PIG. 9. 



The air is the great source from which all the nourishment 

 of the organic creation, whether vegetable or animal, is 

 derived ; its carbonic acid is decomposed by the vegetables, 

 which appropriate the carbon, turning over the oxygen to 

 their companions, the animals ; the ammonia of the air 

 furnishes all the nitrogen of seeds and other nutritious 

 parts of vegetables, which are eaten by animals ; and water, 

 the chief source of all nutriment, passes first from the air 

 before it enters the soil, bringing both carbonic acid and 

 ammonia to fertilise it. That all this nourishment is derived 

 from the air is evidently shown by the formation and 

 increase of mould in forests which have grown for centuries ; 

 this black mould is nearly all decayed vegetable matter, 

 formed by the continuous fall and decay of leaves and trees, 

 but which, instead of diminishing, increases. Now, where 

 does all this come from ? certainly not out of the earth, for 

 it does not contain the necessary elements. Expose the 

 surface of the bare earth for several centuries, and first 

 small plants, then larger ones, will grow upon it, until the 

 state of things described above takes place, the earth being 



