A Handbook of Health

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When you wish, for instance, to lift your hand toward your face, you
unconsciously send a message from your brain down the nerve cables in
your spinal cord, out through the nerve-wires of your neck and shoulder,
to the big _biceps_ muscle on the front of your upper arm. This muscle
then contracts, or shortens, and pulls up the forearm and hand, by
bending the elbow joint. Just in proportion as the muscle becomes
shorter, it becomes thicker in the middle; and this you can readily
prove by grasping it lightly with your fingers when it contracts, and
feeling it bulge.[22]

The food tube is surrounded with muscles, as you will remember, for
moving the food along it, or churning it. These internal muscles,
requiring only the presence of food to cause them to act, and not
needing attention on the part of the brain or the will, are known as the
_involuntary_ ("without the will") muscles.

The great group of the _voluntary_, or bone-moving muscles, which move
"with the will" and are under our direct control, may be divided roughly
into two divisions--those that move the trunk, or body proper, and run,
for the most part, lengthwise of it; and those that move the limbs.

On the body, they may be divided into two great sheets--one running up
the front, and the other up the back. When those running up the front of
the body contract, they naturally bend the back, and pull the head and
shoulders forward and downward. Or, as when you spring up and catch the
branch of a tree or a horizontal bar with your hands, these same muscles
will pull the lower part of the body and legs upward, so that you can
climb into the tree.

The largest and thickest bands of these front body muscles are found
over the abdomen, or stomach, where you can feel them thicken and harden
when you bend your body forward and pull with your arms, as in hauling
on a rope. By their pressure upon the intestines, they give the bowels
valuable support, assist in their movements, and help the circulation of
the blood through them; so that it is of considerable importance to keep
this entire group of muscles well toned up by exercises, such as
swinging your arms back over your head, and then down between your legs;
bending the head and shoulders backward and forward; swinging the legs
up over the body, either when hanging from a bar or lying on your back.
Proper exercising and toning up of these muscles will often cure
constipation and dyspepsia, by their influence upon the bowels and
stomach, and also keep one from taking on fat around the waist too
rapidly.

On the back of the body, the muscle-sheet has grown into great, thick
ropes of muscle on each side of the backbone, which you can feel
hardening and softening in the small of the back, when you stoop down or
lift weights. These are the muscles that hold the body erect, and keep
the back straight when you stand, and are the largest and hardest
working group of muscles in the body. Every minute that you sit, or
stand, they are at work; and that is why they so often get tired out,
and ache, and you say you have "a backache." They have to work harder to
keep you erect or upright when you are standing perfectly still than
when you walk or run, so that standing perfectly still is the hardest
work you can do. Next to standing still, the hardest thing is to sit
still, as you probably have found out. If it were not for these great
muscles of the back and abdomen, we should double up like a jack-knife,
either forward or backward, when we tried to stand up. It is not our
skeleton that keeps us stiff or erect, but our muscles.

[Illustration: THE MUSCLE-SHEET

Showing how the muscles, overlapping and interlocking, give shape to the
body.]

If you want to keep straight and erect, and thus have a good carriage,
you must keep these great body muscles well trained and exercised by
swinging movements, such as bending the back forward, standing with your
feet apart and then swinging your head and shoulders down and between
your legs; or, with your heels together, swinging your hands down till
the fingers touch the ground; or by the different exercises that either
bend your back, or hold it stiff and erect. Swinging from a bar, rowing,
digging with a spade, chopping or sawing wood, dancing, rope-skipping,
ball-playing, hop-scotch, and wrestling, all develop these muscles
finely and are good for both boys and girls.

Other strands of these muscles branch out to fasten themselves to the
shoulder blades and shoulders, where they help to draw the arm back as
for a blow, pull the shoulders into position when you stand upright, or,
when you have leaned forward and grasped something with the hand, help
to pull up the arm and lift it from the ground. These muscles are quite
important in holding the shoulders back and giving a good shape to the
chest and good carriage of the upper part of the body and head. They are
called into play in all exercises like striking, batting,
tennis-playing, ball-throwing, swinging, shoveling, swimming, as well as
in pulling, in lifting weights, in swinging an axe or handling a broom.

