MAMMALIAN COLD ACCLIMATION 



time (Fig. 18A). If the muskrat is overheated slightly either by 

 exercise or by being exposed to a high environmental tempera- 

 ture, his tail is "flushed" immediately. The skin temperatures 

 are practically as high as the body temperature. 



I proceeded by trying to elucidate the mechanisms behind 

 these profound effects and the data acquired from doing nerve 

 blocks of the tail indicate that there exists such a thing as a 

 vasodilator innervation to the skin in the tail of the muskrat. If 

 1 nerve-blocked the tail, the animal became hyperthermic in a 

 very short time and in one instance an animal succumbed and 

 died of heat apoplexia when his tail was not intact (Fig 19 A).* 



In the other project, I tried to assess the importance of the 

 air layer in the fur as an insulator. I compared two groups of 

 animals, one with the fir layer intact and one with the air depleted 

 by way of surface active materials, such as detergents. I anesthe- 

 tized the animals to standardize the condition and to avoid dif- 

 ferences in movement. I found that the intact muskrat had a volume 

 of about 800 cc, of which about 200 cc was air. In other words, 

 almost 25% of the volume of the muskrat is air. If these two groups 

 are subjected to water cooling or to air cooling, the temperature 

 drops five times as fast in the one depleted of the air.** 



HANNON: There is one question I would like to ask Sandy. 

 In animals such as the muskrat and possibly wild rats living 

 outdoors continuously, do you feel it might be possible for these 

 animals to be continually cold-acclimatized, summer and winter? 

 In the muskrat, for example, in these northern areas, the water 

 is still quite cold in the summer. It may be that they get a level 



*Johansen, K. 1962. Heat exchange through the muskrat tail. Evidence for vaso- 

 dilator nerves to the skin. Acta Physiologica Scandinav. (in press). 



**Johansen, K. 1962. Buoyancy and insulation in the muskrat. J. Mammal, (in 

 press). 



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