ISOSPORA HOMINIS 



of the host, the nucleus divides; then the protoplasm 

 separates into two sporoblasts, each with one of the 

 daughter nuclei. Each sporoblast then secretes two walls 

 (sporocysts) about itself and becomes a spore. Within 

 the sporocysts two nuclear divisions occur and four 

 sausage-shaped sporozoites are formed, each with a sin- 

 gle nucleus. Part of the protoplasm is not included in 

 the sporozoites but remains behind as a residue. One 

 or two days are required for the development within 

 the oocyst. 



The asexual and sexual cycles are probably similar to 

 those of Isospora felis of the cat. Fig. 21 presents the 

 stages in these cycles in diagramatic form. 



II. Host-Parasite relations of Isospora hominis 



Transmission. As is true of other intestinal protozoa, 

 infections with coccidia no doubt are brought about by 

 the ingestion of food or drink contaminated with the 

 infective stages (oocysts). These oocysts are no doubt 

 more resistant to conditions outside of the body than are 

 the cysts of the intestinal amoebae and flagellates. 

 Haughwout (1921), for example, exposed oocysts in the 

 sporoblast stage to the sun for three hours every day for 

 a week and found that at the end of this period some of 

 them developed sporozoites when water was added ; and 

 Wenyon (1926) reports the completion of development 

 within the oocysts of Eimeria stiedce from the rabbit 

 after being subjected to a fixing solution of sublimate, 

 stained with hsemotoxylin, dehydrated, cleared, and 

 mounted in balsam. 



191 



