the chest cavity larger. The lungs, which lie within this cavity, are filled by the air rushing into the larger space thus made. An expiration is

simpler than an inspiration, for it requires no muscular effort; the muscles relax, the breastbone and ribs sink into place, while the diaphragm returns to its original position.

A piece of apparatus which illustrates to a degree the mechanics of breathing may be made as follows: Attach a string to the middle of a piece of sheet rubber. Tie the rubber over the large end of a bell jar. Pass a glass Y tube through a rubber stopFasten two small toy

per.

in (a) inspiration; (b) expiration. balloons to the branches of the tube. Close the small end of the jar with the stopper. Adjust the tube so that the balloons 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 balloons within expand, owing to the air pressure down the tube. When the

rubber is allowed to go back to its former position, the balloons collapse.

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 30 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. 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. Respiration under Nervous Control. The muscular movements which cause an inspiration are partly under the control of the will, but in

Apparatus

showing mechanics of breathing.

part the movement is beyond our control. The nerve centers which govern inspiration are part of the sympathetic nervous system. 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. Thus the nervous center which has control of respiration is stimulated to greater activity, and quickened inspiration follows.

Problem LII. A study of the products of respiration. (Laboratory Manual, Prob. LII.)

Residual

Air

100 cu. in.

Changes in Air in the Lungs. — Air is much warmer after leaving the lungs than before it enters them. Breathe on the bulb of a thermometer to prove this. Expired air contains a considerable amount of moisture, as may be proved by breathing on a cold polished surface. This it has taken up in the air sacs of the lungs. The presence of carbon dioxide in expired air may easily be detected by the limewater test. Air such as we breathe out of doors contains, by volume:

Diagram showing the relative amounts of tidal, complemental, reserve, and residual air. The brace shows the average lung capacity for the adult man.

In other words, there is a loss of between four and five per cent oxygen, and nearly a corresponding gain in carbon dioxide, in expired air. There are also some other organic substances present. HUNT. ES. BIO. -25

The volume of carbon dioxide given off is always a little less than the volume of oxygen taken in. This seems to show that some oxygen unites with some of the chemical elements in the body. 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 homoglobin 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

a

b

During

Need of Ventilation. 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. 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

Three ways of ventilating a room: i, inlet for air; o, outlet for air.

Which is the best method of ventilation? Explain.

index by which we may prevent poisoning. Air containing from 6 to 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 to place a board two or three inches high between the

lower sash and the frame of a window. An open fireplace in a room aids. in ventilation because of the constant draft up the flue.

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 can be proved by exposing a sterilized gelatin plate to the air in a schoolroom for a few moments.1

Plate culture exposed for five minutes in a school hall where pupils were passing to recitations. Each spot is a colony of bacteria or mold.

1 Expose two sterilized dishes containing culture media; one in a room being swept with a damp broom, and the other in a room which is being swept in the usual Note the formation of colonies of bacteria in each dish. In which dish does the most growth take place?

manner.

Many of the bacteria present in the air are active in causing diseases of the respiratory tract, such as diphtheria, membranous croup, and tuberculosis. Other diseases, as colds, .bronchitis (inflammation of the bronchial tubes), and pneumonia (inflammation of the tiny air sacs of the lungs), are probably caused by bacteria.

Dust, with its load of bacteria, will settle on any horizontal surface in a room not used for three or four hours. Dusting and sweeping should always be done with a damp cloth or broom, otherwise the bacteria are simply stirred up and sent into the air again. The proper watering of streets before they are swept is also an important factor in health.

Ventilation of Sleeping Rooms.

Sleeping in close rooms is

the cause of much illness. Beds ought to be placed so that a constant supply of fresh air is given without a direct draft. This may often be managed with the use of screens. Bedroom windows should be thrown open in the morning to allow free entrance of the sun and air, bedclothes should be washed frequently, and sheets and pillow covers often changed. Bedroom furniture should be simple, and but little drapery allowed in the room.

Hygienic Habits of Breathing. Every one ought to accustom himself upon going into the open air to inspire slowly and deeply to the full capacity of the lungs. A slow expiration should follow. Take care to force the air out. Breathe through the nose, thus warming the air you inspire before it enters the lungs and chills the blood. Repeat this exercise several times every day. You will thus prevent certain of the air sacs which are not often used from becoming hardened and permanently closed.

The Relation of Tight Clothing to Correct Breathing. - It is impossible to breathe correctly unless the clothing is worn loosely over the chest and abdomen. Tight corsets and tight belts prevent the walls of the chest and the abdomen from pushing outward and interfere with the drawing of air into the lungs. They may also result in permanent distortion of parts of the skeleton directly under the pressure. Other organs of the body cavity, as the stomach and intestines, may be forced downward, out of place, and in consequence do not perform their work properly.