The average size of the amœboid trophozoite is 25 µ to 30 µ. In fæces diluted with salt solution the amœbæ swell to 40 µ and more. There is sometimes separation of the body substance into a strongly refractile vitreous ectoplasm and a corneous endoplasm, pronounced even in repose, although the former is not equally thick at all parts of the periphery. In the endoplasm generally there are numerous foreign bodies (bacteria, epithelial cells, colourless and red blood corpuscles (fig. [6]), and occasionally living flagellates of the intestine). The nucleus is 4 µ to 6 µ in diameter, and may be difficult to recognize because it is sometimes weakly refractile and poor in chromatin. Its shape is slightly variable; it is usually excentric, sometimes wholly peripheral at the limit of the two parts of the body. Vacuoles are not present in quite fresh specimens, but appear later. In the study of E. histolytica, the morphological characters of the trophozoite or vegetative stage of the organism formerly separated as E. tetragena (figs. 5, 6, [8]a) must be considered (see p. [38]).
Fig. 5.—Entamœba histolytica (tetragena form), showing three successive changes of form due to movement. × 1100. (After Hartmann.)
The history of the development of these species, which give rise to amœbic enteritis as distinguished from bacillary dysentery, was formerly not so well known as that of E. coli. Upon being introduced into cats (per anum) dysenteric amœbæ provoke symptoms similar to those in man. In the latter, besides metastatic liver abscesses, abscesses of the lungs, and, according to Kartulis, cerebral abscesses are occasionally produced. Marchoux (1899) states that when the disease has lasted for some time liver abscesses are produced in cats also.
Fig. 6.—Entamœba histolytica which has ingested many red blood corpuscles. × 1100. (After Hartmann.)
