B. Grassi (1879) found in the stools of healthy as well as in those of diarrhœic patients from various localities in Northern Italy, amœbæ similar to those discovered by Lösch. As this was of frequent occurrence, the pathogenicity could not be definitely established. Normand, formerly naval surgeon at Hong-Kong, observed numerous amœbæ in the dejecta of two patients suffering from colitis.
Many further investigations, which cannot be quoted in detail, showed not only that intestinal amœbæ were widely distributed in man, but indicated with greater certainty their rôle as agents of dysentery. The Commission sent out by the German Government in the year 1883 to investigate cholera in India and Egypt—whose members discovered the cholera bacillus—also collected information with regard to dysentery. In five cases of dysentery examined post mortem at Alexandria, with the exception of one case in which ulceration of the colon had already cicatrized or was approaching cicatrization, R. Koch found amœbæ as well as bacteria in sections from the base of the ulcers, although such had previously escaped notice in examination of the dejecta. Encouraged by these results, Kartulis (1885), who had discovered amœba-like bodies in the stools of patients suffering from intestinal complaints at Alexandria, continued his investigations. The results, obtained from more than 500 cases, gave rise to the theory that typical dysentery was caused by amœbæ as were also the liver-abscesses that often accompany it. Kartulis supported his theory not only by the regular occurrence of amœbæ in the stools of dysenteric patients and their absence in other diseases, and by the occurrence of the parasites in ulcers of the large intestine and in the pus from liver-abscesses, but also by experiments which he performed on cats. These were infected by injection per anum of stool material rich in amœbæ from subjects of dysentery. The infection took place also when amœba-containing, but bacteria-free, pus from liver-abscesses was used. It has been objected that the infection of man with Amœba coli, as the dysenteric amœbæ were then generally designated, does not take place per anum but per os. This difficulty, however, diminished in proportion as the encysted states of amœbæ (fig. 2), long known in the case of other Protozoa, became understood. The infection of man (Calandruccio, 1890) and of cats (Quincke and Roos) succeeded solely when material containing such stages was used. Amœbæ introduced into the intestine multiply there by fission (Harris, 1894). However, this theory, to which various other authors gave support on the grounds of their own observations, encountered opposition. Thus it was established that amœbæ were not found in patients in every place where dysentery was endemic, or else they were much rarer than was expected. Further, amœbæ were present in the most varied kinds of intestinal diseases, both of infective and non-infective characters. Also they were present in quite healthy persons.
Moreover, for various reasons, infection experiments on animals failed to supply proof, and finally a bacterium was discovered (Shiga, 1898) to be the excitant of one form of dysentery. Agglutination attested the specific part played by this organism, as it was produced by the blood serum of a person suffering from or recovered from dysentery, but not by the serum of one who was uninfected. Bacillary dysentery consequently was a distinct entity. The final step to be taken was to decide whether there was a specific amœbic enteritis (amœbic dysentery or amœbiasis, according to Musgrave).
Fig. 2.—Encysted intestinal amœbæ showing nuclear multiplication. (After B. Grassi.)
This question should decidedly be regarded from the positive point of view. It is intimately connected with another, namely, whether there are not several species of intestinal amœbæ. The possibility of this had already been recognized. In addition to the Amœba coli Lösch, R. Blanchard distinguished yet another, Amœba intestinalis, and designated thereby the large amœbæ described in the first communication made by Kartulis; later on he stated the distinction between the species. Councilman and Lafleur10 (1891) considered the amœba of dysentery to be Amœba coli Lösch and so re-named the species Amœba dysenteriæ. Kruse and Pasquale (1893) employed the same nomenclature, but retained the old name Amœba coli Lösch for the non-infectious species. Quincke and Roos (1893) set forth three species: a smaller species (25 µ) finely granular, pathogenic for men and cats (Amœba coli Lösch); a larger species (40 µ) coarsely granular, pathogenic for men but not for cats (A. coli mitis); and a similar species non-pathogenic either for man or cat (A. intestini vulgaris). Celli and Fiocca (1894–6) went still further, they distinguished:
(1) Amœba lobosa variety guttula (= A. guttula Duj), variety oblonga (= A. oblonga Schm.) and variety coli (= A. coli Lösch).
(2) Amœba spinosa n. sp. occurring in the vagina as well as in the intestine of human patients suffering from diarrhœa and dysentery.
(3) Amœba diaphana n. sp. found in the human intestine in cases of dysentery.
(4) Amœba vermicularis Weisse, present in the vagina and in dysentery; and
(5) Amœba reticularis n. sp. in dysentery.
Shiga distinguished two species; a larger pathogenic species with a somewhat active movement, and a small harmless species with a somewhat sluggish movement. Bowman mentions two varieties, Strong and Musgrave (1900) two species—the pathogenic Amœba dysenteriæ and the non-pathogenic Amœba coli; Jäger (1902) and Jürgens (1902) mention at least two species. In the following year (1903) a work by Schaudinn was published which marked a real advance. This, in conjunction with the establishing of a special genus (Endamœba or Entamœba) for human intestinal amœbæ first by Leidy11 and then by Casagrandi and Barbagallo,12 for the time cleared up the confused nomenclature, the old name Amœba coli being retained for the harmless intestinal amœbæ of man, whereas the pathogenic species was designated Entamœba histolytica. The history of more recent work is incorporated in the accounts of the entamœbæ given below.
Entamœba coli, Lösch, 1875, emend. Schaudinn, 1903.
Syn.: Amœba coli, Lösch, 1875. Entamœba hominis, Casagr. et Barbag. 1897.
The amœboid trophozoite, according to Lösch, measures 26 µ to 30 µ and upwards; according to Grassi 8 µ to 22 µ; according to Schuberg 12 µ to 26 µ. A separation of the body substance into ectoplasm and endoplasm is only perceived during movement. The pseudopodia, which are generally only protruded singly, are broad and rounded at the end (lobopodia) and are hyaline, while the remainder of the body is granular. The ectoplasm is less refractile than the rest of the cytoplasm; it also stains less intensely (fig. 1), and is best seen on protrusion of a pseudopodium. Red blood corpuscles are rarely, if ever, found ingested in the cytoplasm.
Fig. 3.—Entamœba coli: life-cycle, a-e, stages in binary fission; A-D, schizogony, with formation of eight merozoites; 2–10, cyst formation or sporogony, with formation of eight nucleate cysts. (After Castellani and Chalmers)
The nucleus is vesicular, and is spherical when inactive, measuring 5 µ to 7 µ, with a thick nuclear membrane. In the centre of the nucleus is a chromatinic body or karyosome or sometimes several small nuclear bodies formed of plastin and chromatin; the remaining chromatin is arranged on the achromatic network in the form of fine granules, especially thickly deposited on the nuclear membrane.
Entamœba coli lives as a commensal in the upper portion of the large intestine, where the fæces still possess a pulpy consistency. With their concentration and change in reaction lower in the bowel, the parasites either die or else if they are at a suitable stage of development form resistant cysts. These cysts (fig. 2) can be found in great abundance in normal fæces,