28 INTESTINAL ENTAMOEBAE OF MAN 



a. Cysts of Entamoeba histolytica (Plate III, Fig. 2). 

 These vary in diameter from 5 to 20 microns but the usual 

 range is from 6 to 15 microns. It has been found that differ- 

 ent races exist as regards size and that in one patient the 

 cysts may be only 7 to 8 microns in diameter, in another 

 patient they may be from 10 to 11 microns, and in others 

 from 12 to 14 microns in diameter. The larger races may 

 be confused with small cysts of E. coli and the smaller races 

 with cysts of E. nana. 



"The cyst wall is thin and rather easily penetrated by the 

 iodin-eosin stain and by hematoxylin stains. In the iodin- 

 eosin stain the cytoplasm is first a bluish gray which changes 

 to a yellow and then to a pink color, which gradually deepens 

 to red. The cytoplasm is unevenly vacuolated and is very 

 finely granular but the granules are not so evenly distributed 

 as in E. coli. The glycogen mass, when present, stains a 

 light brown in iodin-eosin, the edges gradually shading 

 into the surrounding cytoplasm. Sometimes its glycogen 

 is diffused throughout the entire cyst which then stains a 

 yellowish brown color. Chromatoid rods are found in a 

 majority of the cysts, represented by either one large rod 

 with blunt ends nearly the diameter of the cyst in length, 

 or by several smaller rods scattered irregularly in the 

 cytoplasm." (Kofoid, Kornhauser, and Swezy.) 



The nuclei furnish the best basis for identification. They 

 range in number from 1 to 4 according to percentages listed 

 in the accompanying table. When stained with iodin-eosin 

 they become visible as distinct circles with a central chro- 

 matin granule, and many small granules distributed rather 

 evenly on the nuclear membrane. In doubtful cases perma- 

 nent iron haemotoxylin preparations should be made. 



6. Cysts of Entamoeba coli (Plate III, Fig. 4). Cysts 

 of E. coli range from 11 to 35 microns in diameter but usually 

 lie within the limits of 17 to 22 microns. They are usually 



