19I91 



MONAZZI—NITRIFICA TION 



199 



ammoniacal salt being added only if the culture showed no 

 ammonia reaction when tested with Nessler's reagent. From 

 these enrichment cultures new cultures were started in solution 

 with small inoculi. The culture solution used in all this work 

 was the one recommended by Omelianski (6), of the following 

 composition: H,0, 1000 cc; FeS04, 0.4 gm.; MgS04, 0.5 gm.; 

 K2HPO4, i.ogm.; NaCl, 2.ogm.; (NH4)2S04, 2.ogm. 



Filtration of the solution was deemed unnecessary, since the 

 addition of MgC03 milk after sterilization would make the practice 

 useless. Growth was not impaired by preliminary filtration of 

 the medium. After several transfers in solution, attempts w^ere 

 made at the isolation of pure cultures by plating in ammonium 

 sulphate washed agar. Two consecutive platings in this medium 



SoU .... 



Solution 



Solution 



Washed agar plates 



Washed agar slants 



Washed agar plates 



Solution 



TABLE I 



o Silica jelly plates 63 



19 Solution 66 



24 SUica jelly plates 71 



34 Solution 76 



40 Solution 84 



50 Solution 86 



59 



gave cultures which did not fulfil the requirements of the "cri- 

 teria of purity." It was only after 3 consecutive platings in a 

 silicic acid jelly medium (6) that cultures were obtained which 

 proved pure to the criteria. The genealogic succession of the 

 cultures is shown in table I, where the series number accompanies 

 the description of the medium used in each generation studied. 



It was only a culture of series 86 in solution that, when 

 inoculated in bouillon of a +1 per cent and a — i per cent reaction, 

 gave no growth whatsoever, either before or after the lo-day period 

 had elapsed. Microscopically no foreign forms were seen, and a 

 perfectly pure culture was indicated by this test. Unfortunately, 

 after this culture was obtained it was observed that its action 

 was relatively slow, and in subsequent transfers the inoculi used 

 were very large, i or 2 cc. Notwithstanding these precautions, 

 after the cultures had been transferred once or twice again they 



