ENERGY SUPPLY OF THE CELL 53 



the formic acid acting also as hydrogen donator (Ilia) 

 to reduce another lactic acid molecule. It is also possible 

 that lactic acid is not formed as such from glucose in 

 this fermentation, but that glyceric aldehyde or methyl 

 glyoxal undergo an oxido-reduction directly, van Niel 

 has made it quite probable that acet aldehyde is not an 

 intermediary product in this fermentation. 



The Colon-T3rphoid Group has a much more varied 

 way of attack. Lactic acid is always formed (la) and 

 there is another process of fermentation going on at the 

 same time, independently. This second process resem- 

 bles that of the yeast fermentation to a certain extent, 

 with acet aldehyde as an intermediary product. It 

 starts with reaction lb, followed up by IIIc and IVe 



lb: CH3-C0C0H = CHs'CHO + HCOOH 



Methyl glyoxal Acet aldehyde Formic acid 



IIIc: CH3-CH0 + H2O = CHg-COOH + 2H 

 IVe: CHs-CHO + 2H = CH3-CH20H 



This accounts for the formation of lactic acid, and 

 without relation to this, for the formation of two mole- 

 cules of formic acid to one each of acetic acid and ethyl 

 alcohol. This would be the type of fermentation by 

 Bad. typhosum. 



Occasionally glyceric aldehyde acts as hydrogen 

 acceptor and small amounts of glycerol are formed. 



In the colon-group, reaction Ilia causes the for- 

 mation of H2 and CO2 in equal volumes from formic acid. 



Succinic acid is also formed in small amounts, and 

 doubtless is derived from sugar (Ayers and Rupp, 1918). 

 Kluyver and Donker believe that glucose which is not 

 in the form of a phosphate ester might be split unevenly 

 into a four carbon and a two carbon chain. 



