556 Protozoa of the Digestive and Urogenital Tracts 



Fig. 11. 6. A-E. Entamoeba coli: A. Rounded amoeboid form, numerous 

 food vacuoles, xl600 (after Kessel). B. Cyst ^\ith large glycogen vacuole, a 

 few chromatoid bodies, two nuclei in division; xl600 (after Kessel). C. Cvst 

 with twelve nuclei; schematic (after Brooke). D. Typical cyst from natu- 

 rally infected monkev; xl8r)0 (after Kessel). E. Cyst with eight interphase 

 nuclei and several chromatoid bodies; xl600 (after Kessel). F-K Entamoeba 

 histolytica: F. Amoeboid form with ingested red corpuscles; xl600 (after 

 Kessel). G. Cyst with large glycogen "vacuole," several sinall chromatoid 

 bodies, nucleus in early division; xl600 (after Kessel). H-K. Cysts of vari- 

 ous sizes; xl600 (after Kessel). 



develop further at room or refrigerator temperature and do not undergo 

 excystment (29a). Cysts of E. histolytica are often passed intermittently, 

 sometimes at intervals of a week or so, whereas cysts of E. coli are more 

 likely to be found at any examination. 



Excystment requires 12-18 hours. The amoeba becomes active and then 



