The Chemical Sialics of Organised Beings. 3 



returns to the atmosphere under the form of carbonic acid; in 

 which hydrogen burnt without ceasing, on its part continually 

 engenders water; whence, in fine, free azote is incessantly ex- 

 haled by respiration, and azote in the state of oxide of ammonium 

 by the urine ? 



Thus from the animal kingdom, considered collectively, con- 

 stantly escape carbonic acid, water in the state of vapour, azote, 

 and oxide of ammonium, simple substances, and few in number, 

 the formation of which is strictly connected with the history of 

 the air itself. Have we not, on the other hand, proved that 

 plants, in their normal life, decompose carbonic acid for the 

 purpose of fixing its carbon and of disengaging its oxygen; that 

 they decompose water to combine with its hydrogen, and to dis- 

 engage also its oxygen; that, in fine, they sometimes borrow 

 azote directly from the air, and sometimes indirectly from the 

 oxide of ammonium, or from nitric acid, thus working in every 

 case in a manner the inverse of that which is peculiar to animals ? 

 If the animal kingdom constitutes an immense apparatus for com- 

 bustion, the vegetable kingdom, in its turn, constitutes an 

 immense apparatus for reduction, in which reduced carbonic 

 acid yields its carbon, reduced water its hydrogen, and in which 

 also reduced oxide of ammonium and nitric acid yield their 

 ammonium or their azote. 



If animals, then, continually produce carbonic acid, water, 

 azote, oxide of ammonium ; plants incessantly consume oxide 

 of ammonium, azote, water, carbonic acid. What the one class 

 of beings gives to the air, the others take back from it ; so that 

 to take these facts at the loftiest point of view of terrestrial phy- 

 sics, we must say that, as to their truly organic elements, plants 

 and animals spring from air, are nothing but condensed air ; 

 and that, in order to form a just and true idea of the constitu- 

 tion of the atmosphere at the epochs which preceded the birth 

 of the first organised beings on the surface of the globe, there 

 must be placed to the account of the air, by calculation, that 

 carbonic acid and azote whose elements have been appropriated 

 by plants and animals. Thus plants and animals come from the 

 air, and thus to it they return ; they are real dependences of the 

 atmosphere. 



Plants, then, incessantly take from the air what is given to 

 it by animals ; that is to say, carbon, hydrogen, and azote, or 

 rather, carbonic acid, water, and ammonia. 



It now remains to be stated, how in their turn, animals ac- 

 quire those elements which they restore to the atmosphere ; and 

 we cannot see without admiring the sublime simplicity of all 

 these laws of nature, that animals always borrow these elements 

 from plants themselves. 



We have, indeed, ascertained, from the most satisfactory re- 



b 2 



