150 



characteristic of BEIJERINCK'S versatility that amongst these cultures 

 there are three bacterial species, viz., Bacillus prodigiosus, Bacillus 

 herbicola and Bacillus indicus, one alga: Chlorella variegata, and a few 

 yeasts amongst which Schizosacharomyces octosporus is especially 

 considered. 



In the final chapter of his paper BEIJERINCK deals exhaustively 

 with the nature of the variations observed. He concludes that the 

 majority of these variations must be considered as mutations which 

 are wholly comparable to the more or less constant bud mutations of 

 higher plants. He also draws a parallel between microbial mutations 

 on the one hand and the occurrence of different forms of heterostyles, 

 and that of the two sexes of dioecious plants on the other hand. But 

 also the formation of the different organs in higher organisms - - a 

 phenonemom usually simply designated as differentiation is 

 considered to present a more or less analogous case i). 



In identifying microbial variations with the well-know T n gene muta- 

 tions of higher organisms BEIJERINCK, of course, is well aware of the 

 fact that in micro-organisms no experimental proof for the correct- 

 ness of this assumption can be furnished, owing to the impossibility of 

 a gene analysis by hybridization. Yet he emphasizes that there is no 

 reason to accept that mutants of organisms showing amphimixis 

 should in any respect be different from those with asexual reproduction 

 only. 



A characteristic feature of BEIJERINCK'S views is his conviction 

 that mutation and atavismus are equivalent processes. 



According to BEIJERINCK many mutation phenomena should be 

 regarded as to be of an atavistic nature. This may even apply, when 

 apparently a new property as, for instance, pigment production is 

 manifested. This may merely mean that a progene is brought back 

 into the active state. In other cases active genes may be reverted into 

 progenes. 



It is here not the place to enter into a detailed consideration of the 

 fate of the mutation theory of microbial variation during the quarter 

 of a century that has passed, since BEIJERINCK gave his masterly ex- 

 pose. Suffice it to state that many of the later investigators in this 

 field have severely criticized BEIJERINCK'S views. Other theories, 

 amongst which VAN LOGHEM'S "individuality theory" 2 ) and HADLEY'S 

 cyclic theory 3) may be especially mentioned, have largely superseded 

 the mutation concept. Of late, however, both LINDEGREN 4 ) and 



') In a recent survey of the variability of bacteria this point of view has again been 

 brought to the fore by O. RAHN. Cf. Scientia, 1937, p. 83. 



) J. J. VAN LOGHEM, Nederl. Tijdschr. v. Geneesk. 65, 2981, 1921; Proc. Kon. 

 Akad.v. Wet. Amsterdam 34, 2, 1931 ; Antonie van Leeuwenhoek 4, 113, 1937. 



J) PH. HADLEY, Journ. of Infect. Dis. 40, 1, 1927; Ibid. 48, 1, 1931; Ibid. 60, 129, 



1 7vJ / . 



) C. C. LINDEGREN, Zentr. f. Hakt. II, 92, 40, 1935; Ibid. 93, 1 13, 1936. 