[Illustration: USE OF MUSCLES IN BOWLING

Showing _A_ thickening of flexors on front of arm, as forearm is swung
forward, and _B_ thickening of extensors on back of arm, as forearm is
swung backward.]

The muscles of the limbs are almost as numerous as those of the trunk of
the body, and even more complex. Most of them, on both arms and legs,
are in two great groups--one known as the "benders," or _flexors,_
which, when they shorten, bend the limb; and the other, the
"straighteners," or _extensors_, which straighten or extend it.

On the front of the arm, for instance, we have the large biceps
("two-headed") muscle, which runs from the shoulder to the bone of the
forearm just below the elbow and, when it shortens, bends the elbow and
lifts the arm toward the body.

On the back of the upper arm is the _triceps_ ("three-headed") muscle,
which is fastened at its lower end to a big spur of bone, the "point" of
the elbow; when it shortens, acting lever fashion, it straightens or
_extends_ the arm. If this is done quickly, the fist is swung outward
with force enough to strike quite a sharp blow, though, as you know, if
you wish to hit really hard, you have to strike with the weight and
muscles of the full arm and the body behind it, or, as we say, "from the
shoulder."

[Illustration: USE OF MUSCLES IN FOOTBALL

Showing _A_ thickening of flexors on front of thigh and leg, as foot is
swung forward; and _B_ thickening of extensors on back of thigh and leg,
as leg is swung backward.]

[Illustration: PATELLA AND MUSCLE

_P_, patella (knee cap); _M_, muscle; _L_, ligament; _T_, tendon.]

In the lower limbs, the muscles are larger because they have heavier
work to do, supporting and moving the whole weight of the body; but they
are simpler in their arrangement since they have not such a variety of
movements to carry out. The principal muscle in the thigh is the great
muscle running down the front of the thigh, and fastening to the upper
border of the _patella_, or knee cap. This muscle, when it shortens,
straightens or extends the limb, or lifts the foot from the ground and
swings it forward as in walking, or raises the knee up toward the body
when we are sitting or lying down. You can easily tell how much it is
used in walking by remembering how stiff and sore it gets when you have
taken an unusually long tramp, particularly if there has been much
hill-climbing in it. On the back of the thigh, runs another great group
of muscles, which bend or flex the limb when they shorten. When the knee
is bent, you can feel their tendons, or sinews, stand out as hard cords
beneath the knee; hence, this group is called the _ham-string_
muscles.[23]

How the Muscles are Fed. Our muscles are not only the largest, but the
"livest" part of our bodies. Their contractions and movements are caused
by their tiny "explosions" (like the chugging of an automobile, except
that we can't hear them); and in this way they burn up the largest part
of the food-fuel which we eat--mostly in the form of sugar. When they
have burned up their surplus food-fuel, they call for more; and when
this demand has been telegraphed to the brain, we say we are hungry, and
that exercise has given us an appetite. While the muscles are at work,
they demand that large supplies of fresh fuel shall be brought to them
through the blood vessels; and this makes the heart beat harder and
faster, and improves the circulation. As they burn up this fuel, they
form smoke and ashes, or waste materials, which must be got rid of--the
fluid part by perspiration from the surface of the skin, and through the
kidneys, and the gas, or "smoke," through the lungs. This is the reason
why, during exercise, we breathe faster and deeper than at other times,
and why our skin begins first to glow and then to perspire.

If these waste-materials form in the muscles faster than the blood can
wash them out, they poison the muscle-cells and we begin to feel tired,
or fatigued. This is why our muscle-cells are often so stiff and sore
next morning after a long tramp, or a hard day's work, or a football
game. A hot bath or a good rub-down takes the soreness out of the
muscles by helping them to get these poisonous wastes out of their
cells.

Thus when we play or run or work, we are not only exercising our muscles
and making them gain strength and skill, but we are stirring up, or
stimulating, almost every part of our body to more vigorous and
healthful action.

