68 



"**. 



Viability of fiact.coh 

 in Conductivity Water 



(/// a/**<T<3 free) 

 containing 0.05% CP NaCI 



/oo 



2OC 

 7/mc. e/a/osed. /n 



3OO 



+00 



That there is a marked correlation between the incidence of the colon 

 group and the probability of pollution may be clearly demonstrated from 

 Houston's observations on brooks and rivers which are more or less sub- 

 ject to pollution, and on two lakes, one of which, Loch Loggan, was re- 

 ceiving some drainage while the other, Loch Ericht, was free from con- 

 tamination of human or domestic animals. It will be observed that in 

 brooks and rivers, colon bacilli were usually present (61.5%) in small 

 portions of water (1 c. c. or less); whereas in the unpolluted, Loch Ericht, 

 the colon group was only occasionally encountered even in 100 c. c. samples. 



TABLE XXXII. ON THE INCIDENCE OF COLON GROUP AND PROBABILITY 

 OF POLLUTION IN SURFACE WATERS. 



(After Houston 1906) 



Gumming in his report on the sanitary conditions of the Potomac 

 River watershed found a striking correlation between the proximity of 

 pollution and the incidence of colon bacilli. 



