E. HISTOLYTICA CYSTS I TESTS OF VIABILITY 



the body under various conditions, and the effects of 

 temperature, disinfectants, etc., on them. 



Viability of cysts when tested on animals and in arti- 

 ficial cidture. Data on the longevity of amoeba cysts have 

 been furnished by various investigators. Walker and 

 Sellards (1913) infected men with cysts of E. histolytica 

 after they had been outside the body in fecal material 

 for two days at tropical temperature, and with cysts of 

 E. coli after 10 days under similar conditions. Experi- 

 ments of Sellards and Theiler ( 1924) with kittens indi- 

 cate that cysts are still infective after six days when left 

 in the original stool at 2° C. but lose their infectiveness 

 after two weeks. Cysts of E. histolytica that were lO 

 days old and had been kept in an ice box in the original 

 stool for 8 days of that period were found by St. John 

 (1926) to excyst when incubated in culture medium. 

 And Dobell and Laidlaw (1926b) discovered that cysts 

 will not excyst in culture until they have been held out- 

 side of the host's body at a lower temperature for two 

 days. 



Viability of cysts when tested with eosin, etc. Some 

 of the results obtained with the .eosin test are as follows. 

 Kuenen and Swellengrebel (191 3) found that some his- 

 tolytica cysts lived for over 7 days in water containing 

 many bacteria and for at least 29 days in water contain- 

 ing few bacteria; Penfold, Woodcock and Drew (1916) 

 kept cysts alive in slowly running water for 15 days; 

 Thomson and Thomson (1916a) observed living cysts 

 in formed, moist feces 16 days after they were passed, 

 and state that they can live considerably over a month 



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