FUNCTION 333 



a large amount of acetic and butyric acids. In fact over one-half 

 of the decomposed cellulose had been transformed into these acids. 

 Later Work on Cellulose Fermentation. Later work which has 

 been carried out by van Iterson has shown that there are certain 

 of the non-sporeforming, denitrifying organisms which have the 

 power of decomposing cellulose. In the presence of nitrates, the 

 chief products are nitrogen and carbon dioxid. According to this 

 investigator, the decomposition is brought about by Bacillus ferru- 

 gineus, which is the chief cause of the brown color of humus due 

 to a pigment formed from cellulose by this organism. 



Recently Kellermann and McBeth have questioned the work of 

 Omelianski. While they admit the great importance of these 

 organisms in the formation of humus in agricultural soils, they 

 claim that the organisms described by Omelianski were not pure 

 cultures and furthermore that cellulose is decomposed under 

 aerobic conditions. These investigators have isolated thirty-six 

 species from various sources. These were found to be much more 

 active than the ones described by Omelianski. They were all rod- 

 shaped organisms varying in length from 0.8 to 3.5 M. Involution 

 forms have been observed for only three species. Five species 

 have been found to produce spores. Twenty-seven species are 

 motile; of these, seven are pseudomonas and twenty are bacilli. 

 A few are facultative anaerobes. The optimum temperature lies 

 between 28 and 33 C,, but they grow well from 20 to 37.5 C. 

 They grow readily on solid media such as beef agar, gelatin, starch 

 and potato. Nineteen species liquefy gelatin. They rapidly 

 decompose cellulose and other carbohydrates with the production 

 of acids, but none of the organisms so far studied produce a gas. 



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

 taken by this class of organisms in returning carbon to the atmos- 

 phere. This is especially the case with the material which passes 

 off in the sewage. In septic tanks there are millions of these 

 organisms busy changing the most resistant organic matter into 

 gaseous products, and many large cities today depend upon this 

 for the disposal of their sewage. Organisms also take a great part 

 in the purification of a city's water supply. They also take part 

 in the formation of soil humus, as was pointed out by Omelianski 

 when he gave the general reaction, 2C 6 Hi O 5 > 5CO 2 + 5CH 4 + 2C, 

 and he says, "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 a mixture 

 of brown and black substances with a high content of carbon, such 

 as is characteristic of fossil coals. But whatever the mechanism 

 of these transformations, the active participation of microorgan- 

 isms in the latter cannot be denied." 



The cellulose ferments break the plant residues into less com- 



