CHEMICAL CHANGES 105 



Lction is more energetic when the products are removed as 

 formed, and the bacteria are suppHed with fresh food.^ 



The fermentations occurring in the first or hydrolytic part of 

 jhe process may be chemically classified as follows : . 



1. Solution and decomposition of albuminous bodies. 



2. Fermentation of urea. 



3. Fermentation of the amido-compounds formed from the 

 Ibuminous bodies. 



4. The formation of organic acids and fermentation of their 



LltS. 



5. Cellulose or methane changes. 



6. Fermentation of carbohydrates. 



7. Decomposition of fats. 



8. The formation of small quantities of sulphur compounds, 

 like H2S, mercaptan, etc. This, from the odour of the pro- 

 ducts, often attracts the most attention. 



These, as a rule, are brought about in sewage by bacteria, 

 rather than by moulds and yeasts, which, as Andreasch showed, 

 may be distinctly prejudicial to normal bacterial action. 



I. Hydrolysis of Albuminous Bodies is caused by a large 

 number of organisms, and the first action is parallel to 

 ordinary digestion — that is, the so-called peptonization, or con- 

 version into a soluble form. The peptones are then split up, 

 amido-acids are formed, together with a number of substances 

 of the aromatic group. 



L. Geret and Martin Hahn ^ describe proteolytic enzymes 

 existing in yeast and also in such bacteria as Sarcina rosea, 

 B. tuberculosis, and B. typhosus, and state that they not only 

 decompose and dissolve the albumin already present, but also 

 attack additional quantities of albumin from other sources. 



Biltz and Krohnke,^ Fowler and Andern,^ have shown that 

 some of the sewage solids are not dialysable, so that part of 

 the organic nitrogen causing opalescence in the liquid is in the 

 colloidal state. Johnston,^ working with Jones and Travis, 

 suggests that surfaces determine the separation of this colloidal 

 matter from solution, so that a mechanical or physical change 



^ The conditions are further worked out by E. Frankland Armstrong {Pro- 

 ceedings of the Royal Society, 1904, Ixxiii., 500-542) ; also, as to the hindrance of 

 fermentation by chemically indifferent substances, see H. Braeuning, Zeit. Phys. 

 Chem., 1904, xliv., 70. 



2 Berichtc, 1899, xxxi., 2335 ; also Emmerlich and Low, Zcits.f. Hyg., 1899, i. 



^ Bcrichte d.Chem. Gcscll., xxxvii., 1745. 



■* Jonrnal of tlic Society of Chemical Industry, xxiv., 483. 



^ Journal of the Royal Sanitary Institute, i<^o6. * 



