E. histolytica: excystation 



or faecal debris. . . . Although at the moment of emer- 

 gence the cytoplasm is either practically homogeneous 

 or, at most, very finely alveolar, with minute granules, 

 it quickly becomes definitely alveolar, and as it ingests 

 bacteria digestive vacuoles appear in large numbers." 



Yorke and Adams also found that cysts would develop 

 at 37° C. and excyst in Locke-serum medium, broth, and 

 physiological saline and would develop even in water at 

 37° C. up to the rupture of the cyst wall, but that in 

 water the amoeba is killed either before, during, or im- 

 mediately after its escape. They conclude that "moisture 

 and a suitable temperature (preferably about 37° C.) 

 are essential for the occurrence of excystation; the pas- 

 sage of cysts through such solutions as liquor pepticus 

 or liquor pancreaticus is unnecessary for excystation." 

 A similar conclusion was reached by Sellards and Theiler 

 (1924) from experiments with histolytica cysts in kit- 

 tens; they state that "For the excystation of amoebae, a 

 suitable temperature and a reasonable supply of water are 

 obvious necessities." 



Dobell and Laidlaw (1926b) bring out the interesting 

 fact that histolytica cysts which have formed in culture 

 or have been freshly passed by human or simian hosts 

 are incapable of excysting in cultures until they have been 

 cooled below body temperature for one or two days. 

 When kept cool they retain their ability to hatch for 

 approximately two weeks. 



Autogamy, gamete formation and the production of 

 amoehulce. The evidence at present available indicates that 

 the amoeba escapes from the cyst in a quadrinucleate 

 condition, the nuclei being closely agglomerated. Autog- 



89 



