Applied Physiology Part 9

First, it takes heat away from the body (see -- 108). Second, it gets rid of the waste matters or ashes of the body. It has very little of these at any one time, but in a day it gets rid of a great deal.

=129. The kidneys.=--The kidneys are close to the backbone, below the heart. They are made of tiny tubes much like the sweat tubes in the skin. The tubes take ashes and other waste matters from the blood, also a great deal of water. They also take away poisons and disease germs when we are sick. The kidneys take away about as much water as the skin, but they get rid of very much more poisons and waste matters than the skin does. If our kidneys should stop their work, we should soon die.

=130. Need of bathing.=--When the perspiration dries from the skin, it leaves the waste and poisons behind. We cannot always see the dried matters, but they always have an unpleasant odor. We should bathe often enough to keep our body from having an unpleasant smell. We should wash the whole body with soap and hot water at least once a week in winter and more often than that in summer.

Another reason for bathing is to wash disease germs from the body.

Most dirt has disease germs in it. Disease germs also float in the dust of the air and stick to our skin when we go into a dusty room. If our skin is dirty, some of the germs may be carried into our flesh when our skin is p.r.i.c.ked, or scratched, or cut. We sometimes catch boils, or erysipelas, or lockjaw, from very little wounds in a dirty skin. Cleanliness of our skin helps to keep us from catching diseases.

=131. Cold baths.=--Sometimes we bathe when we are clean so as to get refreshed. If we bathe in cold water, we feel cold at first. In a little while we feel warm again. Then we feel stronger, and refreshed for work. If we stay in the bath too long, we become cold again and feel weak. When boys go in swimming, they ought to come out before they begin to feel cold.

It is a good plan to take a cold bath every morning when you get up, even if you use only a wash-bowl with a little water. It will take only a few minutes, but will keep you clean and make you feel more like doing your day's work.

=132. A fair skin.=--We must wash often, to make the skin fair and smooth. Use enough good soap to keep the skin clean.

If you eat as you should, and digest the food well, your skin will have the least amount of waste to give off. Then it will look well. A bad looking skin is due to bad food and to bad digestion. If you do not digest your food well, you cannot have a fair skin.

Face paint and powder make the skin look worse, for they hinder perspiration. Nothing of that sort will do the skin any good. You must eat as you should, and you must keep clean. Then your skin will be clear.

=133. Was.h.i.+ng clothes.=--Our clothes rub off a great deal of the perspiration and waste. They become soiled. A great deal of dirt also gets upon the sheets of our beds. Our clothes need to be washed as well as our bodies when they are soiled. Air and the sun as well as water destroy the waste of the body. Our clothes need to be aired at night, and the bed and bedroom should be aired through the day.

=134. Slops.=--After water has been used to wash our body or our clothes it is dirty and is not fit to be used again. It must not be thrown where it can run into a well. If a person has typhoid fever or cholera or other catching disease, the water may carry germs of the disease to the well, and so other persons may get it. Slops from the house should not be poured out at the back door, but they should be carried away from the house. In cities the slops are poured into large pipes and tunnels underground. These pipes are called _sewers_. They empty outside the city.

=135. Alcohol and the skin.=--Alcohol interferes with digestion and causes biliousness. This makes the skin rough and pimply. A drinker seldom has a clear skin.

Alcohol causes the arteries of the face to become enlarged. Then the face is red. A red nose is one of the signs of drinking. When a person uses strong drink he is often uncleanly. He does not care for the bad looks of his clothes and skin, and so he lets them stay dirty. This harms the skin and makes it look bad. The dirt also poisons the skin and may itself be a cause of sickness.

Because alcohol poisons the whole body and often produces kidney diseases, the drinker is apt to catch other diseases. Drinkers are the first to catch such diseases as smallpox and yellow fever. Where there are great numbers of cases, the drinkers are the first and often the only persons to die. This is because their skin and kidneys have been harmed by the alcohol and cannot throw off the poisons of the disease.

Any kind of sickness will be worse in a drinker. Surgeons do not like to operate on drinkers, for their wounds do not heal so quickly as in other people.

When there is too little air, a fire burns slower, and makes a blacker smoke and more ashes. Alcohol takes some air from the cells of the body. So they burn with smoke and ashes of the wrong kind. The skin has to work harder to get rid of these, and sometimes it cannot do it well. Then the body is poisoned. The alcohol is burned and cannot poison the body any more. But it causes the body to make poisons, and so it is to blame. The poisons do great harm to the skin and kidneys.

Alcohol causes more kidney disease than all other things put together.

