10.  Bones out of Joint.—­Sometimes the ligaments are torn so badly that the ends of the bones are displaced, and then we say they are put out of joint.  This is a very bad accident indeed, but it often happens to boys while wrestling or playing at other rough games.

11. Children sometimes have a trick of pulling the fingers to cause the knuckles to “crack.”  This is a very foolish and harmful practice.  It weakens the joints and causes them to grow large and unsightly.

12. When a man uses alcohol and tobacco, their effects upon the bones are not so apparent as are the effects upon the blood, the nerves, and other organs; but when the poisonous drugs are used by a growing boy, their damaging influence is very plainly seen.  A boy who smokes cigars or cigarettes, or who uses strong alcoholic liquors, is likely to be so stunted that even his bones will not grow of a proper length and he will become dwarfed or deformed.

SUMMARY.

1.  To keep the bones healthy they must have plenty of healthful food.

2.  The whole-grain preparations furnish the best food for the bones.

3.  Walking at too early an age often makes the legs crooked.

4.  Hard work at too early an age stunts the growth.

5.  Bad positions and tight or poorly-fitting clothing are common causes of flat chests, round shoulders, and other deformities.

6.  Tight or high-heeled shoes deform the feet and make the gait awkward.

7.  The bones may be easily broken or put out of joint, or the ligaments may be torn by rough play.

8.  Alcohol prevents healthy growth.

CHAPTER XX.

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.