78 VERTEBRATE RESPIRATION 



one and certainly cannot be regarded as a return to a poikilo- 

 thermic condition. 



Aestivation has long been used to describe the state of 

 summer dormancy found in mammals and other animals. It 

 occurs particularly as an adaptation to seasonal drought (e.g. 

 in deserts) rather than seasonal cold and is an effective mechan- 

 ism for surviving periods when food and water are scarce. 

 Several examples have been recently investigated which show 

 that hibernation and aestivation are the same physiological 

 phenomenon. Thus in the Mohave ground squirrel aestivation 

 is characterised by : 



(a) body temperatures within a degree of environmental tem- 

 perature 



(b) O2 consumption very low 



(c) absence of breathing for long periods 



(d) torpor deeper than normal sleep 



(e) enhanced O2 consumption and activity of heat production 

 mechanisms during arousal. 



