“Heat is lost from the body chiefly in two ways; (1) by _heat transfer_, or loss by radiation, conduction, and convection; (2) by _evaporation_, chiefly by the evaporation of the water of perspiration. Pettenkofer and Voit estimated the loss of water by the lungs at 286 grams, and from the skin at from 500 to 1,700 grams daily. This will give some idea of the effects here concerned. The loss by heat transfer diminishes as the temperature of the surrounding air rises. The temperature of the body would rise when the atmospheric temperature goes above 70 degrees F. were not perspiration then secreted. So long as the perspiration can evaporate freely the heat production and heat loss are balanced. With a high humidity evaporation is lessened and the balance is maintained by rushing blood to the skin, which causes an elevation of the temperature of the surface, and thus the loss of heat by radiation, conduction, and convection is facilitated.” Human sensations of temperature are paradoxical. We talk of being “hot” and “cold,” as if we belonged to the class of cold-blooded animals--the fishes and the reptiles--that actually undergo great variations of temperature, with variations in the temperature of their environment. We hear people say, for example, that they are most comfortable at a temperature of 65; yet we know that their temperature is always 98½, except just at the surface of the body. The human body is, in fact, a poor thermometer. Our sensations do not register the temperature of the air, but they do, in a way, register the cooling power of the air, which depends upon temperature, humidity, and air movement, and they register, especially, changes in this cooling power, for within certain limits the body soon adapts itself to a constant rate of cooling, so as to lose any impression of heat or cold. When a steady outflow of heat from the body has been set up and the external cooling power is suddenly increased, we become conscious of a difference between the temperature at the surface of the body and the “blood temperature” beneath. The action of the nerves at the surface and the nerves underneath, under these circumstances, has been compared to that of a thermo-junction, in which an electric current is produced by differences of temperature. The rate of evaporation from the skin, also, has a marked effect upon our sensations of comfort and discomfort.