THREE DECADES PROGRESS IN 

 MICROBIOLOGY 



It is only appropriate that our first thoughts this afternoon go out to 

 that pioneer in the field of microbiology whose birthday, now 104 years 

 ago, we commemorate today. In these surroundings it may be deemed 

 superfluous to pause upon the many important contributions Emil 

 Chr. Hansen has made to pure and applied microbiology during his 

 well-used life-time. There is, however, every reason for the lecturer to 

 acknowledge his great debt of gratitude towards the man who in his 

 last will took measures to promote even after his death the develop- 

 ment of his beloved science for long times to come. In saying this I do 

 not wish to suggest that the superficial considerations which I have 

 the honour to present before you this afternoon will influence in the 

 least the growth of microbiology. But I want to give expression to my 

 conviction that owing to the contact with so many distinguished rep- 

 resentatives of Danish science I shall be on my returning home, if 

 not a better man, at least a better scientist. And it is also at this 

 international diffusion of knowledge that Hansen must have aimed, 

 when he decided to call into existence the 'Fond' which bears his 

 name. 



Having gone back in our minds to the year 1909, incidentally the 

 year in which my own initiation in the world of microbes took place, 

 it is tempting to take a retrospective view of the development of micro- 

 biology as a science, and to compare the present situation with the 

 stage reached about thirty years ago. Such a survey can, of course, 

 not aim at completeness, and I shall have to confine myself to a passing 

 into review some of the major trends of investigation which on looking 

 backward come to the fore. In doing so I hope to bring into relief the 

 considerable progress made in three decades of almost restless research, 

 a progress which is characterized by an ever-increasing recognition of 

 the unity that is at the basis of the at first sight so bewildering diversity 

 in the various manifestations of microbe fife. 



Let us now first dwell for a moment on the stage of development 



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