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THE AMERICAN NATURALIST [Vol. XLIX 



to maintain his body weight, and disturbances of his gen- 

 eral health appeared. 23 



The cold-blooded and warm-blooded animals react dif- 

 ferently to changes in external temperature. Thus, the 

 carbon dioxide output of a frog rose from 0.015 gram 

 per kilogram of body weight per hour when the external 

 temperature was 1.6° C. to 0.639 gram when the external 

 temperature was increased to 34° C. (H. Schultz). But 

 as was first shown by Pfiuger and his pupils, the metab- 

 olism of a warm-blooded animal increases as the external 

 temperature is lowered. If , however, the body tempera- 

 ture is raised there is likewise an increase in the metabo- 

 lism of the warm-blooded animals. Pfiuger regarded the 

 increase in metabolism of the warm-bloodedanimals accom- 

 panying the decrease of external temperature as a later 

 acquisition or as a mechanism which has gradually been 

 evolved in the special interest of a constant temperature. 

 Kubner 's measurements of the metabolism in a dog showed 

 an increase from 30.8 calories an hour when the external 

 temperature was 27.4° C. to 40.6 calories an hour when the 

 external temperature was lowered to 11.8° C, — an in- 

 crease of about thirty-three per cent. These considera- 

 tions are sufficient to suggest that the effect of similar 

 changes in the environment may not only not have effects 

 of equal magnitude upon organisms at different levels in 

 the taxonomic scale, but may even have opposite effects at 

 the two extremes of the scale. 



The upward march of the body temperature is re- 

 stricted by the greater access of blood to the periphery 

 and the increased loss of heat by radiation from the sur- 

 face. A still greater loss of heat, in addition to the rather 

 constant amount lost by evaporation of water from the 

 lungs, is brought about by evaporation of water from the 

 skin or other surface of the body, such as the tongue in 

 dogs. The amount of water on the skin is regulated by 

 the activity of the sweat glands, and these, in their turn, 

 are under nervous control. 



23 Tigerstedt, "Text-Book of Physiology," translated by Murlin, New 

 York, 1906, p. 407. 



