86 DISSOCIATIVE ASPECTS OF BACTERIAL BEHAVIOR 



THE DISSOCIATIVE REACTION 



As I have pointed out in a previous publication/ extreme instability of bacterial 

 types has become recognized in recent years as a commonly observed phenomenon. 

 But its significance has been vastly underestimated and its cause or causes a matter 

 of uncertainty. Although descriptions of bacterial "variants" and "mutants" have 

 appeared with increasing frequency in the literature of the past thirty years, it is seldom 

 that they have been regarded as possessing significance outside of that referable to the 

 Darwinian or De Vriesian conceptions. It has, indeed, been only in quite recent times 

 that the striking orderliness and persistence with which these variants are found to 

 appear in difi'erent bacterial species and groups have enabled us to relate them to a 

 definite law of variation, widely operative in the bacterial world. Indeed, these ob- 

 servations have led us to the view that, within each bacterial species, there are con- 

 stantly occurring certain transformations relating to cell morphology, colonial form, 

 biochemical, serological, and immunological characteristics and to virulence; more- 

 over, that these transformations are neither random variations from a "normal" type 

 in the old Darwinian sense nor sudden saltations characteristic of mutations; but that 

 they represent modifications which occur with a certain degree of precision in many 

 different species when confronted with similar changes in environment. 



It is only within recent years that serious attempts have been made to correlate 

 any of the different characters of the variants, such as virulence with colony form or 

 serological reaction with cell type. Indeed, it has been the common view that such 

 correlations were seldom possible; or, at least, not sufficiently constant to be of impor- 

 tance. We know today, however, that such correlations are the rule rather than the 

 exception, although they may be partly obscured at times, for a variety of reasons; 

 moreover, that these correlations possess supreme importance for bacteriology, pathol- 

 ogy, and medicine. 



The results of many observations have thus served to indicate that pure line cul- 

 tures, of many bacterial species to say the least, are composed of cells all of which are 

 by no means identical. From the same pure line strain may arise, depending on the 

 manner of cultivation and on other environmental conditions, substrains possessing 

 little resemblance either to each other or to the parent-strain. These diflferent culture 

 types may be spoken of conveniently as "dissociated forms" or as "dissociants"; and 

 the phenomenon involved in their production has been termed "microbic dissociation." 

 The terms Umwandlung, Keimiimwandlimg, and Umformung (of bacterial species), 

 employed by certain German and Swedish investigators, may be regarded as referring 

 to the same phenomenon. Microbic dissociation thus becomes established as a new 

 and highly significant field in the wide province of bacteriology. 



But it will be clear that the reactions characteristic of the dissociative phenomenon 

 are, in a sense, superficial. Behind microbic dissociation there must exist a biological 

 mechanism; and this mechanism, we shall come to see, concerns microbic heredity. 

 Through this medium, therefore, dissociation is intimately related to important studies 

 which have been conducted by a small group of investigators dealing with the so- 

 called "life-cycles" of bacteria. 



' Hadley, Philip: loc. cii. 



