34 



THE ANIMAL PARASITES OF MAN 



rise first to four and finally to eight nuclei. Eight amcebulae are thus formed within 

 the cyst. 



According to Hartmann and Whitmore (1911)', however, autogamy does not 

 occur within the cysts of E. coli. They consider that eight small amoebulse are 

 formed (fig. 3, 210} which escape from the cyst and then conjugate in pairs 

 (fig. 3, 10 12\ afterwards growing into a new generation of trophozoites. 



Only some 10 to 20 per cent, of the cysts evacuated with the faeces undergo the 

 full course of development, the majority perish previously. In old dry fieces, only 

 cysts with eight nuclei are found, and it is these alone that cause the infection. 



Entamccba ivilliamsi, E. biitschlii, E. hartmanni and E. poleki (Prowazek) are 

 probably only varieties of E. coli. 



FIG. 4. So-called autogamy of Entamccba coli. A, rounded amoeba; B, nucleus dividing ; 

 c, the two daughter-nuclei giving off chromidia ; D, each nucleus has formed two reduction 

 nuclei ; E, cyst membrane formed, and gamete nuclei are dividing ; F, cyst with two synkarya. 



The principal feature distinguishing Entamccba coli from E. 

 histolytica is the formation of eight-nucleate cysts by the former as 

 contrasted with the tetra-nucleate cysts of the latter. The cyst-wall of 

 E. coli is thicker than that of E. histolytica (tetragena). Further, E. coli 

 does not usually ingest red blood corpuscles, nor are " chromidial 

 blocks" present inside its cyst (see p. 40). 



According to Chatton and Lalung-Bonnaire 2 (1912) the entamoebae 

 of vertebrates should be placed in a separate genus LoscJiia, as they 

 differ in their life-history from E. blattcv, the type species of Entamceba. 

 Leidy (1879), however, named the genus Endamceba, but further 

 researches are necessary on biological variation among these 

 organisms. 



Entamoeba histolytica, Schaudinn, 1903. 



Syn. : Amoeba coli, autt. p. p. Amoeba dysenteric?, autt. p. p. 



The average size of the amoeboid trophozoite is 25 /JL to 30 p. 



In faeces diluted with salt solution the amoebae swell to 40 //, and more. 



There is sometimes separation of the body substance into a strongly 



refractile vitreous ectoplasm and a corneous endoplasm, pronounced 



1 Archiv f. Protistenkunde, xxiv, p. 182. 

 - Bull. Soc. Path. Exotique, v, p. 135. 



