HOST-PARASITE RELATIONS! INTESTINAL PROTOZOA 



and 2.^ per cent quadrinucleate cysts at the time cultures 

 were made had changed after 2.5 hours to 8 per cent 

 uninucleate, 9 per cent binucleate and 75 per cent quadri- 

 nucleate cysts. This indicates that development of imma- 

 ture cysts may take place outside of the body contrary to 

 the general belief at present. The glycogen, which 

 occurred in most of the uninucleate cysts, disappeared 

 in the cultures, and chromatoid bodies, which were rare 

 in the uninculeate cysts, increased during the first few 

 hours of cultivation but decreased again later as tropho- 

 zoites began to appear. It was noted by Dobell (Dobell 

 and O'Connor, 192 1) that cysts when kept outside of the 

 body in moist feces or water gradually lose their glyco- 

 gen and chromatoid bodies. 



Yorke and Adams describe excystation in the follow- 

 ing words. "An individual which is about to excyst 

 presents a characteristic appearance. The cytoplasm is 

 more or less homogeneous and appears to be of a faintly- 

 greenish tint, and is frequently very finely-alveolar ; the 

 nuclei in the living individual can be distinguished only 

 with the greatest difficulty. Careful examination shows 

 that the amoeba is retracted in places from the cyst en- 

 velope and is evidently loose inside it ; from time to time 

 vigorous pseudopodial movements can be seen to take 

 place. Finally a rent apparently occurs in the cyst en- 

 velope, and a clear bead of ectoplasm is protruded ; this 

 progressively enlarges in a spasmodic manner, more and 

 more of the amoeba protruding from the envelope, until 

 finally the creature has escaped completely. It then pro- 

 ceeds to move about in an active, usually slug-like man- 

 ner, frequently drawing behind it the empty cyst envelope 



88 



