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a bell jar. Pass a glass tube through a rubber stopper. Fasten a small toy balloon to the lower end of the tube. Close the small end of the jar with the stopper. Adjust the tube so that the balloon shall hang free in the jar. If now the rubber sheet is pulled down by means of the string, the air pressure in the jar is reduced and the toy balloon within expands, owing to the air pressure down the tube. When the rubber is allowed to go back to its former position, the balloon collapses.

COUGHING, SIGHING, AND SNEEZING. — Coughing is a sudden strong expiration, with the glottis (or top of the windpipe) closed. A sigh is a quick inspiration followed by a quiet expiration. A sneeze is a sharp expiration, the air passing through the nose because the passage to the mouth is closed by the descent of the soft palate.

RATE OF BREATHING AND AMOUNT OF AIR BREATHED. - During quiet breathing, the rate of inspiration is from fifteen to eighteen times per minute; this rate largely depends on the amount of physical work performed. About thirty cubic inches of air are taken in and expelled during the ordinary quiet respiration. The air so breathed is called tidal air. In a "long breath," we take in about 100 cubic inches in addition to the tidal air. This is called complemental air. By means of a forced expiration, it is possible to expel from 75 to 100 cubic inches more than tidal air; this air is called reserve air. What remains in the lungs, amounting to about 100 cubic inches, is called the residual air. (See diagram, page 384.) The value of deep breathing is seen by a glance at the diagram. It is only by this means that we clear the lungs of the reserve air with its accompanying load of carbon dioxide.

The actual amount of oxygen used in the body during the course of a day is nearly 25 ounces; this being almost entirely used in oxidizing the food materials taken into the body during the 24 hours.

RESPIRATION UNDER NERVOUS CONTROL. -The muscular movements which cause an inspiration are partly under the control of the will, but in part the movement is beyond our control. The nerve centers which govern inspiration are part of the sympathetic nervous system of which we shall learn later. That the sympathetic nervous system controls respiratory movements is seen, for example, in the involuntary short breath taken by the bather who plunges into cold water. Anything of an irritating nature in the trachea or larynx will cause a sudden expiration or cough. When a boy runs, the quickened respiration is due to the fact that oxygen is used up rapidly and a larger quantity of carbon dioxide is formed. These facts, together with the presence of certain other poisonous materials in the lung cells, stimulate the nervous center which has control of respiration to greater activity, and quickened inspiration follows.

EXPERIMENTS TO DETERMINE CHANGES UNDERGONE BY AIR IN THE LUNGS.—1. Breathe on the bulb of a thermometer and record any changes. 2. Breathe gently on any polished glass or metal surface. Note what happens.

3. Take a moderate breath, and force air (tidal air) through limewater. Notice what occurs.

4. Force the last part of a deep expiration (reserve air) through limewater. Note result. What is one reason for deep breathing?

Changes in Air in the Lungs. - Air is much warmer after leaving the lungs than before it enters them. Expired air contains a considerable amount of moisture, which it has taken up in the air sacs of the lungs. The presence of carbon dioxide may easily be detected in expired air. Air such as we breathe. out of doors, contains, by volume:



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Loss FROM THE LUNGS.-A man breathes about 540 cubic inches of air per minute; this would make a total of something over 770,000 cubic inches in twenty-four hours. Of this air, about 4 per cent is carbon dioxide, the amount varying with the amount and kind of work performed. There would be at least 31,000 cubic inches of carbon dioxide expired in twentyfour hours; this amount weighs nearly thirty ounces. The amount of water evaporated by the lungs in twenty-four hours is estimated at half a pint, so the lungs are a source of actual loss in body weight.

Changes in the Blood within the Lungs. Blood, after leaving the lungs, is much brighter red than just before entering them. The change in color is due to a taking up of oxygen by the hamoglobin of the red corpuscle. Changes taking place in blood are obviously the reverse of those which take place in air in the lungs. Blood in the capillaries within the lungs gains from four to five per cent of oxygen which the air loses. At the same time blood loses the four per cent of carbon dioxide which the air gains. The water given off is mostly lost from the blood.

Tissue Respiration. It has been found, in the case of very simple animals, such as the amaba, that when oxidation takes place in a cell, work or making of protoplasm results from this oxidation. The oxygen taken into the lungs is not used there, but is carried by the blood to such parts of the body as need oxygen to oxidize food materials either in the performance of work or the building of tissues. The quantity of oxygen used by the body is nearly dependent on the amount of work performed. From twenty to twenty-five ounces is taken in and used by the body every day. Oxygen is constantly taken from the blood by tissues in a state of rest. This oxygen is used up when the body is at work. This is proved by the fact that in a given time a man, when working, gives off more carbon dioxide than the oxygen he has taken in during that time.

