HOST-PARASITE RELATIONS: INTESTINAL PROTOZOA 



but no comprehensive study of this subject has been made. 

 Kuenen and Swellengrebel (191 3) found that mercuric 

 chloride, i in 1000, killed histolytica cysts in 4 hours; 

 that cresol, i in 250, killed them in from 5 to 10 min- 

 utes; but that formalin, 10 per cent, does not destroy 

 them if allowed to act only a few minutes. Emetin, i in 

 100, was not fatal to some cysts when allowed to act for 

 an hour. Cresol, i in 20, was found by Wenyon and 

 O'Connor (19 17) to kill histolytica cysts immediately; 

 in one minute, in a strength of i in 30 ; in half an hour, 

 in I in 100; in one hour, i in 200; but not at all in a 

 strength of i in 2,000. They consider cresol the best dis- 

 infecting agent for dysenteric stools and for the hands 

 of those who are exposed to contamination. These authors 

 record the death of cysts in 15 minutes in carbolic acid, 

 I in 40; in 7 hours, i in 100; but state that some cysts 

 were still alive after 8.5 hours, i in 200. Eosin failed to 

 stain cysts subjected to formalin, i in 100, for 4 hours, 

 although the cysts appeared shrunken and distorted. 

 Acid sodium sulphate in tablet form and chlorinated 

 lime tabloids as used for the purification of water had 

 no effect on the cysts, hence drinking water thus treated 

 is not freed from any infective cysts that may be present. 

 Bercovitz (1924) treated cysts of Endamccba coli and 

 Councilmania lafleuri with many of the most common 

 disinfectants and then stained them with hematoxylin 

 to determine whether changes of a lethal nature had 

 occurred. Cysts were placed in vials containing the dis- 

 infectant and allowed to remain there for periods of 15 

 seconds, 15 minutes and one hour. All agents used seemed 

 to kill the cysts within an hour. HCl, i per cent, killed 



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