112 SEWAGE AND ITS PURIFICATION 



very widely, and do not grow on ordinary media, but can be 

 isolated by the method of accumulation.^ One species evolves 

 hydrogen^ 3*22 grammes of cellulose yielding 0*014 gramme of 

 hydrogen, 0*9722 gramme of COg, and 2*24 grammes of fatty 

 acid (i part butyric and 1*7 parts acetic). The second evolves 

 CH4, 2*03 grammes of cellulose yielding 0*14 gramme of CH^, 

 087 gramme of CO2, and i*02 grammes of fatty acids (i part 

 butyric and g parts acetic). Both grow best at 35° to 40° C. 

 This explains the presence of H and CH4 in the septic tank in 

 different proportions. 



Vasculose (Fremy), constituting the harder parts of plants, is 

 also slowly disintegrated by organisms. 



The smaller remains of vegetable matter which pass down 

 sinks occasion considerable nuisance when an attempt is made 

 to remove them by screens, or on the top of a coarse filter. 

 They act objectionably in three ways : 



1. They set up acid fermentation and corrode iron. 



2. A large proportion of domestic vegetable debris (cabbage, 

 etc.) contains sulphur compounds, and evolves on decomposition 

 very offensive odours. 



3. They form a pulp which blocks the strainers. 



Under anaerobic conditions in a closed space they rapidly 

 rot away and disappear, their pectose first dissolving and then 

 their cellulose, while the ammonia takes up the acids. 



Cellulose can also be brought into solution by the action of 

 denitrifying, non-sporulating bacteria with restricted access of 

 air. 2 The presence of considerable quantities of soluble organic 

 matter prevents the nitrification process, but cellulose is without 

 influence if the aeration be good. The conjoint action of nitri- 

 fication and denitrification processes must play an important 

 part in the destruction of cellulose in the self-purification of 

 waters and soils and the biological purification of effluents. 

 Cellulose is also decomposed by aerobic, non-sporulating 

 bacteria, of w^hich a brown pigment bacterium (B . ferrugineus) 

 is the most important. This bacterium is particularly active 

 in symbiosis with a yellow micrococcus, which by itself is 

 inactive. In nutritive solutions, in which the cellulose is 

 decomposed by the aerobic bacteria of mud or garden soil, 

 spirilla cultures are always formed abundantly. The property 

 of attacking cellulose is a general one among the fungi, and is 



^ Journal of the Chemical Society, abstract, 1902, 468. 



2 C. van Iterson, C^;i/y. Bakt. Par., xi., 689 ; Chem. Centr., 1904, i,, 1388. 



