THE SAPROGENIC AND SAPROPHILIC BACTERIA 227 



and converted into nitrites. The nitrites thus formed are 

 again acted upon by the nitrifying bacteria of the soil, and as 

 a result nitrates are produced. In this manner the nitrogen 

 locked in the protein molecule is again made available for 

 plant use. This process is known as nitrification. Bac- 

 teria which have the power of abstracting the oxygen of the 

 nitrate compound are noted in some soils. These organisms, 

 by again breaking up this compound, which is useful to the 

 plant, are, obviously, very detrimental to soil fertility. This 

 class of bacteria is called denitrifying organisms. 



