340 Mutation in Micro-Organisms 



the original bright red colony gave rise to a dark red mutation, and 

 a white reverting mutation. In addition to these, it produced a white 

 modification. And when the dark red form was subjected to the 

 continued action of the bichromate, it produced in turn another white 

 reverting mutation. Certain substances seem, therefore, undoubtedly to 

 cause profound changes in the pigment-metabolism of B. prodigiosus. 

 But it seems that the changes themselves are purely a matter of 

 chance : for they may be permanent, partly permanent, or imper- 

 manent, and in either of two opposite directions. Another note- 

 worthy point is that two quite different poisons may produce the 

 same sort of mutation. For example, HgOla and KgCraOy may both 

 give rise to dark red races. 



In his investigation of Staphylococcus pyogenes aureus, Wolf obtained 

 less definite results'. In some cultures temporary modifications of colour 

 appeared, but he was never able to produce a permanent change — or 

 mutation — by chemical means. Only one mutation occurred, and that 

 was in the control series of cultures on ordinary media. On plating 

 out the organisms at the 22nd transplantation. Wolf found three white 

 colonies among the remaining typical dark-yellow aureus colonies. 

 These white races subsequently bred true. They never reverted to 

 yellow. Moreover, they were found to answer all the cultural and 

 other tests of the organism known as Staph, pyogenes alhus\ It 

 would seem, therefore, that alhus may arise under " normal " condi- 

 tions from aureus : though — as the author says — the mutation arises 

 " from unknown causes." 



Wolf did not obtain any other colour mutations in the case of true 

 Bacteria. But he made some curious observations upon the Myxo- 

 bacteria^ which he also investigated. (He observed a number of 

 transient colour changes (modifications) in Myxococcus races, but these 

 need not be considered here.) 



It had already been shewn by Quehl that physiological differ- 

 ences exist between different races of Myxobacteria. If two swarms* 



1 Neumann had previously stated that he was able to select races of several different 

 colours from this form. Wolf, working upon a pure line, was unable to do this. 



2 Several similar alhus mutations occurred in the course of plating out subsequent 

 sub-cultures of this series. 



3 The Myxobacteria constitute a remarkable group of the Protista. They differ in 

 many ways from ordinary bacteria, and their systematic position is still very doubtful, 



* The swarms consist of large numbers of separate individuals (like ordinary bacteria 

 in some respects) invested with a common covering of slime. The swarms give rise to 

 fructifications (I'esembling those of the Mycetozoa) in which spores are formed in a 

 peculiar manner. 



