ENTAMCEBA HISTOLYTICA 199 



The precystic forms of E. histolytica were first seen by Elmassian 

 (1909). He did not realize their nature, and, thinking he was dealing with 

 a new amoeba, gave it the name E. minuta. The name was employed 

 subsequently by Woodcock and Penfold (1916) for the smallest races of 

 E. histolytica, but Elmassian did not use it for the small race, of the 

 existence of which he was not aware, but for the one of average size which 

 everyone now admits is undoubtedly E. histolytica. Walker (1911), and 

 Walker and Sellards (1913), appear to have been the first to realize that 

 the small amoebae with clear cytoplasm were the precystic forms of the 

 large tissue-invading amoebae. This has been amply confirmed by many 

 observers. Shortly before encystment takes place the amoeba often 

 develops a vacuole containing glycogen, which colours brown with iodine, 

 as well as one or more refractile bodies. The latter, which often have the 

 form of rods with rounded ends, were named chroynatoid bodies by Dobell. 

 They show no marked affinity for iodine, but stain black with iron 

 hsematoxylin. It is very improbable that they are chromatic in nature. 

 They have well-defined edges, and are readily seen as greenish refractile 

 bars in the living amoebae or cysts. The margin of the glycogenic vacuole, 

 as stained with iodine, is not sharply defined, for it gradually shades off 

 into the surrounding cytoplasm. In the case of the cysts of lodatnoeba 

 butschlii, the substance in the vacuole is much denser than that in the 

 vacuole of the cysts of E. histolytica, and in iodine-stained specimens the 

 limits of the vacuole, or more correctly those of the glycogenic body 

 within it, are very sharply defined, the brown colour of the included 

 substance ceasing abruptly at the margin of the vacuole (Plate II., 5, 6, 9, 

 and 11-14, p. 250). 



The nuclei of the precystic amoebae resemble those of the tissue- 

 invading forms, except that the chromatin on the membrane often occurs 

 in larger masses. In some cases the nuclei possess a single large crescentic 

 mass in addition to smaller ones. Dobell (1919) states that chromatin 

 granules occur also on the linin network, a condition which he does not 

 find in the normal nuclei of the tissue-invading forms. 



The precystic amoebae are not so active as the tissue-invading forms, 

 and on account of the larger chromatin gratiules of the nuclei they may 

 be difficult to distinguish from the corresponding stages of E. coli. In these 

 cases it will be necessary to discover the characteristic cysts. The smaller 

 races are still more difficult to distinguish, as they may be confused with 

 Endolimax nana. The structure of the nucleus, as seen in stained pre- 

 parations, is important, and a final diagnosis may not be possible till 

 cysts have been found, it may be after repeated examinations on different 

 days. 



The precystic amoebae and the cysts of E. histolytica were first 



