The Chemical Statics of Organised Beings. 63 



But is there any need to remark here, that the urinary organs 

 would be changed in their functions and in their vitality by the 

 contact of ammonia ? the contact of the carbonate of ammonia 

 would even effect this ; and so nature causes us to excrete urea. 



Urea is carbonate of ammonia, that is to say, carbonic acid 

 like that which we expire, and ammonia such as plants require. 

 But this carbonate of ammonia has lost of hydrogen and oxygen 

 so much as is wanting to constitute two molecules of water. 



Deprived of this water the carbonate of ammonia becomes 

 urea ; then it is neutral, not acting upon the animal membranes; 

 then it may pass through the kidneys, the ureters, and the 

 bladder, without inflaming them : but, having reached the air, 

 it undergoes a true fermentation, which restores to it these two 

 molecules of water, and which makes of this same urea true 

 carbonate of ammonia ; volatile, capable of exhaling in the air; 

 soluble, so that it may be taken up again by rain ; and conse- 

 quently destined thus to travel from the earth to the air, and 

 from the air to the earth, until, pumped up by the roots of a 

 plant and elaborated by it, it is converted anew into an organic 

 matter. 



Let us add another feature to this picture. In the urine, 

 along with urea, nature has placed some traces of albuminous or 

 mucous animal matter, traces which are barely sensible to ana- 

 lysis. This, however, when it has reached the air, is there mo- 

 dified, and becomes one of those ferments of which we find so 

 many in organic nature ; it is this which determines the conver- 

 sion of urea into carbonate of ammonia. 



These ferments, which have so powerfully attracted our atten- 

 tion, and which preside over the most remarkable metamor- 

 phoses of organic chemistry, I reserve for the next year, when I 

 shall give you a still more particular and full account of them. 



Thus we discharge urea accompanied by this ferment, by this 

 artifice, which, acting at a given moment, turns this urea into 

 carbonate of ammonia. 



If we restore to the general phenomenon of animal combus- 

 tion that carbonic acid of the carbonate of ammonia which of 

 right belongs to it, there remains ammonia as the characteristic 

 product of urine. 



Thus, by the lungs and the skin, carbonic acid, water, azote. 



By the urine, ammonia. 



Such are the constant and necessary products which exhale 

 from the animal. 



These are precisely those which vegetation demands and 

 makes use of, just as the vegetable in its turn gives back to the 

 air the oxygen which the animal has consumed. 



Whence come this carbon, this hydrogen burnt by the animal, 



