THERMAL EXCHANGES BETWEEN THE HUMAN BODY AND ITS ATMOSPHERIC ENVIRONMENT

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Abstract
A series of 267 tests was made on 7 normal adult c? subjects in atmospheric conditions ranging from 6.7 to 37.8[degree] effective temp. and 20 to 95% relative humidity in still air, and air velocities of 1.19 and 1.96 m. per sec. Subjects had partaken of regular diet, were normally clothed and seated, but were not restrained from normal movement of limbs and body. A minimum metabolic rate of 53.4 cal. per sq. m. per hr. was found for the temp. range 19.3[degree] to 28.7[degree] C, while for higher and lower temp. there is an increase. The effective temp. index is defined; and the rate of heat production within, and loss from, the body are shown to be functions of this index for both still and moving air. Total heat loss from the body is divided into latent loss or loss by evaporation and sensible loss or combined loss by radiation and convection, both of which are functions of dry bulb temp.; the former increases and the latter decreases as the dry bulb temp. scale is ascended. Sensible heat loss from the respiratory tract is always an insignificant figure. Latent heat loss from the respiratory tract is small compared to the total heat loss from the entire body, but is a large percentage of the total latent heat loss for dry bulb temp. below 20[degree] C. and decreases slightly for higher temp. Change from insensible to sensible perspiration takes place at 22.8 and 23.9[degree] effective temp. with 95 and 20% relative humidity respectively. The change in degree of perspiration with temp. and humidity was determined. The human body maintains temp. equilibrium in atmospheres of varying temp. and humidities and air motion by controlling heat production at low temp. and by controlling evaporation by control of available perspiration at high temp.

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