WHAT WE HAVE LEARNED

1. Little tubes in the skin are always giving off ashes and waste matters in the perspiration.

2. Perspiration dries on the skin. So the skin must be washed often.

3. The kidneys get rid of more water and waste matter than the skin does.

4. Perspiration also gets upon the clothes and bed sheets. These must be washed too.

5. Dirty water from was.h.i.+ng should be thrown out where it cannot run into a well.

6. The skin is thick and strong and keeps the body from being hurt.

7. The skin is covered with a layer of scales. The scales have no feeling.

8. The scales form the nails on the ends of the fingers.

9. The scales also form the hair.

CHAPTER XII

THE NERVES, SPINAL CORD, AND BRAIN

=136. Need of nerves.=--The cells of the mouth, stomach, and intestine digest food; the cells of the liver change the food to blood; the cells of the heart pump the blood to feed all the cells of the body; the red blood cells carry air for the cells to breathe; and the cells of the skin and kidneys carry away the waste of the rest of the cells.

Each set of cells works for all the rest. If the cells of the body were only tied together, each one would do as it pleased, and no two would work together. But something tells each cell of the body to work with the others. The cells all obey the mind. A tiny thread goes to each cell of the body. Each thread is a _nerve_. The mind and the cells signal to each other over the nerves. By means of the nerves the mind makes the cells work together.

[Ill.u.s.tration: =A nerve thread (400).=

_a_ central conducting fiber.

_b_ covering of fat.]

[Ill.u.s.tration: =A thin slice for the end of a cut nerve (200).=

_a_ nerve thread.

_b_ connective tissue binding the threads into a cord.]

=137. Nerve messages.=--The nerve threads run in bundles and form nerves large enough to be seen. The mind uses the nerves to tell the cells to do work. It tells the muscles to move the arms and legs. It tells the heart to beat and stomach to pour out gastric juice; and it tells each of the cells to eat.

The cells also send word over the nerves to the mind. They tell the mind when they are touching anything, and whether it is hard, or smooth, or hot, and many other things about it. The cells also tell the mind if they need more food, or are tired.

The nerves are always carrying messages to and from the cells. The cells depend upon these messages to tell them when and how to work. If the nerve of any part of the body is hurt or cut, we cannot feel with the part or move it, and its cells do not act in the right way. We do not feel the nerves while they are carrying the messages. We wish the cells of the arm to work, and they work, but we do not feel the message as it goes from the mind to the cells of the arm.

[Ill.u.s.tration: =A thin slice from the spinal cord with the cells and nerves magnified 200 diameters.=

_a_ cells in the gray matter.

_b_ fibers in the gray matter.

_c_ nerve threads in the white matter.]

=138. The spinal cord.=--The nerves start inside the backbone. The backbone is hollow. It has a soft, white cord inside, as thick as the little finger. Part of the mind lives in this cord. The cord is called the _spinal cord_. Some of the nerves start from cells of the spinal cord. These cells send word to the muscles to move and to all the cells of the body to eat and grow. They also send word to the arteries to carry the right amount of blood to the cells.

From the nerves the spinal cord gets word when something hurts any part of the body. You may put your finger on a sharp pin. The spinal cord feels the p.r.i.c.k, and quickly sends word to s.n.a.t.c.h the finger away. So the finger is taken away before you really feel the p.r.i.c.k.

When some one sticks a pin into you, you cannot help jumping. This is because the spinal cord sends word for you to jump away from the pin before it can harm you much. Thus the spinal cord keeps the body from being hurt. It acts while we are asleep as well as when we are awake.

=139. Need of a spinal cord.=--We do not feel the spinal cord acting, and we cannot keep it from acting. It tells the cells when to eat and grow, and it tells the heart and arteries how much blood to send to each cell. If we had to think about feeding an arm or a leg, we should sometimes forget it, but the spinal cord keeps doing it without our thinking of it. We put food into the body, and the spinal cord tells the cells to use it. If it stops acting for an instant, the cells stop work and we die. We cannot change its action by any amount of thinking.

[Ill.u.s.tration: =Regions of the head and action of the different parts of the brain.=]

=140. The brain.=--The nerves of the body go to the brain as well as to the spinal cord. The brain lies in the top of the head. A hard cover of bone keeps it from getting hurt. It is a soft white ma.s.s, and weighs about three pounds. Its outside is made of cells, while its inside is the very beginning of the nerves of the body.

=141. The mind.=--The mind is the real man. It is the thinking part of himself. It lives in the body and works by means of the cells of the brain. If these cells are hurt or killed, the body seems to have no mind, but yet it may keep on living. If all the mind leaves the body, the body is dead.