So far as the heat of the body is concerned, whether in health or disease, every degree of external heat which is above the complement to form 98.6 degrees Fahrenheit with the heat of the body itself at the time, is useless and may do harm. It follows that in fever the surrounding atmosphere should be kept cool; in depressing disease, when the heat-producing powers of the organism are small, the air around should be warm. These are precisely the conclusions to which experience and observations conduct us; and the facts now briefly stated explain the reason why. There is no warmth in clothes; the heat comes from the body itself, generated within, or the surrounding atmosphere, or from substances with which the body may be in contact. Of course clothes, like any other materials, can be charged with heat, and will take up as much thermic or heating property as their specific capacity allows. It is this capability of receiving heat which constitutes the first condition of warmth in the comparative value of different materials of dress. The second condition consists in the physical power of any fabric to hold the heat with which the article has been charged. For example, some materials will become warmer in a given time and retain their heat longer than others under the same conditions of exposure, first to heating and then to cooling influences. The principle of clothing should be to protect the body from external conditions which tend to abstract heat, when the surrounding temperature is lower than that of the body; and to strike heat into the organism, when the temperature of the outside air and of the substances with which the skin may be brought into contact is higher than that of the animal body itself.