Fig. 59.—Entamoeba histolytica. The same living individual drawn at brief intervals while moving. (From Doflein after Hartmann.)
For the nonpathogenic E. coli he noted: (1) No distinction between a granular endoplasm and refractile ectoplasm; (2) centrally placed and sharply outlined nucleus, rich in chromatin; and (3) encystment with the formation of eight nuclei, which cysts with their nuclei or amoebulae form the infecting stage.
The pseudopodia of E. histolytica are actively projected as long finger-like processes which show the ectoplasm quite distinctly, while the pseudopodia of E. coli are lobose and sluggishly projected and show a uniformly opaque grayish color. In dysenteric stools E. histolytica tends to show contained red cells. E. coli never contains them but instead shows bacteria and food particles.
In 1907 Viereck and later Hartmann recognized a pathogenic amoeba with four nuclei in its encysted form, to which was given the name E. tetragena.
All authorities now consider that Schaudinn made an error in observation as to the existence of peripheral budding for E. histolytica, so that we recognize but two types of encystment, one with a larger cyst and thicker cyst wall, with eight nuclei and an absence of chromidial bodies—E. coli—the other, smaller, with a thin cyst wall one to four nuclei and chromidial bodies in the encysted stage, the pathogenic amoeba, E. histolytica. Synonym, E. tetragena.
In the vegetative stage the human amoebae are best differentiated by the nuclear structure as shown in stained specimens. In E. coli the nucleus is vesicular with a thick nuclear membrane and the chromatin chiefly deposited on the under surface of the nuclear membrane. This chromatin often seems deposited in quadrant aggregations. The karyosome is eccentric.
For the pathogenic amoeba we recognize a histolytica type of nucleus, which is found in dysenteric stools, and a tetragena type, which is found in diarrhoeal or more or less normal stools. Dobell does not recognize this differentiation.
