CHAPTER XIV. 

 DISEASES DUE TO PROTOZOA. 



THERE are not many recognized specific diseases in 

 man due to these lowest animal forms, but those well 

 known are of the greatest importance, because of their 

 prevalence in some parts of the world and on account 

 of the difficulties presented to medical treatment. It 

 may be said in general that the protozoan diseases of 

 man represent a phase in the life history of the causative 

 microorganism, and are in fact stages through which 

 the protozoa pass in order to fulfil their cycle of life. 

 The subject of protozoology is of enormous magnitude, 

 and it is impossible even to outline in a work like this 

 all the steps which may be passed through. An attempt 

 will, therefore, be made to describe the important 

 diseases due to protozoa, with a general statement 

 covering the morphology and life history of the 

 organism. Of the many thousands of species in nature 

 only a handful are pathogenic for man. The disease- 

 producing types fall into the following zoological 

 families or genera: Sarcodina (rhizopoda, amebse) 

 Mastigophora (flagellata, trypanosoma), Infusoria 

 Heterotricha (balantidium), Sporozoa (coccidia, hemo- 

 sporidia, plasmodium). The diseases, we shall see, all 

 fall into these groups. They are for the most part 

 dependent upon the animal body for the continuance of 



