SELECTED PAPERS 



After Reyniers has demonstrated the possibility of a microbe-free 

 existence for monkeys, we may assume that this would equally apply 

 to man. In principle he might thus manage, by combustion of the 

 dead vegetable matter, and with the aid of his fertilizer industry, to 

 keep up at least part of the vegetation, and hence also part of the 

 animal world. But only a burdensome existence would allow him to 

 maintain this unnatural community in a restricted area; and the lack 

 of foodstuffs such as butter, bread, and cheese, and of luxuries such as 

 beer, wine, and liqueurs, would further enhance the drabness of this 

 existence. From these considerations the microbiologist acquires an 

 appreciation of the remarkable interrelatedness of all forms of life, 

 utterly divergent as they are; and in due course he is forced to the 

 notion that there must be a fundamental unity at the bottom of it. 



However, the explorations which the exponents of experimental 

 microbiology have undertaken in the microbial world during the cen- 

 tury of the existence of this science have initially led to the emergence 

 of quite different points of view. For there soon appeared to be a 

 bewildering diversity of living organisms with which in the early days 

 the investigator could familiarize himself only with the aid of his 

 microscope, although gradually he also became acquainted with their 

 stupendous activities after he had learned to cultivate these organisms 

 in his laboratory. Yet it was not so much the wealth of shapes that 

 caused the astonishment ; rather was it the ecological observations that 

 confused his mind. In particular did this apply to the experience that 

 microscopic life can flourish under conditions under which neither the 

 green plants nor the animals can live. It is no exaggeration to say 

 that the pertinent and extensive studies have added an entirely new 

 chapter to general physiology. The following remarks may serve as 

 an, admittedly superficial, documentation of this statement. 



From early times the biologist had experienced that every system 

 that may lay claim to the predicate 'living', with the exception of 

 some special cases of dormant stages, is characterized by its dynamic 

 nature which manifests itself for instance in the phenomenon that is 

 generally referred to as metabolism. This is predicated on the empir- 

 ical fact that for its continued existence and eventual multiplication 

 every living cell depends upon a continuous supply of certain food- 

 stuffs that undergo chemical transformations which yield partly cel- 

 lular building blocks, and partly products that the cell excretes into 



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