PROBLEMS AND METHODS OF RESEARCH 

 IN PROTOZOOLOGY 



CHAPTER I 

 INTRODUCTION 



By 



Robert Hegner 



The Johns Hopkins University School of Hygiene and 

 PubHc Health 



The science of protozoology includes the study of both free- 

 living and parasitic protozoa. This book is devoted primarily to 

 protozoa that are parasites of plants and animals. Parasitic pro- 

 tozoa do not differ in any fundamental respect from free-living 

 protozoa. The principal difference between these two types is that 

 of habitat but free-living protozoa differ among themselves and 

 parasitic protozoa also differ among themselves in habitat about 

 ae widely as parasitic forms differ from free-living species in 

 this respect. Both types carry on activities necessary for the main- 

 tenance of the individual and for the maintenance of the race. The 

 individual must protect itself within its environment, secure food 

 and carry on various physiological processes. Asexual reproduction 

 and often sexual reproduction serve to maintain the race. A com- 

 parison of the morphology^ physiology and activities of free-living 

 and parasitic protozoa (Hegner, 1926) rev^eals no fundamental 

 differences between these two types of organisms. 



Protozoa are studied in various types of institutions and by men 

 interested in a number of fields. A protozoologist is one who is 

 primarily interested in protozoa as a phylum of animals. Proto- 

 zoologists are usually zoologists. If they take up the study of 

 parasitic protozoa they usually confine themselves to the morphol- 

 ogy, life-cycle, taxonomy and activities of the protozoon, devoting 

 very little attention to the host. Many zoologists who spend much 

 of their time in the study of protozoa do not consider themselves 

 protozoologists but biologists since they are simply using protozoa 



