First Book In Physiology And Hygiene Part 12

This causes the legs to become crooked. In some countries young children work in factories and at various trades. This is wrong, because it dwarfs their growth, and makes them puny and sickly.

~3. Improper Positions.~--The bones are so soft and flexible when we are young that they are very easily bent out of shape if we allow ourselves to take improper positions in sitting, lying, or standing.

This is the way in which flat and hollow chests, uneven shoulders, curved spines, and many other deformities are caused.

[Ill.u.s.tration: IMPROPER POSITION.]

~4.~ In sitting, standing, and walking, we should always take care to keep the shoulders well back and the chest well expanded, so that we may not grow misshapen and deformed. Many boys and girls have ugly curves in their backbones which have been caused by sitting at high desks with one elbow on the desk, thus raising the shoulder of that side so high that the spine becomes crooked. The ill.u.s.trations on this and the following page show good and bad positions and also the effects of bad positions.

[Ill.u.s.tration: PROPER POSITION.]

~5. Seats and Desks.~--The seats and desks of school-children should be of proper height. The seats should be low enough to allow the feet to rest easily upon the floor, but not too low. The desk should be of such a height that, in writing, one shoulder will not be raised above the other. If a young person bends the body forward, he will, after a time, become round-shouldered and his chest will become so flattened that the lungs cannot be well expanded.

[Ill.u.s.tration: DESK TOO HIGH.]

~6.~ Standing on one foot, sitting bent forward when reading or at work, sleeping with the head raised high upon a thick pillow or bolster, are ways in which young persons often grow out of shape.

[Ill.u.s.tration: SEAT TOO HIGH.]

~7. The Clothing.~--Wearing the clothing tight about the waist often produces serious deformities of the bones of the trunk, and makes the chest so small that the lungs have not room to act properly. Tight or high-heeled shoes also often deform and injure the feet and make the gait stiff and awkward.

~8. Broken Bones.~--By rough play or by accident the bones may be broken in two just as you might break a stick. If the broken parts are placed right, Nature will cement them together and make the bone strong again; but sometimes the bones do not unite, and sometimes they grow together out of proper shape, so that permanent injury is done.

~9. Sprains.~--In a similar manner the ligaments which hold the bones together, in a joint, are sometimes torn or over-stretched. Such an accident is called a sprain. A sprain is a very painful accident, and a joint injured in this way needs to rest quite a long time so that the torn ligaments may grow together.

~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.

[Ill.u.s.tration: 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.