36 



made of the latter fundamental sciences were nearly always restricted 

 to those which he could easily verify in his own experiments; phen- 

 omena which lay beyond that boundary did not interest him. Even 

 his knowledge of mathematics was mainly of an experimental char- 

 acter, he deduced mathematical theses by geometrical constructions. 

 Especially in the latter part of his life he was not seldom led astray 

 by this procedure, he then "discovered" peculiarities which could have 

 been proved - - or disproved - - in a much simpler way. 



Another feature of BEIJERINCK'S life work is its great diversity. The 

 contents of his "Collected Papers" reveal an astonishing variation in 

 subjects, even of consecutive papers. BEIJERINCK'S mind was so rich 

 that he could not centre his attention for long on any one subject. 

 New thoughts continuously took hold of him and forced him to leave 

 recently-conquered ground. In consequence of this, as a rule, BEIJE- 

 RINCK was occupied with several problems at the same time. Even in 

 the period of his microbiological activity he not seldom returned to 

 purely botanical studies. 



This mercuriality of BEIJERINCK'S mind was also clearly manifest 

 in his conversations, and - at least in later years - - in his lectures 

 which, although always sparkling, often lacked logical consistency. 



All this should not be understood to mean that BEIJERINCK had 

 no general scientific program. On the contrary, the chief aim in his 

 microbiological work has always clearly been to create order in the 

 chaos of the microbe world. The very consciously-applied "enrichment 

 culture method" led to the recognition of numerous well-defined 

 physiological groups in the bacterial kingdom, and has furnished a 

 stable basis for future work. 



Nor can it be said that BEIJERINCK was always unfaithful to those 

 subjects which had once engaged his full interest ; he often came back 

 to an old theme after several years, and then dealt with it in a broader 

 and more profound way. 



The scientific unrest which was so prominent in BEIJERINCK on the 

 other hand explains why he was never able to persuade himself to 

 write textbooks or monographs. Such writing demands introspection 

 and patience. 



The most marked trait of BEIJERINCK'S scientific personality was 

 undoubtedly his passion for experiment. However, he liked only 

 simple, and if possible, elegant experiments. Galvanometers, re- 

 gistration apparatuses, etc. are nowhere mentioned in his papers. One 

 could almost say that he abhorred complicated instruments, and one 

 of his favourite sayings was: "An experiment should be simple". 

 This attitude was also manifest in the use of the microscope. Oil 

 immersions were rejected as being "dirty", dark field illumination, as 

 being too complicated. His usual optical outfit consisted of a ZEISS 

 microscope with achromatic objectives 8 and 40 <, and the from 

 the optical standpoint rather unsatisfactory dry system 90 x (N.A. = 



