SELECTED PAPERS 



Now it gradually became evident that the fermentation processes 

 brought about by various types of micro-organisms mutually show- 

 great differences. Although they may attack the same substrate, the 

 products of the conversion often differ considerably. While in the 

 best-known fermentation process, the conversion of sugar into carbon 

 dioxide and ethyl alcohol, the products are stoechiometrically related 

 both mutually and to the sugar fermented, in many other cases in 

 which numerous fermentation products are formed such relations do 

 not exist. Moreover, the quantities in which these products are formed 

 may vary largely owing to differences in the external conditions to 

 which the fermenting organism is exposed. 



Altogether, a quarter of a century ago the biochemistry of catabolic 

 processes in the microbe world showed such an extreme diversity that 

 at that time one might well despair of any attempt to elucidate this 

 superchemistry. 



It is undoubtedly one of the greatest results of three decades of 

 microbiological investigation that nowadays this aspect has so funda- 

 mentally changed. If we try to survey the causes which have led to 

 this revolution it is at once clear that we owe this progress mainly to 

 the splendid investigations of both Meyerhof and Warburg and their 

 co-workers. Concentrating their efforts on an analysis of the processes 

 of alcoholic fermentation and glycolysis, and building on the work of 

 pioneers like Harden and Neuberg, they have been able to give us a 

 clear insight into these processes. 



Stimulated by these so successful investigations other types of fer- 

 mentations have likewise been more or less intensively studied in 

 several other laboratories. The chief result of all this has been that 

 the so amazing diversity of the various fermentation processes has 

 given way to a quite unexpected unity in principle. 



The main points of the insight gained can be summarized as follows. 



All these fermentation processes consist of a series of individual step- 

 reactions, each of which constitutes a chemically intelligible, and ex- 

 tremely simple type of reaction, the greater part of these step-reactions 

 being typical equilibrium reactions. Moreover they show great uni- 

 formity in so far that many of them can be characterized as reactions 

 in which hydrogen atoms (or electrons) are transferred from one con- 

 stituent to another. 



Another feature of our present insight into the fermentation proc- 



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