Applied Physiology Part 7

_a_ larynx or voice box.

_b_ trachea or windpipe.

_d_ air sacs, each like a tiny frog's lung.]

Besides food, air is always getting into our bodies. In breathing, air pa.s.ses through the nose into a tube in the neck. This tube is called the _windpipe_. You can feel it as a pile of hard rings in the front part of the neck. The windpipe divides into many branches. At the end of its smallest branches are little bags or sacs. The branches and the sacs make the two lungs. So a lung is a soft and spongy piece of flesh, and can be blown up like a rubber bag. A frog's lung is a single, thin bag, about half an inch across it. Each little sac of a man's lung is like a tiny frog's lung.

[Ill.u.s.tration: =A frog's lung (4).=]

=101. The diaphragm.=--The lungs fill the upper part of the body just below the neck. They are covered by the bony ribs, and rest upon a broad muscle. This muscle is called the _diaphragm_. It divides the inside of the body into two parts. The upper part is the _chest_, and holds the heart and lungs. The lower part is the _abdomen_, and holds the stomach, intestine, and liver, and a few other parts.

[Ill.u.s.tration: =The parts inside the body.=

_a_ lungs.

_b_ heart.

_c_ diaphragm.

_d_ stomach.

_e_ liver.

_f_ intestine.]

=102. Breathing.=--When the diaphragm lowers itself, or the ribs are raised, the chest is made larger. Then the air rushes through the nose and swells out the lungs to the size of the chest. This is taking a breath. Then the chest becomes smaller again, and blows the air out.

A man breathes about eighteen times a minute. He does not seem to rest in breathing, but as he works only when he takes in breath, he rests one half of the time.

=103. How air gets into the blood.=--After the blood has been around the body through the arteries and capillaries and veins, the heart sends every drop to the lungs before it sends it out to feed the cells again.

The blood flows through little capillaries upon the sides of the air sacs. There the red blood cells take up some of the air, and carry it with them. When they have a load of air, they become of a brighter red color. The blood in the arteries on its way to the cells is bright red.

=104. How the cells get air.=--When the blood reaches the capillaries around the cells of the body, the red blood cells give up some of the air to the cells. Thus each cell of the body gets some air, and so it breathes. The cells cannot reach the air themselves, and so the red blood cells bring it to them. We breathe so as to supply the cells with air.

=105. What burning is.=--When meat is put into a hot stove it quickly burns, and pa.s.ses off in smoke, and leaves only a little ashes. The ashes are the mineral parts of the meat. If the fire is very hot, you cannot see the smoke. The burning of the meat makes heat. Heat in a steam engine makes the machine do work.

Every fire must have plenty of air. If air is shut off, the fire goes out. When meat burns, the air unites with the meat and makes smoke, and ashes, and gives out heat. Air unites with something in every fire.

=106. Burning inside the body.=--In every part of a man's body a very slow fire is always burning. The blood brings to the cells food from the intestine, and air from the lungs. The food and air join in a burning. The smoke goes back to the blood and is carried to the lungs, and breathed out with the breath. The ashes, also, go back to the blood, and are carried away by the skin and kidneys. The burning makes no flame or light for it goes on very slowly. You cannot see the smoke, but you can feel the warmth of the burning. Some of the heat is turned to power, and gives the body strength to do work. The body is like a steam engine. It burns up all its food.

=107. How the body is warmed.=--The body is warmed by the slow burning in the cells. This burning keeps the body always at the same warmth.

On a hot summer's day you feel warmer than on a cold snowy morning.

But your body is no warmer. Only your skin is warmer.

If the skin is warm, the whole body feels warm, but if the skin is cold, the whole body feels cold. On a hot summer's day the heat is kept in the skin, and we feel warm. On a cold winter's day a great deal of heat pa.s.ses off from the skin, and we feel cold. Yet our bodies have the same warmth in winter as in summer.

=108. How the sweat keeps us cool.=--When your hands or feet are wet, they are cold. On a hot summer's day, your body becomes wet with sweat. This cools the body as if water were poured over it. So sweating keeps you from getting too warm, and from being sunstruck.

We are sweating all the time, but the sweat usually dries as fast as it forms. When we are too warm it comes out faster than it dries. On a winter's day we sweat only a little, and so we save the heat. But more heat pa.s.ses off from the skin into the cold air, and we do not grow warmer.

=109. Clothes.=--We wear clothes to keep the heat in the body. They do not make heat, but they keep it from going off. Wool and flannel clothes keep the heat in better than cotton. We wear woolen in the winter, and cotton in the summer.

Fur keeps in heat the best of all. In very cold lands only fur is worn.

Linen lets heat out easily. It makes good summer clothes.

