274 BACTERIOLOGICAL CHEMISTRY 



fermenting solution is made alkaline ])y addition of 

 sodium bicarbonate. These conditions favour a 

 Cannizzaro reaction of the acetaldehyde with formation 

 of acetic acid and alcohol : — 



CH3CHO O CH3COOH 



+ + II — > + 

 CH3CH0 H2 CH3CH2OH 



Since some of the aldehyde is removed in this way it can 

 no longer act as hydrogen acceptor in the dismutation of 

 methylglyoxal, and an equivalent amount of the latter 

 is reduced to glycerol. Since two molecules of acetalde- 

 hyde, by the Cannizzaro reaction, give one molecule each 

 of alcohol and acetic acid, and one molecule of glycerol 

 is formed for every molecule of acetaldehyde diverted 

 from acting as hydrogen acceptor, it is obvious that for 

 each molecule of alcohol produced under these conditions 

 there will be two molecules of glycerol formed : — 



^CsHiaOe > 2C02 + 2CH3CHO+2CH20H.CHOH.CH,OH. 



2CH3CHO + H2O > CH3COOH+CH3CH2OH. 



The chief deficiencies of Neuberg's theories are that 

 no account is given of the phosphorylation processes, 

 nor of the influence of co -enzyme, and that the chief 

 intermediate, methylglyoxal, has not been detected in 

 normal fermentations, and is not fermented when added. 

 It has the advantage that it accounts for the constant 

 small amount of glycerol in normal fermentation and 

 explains the increased yields in special circumstances. 



Meyerhof's theory has points of similarity with both 

 Kluyver's and Neuberg's schemes but is based on more 

 complete experimental evidence. Some of the evidence 

 is derived from the work of Embden, Lohmami and 

 others on the course of muscle glycolysis, 'many of the 

 steps in which have been shown also to occur in yeast 

 fermentation. The main evidence in addition to that 

 mentioned on p. 269 is that hexose diphosphate, dihydroxy- 

 acetone phosphate and 3-glyceraldehyde phosphate have 



