BIOLOGICAL TEEATMENT ON PATHOGENIC ORGANISMS. 255 



has been shown that some of the bacteria that are present in the- effluent 

 are capable under certain conditions of engendering diseases of various 

 kinds, so that it is considered dangerous to allow effluents to enter 

 streams, the waters of which in the immediate neighbourhood are used 

 for drinking purposes. There is at present no known method which 

 can be absolutely relied upon to free sewage altogether from the germs 

 of disease, and we are not yet in possession of much definite information 

 as to the exact extent of the danger arising from the effluents of the 

 existing methods. Houston's work indicates the " inadvisability of 

 relying on septic tanks, contact beds or continuous filters to remove 

 altogether the element of potential danger to health associated with the 

 discharge of effluents from these processes of sewage treatment, into 

 drinking-water streams." There can, however, be no doubt that the 

 treatment of sew r age is highly beneficial to the community, and we may 

 conclude with Dr. Reid's declaration that if he had to choose between 

 "the discharge into a stream of the crude sewage of 29,000 people" 

 and that "of the treated, therefore non-putrefactive, sewage of a popu- 

 lation of 420,000 odd," all he could say would be " it would not be the 

 crude sewage of 29,000 people which he should select in the case 

 of a stream over which he had control, as an alternative to the treated 

 sewage of a population, no matter how large." 



