ENTAMCEBA COI.I 33 



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. 



Entamceba coll lives as a commensal in the upper portion of the 

 large intestine, where the faeces 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 faeces, as Grassi first observed. Slight 

 laxantia or intestinal diseases of any kind producing increased 

 peristalsis, however, show amoebae even in the unencysted condition, 

 provided that the person harbours intestinal amoebae 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 amoebae 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 //, to 20 p. 



There are varying accounts of the details of the life-cycle of Entamceba coli in its 

 different stages. Thus, regarding schizogony or multiple fission it was formerly 

 stated that the nucleus of the parent amoeba 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 amcebulae. 



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 amoeba 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 fj. to 30 /*, and averages about 15/4. 

 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 



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