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This eBook from the Gutenberg Project consists of approximately 124 pages of information about First Book in Physiology and Hygiene.

[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.

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