PROTOZOOLOGY 



this work was done with free-living- species, but, for- 

 tunately, the fundamental structure, life-cycles and activ- 

 ities of the free-living and parasitic protozoa are the 

 same; hence the information gained from the study of 

 the former can be applied almost in its entirety to the 

 parasitic forms. 



Many of the intestinal protozoa of lower animals were 

 described and studied in a more or less haphazard way 

 before those living in man were considered of any impor- 

 tance, and even to-day it is necessary in certain cases to 

 base our account of human infections on what we know 

 of near relatives in animals. For example, the human coc- 

 cidium, I so sp or a hominis, is known only in the oocyst 

 stage, and we are forced to guess at its activities within 

 the host with the help of our knowledge of a closely re- 

 lated species, Isospora felis, in cats and dogs. The discov- 

 ery by Losch in 1875, of Endamccha histolytica in the 

 feces of a patient suffering from dysentery, and the 

 gradual accumulation of evidence that this amoeba is the 

 etiological agent of a certain type of dysentery, stimu- 

 lated the study of this and other species of human intes- 

 tinal protozoa, so that we believe we have to-day a fairly 

 good idea of the species present in man although their 

 host-parasite relations are very inadequately known. 



The term protozoology is not difficult to define ; it in- 

 cludes all we know about the protozoa, both free-living 

 and parasitic. The term protozoologist, however, is not so 

 easily disposed of, and it seems worth while in this place 

 to point out that a protozoologist is one who devotes him- 

 self to the study of the protozoa as a special group of 



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