The Significance of B. Coli in Water. 129 



is clear that the streptococci had killed out colon bacilli, 

 originally present, in a large proportion of the zoo-c.c. 

 samples of polluted waters and in some of the i-c.c. samples, 

 since, in so many cases, gas formation was followed by 

 the isolation of the streptococcus alone. 



Clark and Gage (1903) have published the results of 

 certain studies of Massachusetts ponds which indicate 

 clearly the coincidence of the distribution of B. coli in 

 single centimeter samples of surface waters, with actual 

 sanitary conditions. They show also the slight signifi- 

 cance of the test for this organism in larger volumes of 

 water. Almost every source gave some positive tests in 

 100 c.c., while with i-c.c. samples only those lakes appear 

 suspicious which are, in fact, exposed to dangerous pol- 

 lution. 



DISTRIBUTION OF TOTAL BACTERIA AND B. COLI IN 



SURFACE WATERS. 

 (CLARK AND GAGE, 1903.) 



* Shores used for pleasure resorts. 



