Most of us are interested in machines and the wonderful things they do. A small child, given a new toy, will ask, “What does it do?” and his next question is very likely to be, “How does it do it?”
Boys and girls, and horses and dogs, are just as truly machines as steam engines or walking dolls. The machinery in a person or an animal is much more complicated, however, than the machinery in the steam engine, and a living being can do many things which no other kind of machine has ever done. As we study the way in which the various parts of the body work together, we shall see more, and more what a wonderful thing it is.
The Structure of the Living Machine : Organs and Systems of Organs.-The human body is made up of many organs. Each of these organs has its own special task. The hand, for instance, is the organ by which we grasp things; the eye is the organ by which we see; the heart is the organ which pumps the blood.
These organs are grouped into a small number of sets or systems of organs. The bones form one system, which gives strength and firmness and at the same time allows the body to move. The various muscles make up a system whose work it is to bring about this movement of the parts of the body. The system of organs of digestion prepares the food for use, and each of the other systems likewise performs its own important work.
Tissues.The various organs and other parts of the body are made up of different kinds of living matter which we call tissues. The hand, for instance, has skin on the out-side, and its central framework is made up of bone tissue. Fine threads of nerve tissue run out to all parts of the hand, and the muscles in it are made of still another kind of tissue.
Cells: If we should look at any of these tissues under a strong microscope, we should find that it is built of tiny bits of living matter called cells, each having a denser structure in it called a nucleus. The cells are packed together like bricks in a wall to make a layer of skin tissue, or muscle tissue, or whatever the particular kind may be. The cells of each kind are different from all the others. Muscle and nerve cells are long and slender, blood cells are flattened discs, and skin cells are like irregular blocks.
Protoplasm.The living material of which the cells are made is called protoplasm (pro’ to plaz’m). If you look at protoplasm under a microscope, you can see only a thick liquid with specks in it; but when you know something of the changes which go on in it, you will realize that protoplasm is the most remarkable sub-stance in the world. When you move or see or think, it is because of chemical changes which are going on in the protoplasm of the muscle or nerve or other cells.
Protoplasm contains a great deal of water and some minerals, and some-times sugar and fat, but the chief thing that is always found in protoplasm is a kind of matter called protein (pro’ te in).
How the Cells Work Together.The cells of the body may be compared to the people in a city. Some people do one kind of work and some another; one is a carpenter, another a motorman, another a banker. If the people are good citizens, the work of each one benefits the others. The carpenter makes furniture for the motorman and the banker; the motorman carries the banker to his office and the carpenter to his shop; and the banker takes care of the carpenter’s and the motorman’s savings. Each one does the particular kind of work that he can do best, for the benefit of all the others.
Somewhat the same kind of thing is going on in the human machine. In a healthy body the cells of the different tissues are all good citizens. The stomach cells help to digest food which will build up the muscles, and the muscle cells move the jaws which chew the food so that the stomach can digest it. All the millions of cells are working together in harmony for the common good.
Fuel for the Living Machine.If any piece of machinery is to do the work for which it is intended, two very important things are necessary. First, there must be some force or energy to put the machine into motion and keep it working; and second, as parts of the machine wear out or become broken, they must be replaced.
In the case of a steam engine, the force or energy needed to run it is supplied by coal or oil, or some other fuel, which burns under the boiler and makes the heat that turns the water into expanding steam. In the case of our bodies, the energy needed to keep the different parts at work is supplied by the food we eat. The burning of coal in the engine is the result of chemical action between the oxygen of the air and the coal. In somewhat the same way, the food (or substance formed out of the food) combines within our bodies with the oxygen we inhale, to release the energy needed by the living machine.
Growth and Repair.The constant running of the steam engine causes wear in all its parts, and when a wheel or a rod in the engine becomes worn, it must be replaced by a new one. The shoes you walk in and the bicycle you ride wear out after a while and have to be repaired or discarded. Our bodies, likewise, are wearing out day by day, and if there were no provision for repair, they would soon waste away. There is, however, constantly going on in the body, not only a process of waste, but also a process of growth and repair; and it is the food we eat which supplies the material for this rebuilding.
If the body is built up faster than it wears out, it grows, as it does in children and young people. When you were a day or two old, you probably weighed only seven or eight pounds. All of the fifty or one hundred pounds of weight you have gained since then have been built out of the food you have eaten.
