PREFACE TO THE FIFTH EDITION. 



The request for a fifth edition of THE PATHOGENIC BAC- 

 TERIA was followed by a careful analysis of the reviews of 

 past editions, in the hope that it might be possible to im- 

 prove the work according to the suggestions offered. Ac- 

 cordingly, much new matter has been added and much that 

 was old and worthless eliminated. 



The chapters upon infection and immunity, in which sub- 

 jects the advance of knowledge is rapid, have been entirely 

 rewritten, it is hoped in a more readable and logical manner. 



The original plan of limiting the book strictly to the patho- 

 genic bacteria has not been departed from. 



According to the conception of the author, every well writ- 

 ten text-book must accomplish three purposes ; first, that of 

 interesting the reader in the subject with which it deals; 

 second, that of conveying to him all the essential facts of 

 the subject; and third, that of opening to him the literary 

 sources from which the facts are gleaned. One of the re- 

 viewers complains that the book is too good from a certain 

 point of view and not good enough from another; that is, 

 as an elementary text-book it is too full and contains too 

 many references to the literature, but to be an encyclopedia 

 it is not full enough. There should be no misunderstanding 

 about the footnotes. They do not, and are not intended 

 to, cover the entire literature of the subjects treated, but 

 simply make accessible the original sources in which im- 

 portant facts, theories, methods and suggestions are con- 

 tained. 



PHILADELPHIA, May, 1906. 



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