212 NITRIFICATION 



cloudiness of the solution was noted. The latter disappeared 

 after a time and a microscopic examination showed it to be due 

 to the presence of an oval somewhat spindle-shaped organism 

 which moved about very rapidly. Nitrification was at the same 

 time very active. It was thought that the film on the surface 

 might contain the nitrifying organisms as the acetic acid bacteria 

 and other oxidizing ferments work at the surface where plenty of 

 oxygen can be obtained, but tests with this gave negative results. 

 The plan of work was then somewhat changed. The attempt 

 was made to cultivate the nitrifying organisms more abundantly. 

 To this end a quantity of ammonium sulphate was added to the 



FIG. 30. Surface colonies of nitrosomonas on silicic acid gelatin, stained with 

 Fuchsin without removal from the gelatin. X 1200. (After Gibbs: Soil Science.) 



nitrifying cultures, and the process of nitrification thus continued 

 in the culture for some time. A change was noticed in the mag- 

 nesium carbonate at the bottom of the solution which gradually 

 assumed a grayish color and a gelatinous consistency. By shaking 

 the solution vigorously this mass was broken up into small flakes, 

 which a microscopic examination showed to consist of transparent 

 particles of the salt covered with a mass of oval bacteria, identical 

 in form with those which had previously been noticed as the cause 

 of the cloudiness. These bacteria seemed to be on the particles 

 exclusively and not on the walls of the flask, and slowly enveloped 

 the salt which was finally dissolved. 



