CHAPTER I 



THE SCOPE OF THE ENQUIRY 



DEFINITION OF TERMS 



THE phrase "transmutation of bacteria" is not synonymous 

 with "evolution of bacteria." "Evolution" is the gradual de- 

 velopment of new species and tends towards further differentia- 

 tion. "Transmutation" is the changing of members of one 

 recognised species into those of another and, if proved, would 

 tend towards unification by undermining existing barriers. 



There is no reason to doubt and abundant evidence to 

 support the opinion that in this field of life, as in others, the 

 forces of natural selection and the survival of the fittest have 

 been at work and have resulted, in the course of ages, in the 

 evolution and differentiation of the various types of bacteria 

 which we recognise and distinguish today. 



Andre wes, in the Horace Dobell Lecture for 1906, "traced 

 the evolution of streptococci from the condition of harmless 

 mineral-feeders, through that of saprophytism in the alimen- 

 tary canal, to the development of weak powers of parasitism 

 which have culminated, in certain instances, in the fully 

 developed property of aggressive parasitism seen in the 

 streptococcus pyogenes." 



He showed how, at different stages, natural selection and 

 the survival of those best adapted to the environment in which 

 they found themselves, resulted in the permanent acquisition 

 of new characters, such as the ability, when they had once 

 entered upon a saprophy tic career in the alimentary canal, to 

 flourish most vigorously at the body temperature of their host 

 and to utilise the foodstuffs available in their new habitat ; to 

 resist desiccation during the intervals between their discharge 

 from one host and their reception by another ; and later still 

 to support themselves in the actual living tissues of the host 



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