so that wherever there is a working muscle, there also is the air for it to work with. Thus the insect has no need of lungs, and has none; and therefore, I suppose never gets out of breath, no matter how hard it works.

We human beings, and our four-footed cousins, all backboned animals in fact, do not manage in any of these ways. We breathe the air into our lungs. There, instead of dissolving it in the watery part of the blood, we turn it over to the red corpuscles, which are especially made to do this very thing and do it particularly well. These minute, coin-like corpuscles carry the air all over the body, and deliver it over to the cells as they need it. But of course, as you must have already learned in school, the body handles only the part of the air that it can use, the oxygen. The rest it lets go and doesn’t bother with. That is where we have the advantage over other automobiles, which can’t pick out the part they want but have to take the air as it comes. Still it all comes to the same thing in the end. With all animals the oxygen gets mixed with the fuel and explodes.

Our fuel, moreover, is a good deal like gasoline. Gasoline, as you know, is related to kerosene, benzine, paraffine, and the rest, which are all products of rock oil. They are, then, themselves oils; and gasoline is an oil.

We, too, eat oils; not, to be sure, mineral oils, but animal and vegetable oils, olive oil and butter and cream and all sorts of fats; for fats are merely oils that freeze at common living temperatures and melt only after we get them stowed away.

We, then, burn many sorts of oil. We also burn bread and potatoes and the like, starch and sugar and gums, which though not oils, are much like them; really in a way, oils that are already about half burned. These we finish up in our engines. On the whole, it’s much more convenient than depending on one sort of fuel, and exploding only gasoline.

I am not going to stop now to tell you the long story of how the bread and potatoes and the rest of our food finally gets changed over into a sort of sugar; and is as sugar, packed away in the cells of our muscles and other tissues, mixed with the oxygen of the air, and made ready to explode when the signal through the nerve touches it off. The food is taken apart and put together again, combined and separated, stored up when it isn’t needed, and used sometimes in one way and sometimes in another. Different animals treat their food differently after they get it swallowed; even different human beings, eating the same food, do not always handle it quite the same way.

Most of us take our food into our stomachs, but the earthworm crawls through the earth, and at the same time lets a stream of earth crawl through him, digesting what is food and leaving the rest behind as he moves along. Amoebas sometimes flow round little water plants many times longer than themselves, crawl along the stem, with the stem sticking out front and back, and digest the juices as they go along. The star-fish, which lives on oysters larger than himself, turns his stomach inside out, sticks it into the oyster’s shell; and after he has digested the oyster, pulls his stomach back again. A dog will digest bones; and a cow will digest wood; while a fish will swallow another fish nearly as long as himself, keep the tail, still unswallowed, in his mouth while he digests off the head, and than moves his meal up another notch.

There are all sorts of queer freaks, but the main point is that, in the end, all our food gets built into the cells of our bodies; much of it in the form of sugar, and that this sugar explodes as if it were the gasoline vapor in a gas engine that some man has made. With the force of these explosions, the body does its work; it keeps itself warm with the waste heat.

XXXVII

Men In Glass Boxes

One curious thing about these explosion engines of ours is that, when all goes well with our little insides, we get just exactly the same amount of work out of each mouthful of our food, that we should get, if we should dry the food, grind it to fine dust, and explode the dust mixed with air in the cylinder of an automobile—as it would be quite possible to do, if one wanted to take the trouble.

In fact, the United States Government, for several years, set people to trying just this very thing, by way of finding out how much work can be got out of various sorts of food, and out of which sorts a man can get most for his money. They have a big glass box, as large as a state-room on a steamer, with a bed in it and a table and chairs, and also a stationary bicycle, on which one can ride without moving, and so get his exercise. They put a man in this box, and keep him there for a week. They weight carefully everything that he eats and drinks; and each time he takes a meal they find out, by drying some of the food and burning it and measuring the heat they get from the burning, just how much that food is worth as fuel. Thus they know how much exploding he ought to be able to do in his tiny cylinders.