Basal Metabolism, Radiation, Convection and Vaporization at Temperatures of 22 to 35°C.

It has been possible for the first time to measure quantitatively the total heat loss and the proportions due to radiation and convection from men exposed to various atmospheric conditions. Two normal men were studied naked under basal conditions in the respiration calorimeter of the Russell Sage Institute of Pathology at temperatures between 22°C. and 35°C. The heat lost in vaporization was measured by weighing the water. The heat of radiation was determined by means of a Hardy radiometer. Convection was found by difference. Calculations were based on heat elimination and not heat production. Heat storage, which was not a factor in the basic calculations, was estimated from rectal and surface temperature changes and was measured by the difference between direct and indirect calorimetry. Between 22°C. and 35°C. the average temperature of the skin lay about midway between that of the air and that of the internal parts of the body. At the lower temperatures the surface layer of the body cooled rapidly and heat elimination greatly exceeded heat production. Radiation accounted for about 70% of the total loss at 22°C. to 26°C., but this percentage fell rapidly to zero as skin and air temperatures approached each other. Vaporization dissipated 18% to 30% of the heat at the lower air temperatures but accounted for about 100% at 35°C. Convection remained fairly uniform at about 15% until the air temperature rose above 32°C. Convection is significantly increased by slight movements of the body or the air. The basal metabolism of both naked subjects was level throughout the range of air temperatures from 22°C. to 35°C. At the lower temperatures the temperature of the skin and subcutaneous tissues dropped rapidly. After about 2 hours the men felt distinctly chilly and there was a tensing of the muscles which raised the metabolism slightly. After 10 or 15 minutes this was followed by a shaking chill. The fact that metabolism was not increased until a few minutes before the chill throws doubt on the existence of Rubner’s ‘chemical regulation.’ At the higher temperatures increased sweating took care of the heat loss when radiation and convection were abolished.