Indeed, as our muscles alone, of all our body stuffs, are under the
control of the will, our only means of deliberately improving our
appetites, or strengthening our hearts or circulation, or invigorating
our lungs, or causing a large part of our brains and minds to grow and
develop, is through muscular exercise. This is why nature has taken care
to make us all so exceedingly fond of play, games, and sports of all
sorts, in the open air, when we are young; and, as we grow older, to
enjoy working hard and fighting and "hustling," as we say; and that is
the reason, also, why we are now making muscular exercise such an
important part of education.

FOOTNOTES:

[22] The muscle does not get any bigger when it contracts, as was at one
time supposed; if you were to plunge it into a bath of water, and then
cause it to contract, you would find that it did not raise the level of
the water, showing that it was of exactly the same size as before,
having lost as much in length as it gained in thickness.

[23] In the leg below the knee, and in the forearm, we have two groups
of "benders" or _flexors_, and "straighteners" or _extensors_, as in the
upper arm and leg, only slenderer and more numerous. They taper down
into cord-like tendons at the wrist and ankle to fasten and to pull the
hands and feet "open" and "shut," just as do the strings in the legs and
arms of a puppet or mechanical doll, or the sinews in the foot of a
chicken.

CHAPTER XIX

THE STIFFENING RODS OF THE BODY-MACHINE

What Bones Are. The bones are not the solid foundation and framework
upon which the body is built, as they are usually described. They are
simply a framework of rods and plates which "petrified," or turned into
spongy limestone after the body was built, to make it firmer and stiffen
it for movement. All the animals below the fishes, such as worms,
sea-anemones, oysters, clams, and insects, get along very well without
any bones at all; and when we are born, our bones, which haven't fully
"set" yet, are still gristly and soft. The cores of the limbs, as they
begin to stiffen, first turn into gristle, or cartilage, and later into
bone; indeed, many of our bones remain gristle in parts until we are
fifteen or sixteen years of age. This is why children's bones, being
softer and more flexible than those of grown-up people, are not so
liable to break or snap across when they fall or tumble about; and why,
too, they are more easily warped or bent out of shape through lack of
proper muscular exercise and proper food.

Bones are strips of soft body-stuff soaked with lime and hardened, like
bricklayer's mortar, or concrete.[24] When you know the shape of the
body, you know the bones; for they simply form a shell over the head and
run like cores, or piths, down the centre of the back, and down each
joint of the limbs.

In turning into spongy limestone, or animal concrete, they have become
one of the deadest tissues in the body. They are tools of the muscles,
the levers by which the muscles move the limbs and body about; they
never do anything of their own accord. On account of their lifelessness
and lack of vitality, they are rather easily attacked by disease, or
broken by a blow or fall. There are such a large number of bones (two
hundred and six, all told), and they resist decay and last so much
longer after death than any other parts of the body, that they fill our
museums and text-books of anatomy, form most of our fossils, and have
thus given us rather an exaggerated idea of their importance during
life.

[Illustration: THE HUMAN SKELETON]

The Frame-Work of the Body. Just look at any part of the body and
imagine that it has a bony core of about the same general shape as
itself, and you can reason out all the bones of the skeleton. To begin
at the top, the _skull_ is a box of strong, plate-like bones, which have
hardened to protect the brain as it grew; and the shape of its upper, or
brain, part is exactly that of the head, as you can easily feel by
laying your hands upon it. Then come bony shells, or sockets, for the
eyes and nose; and, below these, two heavy half-circles of bone, like
the jaws of a steel trap, to carry the teeth.

The thickness of the lower jaw and the size and squareness of the angle
where it bends upward to be hinged to the skull, below the ear, are what
give the appearance of squareness and determination to the faces of
strong, vigorous men or women. If we want to imply that a person has a
feeble will, or weak character, we say he has a "weak jaw."

The skull rests upon the top of the backbone, or _spinal column_, which,
instead of being one long solid bone, is made up of a number of pieces,
or sections, known as _vertebrae_. Each one of these vertebrae has a ring,
or arch, upon its back. These, running one after the other, form a
jointed, bony tube to protect the _spinal cord_, or main nerve-cable of
the body, which runs through it.

