GIARDIA LAMBLIA: EXCYSTATION 



40 minutes after feeding ; and from the droppings of one 

 out of 229 wild flies. Root (1921) confirmed certain of 

 these results. He found giardia cysts still viable after 

 16 hours in the intestine of Miisca domestic a and after 4 

 days in drowned flies. 



(2) Localization within the host. Excystation. 

 What happens to the cysts after they enter the human 

 digestive tract is unknown. No one has determined where 

 or in what manner excystation occurs in man. Hegner 

 (1925b) described some peculiar specimens that seemed 

 to be excysting, passed by a patient who had been under 

 observation for several years and, who, both before and 

 after this occasion, passed cysts normal in every way. 

 The trophozoites that seemed to be emerging from these 

 cysts were much smaller than normal trophozoites and 

 their nuclei were larger than those in normal cysts and 

 contained chromatin scattered throughout the nuclear 

 substance. Cysts swallowed by man probably excyst in 

 the duodenum, and this process must be extremely rapid 

 or the cysts would be carried through the duodenum and 

 thus out of their normal habitat. It is of course possible 

 that the newly escaped trophozoites may be able to pro- 

 gress against the action of peristalsis and colonize the 

 duodenum from the ileum or jejunum but this hardly 

 seems possible. The writer (Hegner 1927a) has recently 

 obtained excystation of the cysts of Giardia lamhlia in 

 the intestine of rats and guinea-pigs. Washed cysts in 

 water were injected through the esophagus into the stom- 

 ach by means of a syringe and small rubber tube. No 

 excystation was ever found in the stomach but in a num- 

 ber of animals it occurred in the small intestine, usually 



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