Only by generations of natural selection could we expect to make man immune to the evils of bad air. The robust Indian and the Negro, whose races, until the last generation or two, roamed in the open, fell easy prey to tuberculosis as soon as they adopted the white man's houses and clothes. The Anglo-Saxons who have withstood the influence of indoor living for several generations have, probably by the survival of the fittest, become a little better able to endure it, while the Jews, a race which has lived indoors longer than any other existing race, are now, probably by the same law of survival, the least liable to tuberculosis, except when exposed to especially unfavorable conditions of life. [Sidenote: Compensation for Civilization] But we, of this generation, can not afford to wait for natural selection to fit the race to an indoor environment; hence the supreme importance to us of air hygiene. We must compensate for the construction of our houses by insisting on open windows, or forced drafts, or electric fans, or open-air outings, or sleeping porches, or the practise of deep breathing, or all of these things. [Sidenote: Clothing Artificial] In the same way, clothing has protected our bodies from the cold but enervated or constricted them as well. The aboriginal tribes, even in cold climates, seldom used clothing. The Eskimo is an exception. The tribes toward the South Pole in similarly cold climates often have little more clothing than a blanket which they hang over their shoulders toward the wind. The weak, pale skin--to whose lack of adaptability we owe the chilling preceding a cold--the bald head, the distorted foot, the corns upon it, the cramped waist, are among the results of clothing ourselves wrongly. Hence we are discovering the need of restoring, as far as we can, the original conditions by making our clothes more light, more loose, and more porous, and, when possible, by taking the "barefoot cure," or the air bath. [Sidenote: Cooking Artificial] We come next to foods, and note that civilization has invented cooking and artificial foods. These inventions have greatly widened the variety of man's diet, but the foods of civilization are largely responsible for the decay of our teeth and the abuse of our digestive and eliminating organs. [Sidenote: Soft Foods Artificial]