SLOW ADAPTATIONS IN THE HEAT EXCHANGES OF MAN TO CHANGED CLIMATIC CONDITIONS

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Abstract
Subjects that remained for several days in a room kept hot or cold revealed slow adaptive changes in total heat exchange and in its partition. Deep body temp. remained within normal limits. Caloric intake was significantly greater in cool than in hot conditions and food of greater caloric value and lower equivalent R.Q. was chosen. Heat loss by evaporation, calculated from wt. changes, tended to increase in the 1st 2 days of heat, then to fall progressively. Changes in radiation and convection losses were complementary, i.e., there was an initial fall followed by a progressive rise dependent on increased skin circulation and temp. When cold followed heat, evaporative loss fell to subnormal values by the 3d day, explained in part by very low skin temps., but possibly also by demonstrably abnormal osmotic conditions. Radiation and convection losses also fell in the 1st 2 days, as full vaso-constriction was attained only slowly. Evaporative losses then rose gradually to normal values. The total heat exchanges, advanced from the foregoing and from basal O2 consumptions, showed a slight progressive fall in the heat. With the decreased avg. tissue temp. in the cold there was a marked initial fall followed by a steady rise later. There was a marked metabolic unbalance in the initial days of cold, for increased caloric intake accompanied reduced heat production. Simultaneously a large diuresis occurred, which was partially balanced by the storage of food in the body. Acclimatization to heat achieves a greater loss by radiation and convection; to cold a decreased loss by this route. The new partitions are maintained with less strain after changes in body fluid occur.