CHARACTERISTICS OF THE COLON-AEROGENES GROUP 97 



cultures were identical in all their reactions. So far as the 

 evidence obtained from these twenty-five cultures goes, there 

 is no relation between the type of colony and the fermenta- 

 tion of lactose or the gas ratio. It seems that the tendency to 

 form outgrowths is an expression of an attempt to push out 

 into the medium where conditions are more favorable. Some 

 strains have developed this tendency to a greater extent than 

 others, but it is very evident that it could not be placed on a 

 par with physiological characters for taxonomic purposes. 



The infinity group liquefies gelatin more actively than the 

 cloacae group, but its fermentative ability, as shown in Fig. 

 5 is less. A comparison based on only twelve cultures must 

 be tentative, but some of the differences are of special interest. 

 This is the only group in which the correlation between sac- 

 charose and raffinose is not nearly perfect. 



The amount of gas formed from dextrose by the infinity 

 group is usually much less even than that obtained from 

 the low ratio cultures. Traces of gas and a slight change 

 in the hydrogen ion concentration sometimes observed in 

 lactose broth indicate that there may be a feeble fermentation 

 of this sugar by those cultures classed as lactose negative. 



The general characters of the cultures of the infinity group 

 identify them with the proteus type. While a few of them 

 differ from the usual conception of proteus by fermenting 

 lactose, it seems to us that the nature of the fermentation as 

 indicated by the end products is so much more basic than the 

 nature of the material fermented that the separation into 

 species should be made on the gas ratio rather than on the 

 failure to ferment lactose. A number of cultures sent to us 

 from other laboratories as proteus failed to ferment lactose 

 but gave the carbon dioxide-hydrogen ratio of the aerogenes 

 group. It has been customary to include in the colon-aero- 

 genes group only cultures that ferment lactose. This is 

 largely a matter of convenience and there is no good reason 

 why dextrose -j- lactose cultures should not be included. 



