INDUSTRIAL FERMENTATIONS 327 



which is borne out by the gas ratios actually found. It is 

 considered that the methane from cellulose is formed in 

 this way from fatty acids, w^hich are the first breakdown 

 products of the cellulose. The amino -acids from proteins 

 are also subject to the same sort of degradation, the 

 amino group giving rise to ammonia. 



Citric and Gluconic Acids.— The production of citric 

 and gluconic acids from sugars by fungi has already been 

 described (see p. 292). The processes are used on a com- 

 mercial scale in the United States, making use of shallow 

 pan fermentations, in which a felt of mycelium of A. niger, 

 P. citromyces or P. luteum develops on the surface of the 

 medium. Sometimes a continuous process is used in 

 which fresh sugar solution is fed under the established 

 mycelial felts as the fermented liquor is drawn off. 

 Sometimes fermentation in rotating drums, using sub- 

 merged cultures, has been found more efficacious. 



For further reading : — 



K. R. Butlin, " The Biochemical Activities of the Acetic Acid Bacteria." 



D.S.I.R. Chemistry Research Special Report No. 2. H.M. Stationery 



Office. London, 1936. 

 H. T. Herrick, et alia, "Industrial Fermentations." Ind. Eng. Chem.' 



22 (1930), 1148. 

 A. G. Norman and W. H. Fuller, " Cellulose Decomposition by Micro- 



organisms." Advances in Enzymology, 2 (1942), 239. 

 S. C. Prescott and C. G. Dunn, " Industrial Microbiology." McGraw-Hill 



Book Company, Inc. New York, 1940. 



