THE NERVES, SPINAL CORD, AND BRAIN
=136. Need of nerves.=--The cells of the mouth, stomach, and intestine
digest food; the cells of the liver change the food to blood; the
cells of the heart pump the blood to feed all the cells of the body;
the red blood cells carry air for the cells to breathe; and the cells
of the skin and kidneys carry away the waste of the rest of the cells.
Each set of cells works for all the rest. If the cells of the body
were only tied together, each one would do as it pleased, and no two
would work together. But something tells each cell of the body to work
with the others. The cells all obey the mind. A tiny thread goes to
each cell of the body. Each thread is a _nerve_. The mind and the
cells signal to each other over the nerves. By means of the nerves the
mind makes the cells work together.
[Illustration: =A nerve thread (x400).=
_a_ central conducting fiber.
_b_ covering of fat.]
[Illustration: =A thin slice for the end of a cut nerve (x200).=
_a_ nerve thread.
_b_ connective tissue binding the threads into a cord.]
=137. Nerve messages.=--The nerve threads run in bundles and form
nerves large enough to be seen. The mind uses the nerves to tell the
cells to do work. It tells the muscles to move the arms and legs. It
tells the heart to beat and stomach to pour out gastric juice; and it
tells each of the cells to eat.
The cells also send word over the nerves to the mind. They tell the
mind when they are touching anything, and whether it is hard, or
smooth, or hot, and many other things about it. The cells also tell
the mind if they need more food, or are tired.
The nerves are always carrying messages to and from the cells. The
cells depend upon these messages to tell them when and how to work. If
the nerve of any part of the body is hurt or cut, we cannot feel with
the part or move it, and its cells do not act in the right way. We do
not feel the nerves while they are carrying the messages. We wish the
cells of the arm to work, and they work, but we do not feel the
message as it goes from the mind to the cells of the arm.
[Illustration: =A thin slice from the spinal cord with the cells and
nerves magnified 200 diameters.=
_a_ cells in the gray matter.
_b_ fibers in the gray matter.
_c_ nerve threads in the white matter.]
=138. The spinal cord.=--The nerves start inside the backbone. The
backbone is hollow. It has a soft, white cord inside, as thick as the
little finger. Part of the mind lives in this cord. The cord is called
the _spinal cord_. Some of the nerves start from cells of the spinal
cord. These cells send word to the muscles to move and to all the
cells of the body to eat and grow. They also send word to the arteries
to carry the right amount of blood to the cells.
From the nerves the spinal cord gets word when something hurts any
part of the body. You may put your finger on a sharp pin. The spinal
cord feels the prick, and quickly sends word to snatch the finger
away. So the finger is taken away before you really feel the prick.
When some one sticks a pin into you, you cannot help jumping. This is
because the spinal cord sends word for you to jump away from the pin
before it can harm you much. Thus the spinal cord keeps the body from
being hurt. It acts while we are asleep as well as when we are awake.
=139. Need of a spinal cord.=--We do not feel the spinal cord acting,
and we cannot keep it from acting. It tells the cells when to eat and
grow, and it tells the heart and arteries how much blood to send to
each cell. If we had to think about feeding an arm or a leg, we should
sometimes forget it, but the spinal cord keeps doing it without our
thinking of it. We put food into the body, and the spinal cord tells
the cells to use it. If it stops acting for an instant, the cells stop
work and we die. We cannot change its action by any amount of thinking.
[Illustration: =Regions of the head and action of the different parts
of the brain.=]
=140. The brain.=--The nerves of the body go to the brain as well as
to the spinal cord. The brain lies in the top of the head. A hard
cover of bone keeps it from getting hurt. It is a soft white mass, and
weighs about three pounds. Its outside is made of cells, while its
inside is the very beginning of the nerves of the body.
=141. The mind.=--The mind is the real man. It is the thinking part of
himself. It lives in the body and works by means of the cells of the
brain. If these cells are hurt or killed, the body seems to have no
mind, but yet it may keep on living. If all the mind leaves the body,
the body is dead.
By means of the mind we feel, and know, and think. The mind uses each
part of the brain for only one kind of work.
=142. The senses.=--The cells of the body send word to the brain over
the nerves. The eye tells of sight, the ear of sounds, the nose of
odors, the mouth of tastes, and the skin of feelings. All these
messages go to the back part of the brain. They tell the mind of the
news outside of the body. We get all our knowledge in this way. The
cells also tell of their need of food and drink by means of the
feelings of hunger and thirst.
=143. Motion.=--The mind in the cells of the top part of the head
sends the orders for moving the different parts of the body. When we
wish to run, the mind in the top of our head sends an order over our
nerves to our legs, and they carry the body where we wish. If the top
part of your brain is hurt, as by a blow, it cannot send orders to
move, but you will lie stunned.
=144. Memory.=--The mind lays away all its messages, and often looks
them over again. These old messages are called _memories_. They always
stay with the brain, and the mind can call them up at any time. Our
memories make our knowledge.
