Adaptations of White Men and Negroes to Prolonged Work in Humid Heat

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Abstract
Summary The two environments produced differences in the adaptations of the laboratory group to prolonged walking on the treadmill. The rate of sweating was twice as great after 10 days and 2½ times as great after 6 weeks in Mississippi as in the northern experiments. Body temperature remained within comfortable limits in the North but in most of the men it rose to intolerable levels in Mississippi. The marked elevation in the body temperatures of the subjects in the Mississippi experiments was due to limited radiation and evaporation imposed by the hot, humid environment. Heart rate followed closely the changes in rectal temperature until limiting values were approached. Some of the men were more efficient and performed the task with lower heat production in the hot environment than in the cool one. There was a progressive decline in efficiency during work which tended to be more rapid the greater the elevation of body temperature. The negro sharecroppers who went through the experiments in the hot Mississippi laboratory maintained lower body temperatures than any other group studied including those in the northern experiments. They remained cooler than the Negroes in the North because they were more efficient and were favored by a higher ratio of body surface to weight. The white share-croppers who were studied in Mississippi were less successful in regulating body temperature than the negro sharecroppers only because they were less efficient. When walking in the sun with skin exposed the negro sharecroppers were superior in temperature regulation to partially acclimatized white men of the laboratory staff. During work the white sharecroppers had a higher rate of sweating than the Negroes—this was associated with their greater elevation of rectal and skin temperatures. Negroes are capable of much higher rates of sweating as evidenced by data on two negro servants in Mississippi who underwent marked elevation of temperature during the experiments. Sweat produced by the negro sharecroppers during work contained lower concentrations of total nitrogen, ammonia and urea, and higher concentrations of chloride than the sweat of white men. Both negro and white sharecroppers drank water more freely than the laboratory group. Mean values of R.Q. for the various groups during work in both environments were characterized by their close similarity. Blood sugar values were also very similar. Blood lactate was moderately lower in the northern experiments than in the South.

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