JO HANSEN 



AMBIENT TEMPERATURE 



Figure 13. Oxygen consumption versus ambient temperature for the armadillo. 

 (Johansen, 1961). 



In the light of the observations on the metabolic response to 

 cold, I find it proper to discuss briefly the concept we all have been 

 repeatedly informed about, namely that the effector mechanisms 

 affecting heat dissipation and conser-vation, what we call physical 

 temperature regulation, come first into play and reach their effect- 

 ive limits before metabolic compensation sets in. In other words, 

 at the point of the critical temperature, the ability for physical 

 regulation is exhausted. This fact has been repeatedly stated from 

 studies on temperate and arctic mammals and has received value 

 as a concept in our understanding of temperature regulation. I 

 can see no reason why this strict sequence has to have general 

 value. Martin's data on the platypus and the marsupials indicate 

 a gradual, simultaneous time of action for both processes. My 

 own data on the armadillo likewise support the idea that maximal 

 insulation, including vasomotor adjustment, does not necessarily 

 need to reach the end point before metabolic compensation sets 

 in. The sequential arrangement has, of course, an obvious biologi- 

 cal rationale, by saving fuel. However, in line with my earlier 



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