SEWAGE BACTERIA 155 



4. Sewage Streptococci. — Laws and Andrewes, Houston, Horrocks, 

 and others have isolated streptococci from crude sewage, which 

 appear to be normal sewage organisms, and as such may be taken, 

 when present in water, to indicate contamination, and, if accompanied 

 by B. coli, recent and dangerous contamination. Staphylococci have 

 also been frequently isolated. Houston has described some twenty 

 streptococci as present in London sewage. They are generally 

 present in crude sewage in numbers not less than 1000 per c.c. 

 These_ sewage streptococci are delicate, and readily lose their vitality 

 and die. They are probably little prone to enter on a saprophytic 

 phase or to multiply to any great extent, if at all, under such condi- 

 tions as prevail in sewage. They are present in the intestinal dis- 

 charge of animals, and comprise highly pathogenic organisms. They 

 are usually absent in pure waters and virgin soils, and waters 

 recently polluted with excremental matters. They stain well by 

 Gram's method. The majority form short chains, which sometimes 

 cohere in masses. They grow well at blood-heat in the ordinary 

 media, producing acid in milk without clotting it.* Some streptococci 

 from sewage coagulate milk (Plate 15). 



5. Liquefying bacteria, e.g. Bacillus superficialis (Jordan), B. 

 frondosits (Houston), £. hyalinus (Jordan), B. delicatulus (Jordan), 

 B. cloacae (Jordan), B. fluorescens stercoralis, B. memhraneus patulus, 

 B. eapillareus (Houston), B. cloacce fluorescens (Laws and Andrewes), 

 various forms of Clostridium and the typical B. mesentericus (Plate 16). 



6. Non-liquefying bacteria, e.g. Bacillus suhtilissimus, B.fusiformis 

 (Houston), B. ruhescens (Jordan), B. pyogenes cloacinus (Klein f). 



We have not included in the above classification any bacteria 

 virulently pathogenic to man.| Doubtless, such species {e.g. Bacillus 

 typhosus) not infrequently find their way into sewage. But they are 

 not for various reasons normal habitants, and though they struggle 

 for survival, the keenness of the competition among the dense crowds 

 of saprophytes makes existence for a continuous period in sewage 

 almost impossible for them. In the investigation to which reference 

 has already been made. Laws and Andrewes devoted some attention 

 to the behaviour of B. typhosus in sewage. They found that this 

 bacillus was unable to grow, indeed quickly perished, in sewage 

 sterilised by filtration and heat, whereas the B. coli is able to increase 

 and multiply in such a medium. Sewage, therefore, even in the 

 absence of the normal micro-organisms which it contains, is an 



* Bacterial Treatment of Crude Sewage — Third Report to the London County- 

 Council, by Dr Houston, 1900, pp. 60-68 ; Boyal Commission on Sewage Disposal, 

 Second Report, 1902, p. 2.5. 



t See British. MedicalJournal, 1899, vol. ii., p. 69. 



J Bacillus enteritidis sporogenes, B. pyogenes cloacinus, and other organisms have 

 been held responsible for diarrhoea, abscess formation, etc., but they cannot yet 

 be compared with B. typhosus as regards pathogenic effect. 



