COLON-AEROGENES GROUP OF BACTERIA 



285 



which are used must be scrupulously clean; small amounts of 

 nitrogenous matter left on the walls may furnish sufficient nitro- 

 gen for the organisms to multiply so as to obscure the sharp 

 distinction between the appearance of the B. coli and B. aerogenes 

 tubes after the required time of incubation, four to five days 

 at 30°C. 



A twenty-four hours growth of the organism under observation 

 was used as a rule as inoculum, and this was transferred with 

 precaution, so as to limit as far as possible the amount of cell 

 material and products of bacterial metabolism which are carried 

 over. The results of the tests with the uric acid medium are 

 summarized in the following table. 



All of the aerogenes strains (soil) gave a very pronounced 

 growth in the uric acid medium, while none of the fecal strains 

 of the coli type clouded the medium or in any way showed indi- 

 cations of development. The differentiation was in every in- 

 stance sharp though the degree of turbidity varied much. How- 

 ever, considerable discrepancy was observed among the coli 

 strains isolated from soils. Of the 20 cultures employed 10 were 

 uric acid positive and 10 negative. In the tubes in which the 

 uric acid was attacked the growth was as luxuriant as in typical 

 cultures of the aerogenes type. Lack of correlation here of the 

 10 uric acid positive strains of soil coli with the methyl red test 

 and Voges and Proskauer reaction may be of some significance 

 as pointing to the possibility that these ten strains are of a type 

 intermediate between the coli and the aerogenes. 



The same results were obtained in the xanthine synthetic 

 medium as in the uric acid, except with the soil strains of B. coli, 

 which goes to show further that the failure of B. coli to utilize 

 the nitrogen is due to its inability to disrupt the purin ring, 



