Within the large intestine an active increase of Entamœba histolytica must occur. Nevertheless, Jürgens did not definitely find changes that might be interpreted in this sense. Schaudinn (1903) observed division and gemmation in vivo. Both processes, in which the nucleus divides by amitosis, can only be distinguished by the fact that the daughter individuals are similar in binary fission but dissimilar in gemmation, whether they make their appearance singly or in greater numbers. Schizogony, resulting in the formation of eight individuals, which is so characteristic for Entamœba coli, was not observed. (But schizogony, into four merozoites, is now known to occur. Gemmation processes are apparently degenerative.)
Resistant stages, which serve for transmission to other hosts, are according to Schaudinn17 first formed when the diseased portions commence to heal, or more accurately, the recovery commences when the vegetative increase of the amœbæ in the intestine discontinues. The so-called spores of E. histolytica were distinguished very definitely from those of E. coli; they were said to consist of spheres of only 3 to 7 µ in diameter, which were surrounded by a double membrane, at first colourless, but becoming a light brownish yellow colour after a few hours, and possessing a protoplasmic content containing chromidia. They were said to arise by fragments of chromatin passing outwards from the nucleus of the amœba into the surrounding cytoplasm (fig. 9, a) and undergoing so marked an increase that finally the whole cytoplasm became filled with chromidia. The remainder of the nucleus underwent degeneration and became extruded. On the surface of the cytoplasm there then arose small protuberances containing chromidia. These processes had been observed in the living organisms. They gradually divided and separated from membranes which later became yellow. The remainder of the amœba perished. Craig18 had also seen phases of this process of development. It must be remarked that, according to recent researches, these processes of exogenous sporulation are degenerative in character (see p. 41). The small spores may be fungi. The “sporulation” processes are only mentioned here as a warning. They are now only of historic interest. By means of an experiment made on a cat, Schaudinn ascertained that ingestion of permanent cysts, which resist desiccation, is the cause of the infection. The animal took food containing dry fæces with amœba cysts; these fæces came from a patient suffering from amœbic enteritis in China. On the evening of the third day the cat evacuated blood-stained mucous fæces which contained large numbers of typical Entamœba histolytica. On the fourth day after the infection the animal experimented upon died, and the large intestine showed the changes previously stated.
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.
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.)
(Entamœba tetragena, Viereck, 1907.)
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.
Fig. 9.—Entamœba histolytica (tetragena form). a, emission of chromatin from nucleus; b, nuclear division; c, degenerating form with two nuclei; d, e, f, cysts containing one, two and four nuclei respectively, and showing chromidial blocks. × 2,000. (After Hartmann.)
Some investigators, as Hartmann,19 lay stress on the internal structure of the nucleus (fig. 8, b, c), best seen in preparations fixed wet and stained with iron-hæmatoxylin. The nucleus is limited by a well-marked nuclear membrane, on the inside of which granules or nodules of chromatin may occur. There is a karyosome, which, in successfully stained specimens, shows, at times, a central dot called a centriole. (The nucleus of Entamœba