THREE DECADES PROGRESS IN MICROBIOLOGY 



esses is, however, the important role which phosphoric esters play 

 therein. Not only must we accept that the first conversion of the carbo- 

 hydrate to be fermented is the formation of a hexosephosphoric acid, 

 but it has also become increasingly clear that a transference of the 

 phosphate group from one intermediate product to a second one, ulti- 

 mately leading to a closed phosphate cycle, is an essential counterpart 

 of the hydrogen transference just mentioned. The more so, because at 

 least in several cases a direct linkage between the two types of processes 

 has been proved to exist. 



Especially gratifying is the result that in all these fermentation proc- 

 esses the first steps of the breakdown of the carbohydrate have been 

 proved to be the same, and that only in the final stages of this break- 

 down process specific step-reactions take place which are responsible 

 for the differences in the final fermentation products. 



Still more important is that these attempts to arrive at a unification 

 of microbial catabolism have not remained restricted to the typical 

 cases of sugar fermentation. In this connexion I mention only that 

 also for the long known bacterial processes of denitrification, sulphate 

 reduction and methane fermentation it has been shown that they 

 represent typical cases of catalytic hydrogen transference in which 

 respectively nitrates, sulphates and carbonates act as hydrogen ac- 

 ceptors. 



The greatest triumph of this analysis of microbial catabolism is, 

 however, that it has proved possible to extend these unifying efforts 

 also to the various types of respiration processes encountered in the 

 microbe world. Numerous investigations initiated by Wieland's clas- 

 sical observations leave no doubt that these processes too consist of a 

 series of step-reactions of the hydrogen or electron transference type, 

 the free oxygen acting as the final hydrogen acceptor. This, of course, 

 is a result with wide implications. For it means that at the bottom of 

 the physiological equivalence of respiration and fermentation as ad- 

 vocated by Pasteur there is a conformity in essence which is highly 

 edifying to the scientific mind. It is clear that hereby new perspectives 

 have been opened for a satisfactory understanding of the interrelation 

 between fermentation and respiration in one and the same type of cell 

 as manifested in the so-called reaction of Pasteur. But the unification in 

 question also opens the way for a better appreciation of evolutionary 

 developments which have taken place in the microbe world, since the 



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