E. HISTOLYTICA CYSTS: TEMPERATURE 



been studied. We know something, however, about the 

 effects of temperature on the cysts of E. histolytica and 

 E. coli. As noted above cysts remain aHve for a consider- 

 able period at room temperature in both the tropics and 

 temperate zones and when stored at 2° C. Boeck (1921a) 

 attempted to find the upper temperature Hmit with the aid 

 of the eosin test. He found that all cysts of E. histolytica 

 were killed at 68° C, of E. coli at 76° C, of Endolimax 

 nana at 64° C, and of lodamceba milliamsi at 64° C. ; 

 many of the cysts were killed at temperatures 10° below 

 these. The temperatures recorded are not ordinarily en- 

 countered in nature, but Boeck held cysts at these tem- 

 peratures for only 5 minutes, whereas in nature high 

 temperatures often continue for long periods and it is 

 well known that organisms can withstand a certain tem- 

 perature for a short time that would destroy them if 

 maintained for a longer period. Yorke and Adams 

 (1926b) found that cysts would withstand a temperature 

 of 45° C. for 30 minutes but were all killed in 5 minutes 

 at 50° C. The possibility of destroying parasites in night 

 soil by means of the heat from the sun has recently been 

 discussed by Barnes (1925) who obtained temperatures 

 of over 60° C. in glass-covered de Saussure boxes over 

 a continuous period of at least 4 hours ( 11 :oo A. M. 

 to 3:00 P. M.). Such a temperature would doubtless be 

 fatal to all protozoan cysts and the method suggested by 

 Barnes might therefore be employed to prevent the 

 spread of intestinal protozoa where night soil is used as 

 fertilizer. 



Resistance of cysts to chemicals. Various investigators 

 have tested the effects of chemicals on protozoan cysts, 



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