HOST-PARASITE RELATIONS: INTESTINAL PROTOZOA 



between ectoplasm and endoplasm. Locomotion is slug- 

 gish. The endoplasm is usually crowded with food va- 

 cuoles containing bacteria and intestinal debris but no 

 red cells. The nucleus is like that characteristic of the 

 genus. 



Precystic stage. As in other species the trophozoites be- 

 fore encysting lose their food vacuoles, but decrease very 

 little in size. 



Cyst. The cysts (Fig. 4b) are spherical or irregular in 

 shape and measure from 6/^10 i6fx in diameter, averaging 

 about gfjL. They contain a single nucleus except on rare 

 occasions when two are present. The karyosome of the 

 nucleus lies on one side and the rest of the space is filled 

 with globules. Large glycogen vacuoles are seldom absent 

 from the cysts. No chromatoid bodies are present. 



Life-cycle. lodamceba williamsi inhabits the intestine 

 of man and is present in about 10 per cent of the general 

 population. Binary fission of the trophozoite has been re- 

 ported but no other method of reproduction is known. 



6. DIENTAMCEBA FRAGILIS 



Trophozoite. This rare species (Fig. 6) is only 3.5/x 

 to I2M in diameter. It is active, has clearly defined ecto- 

 plasm and endoplasm and sends out leaflike, hyaline 

 pseudopodia. Two nuclei with the characteristics already 

 described are usually present although specimens with 

 one nucleus are not uncommon. The food consists of 

 bacteria and yeasts. 



Cyst. Only one observer has noted cysts (Kofoid, 

 1923). These "are spherical with glycogen vacuoles and 

 small chromatoidal bodies." 



64 



