Source of Carbon and Nitrogen in Plants and Animals. 3G3 



have been in an equally forward condition, so as to be ready at the same , 

 moment for the reception of a redundant vegetation. If, however, we 

 were to grant that the whole of the primary vegetation of the globe had 

 started into being at once, as soon as the conditions of the earth's sur- 

 face admitted, we should be bound to suppose the character of the 

 plants analogous rather to those existing in countries not yet brought 

 under the dominion of man, than to those of cultivated districts. 



Now, it is to be remarked, that the plants most useful to the higher 

 classes of animals, inasmuch as they afford the greatest abundance of 

 nourishment, are comparatively rare in a wild condition, and when they 

 occur, are generally deficient in those principles on which their value as 

 articles of food depends. 



The forests which, under such circumstances, cover so large a portion 

 of the surface, contain but a small amount of nitrogen, for woody fibre, 

 which constitutes the greater part of their bulk, is wholly destitute of 

 that principle. The cruciferee, the different species of cereal grasses, and 

 other plants rich in nitrogen, require for their full development animal 

 manure, and therefore, if they had come into being at all at this early, 

 period, must have been stunted in their growth and limited in their dis- 

 tribution. 



Thence, it may be fairly doubted whether the whole amount of the 

 plants which existed at one time on the surface of the globe, would have 

 furnished azote enough for the animals of any given period. 



Thirdly, it seems reasonable to suppose that civilization has, upon the 

 whole, increased the aggregate of animal life as well as that of such vege- 

 tables as contain the largest quantity of nutritious matter. I am aware 

 how difficult it would be to establish this last position in a manner per- 

 fectly unexceptionable, because the progress of human society is attended 

 by a corresponding diminution in the amount of those animals and of 

 those plants which are not dependent on man, and it seems impossible to 

 strike a correct balance between the effects attributable to these two 

 counteracting causes. Nevertheless, the following considerations may 

 perhaps be allowed to favour the opinion which I have been advocating. 



There can be little doubt that, within the area embraced by culture, 

 the amount of nutritious matter goes on increasing with the care bestowed 

 upon the land, and that the number of animals maintained is in consequence 

 proportionably increased. This will be the case on a well-managed farm, 

 even where (being situate at a distance from a town), it consumes no 

 more manure than is obtained on the premises. At the end of a century 

 the live stock may be increased, the crops may be more abundant than 

 they were at the beginning, and yet every year a large quantity of car- 

 bon and nitrogen will have been carried off in the shape of the corn and 

 cattle sold. Whence does this excess of carbon and of nitrogen then 

 proceed ? If from the decomposition of animals and vegetables extraneous 

 to the farm, other portions of the globe must suffer in proportion to what 

 is gained by those in cultivation, and hence the vegetation, as well as the 



