BACTERIA OCCURRING IN SEWAGE 89 



their chemical poisons are toxic in proportion to the dose, and, 

 moreover, are highly unstable, and readily break down into their 

 elementary and innocuous constituents ; and, lastly, that in some 

 cases it may not be necessary to attempt to complete purification 

 of the sewage, the solution of the suspended matters and partial 

 [destruction of the putrescible matter in solution being all that is 

 urgently called for, as, for example, where the effluent is of rela- 

 :tively small bulk and is turned into a stream, the water of which is 

 not used for domestic purposes (as is the case in the Lower Thames), 

 or else when the effluent is to be subsequently treated by land 

 irrigation." 



He does 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 experiments 

 with the particular sewage in question, he is not prepared to 

 say more than that he believes that if these germs did gain 

 access to the sewage they would suffer diminution in numbers, 

 primarily in the sewers, and secondarily in the coke-beds. 



Dr. Houston, early in 1898, isolated from Thames mud four 

 organisms, named by him B. typhosus simulans a, b, c, d, which 

 differed from the true typhoid organism in failing to sediment 

 with typhoid serum and in possessing a less number of flagella. 

 They might, therefore, possibly be degenerate varieties of active 

 typhosus caused by prolonged existence in sewage-polluted 

 water. Horrocks^ studied the behaviour of the B. typhosus in 

 sewage, and concludes that the bacillus will usually be found 

 alive after sixty days' immersion in sewage freed from other living 

 organisms. The power of sedimentation will be unchanged, 

 but the colonies may present a dark, granular, crumpled appear- 

 ance, and the bacillus will show diminished resistance to 

 carbolic acid. In unsterilized sewage he failed to obtain any 

 evidence of their survival after fourteen days, and inferred that 

 the life of the bacillus is much shorter in unsterilized than in 

 sterile sewage. 



Among the organisms which can be easily identified as 

 directly derived from sewage, and which are either themselves 

 pathogenic or are associated with organisms causing disease, 

 the B. enteritidis sporogenes of Klein (Fig. 8, Plate II.) and 

 B. coli communis are the most important. 



At Crossness, in the crude sewage and the effluents from the 



^ Journal of the Sanitary Institute, xx., part iv., 1899. See also " Enteric 

 Fever and Sewage Disposal in Foreign Countries," by Major Aldridge [Journal 

 of Hygiene, July, 1902, p. 360). 



