52 PHYSIOLOGY OF BACTERIA 



The Lactic Fermentation is essentially type la which 

 is a typical intramolecular oxido-reduction. 



la: CsHeOs = CsHeOs 



Methyl glyoxal Lactic 



hydrate acid 



This describes the fermentation of about 90% of the 

 sugar by Streptococci, and by some of the Lactobacilli. 

 There are other Lactobacilli, however, which form also 

 alcohol and CO2. This means that these organisms 

 have also the power (i.e. the enzymes) to bring about 

 reactions lb, Ilia, IVc and IVe producing formic acid 

 as intermediate product which is decomposed further, 

 liberating CO2, ethyl alcohol and glycerol. 



To which type of fermentation the volatile acids which are formed 

 in relatively large amounts by certain groups of streptococci (Ham- 

 mer, 1920, Hucker 1928) should be ascribed, cannot be stated until 

 we know whether this fermentation is accompanied by corresponding 

 amounts of glycerol and ethyl alcohol. The presence of propionic 

 acid with some species suggests also the fermentation type IVd, 

 while others producing formic acid apparently include type lb. 



The Propionic Acid Fermentation has been summarized 

 by van Niel in a monograph (1928). Several possi- 

 bilities are presented among which no experimental 

 decision has as yet been possible. It may be that lactic 

 is formed as such (la) and fermented further according to 

 equation 



IVd: CH3-CH0H-C00H + 2H = CHa-CHz'COOH + 



Lactic acid Propionic acid 



H2O 



where the hydrogen derives from a different mode of 

 attack, perhaps like this: 



CH3-CH0H-C00H + H2O = CH3COOH + 



HCOOH + 2H 



