PREFACE 



In the preparation of this work the author has aimed to present 

 clearly, concisely, and in orderly manner such matter pertaining to the 

 subject at hand as seems most essential to the needs of the student and 

 the practitioner. Notwithstanding its elementary character, the present 

 rapid advances in parasitology have necessitated numerous changes and 

 additions to the manuscript during its preparation. New species and 

 unsettling facts and theories as to some which are not new are, in these 

 days of intensive research, frequently being brought to light and re- 

 ported upon. Some of these findings represent or lead to a distinct 

 advance and, though the observations be in certain cases upon obscure 

 and in themselves imimportant species, they may, by analogy, shed 

 valuable light upon life histories and modes of infection of related forms 

 known to be injurious to domestic animals and man. So frequent are 

 these steps forward that it might almost seem better to leave compara- 

 tive parasitology at the present time to the fragmental attention it has 

 mainly received, and possibly it is to this view that the lack of a recent 

 American volume upon the subject may be attributed. Be that as it 

 may, this book is not intended to be comprehensive, and it contains but 

 httle discussion, historical or otherwise, of investigations in the field of 

 medical zoology, — limitations which may, in measure, contribute to it a 

 longer period of usefulness in its present form than could be hoped for 

 in an exhaustive treatise. With but few exceptions, the parasites con- 

 sidered are those most likely to be met with and as to which most of the 

 facts pertaining to their biology and pathogenicity have been well 

 established. 



The treatment of the subject is based upon the advantages of pre- 

 senting it with at least a rudimental attention to the biologic principles 

 involved in parasitism, a knowledge of which is requisite to the proper 

 conception of parasitology and certainly essential to intelligently 

 apphed measures of control. The direct and lucid style of the text 

 throughout will, it is hoped, bring these briefly considered fundamentals 

 before the reader in their true bearing upon the whole subject and render 

 the book particularly acceptable to the general practitioner as well as to 

 the student. 



Teachers wiU appreciate that laboratory work should supplement the 

 class-room method of study. Of course the student should in everj^ 

 case see the parasite under consideration in so far as this is possible. 

 Methods of laboratory technique and the selection of type specimens for 



