^18 BACTERIOLOGICAL CHEMISTRY 



and similarly the small amyuiit of /6o-propyl alcohol 

 arises by reduction of acetone :— 



(9) CH3.GO.CH3 + 2H — > CH3.CHOH.CH3. 



Kluyver's scheme outlined above should be modified 

 so that the preliminary stages, represented by equations 

 (1) to (3), agree with modern knowledge of the mechanism 

 of alcoholic fermentation. In other words the various 

 phosphorylation reactions leading to the formation of 

 pyruvic acid (see p. 275) are very probably those really 

 involved, rather than the formation and breakdown of 

 methylglyoxal. In the present state of our knowledge 

 there seems to be no reason to change the suggestions 

 concerning the later stages. 



Lactic Acid Fermentation. — Lactic acid is one of the 

 commonest of bacterial products and is produced by a 

 wide variety of bacteria and yeasts. The earlier work was 

 largely done in connection with the dairy industry and 

 more particularly cheese manufacture. The first fer- 

 mentation method for the production of lactic acid was 

 described in 1841 by Boutron and Fremy before, however, 

 it was realised that the action was bacterial. When it 

 was established by Pasteur that this was the case, im- 

 provements were made, although it was not until 1896 

 that pure cultures of lactic acid bacteria were used. 



The lactic acid bacteria were classified by Orla-Jensen 

 in 1919 into two main groups : — 



1. The Homofermentative or True Lactic Acid Bacteria 

 which produce almost pure lactic acid from sugars. They 

 are Gram positive, non-sporing, non-motile rods and cocci 

 which give no surface growth on liquid media. They 

 will not grow in the absence of organic nitrogen com- 

 pounds ; they produce no catalase and do not reduce 

 nitrates. The true lactic acid bacteria are further sub- 

 divided into : — 



