The Significance of B. Coli in Water. 127 



not extreme, colon bacilli may be isolated in about half 

 the i-c.c. samples examined. Such rivers are of course 

 inadmissible as sources of water-supply, according to 

 modem sanitary standards, unless subjected to purifica- 

 tion of some sort. 



More recently Hunnewell and one of us (Winslow and 

 Hunnewell, 1902'') examined a considerable series of 

 normal waters for B. coli, testing i c.c. from each by the 

 dextrose-broth method and a larger portion of 100 c.c. by 

 incubation with phenol broth as described in Chapter VI. 

 The samples were obtained from the public supplies of 

 Taunton, Boston, Cambridge, Braintree, Brookline, Need- 

 ham, and Lyim in Massachusetts, and Newport, R. I., 

 from the Sudbury River, from the ocean, from the waters 

 of, springs bottled for the market, from ponds, pools of 

 rain and melted snow, springs, brooks, shallow wells, and 

 driven weUs in various towns near the city of Boston. For 

 comparison 50 samples of polluted waters from the Charles, 

 Mystic, Neponset, and North Rivers were examined. The 

 colon bacillus was defined as outlined in Chapter VI, and 

 organisms which lacked the power to reduce nitrates or to 

 form indol were classed in the "Paracolon group." The 

 results are summarized in the following table: 



