RELATION OF FOOD TO WORK, AND 273 



If we use Lavoisier's data just given, and the known atomic weights 



of carbon, oxygen, and hydrogen, we shall have, for 81 parts of oxygen 



in the form of carbonic acid, and 19 parts of oxygen in the form of 



water, the following quantities of carbon and hydrogen consumed by 



the respiration of his Guinea pig in the same time : 



r^ u 6 X 81 , , 19 



Carbon = — ^ — ; hydrogen = -^ 



Multiplying these numbers by the heat-coeflScients of Favre and Sil- 

 bermann, we find — 



Heat produced by carbon = ^-^1^ X 8080 



16 



19 

 Heat produced by hydrogen = -_ x 34462 



8 



It has been already shown that the heat developed by the combustion 

 of carbon in Lavoisier's experiment amounted to 90.68 per cent, of the 

 heat emitted by the animal; hence the heat produced by the combustion 

 of the hydrogen will amount to — 



90.68 X ^213^63 ^ 16 30.24 



8 6 X 81 X 8080 



By adding together the heats due to the carbon and hydrogen, we find 

 that Lavoisier's experiments, when fairly interpreted by the data of 

 modern science, give the following results : 

 Heat produced by the combustion of carbon and hydrogen .... 120. 92 



Animal heat 100. 00 



Finally, in 1789, Lavoisier published further experiments, by which 

 he showed conclusively that the consumption of oxygen by the body is 

 notably increased by three causes — 



1. By a lowering of the external temperature. 



2. By the act of digestion. 



3. By muscular exercise. 



The experiments of Lavoisier were repeated in 1822 by Dulong and 

 Despretz, and their results, when corrected, like those of Lavoisier, by 

 using the modern heat-coefiicients of carbon and hydrogen, are as fol- 

 lows: 



The mean of Dulong's experiments on sixteen animals and birds is 

 90.6 per cent, of the animal heat given out ; the lowest number, 85.5, 

 belonging to a kitten sixty days old ; and the highest number, 99.4, 

 belonging to a puppy fifty days old. 



M. Despretz obtained an average of 92.3 from sixteen mammals and 

 { birds ; his highest number being 101.8, derived from an old female rab- 

 bit; and his lowest number being 84.2, derived from four owls. 



The foregoing experiments left no doubt remaining in the minds of 

 men of science as to the substantial truth of Lavoisier's doctrine of ani- 

 mal heat; and led immediately to a number of supplementary experi- 

 ments, among the most remarkable of which were those of Eegnault 

 and Eeiset. 



18 S 



