INTRODUCTION 7 



Minchin in a presidential address to the Quekett Micro- 

 scopical Club points out that syngamy (sexual reproduction, 

 e.g. conjugation) is of the greatest importance in preserving 

 differentiation of species, and that without it a species 

 will tend to break up into races. It therefore follows 

 that there are no true species among organisms of the 

 bacterial grade, if it be true, as is usually held, that 

 syngamy does not occur amongst them, and the so-called 

 species of bacteria are to be regarded as mere races or 

 strains capable of modification in any direction. 



While much progress has been made during the last 

 two or three decades, a vast amount still remains to 

 be done. We have only touched the fringe of the explana- 

 tion of the perplexing problems of susceptibility and 

 immunity, and of the important question of cure in, and 

 prevention of, infective diseases, while the chemistry of 

 the products of bacterial activity is still in its infancy. 



The literature of Bacteriology has now become somewhat exten- 

 sive. In the following pages references to original papers have 

 been freely introduced, many of which contain a more or less full 

 bibliography on the subject referred to, so that further information 

 may be obtained if required. Kolle and Wassermann's Handbuch 

 der Pathogenen Mikroorganismen, ed. ii, is the most encyclopedic 

 work on pathological bacteriology yet published. 



