MAMMALIAN COLD ACCLIMATION 



Oxygen consumption and body temperatures of animals placed 

 in a small tank of water for about three fourths of an hour increased 

 progressively with lowering of water temperature below a critical 

 level of about 30 G. Colonic temperatures fell after the animals 

 were in water at all temperatures below about 20 C. During both 

 summer and winter, it was apparent that the heat production was in- 

 adequate to offset hypothermia for prolonged periods at winter tem- 

 peratures around C. Skin temperatures measured under the fur 

 confirmed the presence of an air layer, because a gradient of ap- 

 proximately 7° C was maintained in the fur at a water temperature 

 of 0° G. Nevertheless, this air was insufficient to prevent general- 

 ized cooling. Since the animals were all healthy, muskrats in nature 

 may tolerate limited hypothermia during winter while under the ice 

 and may limit exposure to cold water to shorter excursions than the 

 test exposures in these experiments. 



Bare Skinned and Aquatic Mammals 



Metabolic studies have been carried outby Irving and coworkers 

 on swine in Alaska (19 56) and on seals of the Atlantic coast (1957, 

 1959). Swine and aquatic mammals willbe considered together in this 

 section because of similarities in problems of temperature regula- 

 tion associated with the presence of a minimal fur cover and an in- 

 sulating subcutaneous layer of fat or blubber. 



Both the swine at various air temperatures (Figure 8) and the 

 harbor seals ( Phoca vitulina) in air and in water (Figure 9) showed 

 marked temperature gradients through the tissues which were char- 

 acteristic of the insulating layers of fat and the different outside 

 cooling effects. The distributions of surface temperatures on the 

 body surfaces of swine and seals were also rather similar at com- 

 parable air temperatures, indicating similarity in physiological in- 

 sulation by cooling in these two animals. The critical temperatures 

 for increase in metabolic rate (about C) were also comparable in 

 Alaska swine and harbor seals during the summer. 



In water, the surface temperatures of harbor seals were, as 

 anticipated, only slightly greater than ambient, and the critical tem- 

 perature was elevated from approximately Cto20 G (Figure 10). 



215 



