AMOEBINA 447 



as the precystic forms. The precystic amoeba secretes presently a 

 resistant wall and becomes encysted. The highly refractile cyst is 

 spherical and measures 5-20/* in diameter. At first it contains a single 

 nucleus which divides twice. The mature cyst contains four nuclei. 

 In addition the cyst contains diffused glycogen and elongated refrac- 

 tile rod-like bodies with rounded extremities which stain deeply 

 with haematoxylin (hence called chromatid bodies). These inclusions 

 are absorbed and disappear as the cyst matures. No further changes 





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up • 



o 



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IPS 



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7 p 



Fig. 190. Entamoeba histolytica, X1150 (Kudo). 1, a living trophozoite; 

 2-4, stained trophozoites; 5, a fresh cyst; 6-9, stained cysts. 



take place in the cyst as long as it remains outside the host's intes- 

 tine. The trophozoites are found in dysenteric or diarrhoeic faeces, 

 but formed faeces usually contain cysts. The cyst is the stage by 

 which the organism begins its life in a new host. 



The life-cycle of Entamoeba histolytica in human host is unknown. 

 The amoeba has, however, been cultivated in vitro by numerous 

 investigators since the first successful cultivation by Boeck and 

 Drbohlav (1924) (p. 887). The excystment of cysts and metacystic 

 development have also been observed and studied especially by 

 Dobell (1928) and Cleveland and Sanders (1930) in cultures. Snyder 



