viii PREFACE 



trypanosome nature of the African cattle disease, nagana, and its con- 

 veyance by tsetse flies, opened an entirely new field of enquiry which has 

 led to a most extensive study of parasitic Protozoa. The thousands of 

 papers on the subject which have been published during the past twenty 

 or thirty years are scattered in numerous journals, many of which are 

 difficult to obtain by any worker, and impossible by those who are 

 stationed in parts of the world where good libraries are not available. 

 Many workers have spoken to the writer of the difficulties associated 

 with this separation from literature, and it has been largely a desire to 

 remove at least a part of these difficulties that has led him to undertake 

 the present work on the subject of Protozoology. 



The book deals with all groups of parasitic Protozoa, as well as with 

 free-living forms, though the latter have been dealt with very briefly, 

 except in the case of those which are coprozoic in habit and may lead 

 to confusion with parasitic organisms. The part played by invertebrates 

 in the transmission of certain parasitic Protozoa of vertebrates necessitates 

 the examination of invertebrates in order to trace the life-history of any 

 parasite which may develop in them. As knowledge of the parasites 

 which are peculiar to these invertebrates is essential if errors are to be 

 avoided, they have accordingly received special attention. 



In reviewing the extensive literature on the subject of Protozoology 

 it has been necessary to criticize many statements and claims which have 

 been made, but, in expressing his own views, the writer hopes that he 

 has explained clearly the reasons which have led him to their adoption, 

 and that he has treated fairly those records which appear to him to be 

 of doubtful value. 



One of the chief difficulties associated with the production of a manual 

 like the present one is that hardly a week passes without the publication 

 of some paper of importance; but an earnest endeavour has been made 

 to incorporate all new and essential data as they appeared, so that as the 

 book goes to press in its final form a fair claim can be made that it is 

 as complete as it reasonably can be. Rapid advances are being made 

 in the elucidation of the methods of transmission of kala azar and Oriental 

 sore, and there is every prospect that very soon the sand fly will be in- 

 criminated definitely as the vector of one or both of these diseases. The 

 treatment of general paralysis by inducing in patients attacks of malaria 

 is leading indirectly to the discovery of many interesting facts regarding 

 the development of malarial parasites. The recently described method 

 of cultivation of intestinal amoebse is assisting in the solution of many 

 problems connected with the life-history of these organisms. Three 

 hitherto supposed coccidia of man have been shown to be nothing more 

 than parasites of edible fish which are passing casually through the human 



