642 AMCEBIC DYSENTERY 



respectively. Since his observations various other species have 

 been described, of which the -entamoeba tetragena (Viereck) has 

 been most definitely established as a pathogenic organism. We 

 shall first describe these three organisms and afterwards refer to 

 some others. 



Entamoeba histolytica, as seen in dysenteric stools, occurs in 

 the form of rounded, oval, or pear-shaped cells, measuring 

 15-50 p., usually about 30 /x, 1 in diameter (Fig. 186, and Plate 

 VI., Fig. 23). Considerable variations in size are met with in 

 different cases of dysentery ; in some acute cases few amoeba may 

 exceed 20 p, in diameter. When at rest, a somewhat clear, 



FIG. 186. Amoebae of dysentery. 



a and b, amoebae as seen in the fresh stools, showing blunt amoeboid 

 processes of ectoplasm. The endoplasm of a shows a nucleus, three red 

 corpuscles, and numerous vacuoles ; that of b, numerous red corpuscles 

 and a few vacuoles. 



c, an amoeba as seen in a fixed film preparation, showing a small rounded 

 nucleus (Kruse and Pasquale). x600. 



highly refractile ectoplasm and a granular endoplasm can be dis- 

 tinguished, a feature which differentiates the organism from 

 the entamoeba coli. The nucleus is rounded or oval, and 

 is seen with difficulty ; its position is usually excentric, and is 

 sometimes quite at the margin of the endoplasm. In stained 

 specimens it is seen to be poor in chromatin and the nuclear 

 membrane is ill defined. The pseudopodia, which are quickly 

 protruded and retracted, are blunt and appear to be of a tough 

 consistence, a property which Schaudinn considers of importance, 

 as enabling the organism to penetrate the mucous membrane, 

 etc. The amoebic movements are often of an active kind, .and 



1 The measurements given by different observers vary considerably. Thus 

 Hartmann says that, unless when cyst formation is taking place, it measures 

 15-20 fji t and is the smallest of the three species under consideration. 



