THERMOTAXIS 693 



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 contraction. 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, through which the ' chemical ' regulation of the body- 

 temperature is achieved, as the ' physical ' regulation is accom- 

 plished by the nervous mechanisms that control the circulation, 

 the sweat-glands, and the respiratory movements. It is a matter 

 of everyday experience that cold causes involuntary shivering 

 involuntary muscular contractions the object of which seems to be 

 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 production 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 increased 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 of a heat-regulating mechanism may exist 

 in such animals as the frog, the newt, and even the earthworm 

 (Vernon), it is only able to modify to a certain extent the effects of 

 changes of external temperature, not to balance or even override 

 them, as in the homoiothermal animal. In resting frogs and snakes 

 the rate of heat-production, as measured by the micro-calorimeter, 

 increases two to three times when the temperature rises 10 C. 

 (Hill). The warm-blooded animal loses its heat-regulating power 

 when a dose of curara sufficient to paralyze the voluntary muscles 

 is given. A curarized rabbit, kept alive by artificial respiration, 

 reacts to changes of external temperature like the cold-blooded 

 frog. Now, the only action of curara adequate to account for this 



