[17] _Arb. a. d. kaiserl. Gesundheitsamte_, xix, pp, 547–576.
[18] “Life cycle of _Amœba coli_ in Human Body,” _American Medicine_, 1904, vii, p. 299; viii, p. 185.
_E. histolytica_ also is found in the large intestine. This was originally shown to be the case by Kartulis, and the fact has recently been confirmed from many quarters. It is also present in the metastatic abscesses of which it is the cause (_cf._ among other authors, Rogers, _Brit. Med. Journ._, 1902, ii, No. 2,177, p. 844; and 1903, i, No. 2,214, p. 1315).
It should lastly be pointed out in this connection that mixed infections also take place. For instance, in addition to _E. histolytica_, _E. coli_, and, under certain circumstances, flagellates may be found together. In the same way _E. coli_ may come under observation even in bacillary dysentery. On the other hand, Schaudinn stated that in cases of dysentery endemic in Istria, _Entamœba coli_, if it had hitherto been present, disappeared, to return again after recovery from the illness.
[Illustration: FIG. 8.--_Entamœba histolytica_. _a_, trophozoite (_tetragena_ type) containing red blood corpuscles, × 1,300; _b_ and _c_, two isolated nuclei showing different appearances of karyosome, centriole and nuclear membrane, × 2,600. (After Hartmann.)]
This amœba must now be considered to be a part of the lifecycle of _Entamœba histolytica_, in fact a very important part of that cycle, especially in its tetranucleate cystic stages.
This organism, the so-called _Entamœba tetragena_, may occur in the human intestine in cases of amœbic dysentery, especially in mild or chronic cases. It was discovered by Viereck in 1907 in patients suffering from dysentery contracted in Africa. Soon afterwards an independent description was published by Hartmann, who called the amœba _E. africana_. It was also studied by Bensen and Werner. Recently (1912–13) much work has been published on this amœba by Darling and others; in this way its relationship to Schaudinn’s _E. histolytica_ has been made known.
In general morphology it somewhat resembles _Entamœba coli_, and its discoverer at first mistook it for a variety of that species. According to Hartmann, a distinct ectoplasm is only clearly visible when a pseudopodium is protruded (fig. 5). The granular endoplasm may contain ingested red blood corpuscles (fig. 6). The large, round nucleus is visible in the fresh state (fig. 8, _a_). So-called chromidial masses (? crystalloidal substances) may occur in the cytoplasm.