THE MUSCLES AND HOW WE USE THEM.
~1. The Muscles.~--Where do people obtain the beefsteak and the
mutton-chops which they eat for breakfast? From the butcher, you will
say; and the butcher gets them from the sheep and cattle which he kills.
If you will clasp your arm you will notice that the bones are covered by
a soft substance, the flesh. When the skin of an animal has been taken
off, we can see that some of the flesh is white or yellow and some of it
is red. The white or yellow flesh is fat. The red flesh is lean meat,
and it is composed of muscles.
~2. The Number of Muscles.~--We have about five hundred different
muscles in the body. They are arranged in such a way as to cover the
bones and make the body round and beautiful. They are of different forms
and sizes.
~3.~ With a very few exceptions the muscles are arranged in pairs; that
is, we have two alike of each form and size, one for each side of the
body.
~4. How a Muscle is Formed.~--If you will examine a piece of corned or
salted beef which has been well boiled, you will notice that it seems to
be made up of bundles of small fibres or threads of flesh. With a little
care you can pick one of the small fibres into fine threads. Now, if you
look at one of these under a microscope you find that it is made of
still finer fibres, which are much smaller than the threads of a
spider's web. One of these smallest threads is called a _muscular
fibre_. Many thousands of muscular fibres are required to make a muscle.
[Illustration: MUSCULAR FIBRES.]
~5.~ Most of the muscles are made fast to the bones. Generally, one end
is attached to one bone, and the other to another bone. Sometimes one
end is made fast to a bone and the other to the skin or to other
muscles.
~6. The Tendons.~--Many of the muscles are not joined to the bones
directly, but are made fast to them by means of firm cords called
_tendons_. If you will place the thumb of your left hand upon the wrist
of the right hand, and then work the fingers of the right hand, you may
feel these cords moving underneath the skin.
~7. What the Muscles Do.~--With the left hand grasp the right arm just
in front of the elbow. Now shut the right hand tightly. Now open it.
Repeat several times. The left hand feels something moving in the flesh.
The motion is caused by the working of the muscles, which shorten and
harden when they act.
~8.~ All the movements of the body are made by means of muscles. When we
move our hands, even when we close the mouth or the eyes, or make a wry
face, we use the muscles. We could not speak, laugh, sing, or breathe
without muscles.
~9. Self-acting Muscles.~--Did you ever have a fit of sneezing or
hiccoughing? If you ever did, very likely you tried hard to stop but
could not. Do you know why one cannot always stop sneezing or
hiccoughing when he desires to do so? It is because there are certain
muscles in the body which do not act simply when we wish them to act,
but when it is necessary that they should. The muscles which act when we
sneeze or hiccough are of this kind. The arm and the hand do not act
unless we wish them to do so. Suppose it were the same with the heart.
We should have to stay awake all the while to keep it going, because it
would not act when we were asleep. The same is true of our breathing. We
breathe when we are asleep as well as when we are awake, because the
breathing muscles work even when we do not think about them.
~10.~ The stomach, the intestines, the blood-vessels, and many other
organs within the body have this kind of muscles. The work of these
self-acting muscles is very wonderful indeed. Without it we could not
live a moment. This knowledge should lead us to consider how dependent
we are, each moment of our lives, upon the delicate machinery by which
the most important work of our bodies is performed, and how particular
we should be to keep it in good order by taking proper care of
ourselves.
SUMMARY.
1. The flesh, or lean meat, is composed of muscles.
2. There are five hundred muscles in the body.
3. Muscles are composed of many small threads called muscular fibres.
4. Many of the muscles are joined to the bones by strong white cords
called tendons.
5. Muscular fibres can contract so as to lessen their length. It is in
this way that the muscles perform their work.
6. All bodily motions are due to the action of the muscles.
7. Most of the muscles act only when we wish them to do so. Some
muscles, however, act when it is necessary for them to do so, whether we
will that they should act or not, and when we are asleep as well as when
we are awake.