266 NUTRITION OF FARM ANIMALS 



lation already described. It is only when the external tem- 

 perature sinks below this point that the katabolic processes 

 are stimulated and more heat is produced, and only below this 

 point, therefore, does the external temperature influence the 

 energy requirement. 



357. Effects of extremes of temperature. The regulation of 

 body temperature described in the foregoing paragraph is possible 

 only within certain limits. 



At very low temperatures the possibilities of chemical regulation 

 may be exhausted, so that the animal is unable to produce heat as 

 fast as it is abstracted and the body temperature begins to fall. An 

 actual lowering of the body temperature, however, reduces the inten- 

 sity of the katabolism exactly as it does in the case of a cold-blooded 

 animal ; the heat production sinks, bringing about a further fall in 

 body temperature which again further diminishes the heat production, 

 so that the animal speedily perishes from cold. 



At very high temperatures the reverse process 'may take place. 

 When the possibilities of physical regulation are exhausted, the body 

 temperature rises. A very slight rise, however, has been shown to 

 stimulate the katabolism and therefore the heat production, giving 

 rise to a "vicious circle" which is the converse of that occurring at 

 very low temperatures and which speedily leads to the animal being 

 overcome by heat. 



