RELATION TO DISEASE ORGANISMS 177 



after land filtration practically an effluent might be free from B. 

 coli* Pickard has recently shown that the typhoid bacillus vanishes 

 from crude sewage in about fourteen days. If the percentage of 

 original amount of typhoid bacillus introduced into the sewage for 

 experimental purposes be 100 ; in twenty-four hours it has fallen to 

 76 per cent., in thirty-two hours to 71 per cent., in forty-eight hours 

 to 60 per cent., in seven days to 8 per cent., and in fourteen days to 

 0"73 per cent. He also demonstrated that a large proportion (90 

 per cent.) of typhoid bacilli are actually destroyed in filter-beds such 

 as are used in the bacterial treatment of sewage.f 



Houston likewise has found the B. anthracis in septic-tank 

 liquor and sludge, and Ln the secondary beds and general effluent. He 

 also found the anthrax bacillus in the mud of the banks of the river 

 Yeo at Yeovil within 150 feet of the main sewer. The spores of 

 anthrax are peculiarly resistant, and it is in this form that the bacillus 

 can pass through sewage unaffected J (Plate 17). The same author 

 has demonstrated that the B. pseudo-tuberculosis of Pfeiffer may be 

 present in the effluent of various sewage processes, and the same is 

 true of B. pyocyaneus which, however, occurs more rarely. Both 

 these organisms are highly pathogenic to lower animals, and are 

 also related to morbid processes occurring in the human subject.§ 

 Houston, who has made extended inquiries on this question of the 

 effect of bacterial treatment of sewage on pathogenic organisms, 

 summarises his conclusions by stating that biological treatment on 

 land, or by artificial processes, does not necessarily remove patho- 

 genicity from the sewage effluent ; that the absence of pathogenic 

 result when sewage has been filtered shows that the products of 

 pathogenic bacteria in sewage are not of a markedly poisonous 

 nature ; and that the pathogenicity of sewage may depend on spores 

 rather than bacilli. || These conclusions must, however, be accepted 

 with reserve, and in a relative sense only, at present. Broadly, it 

 may be said that if sewage contains pathogenic bacteria, and is then 

 treated by bacterial methods, the effluent cannot be certainly 

 assumed to be safer in this respect than the raw sewage slightly 

 diluted ; or, expressed in other words, Houston's work indicates " the 

 inadvisabiHty 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 drinhing-waier streams." II 



* Thompson-Yates Laboratory Report, vol. iii., part i., 1900. 



t Jour, of State Medicine, 1903, pp. 203-210. 



X Royal Commission on Sewage Disposal, Second Report, 1902, p. 39. 



% Ibid., p. 5i. \\ Ibid., p. 58. 



IT Ibid., Fourth Report, 1904, vol. Hi., pp. 77-96. 



M 