Diagram to show the respiration of cells.

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Carton dioxide

"Alcohol interferes with the Respiration of the Cells.-Alcohol is quickly absorbed from the stomach and intestine and as quickly disappears. After it is taken, little or no alcohol, or any substance like alcohol, or any substance containing so little oxygen as alcohol, can be found in any waste of the body. Hence the inference is that it must be oxidized, although the exact point and the manner of its oxidation may not be known. But the evidence for its oxidation is the same as that for the oxidation of sugar.


Every ounce of alcohol requires nearly two ounces of oxygen to oxidize it fully. Taking twenty-five ounces of oxygen gas as the amount used in a day, there will be only one ounce used in an hour. So to oxidize an ounce of alcohol takes an amount of oxygen equal to the whole supply of the body for two hours. Three or four drinks of whisky contain this ounce of alcohol. If this amount is drunk, there will soon be a lessened action and a narcotic effect throughout the body, due mainly to the lack of oxygen. A noticeable degree of uncertain action is called intoxication.

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"Using alcohol in the body is like burning kerosene in a coal stove. By taking great care a little kerosene can be made to give out some heat from the stove, but the operation is dangerous. Some people seem to oxidize alcohol within the body with but little harm; but they run great risks of doing themselves harm, and the result is not nearly so good as if they had used proper food.

"Poisons produced by Alcohol. — When too little oxygen enters the draft of the stove, the wood is burned imperfectly, and there are clouds of smoke and irritating gases. So, if oxygen goes to the alcohol and too little reaches the cells, instead of carbonic acid gas, and water, and urea being formed, there are other products, some of which are exceedingly poisonous and which the kidneys handle with difficulty. The poisons retained in the circulation never fail to produce their poisonous effects, as shown by headaches, clouded brain, pain, and weakness of the body. The word intoxication means, 'in a state of poisoning.' These poisons gradually accumulate as the alcohol takes oxygen from the cells. The worst effects come last, when the brain is too benumbed to judge fairly of their harm. It is not true that alcohol in a small amount is beneficial. A little is too much, if it takes oxygen which would otherwise be available to oxidize wholesome food. "Effects of Tobacco. Tobacco smoke contains the same kind of poisons as the tobacco, with other irritating substances added. It is usually sucked into the mouth and at once blown out again, but cigarette smoke is commonly drawn into the lungs and afterwards blown out through the nose. It is irritating to the throat,

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causing a cough and rendering it more liable to inflammation If inhaled into the bronchi, it produces still greater irritation, and the vaporized nicotine is more readily absorbed as the smoke is inhaled the more deeply. Cigarettes contain the same poisons as other forms of tobacco, and often contain other poisons which are added to flavor them."-OVERTON, Applied Physiology.

NEED OF VENTILATION.-During the course of a day the lungs have lost to the surrounding air nearly two pounds of carbon dioxide. This means that about three fifths of a cubic foot is given off from each person during an hour. When we are confined for some time in a room, it becomes necessary to get rid of this carbon dioxide. This can be done only by means of proper ventilation. Other materials are passed off from the lungs, with carbon dioxide. It is the presence of these wastes in combination with carbon dioxide that makes breathed air particularly unwholesome. It has been determined that as little as one per cent carbon dioxide is injurious in expired air, although a much greater percentage than this may be safely breathed if the carbon dioxide is introduced into fresh air. The presence of impurities in the air of a room may easily be determined by its odor. The "close" smell of a poorly ventilated room is due to organic impurities given off with the carbon dioxide. This, fortunately, gives us an index by which we may prevent poisoning. Air containing 8 parts of carbon dioxide to 10,000 parts of air is bad; while from 12 to 14 parts in 10,000 makes a very dangerous amount. Among the factors which take oxygen from the air in a closed room and produce carbon dioxide, are burning gas or oil lamps, stoves, the presence of a number of people, etc.

Proper Ventilation. - Ventilation consists in the removal of air that has been used, and the introduction of a fresh supply to take its place. If we remember that warm air is lighter than cold air, and carbon dioxide is heavier than air, we can see that ventilation outlets should be on the level of the floor. The inlets should be near the top of the room, especially in houses heated by any method of direct radiation, such as steam or hot water. A good method of ventilation for the home is obtained by placing a board two or three inches high between the lower sash and the frame of a window.

Sweeping and Dusting. It is very easy to demonstrate the amount of dust in the air by following the course of a beam of light in a darkened room. We have already proved that spores of mold and yeast exist in the air. That bacteria are also present

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