PREFACE 



Eighteen years ago, when my interest in the pro- 

 tozoa of the alimentary tract of man was first aroused 

 by my former chief and lamented teacher, the late 

 Professor Allen J. Smith, of the University of Penn- 

 sylvania, there was but little actual knowledge con- 

 cerning them in the possession of the medical profes- 

 sion. 



In fact the whole subject of the relations existing 

 between man and these lower animals, particularly 

 in regard to the effect of the parasite upon the host, 

 and, also, in reference to the relation of these pro- 

 tozoa of man to similar species in other animals, 

 was in a state of confusion. 



There had been, prior to that time, excellent work 

 done in the subject, in fact, on the average, probably 

 of better calibre than that of more recent studies, but 

 it had not reached the stage of useful information 

 available to the medical world. 



Existing knowledge of protozoa in general was in 

 the hands of a few men, biologists, or buried in scien- 

 tific literature not available except by particular 

 search ; and the interest of the medical world in the 

 matter had not been aroused. The conception of the 

 protozoa of the alimentary tract, and of the nature of 



