86 BACTERIA 



1. Bacillus coli communis and all its varieties and allies. 



2. Proteus vulgaris and the various protean species. 



3. B, enteritidis sporogenes (Klein). 



4. Liquefying bacteria, e.g. , Bacillus fluorescens liquefa- 

 ciens, B, subtilis^ B, mesentericus. 



5. Non-liquefying bacteria. 



6. Sarcinae, yeasts, and moulds. 



Proteus Vulgaris 



We have not included in the above inventory any patho- 

 genic bacteria. Doubtless such species (e.g., typhoid ') not 

 infrequently find their way into sewage. But they are not 

 normal habitants, and though they struggle for survival, the 

 keenness of competition among the dense crowds of sapro- 

 phytes makes existence almost impossible for them. Nor 

 can they expect much sympathy from us in the difficulties 

 of life which fortunately confront them in sewage. 



Of those we have named as normally present it is unneces- 

 sary to speak in detail, with the exception of the newly 



' The bacilli of typhoid can live in crude sewage (Klein), but only for a very 

 short period. When sewage is diluted with large quantities of water the case 

 is very different. Bacillus coli flourishes in sewage. 



