Those we have learned about feel pain. Others feel objects. If you take a marble or a pencil in the hand you know what it is by the feeling of the object. This kind of feeling is called the sense of touch.
~13.~ There are other nerves of feeling by means of which we are able to hear, see, taste, and smell, of which we shall learn in another lesson.
Besides these we have nerves which tell us whether objects are cold or hot, and heavy or light. Nerves of feeling also tell us when we are hungry, or thirsty, or tired, and when we need more air to breathe.
~14. Nerves of Work.~--There are other nerves which are made just like the nerves of feeling, but which do not feel. These nerves have a very different use. They come from cells in the brain which have charge of the different kinds of work done in the body, and they send their branches to the parts which do the work; hence we call them _nerves of work_.
~15.~ One set of cells sends nerves to the heart, and these make it go fast or slow as is necessary. Another sends nerves to the liver, stomach, and other digestive organs, and causes them to do their part in the digestion of the food. Other cells send branches to the muscles and make them act when we wish them to do so. Thus you see how very useful the brain and nerves are. They keep all the different parts of the body working together in harmony, just like a well-trained army, or a great number of workmen building a block of houses. Without the brain and nerves the body would be just like an army without a commander, or a lot of workmen without an overseer.
~16. How we Use the Nerves.~--If you happen to touch your hand to a hot stove, what takes place? You will say that your arm pulls the hand away.
Do you know why? Let us see. The nerves of feeling in the hand tell the nerve cells in the brain from which they come that the hand is being burned. The cells which feel cannot do anything for the hand, but some of their branches run over to another part of the brain, which sends nerves down to the muscles of the arm. These cells, through their nerve branches, cause the muscles to contract. The cells of feeling ask the cells which have charge of the muscles to make the muscles of the arm pull the hand away, which they do very quickly.
~17.~ So you see the nerves are very much like telegraph or telephone wires. By means of them the brain finds out all about what is happening in the body, and sends out its orders to the various organs, which may be called its servants.
~18. An Experiment.~--A man once tried an experiment which seemed very cruel. He took a dove and cut open its skull and took out its large brain. What do you think the effect was? The dove did not die at once, as you would expect. It lived for some time, but it did not know anything. It did not know when it was hungry, and would not eat or drink unless the food or water was placed in its mouth. If a man gets a blow on his head, so hard as to break his skull, the large brain is often hurt so badly that its cells cannot work, and so the man is in the same condition as the poor dove. He does not know anything. He cannot think or talk, and lies as though he were asleep.
~19.~ By these and many other facts we know that the large brain is the part with which we remember, think, and reason. It is the seat of the mind. We go to sleep because the large brain is tired and cannot work any longer. We stop thinking when we are sound asleep, but sometimes we do not sleep soundly, and then the large brain works a little and we dream.
~20. What the Little Brain Does.~--The little brain[B] thinks too, but it does not do the same kind of thinking as the large brain. We may use our arms and legs and many other parts when we wish to do so; and if we do not care to use them we may allow them to remain quiet. This is not the case with some other organs. It is necessary, for example, that the heart, the lungs, and many other organs of the body should keep at work all the time. If the large brain had to attend to all of these different kinds of work besides thinking about what we see, hear, and read, and other things which we do, it would have too much work to do, and would not be able to do it all well. Besides, the large brain sometimes falls asleep. So the large brain lets the little brain do the kinds of work which have to be attended to all the time, and the little brain keeps steadily at work when we are asleep as well as when we are awake.
~21. What the Spinal Cord Does.~--If you tickle a person"s foot when he is asleep, he will pull it up just as he would if he were awake, only not quite so quickly. What do you suppose makes the muscles of the leg contract when the brain is asleep and does not know that the foot is being tickled? And here is another curious fact. When you were coming to school this morning you did not have to think about every step you took.
Perhaps you were talking or looking over your lessons; but your legs walked right along all the time, and without your thinking about them.
Can you tell how?
~22.~ It would be too much trouble for the large brain to stop to think every time we step, and the little brain has work enough to do in taking care of the heart and lungs and other organs, without keeping watch of the feet when we are asleep, so as to pull them up if some mischievous person tickles them. So Nature puts a few nerve cells in the spinal cord which can do a certain easy kind of thinking. When we do things over and over a great many times, these cells, after a time, learn to do them without the help of the large brain. This is the way a piano-player becomes so expert. He does not have to think all the time where each finger is to go. After the tunes have been played a great many times, the spinal cord knows them so well that it makes the hands play them almost without any effort of the large brain.
SUMMARY.
