176 BACTERIAL TREATMENT OF SEWAGE 



deposit which accumulates on coke fragments used in the beds at 

 Barking and Crossness.* The coke was found to be coated with a 

 black-coloured slimy deposit, free from objectionable smell, and 

 almost odourless. On examination of the deposit, diluted with 

 sterile water, and making cultures, it was found that the number of 

 bacteria per gramme of the deposit was 1,800,000. This number, 

 large as it may seem, would weigh only a minute fraction of a 

 gramme,")* so that it is evident that the number of living bacteria do 

 not in themselves account in any way for the deposit. As to the 

 nature of these organisms, Dr Houston adds : " The character of the 

 microbes appearing in the cultures differed somewhat from those 

 found in crude sewage. For example, there was an increase in the 

 number of spores of Bacillus enteritidis sporogenes (Klein), and a 

 decrease in the number of B. coli. Proteus-like germs were present 

 in abundance, many being of P. mirabilis type. Further, B. 

 arborescens and an allied form were present in considerable numbers. 

 An organism apparently identical with B. prodigiosus was also 

 isolated/'J The deposit also contained a number of bacilli with pre- 

 cisely similar staining properties as those of tubercle bacilli (acid- 

 fast). They were also morphologically indistinguishable from the 

 tubercle bacillus. In one instance Houston isolated a virulent 

 tubercle bacillus from a sewage effluent. Such facts are of evident 

 practical importance in relation to the final disposal of the effluent, 

 whether it is discharged into a stream used for drinking purposes or 

 otherwise. 



Many of the researches having for their object the fate of 

 pathogenic organisms in sewage have been based upon the typhoid 

 bacillus as a type. Laws and Andrewes, in addition to demonstrat- 

 ing that this organism could only live in sewage a short time, showed 

 that one sewage bacillus {B. fluorescens stercoralis) possessed the chief 

 powers of antagonism, and it is probable that the contained bacteria 

 rather than the chemical products of sewage act as unfavourable 

 conditions for the typhoid bacillus. Horrocks found that in sterilised 

 sewage the typhoid bacillus could live for sixty days. Houston has 

 thrown light upon the fate of B. typhosus by his work on the 

 occurrence of B. coli and B. enteritidis sporogenes in effluents,) | and 

 Miss Chick has furnished evidence in respect of B. coli, tending in 

 the direction of showing that after sewage had passed over double 

 contact beds about 75 per cent, of the B. coli were removed, and 



* Bacterial Treatment of Crude Sewage (Supplement to Second Report), 1899, 

 p. 4. 



t Dr Houston finds that 1,800,000 typhoid bacilli weigh only '0000147 

 gramme. 



J Ibid., p. 4. 



Jour, of Sanitary Institute, January 1900. 



|| First, Second, and Third Reports to the London County Council (vide supra}. 



