Heat reactions of Bushmen.

Abstract

When Bantu males are exposed to ambient air temperatures of 78, 82, 86 and 90 °F Effective Temperature it is possible to distinguish clearly between unacclimatised, partially acclimatised and highly acclimatised states. A sample of Bushmen was exposed to this range of E. T.'s in a portable climatic chamber. Their rectal temperatures at the end of the third hour of exposure reached 101 °F at 78 ° and 82 °F E.T., 102.2 °F at 86 °F E.T. and 102.5 °F at 90 °F E.T. Sweat rates were highest in the first hour of exposure in all four heat stress conditions. Sweat rates decreased generally throughout the three-hour period, but the rank order of sweat rates were maintained. Sweat rates were plotted against rectal temperatures for each hour and also for the average values of the three hours of exposure. Curves fitted to the Bushmen data lie between the curves fitted to the data of unacclimatised and acclimatised Bantu for each of the three hours. When curves relating the mean sweat rates for the three hours of exposure at each of the E.T. conditions are compared with those for unacclimatised and acclimatised Bantu, it is found that the curve drawn on the Bushmen data again occupy a position midway between the other two curves. These three groups and a group of U. S. students are also compared in this paper in terms of physiological limits based on a steady level of rectal temperature, and based on the percentages of the samples exceeding a rectal temperature of 101 °F and 102.5 °F. The limiting E.T.'s for the Bushmen were found to be similar to those of unacclimatised Bantu and, generally, higher than for the U. S. students.