AMOEBINA 561 



6. Cysts in relation to passage through the intestine of insects. 

 Wenyon and O'Connor found that the cysts of E. histolytica sur- 

 vived as long as 24 hours in the intestines of flies, Musca domestica, 

 Calliphora, and Lucilia, and living cysts were voided for 16 hours 

 after feeding on faecal material containing cysts. Roubaud using 

 Musca domestica, found also unaltered cysts for over 24 hours (but 

 rarely after 40 hours) after taking the cysts in its gut, and if a fly 

 drowned in water, the cysts remained viable for about a week. Root 

 (1921) using Musca domestica, Calliphora erythrocephala (and 

 Fannia canicularis, Lucilia caesar, and Chrysomyia macellaria) found 

 that about half the cysts were dead after 15 hours and last living 

 cysts were found after 49 hours in the intestines of these flies after 

 feeding on cyst-containing material, and that when the flies which 

 ingested cysts were drowned in water, about half the cysts were 

 found dead in 3 days and last living cysts were noticed on the 7th 

 day. Frye and Meleney (1932) found C3^sts in the intestines of flies 

 which were caught in 4 of 12 houses where infected subjects lived. 



Macfie (1922) reported that the cysts of Entamoeba histolytica he 

 observed in the intestine of Periplaneta americana appeared un- 

 harmed. Tejera (1926) reports successful experimental infection in 

 two kittens that were fed on the droppings of cockroaches (sp.?) 

 caught in a kitchen, which contained cysts resembling those of 

 E. histolytica. Frye and Meleney (1936) observed that the cysts 

 passed through the intestine of Periplaneta americana in as early as 

 10-12 hours and remained in the intestine for as long as 72 hours, 

 after feeding on experimental material. Cysts which stayed in the 

 cockroach intestine for 48 hours gave good cultures of trophozoites 

 in egg-horse-serum-Ringer medium. 



In addition to E. histolytica, there are now known four other 

 intestinal amoebae living in man. They are E. coli, Endolimax nana, 

 lodamoeba biitschlii and Dientamoeha fragilis. In Table 8 are given 

 the characteristics necessary for distinguishing E. histolytica from 

 the other four amoebae. 



E. coli (Grassi) (Fig. 169). The trophozoite measures 15-40/i in 

 diameter; average individuals 20-35iu; cytoplasm not well differenti- 

 ated; movement sluggish; endoplasm granulated, contains micro- 

 organisms and faecal debris of various sizes in food vacuoles; erythro- 

 cytes are not ingested, though in a few cases (Tyzzer and Geiman) 

 and in culture (Dobell, etc.), they may be taken in as food particles; 

 nucleus, 5-8)u in diameter, seen in vivo ; compared with E. histolytica, 

 the endosome is somewhat large (about 1^ in diameter) and located 

 eccentrically; peripheral chromatin granules more conspicuous. The 



