HOST-PARASITE RELATIONS: INTESTINAL PROTOZOA 



regurgitated by flies that had fed on infected fecal 

 matter. 



Roubaud's (191 8) data confirm certain of these re- 

 sults. He found viable histolytica and coli cysts in flies' 

 feces for over 24 hours but only rarely after 40 hours. 

 Cysts in drowned flies lived for about a week but were 

 all dead by the time the flies decomposed sufficiently to 

 liberate them, which requires a month or more. Similar 

 experiments were carried out by Root (1921) who found 

 that half of the histolytica cysts ingested by house flies 

 and blow flies were dead after 15 hours and that some of 

 the cysts lived at least 49 hours. In Mesopotamia wild 

 house flies were found by Buxton (1920) to be carriers 

 of parasites that occur in human feces. Flies were col- 

 lected from Arab compounds, Indian latrines and incin- 

 erators, and British mess and cook houses. The dissection 

 of 1,027 flies revealed that 63 per cent had apparently 

 ingested human feces; that 4.09 per cent contained hu- 

 man intestinal parasites; and that 0.3 per cent contained 

 cysts of E. histolytica. Cysts of E. coli and Giardia 

 lamhlia were also found in the flies. 



Not all experiments with flies have been as successful 

 as those described above. Jausion and Dekester (1923b), 

 working at Fez, fed 40 flies on stools containing cysts and 

 trophozoites of E. histolytica but recovered only a few 

 amoebae from them in a very bad state of preservation. 

 No amoebae were found in seventy-three flies caught in 

 the laboratory and in the latrines at a time when 23 per 

 cent of the inhabitants were infected. The injection into 

 the rectum of a young cat of 50 flies that were caught 

 in the latrines did not result in an infection. The con- 



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