ENTAMCEBA HISTOLYTICA 197 



The writer and O'Connor (1917) noted the occasional inclusion of the 

 spores of a large bacillus, and on one occasion a large yeast-like organism. 

 E. histolytica is very fastidious about the kind of food it takes up, and in 

 the cases just mentioned, though many other structures were present in 

 the surrounding medium apart from the spores or yeasts, all the amcebse 

 had selected these particular objects for ingestion. The question arises 

 as to whether these were taken up by the amoebae before they were 

 discharged from the ulcers, as probably happens in the case of the included 

 red blood-corpuscles and other cells, or whether they were ingested during 

 the passage of the amoebae down the large intestine. E. coli, on the other 

 hand, ingests indiscriminately all kinds of objects in the intestine, but 

 apparently not red blood-cells, so that the presence of the latter in an 

 amoeba is strong presumptive evidence of its being E. histolytica. Occa- 

 sionally, however, undoubted E. histolytica, as seen in the stool, possess 

 vacuoles with included bacteria. These organisms are sometimes seen 

 in amoebae in sections of ulcers from human beings and cats when the 

 ulcer is invaded by intestinal organisms. This condition is only seen in 

 the superficial layers. Amoebae, both in faeces and in sections of intestinal 

 ulcers and liver abscess, especially in cats, may contain numerous irre- 

 gularly-shaped bodies which appear to be chromatoid in nature. Some- 

 times they bear some resemblance to Charcot-Leyden crystals (Fig. 95, 5). 

 In the cultures of E. histolytica, as described by Boeck and Drbohlav 

 (1925), the amoebae, when grown on egg media, feed largely on bacteria. 

 In blood media they ingest red cells also. 



The nucleus of E. histolytica is a spherical structure 4 to 7 microns in 

 diameter. It consists of a fine membrane enclosing an alveolar substance 

 which in fixed material assumes the form of a network of linin threads, 

 some of which may be radial. At the centre of the nucleus is a small 

 karyosome surrounded by a clear area, the outer limits of which represent 

 the inner limits of the alveolar material. In fixed specimens, again, the 

 clear area appears in optical section to be limited by a ring of fine granules. 

 The small karyosome is homogeneous, and is said to consist entirely of 

 chromatin. Hartmann and others claim to have detected a centriole in 

 the karyosome, but it is very doubtful if such a structure exists. Chromatin 

 granules are arranged uniformly over the inner surface of the nuclear 

 membrane. In amoebae which have partially degenerated the nuclei 

 may have a very different appearance. The karyosome may appear larger 

 and be definitely excentric in position, while the chromatin on the 

 membrane may be distributed more irregularly in the form of several larger 

 masses. Amoebae with nuclei which do not conform to the type are 

 frequently encountered in perfectly fresh stools. The position of the 

 nucleus in the endoplasm varies considerably, and is subject to constant 



