ANIMAL HEAT 509 



much in accordance with physiological laws, that a man 

 overpowered by the heat should lie down, as it is that he 

 should walk about and stamp his feet or clap his hands on 

 a cold winter morning. In the one case a diminution, in the 

 other an increase, in the heat-production is aimed at by a 

 corresponding change in the amount of muscular contrac- 

 tion. The quantity and quality of the food also influence 

 the production of heat. The Eskimo, who revels in train-oil 

 and tallow-candles, unconsciously illustrates the experimental 

 fact that the heat of combustion of fat is high ; the rice 

 diet of the ryot of the Carnatic, with its low heat equivalent, 

 seems peculiarly adapted to the dweller in tropical lands. 

 But it would be easy to attach too much weight to con- 

 siderations such as these. The Arctic hunter eats animal 

 fat, and the Indian peasant vegetable carbo-hydrate, not 

 only because fat has a high and carbo-hydrate a low heat- 

 equivalent, but because in the climate of the far North 

 animals with a thick coating of badly-conducting fat are 

 plentiful, and vegetable food scarce; whereas in the river- 

 valleys of India nature favours the growth of rice, and 

 religion forbids the killing of the sacred cow. 



The production of heat is also controlled by an involuntary 

 nervous mechanism, upon which much light has been thrown 

 by the researches of the last twenty years, and especially 

 by those of Pfliiger and his school (p. 228). It is a matter 

 of everyday experience that cold causes involuntary shiver- 

 ing involuntary muscular contractions the object of which 

 seems a direct increase in the heat-production. But besides 

 this visible mechanical effect, the application of cold to a 

 warm-blooded animal, when not carried so far as to greatly 

 reduce the rectal temperature, is accompanied by a marked 

 increase in the metabolism, as shown by an increased pro- 

 duction of carbon dioxide and consumption of oxygen. In 

 cold-blooded animals like the frog the metabolism, on the 

 other hand, rises and falls with the external temperature ; 

 there is no automatic mechanism which answers an in- 

 creased drain upon the stock of heat in the body by an 

 increased supply. Or, in the light of recent experiments, 

 we ought rather to say that, although the rudiments 