Every act of the mind leaves some mark on the memory. We may not be
able to bring it back when we want to, but it will come back some
time. Every bad word and evil deed will tend to come back and make us
bad again. Every good work and word will leave its memory and make us
better. We ought to fill our minds with good memories.
=145. Thinking.=--The brain also thinks. Thinking is different from
feeling and from moving, but we can think about our feelings and about
our movements. The brain just back of the forehead does all our
thinking. A dog has only a little forehead, and cannot think much. But
the rest of its brain is large, for it can see and hear and run as
well as a man. A baby can see and hear and move, but it cannot think
until it is taught how. Boys and girls go to school to learn to think.
Thinking is work, just as truly as running is work. At school, no one
can learn to think without working. Looking at things and hearing some
one talk about them will not make you a strong-minded man, but
thinking about these things will. Boys and girls should study and
think, as well as look around and listen.
=146. How thought rules the body.=--We are always feeling and moving.
We often do these things without trying, but we must make ourselves
think. We can make our bodies move, or keep still, and we can keep
from too much feeling. Our thoughts direct our natural desires to move
and feel. In an animal, the feelings and movements direct the
thoughts. When men let their feelings rule their thoughts, they are
like animals. When the thoughts control the feelings and acts, we are
men. If you get angry and cry, when you hurt your finger, then you are
like an animal; but if you think about it and control your feelings,
you are behaving like a strong and noble man. The thought part of the
brain ought to rule all the rest.
=147. Sleep.=--Most of the brain does its work without our knowing it,
but we know when we think. The thinking part of the brain gets tired,
like any other part of the body. When it stops work, we are asleep.
We must give the brain a rest in sleep, just as we must rest an arm or
a leg. We ought to give it regular rest. Every night we ought to go to
bed early. Then we shall be ready to get up early and shall feel like
working. Boys and girls need nine or ten hours' sleep each day. When
they are grown, they need seven or eight hours' sleep each day.
The spinal cord and some parts of the brain must always stay awake to
make the cells of the body eat and grow. When we are asleep, they must
be wide awake, and must repair the worn-out parts. They do not seem to
rest at all. If they rested for any length of time, then the lungs,
heart, stomach and all other parts of the body would stop work, and we
should die. But they really rest a part of the time. Like the heart,
they act for a second, and then stop for a second. They seem to act
all the time, but in all they rest half the time.
=148. Worry.=--The mind can do a great deal of work, if it gets good
sleep. If a person gets enough sleep and rest, he cannot harm his mind
by hard work. Sometimes the mind is troubled and worried over a danger
or a loss. Then it cannot rest, but soon wears itself out. Worry is
far more tiresome than hard work. By an effort, we can keep from
worrying. It never does us good to worry, and we ought to keep from it.
=149. Nervousness.=--The thoughts are able to rule all the rest of the
mind. They can keep us from feeling ill-tempered when we cannot have
our own way. Sometimes a little unpleasant feeling makes us very
unhappy, and keeps us from thinking about our work. A little noise or
pain keeps some children from study, while others can bear a great
deal without being disturbed by it. Some persons jump at a little
noise, and are afraid of a tiny bug or mouse. This is because their
feelings rule their thoughts. Such persons are called _nervous_.
A nervous person is very uncomfortable and makes others so too. Yet
any one can get over the habit of being nervous, if he will try. You
ought not to laugh at a nervous person if he is afraid of some little
thing while you are not. You should help him to get over his
nervousness and to become brave.
=150. Fear.=--Some persons are always brave. In danger they calmly
stop to think, and then know how to save themselves. A timid person
does not think, but rushes where his feelings lead. When a crowd is
in danger, all will rush to do one thing. All will run for a door, and
perhaps tread on one another. Then some one will surely be hurt. At a
fire, or in any other danger, you should always stop to think how to
act. If you rush with the crowd, you may be hurt. You will be more
likely to be safe, if you stay away from them. Then, if help comes,
you will be able to receive it. Besides, if you are cool and brave,
you will help others around you to be brave too.
=151. Fire drill.=--In schools the children are taught how to go out
of the building when there is a fire. A bell is struck when the
children do not expect it. Then every child must leave his seat at
once and march out of the building. The bell is struck every few days.
Then, when the bell really sounds for a fire, the children know how to
march out quickly, and so they learn to be brave.
By training we can learn to be brave at all times. We fear many
harmless things, and in many cases do not fear real dangers. We are
liable to be hurt at any time. We are more liable to be hurt by a
horse when we are out driving than we are by the dark. Yet we do not
fear the horse, while some do fear the dark. We ought to learn to
think, so as to control our fear.
Some are afraid of the dark, some are frightened by ghost stories,
and others expect to see a wild animal jump from behind every bush. No
one fears these things unless he has been told about them. We ought to
be careful not to tell children of these things. We ought to teach
them to control their fear.
