246 BACTERIOLOGICAL CHEMISTRY 



Pyruvic acid (which is, as we shall see, the normal 

 precursor of acetaldehyde) has also frequently been 

 isolated from bacterial fermentation solutions by appro- 

 priate " trapping " methods, for example, by the use of 

 [3-naphthylamine with which it forms the insoluble 

 compound, a-methyl- p-naphthocinchoninic acid : — 

 CH CH N 



CH C C— NHg Q: =C— CH. 



I II I ^ I 



I II I... ^.. + i COO:!! 



CH C CH- 



^/\^: HO:-C=CH:- 



CH CH I 



C.CHg 



CH 



r*nnTT COOH 



+ 2H2O+H2 + CO2 



(3-naphthylamine) (2 pyruvic acid) (a-methyl- 3-naphtliociuchomnic acid) 



In this way pyi'uvic acid has been identified as an inter- 

 mediate in the fermentation of lactic and fumaric acids 

 by Esch. coli, and of glucose, maltose and glycerol by 

 B. aceto-ethylicus. It has been shown, too, that pyruvic 

 acid can be utilised by bacteria. 



Methylglyoxal is converted into lactic acid by the 

 action of the enzyme glj^oxalase, which occurs in the 

 liver, muscle tissues and many bacteria including Esch. 

 coli, Str. lactis, L. casei, and Acetohacter : — 

 (HO COOH 



I I 



CO +H2O > CHOH 



1^ I 



CH3 CH3 



methylglyoxal) (lactic acid) 



Methyl glyoxal has been detected following the action 

 of Esch. coli or of A. xylinurn on magnesium hexose 

 phosphate in presence of toluene, and in the fermentation 

 of glycerol by the propionic acid bacteria. 



Lusk suggested that glucose is fermented to give 

 lactic, acetic and formic acids according to the scheme 

 shown at tlio top of the following page. 



