162 Bacteria in Relation to Country Life 



plant-food from the soil-moisture by certain species 

 to the disadvantage of the crop is an important factor 

 in cultivation of the soil. 



Ammonification. — Plants take up most of their 

 nitrogen in the form of nitrates, which are simple sub- 

 stances when compared with the humus from which 

 they are drawn. According to our present knowledge, 

 the change of humus-nitrogen into nitrate cannot be 

 accomplished by a single kind of bacteria. There are 

 at least three well-defined steps in this process of change, 

 each accomplished by a different species. The first step 

 in the transformation involves the production of am- 

 monia, the second, the change of ammonia to nitrite, 

 the third, the change of nitrite to nitrate. The last 

 named is the final product of these combined activities 

 which may serve as a splendid illustration of the speciali- 

 zation in the work of soil bacteria. In the course of 

 many ages there has been established this division of 

 labor by the adaption of certain bacteria to only one 

 kind of work. The microorganisms that can change 

 protein nitrogen to ammonia cannot transform the 

 latter to nitrite; nor can the nitrite bacteria change 

 nitrite to nitrate. The formation of ammonia as the 

 first step in the decomposition of protein substance is 

 designated as "ammonification." 



Ammonifying bacteria. — The bacteria capable of 

 producing ammonia out of protein compounds are 

 called "ammonifying bacteria." There are many kinds 

 of ammonifying bacteria. Some of them are aerobic 

 others are anaerobic. Some can produce large amounts 

 of ammonia in a given time, others but a slight amount 



