CARBON METABOLISM 249 



lactic acid and the other half to alcohol, acetic acid and 

 formic acid. The formic acid Avas further broken down 

 to hydrogen and carbon dioxide by Esch. coli (to give the 

 typical " acid and gas " fermentation), but it was not 

 attacked by Eherth. typhosa (" acid, no gas " fermenta- 

 tion). 



The lactic acid fermentation seems to be more or 

 less independent of the other acid fermentations, in that 

 its formation may be stopped without affecting that of the 

 other products. For instance, Virtanen has shown that 

 washed suspensions of Esch. coli, which are deprived of 

 cozymase (see Chapter XV) in this way, no longer 

 produce lactic acid from glucose, though the other pro- 

 ducts are formed as usual. Virtanen considers that the 

 first stages of lactic acid fermentation are identical with 

 those of alcoholic fermentation by yeast and involve 

 phosphorylation of the glucose, for which process cozymase 

 is essential ; methylglyoxal, the j)recursor of lactic acid, 

 is then formed. That phosphorylation does play a part 

 in lactic acid fermentation is shown by the fact that 

 the addition of inorganic phosphates to such a fermenta- 

 tion brings about an acceleration of the process just as 

 it does in alcoholic fermentation. Bacterial cozymase 

 can replace that from yeast in alcoholic fermentation. 

 Virtanen claims that cozymase does not play a part in 

 the formation of the other products. It has been shown 

 that the propionic acid bacteria behave similarly ; washed 

 suspensions no longer produce propionic acid, but still 

 give rise to the formation of alcohol, acetic acid, succinic 

 acid and carbon dioxide. 



By grinding Esch. coli Avith powdered glass cell free 

 extracts can be obtained which contain enzymes which 

 are capable of converting phosphoglyceric acid to phos- 

 phopyruvic acid, as occurs in yeast fermentation (see 

 p. 276). The equilibrium between 3-phosphoglyceric 

 acid and 2-ph(jsph()glyceric acid also occurs in the presence 

 of the bacterial enzymes as well as in the yeast and 



