CRITICAL TEMPERATURE OF AN ANIMAL 271 



THE CRITICAL TEMPERATURE OF AN ANIMAL 



At a certain temperature, which has been called the " critical 

 temperature," the metabolism of the fasting animal is minimal, 

 for man at 15, dog 20, guinea-pig 30-35. Below this point the 

 production of heat rises or falls with the fall or rise of temperature, 

 and the regulation of the body heat is chiefly brought about by 

 chemical means. Above it the heat production slightly increases, 

 and the regulation depends mostly on physical means. The 

 increased production is to be explained by the greater activity 

 of the vascular, respiratory, and sudorific organs. Above a certain 

 temperature the loss by conduction, convection, and radiation 

 diminish to such an extent that visible sweating appears, and at 

 this stage the heat production becomes further increased. In 

 the fasting dog Rubner found : 



The metabolism at the " critical temperature " of the fasting and 

 resting animal is that which is needful for the performance of the 

 various functions of its organs, and the heat production at this 

 temperature indicates the amount of energy which must be con- 

 sumed in the internal work of the body. The reactions of the body 

 under changes of the temperature of the environment can be com- 

 pared to that of a cook in regard to her kitchen fire. In spring 

 just enough fuel is used necessary for cooking, in winter more fuel 

 is used, while in summer the windows are opened, and if very hot 

 the walls and floor may be sprayed with water (Armsby). Between 

 20 and 30 the heat production of the fasting animal remains 

 practically stationary, and the regulation of the body temperature 

 becomes dependent on the increased evaporation of water. 



Now the heat production can be greatly and suddenly increased 

 by rich feeding even to the extent of 44 per cent. (Rubner, 



