346 Mutation in Micro-Organistns 



more or less alike. The majority represented merely temporarily 

 modified individuals : only a very few were permanently mutated 

 organisms. There is, of course, nothing to indicate what factors may 

 have been concerned in the production of these forms in the first 

 place. 



I will end this section by referring to some work which has just 

 been published by Revis (1912). His observations also concern B. colt. 

 A typical strain of this organism was grown in peptone broth to which 

 malachite green had been added'. The effect of this dye was to 

 produce a new race of organisms which differed both structurally and 

 culturally from typical B. coli. When the organisms were grown 

 subsequently at 20° C. on ordinary gelatin or agar, they formed " large 

 viscous, circular masses," consisting of "a mixture of very long fila- 

 ments- and short bacilli, together with a gummy cementing substance." 

 Presumably the race breeds true to these new characters. The 

 organisms were not propagated by the isolation of individuals, but the 

 cultures were very carefully plated out. The purity of the original 

 culture is guaranteed. Revis therefore claims to have produced — by 

 means of malachite green — from a typical B. coli a new race " which 

 is neither physiologically, morphologically, nor culturally a colon 

 bacillus." Further details and confirmation of these observations are 

 to be desired. 



Concluding Remarks. 



To epitomize in few words the numerous facts given in the fore- 

 going pages is hardly possible, for what has been written is itself one 

 long epitome of facts and their interpretations. A few general remarks 

 may, however, be permissible to a writer who has travelled thus far 

 over very stony ground. They may serve, moreover, to call attention 

 to certain facts which are undoubtedly important — though the magni- 

 tude of their importance and their significance may well be appraised 

 in very different terms by diffei'ent individuals. It must be understood, 



' See also p. 337 supra. 



- It was already known that organisms o{ the coli-typ}wsns group — and others also — 

 assume a remarkable filamentar form when grown on media containing certain dyes. 

 The first observations in this connexion were made in 1904 by Walker and Murray 

 (British Med. Journ., Vol. ii. p. 16). Similar results have since been obtained by Vay 

 (C. B. Bakt., I. Orig. 55, 1910, p. 193) and others. 



