1 9 1 q] bona ZZI—NI TRIFICA TION 20 I 



Cultures in solution 



Macroscopic examination of young solution cultures reveals 

 no indication of bacterial growth, and it is not until much ammonia 

 has been oxidized to nitrite that any macroscopic growth is 

 apparent. By observing the bottom of the culture flask 30-40 

 days' old an inconspicuous slimy deposit is visible which is 

 easily dispersed by shaking. Before this pomt is reached no cloud- 

 ing or movement of the solution is visible, such as the "trouble" 

 imparted to the solution by the "monad stage" of the European 

 organisms. In fact no distinction can be drawn between the 

 inoculated and non-inoculated flasks incubated for the same 

 period of time. This similarity is maintained throughout the 

 life of cultures which have been kept in this laboratory for over 2 

 months. No surface growth is visible, even when the cultures have 

 attained very old age. Two cultures, which had nitrified 74.41 

 and 48 . 10 mg. of ammoniacal nitrogen while at rest, showed no 

 surface growth whatever. Xo motility can be observed in the 

 cultures, and this is in conformity with the behavior of the South 

 American cultures described by Winogradsky. In all the work 

 with solutions at rest we have adopted the use of 20 or 25 cc. of 

 solution in 250 or 300 cc. Erlenmeyer flasks, since this depth of 

 solution furnishes a relatively good aeration. 



Cultures on solid media 



Several solid media have been tried in this laboratorv in the 

 hope that a satisfactory method could be found which would be 

 advantageous to the speedy growth of the organism of " nitrosofer- 

 mentation." Among others there were tried the paper pad method 

 and the gypsum block method of Omelianski (6), the magne- 

 sium carbonate block method of Perotti (7), the magnesium 

 carbonate and ammonium-magnesium-phosphate block method 

 of Makrinoff (5), the ammonium sulphate washed agar method 

 of Beijerinck (i),4 the sihcic acid jelly method of Stevens and 



* The method of Beijerinck was also modified so that the washed agar only 

 came in contact with the salts a few minutes before inoculation. This was accom- 

 plished by incorporating, just before plating, the necessary quantity of salts dissolved 

 in 5 cc. of water with 5 cc. of a melted washed agar jelly, mixing thoroughly, inoculat- 

 ing, and plating. The action of the salts on the agar at high temperatures was thereby 

 avoided. 



