Protozoa of the Digestive and Urogenital Tracts 555 



AMOEBIASIS 



This term is restricted, in the present discussion, to infections with 

 Entamoeba histolytica and the resuhing effects in man. 



The causative organism 



Entamoeba histolytica Schaudinn ol man apparently is identical 

 with an intestinal amoeba of monkeys (47). The amoeboid forms (Fig. 

 11. 6, F) usually measure 20-30[x, with a range of about 8.0 to almost 60[x. 

 The size apparently varies in different strains. Locomotion of E. histolyt- 

 ica is much more rapid than that of E. coli, and the pseudopodia of the 

 former are usually clear. Food vacuoles of E. histolytica in stool samples 

 may contain red corpuscles or other tissue elements but rarely bacteria or 

 other material from the limien of the colon. Feeding activities and diges- 

 tion have been described by Hopkins and Warner (77). The typical 

 stained nucleus shows a small central endosome and relatively fine periph- 

 eral granules near the membrane. The Feulgen technique stains only a 

 zone of small periendosomal granules (169a). Characteristic changes in 

 nuclear structure occur in mitosis (106). 



The relatively inactive, rounded precystic forms usually measure 7-20[j,. 

 Even before secretion of the cyst membrane, the cytoplasm may contain 

 glycogen and chromatoid bodies. Origin of the chromatoid bodies from 

 cytoplasmic vacuoles or globules has been traced in living material (77). 

 The chromatoid material is usually interpreted as stored food (46). 



The approximately spherical cysts (Fig. 11. 6, G-K) measure about 

 6.0 to 2O1J1,, the range varying in different strains (50, 146, 179). Although 

 the recognition of hereditarily distinct "large" and "small" races seems 

 justified, the transformation of a small race (average, 8.5[jl) into a large 

 race (average, 19.0[x) has occinred after maintenance of a strain in the 

 laboratory for six years (122). Small races apparently differ from large 

 races in other respects as well as in size. Small races seem to grow less 

 readily in standard media (146, 152) and seldom or never show ingested 

 red corpuscles (62). Differences in pathogenicity also have been correlated 

 with differences in size. 



Chromatoid bodies and glycogen are usually seen in young cysts, but 

 the glycogen and later the chromatoids disappear as the cysts reach ma- 

 turity. The uninucleate cyst sometimes contains so much glycogen that 

 the nucleus is displaced toward the surface. The chromatoid bodies are 

 typically rod-like, often with rounded ends. Both size and shape are vari- 

 able, and the inclusions may form clumps instead of being scattered 

 through the cytoplasm. There are commonly a few large (5-10[;l) plump 

 rods. At the other extreme, there may be as many as 30 or so small bodies. 

 The mature cysts usually contain four, and rarely eight or more nuclei. 

 After elimination from the intestine, immature cysts apparently do not 



