RESPIRATORY EXCHANGE IN DIFFERENT ANIMALS 143 



for the rabbit that the percentage of organ nitrogen is lower in this 

 animal than in the rest This appears doubtful, however. 



Voit points out that his comparisons are valid only for well- 

 nourished animals after a fast which must not be unduly prolonged. 

 Underfed animals have at once, and other animals after prolonged 

 starvation (Table XXIX, p. 120), a considerably lower exchange in 

 twenty-four hours. Voit ascribes this to differences in oxidative 

 energy ( of the tissues, but it may easily be due to differences in 

 muscular activity or tone. 



In the comparisons between different warm-blooded animals no 

 account has ever been taken of the differences in body temperature 

 which are not quite negligible. I have given Tigerstedt's [W.] figures 

 for the temperature of the animals mentioned in column 3 of Table 

 XXXIX. 



It is at present not possible to determine accurately the influence 

 of these differences upon the standard metabolism, but to judge from 

 the material available in Krarup's experiments (p. 94) and the curve 

 given by Krogh (p. 94) for a young dog, it should be of the order 5 to 

 6 per cent, decrease in metabolism for each degree lowering of the 

 body temperature. 



Comparison between Warm-blooded and Cold-blooded and 

 between different Cold-blooded Animals. 



Very few investigations have been undertaken with the definite 

 object of comparing the standard metabolism of different cold-blooded 

 animals. 



Cohnheim [1912] has compared forms which possess striped muscles 

 (Crustacea) with such which do not'(molluscs), but did not find any dis- 

 tinct difference when the results were calculated on the basis of the fresh 

 weight. The experiments were not made under standard conditions. 



Vernon [1896] has made an extensive and very valuable series of 

 experiments on transparent pelagic animals, the oxygen absorption 

 of which he compared with that of fishes and cephalopods. Though 

 standard conditions were not maintained it is probable that the results, 

 so far as the pelagic animals are concerned, have not been seriously 

 affected by the activity. Vernon found that the respiratory activity 

 of the lower pelagic animals (Ccelenterata, Tunicata, and Mollusca) is 

 very small when compared by weight with that of higher animals, 

 such as a teleost fish. Per kilogram and hour he found the following 

 oxygen absorptions in deci-mg. at 16 as averages in most cases of 

 a number of determinations : 



