10 RESEARCH IN PROTOZOOLOGY 



parasitize a particular host species. Many interesting problems in- 

 volving host-parasite specificity are available for study (Hegner, 

 1926). 



The study of host-parasite relations as indicated in the preceding 

 paragraphs can be directed tov^ard one or more of the phases 

 described. As a rule it is necessary to use material that can be 

 obtained easily. One does not need to import parasitized animals 

 from abroad in order to secure satisfactory types for investigation. 

 As a matter of fact the parasites of our common laboratory and 

 domesticated animals are very little know^n and problems of the 

 greatest scientific importance can be undertaken with them. In 

 special cases it is necessary to obtain species of parasites from 

 foreign localities and to study them in culture or in laboratory 

 animals but no one need hesitate to undertake investigations of 

 host-parasite relations because of lack of material or of important 

 problems for study. 



