326 Biological Chemistry. 



At the expiration of this period it was again analyzed, and 

 it was found that the amount of organic nitrogen had 

 diminished, whereas the quantity of nitrates had increased. 

 In 1877 Schlosing and Miintz carried out some experi- 

 ments which indicated that the nitrification (nitrate for- 

 mation) of the organic nitrogen compounds was probably 

 due to the presence of bacteria. They allowed ammoniacal 

 sewage water to pass slowly through a filter of sand and 

 chalk, and found that part of the ammonium salts was 

 converted into nitrates. If, however, the filter bed had 

 been treated with chloroform, nitrate formation did not 

 take place. The actual isolation of nitrifying organism in 

 the soil is due to Winogradsky (1890). This observer 

 succeeded in isolating three classes of bacteria which take 

 part in the nitrification process. Of these, two classes, 

 namely nitrosomonas and nitrosococcus, of which the latter 

 is found on the American continent, can, under suitable 

 conditions of cultivation, convert ammonium salts into 

 nitrites. A third class of bacteria, nitrobacter, converts 

 nitrites into nitrates. These bacteria by themselves will 

 not, however, convert organic nitrogen compounds into 

 nitrates ; ammonium derivatives must first be formed 

 before the above nitrifying bacteria can carry out the pro- 

 cess of nitrification. There is a large number of organisms, 

 however, which can bring about the formation of ammonia 

 from complex organic compounds ; in fact, ammonia is a 

 common product of putrefaction, and is produced in appre- 

 ciable quantities when proteins are allowed to undergo 

 putrefactive decay. Omeliansky has shown that when the 

 source of nitrogen contains only complex organic com- 

 pounds it can serve as a source of nitrates when submitted 

 to the action of three species of bacteria. Using a substrate, 

 of which the nitrogen source was a meat bouillon, he 

 obtained nitrates, when the following three bacteria were 



