PREFACE 



TO THE 



FOURTH EDITION. 



THIS book, though nominally a fourth edition, is practically 

 speaking a new work. The progress of Bacteriology has been 

 very rapid, and many new investigations have been made in 

 connection with the etiology, prevention and treatment of 

 communicable diseases. It has been necessary to reconstruct, 

 enlarge and thoroughly revise the text of the third edition, 

 and I have added twenty-six chapters. 



The most important researches conducted in bacteriological 

 laboratories are those relating to the contagia. In many 

 diseases of man and animals it has not been possible to 

 identify the contagium with a bacterium, or indeed with any 

 micro-organism ; but when the virus is chemically examined, 

 or investigated with a view to protective inoculation, or utilised 

 for experiments in serum-therapeutics, such researches are 

 within the province of the bacteriologist. 



The recognition of the fact that in so many diseases the 

 nature of the contagium has not yet been determined will 

 have the effect of encouraging continued activity in this 

 important Hi-Id of scientific investigation. 



I hope that this work will continue to be of use as a text- 

 book for the bacteriological laboratory, and that the chapters 

 on the etiology and prevention of the communicable diseases 



