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Our Telephone Exchange And Its Cables

Sources: A Handbook Of Health

The Brain. We are exceedingly proud of our brain and inclined to

regard it as the most important part of our body. So it is, in a sense;

for it is the part which, through its connecting wires, called the

nerves, ties together all the widely separated organs and regions in

our body, and helps them to work in harmony with one another. We speak

of it as the master and controller of the body; but this is only

partially tru

The brain is not so much the President of our Cell Republic as a great

central telephone exchange, where messages from all over the body are

received, sifted, and transmitted in more or less modified form, to

other parts of the body. Three-fourths of the work of the brain consists

in acting as middle-man, or transmitter, of messages from one part of

the body to another. In fact, the brain is far more the servant of the

body than its ruler; and depends for its food supply, its protection,

its health, and its very life, upon the rest of the body. The best way

to keep the brain clear and vigorous is to keep the muscles of the

stomach, the liver, the heart, and the entire body in good health.

What the Brain Does. The brain is the very wonderful organ with which

we do what we are pleased to call our thinking, and also a number of

other more important things of which we are not conscious at all. It is

a large organ, weighing nearly three pounds when full grown. In shape it

is like an oval loaf of bread split lengthwise by a great groove down

the centre, and with a curiously wrinkled or folded surface. The two

halves of the brain, called hemispheres (though more nearly the shape

of a coffee-bean), are alike; and each one, by some curious twist, or

freak, of nature, receives messages from, and controls, the opposite

half of the body--the right half controlling the left side of the body,

while the left half controls the right side of the body. Thus an injury

or a hemorrhage on the left side of the brain will produce paralysis of

the right side, which is the side on which a stroke of paralysis most

commonly occurs.

All the nerve fibres in each half or hemisphere of the upper brain run

downward and inward like the sticks of a fan, to meet in a strap-like

band, or stalk, which connects it with the base of the brain and the

spinal cord. A very small amount of damage at this central part, or

base, of the brain will produce a very large amount of paralysis. We may

have large pieces of the bones of the skull driven into the outer

surface of the brain, or considerable masses of our upper brain removed,

or destroyed by tumors or disease, without very serious injury. But any

disease or injury which falls upon the base of the brain, where these

stalks run and big nerve-knots (ganglia) lie, will cause very serious

damage, and often death.

The whole upper brain is a department of superintendence, which has

grown up from the lower brain to receive messages, compare them with

each other, and with the records of previous messages which it has

stored up, thus giving us the powers which we call memory, judgment, and

thought. Unfortunately, however, long and carefully as we have studied

the brain, we really know little about the way in which it carries out

these most important processes of memory, of judgment, and of thought,

or even of the particular parts of it in which each of these is carried


No part of the brain, for instance, seems to be specially devoted to, or

concerned in, memory or reason or imagination, still less to any of the

emotions, such as anger, joy, jealousy or fear; so all those systems

which pretend to tell anything about our mental powers and our

dispositions by feeling the shapes of our heads, or the bumps on them,

are pure nonsense.

The most important and highest part of the brain is its surface, a thin

layer of gray nerve-stuff, often spoken of as the gray matter (the

cortex, or bark), which is thrown into curious folds, or wrinkles,

called convolutions. This gray matter is found in the parts of the

nervous system where the most important and delicate work is done. The

rest of the nervous system is made up of what is called white matter,

from its lighter color; and this is chiefly mere bundles of telephone

wires carrying messages from one piece of gray matter to another, or to

the muscles.

We also know that a certain rather small strip of the upper

brain-surface, or cortex, about the size of two fingers, running upward

and backward from just above the ear, controls the movements of the

different parts of the body. One little patch of it for the hand,

another for the wrist, another for the arm, another for the shoulder,

another for the foot, and so on. We can even pick out the little patch

which controls so small a part of the body as the thumb or the eyelids.

So when we have a tumor of the brain or an injury to the skull in this

region, we can tell, by noticing what groups of muscles are paralyzed,

almost exactly where that injury or tumor is. Then we can drill a hole

in the skull directly over it and remove the tumor, lift up the splinter

of bone, or tie the ruptured blood vessel.

Three other patches, or areas, running along the side of the brain, each

of them about two inches across, are known to be the centres for smell,

hearing, and sight, that for sight lying furthest back. Damage to one of

these areas will make the individual more or less completely blind, or

deaf, or deprived of the sense of smell, as the case may be.

At the lower part of the area which controls the muscles of the

different parts of the body, above and a little in front of the tip of

the ear, lies a very important centre, which controls the movements of

the tongue and lips, and is known as the speech centre. If this should

be injured or destroyed, the power of speech is entirely lost. This,

curiously enough, lies upon the left side of the brain, and is the only

one-sided centre in the body. Why this is so is somewhat puzzling,

except that as speech is made up both of sound and of gesture, and our

gestures are usually made with the right hand, it is not unreasonable to

suppose that the speech centre should have grown up on that side of the

brain which controls the right hand, which is, as you remember, the left

hemisphere. What makes this more probable is that in persons who are

left-handed, the speech centre lies upon the opposite or right side

of the brain. So it is waste of time and does more harm than good to try

to break any child of left-handedness.

