AMOEBINA 359 



5. Cysts in relation to chemicals. 



Hg2Cl. 0.1% solution kills cysts in 4 hours (Kuenen and 

 Swellengrebel; a); kills readily (Lin; b). 1 : 2500 solution kills 

 cysts in 30 minutes at 20-25°C. (Yorke and Adams; h). 



Creolin. 1 :250 solution kills cysts in 5-10 minutes (Kuenen and 

 Swellengrebel; a). 



Alcohol. 50% alcohol kills cysts immediately (Kuenen and 

 Swellengrebel; a); in one hour (Kessel; a). 



Formaldehyde. Cysts treated in 1% solution for 4 hours were 

 apparently dead, though not stained with eosin (Wenyon 

 and O'Connor). 0.5% solution kills cysts in 30 minutes at 

 20-25° or 37°C. (Yorke and Adams; h). 



Cresol. 1:20, 1:30, and 1:100, killed the cysts immediately, 

 in one minute and in 30 minutes respectively (Wenyon and 

 O'Connor; a). 



Phenol. 1 :40 and 1 : 100 killed cysts in 15 minutes and 7 hours 

 respectively (Wenyon and O'Connor; a). 1% solution of 

 phenol or lysol kills cysts in 30 minutes at 20-25° or 37°C. 

 (Yorke and Adams; h). 



HCl. 7.5% solution at 20-25°C. and 5% at 37°C. kill the 

 cysts in 30 minutes (Yorke and Adams; b). 



NaOH. 2.5% solution kills cysts in 30 minutes at 20-25° or 

 37°C. (Yorke and Adams; b). 



Chlorine. 1:10,000 solution did not have any effect on cysts 

 after several hours (Wenyon and O'Connor; a). 0.2% and 

 0.5% solutions kill the cysts in 7 days and 72 hours respec- 

 tively (Kessel; a). 0.5% and 1% solutions kill the cysts in 

 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). Thus the cysts of E. histoly- 

 tica are resistant to chlorinated water far above the concen- 

 tration which is used ordinarily in water treatment. 



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

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

 1% solution does not kill cysts at 20-25° or 37°C. in 30 

 minutes (Yorke and Adams; 6). 



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; b). 



