RESPIRATORY EXCHANGE IN DIFFERENT ANIMALS 135 



holism, and deprecates especially the use of the surface as a basis for 

 comparisons. His own figures and charts show very clearly, however, 

 that such relationships exist, that the metabolism per kilogram of body - 

 weight decreases fairly regularly with increasing size (weight), while 

 the figures per square metre (as computed) do not show any marked 

 tendency but are fairly evenly distributed. Benedict has concentrated 

 his attention on the other factors which influence undoubtedly the 

 standard metabolism : the " amount of active protoplasmic tissue " 

 and the varying "stimulus to cellular activity" and this has led to 

 an under-estimation of the size relationship. 



It is quite possible of course that the surface as at present defined 

 cW$ does not give the very best agreement in comparisons of different 

 individuals. The main point is that metabolism in warm-blooded 

 animals is not proportional to the weight (W) but to W n (Dreyer 

 [1912]) where n is certainly not far from . When the " best n " has 

 been determined by mathematical analysis of the material, and the 

 size factor excluded by reducing all the observations to this standard, 

 it would certainly be possible by dividing the subjects into groups 

 according to a number of points of view (sex, age, height, indices of 

 build, etc.), and treating the observations statistically, to obtain 

 numerical results of great reliability and value. 



From a calculation by the writer of some of Benedict and Talbot's 

 material mentioned above (p. 116) it appears probable that the surface 

 relationship holds also when young warm-blooded animals are com- 

 pared with adults of the same species, though a very important age 

 factor must be superimposed. In the embryo on the other hand the 

 determinations of Bohr and Hasselbalch [1900] show that the respira- 

 tory exchange is simply proportional to the weight. 



The results obtained on cold-blooded animals are conflicting and 

 uncertain. Experiments made by Jolyet and Regnard [1877] and 

 Knauthe (published by Cronheim [1911]) on fish and other marine 

 animals have been utilized by Hoesslin [1888] and Zuntz [1906] to 

 establish the " surface law," but the observations are too few, and while 

 some of them undoubtedly indicate that smaller animals have the 

 larger respiratory exchange per kg., the results per unit surface being 

 more or less constant, 1 other experiments by the same authors show 

 quite the reverse. Standard conditions were in no case maintained. 



Buytendijk [1909] made a few determinations on different cold- 



1 In Knauthe's experiments on carps the respiratory exchange of fish of 12 gr. weight 

 is much higher per kg. than of any other size, but for fish from TOO gr. to 700 gr. the 

 differences are irregular and within the limits of error. The high result obtained for the 

 very small and young fish may very well be due exclusively to their livelier movements. 