[Illustration: THE SPINAL COLUMN

_V_, vertebra; _C_, cartilage protecting spinal cord; _A_, point of
articulation on the right side.]

Although the backbone can bend forward or backward, or twist from side
to side a little, by the little pieces of bone of which it is built up
gliding and turning upon one another, it is really very stiff and rigid,
so as to protect the spinal cord and prevent its being stretched or
pinched. Most of the movements which we call bending the spine are
really movements of other joints which connect the body or head with
it. When we bend our necks, for instance, we hardly bend the backbone at
all, as most of the movement is made in the joint at the top of it,
between it and the skull. Similarly, when we bend our backs, we really
bend our backbones very little; for most of the movement comes at the
hip joints, between the thighs and the hip bones.

Each of the limbs has a single, long, rounded bone in the upper part,
known in the arm as the _humerus_, and two bones in the lower part.
These last are known as the _radius_ and _ulna_ (the "funny bone") in
the forearm, and the _tibia_ and _fibula_ in the leg. The shoulder-joint
is made by the rounded head of the humerus fitting into the shallow cup
of the _scapula_, or shoulder-blade. It is shallower than the hip joint
to allow it freer movement; but this makes it weaker and much more
easily dislocated, or put out of joint,--the most so, in fact, of any
joint in the body.

[Illustration: A BALL-AND-SOCKET JOINT

Hip joint.]

[Illustration: A HINGE JOINT

Knee joint, with the knee cap removed]

The hip joints are deep, strong, cup-shaped sockets upon each side of
the hip bones, or _pelvis_, into which fit the heads of the _femurs_ or
thigh bones. When the hip joint does become dislocated, it is very hard
to put back again, on account of its depth and the heavy muscles
surrounding it. It is quite subject to the attack of tuberculosis, or
"hip-joint disease."

[Illustration: LENGTHWISE SECTION OF BONE]

The _joints_, or points at which the bones join one another, look rather
complicated, but they are really as simple as the bones themselves. Each
joint has practically made itself by the two bones' rubbing against each
other, until finally their ends became moulded to each other, and formed
the ball-and-socket, or the hinge, according to whichever the movements
of the "bend" required. The ends, or heads, of the bones which form a
joint are covered with a smooth, shining coating of _cartilage_, or
gristle, so that they glide easily over each other.

[Illustration: CROSS SECTION OF BONE]

Around each joint has grown up a strong sheath of tough, fibrous tissue
to hold the bones together; and, inside this, between the heads of the
bones, is a very delicate little bag, or pouch, containing a few drops
of smooth, slippery fluid (_synovial fluid_) to lubricate the movements
of the joint. This is sometimes called the "joint oil," though it is not
really oil.

Bones are covered with a tough skin, or membrane (_periosteum_). They
are hardest and most solid on their surfaces, and hollow, or spongy,
inside. The long bones of the limbs are hollow, and the cavity is filled
with a delicate fat called _marrow_--just as an elderberry stem or
willow-twig is filled with pith. This tubular shape makes them as strong
as if they were solid, and much lighter.[25]

The short, square, and flattened bones of the body, such as those of the
wrist, the skull, and the hips, instead of being hollow inside are
spongy; and the spaces in the bone-sponge are filled with a soft tissue
called the _red marrow_ in which new red and white corpuscles for the
blood are born, to take the place of those which die and go to pieces.

FOOTNOTES:

[24] You can easily prove that a bone is made up of living tissue soaked
and stiffened with lime, by putting it into a jar filled with weak acid.
This will gradually dissolve and melt out the lime salts, and then you
will find that the bone has lost three-fourths of its weight and that
what remains of it is so soft and flexible that it can be bent, or even
tied into a knot.

[25] The hollow spaces in the bones of birds, however, are filled with
air, which makes them lighter for flying.

CHAPTER XX

OUR TELEPHONE EXCHANGE AND ITS CABLES

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 true.

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
out.

[Illustration: THE NERVOUS SYSTEM

Diagram to show brain, spinal cord, and larger nerves.]

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.

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