RELATION TO DISEASE ORGANISMS 175 



longer any doubt that some form of such agency is the only efficient, 

 because the only natural, means of disposing of sewage. 



The Effect of the Bacterial Treatment upon Disease- 

 Producing* Organisms 



It has been urged from time to time by the advocates of the vari- 

 ous methods of bacterial treatment, that pathogenic organisms are 

 destroyed during the purification in many of these processes. It is 

 clearly a matter of importance to know how far an effluent, in 

 addition to being non-putrescible and fully nitrified, also possesses 

 no disease-producing capacity. We have already seen, from the 

 researches of Klein, and Laws and Andrewes, that sewage is not a 

 favourable medium for B. typJiosus. The bacillus of Asiatic cholera 

 is known to be but little less favoured by sewage. The spread of 

 diphtheria by sewage is at least a matter of doubt, and Shattock's 

 experiments tend to prove that in any case the virulence of the 

 Bacillus diphtherice is not increased by sewer air. 



Anything like exhaustive researches into the effect of the septic 

 tank or cultivation beds upon pathogenic germs has not been under- 

 taken up to the present, and we can only conjecture as to their fate. 

 Dr Houston has made a cautious declaration upon this matter, and at 

 present we have not evidence to justify a more certain statement. 

 " The balance of evidence," he says, " points to the probability that 

 some, at all events, of the pathogenic organisms are crowded out in 

 the struggle for existence in a nutritive medium containing a mixed 

 bacterial flora, their vitality being weakened or destroyed by the 

 enzymes of the saprophytic species." * He further adds : " It must 

 be distinctly understood that I do not imply that such organisms as 

 the typhoid bacillus or the cholera vibrio would necessarily lose their 

 vitality, or even suffer a diminution in virulence under the conditions 

 prevailing in a biological filter. In the absence of actual experi- 

 ments, I am not prepared to say more than that I believe that if these 

 germs did gain access to the sewage they would suffer a diminution 

 in numbers primarily in the sewers [or septic tank], and secondarily 

 in the coke-beds [or cultivation beds]." Subsequently, as a result of 

 further experience of the effluent from the Crossness Sewage Works, 

 Houston wrote, " However satisfactory the process may be from the 

 chemical and practical point of view, the effluents from the bacterial 

 beds cannot reasonably be assumed to be more safe in their possible 

 relation to disease than raw sewage." f 



Indirectly connected with this point, a word or two may be added 

 concerning some recent investigations made by Dr Houston upon the 



* Bacterial Treatment of Crude Sewage, 1899 (Second Report), p. 19. 

 t Edin. Med. Jour., Feb. 1901. 



