S6 SEWAGE AND ITS PURIFICATION 



evidence on most of the systems is now available, from which, 

 I think, we are justified in concluding that, even if towns on a 

 river like the Thames adopted bacterial schemes, the patho- 

 genicity of the London water-supply would not be adversely 

 affected. That the health of fish is not injured appears from 

 the fact that, with intermittent fine-bed filters following coarse- 

 bed or chemical treatment, as at Leeds and London, they have 

 lived in the filtrate. 



At Exeter the tank effluent, the filtrate, and the river water 

 were examined before and after admixture. Broth inoculated 

 with these fluids and incubated for forty-eight hours had no 

 effect upon rabbits or guinea-pigs when 2 c.c. was injected 

 subcutaneously. Incubated for eleven days, the tank effluent, 

 and the water at Belle Isle contaminated with the untreated 

 town sewage, were found to be morbific, but the filtrate and the 

 water at Salmon Pool Weir, some little distance below the 

 town, contained so little morbific material of any kind that 

 even with this severe test both kinds of animals remained alive 

 and perfectly well. Dr. Woodhead in his report concludes 

 " that none of the organisms found in the tank effluent are 

 themselves capable, in the quantities present or in which they 

 can grow even in broth, of setting up any morbid changes." 



With regard to typhoid fever, Lawes and Andrews showed 

 that some liquefying organisms have a germicidal effect upon 

 typhoid bacilli, so that their sojourn in a septic tank, or their 

 arrest in an anaerobic upward filter, with such organisms 

 diminishes instead of increases their chances of survival. 

 Dr. Pickard, of Exeter, has proved this fact again experi- 

 mentally by introducing an emulsion of the typhoid bacilli into 

 a septic tank, when he found that, instead of increasing, they 

 rapidly diminished, until after fourteen days less than i per 

 cent, of the number introduced were surviving. The same 

 investigation also proved that filtration was even more efficient 

 in removing typhoid bacilli, as he found that filtration, as con- 

 ducted at Exeter, removed about 90 per cent, of typhoid 

 bacilli from sewage inoculated with this organism, and that 

 subsequent filtration of tank effluent containing no typhoid 

 through the same filter yielded filtrates containing only about 

 I per cent, of the bacilh introduced in the first filtration, show- 

 ing that the environment was unsuitable for their development 

 if their absence from the first filtrate was due only to a straining 

 action. 



