71 



sewage pollution, led Prescott and Winslow to conclude that it was the 

 number rather that the presence of colon bacilli that should be used 

 as a criterion for recent sewage pollution. Thus they state that the rind- 

 ing of a few colon bacilli in large samples of water or their occasional 

 isolation from small samples is not of any special significance but if these 

 organisms are present in a large proporotion of small samples (I c. c. or 

 less) then the evidence of recent sewage pollution is significant. 



Gartner (1910) estimates the number of colon forms in cultivated 

 soil at 1,500,000 per square meter and naively remarks that it is no wonder 

 the rain should wash a few of them into neighboring wells. The recent 

 work of Johnson and Levine, Burton and Rettger, Chen and Rettger and 

 others have shown quite conclusively that the organisms in the soil are 

 markedly different from those habitually present in the human and animal 

 intestine. Furthermore the "B. coli" of Houston and other English in- 

 vestigators does not include many of the soil forms for they regard only 

 lactose positive-indol positive varieties as "typical" B. coli, whereas most 

 of the Bact. aerogenes and Bact. cloacae are indol negative. German 

 opinion is gradually becoming more favorable toward acceptance of the 

 colon test, provided that preliminary enrichment is carried out at 46 C. 

 (Eijkman test). This procedure, as has been pointed out before, serves 

 to eliminate the Bact. aerogenes and Bact. cloacae or characteristic soil 

 types. It appears that the contentions of the German school were really 

 against these soil forms as indices of pollution. It thus becomes possible 

 to reconcile their opinions with those of English and American bacteriol- 

 ogists if we recognize that not only is the numerical incidence of the colon 

 group significant as an index of pollution, but that the type of organism 

 must also be considered. 



THE COLI AND AEROGENES SECTIONS AS INDICES 

 OF POLLUTION 



The question arises as to whether the aerogenes and coli sections are to 

 be accorded the same sanitary significance. Considerable work is still needed 

 along these lines, but the following is presented as to (1) their distribu- 

 tion in nature, (2) correlation of their relative incidence with the sanitary 

 qualities of water, (3) relative viability in water, and (4) relative resis- 

 tance to treatment and chlorination. 



Incidence of the Coli and Aerogenes Sections in Feces. Rogers, 

 Clark, and Evans called attention to the scarcity of the high ratio group 

 (aerogenes section) in cow dung. Only one colony of 150 fished was of 

 this type. Levine observed that among 117 cultures isolated from cow, 

 horse, sheep, pig, and man, not a single organism proved to be Bact. aero- 

 genes. A study of the literature employing the \ 7 oges-Proskauer test as a 

 means of differentiation of the two colon sections disclosed that these ob- 

 servations as to the scarcity of the aerogenes types in human and animal 

 feces has long been recognized although not adequately appreciated. 



Thus MacConkey (1905) remarks on the scarcity of Bact. (lactis) 

 aerogenes in human feces. In the examination of 241 strains obtained from 



