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. [Illustration: FIG. 60.—The more important intestinal amoebae of man showing nuclear structure when stained. 1. _E. histolytica._ 1(a). _E. histolytica_ cyst. 2. _E coli._ 2(a). _E. coli_ cyst. 3. _E. nana._ 3(a). _E. nana_ cyst. 4. _I. bütschlii._ 4(a). _I. bütschlii_ cyst. (After Dobell.)] The histolytica nucleus has a thin nuclear membrane and is poor in chromatin while the tetragena nucleus has more chromatin, showing radial projections from the inner surface of the nuclear membrane, and a loose central spherical karyosome, which contains a central chromatin dot or centriole, with a clear halo surrounding it. Dobell states he has not been able to note this centriole. The preëncysted _E. histolytica_ has a nucleus resembling that of _E. coli_. The smaller size and chromidial bodies are differentiating. Animal experimentation upon kittens with _E. coli_ by Schaudinn, Craig and Wenyon have been unsuccessful as to production of dysenteric manifestations. On the other hand all of these experimenters produced typical lesions and dysenteric manifestations in kittens injected rectally or fed with material containing pathogenic amoebae. Wenyon as previously stated produced a liver abscess in one of his experiments.