COLON-AEEOGENES GROUP OF BACTERIA 263 



low and Walker (1907) found that raffinose is generally attacked 

 by sucrose-positive organisms. 



Bergey and Deehan (1908) also adopted McConkey's classi- 

 fication, and by adding other cultural tests extended the group- 

 ing in a most bewildering manner. They derived 16 groups and 

 256 varieties. In 1909 McConkey again subdivided his four main 

 groups by introducing more fermentable substances. Over 100 

 types were separated out in this way. 



Jackson's classification (1911) was a modification of Mc- 

 Conkey's four primary divisions. He divided these into 16 

 distinct types by the additional use of raffinose and mannitol. 

 This was formally adopted in 1912 by the Committee on Standard 

 Methods. 



Rogers, Clark and Evans (1914) concluded from their study 

 of the colon-aerogenes organisms in milk and milk products that 

 the acid production from a fermentable substance can not be 

 used to advantage. They claimed that the measurement of the 

 gas ratio is far more reliable and constant than the titratable 

 acidity. In his careful study of the acid production of the colon 

 group in many different sugars and under varying experimental 

 conditions Browne (1914) came to the conclusion that the degree 

 of acidity produced by the various members of the colon group 

 is directly proportional to the complexity of the sugar fermented, 

 and that each type within the group has its own limit of acid 

 toleration. One interesting fact brought out is that strains of 

 colon bacilli isolated from feces produced more acid in fermentable 

 sugars than those which were isolated from oysters. 



Kligler (1914) studied 80 laboratory strains of B. coli and con- 

 cluded that salicin fermentation offers a better basis of classi- 

 fication than dulcitol. He thus modified McConkey's scheme 

 as follows: Sucrose— salicin + type (B. communis), sucrose + 

 salicin — type (B. communior), sucrose + salicin, + (B. aerogenes) 

 and sucrose — salicin-(5. acidi-lactici) . Glycerol was further used, 

 to differentiate B. aerogenes from B. cloacae, the latter being a 

 non-glycerol fermenter. 



Rogers, Clark and Evans (1915) again maintained that "the 

 acid from the fermentation of sugar may be masked by a second- 



THE JOURNAL, OF BACTERIOLOGY, VOL. V, NO. 3 



