13 



These results are well in accord with those of Winslow and Walker, 

 who observe: "Gas-formation coincided with acidity except in the case of 

 dextrin." 



All investigators are agreed that members of the colon group normally 

 ferment the monosaccharids with production of both acid and gas. Very 

 detailed studies have been carried out on the products of the fermenattion 

 of glucose, particularly the gas ratio and the H + ion concentration. These 

 careful observations have yielded very fruitful results. 



The disaccharid lactose is of course fermented by all members of 

 the group and maltose is also attacked. Sucrose is practically always de- 

 composed by strains obtained from the soil, from grains, or from animal 

 feces, but less frequently by strains isolated from human dejecta or sewage. 

 The fermentation of sucrose has been recognized by many investigators as a 

 convenient and important character for subdivision. It is the primary 

 character in the MacConkey classification, it is employed by Jackson, and 

 has been recognized by all the more recent investigators of the colon group 

 as a most important and convenient differential characteristic. 



The trisaccharid raffinose is fermented by practically all strains 

 which ferment sucrose. This marked correlation between sucrose and raf- 

 finose fermentation was emphasized by Howe, who observed that dextrose, 

 lactose, sucrose, and raffinose constitute a metabolic gradient, noting that 

 fermentation of any of these carbohydrates was always accompanied by 

 fermentation of the less complex sugar in the series. 



TABLE IV. CORRELATION OF SUCROSE AND RAFFINOSE 

 FERMENTATION IN COLON GROUP. 



In a study of 333 strains obtained from soil, sewage, and feces of 

 various animals and man, Levine found only 8 sucrose nonfermenters 

 among 241 strains which attacked raffinose, whereas of 92 raffinose non- 

 fermenters, 84 failed to ferment sucrose. 



Both sucrose and raffinose need hardly be employed simultaneously 

 in a study of the colon group. The correlation between fermentability of 

 these carbohydrates has also been observed by Winslow and Walker; Birk; 

 Rogers, Clark and Davis; Kligler; Murray; Rogers, Clark and Lubs; and 

 others. The fact that these two sugars are similar in chemical construc- 

 tion (neither possesses a reacting aldehyde group), may explain the similar- 

 ity in the behavior of colon bacilli towards them. 



The polysaccharids are fermented by relatively few of the 1 species 

 or varieties in the colon group. Ford pointed out that the Bact. aerogenes 

 was a starch fermenter and that a few strains also fermented inulin. Gly- 

 cogen is very rarely attacked. Laybourn reports that Bact. aerogenes 

 usually attacks starches from many different sources. 



