ABSORPTION OF NITROGEN. 545 



So far as these analyses are to be relied on, (and 

 they are perhaps the most correct of any yet 

 published,) they show that the proportions of 

 carbon and hydrogen are greater in venous than 

 arterial blood ; viz. immediately before, than after 

 passing through the lungs ; consequently, that 

 they must be there given off. They also show 

 that the ratios of oxygen and nitrogen are greater 

 in arterial than venous blood. That a portion of 

 nitrogen is absorbed from the atmosphere and 

 united chemically with the blood, might reason- 

 ably be inferred from the fact, that there is very 

 little of it in the food of herbivorous animals, in 

 whose blood it is no less abundant than in that 

 of carnivora. 



Accordingly, it has been ascertained by the 

 experiments of Sir H. Davy, Pfaff, Henderson, 

 and others, that variable proportions of nitrogen 

 disappear during the respiration of man and 

 other animals ; while Edwards contends, that it 

 is both absorbed and exhaled at the same time, 

 (but without stating whether herbivorous animals 

 consume more of it than carnivora,) which Ber- 

 zelius regards as incredible. More varied and 

 accurate experiments on different species of 

 animals are required to furnish data on which 

 to found a sure induction. So vague are the 

 views of physiologists, in regard to the im- 

 portance of attending to the elementary compo- 

 sition of the blood in different animals, that in 



