CELLULOSE FERMENTATION 



187 



is obtaining energy required to accomplish its tasks. Hence, cellu- 

 lose is to these microbes what coal is to the engine. 



Function. — It may be well to call attention to the great part 

 played by these microorganisms in returning carbon to the atmos- 

 phere. They are especially valuable in decomposing the cellulose 

 which passes off in the sewage. In septic tanks there are millions 

 of these organisms busy changing the most resistant organic mat- 



1 Xy'^>\ 



,-;t.: 





4 ^/ i'ls-r ;J| ^H** 



.-.-i. 



11"*^ 









^tj ..< 



Fig. 37. — Cellulose ferments. (After McBeth.) 



ter into gaseous products, and today many large cities depend 

 upon them for the disposal of their waste. They also take 

 a great part in the purification of a city's water supply. Omelian- 

 ski considers them of prime importance in the formation of soil 

 humus, for he writes, "It is possible that a general reaction of 

 this sort forms the basis of the universal processes of humification, 

 that is, the gradual transformation of organic substances into 

 mixture of brown and black substances with a high content of 

 carbon, such as is characteristic of fossil coals. But whatever the 

 mechanisms of these transformations, the active participation of 

 microorganisms in the latter cannot be denied." 



The cellulose bacteria break the plant residues into less com- 

 plex organic compounds which are fermented by other microor- 

 ganisms with the generation of large quantities of organic acids. 

 These would react with the minerals of the soil and render them 



