452 PROTOZOOLOGY 



36-48 and 12-24 hours respectively (Lin; 6). 1/64 of a 

 saturated solution of chlorine (about 0.7 weight %) at 

 20-25°C. and 1/320 solution at 37°C. killed the cysts in 30 

 minutes (Yorke and Adams; b). Exposure to the residual 

 chlorine 5, 8 and even 10 parts per million for 30 minutes al- 

 lowed cysts to remain viable (Becker et al.). Thus the cysts 

 of E. histolytica are resistant to chlorinated water far above 

 the concentration which is used ordinarily in water treat- 

 ment. 



Potassium permanganate. 2% solution kills the cysts in 3 days 

 (Kessel; a). 1 :500 solution kills cysts in 24-48 hours (Lin; b). 

 ]% solution does not kill cysts at 20-25° or 37°C. in 30 

 minutes (Yorke and Adams; b). 



Emetin hydrochloride and yatren. 5% solutions of the two 

 drugs did not have any effects upon cysts at 20-25° or 37°C. 

 in 30 minutes (Yorke and Adams; 6). 



Antibiotics. The majority of antibiotics appear to inhibit the 

 growth of bacteria, which results in the death of the amoeba 

 in culture. Prodigiosin, however, according to Balamuth and 

 Brent (1950), kills the amoebae when added in the dilution 

 of 1:400,000, while bacterial flora, oxidation-reduction po- 

 tentials and pH are not affected by it. 



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 caniadaris, 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 cysts 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- 



