PRODUCTS OF MICROBIAL ACTIVITIES 237 



the slimy fermentations, as manifested in ropy milk and the mannit 

 fermentation. The latter is one of the very few reduction processes 

 brought about by bacteria, and one which causes trouble in wine. 



What has been stated broadly for sugars holds to some extent true 

 also for the alcohols derived from sugars, including glycerin. Many 

 bacteria fermenting dextrose can also ferment mannit and glycerin 

 with a slight variation of the products, but some do not do this. 



Among disaccharides there is a great variation of fermentation. 

 Some groups ferment lactose readily as the coli organisms and Strept. 

 lacticus, while among yeasts, fermentation of lactose is rare. Practi- 

 cally all yeasts ferment saccharose, however, and among the lactic 

 bacteria and the coli group many strains cannot ferment saccharose. 



STARCH. Quite different is the fermentation of the insoluble carbo- 

 hydrates of which we can mention only starch and cellulose. Insoluble 

 compounds can be fermented only after being made soluble by an 

 enzyme, the amylase (see mechanism of metabolism). Amylase is 

 produced by most molds, by none of the fermenting yeasts, by a few 

 torulas, and perhaps mycodermas, and by a great many of the bacteria. 

 The sugar thus produced from starch is decomposed according to the 

 main types mentioned under sugars. The lactic bacteria and the coli 

 bacteria do not attack starch, but some acid-gas fermentations of 

 starchy foods do take place. Butyric fermentation of starch is com- 

 mon. Alcoholic fermentation can be accomplished only by some of 

 the Mucors, and Aspergilli. 



CELLULOSE is decomposed only by very few organisms; these must 

 be very active and very numerous, to judge from the enormous amounts 

 of cellulose produced and destroyed every year on earth. Molds and 

 higher fungi play probably the main role in its decomposition; the 

 products have not been determined, but we may well assume a complete 

 oxidation, since no intermediate products have ever been mentioned. 

 No yeast is known to decompose cellulose, and among the bacteria we 

 find but very few species. Some species have recently been isolated 

 which decompose cellulose in the presence of air; the products have not 

 been determined; we can, however, assume a partial oxidation, eventu- 

 ally a complete oxidation. Besides the aerobic fermentation, we have 

 two types of anaerobic fermentation which are ordinarily described as 

 the hydrogen fermentation and the methane fermentation. In these 

 fermentations the gases mentioned, together with carbon dioxide, are 



