With the coming of modern air conditioning, there is more and more tendency toward proper ventilation. The average home, however, can easily be ventilated by opening the windows occasionally and allowing a brisk circulation of air through the rooms. Indeed the ordinary home as now built contains enough chinks, cracks, and space under doors and windows to permit a good deal of fresh air to circulate constantly.

Once it was thought that only the chemical constituents of the air were important in distinguishing good air from bad air. More recently it has been recognized that the physical qualities of the air are also important. Dusts and pollens may be primarily responsible for symptoms like those of hay fever and asthma from which many people suffer.

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.

With the coming of modern air conditioning, there is more and more tendency toward proper ventilation. The average home, however, can easily be ventilated by opening the windows occasionally and allowing a brisk circulation of air through the rooms. Indeed the ordinary home as now built contains enough chinks, cracks, and space under doors and windows to permit a good deal of fresh air to circulate constantly.

Once it was thought that only the chemical constituents of the air were important in distinguishing good air from bad air. More recently it has been recognized that the physical qualities of the air are also important. Dusts and pollens may be primarily responsible for symptoms like those of hay fever and asthma from which many people suffer.

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.

In vocabulary, comprehension, and arithmetic only a slight difference is found between the scores made by people in their thirties, the period when their abilities in these areas are highest, and the scores made by people 70 years old.

Many of the common sayings and beliefs about growing old have had to be revised in the light of new information that hasbeen developed by medical science in the last twenty years. We used to say that a man is as old as his arteries. Now we realize that changes in the arteries may go on without aging of all the rest of the body. A man is as old as his skin, his adrenal glands and his nervous system, even more than his arteries. Aging shows up most definitely in the skin and in the brain.

Just above the kidneys lie glands which in recent years have assumed so much significance that the knowledge concerning them has created a new era in medicine.

In most instances people pick out a child because he is dark or fair, fat or lean, because his hair is curly or straight, blond or brunette. The wise couple will realize from the first that the health of the child is much more important than the tilt or turnup of his nose.

An extremely cute baby may be just the opposite when he reaches eight years of age. The fat babies get thin and the thin ones get fat; the curly-headed blond six months of age may be a straight-haired raven at fifteen.