CH. I] THE SCOPE OF THE ENQUIRY 9 



reactions constituting the tests, these observers noticed that 

 variation in virulence was sometimes accompanied by changes 

 in chemical behaviour. They also acknowledged that slight 

 differences in the composition of the media might possibly 

 aflfect the series of reactions to some slight extent. 



Subsequently Ainley Walker (1911) offered evidence to 

 show that greater differences in the media do actually affect 

 the reactions to a remarkable extent, so much so as, in his 

 opinion, to invalidate any claim that they should be re- 

 garded as specific, and he fell back on the position held by 

 Marmorek. 



Still later Jensen and Holth, after a prolonged investiga- 

 tion, came to the opposite conclusion, that is to say in favour 

 of the stability of the differences brought out by Gordon's 

 tests, but they also showed that these differences were in no 

 way closely related to virulence or pathogenic action so that 

 the method of classification founded on them was imperfect. 



We have thus demonstrated that the term "species" when 

 applied to bacteria must be interpreted much more loosely 

 than in the case of plants or the higher animals and the phrase 

 "transmutation of species" is thereby absolved of the accusa- 

 tion of being self- contradictory. 



The aim of this paper is to show how far transmutation 

 does occur, and what is its significance. 



It will be obvious, from what has already been said, that 

 in considering the evidence of transmutation it will be neces- 

 sary to consider also the evidence of variation. The difference 

 between the two is one of degree only. A member of one 

 "species" of bacteria is distinguished from a member of 

 another " species " by its morphological and other characters. 

 If these characters become altered, within certain limits, the 

 process may be regarded simply as variation ; if outside these 

 limits it must be regarded as transmutation. 



We have first of all to consider then, what are the possi- 

 bilities in the direction of such alteration in character. 