=152. Habit.=--After we have thought about a thing a few times, its
hold on our memory becomes strong, and leads us to think about it
often. When we have done a thing a few times, we are likely to do it
again without knowing it. We call this doing things over again
_habit_. When we once form a habit, we find it very hard to break. We
can form habits of doing right or of doing wrong. We can get into the
habit of swearing or of drinking by doing these things a few times.
Then we shall do these things when we do not want to. When a drinker
begins, he does not expect to keep on drinking. But his habit makes
him drink, and he cannot help it. We should be careful not to do bad
things, for we easily form the habit of doing them.
=153. Good habits.=--We can form habits of doing right. We can speak
kindly and be generous. Then we shall do these things as easily as
others get cross. After a person has tried to do good a few times, he
will find it much easier to do good. Then he will speak kindly and
give generously just as easily as others get angry and keep their good
things to themselves.
=154. Alcohol takes away thought.=--Alcohol affects and weakens the
cells of the brain sooner than it does those of any other part of the
body. It first makes the thought cells weak. Then a person does not
think how he acts. He lights his pipe in the barn and throws the match
in the hay. He drives his horse on a run through a crowded street. He
swears and uses bad language. He gets angry at little things and wants
to fight. He seems to think of himself, and of no one else. He is
happy, for he does not think of the bad effects of the drink. He has a
good time, and does not care for its cost. He likes to drink, because
it makes him feel happy.
=155. Alcohol spoils motion.=--Some cells of the brain cause the arms
and legs, and all other parts of the body, to move. Alcohol next makes
these weak. Then a person cannot move his legs right, but he staggers
when he walks. He cannot carry a full cup to his lips. His hands
tremble, and he cannot take care of himself. He is now really drunk.
=156. Alcohol takes away feeling.=--After a man is drunk, he loses the
sense of feeling. He does not feel cuts and blows. Because he does
not feel tired, he feels very strong. He often sees two things for
one, and hears strange noises. The whole brain at last gets weak, and
cannot act. Then the drinker lies down in a drunken sleep, and cannot
be waked up. Some die in this state.
=157. Insanity.=--When the brain is misused by alcohol for some time,
it cannot get over it. Then the person becomes insane. Drink sends
more persons to the insane asylum than all other causes put together.
=158. Delirium tremens.=--If a drinker gets hurt, or becomes sick, he
sometimes has terrible dreams. In them he sees dirty and savage
animals coming to harm him. These dreams seem very real to him, and he
cries out in his fright. This is called _delirium tremens_. A person
is liable to die from it.
=159. Alcohol harms a drinker's children.=--The children of drinkers
are apt to be weak in body and mind. A drinker hurts his children even
more than he hurts himself. They are liable to catch diseases, and are
often cross and nervous, or weak-minded. It is a terrible thing for a
man to make his children weak and nervous.
=160. Other bad things about drink.=--There are many other terrible
things about drink, besides the harm it does a man's body. Many a man
has made himself drunk so as to steal or kill. No man can drink long
without becoming a worse man for it. Men will not trust him, and he
loses the respect of his friends.
Making strong drink takes thousands of men away from good work. They
might work at building houses, or raising grain, or teaching school.
As it is, their work is wasted.
A great deal of money is wasted on strong drink. All the mines of the
world cannot produce enough gold and silver to pay the drink bill. The
people of the United States pay more for strong drink than for bread.
The price of two or three drinks a day would amount to enough, in ten
years, to buy a small home.
The cost of strong drink is made much greater if we count the cost of
jails and insane asylums. Over one half of all crimes and cases of
insanity are caused by strong drink.
We must also add the misery and suffering of most children of drunken
fathers. This loss cannot be counted in money. Numbers of children
become truants from school and learn theft and falsehoods from lack of
a father's care. When all the cost is counted, nothing will be found
so expensive as strong drink.
On the other hand, what do people get for their money and suffering?
They get only a little pleasure, and then they are ashamed of it. Men
use strong drink only because they like it more than they dislike its
bad effects.
Since drink does a great deal of harm, with no good to any one, it is
right to make laws to control its sale.
=161. How tobacco affects the brain.=--Some men smoke to make
themselves think, and some to keep themselves from thinking. Now,
smoking cannot do both things. It really makes the brain less able to
think, for it weakens the whole body. A school-boy's brain will surely
be harmed if he uses tobacco at all.
WHAT WE HAVE LEARNED
1. The mind makes all the cells of the body work together.
2. Tiny nerve threads carry messages from the mind to the cells.
3. Most of the nerves begin at the spinal cord in the backbone.
4. The mind in the spinal cord tells the cells to eat and grow.
It tells the arteries how much blood to carry to the cells.
5. The cells tell the spinal cord if they need food, or if
something suddenly hurts them. The spinal cord sends word to
snatch the part from danger.
6. Nerves carry to the brain news of sight, sound, odor, taste,
and touch.
7. The brain sends word to the muscles to move the arms, the
legs, and the rest of the body.
8. The brain thinks.
9. The brain stores up all its messages; these make memory and
knowledge.
10. The thought part of the brain can control the feelings and
the movements of the body.
11. Alcohol is more harmful to the brain than to any other part
of the body.