SELECTED PAPERS 



microbiology had reached in the period immediately after Hansen's 

 decease. 



Seen from the distance of to-day it is clear that microbiological sci- 

 ence passed through a phase of transition then. The glorious period of 

 exploration of the microbe world had practically come to an end. 

 The preceding quarter of a century had witnessed an almost endless 

 series of triumphs in the discovery and isolation of numerous microbial 

 species. In the hands of masters like Winogradsky and Beijerinck the 

 principle of the elective culture had opened the world of invisible life. 

 Owing to the so pronounced diversity in nutritional requirements of 

 the various types of micro-organisms it proved possible to bring about 

 accumulations of many diverse microbes, thus facilitating their isola- 

 tion and a first investigation of their properties. By these studies a clear 

 light was thrown on the almost ubiquitous occurrence of numerous 

 microbes on earth. But still more impressive was the manifestation of 

 the extreme diversity of chemical systems which proved to be able to 

 support microbial life. I have only to remind you of Winogradsky's 

 great discovery of the so-called autotrophic bacteria characterized by 

 their ability to proliferate in fully inorganic media in the absence of 

 radiant energy. Other forms of life again were found which satisfied 

 their nutritional demands with single organic compounds either con- 

 sidered to be almost chemically inert like the paraffin hydrocarbons, 

 or even known to be harmful for the greater part of microbes like 

 phenols. In short it can be said that one specialist amongst the mi- 

 crobes was hardly discovered, or already a second specialist with still 

 greater achievements was being announced. The microbiological scen- 

 ery seemed to be one grand scientific 'Tivoli'. 



However, around 1910 the activity in this direction had obviously 

 slackened: the great explorers of the microbe world had done their job 

 efficiently. One would go too far by stating that since then no new 

 species have been discovered. But how poor has the harvest been in 

 later years when compared with that in the earlier period. And this 

 notwithstanding the enormous increase in the number of 'microbe- 

 hunters' during the last three decades. Is it not characteristic that the 

 almost incredible extension of the study of bacteriology in the 'New 

 World' since the first world war has not at all led to the discovery of 

 a 'new microbe world'? It is true that the number of micro-organisms 

 annually described as new species is still alarmingly large. But how 



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