7io 



CHEMISTR Y OF RESPIRA TION. 



There are, however, several conditions which prevent these results 

 from being considered comparable ; the hibernating 1 animal has a very 

 low respiratory exchange, even when the external temperature is higher 

 than 7*3 ; in the last experiment the food would increase the respira- 

 tory exchange; the observations were made at intervals of several 

 months, and are complicated by the large discharge of nitrogen, which 

 is probably to be attributed to an error of experiment. 2 



Biitschli 3 showed that the respiratory exchange of insects varied in 

 the same direction as the temperature of their surroundings. 



The most complete series of observations appear to be those of 

 Schulz 4 upon the edible frog (Rana esculenta). The following table 

 gives his chief results, obtained upon frogs in summer : 



It is to be noted that in Schulz's experiments the frogs were kept in 

 the warm or cold surroundings until their temperature was equal to 

 that of the air, so that the results are strictly upon frogs at different 

 temperatures. The response of a frog, as shown by its temperature and 

 respiratory exchange, to a change of external temperature is very slow, 

 and for this reason observations upon the metabolism of cold-blooded 

 animals can only be properly compared when the temperature of the 

 animal and that of the air are known. The above results show that at 

 temperatures a degree or two above zero the output of carbon dioxide 



1 See ''Animal Heat," this Text-book, vol. i. 



2 See also Pfliiger, Arch. f. d. ges. PhysioL, Bonn, 1877, Bd. xiv. S. 73. 



3 Arch.f. Anat., PhysioL, u. wissensch. Med., 1874, S. 348. 



4 Arch.f. d. ges. PhysioL, Bonn, 1877, Bd. xiv. S. 78. 



