It is a mistaken notion that clothing keeps the cold out. Its purpose is to keep the heat in, or, in other words, to prevent the rapid radiation of heat. We speak of warm clothing and of cool clothing. That clothing is warm which retards the giving off of heat from the body. The Indian wraps a blanket about his body to keep it warm; we wrap a blanket around a piece of ice to keep it from melting.
Any clothing that prevents the rapid escape of heat from the body is said to be a bad conductor, and is called warm. Woolen textures rank first among dress materials as poor conductors, and are therefore best adapted for winter clothing. Silk and cotton come next. Linen is a good conductor of heat; that is, it carries off the heat from the surface of the body very rapidly, and produces a sensation of coolness; therefore, all dress materials made from flax are said to be cool.
Materials.—The principal materials used for clothing are wool, cotton, linen, and silk. These differ greatly in weight, texture, warmth, porosity, power to absorb moisture, and in other less important qualities.
In a climate so changeable as that which prevails in most parts of the United States, the body, and especially the trunk, should be protected at all seasons from sudden chill by the use of under garments containing wool. Even in the warmest weather it will be found that a light woolen fabric absorbs the perspiration, and is more agreeable to the skin than cotton. The wearing of a flannel band, eight to ten inches in width, buttoned around the waist next to the skin, will prove an excellent protection to the kidneys and the abdominal region. Silk is light and soft, and as it retards the giving out of heat from the body, is worn for under garments, especially by those to whom wool is irritating or otherwise unpleasant. Rubber cloth is useful for rain coats, but as it prevents evaporation of the perspiration, it increases the liability to chill, and renders the wearer uncomfortable except in cold weather.
Animal Heat.—The bird is warmer than the air in which it moves; the fish possesses a higher temperature than the water. As before remarked, chemical changes are constantly going on in the system which give rise to this result. Even plant life is subject to this law. A delicate thermometer placed among a cluster of geraniums about to burst into flower will show a temperature a degree or two higher than the surrounding air.
Warm-Blooded Animals.—Those animals possessing well-developed lungs and large breathing capacity are usually active in movement, and are classed among the warm-blooded animals. They comprise birds, quadrupeds, and man. The animals possessing small lung development are for the most part inactive, and are cold to the touch, indicating a low temperature. Such are the frog, toad, lizard, snake, and tortoise.
These facts show the connection between respiration and animal heat, the temperature being in proportion to the amount of oxygen consumed. Birds have the largest lung development in proportion to size, are most active in movement, and indicate the largest amount of animal heat.
Adaptation to Climatic Conditions.—The Polar bear suffers from the heat of the Temperate zone, and would not survive a week in the Torrid. The African lion would fare no better were he suddenly transported to the Frigid zone. Man alone, of all the animal creation, is able to adapt himself to the extremes of heat and cold. By changing his clothing, shelter, and food, he is able to create for himself an artificial climate wherever he may choose to reside. No Arctic winter has been found too cold for a Peary, Nansen, or Greely to withstand, and no African plain or jungle too hot for a Livingstone or Stanley to explore.
Evaporation.—The temperature of the body is regulated by means of perspiration. Heat induces perspiration, and its evaporation lowers the temperature of the body. Cold retards perspiration, and the heat is retained within. The principle of evaporation is illustrated in the manufacture of artificial ice. Men who labor in glass works, iron and steel foundries, and in the engine rooms of large steam vessels are exposed to great heat, yet enjoy as good health as those who are engaged in other occupations. Persons have been known to remain several minutes in an atmosphere heated above the boiling point, without materially increasing the temperature of their own bodies.