278 BACTERIOLOGICAL CHEMISTRY 



inhibited by mono-iodoacetate which blocks the conver- 

 sion of glyceraldehyde phosphate to phosphoglyceric 

 acid, the system continues in the initial phase and 

 glycerol, via « -glycerophosphate, accumulates at the 

 expense of alcohol. 



This scheme differs from Neuberg's in that glycer- 

 aldehyde phosphate and not methylglyoxal is the inter- 

 mediate in the formation of pyruvic acid (compare 

 Kluyver's scheme). The formation of glycerol under 

 alkaline conditions is explained in the same way as in 

 Neuberg's scheme, the acet aldehyde undergoing a 

 Cannizzaro reaction rather than being reduced to alcohol 

 at the expense of dihydro -co -enzyme I. 



Biological Reduction. — It will have been gathered 

 from what has gone before that reduction plays an 

 important part in alcoholic fermentation, particularly 

 the reduction of acetaldehyde to alcohol and of glycer- 

 aldehyde to glycerol. If other hydrogen acceptors are 

 introduced into the system they will compete for the 

 hydrogen available and themselves become reduced. 

 For instance, Neuberg showed that if an excess of acet- 

 aldehyde was introduced into a fermenting mixture it 

 first of all underwent condensation, as a result of the 

 action of the enzyme carboligase, present in yeast, to 

 give acetoin, CH3CO.CHOH.CH3 ; the acetoin could act 

 as a hydrogen acceptor, and in doing so became reduced 

 to give 2 : 3-butylene glycol, CH3.CHOH.CHOH.CH3. If 

 the aeration of the solution was increased, or if other 

 hydrogen acceptors such as methylene blue or sulphur 

 were added, the yield of butylene glycol was lessened and 

 acetoin accumulated, because oxygen or the other sub- 

 stances diverted a considerable portion of the available 

 hydrogen . 



A great variety of compounds can be reduced in the 

 presence of actively fermenting yeast. Thus nitro- 

 benzene gives aniline, benzaldehj^de is converted to 

 ]}onzyl alcohol, and the ketone, methylheptanone, gives 



