AMOEBINA 455 



and in culture (Dobell, etc.), they may be taken in as food particles 

 (see below); nucleus, 5-8ju in diameter, seen in vivo; compared with 

 E. histolytica, the endosome is somewhat large (about 1m in diame- 

 ter) and located eccentrically; peripheral granules more conspicuous. 

 The precystic form, 10-30/x in diameter, resembles that of E. his- 

 tolytica. Separation of the two species of amoebae by this stage is 

 ordinarily impossible. 



The cyst is spherical or often ovoid, highly refractile; 10-30^ in 

 diameter; immature cyst contains 1, 2 or 4 nuclei, oneor more large 

 glycogen bodies with distinct outlines, but comparatively small 

 number of acicular, filamentous or irregular chromato id bodies with 

 sharply pointed extremities; when mature the cyst contains 8 

 nuclei and a few or no chromato id bodies. The trophozoites and 

 small number of cysts occur in diarrhoeic or semiformed faeces and 

 the formed faeces contain mostly cysts. 



This amoeba lives in the lumen of the colon and does not enter the 

 tissues of the wall. As noted above, it has been observed in a few 

 instances to ingest erythrocytes, but there is no evidence to show 

 that it takes them in from living tissues. This amoeba is therefore 

 considered a commensal. The abundant occurrence of the tro- 

 phozoite in diarrhoeic faeces is to be looked upon as a result and not 

 the cause of the intestinal disturbance. This amoeba is of common 

 occurrence and widely distributed throughout the world. 



Nothing is known about its life-cycle in the human intestine. 

 Cultivation of cysts in vitro indicates, according to Dobell (1938), 

 the following changes : The cyst content usually emerges as a single 

 multinucleate amoeba through a large opening in the cyst wall. 

 Prior to or during the emergence, the amoeba may divide. Normal 

 mature cysts "frequently lose" 1-4 of their original 8 nuclei before 

 germination, thus becoming "infranucleate" (with 4-7 nuclei). Un- 

 like in E. histolytica, there is no nuclear division in the metacystic 

 stages. By a series of binary divisions with random nuclear distribu- 

 tion, uninucleate amoebulae are finally produced. These are young 

 amoebae which develop into large trophozoites. Here also, there is 

 no sexual phenomenon in the life-cycle. Nomenclature and morphol- 

 ogy (Dobell, 1919, 1938). 



E. gingivalis (Gros) (E. buccalis Prowazek) (Fig. 193). This 

 amoeba lives in carious teeth, in tartar and debris accumulated 

 around the roots of teeth, and in abscesses of gums, tonsils, etc. The 

 trophozoite is as active as that of E. histolytica; 8-30> (average 

 10-20>) in diameter; cytoplasm well differentiated; monopodal 

 progressive movement in some individuals; endoplasm hyaline, but 