1. The part of the body with which we think is the brain.
2. The brain is found filling the hollow place in the skull.
3. There are two brains, the large brain and the small brain.
4. Each brain is divided into two equal and complete halves, thus making two pairs of brains.
5. The brain is largely made up of very small objects called nerve or brain cells.
6. The nerve cells send out very fine branches which form the nerves.
7. The nerve branches or fibres run to every part of the body. They pa.s.s out from the brain to the rest of the body through a number of openings in the skull.
8. Most of the nerve branches pa.s.s out through a large opening at the back of the skull, in one large bundle called the spinal cord.
9. The spinal cord runs down through a ca.n.a.l in the backbone, and all along gives off branches to the various parts of the body.
10. It gives us pain to p.r.i.c.k or hurt the flesh in any way, because when we do so we injure some of the little nerve branches of the brain cells.
11. When we suffer, we really feel a pain in the brain. We know this because if a nerve is cut in two, we may hurt the part to which it goes without giving any pain.
12. We have different kinds of nerves of feeling.
13. There are other nerves besides those of feeling. These are nerves of work.
14. The nerves of work have charge of the heart, the lungs, the muscles, the liver, the stomach, and every part of the body which can work or act.
15. The brain and nerves control the body and make all the different parts work together in harmony, just as a general controls an army.
16. The brain uses the nerves very much as a man uses the telephone or telegraph wires.
17. With the large brain we remember, think, and reason.
18. The little brain does the simple kind of thinking, by means of which the heart, lungs, and other vital organs are kept at work even when we are asleep.
19. The spinal cord does a still more simple kind of work. It enables us to walk and to do other familiar acts without using the large brain to think every moment just what we are doing.
CHAPTER XXIII.
HOW TO KEEP THE BRAIN AND NERVES HEALTHY.
~1. Uses of the Brain.~--What do you think a boy or girl would be good for without any brain or nerves? Such a boy or girl could not see, hear, feel, talk, run about, or play, and would not know any more than a cabbage or a potato knows. If the brain or nerves are sick, they cannot work well, and so are not worth as much as when they are healthy.
~2. The Brain Sympathizes with Other Organs.~--Did you ever have a headache? Did you feel happy and good-natured when your head ached hard, and could you study and play as well as when you are well? It is very important that we should keep our brain and nerves healthy, and to do this we must take good care of the stomach and all other organs, because the brain sympathizes with them when they are sick.
~3. We must have Pure Air.~--How do you feel when the school-room is too warm and close? Do you not feel dull and sleepy and so stupid that you can hardly study? This is because the brain needs good, pure blood to enable it to work well. So we must always be careful to have plenty of pure air to breathe.
~4. We should Exercise the Brain.~--What do we do when we want to strengthen our muscles? We make them work hard every day, do we not? The exercise makes them grow large and strong. It is just the same with our brains. If we study hard and learn our lessons well, then our brains grow strong, and study becomes easy. But if we only half study, and do not learn our lessons perfectly, then the study does not do our brains very much good.
~5. We should Take Muscular Exercise.~--When you get tired of study, an hour"s play, or exercise of some sort, rests you and makes you feel brighter, so that you can learn more easily. This is because exercise is necessary to make the blood circulate well. It will then carry out the worn-out particles and supply the brain and nerves with fresh, pure blood. So the same exercise which makes our muscles strong makes our brains healthier also.
~6. We should be Careful of our Diet.~--We ought to eat plenty of good, simple food, such as milk, fruits, grains, and vegetables. It is not well for children to eat freely of meat, as it is very stimulating and likely to excite the brain and make the nerves irritable. Mustard, pepper, and all hot sauces and spices have a tendency to injure the brain and nerves.
~7. We should Allow the Brain to Rest at the Proper Time.~--When we are tired and sleepy we cannot think well, and cannot remember what we learn if we try to study. If we have plenty of sleep, free from bad or exciting dreams, we awake in the morning rested and refreshed, because while we have been asleep Nature has put the brain and nerves in good repair for us. We ought not to stay up late at night. We should not eat late or hearty suppers, as this will prevent our sleeping well.
~8. We Ought Not to Allow Ourselves to Become Angry.~--When a person flies into a pa.s.sion he does his brain and nerves great harm. It is really dangerous to get angry. Persons have dropped dead instantly in a fit of anger.
~9. We should Shun Bad Habits.~--Bad habits are very hard to give up, and hence we should be careful to avoid them. When a child learns to swear, or to use slang phrases, the brain after a while will make him swear or use bad words before he thinks. In a similar manner other bad habits are acquired.
SUMMARY.
1. A person without a brain or nerves would be of no more account than a vegetable.
2. When the brain or nerves are sick they cannot perform their duties properly.