Your Wonderful Body
( Originally Published 1920 )
Living Things and Lifeless Things.—What are the things that interest you most as you walk home from school or wander about in the woods? Smooth shiny stones are attractive, particularly if they have bright colored specks in them. If you are like most children, however, you find flowers more beautiful than stones—and there are a great many more kinds of flowers than there are of stones. Animals are most interesting of all. Beetles crossing the path, butterflies slowly waving their wings on a thistle head, frogs in the meadow, fishes in the stream, squirrels in the trees, or birds balancing on the telegraph wires,—how fascinating it is to try to get near them and see what they are doing!
It is the same in the city. It is pleasant to see the automobiles gliding by and to look up at the buildings and think how high they are. Most of us, however, would rather watch a good horse than an automobile; and the most interesting things to me about the houses I pass are the cats on the window sills and the dogs playing about the doorsteps.
The flowers, butterflies, birds, squirrels, cats, and dogs are all alive; and life is, after all, the most wonderful thing in the world.
The Human Body.—The most wonderful of all kinds of living things are men and women (and of course girls and boys). We cannot "run like a deer," nor is any man "as strong as a horse," though we often use these expressions to mean that a person is unusually quick or unusually powerful. When it comes, however, to things which need skill and delicacy, no animal can match us. You have probably seen a conjuror do his tricks with cards and. coins, moving his fingers so swiftly that you could not guess how he managed to make something disappear that had been right under your eye thé minute before. Or you have watched a good tennis player and wondered at the way in which he gets just to the place in the court where the ball is coming, and hits it back so that it barely skims the net and goes to the one spot where it will be hardest for his opponent to return it.
The human body is in some ways very much like a bit of machinery—a watch or a steam engine—but it can do many things that no lifeless machine will ever do. We all like to know how machines work; for instance, how the burning of gasoline in an automobile makes the wheels go round. We ought to be still more eager to learn how our own body-machine works. Do you know why you have to breathe and eat and sleep; how you move about; how the blood circulates in your body; and how you learn to do things like riding a bicycle or playing the piano, which become so easy at last, though at first you could hardly do them at all?
It is interesting to learn about all the things that go on inside that body-machine of yours. It is also very important to learn about them, because when you know how a machine works, you can make it run well and get the most possible out of it. The art of keeping the body-machine in good order is called hygiene.
The Parts of the Living Machine. One of the striking things about a machine is that it is always made up of many different parts, each of which performs some special part of the work. Think whether this is not true of the human body. First of all, the body is divided into the trunk, head, arms, and legs. You know what the arms and legs are for, but it might be interesting to make a list of the things you can do with each and see which list is the longer one.
The trunk contains many important parts of the body. Some of 'them are shown in Fig. 9, and we shall later learn what they are like and what they do. The head includes the brain, where our thinking and feeling goes on. It contains also the eyes with which we see, the nose through which we breathe and smell, the ears with which we hear, and the mouth and throat and tongue, with which we eat, taste, and speak.
A living body, then, is made up of different parts, each having some work to do for the common good. These parts are called organs.
The Organs by Which the Body Moves.—Bend your finger and notice what happens. It bends at two places, does it not? These bending places are called joints. Between the joints, the finger is quite rigid and cannot be bent at all. This is because the finger is strengthened and supported by solid pieces of bone. The bones are fastened together at the joints in such a way that they can move up and down. Think what the hand would be if it lacked this bony framework and were soft and flabby; or if the joints were not there and the hand were in one stiff piece. Sometimes in certain diseases the joints do stiffen so that the fingers cannot be moved and the hand becomes almost useless.
The arms and legs are supported by large bones and can bend only at the joints where the bones meet. The upper part of the trunk is enclosed in a cage of bones, which you can feel moving up and down when you breathe deeply. The brain is enclosed in a box of bone. These bones help to protect the softer parts inside. All the bones of the body together make up the skeleton.
Did you ever wonder how it is that you are able to move the different parts of your body at all? What happens inside your hand when you bend that finger we have been thinking about?
Every movement of this kind is caused by a special sort of living matter in the body called muscle. The muscles are fastened at each end to bones. They have the power of growing shorter; and when they shorten, they change the position of the two bones to which they are fastened.
Food and Digestion.—An automobile will not go unless it has gasoline to burn or electricity in its storage battery. A steam engine will not run unless coal is put in under its boiler. The gasoline, or electricity, or coal, supplies what we call energy to run the machine. The body is just the same, in this respect. In order to live and move and grow, it must be given food, for food is to the body what gasoline is to the automobile or coal to the steam engine. The more active we are, the more food we need; and without food we become weak and waste away.
Several things must happen to our food before we can use it. It must be broken up into a fine pulp by the teeth, and then swallowed, and then changed in the stomach and other organs before it can be used. The process of preparing the food for the use of the body is called digestion. As AEsop has taught us in his fable, the work of the organs of digestion is very important for the health of the body as a whole.
Breathing.—You probably know that the fire in the kitchen stove will not burn well unless there is a good draft, or current of air. There is something in the air called oxygen, which makes a fire burn. If a piece of burning wood in the fireplace were covered with ashes so that the air could not reach it, the fire would soon go out.
The body is like a fire, in the fact that it must have oxygen all the time; and this is the reason why we breathe. We can go without food for hours or even days, but we cannot live for many minutes without breathing, or taking in air. The organs by which we draw the air in and get oxygen from it are called the organs of respiration. (The word respiration means breathing.)
Do you know how many times a minute you breathe? Watch the clock some day and count your breaths for a minute.
The Heart and the Blood Vessels.—The food is taken in by certain organs of the body, and the oxygen by others. Somehow these things must be carried to every part of the body, for all the organs need them in order to keep alive.
The special organs which do this work—the railroad system of the body—are the heart and the blood vessels. You know that the blood seems to be in all parts of the body, for when you cut yourself deeply anywhere the blood flows. All through the living parts of the body the blood is carried, inside a system of closed tubes, the blood vessels, which branch like the branches of a tree, getting finer and finer. Through each tube blood is moving; and whenever blood flows from a cut or a scratch, it is because the walls of some of these fine tubes have been broken.
The blood is driven through these blood vessels by the heart. This organ beats nearly a hundred times a minute, each beat forcing blood out into the blood vessels. Everywhere the blood goes, it carries with it the food and the oxygen needed by the different parts of the body.
You can feel your heart beating away as regularly as a clock ticks, if you put your hand on the left side of your chest. You will learn in Chapter XI what the heart is like and how it does its work.
The Brain and the Nerves.—We have seen that a movement like the bending of your finger is caused by the shortening, or contraction, of a muscle. But what makes the muscle contract? When you make up your mind to bend one special finger, how is the message carried to the right place?
This task of keeping all parts of the body working as we want them to work is accomplished by a group of organs which we call the nervous system. The brain, where our thinking goes on, is connected with all parts of the body by tiny white threads called nerves. It is along one of these nerves that the message goes out from the brain when you make your finger bend.
The nervous system does much more, however, than merely make it possible for us to move various parts of our bodies as we wish. All the time, whether we think about it or not, a great many things are going on inside our bodies, like the breathing and the beating of the heart. All these activities are kept going in an orderly fashion by messages which are constantly passing from one part of the body to another through the nerves.
The principal parts, or organs, of the body are: The bones.
The organs of digestion.
The organs of respiration.
The heart and the blood vessels.
The brain and the nerves.