69 



TABLE XXXIII. ON THE RELATION OF THE NUMBER OF COLON BACILLI 

 AND PROXIMITY OF POLLUTION IN SURFACE WATER (POTOMAC RIVER). 



(After Gumming 1916) 



The high incidence of the colon group in the vicinity of sewer out- 

 lets, its elimination as the distance from the source of pollution increases, 

 and its rarity at points remote from contamination is clearly shown. 



In connection with the purification of water, some correlation has 

 been observed between the incidence of colon bacilli in the filtered water 

 and the typhoid fever rate in the community. Thus in Lawrence, Massa- 

 chusetts, Clark and Gage report the following incident, which occurred in 

 1898. In relaying some under drains of a filter the sand on the beds was 

 seriously disturbed resulting in a marked increase in tests for colon bacilli 

 in the filter effluent. This was followed by a rapid rise in the number 

 of cases of typhoid fever, and as the colon content fell to normal, the cases 

 of typhoid fever disappeared. 



TABLE XXXIV. SHOWING RELATION OF COLON INCIDENCE TO TYPHIOD 

 MORBIDITY RATE, LAWRENCE, MASS., 1898-9. 



(After Prescott & Winslow, 1915) 



Caird, in a report on twenty years' experience with the filter plant at 

 Elmira, New York, also notes that there is some correlation between the 

 percent of positive colon tests and the typhoid fever rate. 



Opinions as to the Value of the Colon Test. It appears, from 

 the foregoing discussion, that the colon group possesses many of the at- 

 tributes of an excellent indicator of pollution. Unfortunately, however, 

 it is not characteristic and distinctive of the human intestine. Some of its 

 members have been isolated from grain and other sources which are far 

 removed from human or even animal contamination. This has lead to 

 disagreement as to the value of the colon test in water analysis. 



