MUSCLES.
[Illustration: W]HAT makes the limbs move?
You have to take hold of the door to move it back and forth; but you
need not take hold of your arm to move that.
What makes it move?
Sometimes a door or gate is made to shut itself, if you leave it open.
This can be done by means of a wide rubber strap, one end of which is
fastened to the frame of the door near the hinge, and the other end to
the door, out near its edge.
When we push open the door, the rubber strap is stretched; but as soon
as we have passed through, the strap tightens, draws the door back, and
shuts it.
If you stretch out your right arm, and clasp the upper part tightly with
your left hand, then work the elbow joint strongly back and forth, you
can feel something under your hand draw up, and then lengthen out again,
each time you bend the joint.
What you feel, is a muscle (m[)u]s'sl), and it works your joints very
much as the rubber strap works the hinge of the door.
One end of the muscle is fastened to the bone just below the elbow
joint; and the other end, higher up above the joint.
When it tightens, or contracts, as we say, it bends the joint. When the
arm is straightened, the muscle returns to its first shape.
There is another muscle on the outside of the arm which stretches when
this one shortens, and so helps the working of the joint.
Every joint has two or more muscles of its own to work it.
Think how many there must be in our fingers!
If we should undertake to count all the muscles that move our whole
bodies, it would need more counting than some of you could do.
TENDONS.
You can see muscles on the dinner table; for they are only lean meat.
[Illustration: _Tendons of the hand._]
They are fastened to the bones by strong cords, called tendons
(t[)e]n'd[)o]nz). These tendons can be seen in the leg of a chicken or
turkey. They sometimes hold the meat so firmly that it is hard for you
to get it off. When you next try to pick a "drum-stick," remember that
you are eating the strong muscles by which the chicken or turkey moved
his legs as he walked about the yard. The parts that have the most work
to do, need the strongest muscles.
Did you ever see the swallows flying about the eaves of a barn?
Do they have very stout legs? No! They have very small legs and feet,
because they do not need to walk. They need to fly.
The muscles that move the wings are fastened to the breast. These breast
muscles of the swallow must be large and strong.
EXERCISE OF THE MUSCLES.
People who work hard with any part of the body make the muscles of that
part very strong.
The blacksmith has big, strong muscles in his arms because he uses them
so much.
You are using your muscles every day, and this helps them to grow.
Once I saw a little girl who had been very sick. She had to lie in bed
for many weeks. Before her sickness she had plenty of stout muscles in
her arms and legs and was running about the house from morning till
night, carrying her big doll in her arms.
After her sickness, she could hardly walk ten steps, and would rather
sit and look at her playthings than try to lift them. She had to make
new muscles as fast as possible.
Running, coasting, games of ball, and all brisk play and work, help to
make strong muscles.
Idle habits make weak muscles. So idleness is an enemy to the muscles.
There is another enemy to the muscles about which I must tell you.
WHAT ALCOHOL WILL DO TO THE MUSCLES.
Muscles are lean meat. Fat meat could not work your joints for you as
the muscles do. Alcohol often changes a part of the muscles to fat, and
so takes away a part of their strength. In this way, people often grow
very fleshy from drinking beer, because it contains alcohol, as you will
soon learn. But they can not work any better on account of having this
fat. They are not really any stronger for it.
REVIEW QUESTIONS.
1. How are the joints moved?
2. Where are the muscles in your arms, which help
you to move your elbows?
3. Show why joints must have muscles.
4. What do we call the muscles of the lower
animals?
5. What fasten the muscles to the bones?
6. Why do chickens and turkeys need strong muscles
in their legs?
7. Why do swallows need strong breast muscles?
8. What makes the muscles of the blacksmith's arm
so strong?
9. What will make your muscles strong?
10. What will make them weak?
11. What does alcohol often do to the muscles?
12. Can fatty muscles work well?
13. Why does not drinking beer make one stronger?