MAMMALIAN COLD ACCLIMATION 



of acclimatization and just maintain it. And that is why you cannot 

 see the difference between summer and winter. 



HART: I always think of it as a matter of degree. The musk- 

 rat is probably to a certain extent acclimatized in the summer, 

 too, but you would think that they would be more so in the winter. 



JOHANSEN: We did some measurements in the field here 

 and the temperatures in the pushups of the muskrats are rather 

 strikingly high during winter. They are from 5 C to 10 G above 

 freezing in the -40 C weather. We do not really know how much 

 time they spend in the cold water; this is what we should find out. 



HANNON: You have essentially C water in the winter time, 

 and maybe it will go as high as 15 C in the summer and maybe 

 a little higher. You still have a pretty big differential, but on the 

 other hand they may be a little more active in the summer time in 

 the water, so they get a longer exposure. , 



HART : It is possible. 



IRVING; Dr. Fay has been making some measurements from 

 time to time in the New York Zoo on the temperature on the body 

 skin and flippers of walrus, both young and old. He has been able 

 to get some measurements of wild walrus around St. Lawrence 

 Island, too, and he finds a fair regularity in the relation between 

 the temperature of the skin of the body in air or water. As Hart 

 and I found in harbor seals, the flippers may be quite different 

 from the body and apparently fluctuate as if for fine adjustment 

 of temperatures. Fluctuations in the extremities are also subject 

 to non-thermal excitation, and in absence of obvious relation to 

 heat, are ascribed to plain nervousness. 



PROSSER: In your summary slide, comparing the different 

 mammals, you suggested that there might be differences in the 

 sensory sensitivity. 



HART; Do you mean sensitivity to skin temperature? 



239 



