70 PHYSIOLOGY OF BACTERIA 



acceptor. We should distinguish, for practical pur- 

 poses, three different cases: 



(1) The hydrogen acceptor is molecular oxygen. 

 Then we have a direct oxidation, as in the vinegar 

 fermentation, or in the action of molds or mycobacteria 

 upon sugar. 



(2) Hydrogen acceptor and hydrogen donator are the 

 same molecule. This we call intramolecular fermenta- 

 tion. The chemical equation shows this most simply: 



C6H12O6 = 2C3H6O3 



No oxygen and no hydrogen from outside are apparently 

 needed to bring about this fermentation. It consists 

 of nothing but a rearrangement of the H- and 0-atoms 

 (see p. 75). The same is true with all the typical 

 sugar fermentations. 



As a matter of fact, the case is not quite so simple 

 because we must consider the separate stages of fer- 

 mentation. But the term '' intramolecular fermenta- 

 tion" indicates that one substance alone is sufficient 

 as source of energy. 



(3) Hydrogen acceptor and donator are different 

 molecules. Two different compounds are required to 

 bring about the change. The acceptor may be oxygen; 

 this proves type (1) to be just a special case of type 

 (3), sufficiently speciaUzed, though, to remain classified 

 by itself. Examples of type (3) have been given in 

 the discussion of interaction between proteins and 

 carbohydrates. Another example which brings the 

 oxygen into the foreground again is the anaerobic fer- 

 mentation at the expense of oxygen from nitrates, 

 sulphates, methylene blue and similar, highly oxidized 

 compounds. Allyn and Baldwin (1930) could make 



