PREFACE TO THIRD EDITION 



The need for a new edition of the Text Book has offered a welcome 

 opportunity for the addition of the many new facts revealed by investi- . 

 gation during the last two years. A thorough revision of the entire 

 book has incidentally been made since experience with it in teaching, 

 the questions of students, and the comments of associates have in- 

 dicated sections, here and there, in which slight changes, elabora- 

 tions or omissions, would add to clearness and simplicity. In this,- as 

 in the choice of new material, the writer has again been guided chiefly 

 by the desire to enhance the practical usefulness of the treatise for medi- 

 cal students and workers interested primarily in infectious diseases. 



In the section on Biology and Technique, the changes have been 

 relatively few. To the chapter on culture media, there have been added 

 Kendall's modification of Endo's medium, Petroff s media for tubercle 

 bacillus cultivation, Krumwiede's brilliant green medium, and R,usselPs 

 double sugar medium. Many other minor, yet, in our opinion impor- 

 tant, alterations have been made in this chapter, but throughout the 

 book only such methods have been added as have been found to be 

 actually useful in our own practice or in that of our associates. 



The section on Immunity has been very thoroughly revised in order 

 to keep within the same small space a more accurately modern pres- 

 entation of this complicated subject. It has not, of course, been possible 

 to cover this field as thoroughly as it might be covered in a volume 

 separately devoted to the subject, but the outline here given is intend- 

 ed mainly to furnish a sound foundation for further study. 



In the chapter on the pathogenic microorganisms themselves, the 

 most extensive changes have been necessary in the pneumococcus sec- 

 tion and in the one on treponema pallidum. However, all the chapters 

 have been revised with care and many small additions and omissions 

 made where new facts and the revision of older opinions have made this 

 desirable. 



H. Z. 

 College of Physicians and Surgeons, Columbia University N. Y. 



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