The Spinal Cord. Running downward from the base of the brain, like the

stalk of a flower, is a great bundle of nerve-fibres, the central cable

of our body telephone system, the spinal cord. This, you will remember,

runs through a bony tube formed by the arches of the successive

vertebrae; and as it runs down the body, like every other cable it gives

off and receives branches connecting it with the different parts of the

body through which it passes. These branches are given off in pairs, and

run out through openings between the little sections of bone, or

vertebrae, of which the spinal column is made up. They are called the

spinal nerves, and each pair supplies the part of the body which lies

near the place where it comes out of the cord.

The spinal nerves contain nerve wires of two sorts--the inward, or

sensory, and the outward, or motor, nerves. The sensory, or ingoing,

nerves come from the muscles and the skin and bring messages of heat and

cold, of touch and pressure, of pain and comfort, to the spinal cord

and brain. The outward, or motor, nerves running in the same bundle go

to the muscles and end in curious little plates on the surface of the

tiny muscle fibres, and carry messages from the spinal cord and brain,

telling the muscles when and how to contract.

As the spinal cord runs down the body, it becomes gradually smaller, as

more and more branches are given off, until finally, just below the

small of the back and opposite the hip bones, it breaks up by dividing

into a number of large branches which go to supply the hips and lower


While most of the spinal cord is made up of bundles of white fibres,

carrying messages from the body to the brain, its central portion, or

core, is made of gray matter. The reason for this is that many of the

simpler messages from the surface of the body and the movements that

they require are attended to by this gray matter, or ganglia, of the

spinal cord without troubling the brain at all.

For instance, if you were sound asleep, and somebody were to tickle the

sole of your bare foot very gently, the nerves of the skin would carry

the message to the gray matter of the spinal cord, and it would promptly

order the muscles of the leg to contract, and your foot would be drawn

away from the tickling finger, without your brain taking any part in the

matter, though, if you had been awake, you would of course have known

what was going on.

This sort of reply to a stimulus, or stirring up, without our knowing

anything about it, is known as a reflex movement. Not only are many of

these reflexes carried out without any help from the will, or brain, but

they are so prompt and powerful that the brain, or will, can hardly stop

them if it tries, as, for instance, in the case of tickling the feet.

You can, if you make up your mind to it, prevent yourself from either

wriggling, pulling your foot away, or giggling, when the sole of your

foot is tickled; but if you happen to be at all ticklish, it will take

all the determination you have to do it, and some children are utterly

unable to resist this impulse to squirm when tickled.

This extraordinary power of your reflexes has developed because only the

promptest possible response, by jerking your hand away or jumping, will

be quick enough to save your life in some accidents or emergencies, when

it would take entirely too long to telephone up to the brain and get its

decision before jumping. When you are badly frightened, you often jump

first and discover that you are frightened afterwards; and this jump,

under certain circumstances, may save your life. On the other hand, like

all instinctive or impulsive movements, it may get you into more trouble

than if you had kept still.

As you will see by the picture, the spinal nerves, which are given off

from the cord in the lower part of the neck and between the shoulder

blades, are gathered together into a great loose bundle to form the long

nerve-wires needed to supply the shoulders and arms. Those given off

from the small of the back just above the hips also run together to

form, first a network and then a big single nerve-cord, called the

sciatic nerve, which many of you have probably heard of from the

frightfully painful disease due to an inflammation of it, called

sciatica. It is the largest nerve-cord in the body, running down the

middle of the back of the thigh to supply the muscles of two-thirds of

the leg.[26]

The substance of both the spinal cord and the brain is made up of

millions of delicate, tiny cells, called neurons, most of which, with

very long branches, are arranged in chains for carrying messages,

forming the white matter; while the others lie in groups, or ganglia,

for sorting and deciding upon messages, forming the gray matter.

Just at the top of the spinal cord, where it passes into the skull and

joins with the brain, it swells out into a sort of knob, about the size

of a queen olive or the head of a gold-headed cane, which is known as

the medulla, or pith. This is the most vital single part of the

entire brain and nervous system; and the smallest direct injury to it

will produce instant death, partly because all the messages which pass

between the brain and the body have to go through it, and partly because

in it are situated the centres which control breathing and the beat of

the heart, and another quite important but less vital centre,--that for


How Messages are Received and Sent. Now to learn how smoothly and

beautifully this nerve telephone system of ours works, and how simple it

really is, although it has such a large number of lines and so many

telephones on each line, and such a large central exchange, let us see

how it deals with a message from the outside world. Suppose you are

running barefoot and step on a thorn. Instantly the tiny nerve bulbs in

the skin of the sole of your foot are stimulated, or set in vibration,

and they send these vibrations up the sciatic nerve, into and up the

whole length of the spinal cord, through the medulla, which switches

them over to the other side of the brain up through the brain stalk,

and out to the part of the surface (cortex) of the brain which controls

the movements of the foot. All this takes only a fraction of a second,

but it is not until the message reaches the brain-surface that you feel

pain. If you were to cut the sciatic nerve, or even tie a string tightly

around it, you could prick or burn the sole of your foot as much as you

pleased, and you would not feel any pain at all.

