COLON-AEROGENES GROUP OF BACTERIA 293 



be obtained, however, in the theobromine and caffeine synthetic 

 media, either of the coli or of the aerogenes type. This was 

 due, in all probability, to an inhibitive or antiseptic action of 

 these substances, even in the small amount in which they were 

 used. B. aerogenes is able to attack the purin ring of xanthine, 

 hypoxanthine and uric acid, and thus appropriate nitrogen in 

 a sufficient degree to develop in the synthetic medium more or 

 less luxuriantly, whereas B. coli lacks this property. The dif- 

 ferentiation is sharp. 



SUMMARY 



The present study of coli-like organism in soils of known 

 sanitary quality has shown the great predominance of the aerog- 

 enes-cloacae type. Of 467 strains of bacteria isolated from vari- 

 ous soils 430 were identified as B. aerogenes, 17 as B. cloacae, 

 and only 20 as B. coli. Furthermore, the sources of the coli 

 strains were shown by the sanitary survey to be not entirely 

 free from animal pollution. All of the 173 organisms found in 

 the feces of 7 men, 2 monkeys and 14 domestic animals were 

 typical B. coli. It is apparent from these observations that 

 there is a definite correlation between these types of bacteria 

 and their origin. 



An almost perfect correlation could be established by the 

 methyl red, Voges and Proskauer and the uric acid tests. 



The limiting hydrogen ion concentration of the coli cultures, 

 as determined by the colorimetric method, varied from pH 4.5 

 to 5.6 in the synthetic medium, and from 4.6 to 5.8 in the Witte 

 peptone-phosphate-glucose medium. The final hydrogen ion 

 concentration of the cloacae-aerogenes type could not be accur- 

 ately determined on account of the simultaneous acid and alkali 

 production. The pH value obtained under similar conditions 

 ranged from 6.0 to 7.4 in the Witte peptone medium, and from 

 6.0 to 6.8 in the synthetic medium. 



The respective hydrogen ion concentrations of the colon and 

 aerogenes types of bacteria may be adequately determined for 

 practical purposes by methyl red as an indicator, provided the 

 neutral tint reactions are compared with the reactions obtained 

 by brom cresol purple or some other sharp indicator as a check. 



