THREE DECADES PROGRESS IN MICROBIOLOGY 



other trends of investigation besides that of ordering and classification 

 are easily discerned. 



In the foregoing I have already emphasized the diversity in metab- 

 olism characteristic for the various types of micro-organisms, and it is 

 only self-evident that the often quite amazing chemical activities of 

 many microbes has led to attempts to penetrate deeper into the secrets 

 of their metabolism. In order to give you some idea of the achieve- 

 ments attained along this line during the last three decades I should 

 remind you that in metabolism two counterparts can and should be 

 distinguished, viz., anabolism and catabolism. The term anabolism 

 comprises the processes leading to the building up of cell constituents, 

 while we designate with catabolism those processes which are only of 

 significance to the cell from the standpoint of energy supply. 



As for the catabolic processes in higher organisms, plants as well as 

 animals, it has been known since Lavoisier's fundamental observations 

 that they have to be considered as a slow combustion process of the 

 carbohydrate constituents of the food, and that, therefore, they are 

 characterized by a consumption of oxygen and a simultaneous pro- 

 duction of an equivalent amount of carbon dioxide. This so-called 

 respiration process has consequently long been considered to be an 

 essential attribute of life. 



Already a first survey of microbial life did bring to light that herein 

 this uniformity in catabolism so characteristic of the higher forms of 

 life is absent. In the first place it soon became evident that, although 

 the proliferation of many microbes is indeed dependent on the avail- 

 ability of free oxygen, the respiration processes differed widely in the 

 nature of the compounds acceptable as substrates for the oxidation 

 process. Moreover, with many types of microbes this process did not 

 yield the final oxidation products carbon dioxide and water, but led 

 to the excretion of incomplete oxidation products in the medium. 



Even more startling was the observation made by Pasteur already 

 in i860 that there were several microbes which not only could thrive 

 in the absence of oxygen, but for which this gas even was decisively 

 harmful. It did, however, not escape Pasteur's attention that this un- 

 expected observation correlated with the occurrence of other chem- 

 ical conversions known from time immemorial as fermentation (or 

 putrefaction), and his genius made him at once conclude to the 

 physiological equivalence of respiration and fermentation. 



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