Since the time of Hippocrates it has been known that the human body loses weight through emanations of carbon dioxide and water vapor from the skin and lungs.1 The study of this so-called perspiratio insensibilis was an attractive medical undertaking even in ancient days.
The exact nature of the phenomenon is still a moot point. Investigators differ as to whether it is a matter of physical diffusions2 or an active physiologic process;3 whether it is partly4 or entirely5 dependent on the activity of the sweat glands or occurs independently.6 All observers have agreed, however, that the loss of weight, although invisible and intangible, is weighable.
By means of a sensitive balance (Sauter) the insensible perspiration has been shown to be constant, daily variations in the same subject not exceeding 10 per cent. It has further been shown that this loss of weight is closely