912 DO ANIMALS EVER OBTAIN NITROGEN 



and growth of animals. He therefore reduces 

 all aliments to two classes, one of which he calls 

 elements of inspiration, and the other, elements of 

 nutrition, maintaining, that if animals were not 

 supplied with the former, their organism would 

 be destroyed by the action of atmospheric oxy- 

 gen ; and that if not supplied with nitrogenized 

 matter, they would perish from starvation. (Vol. 

 ii. pp. 43, 45, 75, 76, 96.) 



In support of the assertion, that all the nitro- 

 gen contained in the blood and organized tissues 

 of animals is obtained with their food, and none 

 from the atmosphere by respiration, Liebig has 

 offered no experiments of his own ; and what is 

 rather surprising, has not taken the slightest no- 

 tice of the numerous and accurate experiments of 

 many distinguished chemists, whose results are 

 in direct opposition to his theory. Passing over 

 those of Priestley, it was found by the varied and 

 often repeated experiments of Spallanzani, on 

 birds, mammalia, reptiles, and insects that in 

 nearly all cases, respiration was attended with a 

 notable disappearance of nitrogen. The same 

 results were obtained by the still more careful 

 experiments of Humboldt and Provencal, who 

 found that during the respiration of fishes, the 

 mean proportion of nitrogen that disappeared, 

 was as 57*6 to 145*4 of oxygen. It was also as- 

 certained by numerous experiments of Sir Hum- 

 phrey Davy on himself, that about 18 per cent. 



