mviNG 



IRVING: I am not sure there is among the different caribou; 

 the smallest of all is also the most northern. You find many excep- 

 tions to that; and as Scholander says, if this were a matter of a 

 law of heat you should not find any exceptions. Thus, one exception 

 would invalidate the significance of such a law. It may be true that 

 many birds as they go north get longer tails, larger bodies, or 

 bigger claws. On the other hand, some do just the opposite. I do 

 not think it has ever been shown that any of these differences in 

 body dimensions are significant to the heat economy of the animal. 

 I will go farther and say that the surface of an animal has no rela- 

 tion to its heat exposure; there is no relation that you or I can 

 define, because in the first place there is no geometrician who can 

 define the surface of such an irregular object as an animal. It is 

 indescribable, mathematically. If it were describable, it would not 

 be worth the time or the effort, and further, attributing the heat 

 loss simply to the surface disregards practically all that we know 

 that is interesting and important with regard to the conservation 

 and dissipation of heat. In other words, it is not a matter strictly 

 of surfaces. For example, the circulation through the skin of the 

 fingers is one hundred times what it is through the skin on the 

 forearm or on the rest of the body. The variability in the amount 

 of circulation, the amount of heat exchange, and the temperature 

 of blood passing through the extremities are far more important 

 factors than is the extent of the skin surface. And those are the 

 variable factors in heat economy, while surface, if there be such 

 a thing, is an invariable function unless the animal chooses to 

 alter his posture, as he does in sleep. 



PROSSER: But still there is a general correlation between 

 size and distribution; it may have no relation to temperature regula- 

 tion at all, but it remains as a correlation. 



IRVING: That may be, but it is not of any great interest or 

 importance to physiology. 



PROSSER: I am not willingtosaythat.lt may have some mean- 

 ing which we do not know. 



MORRISON: Do you think it is fair to say that a factor has no 

 significance simply because there are other factors which are 

 more significant? 



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