40 FIELD, FOREST AND FARM 



in the process of combustion releases carbon, phos- 

 phorus, sulphur, and other combustibles, to combine 

 with them and produce a compound known as car- 

 bonic acid gas in the case of burnt carbon, phos- 

 phoric acid in the case of phosphorus. In fact, to 

 it belong the properties that we have until now at- 

 tributed to the atmosphere as a whole. As for 

 nitrogen, it has no other purpose in the atmosphere 

 than to moderate by its presence the too violent ener- 

 gies of oxygen ; it plays there the part of the water 

 that we put into too strong wine. 



"All vegetation requires nitrogen. "Wheat, for 

 example, must have it to develop the grain in the 

 ear ; peas, beans, lentils demand it in order to fill out 

 their pods; the pasture and the hay-field need it if 

 they are to furnish the nutriment that the sheep and 

 the cow will transform into milk. But plants can- 

 not take this nitrogen from the air, where it is so 

 abundant ; it must be served up to them after a cer- 

 tain necessary preparation. We ourselves need 

 phosphorus, since it enters into the composition of 

 our bones; we need carbon still more, the principal 

 fuel used in maintaining the heat of the body. But 

 are we to eat the charcoal that the charcoal-burner 

 manufactures in his furnace, and the phosphorus 

 used in the making of matches? Certainly not. 

 The first would be a frightful mouthful, the second 

 an atrocious poison. We must have them prepared 

 in a suitable way, such as they are found in bread, 

 milk, meat, fruits, vegetables. In the same manner 

 plant-life requires nitrogen, not as it occurs in the 



