MORRISON 



MORRISON: Exactly. Operationally, it is just the same kind 

 of situation. In the ground squirrel, the thermogenesis seems to 

 act as an alarm system rather than a thermostat. If its body tem- 

 perature drifts down below a fixed point, near freezing, it awakens 

 and normal body temperature is maintained thereafter. These bats 



act in the same manner except that the alarm is set for 30 C to 



o 

 33 C. 



JOHANSEN: We saw exactly the same thing in the birchmouse, 

 Sicista betulina, in regard to these diurnal variations. If you force 

 on them a large negative heat load their body temperatures rise 

 quickly. 



IRVING: Or you can say the same thing then, perhaps with 

 reference to the excellent discussion of the torpidity in birds. At 

 the small power output it is possible that the cold metabolic animal 

 could not tolerate very low temperatures. 



MORRISON: Torpidity is incompatible with temperatures below 

 freezing. 



IRVING: Yes, they either have to reawaken or die. 



MORRISON: I do not know whether they would be able to or not. 



IRVING: Do you think birds can be reawakened from torpidity 

 by excessive lowering of temperature? 



MORRISON; Yes, very definitely. 



IRVING: I was just wondering how you would compare them 

 with the faculty which you have shown to be so rather widespread 

 in mammals. I have not seen it mentioned. That is why I inquired. 



MORRISON: It would be well worth looking into, particularly 

 in some of the Califomian species. 



IRVING: It is always stuck in my crop that there is something 

 that distinguishes torpidity in birds but it may be only in the way 

 that people have looked at it. 



418 



