COMPARATIVE STUDY OF AMCEB^. 269 



the' intestine of man and other animals, are at most only temporary com- 

 mensals in the intestinal tract, and more probably that they are, as Werner 

 ;(1908) has suggested, only cysts of free-living amcebje which have been 

 ingested with water or food and have passed unchanged through the 

 intestinal canal. 



The entamoebse found in the stools of healthy persons or of persons 

 suffering from disease other than dysentery present characters that 

 correspond in part with those of Entamosba coll Schaudinn and in part 

 with those of Entamceha nipponica Koidzumi. In stools of such persons, 

 in which there exists a natural diarrhoea or diarrhoea induced by a 

 cathartic, the vegetative or trophozoite forms are commonly present. 

 The living trophozoite is rounded in the resting condition, 7.5 to 34.5 

 /* in diameter, oval, ligulate or irregular when in motion, and porcela- 

 neous and refrangent in appearance. The ectoplasm is ordinarily visible 

 only in the pseudopods. There is no contractile vacuole and the ento- 

 plasm is normally free from all vacuolization. The nucleus is distinctly 

 visible in the living entamoeba. It occupies an eccentric position, but in 

 the rotation of the rounded entamoeba the nucleus frequently appears 

 central in optical section. It has the form of a rather heavy ring of 

 refrangent material, that may be of uniform or of irregular thickness, 

 which surrounds a non-refractive nucleoplasm and within which there 

 may or may not be present a few refractive granules. The movements of 

 those entamoebse are sluggish, even in fresh stools and they quickly loose 

 all motility in cold stools. 



In preparations fixed wet and stained with aqueous alum hematoxylin 

 the trophozoite shows a deeply-staining granular cytoplasm, usually 

 without distinction from the ectoplasm. Occasionally a narrow rim of 

 homogeneous, more feebly-staining ectoplasm is present. The ringform 

 nucleus is seen in optical section to consist of a nuclear membrane en- 

 closing an archromatic nucleoplasm and a relatively large amount of chro- 

 matin. Two varieties in the distribution of the cliromatin in the nucleus 

 can be distinguished. In the first of these the chromatin appears in 

 optical section as a continuous, segmented or granular ring of approxi- 

 mately uniform thickness about the inner surface of the nuclear membrane, 

 with or without some granular chromatin scattered in the nucleoplasmic 

 network or collected in a small karyosome. This variety corresponds 

 with the coli species of Schaudinn (fig. 9). In the second variety the 

 chromatin is collected in several discrete clumps on the inner surface of 

 the nuclear membrane. This variety corresponds with the nipponica 

 species of Koidzumi (fig. 10). 



Reproduction in the trophozoite appears to take place exclusively by 

 simple division. I have seen no evidence of a schizogony, such a de- 

 scribed by Schaudinn in Entamoeba coli and by Koidzumi in Entamoeba 

 nipponica, in either fresh or stained preparations. 



