278 MICROBIOLOGY OF WATER AND SEWAGE 



by. prolonged boiling in dilute acids. Pectin substances, starches and 

 finally sugars are produced while butyric and other organic acids, carbon 

 dioxide and methane appear as by-products. Bacteriologically, al- 

 though it has variously been ascribed to one or another organism, it is 

 probably the result of the activities of many and is possibly not the 

 principal activity of any one of these. In other words, cellulose fermen- 

 tation is probably a series of side reactions produced during the fermen- 

 tation of the nitrogenous material rather than a definite reaction upon 

 which the metabolism of any single species depends. This view is 

 strengthened by the general observations that this fermentation is in 

 most cases due directly to enzymes. Viewed in this light it is easy to 

 understand the dijE&culty that has surrounded the isolation of definite 

 cellulose fermenting organisms. Many have been described, chief of 

 which are B. butyricus or B. amylobacter, B. omelianski, Sp. rugula. 



The Saponification of Fats. — A third great group of tj^e reactions 

 occurring under anaerobic conditions is the saponification or split- 

 ting of fat. Our knowledge of this process is even less definite 

 than of the cellulose fermentations. It is a fact that there does take 

 place in sewage a gradual saponification and emulsification by which 

 the fat loses its identity and mingles with the liquid. This effect is 

 most noticeable in the case of long sewers in which considerable veloci- 

 ties are maintained. In quiescent tanks there is a tendency for the fats 

 to rise to the surface and thus become removed from the influence of 

 this action. Thus in small installations enormously heavy scums form 

 upon the tanks and analysis shows a considerable percentage of fat 

 in this material. In larger systems on the other hand there is less and 

 less evidence of fatty material as such. It is true that there is a deposit 

 upon the walls and tops of such sewers and that small floating objects, 

 like matches, roUing along such a wall will accumulate layers of grease 

 and become eventually the famiUar "grease-balls" found in the dis- 

 charge, but in the main the fatty material has become well disintegrated 

 before the outlet is reached. 



In this case also as in that previously discussed it is not beheved that 

 the action is a direct result of the activity of any particfular organism. 

 Xhe proteolytic changes are accompanied by the freeing of alkaUne 

 products, ammonia and amines, which leads to some saponification, 

 and which, in turn, leads to a further emulsification. It has also been 

 demonstrated that bacterial activity is commonly associated with fat 



