IMPORTANCE 37 



the parasites of obscure nature associated with smallpox, rabies 

 and other important diseases may prove to be members of this 

 group. 



Importance. — Taken as a whole the Protozoa must be looked 

 upon as a group of organisms of prime importance as human para- 

 sites. Although Leeuwenhoek discovered the existence of Pro- 

 tozoa nearly 250 years ago, the first parasitic species, Balantidium 

 coli, was discovered by Malmsten in 1856, only 61 years ago. 

 At the present time a large proportion of medical practice and 

 disease prevention in tropical countries, and a considerable pro- 

 portion in all countries, depends on our knowledge of the habits 

 and life history of parasitic Protozoa, nearly all of which has been 

 gained in the last 35 years, and much of it in the last 15 years. 

 Almost daily new discoveries in connection with disease-causing 

 Protozoa are being made; there are few branches of scientific 

 research which offer a brighter or more promising field of endeavor 

 for students at the present time than the investigation of patho- 

 genic Protozoa. 



