224 PROTOZOAN PARASITISM 



fifty cases put on record since Woodcock and Wenyon 

 initiated the modern interest in the infection, in 1915. 

 The most recent light on the nature of the species 

 occurring in man may be had from Wenyon (1926). 

 According to this authority intestinal coccidiosis of 

 man, in so far as it is known at the present, is due to 

 the species named by him Isospora belli. 



ISOSPORA BELLI 



Woodcock (1915), according to Wenyon (1926), 

 first discovered the immature oocyst of this coccidium 

 in feces of English soldiers invalided from Gallipoli. 

 Wenyon (1923) observed the complete development 

 of the oocyst, proving it of the genus Isospora, and 

 named it Isospora belli. According to him the coc- 

 cidium found in some one hundred and fifty cases of 

 intestinal infection since his and Woodcock's dis- 

 coveries belong to this species. They have usually 

 been identified as Isospora hoviinis. 



The organism has been seen only in the oocyst 

 stage. It measures 25 to 33 microns in length and 

 about half that in width. It is elongated, one end 

 being constricted to the appearance of a neck. 



The wall is of a double contoured outer layer and 

 a thin inner membrane. Within this cyst is a 

 rounded body of globules of refractive material, 

 within a clear space, the size of this body and that of 

 the surrounding space varying with the age of the 

 cyst, the older the smaller the body of the enclosed 



