The human being is sensitive to the atmosphere in which he lives. Air is the most necessary of all substances needed for life. A human being can live about forty days without food, about four days without water, but only about four minutes without air.
Air is a mixture containing approximately 21 per cent oxygen, 78 per cent nitrogen, and a fraction of 1 per cent of a number of other gases. The air of our large cities is contaminated by the gases that come from the bodies of man and from industry, by dust and germs of various kinds, and even by droplets of fluid.
The air that surrounds the human body is used, first, for breathing, second, to help control the temperature of the body. There is a heat-regulating center in the brain. When the body gets cool, the amount of blood circulating through the skin is increased and radiation takes place from the surface of the body.
All air contains a certain amount of moisture. The moisture increases withthe temperature. The moisture in the air is reflected by the measurement of the humidity. The effects of bad air are due to high temperature, the high relative humidity, and the lack of motion. When the air is in motion, it tends to evaporate water from the surface of the body more rapidly than when it is not in motion. This produces a cooling effect.
The best temperature for a room is from 65 to 68 degrees, with sufficient water vapor in the air to produce a relative humidity of from 30 to 60 per cent.