PREFACE TO THE FOURTH EDITION 



The most important change incorporated in the fourth edition of 

 our Text-Book is the section on Pathogenic Protozoa written by 

 Major Frederick F. Russell, of the Medical Corps of the United 

 States Army. When the first edition of this book was written the ad- 

 dition of a section on Protozoa was seriously considered, but was 

 finally omitted because it was the desire of both the writers at that 

 time that nothing should go into the book that could not be based 

 on personal knowledge, and, since neither the late Dr. Hiss nor the 

 undersigned had worked systematically in the field of protozoology, 

 it was thought better to limit the book to our own field of bacteriology. 

 The book has since then gone through three editions and it has be- 

 come more and more apparent that It has found its greatest useful- 

 ness as a text-book for medical students and a reference book for 

 physicians and laboratory workers. For these purposes, however, 

 it has had the serious defect of giving no information about such 

 microorganisms as the malaria plasmodia, the trypanosomes and 

 other pathogenic microorganisms, which, though technically protozoa, 

 are necessary objects of interest to all medical laboratory workers. 

 It has appeared to us, therefore, that the practical value of the book 

 would be greatly enhanced by the addition of a short treatise on the 

 protozoa, if written by someone who had been in touch with this field, 

 rather from the practical medical point of view than from that of the 

 zoologist. Major Russell has kindly consented to supply this de- 

 ficiency in a section which makes no claim to zoological complete- 

 ness, but is written with the definite purpose of giving medical 

 workers concise information concerning the important pathogenic 



