132 RESPIRATORY EXCHANGE OF ANIMALS AND MAN 



from what has been said above on the variation of the metabolism 

 in one and the same individual. The results obtained range from 

 2 '8 c.c. oxygen absorbed per kg. and minute (Jaquet [1902]) to 5-5 

 (Caspari [1905]), or from about 0*8 Cal. per kg. and hour to 1-6 Cal. 

 The differences are to be ascribed in many cases to differences in the 

 proportion of fat in the body, as the fatty tissues appear to have a 

 very slight metabolism only. Fat persons have also been directly 

 observed to have a smaller respiratory exchange than lean ones 

 (Geppert [1887], Magnus-Levy and Falk [1899] and Schattenfroh 

 [1900]). In other cases differences in the development of the muscles 

 and differences in muscular training are responsible for differences in 

 metabolism (see above, p. 119). The value 5-5 c.c. O per kg. and 

 minute (= I '6 Cal. per kg. and hour), which is very unusual, was ob- 

 served by Caspari on a trained athlete, and recently Benedict and Smith 

 [1915] have shown by comparing a number of athletes with " normal " 

 subjects of similar height and weight that the metabolism of athletes 

 is on an average distinctly greater than that of non-athletes (i -083 

 Cal. per kg. and hour as against I "017). 



By the earlier writers no systematic difference was detected be- 

 tween the sexes (Magnus-Levy and Falk), but a comparison instituted 

 by Benedict and Emmes [1915] on a large material (determinations 

 of standard metabolism on eighty-nine men and sixty-eight women) 

 appears to show that the metabolism of men is slightly greater than 

 of women. The data have not been treated statistically and are, 

 therefore, difficult to judge. 



In individual cases it is often difficult or impossible to account for 

 the deviation of the metabolism from the average, and there can be 

 little doubt that " standard metabolism " as defined at present does not 

 mean quite the same thing in different individuals. In the writer's 

 opinion differences in muscular tone are probably at the bottom of the 

 metabolic differences, and when it becomes necessary to obtain a 

 greater uniformity of results a more strict definition of standard con- 

 ditions will have to be adopted, and it will probably be the safest plan 

 to compare the metabolic activities of different individuals during deep 

 sleep, as suggested by Benedict 



On the other hand the uniformity obtainable with the present 

 definition should not be underestimated as it has been recently by 

 Benedict and his collaborators. 



Tigerstedt (Op.) has averaged the results of long series of deter- 

 minations of the standard metabolism of man, and found that all the 



