2l6 BESPIRATIOX. 



returned in the exhaled carbonic acid, all observers agree, 

 though as to the actual quantity of oxygen so absorbed 

 they differ even widely. 



The quantity of oxygen that does not combine with the 

 carbon given off in carbonic acid from the lungs, is probably 

 disposed of in forming some of the carbonic acid and water 

 given off from the skin, and in combining with sulphur and 

 phosphorus to form part of the acids of the sulphates and 

 phosphates excreted in the urine, and probably also, from 

 the experiments of Dr. Bence Jones, with the nitrogen of 

 the decomposing nitrogenous tissues. 



The quantity of oxygen consumed seems to vary much, 

 not only in different individuals, but in the same individual 

 at different periods ; thus it is considerably influenced by 

 food, being greater in dogs when fed on farinaceous than 

 on animal food, and much diminished during fasting, while 

 it varies at different stages of digestion. Animals of small 

 size consume a relatively much greater amount of oxygen 

 than larger ones. The quantity of oxygen in the atmosphere 

 surrounding animals, appears to have very little influence 

 on the amount of this gas absorbed by them, for the quan- 

 tity consumed is not greater even though an excess of 

 oxygen be added to the atmosphere experimented with 

 (liegnault and Reiset). 



The Nitrogen of the Atmosphere, in relation to the respira- 

 tory process, is supposed to serve only mechanically, by 

 diluting the oxygen, and moderating its action upon the 

 system. This purpose, or the mode of expressing it, has 

 been denied by Liebig, on the ground that if we suppose 

 the nitrogen removed, the amount of oxygen in a given 

 space would not be altered. But, although it be true that, 

 if all the nitrogen of the atmosphere were removed and 

 not replaced by any other gas, the oxygen might still 

 extend over the whole space at present occupied by the 

 mixture of which the atmosphere is composed; yet since, 

 under ordinary circumstances, oxygen and nitrogen, when 



