10 The Chemical Statics of Organised Beings. 



for nothing the influence of vegetables, and that, nevertheless, 

 these restore oxygen to it incessantly in quantity at least equal 

 to that it loses, and perhaps more ; for vegetables live just as 

 much at the expense of the carbonic acid furnished by volcanoes, 

 as at the expense of the carbonic acid furnished by animals them- 

 selves. It is not then for the purpose of purifying the air that 

 these breathe, that vegetables are especially necessary to animals; 

 it is, above all, to furnish them, incessantly, with organic matter 

 quite ready for assimilation ; organic matter, which they may 

 burn to their advantage. 



There is, therefore, a service necessary, without doubt, but 

 so remote, that it can scarcely be recognised, which vegetables 

 render us, in purifying the air which we consume. There is 

 another service so immediate, that if, during a single year, it 

 were to fail us, the earth would be depopulated ; it is that which 

 these same vegetables render us by preparing our nutriment, 

 and that of all the animal kingdom. In this, especially, is found 

 the chain that binds together the two kingdoms. Annihilate 

 plants, and the animals all perish of a dreadful famine ; organic 

 nature itself entirely disappears with them in a few seasons. 



We have, however, said that the carbonic acid of the air 

 varies from 4 to 6 10,000ths. These variations are very frequent, 

 and very easy to observe. Is not this a phenomenon reproach- 

 ing the influence of animals who introduce this acid into the air, 

 and that of vegetables which deprive it of it ? 



No ; this phenomenon, you are aware, is a simple meteor- 

 ological phenomenon. It is with carbonic acid as with aqueous 

 vapour, which forms on the surface of the sea, to become con- 

 densed elsewhere, fall again in rain, and be reproduced under 

 the form of vapour. This water, which is condensed and falls, 

 dissolves, and carries with it carbonic acid; this water, which 

 evaporates, yields up this same gas to the air. 



A great meteorological interest would attach to the observation 

 of the variations of the hygrometer, and those of the seasons, or 

 of the state of the sky with the variations of the carbonic acid 

 of the air; but hitherto all tends to show that these rapid 

 variations constitute a simple meteorological event, and not, as 

 had been thought, a physiological event, which, singly con- 

 sidered, would infallibly produce variations infinitely slower 

 than those which are, in fact, observed as much in towns as in 

 the country itself. 



Thus the air is an immense reservoir, whence plants may for 

 a long time derive all the carbonic acid necessary for their 

 wants ; where animals, during a much longer time still, will 

 find all the oxygen that they can consume. It is also from the 

 atmosphere that plants derive their azote, whether directly or 

 indirectly : it is there that animals finally restore it. 



