COMPARATIVE STUDY OF AMCEB^. 271 



fairly constant, and which in their sum serve to distinguish the enta- 

 nioebge from the two sources. The characters of the entamoebEe from 

 dysenteric material correspond in part with those of Entamoeba histoly- 

 tica Schaudinn, in part with those of Entamoeba tetragina Viereck and, 

 under certain conditions, with those of Entamoeba minuta Elmassian. 

 The trophozoites in fresh stools in acute dysentery are usually, but not 

 invariably, larger, more often oval in the resting condition, and more 

 hyaline and less refrangent in appearance than the trophozoites from 

 normal stools. The cytoplasm is uniformly hyaline in appearance with 

 no distinction between ectoplasm and entoplasm. It contains a variable 

 amount of granular material and often red blood corpuscles of the ho^t 

 as inclusions which, when collected near the center of the organism, leavi' 

 a hyaline periphery that has the appearance of an extensive ectoplasm 

 described by other authors. There is no contractile vacuole and the 

 entoplasm is normally free from other vacuoles; it is only following 

 changes in temperature or tonicity of the medium or in consequence of 

 degenerative changes that vacuolization is present. The position of the 

 nucleus is eccentric, and in the more actively motile entamoeba? in d : en- 

 teric stools the nucleus more frequently changes its relative position 

 and is more subject to pressure that tends to deform it than the nucleus 

 of the more sluggish entamoeba in normal stools. The nucleus, in con- 

 trast to entamoebge of the coli and nipponica varieties, is usually distin- 

 guished with difficulty in the living trophozoite. Contrary to Schaudinn 

 I distinguish a thin but distinct nuclear membrane. This membrane 

 encloses a homogeneous niicleoplasm which is slightly less refrangent than 

 the surrounding cytoplasm and which contains a small amount of gran- 

 ular material arranged about the inner surface of the nuclear membrane 

 and scattered in the nucleoplasm. In consequence of this thin peripheial 

 layer and the low index of refraction of the nucleoplasm the nucleus has 

 the appearance of an extremely pale vacuole and is distinguished with 

 difficulty, especially in motile or vacuolated entamoebse These entamoebse, 

 in contrast to those of normal stools, exhibit an active motility in fresh 

 stools which often persists in cold stools several hours old. 



In preparations that have been iixed wet in Zenker's fluid and stained 

 with aqueous alum hematoxylin the trophozoite in dysenteric stools usually 

 stains feebly and shows a reticulated rather than a granular structure 

 of the cytoplasm with no distinction between ectoplasm and entoplasm. 

 In the stained preiDarations the difference in the appearance of the 

 nucleus from the nucleus of entamoebse in non-dysenteric stools is seen 

 to be due to the much smaller amount of chromatin in the nucleus of the 

 dysenteric entamoebse. Two varieties in the distribution of the chromatin 

 can be distinguished. In the one the chromatin is extremely scanty and 

 is arranged as a barely perceptable layer about the inner surface of the 



