HETEFOTHERMY IN HOMEOTHEBMS 



the daily caloric intake of huskies was measured throughout the 

 entire year. In addition, the daily caloric intake of beagles was 

 measured over a period extending from late winter to summer to 

 early winter again. Contrary to what you might suspect from reports 

 in the literature, there is a marked seasonal difference in caloric 

 intake in both groups of dogs— very high rate in winter and low rate 

 in summer. In the husky this occurred despite a large increase in 

 winter insulation. The difference between the amount of calories 

 they took in in summer and winter was in the neighborhood of 60% 

 in the husky and 70% in the beagle. 



The data of Scho lander and Irving's group at Barrow* indicate 

 that a few arctic animals show no effect on metabolism through a 

 temperature range. We saw a similar thing in the caloric intake of 

 huskies during midwinter, when the environmental temperature 

 made a sudden drop from -7° C to -44 C. This temperature change 

 had no effect on caloric intake. We did not take a look at this type 

 of thing in the beagles, but the beagles between winter and summer 

 showed changes very similar to those seen in the huskies from the 

 standpoint of caloric intake— a little greater, but not appreciably 

 so. As a result ofthese observations on caloric intake, we are com- 

 ing to the conclusion that in these animals the basic response 

 appears to be metabolic and the insulative change probably serves 

 to increase their capacity to tolerate even lower environmental 

 temperatures. 



In the husky it is interestingthat early in the winter, in Novem- 

 ber in particular, his caloric intake is somewhat above that seen 

 later in the winter. For example, it may go up to 70% above the 

 summer level and then drop back down to a plateau that is main- 

 tained for the remainder of the midwinter. This would suggest that 

 as he picks up his winter insulation he is able to compensate some- 

 what for the increased caloric demand of the environment. We did 

 not carry the beagles far enough into the winter to see if there was 

 a similar sort of reduction in caloric intake. However, no gross 

 changes in fur insulation were apparent. 



*Scholander, P. F., et al. 1950. Biol. Bull. 99:259 



165 



