viii, B, 4 Walker and Sellards: Entamoebic Dysentery 317 



The cysts of Entamoeba histolytica (Plate I, fig. 8) are rela- 

 tively small, from 10 to 15 microns in diameter. They are 

 round, or occasionally oval, moderately refractive, and have 

 a thin cyst wall. The completely encysted entamoeba contains 4 

 ring-form nuclei and, usually, one or more elongated refractive 

 bodies, that stain with chromatin stains and which have been 

 designated by Hartmann as chromidial bodies. On the other 

 hand, the cysts of Entamoeba coli (Plate I, fig. 4) are larger 

 (from 15 to 20 microns in diameter), more refractive, and 

 usually possess a thicker cyst wall. The completely encysted 

 entamoeba contains 8 (occasionally more) nuclei and does not 

 include "chromidial bodies." The encystment of Entamoeba coli 

 appears to proceed more rapidly than that of Entamoeba histo- 

 lytica, so that from 2 to 6 nuclear stages are infrequently met 

 with. In the case of Entamoeba histolytica, nuclear multiplica- 

 tion appears to take place early, so that from 2 to 4 nuclear stages 

 are frequently seen before encystment is complete ; indeed, occa- 

 sionally in the motile entamoeba. 



For convenience of reference, the more distinctive and con- 

 stant characters of Entamoeba histolytica arrd Entamoeba coli are 

 tabulated. 



Motile stage. 



A. Entamceba histolytica. B. Entamoeba coli. 



1. Appearance hyaline. I 1. Appearance porcelaneous. 



2. Refractiveness more feeble. 2. Refractiveness more pronounced. 



3. Movements active in the fresh 3. Movements sluggish. 



stools. 4. Nucleus distinct. 



4. Nucleus more or less indistinct. 5. Chromatin of nucleus abundant. 



5. Chromatin of nucleus scanty. 



Encysted stage. 



A. Entamatba histolytica. B. Entavioeba coli. 



1. Cyst smaller. 1. Cyst larger. 



2. Cyst less refractive. 



3. Cyst usually contains elongated 



refractive bodies known as 

 "chromidial bodies." 



4. Nuclei never more than 4. 



5. Cyst wall thinner. 



Therefore, in dysenteric stools and sometimes in diarrhoeal 

 stools, the characters of the motile Entamceba histolytica are 

 fairly distinctive, and the experienced observer will have little 

 difficulty in identifying the species. Unusually, however, in 

 diarrhoeal stools and in stools after a purgative Entamoeba his- 

 tolytica is in a preencysted stage in which it closely resembles 

 Entamoeba coli, especially in its sluggish motility and its distinct 



119781 5 



2. Cyst more refractive. 



3. Cysts do not contain "chromid- 



ial bodies." 



4. Nuclei 8, occasionally more. 



5. Cyst wall thicker. 



