Some Concepts in Mycology. William B. Brierley. 227 



cinerea Pers. : and experience in laboratories of medical 

 pathology during the last two or three years has shewn that 

 bacterial cultures which for years have been regarded as of 

 specific purity, and regularly transplanted in the usual way, 

 have in reality consisted of mixed populations, and that under 

 the influence of unusual conditions the components have shewn 

 characteristic and divergent reactions. It is absolutely impera- 

 tive therefore that the experimental organism in all investiga- 

 tions dealing with the educabihty of micro-organisms should 

 be above suspicion regarding its specific purity. Possibly in 

 such a direction may be sought the explanation of the arresting 

 claims of Rosenow(36) to which reference has already been 

 made. 



A second direction of research which may possibly throw a 

 flood of light on the so-called mutations in the bacteria lies in 

 the investigation of the life-cycles and developmental and 

 reproductive phases of these organisms. 



Since the days of Cohn(7), who established the morphological 

 constancy of the bacteria, these organisms have been regarded 

 as characterised by an extremely simple life-history, and 

 although in the intervening period many observations have 

 been put on record which have contravened this idea, the 

 weight of dogma has been so heavy that these have not received 

 serious consideration. There can be no doubt that progress 

 in bacteriology has been very severely checked by the rigid 

 adherence of all but a few investigators to a conventional 

 conception of a very simple and constant bacterial organism. 

 The recent researches of many workers, among whom may be 

 particularly mentioned Hort(i7) in this country, Lohnis and 

 Smith(22) in America and de Negri(3o) in Germany, indicate 

 that the life-cycles of the bacteria may be very complex and 

 characterised by the regular occurrence of many different forms 

 and stages of growth connected with each other by constant 

 relations. Under ordinary conditions simple binary fission 

 and endospore formation are probably only two of many 

 phases in the life-cycle which there would seem reason to believe 

 includes an almost invisible filterable stage and a naked 

 plasmodial or symplastic condition. According to Lohnis and 

 Smith(22), "The life-cycle of each species of bacteria studied is 

 composed of several sub-cycles shewing wide morphological 

 and physiological differences. They are connected with each 

 other by .the symplastic stage. Direct changes from one 

 sub-cycle into another occur, but they are rather rare 

 exceptions." 



The foregoing very brief sketch may give some idea of the 

 hitherto unrealised complexities involved in investigations, 



