LECT. VII. SOURCE OF THE CARBON EVOLVED. 143 



When the serpent had regained its original weight no 

 trace of its prey was discoverable. Let us analyze this 

 simple case of nutrition. The urate of ammonia contains 1 

 equivalent of azote for 2 equivalents of carbon ; the muscles 

 and the blood of the animal eaten contain 8 equivalents of 

 carbon for 1 of azote ; and if we add to this the carbon con- 

 tained in the fat and nervous substance, it is obvious that 

 the serpent took more than 8 equivalents of carbon for 

 every equivalent of azote. Now in the excrements only 2 

 equivalents of carbon were found ; the 6 equivalents missing, 

 must have been given out in the form of carbonic acid. I 

 shall not stop to repeat to you our belief that the urate of 

 ammonia and carbonic acid are derived from the trans- 

 formed animal tissues, the place of which has been supplied 

 by equivalents taken from the organic elements of the di- 

 gested animal. We always find as much carbon and azote 

 in the products of the transformation which the tissues 

 suffer, in the presence of arterial blood, as the tissues them- 

 selves derive from the blood or the aliments. 



What I have now told you of the serpent, holds good 

 with the lion and all carnivora: in their urine there is urea 

 only, which contains an equal number of equivalents of 

 azote and carbon. As these animals are nourished on 

 meat which contains azote and carbon in the ratio of 8 

 equivalents to 1, it follows that all the introduced carbon, 

 beyond the amount which we find in the urine, must have 

 disappeared in the process of respiration, have been burnt 

 and converted into carbonic acid. The respiration of the 

 lion is certainly much more active than that of the serpent. 



The fifteen or twenty grammes [about 231 J grs. to about 

 309 grs. troy] of azote which a man daily passes in his 

 urine, as well as the excess of azote which he expires, 

 comes from the neutral azotised substances with which he 

 is nourished, and more directly from the transformed tissues 

 which the alimentary substances are about to replace. 



