. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. HEAT REGULATION IN MAMMALS AND BIRDS 255 tabolism 30-40 per cent, whereas the same increase in metabolism in a tropical animal will only help him by a few degrees. The critical temperature in naked man is known to be around 27° C. (DuBois, 1936) to 29° C. (\Yinslow and Herrington, 1949), which places him among the more temperature sensitive of the tropical mammals. We have no data as to the critical temperature of Eskimos. They wear just as warm clothing as white men in the same environment, often warmer, and it is likely th
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. HEAT REGULATION IN MAMMALS AND BIRDS 255 tabolism 30-40 per cent, whereas the same increase in metabolism in a tropical animal will only help him by a few degrees. The critical temperature in naked man is known to be around 27° C. (DuBois, 1936) to 29° C. (\Yinslow and Herrington, 1949), which places him among the more temperature sensitive of the tropical mammals. We have no data as to the critical temperature of Eskimos. They wear just as warm clothing as white men in the same environment, often warmer, and it is likely that the Eskimo is as sensitive to temperature as other people that wear clothing. Man is indeed a tropical animal carrying his tropical environment with him. By using different amounts of clothing, tropical man can span the whole range from the tropics to the arctic and it could be assumed that his energy requirements below the critical temperature for each clothing assembly would essentially follow BIRDS METABOLISM 100 400 700 200 100 WOO 300 200 100 R c r i c T R 0 P I C A L. -ORSFfWtD I 70 \ -60 LOWEST TP On EflRTh •50 -HO -50 -2O -10 O '0 A I R IN CENT IGR flOE 20 10 BODVTR FIGURE 11. Heat regulation and temperature sensitivity in arctic and tropical birds, based on plots in Figures 5, 6, and 9. Newton's law of cooling. It seems a challenge that we have been unable to unearth in the literature experiments in man, naked or clothed, with enough data to demon- strate adequately the thermoneutral zone and the slope of energy expenditure beyond it. In Figure 10 man's line below the critical temperature is hence dotted. It is known however, from studies at the Climatic Research Laboratory, Lawrence, Mas- sachusetts, that the insulation value of clothing may drop considerably (50 per cent) during exercise (Belding, 1949. and personal communication), which would move the curves upward. Man cannot usually spend a night at • 40° C. in one-layer arctic fur clothing
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