FORM IN WHICH AMMONIA IS PRESENTED. 51 



The azotised constituents of the food are transformed into 

 blood, which then nourishes the animal by restoring its wasted 

 tissues to their original condition. 



The uniform weight of an animal proves that a quan- 

 tity OF NITROGEN must have been expelled from the system, 



EXACTLY CORRESPONDING TO THE AMOUNT CONTAINED IN THE FOOD 



consumed. The compounds consisting of carbon and hydrogen, 

 derived from the waste matter, are separated by the lungs and 

 skin ; whilst those containing nitrogen are eliminated in the 

 urine. When the body increases in weight, a smaller quantity 

 of nitrogenous compounds must be separated by the urine ; a 

 diminution in weight indicates, on the other hand, a greater 

 separation of these compounds. These considerations prove that 

 the nitrogen e'xtracted from the atmosphere by plants as food, is 

 again in a great measure returned in the urine of man and other 

 animals. 



It is obvious that, by collecting both the solid and liquid excre- 

 ments of an animal fed upon the produce of a certain surface of 

 land, we are enabled to supply to it nearly the same quantity of 

 nitrogen as that contained in the original produce. Thus we 

 supply to the land a certain quantity of ammonia, in addition to 

 that which may be extracted from the atmosphere by the plants 

 growing upon it. 



In a scientific point of view, it should be the care of the agri- 

 culturist so to employ all the substances containing a large pro- 

 portion of nitrogen, which his farm affords in the form of animal 

 excrements, that they shall serve as nutriment to his own plants. 

 This will not be the case unless those substances are properly 

 distributed upon his land. A heap of manure lying unemployed 

 upon his land would serve him no more than his neighbors. The 

 nitrogen in it would escape as carbonate of ammonia into the 

 atmosphere, and a mere carbonaceous residue of decayed plants 

 would, after some years, be found in its place. 



Tacitus informs us that the surface of Germany was in his 

 time completely covered with impenetrable forests. But now 

 these no longer exist, and all their constituents have disappeared. 

 The carbon and nitrogen deposited in the soil in the form of 

 humus and ammonia have now returned to the atmosphere. 



