Fig. 7.—Section through wall of large intestine (of a man) close under an ulcer caused by Entamœba histolytica. A, amœbæ that have penetrated partly in blood-vessels (Bv), partly in tissue of submucosa to the muscularis. Magnified. (After Harris.)
In the large intestine of infected cats the amœbæ creep over the epithelium, and here and there they force the epithelial cells apart, as well as removing them or pushing them in front of them; the amœbæ thus insert themselves into the narrowest fissures. They penetrate also into the glands through the epithelium, and thence into the connective tissue of the mucosa. Intestinal and glandular epithelia perish under the influence of these parasites: the cells are pushed aside, fall to pieces or are absorbed by the amœbæ. In the connective tissue of the mucosa the amœbæ migrate further, and often accumulate above the muscles. Finally they rupture this and force their way into the submucosa. In cats, apparently, the penetration is not so great as in men, according to Kruse and Pasquale. During their migration the parasites also gain access to the lymph-follicles of the wall of the intestine, which become swollen and commence to suppurate; follicular abscesses arise and after their rupture follicular ulcers. The diseased patches in the mucosa are markedly hyperæmic and numerous hæmorrhages are set up. Roos and Harris state that the amœbæ also penetrate into the blood-vessels (fig. 7) and this explains the occurrence of metastatic abscesses.[15] The whole submucosa is severely swollen at the diseased spot and undergoes small-celled infiltration in the neighbourhood of the colonies of amœbæ. From these findings Jürgens (1902) draws the conclusion[16] which is followed here, that the amœbæ are causative agents of the enteritis of cats, which disease is well defined, both pathologically and anatomically. Subsequent researches confirm the experience of earlier authors; great precautions were taken to exclude errors, hence, as with Gross and Harris, no exception can be taken to their results. The inoculation material was derived from soldiers who suffered from amœbic enteritis in China and who were admitted into the garrison hospital at Berlin. In order to be independent of the patients themselves, transmission experiments from cat to cat were performed, after the first experiments on cats yielded positive results. This was also effected by rectal feeding as employed by earlier workers. Such appeared necessary in order to prevent the evacuation of the inoculation material per anum, as well as to avoid the employment of morphia and ether narcosis. Forty-six cats were used for the experiments. Ten cats received tested stools containing motile amœbæ from soldiers suffering from amœbic enteritis contracted in China. Sixteen other cats received stools from cats infected by inoculation. All the animals sickened and suffered from the disease. Five cats received dejecta from human amœbic enteritis in which, however, no motile amœbæ were present. Thirteen cats received stools from soldiers who suffered from bacillary dysentery. None of the latter cats took the complaint and none showed changes in the large intestine upon sectioning. The injection of various bacteria, obtained from a stool of amœbic enteritis pathogenic to cats, remained without result in both the cats employed for this experiment. Lastly, two cats, which had been kept with those artificially infected, were taken ill spontaneously and suffered from the disease. In the opinion of Harris, who ascertained the harmless nature of bacteria derived from the intestinal flora containing dysenteric amœbæ, young dogs are capable of being infected.
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 Schaudinn[17] 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. Craig[18] 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.)