246 FAMILY: AMCEBID^ 



The cysts of 7. biUschlii, when spherical, vary in diameter from 7 to 

 15 microns, but very marked irregularities in shape occur (Fig. 114, 6-15). 

 There is a definite cyst wall, and in the cytoplasm within the cyst is found 

 a more or less rounded refractile body and a number of small refractile 

 granules which are possibly composed of volutin. The single nucleus can 

 usually be detected in the thickest portion of the cytoplasm, between the 

 refractile body and the cyst wall. In iodine solution the refractile body 

 assumes a dark brown colour, and is seen to have a sharply-defined margin, 

 thus contrasting with the ill-defined limits of the glycogenic vacuoles in 

 cysts of Entamoeba coli and E. histolytica (Plate II., 11-16, p. 250). The 

 " iodophilic body " is rarely absent from the cysts. It may be quite 

 small, but usually has a diameter of a quarter to a third of that of the cyst. 

 Occasionally two or three separate iodophilic bodies are present. In the 

 process of staining with iron hsematoxylin and mounting in balsam in the 

 ordinary manner they are dissolved, the vacuoles alone remaining. As 

 pointed out by Dobell, the iodophilic body is gradually absorbed in 

 living cysts kept outside the host. Usually there is a single nucleus 

 in the cysts, though cysts with two nuclei are not uncommon in some 

 infections (Fig. 114, 14 and 15). Taliaferro and Becker (1922) found only 

 four cysts with two nuclei amongst 2,000 consecutive cysts examined. 

 The nucleus of the encysted form differs from that of the free amoebae in 

 that the karyosome, instead of occupying a central position, conies to lie 

 against the nuclear membrane, while the rest of the space within the 

 membrane is filled with the globules which surrounded the karyosome 

 in the free amoeba. These may retain the stain irregularly, and give rise 

 to the appearance of secondary karyosomes in the nucleus. Brug (1919 

 and 1921) describes the karyosome as being applied to the nuclear 

 membrane, while between it and the opposite side of the nucleus is a body 

 which is semilunar in outline in side view, or watch-glass in shape, with 

 the karyosome at the centre, when viewed in a direction at right angles to 

 this. It is possible that this appearance is a result of shrinkage of the 

 globular material filling the space within the nuclear membrane, so that 

 it forms a more compact body separated from the karyosome and nuclear 

 membrane by a clear space. The karyosome does not always stain 

 uniformly, as often a more deeply staining portion can be distinguished 

 from another staining less intensely. 



Dobell (1919) believes that there occur races of /. butschlii which can be 

 distinguished by the average size of the cysts. 



I. bUtscJilii is a fairly common inhabitant of the human intestine. A 

 remarkable feature of the infections is that often enormous numbers of 

 cysts are passed without there being any indication of the free forms. 

 There seems to be no evidence that the amoeba has any pathogenic 



