M. Dumas o?^ the Chemical Statics of Organized Beifigs. 363 



plants, which, like Jerusalem artichokes, draw their azote di- 

 rectly from the air. 



But this is not all the azote which animals exhale. Every 

 one gives out by the urine, on an average, as M. Lecanu has 

 proved, 230 grains of azote a day, of azote evidently drawn 

 from our food, like the carbon and hydrogen which are oxi- 

 dized within us {que ?ious brulo7is). 



In what form does this azote escape? In the form of am- 

 monia. Here indeed, one of those observations presents it- 

 self which never fail to fill us with admiration for the simpli- 

 city of the means which nature puts in operation. 



If in the general order of thincfs we return to the air the 

 azote which certain vegetables may sometimes directly make 

 use of, it ought to happen that we should also be bound to 

 return ammonia, a product so necessary to the existence and 

 development of most vegetables. 



Such is tiie principal result of the urinary secretion. It is 

 an emission of ammonia, which returns to the soil or to the air. 



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

 organs would be changed in their functions and in their vi- 

 tality by the contact of ammonia? the contact of the carbo- 

 nate 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 hydro- 

 gen and oxygen, so much as is wanting to constitute two mo- 

 lecules of water. 



Deprived of this water the carbonate of ammonia becomes 

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

 branes; 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 ex- 

 haling in the air; soluble, so that it may be taken up again by 

 rain ; and consequently 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 

 analysis. This, hovvever, when it has reached the air, is there 

 modified, and becomes one of those ferments of which we find 

 so many in organic nature; it is this which determines the 

 conversion of urea into carbonate of ammonia. 



