PREFACE 



tween these and methods of prevention and control. 

 Free-living protozoa comprise an enormous and exceed- 

 ingly interesting group of animals, but their parasitic 

 relatives are likewise numerous in species and funda- 

 mentally similar, as is shown in part 2 of the Introduction 

 in Chapter I. The control of the parasitic species, to be 

 effective, must be based on a knowledge of the relations 

 between the parasite and its host. What these relations 

 are is discussed in Section II of Chapter I, and how little 

 we know about them is evident from the vast number of 

 lacunae disclosed in the accounts presented in Chapters 

 II, III, IV and V of the groups of intestinal protozoa 

 that have representatives living in man. 



It is, therefore, the purpose of this book to gather 

 together the more relevant data regarding the host- 

 parasite relations of the intestinal protozoa of man and 

 to present them in logical order in such a way as to 

 bring out the state of our knowledge with special refer- 

 ence to the desirability of further studies. It has seemed 

 unnecessary to include detailed accounts of the history, 

 nomenclature, morphology, life-cycles, geographical dis- 

 tribution, pathology, symptomatology, treatment and 

 cultivation of the various species discussed since this in- 

 formation has been presented in several recently pub- 

 lished books. The writer has not attempted to include 

 all of the data contained in the literature relating to the 

 subjects discussed, but has selected examples, particu- 

 larly from recent publications, as illustrative material. 



One of the most striking features of this volume is the 

 inadequacy of the data available on the particular phases 

 of protozoology considered. Information is widely scat- 



vi 



