540 WASTE-PRODUCTS 



In cold-blooded animals, in which the temperature of the tissues approx- 

 imates to that of the environment, the rate of oxidations is increased, 

 as might be expected, by a rise in external temperature, and the 

 carbon-dioxide output is even more than proportionately increased, 

 since the respiratory quotient generally undergoes a slight rise with 

 temperature also. This is illustrated by the following experiments of 

 C. J. Martin on the carbon dioxide output of the Australian Lizard 

 Cyclodus gigas. 



COz output per kilogram 



Temperature of Temperature of and hour, 



the air. the animal. mg. 



5 . . 5.5 13 



9 9.2 42 



15 15.2 53 



20.5 20.4 55 



25. .. 24.5 64 



30. .... . . . . V . . . 29.3 78 



35. -.-; v . . . 34.8 97 



39. 38.5 292 



The effect of rising temperature upon the carbon-dioxide output of 

 warm-blooded animals is, within certain limits, the reverse of this. 

 The Body-temperature of the warm-blooded animals varies but slightly 

 with the temperature of the environment and this uniformity of tem- 

 perature is secured by a number of cooperating factors, among which 

 the radiation of heat from the surface of the body, the loss of heat by 

 the latent heat of evaporation of perspiration, and the adjustment of 

 the production of heat by the oxidations of the body to the need for 

 heat to maintain the normal temperature of the tissues. The increase 

 of metabolism which low temperatures induce in the warm-blooded 

 animals is probably brought about, in part at least, by the stimulation 

 of the skin by cold air inducing reflex movements, such as shivering 

 or reflex alterations of muscular tone which necessitate an enhanced 

 combustion of carbohydrates with the performance of a minimum of 

 external work. 



The regulation of the temperature of the body between the normal 

 "comfortable" temperature-limits of the environment is mainly 

 brought about by the modification of the purely physical factors of 

 radiation and evaporation which govern the rate of loss of heat from 

 the body. Below the external temperature of 20 C. (68 R), however, 

 the "chemical regulation" of the bodily temperature becomes an 

 exceedingly important factor, the rate of metabolism rising continu- 

 ously, and^considerably with falling temperature. Above 30 C.-35 C. 

 (86 F.-95 F.) the effect of temperature upon the oxidations of the body 

 vanes with the humidity of the air. The greater part of the heat-loss 

 at these high temperatures is accomplished through the evaporation 

 of perspiration, and if the humidity of the atmosphere be so great as 

 to interfere with this method of heat-dissipation the regulatory mechan- 

 isms of the body become inadequate, the bodily temperature rises and 

 with it the rate of oxidation and the total output of heat, just as it 



