MUSCLES
=187. Shape of muscles.=--Bones are covered with muscles. Muscles give
shape to the body, and move it about. One half of the body consists of
muscles. These are arranged in bundles, and each causes a bone to make
one motion. There are over four hundred separate bundles of muscle in
the body.
One end of a muscle is large and round and is fast to a bone. The
other end tapers to a strong string or tendon. The tendon passes over
a joint, and becomes fast to another bone. You can easily feel the
tendons in the wrist and behind the knee.
[Illustration: =Muscle cells, cut across (x200).=
_a_ muscle cell.
_b_ connective tissue binding the cells together.]
A muscle is made of tiny strings. You can pick them apart until they
are too fine to be seen with the eye. Each string is a living muscle
cell. It is the largest kind of cell in the body. You can see the fine
strings in cooked meat.
[Illustration: =A thin slice of a voluntary muscle, cut lengthwise
(x100).=
_a_ muscle cell.
_b_ capillaries surrounding the cells.
_c_ connective tissue binding the cells together.]
=188. How muscles act.=--A nerve runs from the brain, and touches
every cell of the muscle. When we wish to move, the brain sends an
order down the nerve. Then each muscle cell makes itself thicker and
shorter. This pulls its ends together, and bends the joint. We can
make muscle cells move when we wish to, but we cannot make any other
kind of cell move. We make all our movements by means of our muscles.
=189. Where you can see muscles.=--In a butcher's shop you can see lean
meat. This is the animal's muscle. White and tough flesh divides the
tender red meat into bundles. Each red bundle is a muscle. You will see
how the muscle tapers to a string or tendon. The butcher often hangs up
the meat by the tendons. You can see the muscles and tendons in a
chicken's leg or wing when it is being dressed for dinner.
Roll up your sleeve to see your own muscles. Shut your hand tight. You
will see little rolls under your skin, just below the elbow. Each roll
is a muscle. You can feel them get hard when you shut your hand. You
can feel their tendons as they cross the wrist.
Open your hand wide. You can see and feel the tendons of the fingers
upon the back of the hand. These tendons come from muscles on the back
of the arm. You can feel the bundles of these muscles when they open
the fingers. There are no muscles in the fingers, but all are in the
hand or arm. You cannot open your hand so strongly as you can close it.
=190. Strength of muscle.=--By using a muscle you can make it grow
larger and stronger. If you do not use your muscles they will be small
and weak. Children ought to use their muscles in some way, but if they
use them too much, they will be tired out. Then they will grow weaker
instead of stronger. Lifting heavy weights, or running long distances,
tires out the muscles, and makes them weaker. Small boys sometimes try
to lift as much as the big boys. This may do their muscles great harm.
=191. Round shoulders.=--The muscles hold up the back and head, and
keep us straight when we sit or stand. A lazy boy will not use his
muscles to hold himself up, but will lean against something. He will
let his shoulders fall, and will sit down in a heap. Sometimes he is
made to wear shoulder braces to keep his shoulders back. This gives
the muscles nothing to do, and so they grow weaker than ever. The best
thing to do for round shoulders is to make the boy sit and stand
straight, like a soldier. Then he will use his muscles until they are
strong enough to hold his shoulders back.
=192. How exercise makes the body healthy.=--When you use your
muscles, you become warmer. Your face will be red, for the heart sends
more blood to the working muscle cells. You will be short of breath,
for the cells need more air. You will eat more, for your food is used
up. Your muscles are like an engine. They get their power from burning
food in their own cells. When they work they need to use more food and
air. So working a muscle makes us eat more and breathe deeper. The
blood flows faster, and we feel better all over. The muscle itself
grows much larger and stronger.
If we sit still all day, the fires in our bodies burn low and get
clogged with ashes. We feel dull and sleepy. If we run about for a few
minutes, we shall breathe deeply. The fires will burn brighter. Our
brains will be clearer, and we shall feel like work again. Boys and
girls need to use their muscles when they go to school. Games and play
will make you get your lessons sooner.
=193. How to use the muscles.=--You should use your muscles to make
yourself healthy, and not for the sake of growing strong. Some very
strong men are not well, and some men with small muscles are very
healthy. Some boys have strong muscles because their fathers had
strong muscles before them. Strength of muscle does not make a man.
You ought to have healthy muscles. Then your whole bodies will be
healthy, and you can do a great deal of work. You ought to learn how
to use your muscles rather than how to make them strong. An awkward
and bashful boy may be very strong, but he cannot use his muscles. A
boy is graceful because he can use them.
The best way to use your muscles is in doing something useful. You can
help your mother in the house and your father at the barn. You can run
errands. You can learn to use carpenter's tools or to plant a garden.
Then you will get exercise and not know it. You will also be learning
something useful.
Play is also needed. Work gets tiresome, and you will not want to use
your muscles. Play is bad when it takes you from your work or when you
hurt yourself trying to beat somebody.
=194. Alcohol and the muscles.=--Men use alcohol to make themselves
strong. It dulls their weak feelings, and then they think themselves
strong. They are really weaker. The alcohol hinders digestion and
keeps food from the cells. Then the fires in the body burn low, and
there is little strength.
Alcohol sometimes causes muscle cells to change to fat. This weakens
the muscles.
Men sometimes have to do hard work in cold countries; and at other
times they must make long marches across hot deserts. Neither the
Eskimos in the cold north, nor the Arabs in the hot desert, use strong
drink. Alcohol does not help a man in either place. It really weakens
the body. The government used to give out liquor to its soldiers; but
soldiers can do more work and have better health without liquor and it
is no longer given out.
A few years ago men were ashamed to refuse to drink. Even when a new
church building was raised, rum was bought by the church and given to
the workmen. Farmers used to give their men a jug of rum when they
went to work. Farm hands would not work without it.
Now all this has changed. Men do not want drinkers to work for them. A
railroad company will discharge a man at once if he is known to drink
at all. A man can now refuse to drink anywhere and men will not think
any less of him.
=195. Tobacco= poisons the muscle cells and makes them weak. At first
it makes boys too sick to move. It always poisons the cells even if
they do not feel sick.
=196. A long life.=--A man's body is built to last eighty years, but
only a few live so long. If you are careful in your eating and
drinking, if you breathe pure air, and if you use your muscles, your
body will be healthy and will last the eighty years and more. All
through your life you will be strong and able to do good work.
WHAT WE HAVE LEARNED
1. Muscles cover the bones and move the body.
2. Muscle is lean meat. It is made of bundles of cells like
strings. Nerves from the brain touch each cell.
3. Each muscle is fast to a bone. It becomes a small string or
tendon at the other end. The tendon crosses a joint and is
fast to another bone.
4. When we wish to move, the brain sends an order to the muscle
cells to make themselves thicker and shorter and so bend the
joint.
5. You can feel the muscles and tendons in the arm and wrist.
6. Muscle work makes us breathe deeper, and eat more food. It
makes the blood flow faster. So it makes our whole bodies
more healthy.
7. Every one ought to use his muscles some part of the day.
8. Alcohol and tobacco lessen the strength of the muscles.