ARCTIC METABOLIC ECONOMY 



337 



HAMMALS 





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METflSOLISM 

 BAV(L> rto 



100 



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METAAOUSM 



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Al A. TEMPERATURE IN CENTIMAOE 



Figure 18. — Heat regulation and temperature sensitivity in arctic and tropic mammals 

 (top) and birds (bottom). (From Scholander, Hock, Walters, Johnson, and L. Irving, 

 Biol. Bull., vol. 99, figs. 10 and 11.) 



other hand, started to increase their metabolism at temperatures only 

 a little below those normal in their natural environment. 



By using this method of formulation it was found that the metabolic 

 measurements by a number of investigators working in temperate 

 climates produced curves showing the same pattern of relation between 

 metabolism, insulation, and temperature. The formulation was suc- 

 cessfully used by Hart (1952) for defining the character of the metab- 

 olism in cold of several kinds of wild and domesticated mice. The 

 formulation also served to compare the metabolism in summer and 

 winter of three species of mammals and of two birds in Alaska (L. 

 Irving, H. Krog, and M. Monson, 1955), to describe the metabolism 

 in cold of an Alaskan mountain goat (H. Krog, and M. Monson, 1954) , 

 and to compare the endurance of cold by wild brown rats and by rats 

 of the white laboratory form (H. Krog, M. Monson, and L. Irving, 

 1955). 



