HOW WE FEEL AND THINK.
~1. How we Think.~--With what part of the body do we think? You will at
once say that we think with the head; but we do not think with the whole
head. Some parts of the head we use for other purposes, as the mouth to
eat and speak with, and the nose to smell and breathe with. The part we
think with is inside of the skull, safely placed in a little room at the
top and back part of the head. Do you remember the name of this organ
which fills the hollow place inside of the skull? We learned some time
ago that it is called the _brain_. It is with the brain that we study
and remember and reason. So the brain is one of the most important
organs in our body, and we must try to learn all we can about it.
~2. The Brain.~--You cannot see and examine your own brain because it is
shut up in the skull; but perhaps you can find the brain of a sheep or a
calf at the meat market. The brain of one of these animals looks very
nearly like your own.
~3. The Large Brain and the Small Brain.~--In examining a brain we
should notice first of all that there are really two brains, a _large
brain_ and a _small brain_. The large brain is in the top and front of
the skull, and the small one lies beneath the back part of the larger
one, If we look again we shall see that each brain is divided in the
middle into a right and a left half. Each half is, in fact, a complete
brain, so that we really have two pairs of brains.
[Illustration: THE BRAIN.]
~4. Brain Cells.~--The brain is a curious organ of a grayish color
outside and white inside. It is soft, almost like jelly, and this is why
it is placed so carefully in a strong, bony box. If we should put a
little piece of the brain under a microscope, we should find that it is
made up of a great number of very small objects called _nerve_ or
_brain cells_. In the illustration you can see some of these brain
cells.
[Illustration: BRAIN CELLS.]
~5. The Nerves.~--Each cell has one or more branches. Some of the
branches are joined to the branches of other cells so as to unite the
cells together, just as children take hold of one another's hands. Other
branches are drawn out very long.
~6.~ The long branches are such slender threads that a great number of
them together would not be as large as a fine silk thread. A great many
of these fine nerve threads are bound up in little bundles which look
like white cords. These are called _nerves_.
~7.~ The nerves branch out from the brain through openings in the skull,
and go to every part of the body. Every little muscle fibre, the heart,
the stomach, the lungs, the liver, even the bones--all have nerves
coming to them from the brain. So you see that the brain is not wholly
shut up in the skull, because its cells have slender branches running
into all parts of the body; and thus the brain itself is really in every
part of the body, though we usually speak of it as being entirely in the
skull.
~8. The Spinal Cord.~--There are a number of small holes in the skull
through which the nerves pass out, but most of the nerves are bound up
in one large bundle and pass out through an opening at the back part of
the skull and runs downward through a long canal in the backbone. This
bundle of nerves forms the _spinal cord_. The spinal cord contains cells
also, like those of the brain. It is really a continuation of the brain
down through the backbone.
[Illustration: BRAIN AND SPINAL CORD.]
~9. Nerves from the Spinal Cord.~--The spinal cord gives off branches of
nerves which go to the arms, the chest, the legs, and other parts. One
of the branches which goes to the hand runs along the back side of the
arm, passing over the elbow. If we happen to strike the elbow against
some sharp object, we sometimes hit this nerve. When we do so, the under
side of the arm and the little finger feel very numb and strange. This
is why you call this part of the elbow the "funny" or "crazy bone." The
cells of the spinal cord also send out branches to the body and to other
cells in the brain.
~10. How we Feel.~--If we cut or burn ourselves we suffer pain. Can you
tell why it hurts us to prick the flesh with a pin, or to pinch or burn
or bruise it? It is because the flesh contains a great many
nerve-branches from the brain. When we hurt the skin or the flesh, in
any way, these nerves are injured. There are so many of these little
nerves in the flesh and skin that we cannot put the finest needle into
the flesh without hurting some of them.
~11. The Use of Pain.~--It is not pleasant for us to have pain, but if
the nerves gave us no pain when we are hurt we might get our limbs
burned or frozen and know nothing about it until too late to save them.
~12. Nerves of Feeling.~--We have different kinds of nerves of feeling.
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 pass
out from the brain to the rest of the body through a number of openings
in the skull.
8. Most of the nerve branches pass 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 canal in the backbone, and all
along gives off branches to the various parts of the body.
10. It gives us pain to prick 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.