PHILIP HADLEY 87 



One of the first to suggest that bacterial reproduction was characterized by phenomena 

 more complex than those appertaining to simple fission, and something even more diversified 

 than simple back-and-forth variation between two or three variants, was Fiihrmann' who 

 in 1907, proposed his Eiitwicklungscydus. This conception of a cyclical development in bac- 

 teria was further indicated in a work by Hort^ in England in 1916, by Lohnis and Smiths in 

 the United States, and by Enderlein^ in Berlin, also in 1916. It was at this time that the 

 latter worker introduced into bacteriological terminology the term "cyclogeny" {Cydogenie) , 

 implying the cycle through which the microbe passes in leading up to the highest cytological 

 state (Kulmi)ianle) and returning to its basal state (Mychil). Many of the papers by Alm- 

 quists and Mellon^ on microbic heredity have dealt with the problem of life-cycles among 

 bacteria; and in recent years this term, often used rather loosely to indicate certain obscure 

 cellular transformations, has occurred in the literature with considerable frequency. 



While it seems probable that the time will eventually arrive when we can speak intelli- 

 gently regarding definitely cyclical aspects of bacterial reproduction, and even though at the 

 present moment we can often detect a certain direction in the serial transformations observed, 

 it has seemed to me that our present knowledge of cyclical development in its details is still 

 too slight to justify a common use of this term as describing the transformations thus far ob- 

 served. Until more definite knowledge of the distinctly cyclical development of some one 

 species is at hand, it is perhaps more appropriate to employ a term suggesting merely cultural 

 transformations, often, it is true, apparently directive, but not overemphasizing the cyclical 

 feature. For such a term, "microbic dissociation" will for the present suffice. The ultimate 

 realities on which it depends are those involving the mechanics of microbic heredity. Micro- 

 bic dissociation might therefore be defined as embracing those distinctly transformatory 

 processes occurring in bacterial cultures, in vitro or in vivo, through which there arise one or 

 more new culture forms which differ from the mother-type, and which (i) may persist for a 

 variable time in an apparently stable state, or (2) may become transformed into still another 

 culture type, or (3) may "revert" to the original form. 



The studies that bear on the problems of microbic dissociation may be grouped under 

 two headings: (i) those random observations on culture variations which, even by the 

 authors themselves, were not recognized at the time when the work was conducted as related 

 to the fundamental problem of microbic heredity; (2) those later and more concise studies 

 definitely directed upon the meaning of bacterial variation, its causes and effects. Regarding 

 the first category, little need be said except that there exist in the bacteriological literature 

 of the past thirty years or more numerous isolated citations which, by virtue of our present 

 knowledge of the dissociative process, we are able to translate into the terms of microbic dis- 

 sociation. Some of these I have brought together in a previous publication.' The second cat- 

 egory of studies mentioned above includes those which consciously attack the problem of 

 bacterial variation. These, in turn, are divisible into two groups, each differing from the 

 other in its mode of approach to the fundamental problem. These involve (i) the C3^tologi- 

 cal approach and (2) the cultural approach. In the latter group may also conveniently be 

 included the biochemical and serological characteristics of the variants. 



' Fiihrmann, F.: loc. cil. ' Hort, E. C: /. Roy. Micr. Soc, p. 11. 1926. 



3 Lohnis, F. and Smith, E. R.: Jour. Agr. Res., 6, 675. 1916. See also Lohnis: ibid. 23, 401. 

 1923; also Men. Nal. Acad. Sc., 16, 252. 1921. 



■•Enderlein, G.: Sitzungsb. ges. naturf. Frennde. Berlin, 1916. 



5 Almquist, E.: Cenlralbl. f. BaklerioL, Abt. I, Orig., 60, 167. 191 1; Biologische Forschiing tiber 

 die Bakterien. Stockholm, 1925. 



* See Hadley, Philip: loc. cit. ^ See ibid. 



