68 ORIGIN AND ASSIMILATION OF NITROGEN. 



as an invariable rule, the seed of all plants con- 

 tains a much larger quantity of nitrogen, than 

 the leaves and stalks, and a lesser quantity of 

 carbon, and inversely, the leaves and stalks 

 contain a much greater quantity of carbon, 

 and a lesser quantity of nitrogen. Now when 

 a horse is fed on grass, his food consists almost 

 entirely of carbon, and the result is, that when 

 he has a sufficient supply he gets fat ; that is, 

 that particles of oily fatty matter are deposited 

 on the muscles under the skin, but as it is well 

 known, a horse in this condition is quite un- 

 equal to any work, and the least exertion re- 

 duces his bulk. But when the same horse 

 under other circumstances is fed on corn, his 

 food consists principally of nitrogen, and al- 

 though he may never under this keep, get as 

 fat as under the other, still the increase he does 

 acquire will be pure muscle, or as it is techni- 

 cally called, sound flesh ; and on this keep he 

 can perform infinitely more work with less 

 fatigue, than on food containing no nitrogen. 



A more comiplete instance could not be ad- 

 duced to show^ that animals as well as plants 

 can only assimilate that food which is pre- 

 sented them: in the first case, carbonaceous 

 matters being the food of the horse, carbon is 

 deposited in the shape of fat; in the latter, 

 when more nitrogen enters into the composi- 

 tion of his food, the deposite of muscle prepon- 

 derates. So it is with wheat. With a manure 

 that only supplies carbonaceous matter, starch 

 is the result. With a manure containing ni- 

 trogen, gluten is formed — both cases being 



