PATHOGENIC PEOTOZOA 409 



PATHOGENIC PEOTOZOA 1 



By Professor GARY N. CALKINS 



COLUMBIA UNIVERSITY 



A T the present time the importance of protozoa-study is recognized 

 ■*--*• in all branches of biological science where, as single-celled 

 organisms, they illustrate the manifold principles of living tilings. 

 Thus it is in physiology, in cellular biology, in psychology and in 

 general biology. There is one field, however, a field that is daily 

 growing more extensive, in which the importance of protozoa has 

 only recently been recognized, and this is the field of pathology. 

 To the medical world for the most part, the group of protozoa 

 consists of the few types of parasitic forms that cause human 

 disease, and in this world any one who has a knowledge of Try- 

 panosoma, or Amoeba, or Plasmodium, is a student of the protozoa, 

 while a deeper knowledge makes him a biologist. At the present time 

 there are many students of the group in this sense, and the relations of 

 protozoa to human welfare bid fair to be the most popular aspect of 

 protozoan study, while in the public mind already the term protozoa is 

 apparently the synonym of some new and fearsome thing. Commis- 

 sions for the study of protozoan diseases have been appointed in many 

 countries and chairs for the study of protozoology have been established 

 in the universities of Cambridge and London mainly for the study of 

 the pathogenic forms of these unicellular animals. The present paper 

 deals with a few aspects of this more recent field of protozoa work. 



Malaria 



Few pathologists in good standing gave a thought to protozoa until 

 after the malarial organisms had been worked out and the life history 

 completely known through the researches of biologists and surgeons. 

 Thanks to the work of Laveran, Eoss, Grassi and Schaudinn, there is 

 no longer a phase in this disease that is unknown, and the relations of 

 the various symptoms of the malady to stages in the life history of the 

 organisms are perfectly established. I do not need to go into the 

 malaria problem, for the life history of the organisms, their relations to 

 the mosquito Anopheles, the coincidence of merozoite ' spore ' forma- 

 tion and pyrexial attacks of the disease, are familiar to all who have 

 followed, even remotely, the progress of medical science. I will pass 



1 A lecture delivered at Woods Hole, July 10, 1906. 



