The Animal Parasites of Man. Max Braun
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Название: The Animal Parasites of Man
Автор: Max Braun
Издательство: Bookwire
Жанр: Медицина
isbn: 4057664648037
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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, as Grassi first observed. Slight laxantia or intestinal diseases of any kind producing increased peristalsis, however, show amœbæ even in the unencysted condition, provided that the person harbours intestinal amœbæ generally. The intensity of infection varies according to the locality; thus Schaudinn found that 50 per cent. of the persons examined were infected with harmless amœbæ in East Prussia, 20 per cent. in Berlin and about 66 per cent. on the Austrian littoral.
The life-history (fig. 3) of the parasite exhibits two phases: (a) asexual multiplication in the intestine, either by binary fission or by schizogony with formation of eight merozoites, and (b) sporogony leading to the production of eight-nucleate cysts. Infection results from ingestion of cysts. Only cysts with eight nuclei are infective. The diameter of such cysts is about 15 µ to 20 µ.
There are varying accounts of the details of the life-cycle of Entamœba coli in its different stages. Thus, regarding schizogony or multiple fission it was formerly stated that the nucleus of the parent amœba divided into eight portions, which after dissolution of the nuclear membrane, passed outwards into the cytoplasm, which segregated around each. Eight merozoites were thus produced. More recently the process of schizogony has been considered to consist in the repeated division of the nucleus into two, four, and finally eight nuclei (fig. 3, A-D), and the formation of eight merozoites or amœbulæ.
The process of encystment is initiated by the extrusion of all liquid and foreign bodies from the protoplasm, which assumes a spherical form (fig. 4, A). The rounded uninucleate amœba then secretes a soft gelatinous coat, which finally differentiates into a double contoured cyst wall in older cysts. According to Casagrandi and Barbagallo, the size of the cyst varies from 8 µ to 30 µ, and averages about 15 µ. According to Schaudinn (1903) the cytological changes during cyst formation are as follows. The nucleus of a rounded uninucleate form divides into two (fig. 4, B). Each of these nuclei fragments into chromidia (fig. 4, C), some of which are absorbed, while others reunite so that the cell becomes binucleate again. Each of these nuclei, by a twice repeated division, produces three nuclei (fig. 4, D), the smaller two of which degenerate and were regarded as reduction nuclei. There is a clear zone or vacuole in the middle of the cyst during these maturation processes, dividing the cyst into two halves. After the nuclear reduction the clear space disappears, and each nucleus (termed by some a gamete nucleus) divides into two pronuclei (fig. 4, E). The pronuclei of the pairs were said by Schaudinn to differ slightly. Copulation occurs between pairs of unlike pronuclei, and is an example of autogamy (fig. 4, F). When complete, each of the fusion nuclei (synkarya) divides twice, giving rise first to four and finally to eight nuclei. Eight amœbulæ are thus formed within the cyst.
According to Hartmann and Whitmore (1911)13, however, autogamy does not occur within the cysts of E. coli. They consider that eight small amœbulæ are formed (fig. 3, 2-10) which escape from the cyst and then conjugate in pairs (fig. 3, 10-12), afterwards growing into a new generation of trophozoites.
Only some 10 to 20 per cent. of the cysts evacuated with the fæces undergo the full course СКАЧАТЬ