As soon as the surface of the brain has recognized the pain and where it

comes from, it promptly sends a return message back down the same cable,

though by different nerve-wires, to the muscles of the foot and leg,

saying, Jerk that foot away! As a matter of fact, this message will

arrive too late, for the centres in the spinal cord will already have

attended to this part of the matter, often almost before you know that

you are hurt.

However, there is plenty of other work for the brain to do; and its next

step, quicker than you can think, is to wake up a dozen muscles all over

the body with the order, Sit down! And you promptly sit down. At the

same time, the brain central has ordered the muscles of your arms and

hands to reach down and pick up the foot, partly to protect it from any

further scratch, and partly to pull the thorn out of it. Next it rushes

a hurry call to the muscles controlling your lungs and throat, and says,

Howl! and you howl accordingly. Another jab at the switchboard, and

the eyes are called up and ordered to weep, while at the same time the

muscles of the trunk of your body are set in rhythmic movement by

another message, and you rock yourself backward and forward.

This weeping and rocking yourself backward and forward and nursing your

foot seem rather foolish,--indeed you have perhaps often been told that

they are both foolish and babyish,--but, as you say, you can't help

it, and there is a good reason for it. The howl is a call for help; and

if the hurt were due to the bite of a wolf or a bear, or the cut had

gone deep enough to open an artery, this dreadfully unmusical noise

might be the means of saving your life; while the rocking backward and

forward and jerking yourself about would also send a message that you

needed help, supposing you were so badly hurt that you couldn't call

out, to anyone who happened to be within sight of you. So that it isn't

entirely babyish and foolish to howl and squirm about when you are

hurt--though it is manly to keep both within reasonable limits.

If the message about the thorn had been brought by your eyes,--in other

words, if you had seen it before you stepped on it,--then a similar but

much simpler and less painful reflex would have been carried out. The

image of the thorn would fall on the retina of the eye and through its

optic nerve the message would be flashed to the brain: There is

something slim and sharp in the path,--looks like a thorn. When this

message reached the brain, and not till then, would you see the thorn,

just as in the case of the pain message from the foot. Then the brain

would take charge of the situation just as before, flashing a hasty

message to the muscles of the legs, saying, Jump! while its message to

the throat and lungs, instead of Yell, would be merely, Say,

'Goodness!' or 'Whew!' and you would say it and run on.

If the thing in the grass, instead of a thorn, happened to be a snake,

and you heard it rustle, then the warning message would come through

your ears to the brain, and you would jump just the same; though, as it

is not so easy to tell by a hearing message exactly where the sound is

coming from, you might possibly jump in the wrong direction and land on

top of the danger.

This is the way in which you see, hear, and form ideas of things. Your

eye telegraphs to the brain the colors; your ear, the sounds; and your

nose, the smells of the particular object; and then your brain puts

these all together and compares them with its records of things that it

has seen before, which looked, or sounded, or smelt like that, and

decides what it is; and you say you see an apple, or you hear a

rooster crow, or you smell pies baking. Remember that, strange as it

may seem, you don't see an orange, for instance, but only a circular

patch of yellowness, which, when you had seen it before, and felt of it

with your hand, you found to be associated with a feeling of roundness

and solidness; and when you lifted it toward your nose, with the

well-known smell of orange-peel; so you called it an orange. If the

yellow patch were hard, instead of elastic, to the touch, and didn't

have any aromatic smell when you brought it up to your nose, you would

probably say it was a gourd, or an apple, or perhaps a yellow croquet

ball. This is the way in which, we say, our senses may deceive us, and

is one of the reasons why three different people who have seen something

happen will often differ so much in their accounts of it.

It is not so much that our senses deceive us, but that we draw the wrong

conclusions from the sights, sounds, and smells that they report to our

brains, usually from being in too great a hurry and not looking

carefully enough, or not waiting to check up what we see by touching,

hearing, or tasting the thing that we look at.

This message-and-answer system runs all through our body. For instance,

if we run fast, then the muscle cells in our legs burn up a good deal of

sugar-fuel, and throw the waste gas, or smoke, into the blood. This is

pumped by the heart all over the body, in a few seconds. When this

carbon dioxid reaches the breathing centre in the medulla, it stirs it

up to send promptly a message to the lungs to breathe faster and deeper,

while, at the same time, it calls upon the circulation centre close to

it, to stir up the heart and make it beat harder and faster, so as to

give the muscles more blood to work with. If some poisonous or very

irritating food is swallowed, as soon as it begins to hurt the cells

lining the stomach, these promptly telegraph to the vomiting centre in

the brain, we begin to feel sick at the stomach, the brain sends the

necessary directions to the great muscles of the abdomen and the

diaphragm, they squeeze down upon the stomach, and its contents are

promptly pumped back up the gullet and out through the mouth, thus

throwing up the poisons.

And so on all over the body--every tiniest region or organ in the body,

every square inch of the skin, has its special wire connecting it with

the great telephone exchange, enabling it to report danger, and to call

for help or assistance the moment it needs it.