588 THE ANIMAL BODY AS A MACHINE 



a regular solid varies as the two-thirds exponent of the volume or as 

 W ! , if we measure volume in terms of weight. Now Rubner has 

 observed that the metabolism per unit of Body-surface is much more 

 uniform in different species than the metabolism per unit of body- 

 weight. E. Voit has determined the heat-production in resting animals 

 of various sizes per kilo and also per square-meter of surface with the 

 following results : 



Calories produced. 



Per sq. M. 



Species. Weight in kilos. Per kilo. surface. 



Horse 441. 11.3 948 



Pig 128. 19.1 1078 



Man 64.3 32.1 1042 



Dog 15.2 51.5 1039 



Rabbit 2.3 75.1 776 



Rabbit (without ears) 2.3 75.1 917 



Goose 3.5 66.7 969 



Fowl 2.0 71.0 943 



Mouse 0.018 212.0 1188 



The metabolism per kilo in these different species displays the 

 greatest diversity, ranging from 11 calories per kilo in the horse to 

 212 calories per kilo in the mouse. The metabolism per square-meter 

 of body-surface is very nearly the same in all of the different species 

 investigated, ranging, with the exception of the rabbit, from 900 to 

 1200 calories per square-meter. Metabolism bears therefore a far 

 closer relationship to surface than it does to weight and the relation- 

 ship extends to different individuals of the same species and explains 

 in part the high metabolism of infants. 



This relationship, which was discovered by Rubner in 1883 and 

 emphasized by Richet in 1885, was at first interpreted to mean that 

 the main factor governing metabolism was the rate of Radiation of 

 Heat from the surface of the body. Doubt was thrown upon this 

 interpretation, however, by the discovery that the production of heat 

 by warm-blooded animals of different sizes continues to be propor- 

 tional to the body-surface even when the temperature of the sur- 

 roundings is uniform or nearly uniform with that of the body, so that 

 the heat-loss through radiation is a negligible proportion of the total 

 energy-production. On referring to the preceding table it will be 

 noted that in a rabbit deprived of its ears, although the radiating sur- 

 face is much diminished, yet the production of heat remains unaltered. 



Although the metabolism per unit of surface varies very much less 

 than the metabolism per unit of weight, yet the proportionality of 

 metabolism to surface-area is not nearly so exact as many observers 

 have in the past decades considered it to be. Thus Benedict, in a 

 critical examination of the ratio of Basal Metabolism to surface in eighty- 

 nine men, sixty-eight women and a large number of infants found very 

 marked deviations from the rate of strict proportionality. As Benedict 

 has stated : " It is obvious that any basis of comparison which involves 

 variations of 40 per cent, with men, of 43 per cent, with women, and 



