ON CARBON. 55 



functions here described and to be the puri- 

 fyers of the atmosphere, how can it be ex- 

 plained that a larger proportion of carbonic acid 

 does not exist in the atmosphere during the 

 winter, when vegetation is completely torpid, 

 than in the summer; seeing that in the one 

 case every source for the supply of carbon 

 exists in excess, and in the other that all the 

 sources for the supply of oxygen are in abey- 

 ance ? 



" This would certainly form a cogent argu- 

 ment did we not look on the whole field of cre- 

 ation at once. The proper, constant, and in- 

 exhaustible sources of oxygen gas are the 

 tropics and warm climates; w^here a sky, sel- 

 dom clouded, permits the sun to shine upon an 

 immeasurably luxuriant vegetation. The tem- 

 perate and cold zones must on the contrary pro- 

 duce a superabundance of carbonic acid, which 

 serves as a supply to the tropical plants, and the 

 same current of air which in its constant pas- 

 sage from the equator to the poles, brings with 

 it a supply of oxygen, also takes away the ex- 

 cess of carbon, and thus equalizes the bless- 

 ings of a pure air to the whole earth." 



Thus plants not only afford the means of 

 nutrition to all animals, but they likewise per- 

 form an important part in the creation in puri- 

 fying the atmosphere from all noxious matter, 

 and furnishing an inexhaustible source of pure 

 oxygen. 



Animals, on the contrary, consume the oxy- 

 gen and expire the carbon, which furnishes 



