PREFACE TO THE SECOND EDITION. 



THE cordial reception with which this book has met, 

 and the demand for a second edition, afford the author 

 no small degree of gratification. In revising The Prin- 

 ciples of Bacteriology advantage has been taken of the 

 valuable suggestions kindly offered by the reviewers of 

 the first edition, for which the writer here acknowledges 

 his indebtedness. 



The section of the work devoted to descriptive bac- 

 teriology has been somewhat extended, but no effort has 

 been made to cover the entire field, only those species 

 being introduced that are comparatively common or of 

 importance in enabling the student to acquire a funda- 

 mental working knowledge capable of wider application. 

 Wherever practicable, these descriptions have been sup- 

 plemented by illustrations, for the majority of which 

 the author is responsible. The introduction of colored 

 figures in the text is a new feature in this edition, and 

 one which should increase its usefulness. A sketch of 

 the evolution of our knowledge upon immunity and 

 infection has been introduced, and an outline of appa- 

 ratus necessary for a beginner's laboratory has been 

 appended. 



