37 



0.90). The latter was mostly used with an ocular (5 :<), so that the 

 magnification of the various micro-organisms was restricted to 450 

 times. Moreover, in his microscopical work BEIJERINCK often violated 

 various optical rules ; he never took into account the thickness of the 

 coverglass of his preparations, the tube-length was never adjusted at 

 160 mm etc. Notwithstanding all this, BEIJERINCK - - like the famous 

 founder of microbiology, ANTONY VAN LEEUWENHOEK - - owing to 

 his excellent eyes and his keen observational power, generally saw 

 more and better than the average microscopist. If BEIJERINCK now 

 and then invited his assistants or students to admire his microscopical 

 preparations, they often had great difficulty in checking his observa- 

 tions. In this connection it is worth mentioning that BEIJERINCK 

 hardly ever made stained preparations; he considered staining an 

 objectionable habit of medical bacteriologists, leading to the produc- 

 tion of artefacts which veiled the real situation. 



Photomicrography w r as always left to his assistants, but this did not 

 mean that BEIJERINCK would not severely criticize the results! 



Although he avoided all complicated constructions, BEIJERINCK 

 was keen on designing simple and handy instruments. Mention may 

 be made of his culture dishes with flat-ground covers which he greatly 

 preferred to ordinary PETRI dishes. A further example is afforded by 

 the special device he invented for the cultivation of anaerobic mi- 

 crobes in the presence of Oidium lactis, which organism was applied to 

 remove the last traces of oxygen. Another of his small inventions was 

 launched under the barbaric German name of "Kapillarhebermikro- 

 skopirtropf enflasche' ' . 



BEIJERINCK used to complain about his defective chemical education, 

 but he exaggerated badly in saying that he knew practically nothing of 

 this science. His fine investigations on the action of various enzymes, 

 on bacterial pigments, and on the chemical constitution of microbial 

 cell walls, and especially his work on sulphate reduction, denitrifica- 

 tion and nitrogen fixation, testify to the contrary. There is ample 

 evidence that next to biology, chemistry was his great love, and also 

 that he had a deep insight into the chemistry of living cells. 



In his own chemical work BEIJERINCK was especially fond of 

 applying all kinds of qualitative analytical tests. 



Quantitative estimations were as a rule too cumbersome for him; 

 he left these to his collaborators. His appreciation for "weight and 

 measure" was rather restricted, and in those cases in which he was 

 inclined to accept a quantitative standard, he was easily satisfied 

 with an approximate result. One of his favourite expressions was the 

 paradoxical phrase: "I have investigated this somewhat quantitativ- 

 ely"! 



His essentially "qualitative" work was, however, not seldom 

 characterized by its elegance and its aesthetic qualities. We need here 

 recall only his auxanographic method, his experiments on "micro- 



