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Scientific Proceedings (130) 



ment inoculated on silica jelly by means of a loop and from the 

 colonies that developed, inoculations were made into synthetic 

 solutions, positive tests would be obtained. This applied to both 

 the "nitrite" and the "nitrate" organisms. Now if these positive 

 cultures were inoculated on nutrient agar, growth would appear. 

 This growth would not cause nitrification, showing the cultures 

 in question were not pure. In one experiment the synthetic 

 solution for nitrate bacteria which gave a positive test was cen- 

 trifuged and inoculated on a gypsum block partly immersed in 

 the synthetic solution. From the growth later obtained, dilu- 

 tions were made and plated on silica jelly. Ten colonies were 

 picked. Five grew on nutrient agar and live did not. The ten 

 cultures were inoculated into the synthetic solution for nitrate 

 formation. The five that did not grow on nutrient agar never 

 developed any nitrates, the other five that were shown contami- 

 nated by the growth on nutrient agar all gave positive tests for 

 nitrate after incubation. The procedure has been varied in many 

 ways, but whenever and by whatever method used, when a 

 positive test was obtained after incubation in the synthetic solu- 

 tion, organisms were present that grew on nutrient agar. 



Two possibilities occurred to the writer. Are the nitrifying 

 organisms filterable or do they get some substance from the 

 bacteria that accompany them, that grow on nutrient agar. 



No nitrification was ever obtained from a Berkefeld filtrate of a 

 solution giving a positive test for nitrites or nitrates no matter 

 what was added to the synthetic solution in addition to the in- 

 organic constituents. 



The work in connection with the second hypothesis was done 

 only with the nitrite organisms, those oxidizing ammonia to 

 nitrite compounds. In transferring cultures about two c.c. are 

 added to 100 c.c. of the synthetic solution. In a week a strong 

 positive test is obtained, when transfers are again made. If less 

 inoculum is used a longer time is required. 



One c.c. of a very weak culture of nitrite bacteria was added 

 to synthetic solutions that had quantities of the following added, 

 Berkefeld filtrate of nutrient agar bacteria, nutrient agar bac- 

 teria, dead nutrient agar bacteria, fresh soil, sterilized soil, and 

 Berk f eld filtrate of soil solution, as well as to the check (syn- 

 thetic solution). It was found after incubation that more nitrite 

 was formed in every case in a given time than in the check. The 



