50 



are inert as respects the more complex disaccarid lactose. Thus Clark 

 and Gage in 1903 pointed out that there were 58 well described species 

 which gave the presumptive test in dextrose broth of which 23 are widely 

 separated from the colon group and since then many other glucose-positive- 

 lactose-negative forms have been described. 



Prescott and Winslow call attention to the seasonal variation in the 

 reliability of this presumptive test noting that Fromme (1910) isolated 

 colon bacilli from 87 percent of positive glucose broth tubes in the fall 

 and winter (Oct. to Mar.) but only 66 percent from similar tubes in the 

 spring and summer (Apr. to Sept.) 



In stored or filtered waters the incidence of glucose fermenters which 

 do not attack lactose is considerably greater than in raw waters. The 

 reports of Houston for 1909-11, which are summarized below, show that 

 only 9.5 percent of coli-like bacteria isolated from raw river water after 

 preliminary enrichment in glucose broth failed to ferment lactose but that 

 with filtered and ground waters 38.3 percent of the isolated bacilli did not 

 attack this disaccharid. 



TABLE XXII. GLUCOSE AND LACTOSE FERMENTATION BY COLI-LIKE 



BACTERIA FROM RAW AND FILTERED WATERS. 



(After Houston 1909 to 1911) 



*Includes ground waters. 



TABLE XXIII. EFFECT OF NATURAL AND ARTIFICIAL PURIFICATION ON 



INCIDENCE OF GLUCOSE AND LACTOSE FERMENTING 



BACILLI IN PULTA WATER. 



(After Clemesha 1912) 



r All glucose fermenters. 



