SEWAGE AND SEWAGE DISPOSAL. 241 



B. megatherium, L. ; liquefaciens, L. ; magnus ; spinosus. 



Streptococcus liquefaciens coli, L.; and mirabilis, N.L. 



B. saprogenes I., II., and IIT. ; pyogenes and coprogenes fetidus. 



B. acidi paralactici. 



B. lactis aerogenes, N.L. (produces COj and H). 



B. coli communis, N.L. (produces much gas, mainly H). 



Cladothrix dichotoma, L. 



Proteus sulphureus, L. (produces HjS and mercaptan). 



Bacterium sulphureum, L. (produces HgS). 



Beggiatoa alba (oxidises HjS into sulphuric acid). 

 The following reduce nitrates to nitrites. 



B. vermicularis, liquidus, ramosus, aquatilis (also B. mycoides and 



Proteus vulgaris). 



This list does not include all the bacteria found in sewage, but 



only those more commonly found there. So many different kinds of 



waste matters find their way into sewage, that a complete list would 



probably number several hundred species of bacteria. 



We will now deal with those species that have a special interest for 

 us, owing either to their pathogenicity or to their abundance in sewage. 

 It is well to have a more intimate knowledge of the latter kind, 

 because it is by their means that sewage contamination can best be 

 detected. The most dreaded of the pathogenic bacteria in sewage is 

 Bacillus typhosus, which gives rise to typhoid or enteric fever. But 

 B. typhosus does not multiply rapidly in sewage ; for even in sterilised 

 sewage, in which there is naturally no competition with other 

 organisms, it fails to grow, and indeed quickly perishes. It seems to 

 lead a very precarious existence in sewage, and cannot strictly be 

 called one of the sewage bacteria. It often, however, finds its way 

 into sewage ; and as drinking water sometimes becomes contaminated 

 with sewage, we see how it is that this dreaded microbe enters the 

 human system. The cause of the fever being known, it is sad to 

 reflect on the enormous waste of life that took place during the late 

 South African War through the ravages of this disease. The number 

 of soldiers who died of enteric fever considerably outnumbered those 

 who died of wounds. The characteristics of Bac. typhosus and its 

 effects on the human system have already been described. There is 

 great similarity between Bac. typhosus and Bacillus coli communis, an 

 organism which is very common in sewage, and which is strongly 

 suspected of being the cause of epidemic diarrhoea, though positive 

 proof is still wanting. It is found as a normal inhabitant of the 

 alimentary canal of most mammalia, is widely distributed, and thrives 



Q 



