E. histolytica: excystation 



The effects of digestive juices on cysts outside of the 

 body. Other investigators have treated cysts outside of 

 the body with various substances. For example, Ujihara 

 (1914) found that pancreatic juice acted upon the cyst 

 wall but not gastric juice at 37° C. for 24 hours; Pen- 

 fold, Woodcock and Drew (1916) also found pancreatic 

 extract effective but had no success with either pepsin in 

 an acid medium, or bile. Cutler (1919b) records excys- 

 tation after the action of liquor pepticus followed by 

 liquor pancreaticus. The trophozoites that emerged pos- 

 sessed four nuclei but were supposed to divide later into 

 4 uninucleate amoebae. 



Excystation in artificial culture. The perfection of 

 methods of cultivating E. histolytica in artificial media 

 by Boeck and Drbohlav (1925a, 1925b) and others has 

 made it possible to study excystation under more favor- 

 able conditions. Boeck and Drbohlav report what seemed 

 to be a case of excystation in one of their cultures and 

 St. John (1926) states that he obtained trophozoites in 

 cultures from a stool that was 10 days old and had been 

 in the icebox for 8 days; this material must have been 

 free from trophozoites. No observations were recorded by 

 these investigators on the hatching of the cysts. Yorke 

 and Adams (1926a) and Dobell and Laidlaw (1926b) 

 have published more extensive studies on excystation in 

 cultures. 



Yorke and Adams found that uninucleate and binu- 

 cleate cysts continued to develop in Locke-egg-serum me- 

 dium when incubated at 37° C. For example, material 

 containing 42 per cent uninucleate, 18 per cent binucleate 



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