KLUYVER S CONTRIBUTIONS TO MICROBIOLOGY AND BIOCHEMISTRY 



guishing pure cultures of bacteria one from another. Usually, how- 

 ever, the identification of a culture did not seem to require the deter- 

 mination of more than a few of such characteristics, and this frequently 

 caused all others to be neglected. As a consequence one and the same 

 organism might be recognized by one specialist on account of its ap- 

 pearance and mode of growth in various culture media, by another 

 because of its effects on experimental animals, by yet others on the 

 basis of the occurrence of particular chemical changes observed in 

 certain environments. The result was that many bacterial cultures 

 were only partially characterized, and not always by means of the 

 same criteria, so that a single type might even be described under a 

 variety of names. 



As long as the total number of known bacterial types was relatively 

 small, the few morphologically characterized groups, the 'form gen- 

 era' established in the early days of bacteriological research, sufficed 

 as a primary basis for descriptive and nomenclatorial purposes. How- 

 ever, the rapid increase in knowledge eventually led to the practice 

 of combining groups of bacteria into genera that were no longer de- 

 marcated primarily or exclusively with reference to morphological 

 features. Especially Winogradsky and Beijerinck introduced many 

 'genera' of this sort ; Nitrosomonas, Nitrobacter, Acetobacter, Azotobacter, 

 Aerobacter, Photobacterium, Thiobacillus, and Lactobacillus may be men- 

 tioned as examples. Now, the great advantage of such genera is that 

 they effectively speed up identification of a newly isolated strain ; any 

 bacterium that lives in an alcohol-containing medium and produces 

 acetic acid therein immediately becomes recognizable as an Aceto- 

 bacter species; a luminous bacterium is, ipso facto, a Photobacterium; or 

 a non-sporeforming nitrogen fixing bacterium an Azotobacter. But the 

 practice of originating such genera also had some distinct disadvan- 

 tages. For example, neither Winogradsky nor Beijerinck had ever 

 taken the trouble to explain his reasons for proposing such genera, 

 probably because they had considered them to be self-evident. As a 

 consequence the undesirable implications of the procedure became 

 clear only at a later date. 



Was it sound practice to include physiological properties amongst 

 the diagnostic features of a genus? As early as 1872 Cohn had dis- 

 cussed this problem in connexion with the differentiation of species 

 within his form genera, and warned of the dangers inherent in this 



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