8 PREFACE TO THE THIRD EDITION. 



prove to be a lucid manner. Considering that we know- 

 little about infection and nothing about immunity, there 

 is no other course left than to consider the theories that 

 have been advanced and to refute them one by one. 

 Other new chapters appear here and there, and much of 

 the substance of the book has been rewritten and altered. 

 The principal changes will be found where the advances 

 have been most rapid — that is, under Tuberculosis, Diph- 

 theria, Tetanus, Plague, etc. 



Many of the changes have been in accord with sugges- 

 tions made in the numerous "reviews," though in this 

 particular no attempt was made to please everyone, or the 

 work would have been doubled in size and its character 

 entirely changed. 



While acknowledging that foot-note references are not 

 ideal, they are less objectionable than references inserted 

 in the text, as they do not interrupt its continuity, and 

 are more likely to be observed than when appended at 

 the end of the chapter or in the form of a general bibli- 

 ography at the end of the book. All the new matter con- 

 tains foot-note references to the original writings, and, 

 where possible, all important subjects are now accom- 

 panied by references to the original communications, ex- 

 perience having shown that many students prefer to con- 

 sult the authorities when references are at hand. 



Experience seems to indicate that the chapters upon 

 the Technic of Bacteriology suffice for the average stu- 

 dent ; and while the work is not intended for a laboratory 

 guide, much new matter upon manipulations has been 

 added. 



In criticising the book, one should not forget that 

 it is upon The Pathogenic Bacteria, and is written for 

 students and practitioners of medicine, and should not 

 condemn it if it does not contain matter outside of its 

 logical limitations. 



JOSEPH McFARLAND. 



August, 1900. 