To get food is the first problem of life, for human beings, as for the birds and the animals in fields and woods. The farmer spends his life cultivating crops for the use of man or for the feeding of animals to be used, in their turn, as human food. The men digging a ditch, or bending over account books in an office, or laboring in a factory, are working for money to be used, first of all, to buy for themselves and their families the food needed to keep their living machines in running order.
The Body as a Chemical Laboratory.The study of what the body does with this food which is secured for itin many cases with much laboris an absorbing one. To change beefsteak and potatoes, bread and butter, bacon and eggs, ice cream and fruit, into human flesh and blood is no simple task. The solid foods must become liquid before they can be used at all, and even liquid foods, like milk, must be changed into other forms.
You perhaps know something about chemical laboratories where chemists study various substances, and combine and change them so as to make new ones. The human body is a kind of laboratory where food is built up into living matter, and where a great many other chemical changes are always going onmany of them so complicated that no chemist in his laboratory can as yet imitate them.
Oxygen, the Supporter of Life.Just as the living body requires food, so also it requires oxygen, a substance contained in the air. A furnace needs both coal and a draft of air to burn the coal; and the body, likewise, needs not only food but air to “burn” the food. From the air we breathe, we get the necessary oxygen; and just as the fire goes out when there is no supply of air, so the body could not live if we ceased to breathe. Perhaps you have an aquarium and have learned that if too many fishes are put into it they soon die, because the supply of oxygen in the water is not sufficient.
The Wastes of the Body.The furnace with which we have been comparing the human body needs another important thing, besides coal and a draft of air. The ashes must be removed or the grate will clog and the fire will be checked. In the body, also, waste matter is formed, which, like the ashes in the furnace, must be regularly carried away.
Team Work in the Body: One of the most striking things about our living machine is the way in which all its parts work together. When you do anything, even as simple an act as walking across the room, there are dozens of different muscles at work to produce the movements of your legs; and each muscle must act at just the right time and in just the right way to take a step. Perhaps you have watched a baby learning to walk and have thought what a hard thing walking really is. Yet how easily you yourself can move about, – and if you are walking or running and come to something in the way, how quickly you can stop short or turn aside to pass it! Did you ever think what happens in such a case? Your eyes see the obstacle in your path and send a message to the brain; and another message, quick as a flash, goes out to the muscles, telling some of them to stop and others to begin to act.
The Normal Working of the Living Machine.When the muscles and the nerves and other parts of the body are all working well, we say that a person is in good health. Such a person feels alert and cheerful and full of energy. But when some part of the body is working badly, there is illness or disease.
Some people are born with bodies that are not very strong; and when such people are ill, we should be very kind and patient with them. A great many cases of illness, however, are due not at all to weak bodies, but to carelessness or ignorance. It is easy to injure a body that is naturally healthy and thus keep it from working well. Many a child has a toothache simply because his teeth have not been cared for, or a headache because he has strained his eyes by working in a poor light. Many a child catches measles or whooping cough merely because he has played with other children who had these diseases.
The Care of the Living Machine.Many kinds of machinery require such careful and skillful attention that books are written about them, to be studied by those in charge of their operation. This book will help you to learn how the living machine works, and what you should do to keep your body in the good working order that we call health.
When we study physiology, we learn about the parts of the body and the ways in which they act. The study of hygiene deals with the management of the body and those things which we can doas well as those we should avoidin order to keep it strong and well. The study of sanitation deals with the effect of outside things on the body, and helps us to protect it from disease germs and other injurious things which might come from outside the body to harm it.
Each one of us has a very complicated and delicate machine in charge. The chief purpose of this book is to teach young people how this machine works and how to care for it properly and get the most out of it.
QUESTIONS FOR DISCUSSION AND REVIEW
1. What are some of the different kinds of cells in your body?
2. What is protoplasm?
3. What advantage is there in having each organ do its own special work? Can you tell something of primitive Indian life and compare it with a modern city, to make the preceding question clearer?
4. During a street-car strike in a large city, the car service was cut to one half. Describe the effects this strike might have had on the life of the city. Show how a corresponding “strike” in the human body might have far-reaching results.
5. In what respects is the body like a furnace?
6. How does the body display force or energy? Where does this energy come from?
7. Can you think of two ways in which the body is superior to a machine?
8. Give some examples of team work in the body.
9. Define health, physiology, hygiene, sanitation.