80 



Rogers studied a section of a stream for a distance of about eleven 

 miles determining the ratio of Bad. aerogenes to Bact. coli above and be- 

 low sewer outlets. 



It will be noted that above the city all cultures isolated were of the 

 aerogenes type and that after passing through the town, where the creek 

 became polluted, the Bact. coli strains predominated, being 10 times as 

 common, but farther down the stream, as the distance from the source of 

 pollution increases, the aerogenes forms again become markedly more 

 numerous. The indications are, therefore, strong that the ratio of aerogenes 

 to coli varies with the proximity of sewage pollution becoming greater as 

 the pollution is more remote. 



Stokes remarks on the scarcity of the low ratio coli group in well 

 waters. Only one low ratio organism was found in 14 samples of water 

 from artesian wells containing members of the colon-aerogenes group. 

 Thirteen of these contained high ratio organisms including Bact. aerogenes 

 and Bact. cloacae. 



In a study of 59 samples of raw waters, Stokes found 38 which showed 

 only one type of the colon group (24 contained Bact. aerogenes, 13 Bact. 

 coli. and 1 Bact. cloacae) determined by fishing 10 colonies from an Endo 

 plate. This striking fact that a large proportion of the samples harbored 

 a single species of the colon group in pure culture suggests the possibility 

 of a correlation between the source of pollution or contamination and the 

 type of colon organism present. He concludes that "In the bacteriological 

 examination of drinking water it would not be safe to assume that the 

 water was free from intestinal pollution if but two or three colonies were 

 studied from each specimen. However, if 20 to 25 colonies be picked 

 from each sample and all are found to be of the high ratio type, it might 

 be safe to regard the water as free from fecal contamination provided a 

 chemical examination and sanitary survey gave no evidence of pollution." 



The writer would suggest that in place of picking such a large number 

 of colonies, which is impractical for routine, a differential medium like 

 the eosin-methylene-blue agar should be employed for confirming the pre- 

 sumptive test. The probable presence of the "fecal" Bact. coli type could 

 be easily recognized. 



Perhaps the most detailed study on the correlation of sanitary quality 

 of ground water and the type of colon bacillus present was carried out by 

 D. R. Wood in England. A large number of samples from various sources, 

 200 of which contained lactose fermenting organisms, were investigated. 

 Sixty-six samples contained the V.-P. positive-methyl-red negative or Bact. 

 aerogenes types and 41 of these showed no evidence of recent excretal con- 

 tamination. He records also that in 22 deep well supplies of good repute 

 (these were sunk through lime-stone 250 to 400 feet into underlying sand, 

 used as public supplies for years, and appeared excellent bacterially, lactose 

 fermenters being rarely present and seldom in less than 100 c. c.) suddenly 

 showed a large proportion of the colon group in the spring of 1918. Lac- 

 tose fermenting organisms were obtained in two cases in 1 c. c., in several 

 instances in 10 c. c., but in every sample in 100 c. c. On further examina- 