=110. Where to wear the most clothes.=--The face and hands are kept warm by the blood and we do not cover them except in the coldest weather. Our feet are more tender and need to be covered enough to keep them warm. We ought to wear thick-soled shoes or rubbers in damp weather so as to keep the feet dry and warm. We ought to dry the stockings every night, for they will get wet with sweat.

The trunk of the body needs the most clothes. The legs ought to be kept warm, too. If the dress reaches only to the knee, thick underclothing is needed for the lower part of the leg.

Do not keep one part of the body warm while another part remains cold.

It is wrong to bundle the neck or wear too much clothing over any part of the body. It is also wrong to wear too little and be cold.

When you are moving about, you need less clothing than when you are sitting still. When you have worked until you are very warm, it is wrong to stop to cool off. When you stop, you ought to put on a thick coat or else go into the house. If you do not, you may be chilled and made weak so that you can easily catch cold or some other disease.

=111. Heating houses.=--In winter our bodies cannot make heat fast enough to keep us warm unless we put on a great deal of clothing. So we warm our houses. Our grandfathers used fireplaces, but these did not give out much heat. People now use stoves, but some use a furnace in the cellar, or heat the rooms by steam. Some use kerosene stoves, but they are not so good, for they make the air bad. A room should feel neither too warm nor too cold. It is of the right warmth when we do not notice either heat or cold.

=112. Change of air.=--After air has been breathed it is no longer fit for use. In an hour or two you would breathe all the air of a small room once if it were not changed. When the air is partly used, you feel dull and short of breath, and your head aches. As soon as you get out of doors, you feel better. Foul air of houses and meeting places often contains disease germs. It is necessary to change the air of all rooms often. You can do this by opening a door or window. It is a good plan to sleep with your bedroom window open, so as to get good air all night.

Air pa.s.ses in and out of every crack in the windows and doors. If only one person is in a room, this may make enough change of air. If many persons are in a room, you will need to change the air in other ways. You can do this by opening a door or window. Do not let the cold air blow upon any one, for it may help to make him catch cold, if the air of the room is impure. If we lower a window from the top, warm impure air may pa.s.s out above it without making a draft.

[Ill.u.s.tration: =Diagram of the natural ventilation of a room.=

The arrows show the direction of the air currents.]

You need fresh air at night as much as in the daytime. You need not be afraid of the night air, for it is good and pure like the day air. You ought to sleep with your window open a little. You ought to open the windows wide every morning and air your bed well. At night you ought to take off all your clothes and put on a night-dress. Then hang your clothes up to air and dry.

=113. When to air a room.=--When you first enter a room full of bad air it smells musty and unpleasant. But after you have been in the room a while, you get used to it. If, however, you go out of doors a minute and then come back, you will smell the bad air again. If the air smells bad, open a door or window until it is sweet again.

=114. How to breathe.=--When you run hard, the cells of your body use up all the air, and then you feel short of breath. While you run, burning goes on faster, and you feel warmer. You can work harder and longer if you can breathe in a great deal of air. You will also feel better and stronger for it. Then if you are sick, you will be able to get well more quickly. You ought to know how to breathe right.

_First_, you ought to breathe through your nose. Even when you run, you ought to keep your mouth closed.

_Second_, you should try to breathe deeply. You should take a very deep breath often, and hold it as long as you can. By practice you can learn to hold it a full minute.

_Third_, you ought to run, or do some hard work, every day. When you get short of breath, you will have to breathe more deeply. After a while you may be able to run a half mile, or even a mile, without getting out of breath. But do not get tired out in your run, for this will harm you.

_Fourth_, you must sit and stand with your shoulders back, and your chest thrown forward. A round-shouldered boy cannot have large lungs or be long winded.

By breathing right, you can make your lungs very much larger and stronger.

=115. The voice.=--We talk by means of the breath. At the upper part of the windpipe is a small box. Its front corner can be felt in the neck, just under the chin, and is called the _Adam's apple_. Two thin, strong covers slide across the top of the box, and can be made to meet in the middle. The covers have sharp edges. When they are near together, and air is breathed out between them, a sound is made. This sound is the _voice_. The tongue and lips change it to form _words_.

=116. Care of the voice.=--The voice shows our feelings, even if we do not tell them in words. We can form a habit of speaking in a loud and harsh tone, as if we were always angry, or we can speak gently and kindly. We shall be more pleasant company to others if we are careful always to speak in gentle but distinct tones.

[Ill.u.s.tration: =Top view of the larynx, with the vocal cords closed, as in speaking.=

_a_ epiglottis.

_b_ vocal cords.]

[Ill.u.s.tration: =Top view of the larynx, with the vocal cords open, as in breathing.=

_a_ epiglottis.

_b_ vocal cords.]

Shouting strains the voice and spoils its tone for singing. Reading until the throat is tired makes the voice weak. Singing or shouting in a cold or damp air is also bad for the voice. Breathing through the mouth is the worst of all for the voice.