BACTERIA OCCURRING IN SEWAGE 91 



bacillus typical of excremental matters through the coke-beds in 

 practically unaltered numbers is not a desirable state of things. 

 It is true that B. coli is not pathogenic in the ordinary meaning 

 |of the word, but its presence in the effluents implies the possible 

 ipresence of other bacteria — it might be of a dangerous sort. Still, 

 on the whole it may be said that the balance of evidence points to 

 .pathogenic aerobic bacteria being liable to be crowded out in the 

 [struggle for existence in a nutrient fluid containing a mixed bacterial 

 iflora and one rich in saprophytic micro-organisms. Lastly, it must 

 be remembered that the effluent is discharged into a large tidal river 

 at a point far below the lowest ' intake ' of water for waterworks 

 purposes. Moreover, the Thames before it reaches the outfalls of 

 the sewage works is already grossly polluted with excremental 

 matters." 



A subsequent report ^ of July, 1900, confirms most of these 

 conclusions, but points out that the effluents from the experi- 

 mental beds at Barking and Crossness cannot be reasonably 

 assumed to be more safe in their possible relation to disease 

 than diluted raw sewage. This must, however, be regarded 

 as only applicable to beds worked in the way described. The 

 chemical results taken generally show that nitrification was 

 never pushed to a satisfactory point, and the main object of the 

 whole inquiry in London has been to produce an effluent suit- 

 able to discharge into tidal waters. 



I examined the effluents from the Scott-Moncrieff filters at 

 Caterham with a view to ascertaining whether the sewage 

 organisms survived the oxidizing influence to which they were 

 subjected in their passage through the nitrifying trays, and 

 found that the number of organisms capable of growing on 

 carbolized gelatine surface plates, amongst which the B. coli 

 communis is found, was reduced from 2,180,000 per c.c. to 

 100,000 in the filtrate from filter C, to 50,000 in that from D, 

 and 80,000 in the filtrate from F, so that, whilst the least 

 efficient of the filters removed 95 per cent, of these organisms, 

 the filter D removed 98*5 per cent. 



Although the addition of o'oooi c.c. of the tank effluent to a 

 broth tube and incubation at blood heat for four days produced 

 indol, the same dilution of the filtrate from D gave no turbidity 

 or indol, whilst the filtrates from C and F, although producing 

 turbidity, also failed to give any indol reaction. 



A disappearance of spores of B. enteritidis also occurred, and 

 may be best seen from the following table, where -|- indicates the 

 presence of such spores, and — their absence. 



^ Royal Commission on Sewage, vol. iii., 1904, pp. 95, 96. 



