62 The Chemical Statics of Organised Beings. 



slight an excess of heat, that it becomes difficult or impossible 

 to observe it. 



But, nevertheless, reflection shows us that the most constant 

 character of animal existence resides in this combustion of car- 

 bon, and in the developement of carbonic acid which is the re- 

 sult of it; beginning, also, in the production of heat, which every 

 combustion of carbon occasions. 



Whether the question be of superior or inferior animals; 

 whether this carbonic acid be exhaled from the lungs or from 

 the skin, does not signify; it is always the same phenomenon, 

 the same function. 



At the same time that animals burn carbon, they also burn 

 hydrogen ; this is a point proved by the constant disappearance 

 of hydrogen which takes place in their respiration. 



Besides, they continually exhale azote. I insist upon this 

 point, and principally in order to banish an illusion which I can- 

 not but believe to be one of the most prejudicial to your studies. 

 Some observers have admitted that there is an absorption of 

 azote in respiration, but which never appears unaccompanied by 

 circumstances that render it more than doubtful. The constant 

 phenomenon is the exhalation of gas. 



We must therefore conclude with certainty, that we never 

 borrow azote from the air ; that the air is never an aliment to us ; 

 and that we merely take from it the oxygen necessary to form 

 carbonic acid with our carbon, and water with our hydrogen. 



The azote exhaled proceeds, then, from the aliments, and it 

 originates in them entirely. This, in the general economy of 

 nature, may in thousands of centuries be absorbed by plants 

 which, like Jerusalem artichokes, draw their azote directly 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 oxidised within 

 us (que nous brulons). 



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

 nia. Here, indeed, one of those observations presents itself 

 which never fail to fill us with admiration for the simplicity of 

 the means which nature puts in operation. 



If in the general order of things 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 ammo- 

 nia, a product so necessary to the existence and developement of 

 most vegetables. 



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

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



