BIOGRAPHICAL MEMORANDA 



challenge by the brave device: "Here I am, I can also act differ- 

 ently!" ' (p. 107). 



But the microbial world also offers many examples of a kind of var- 

 iability that is not primarily induced or controlled by environmental 

 conditions. A fairly common sort is what eventually became known 

 as 'dissociation'; it manifests itself through the appearance of different 

 types of colonies on one and the same culture plate, streaked with a 

 suspension of a pure culture of some micro-organism. Special terms and 

 abbreviations, such as 'smooth' ('S'), 'rough' ('R'), 'mucoid' ('M'), 

 etc., had been introduced to characterize various colony types. The 

 reality of this phenomenon had been established beyond question, but 

 a generally accepted interpretation was lacking even as late as the 

 middle 'thirties. 



As early as 1900, and again in 191 2, long before the name 'disso- 

 ciation' had been introduced, Beijerinck had described several cases 

 of variability of this kind, and claimed that they represented mutations 

 in the sense of Hugo de Vries, regularly occurring in cultures of micro- 

 organisms. This concept had, however, been sharply contested, the 

 opponents arguing that mutations can be observed only in organisms 

 that reproduce sexually. Such a mode of reproduction was unknown 

 amongst the bacteria, which were not even considered to possess a 

 nucleus. Consequently Beijerinck's interpretation of microbial varia- 

 bility had fallen into disrepute. 



Another theory to account for the dissociation phenomenon and 

 which had gained prominence during the nineteen-thirties, had been 

 developed by Hadley. It was based on the assumption that bacterial 

 cultures regularly display ontogenetic variations, and that different 

 'cyclostages' are recognizable by the specific colony types correspond- 

 ing to them, the 'rough' phase representing the culminating, or 'repro- 

 ductively mature' stage through which every species would have to 

 pass in due course. Nevertheless, this concept smacked too much of 

 the 'life cycle' theories of Lohnis and Enderlein, formulated in order 

 to account for morphological variations which others, with good rea- 

 sons, had attributed to the use of impure cultures; and Hadley's spe- 

 culations were not regarded very sympathetically by most of the leading 

 microbiologists. It is clear, therefore, that the situation was confused 

 and that further experiments were needed to resolve it. 



150 



