COLON-AEROGENES FORMS FROM NATURAL WATERS 57 



newly found cultures, using 0.5 per cent, 0.75 per cent and 1 

 per cent Difco in comparison with the standard methyl red 

 broth. While the Difco medium, with whatever concentration 

 used, is not equivalent to the standard broth-, the reversion of 

 acid reaction with definite concentrations of the substituted 

 peptone with a definite buffer reaction presents phenomena 

 affording a basis for division of cultures into provisional groups. 

 From the strains thus segregated some were selected for study 

 with standard media. 



Koser (1918) proposed the use of a medium containing no 

 nitrogen except in the form of uric acid for the discrimination of 

 colon and aerogenes forms, reporting the results with 74 strains 

 of Bad. coli and 50 of Bad. aerogenes: the former showed no 

 growth; the latter grew well. Rettger and Chen found thar, 

 with few exceptions, among the colon strains from soils the uric 

 acid test gave very satisfactory correlation with the other reac- 

 tions when necessary precautions were taken. Their culture 

 comprised 447 strains of the cloacae-aerogenes group and 20 of 

 the colon type from unpolluted soils, and 173 strains from feces 

 of men and of animals. 



To test the validity of this reaction as a criterion of high and 

 low ratio organisms, we have arranged our cultures isolated from 

 waters with reference to their uric acid reactions, for later com- 

 parison with the arrangement of specially studied strains grouped 

 according to their methyl red and Voges-Proskauer reactions. 



STUDY OF CULTURES ISOLATED FROM WATERS 



In the course of this work 392 cultures were isolated which 

 gave gas in lactose broth, more or less characteristic colonies on 

 Endo's medium, and usually gas in lactose broth after transfer 

 from the endo medium. They were tested as to their reaction 

 in Difco methyl red broths after two days; with adonitol and 

 with uric acid broth. The first series comprised 233, the second, 

 159 strains. The results are summarized in table 1. Arranged 

 according to lactose fermentation, adonitol and uric acid reac- 

 tions, they fall into 19 provisional groups to which are assigned 

 reference numbers of purely temporary value. 



