2 INTRODUCTiaN 



and vegetable life, and amongst these variation is of still 

 greater frequency. This fact, confirmed by personal observa- 

 tion and by a perusal of the literature of the subject, suggested 

 to the writer the question whether actual transmutation of 

 species might not occur amongst bacteria, and it was in the 

 hope of answering this question that the investigation here 

 recorded was undertaken. 



An endeavour was made in the first instance to collect 

 the published records of all experiments in which transmuta- 

 tion was alleged to have occurred. These were found to be 

 few in number. In the second place, a series of experiments 

 was carried out by the writer with the object of disproving 

 the contention put forward in one of these cases. Thirdly, 

 with a view to criticising the claim made in the remaining 

 cases, and in the hope that it might throw some light on the 

 problem of transmutation as a whole, a study of the subject 

 of variation amongst bacteria was undertaken. The material 

 on which it is based has been collected from the scattered 

 literature of the subject. With a few exceptions, only papers 

 written in English have been consulted. 



In Chapter I the scope of the enquiry is outlined. In 

 Chapter II the conditions which modify the characters of 

 bacteria are enumerated and in Chapter III the value of the 

 evidence adduced in proof of such modification having 

 occurred is considered. Examples of variation are then studied 

 in detail and their significance is discussed, reference being 

 made more particularly to morphological characters, fer- 

 menting properties, virulence, and pathogenesis (Chapters 

 IV — VII). In Chapter VIII the possibility of transmutation 

 occurring in the animal body is considered. In Chapter IX 

 instances of supposed transmutation are examined. In Chapter 

 X the subject is reviewed at length and the results of the 

 investigation summarised. In Chapter XI the Enzyme theory 

 of disease is discussed, together with its bearing upon the 

 subject of transmutation. In Chapter XII the author's conclu- 

 sions are briefly stated. References are given in the Appendix. 



