PREFACE TO THE THIRD EDITION. 



In this edition the whole subject has been carefully revised, 

 and, as formerly, we have aimed at making the bearings of 

 bacterial action on general pathological processes an outstand- 

 ing feature. 



The advances in bacteriology during the last three years 

 have been neither few nor of small importance, and to incor- 

 porate these and at the same time maintain the work as a 

 convenient hand-book for the student, has been no easy task. 

 In endeavouring to accomplish it, we have condensed various 

 portions and omitted others which appear now to be of sub- 

 sidiary importance. Thus, although much new matter has been 

 introduced, the former length of the volume has been but 

 slightly increased. Additions have been made to most of the 

 chapters and several new subjects are treated of, amongst 

 which may be mentioned the bacteriology of the air, soil, and 

 water, to which a new chapter has been devoted. The chapter 

 on Immunity has been modified and extended so as to include 

 the recent important researches on the subject. A number of 

 new illustrations will be found to have been added, and we 

 trust that these will tend towards the elucidation of the text. 



One result of later research in bacteriology has been to 

 bring into prominence the fact that, in nearly every' instance, 

 each so-called pathogenic organism is a member of a group of 

 bacteria possessing closely allied characters. Hard and fast 

 lines as to distinguishing features can now be less definitely 

 drawn, and accordingly an intelligent conception on the part 

 of the student is more than ever necessary. We have there- 

 fore in many instances merely stated the known facts, when 

 we have considered that these do not justify an advance being 

 made to a definite conclusion. 



January, 1903. ' 



