28 MANUAL OF HUMAN PROTOZOA 



in diameter. There is a delicate membrane. The endosome 

 is comparatively large and more than one-half the diameter 

 of the nucleus itself. The ground mass of the endosome 

 stains less deeply and is made up of plastin material. On 

 its periphery are arranged 4-8 chromatin granules and 

 occasionally a central granule. 



Degenerating trophozoites often develop vacuoles which 

 coalesce into a large one and may resemble Blastocijstis 

 hominis (p. 69-70). Transmission is apparently by the tro- 

 phozoite. According to Wenrich (1940), the amoeba, if kept 

 in faeces, remains viable up to 48 hours at room tempera- 

 ture, but disappears, apparently by disintegration, in 2 

 hours at 3.5 °C. 



Keys to the genera and species of human amoebae 



A. The trophozoites in fresh and stained smears 



1(10) Active trophozoite in dysenteric or diarrhoeic faeces 2 



2(5) Trophozoites large, 20-30ii in diameter 3 



3(4) Trophozoites contain often erythrocytes; nucleus with a 

 small central endosome and comparatixely small pe- 

 ripheral chromatin granules; more actively amoeboid. . . 



Entamoeba histolytica (p. 9-14) 



4(3) Trophozoites do not ingest erythrocytes; nucleus with a 

 large eccentric endosome and large peripheral chromatin 



granules; less active Entamoeba coli (p. 15-19) 



5(2) Trophozoites smaller, average less than 20!ii in diameter 6 



6(7) Trophozoites with 1 or 2 nuclei; endosome central, com- 

 posed of plastin matrix and coarse chromatin granules; 



nuclear membrane without chromatin 



Dientamoeba fragilis (p. 26-28) 



7(6) Trophozoite with only one nucleus 8 



8(9) Trophozoite sluggish, 6-25|.i in diameter; nucleus with a 



large endosome, surrounded by a reticulum 



lodamoeba biitschlii (p. 21-24) 



9(8) Trophozoite actively amoeboid, 6-18!ii in diameter; nucleus 



with an endosome of varied forms and location 



Endolimax nana (p. 24-26) 



