1 66 NUTRITION AND METABOLISM 



does not form gas. It forms, however, formic acid, HCO2H, which, if 

 decomposed, would give H2 + CO2. • ; 



The last type of sugar fermentations is the butyric fermentation, 

 in which butyric acid is the most conspicuous, but not the only fermen- 

 tation product. Acetic acid, hydrogen and carbon dioxide, and, with 

 some organisms at least, ethyl and butyl alcohols are formed along with 

 butyric acid. As aheady mentioned in the paragraph on the equation of 

 fermentation, Kruse believes this fermentation to consist of several 

 simultaneous fermentations, of which the most interesting at this stage 

 is the one showing the formation of butyric acid. 



CcHiaOe = 2H2 + 2CO2 + CiHsOa . ' 



The organisms producing butyric acid are mostly strictly anaerobic 

 ' spore formers with a tendency to form spindle-shaped cells; they stain 

 bluish-black with iodine and Bredemann gave the Clostridium group 

 one species name, B. amylobacter, as he found no distinct and char- 

 acteristic differences between the many strains which he studied. 

 Many members of this group have the abiUty to fix nitrogen, i.e. 

 to build up their protoplasm without using any sources of nitrogen 

 other than nitrogen gas. Most of the so-caUed "Clostridium" species 

 belong in this group. Butyric acid is also formed by B. tetani and by 

 B. hotulinus, the latter of which causes the most dangerous kind of meat 

 poisoning. 



Of other sugar fermentations may be mentioned here only by name, 

 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 grotips ferment lactose readily as the coU 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. 



Stakch.— Quite different is the fermentation of the insoluble carbo- 

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



