TROUT WATERS AND CARP WATERS 



The fact that the trout have a high respiratory 

 quotient, that they consume a greater proportion of 

 oxygen, produce within themselves heat enough to 

 enable them to resist a certain drop in the temperature, 

 does not mean very much. They produce just enough 

 to reach this result and no more. Consequently, 

 what follows is even truer of other aquatic animals 

 which are not so well equipped. None has really 

 any animal heat of its own; all are subject, funda- 

 mentally and completely, to the thermic influence of 

 their environment. The oxidization which goes on 

 in them, their respiratory combustion, is too weak 

 to free them from this control and enable them to 

 ignore it. 



This is not the case with the higher vertebrates on 

 land, the birds and mammals which have a constant 

 temperature. Not only does their organism engender 

 in itself the caloric energy needed for its activities ; it 

 produces enough to have some to give away, to enable 

 itself to become a source of heat. Instead of being 

 subject to the action of its environment, the air which 

 surrounds it; instead of getting warmer or colder 

 with that environment, it is independent of it. More- 

 over, this production of heat goes on in such a way 

 as to maintain a constant degree of temperature within 

 the creature, and to maintain it despite all external 

 changes. Whatever the season, or place, or change 

 in the weather, their body in its normal state retains 

 a definite degree of heat, which either does not vary, 

 or changes very little, and controls the action of the 

 various functions. The organic economy is made to 

 work at such a temperature and not at any other. 

 In this thermal constancy, then, it finds its actions 

 controlled, and it develops a corresponding line of 

 behaviour which is not found in cold-blooded living 

 beings. 



The latter, and the fishes among them, have neither 

 a constant degree of temperature nor the regulation 

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