VIII, B, 4 Walker and Sellards: Entamoebic Dysentery 311 



The entamoebge varj'^ in size within considerable limits, but are 

 usually from 20 to 30 microns in diameter. They are, therefore, 

 larger than pus cells, or other protozoa, with the exception of 

 Balantidium coli, that are found in the stools of man. They are 

 also more refractive than pus, epithelial, or other cells found in 

 the stools. The nuclear structure of the entamoeba is particularly 

 characteristic. The unencysted entamoeba possesses, unless in 

 the process of division, only a single nucleus. This nucleus is 

 round, or occasionally slightly oval or irregular, small with 

 reference to the size of the cell, and appears not solid but as a 

 refractive ring (Plate I, figs. 3, 5, 6, 7). This relatively small, 

 ring-shaped nucleus appears to be absolutely diagnostic of an 

 entamoeba. Only one other kind of cell observed in stools pos- 

 sesses a nucleus in any way resembling that of an entamoeba. 

 This is an epitheloid cell, sometimes found in mucous stools, which 

 has a ring-form nucleus relatively much larger than that of an 

 entamoeba, occupying one-fourth to one-half of the cell. While 

 an entamoeba may occasionally be observed with an abnormally 

 large nucleus, probably preparatory to division, the nucleus never 

 approaches the size of the nucleus of this epitheloid cell. The 

 latter cells are also less refractive and granular than entamoebse. 



The encysted entamoeba is round or slightly oval, more re- 

 fractive than the resting or motile stage, and is surrounded by 

 a more or less distinct cyst wall. The nuclear structure here 

 also is characteristic. The cyst contains several (from 2 to 8, 

 depending upon the species of entamoeba and the stage of develop- 

 ment of the cyst) ring-form nuclei usually smaller than, but 

 of the same structure as, the nucleus of the motile entamoeba 

 (Platel, figs. 4and8). 



The technique and descriptions so far given refer to the exam- 

 ination of living entamoebse in fresh stools. This method of 

 stool examination for entamoebse is the quickest and for general 

 purposes of diagnosis the most satisfactory. The preparation 

 of stained specimens takes more time and a more extensive 

 technique, and certain distinctive characters of the entamoeba 

 are lost in the fixed and stained preparation. On the other 

 hand, staining sometimes assists in bringing out the details of 

 nuclear structure, and is necessary for making permanent prep- 

 arations of entamoebse. 



The technique of fixing and staining entamoebse which has 

 given the most uniformly satisfactory results is as follows. 

 A thin smear of the fresh faeces or liver-abscess pus is made 

 on a cover-glass, fixed in sublimate-alcohol mixture or Zenker's 



