338 THE VITAL FUNCTIONS. 



of the oxygen, which disappears during respi- 

 ration, is employed in the formation of carbonic 

 acid gas : it appears probable, however, from 

 the concurring testimony of many experimen- 

 talists, that a small quantity is permanently 

 absorbed by the blood, and enters into it as one 

 of its constituents. 



A similar question arises with respect to 

 nitrogen, of which, as I have already mentioned, 

 it is probable that a small quantity disappears 

 from the air when it is respired ; although the 

 accounts of experimentalists are not uniform on 

 this point. The absorption of nitrogen during 

 respiration was one of the results which Dr. 

 Priestley had deduced from his experiments : 

 and this fact, though often doubted, appears, on 

 the whole, to be tolerably well ascertained by the 

 inquiries of Davy, PfafF, and Henderson. With 

 regard to the respiration of cold-blooded animals, 

 it has been satisfactorily established by the 

 researches of Spallanzani, and more especially 

 by those of Humboldt and Proven9al, on fishes, 

 that nitrogen is actually absorbed. A confirma- 

 tion of this result has recently been obtained by 

 Messrs. Macaire and Marcet, who have found 

 that the blood contains a larger proportion of 

 nitrogen than the chyle, from which it is formed. 

 We can discover no other source from which 

 chyle could acquire this additional quantity of 

 nitrogen, during its conversion into blood, than 



