76 AGRICULTURAL BACTERIOLOGY. 



RESTORATION OF NITROGEN TO THE SOIL. 



The problem of the nitrogen transformations is of far more 

 significance to the fertility of the soil than that of carbon. 

 Plants assimilate the nitrates from the soil and build them 

 into proteids. Some of these proteids are stored in various 

 plant products and, after the death of the plant, undergo de- 

 composition through the agency of bacteria. But inasmuch 

 as the further history of these bodies is precisely the same as 

 that of animal proteids we may consider them at the same 

 time with the study of animal proteids. 



Animals appropriate a part of the materials built by plants 

 and make further changes in them. They use the sugars, 

 starches, fats and proteids and build them into still other com- 

 pounds. The compounds built by animals are, of course, 

 numerous, but the chief ones are fats, sugars and proteids 

 which are not more complicated than similar bodies in plants 

 and not particularly different from them. Animals, in other 

 words, do not make higher compounds than do plants. But 

 the animal body contains considerably more nitrogen than the 

 plant and considerably less carbonaceous material. In ad- 

 dition to the proteid material, which is very much more abun- 

 dant in animals than in plants, there are other nitrogenous 

 compounds more or less closely related to them. Gelatins, 

 for example, which form the chemical basis of tendons and 

 ligaments, are not true proteids although closely related. 

 Chondrin is a similar nitrogenous body forming the basis of 

 cartilage. The animal body, in short, contains large amounts 

 of nitrogenous material in a highly complex form. 



Thus, starting from the nitrates or ammonia in the soil, the 

 nitrogen has been, by the agency of vegetable life, built up 

 into proteids, and by the animal life is more or less transformed 

 but not changed in its essential chemical nature. It has, how- 

 ever, become somewhat condensed since the animal stores in 

 its tissue the nitrogen obtained from a large amount of vege- 



