Researches on the intestinal protozoa of monkeys and man

Abstract

1. This memoir amplifies my accounts ofEndolimax nanapublished in 1919 and 1933. The complete life-history, as observable in cultures, is now described—special attention being devoted to the nuclear structure at all stages.2. Additional information is also given about methods of cultivation, viability of the cystsin vitro, the ‘nucleal reaction’, natural parasites (Sphaerita, etc.), and other details.3. The life-history has been found to comprise trophic, precystic, cystic, and metacystic stages, comparable with those described inEntamoeba histolytica(1928) andE. coli(1938).4. The trophic amoeba is redescribed, with special reference to the polymorphism of its karyosome.5. Division of the trophic amoeba (by binary fission) has been studied, and the mitosis of its nucleus is now first described in detail. It is characterized by the formation of an intranuclear spindle, with well-developed centrioles and centrodesmus. The granular chromosomes are 10 in number, and arranged in a ring on the equatorial plate.6. Precystic amoebae are smaller than trophic forms —the reduction in size being effected during the last two divisions before encystation.7. The cyst is formed by a precystic amoeba in the usual way. Inside the cyst, the nucleus undergoes two successive mitotic divisions similar to those seen in trophic forms. The ripe cyst is therefore 4-micleate, though supernucleate specimens—which are viable— occur occasionally. Glycogen is normally present in young (1- and 2-nucleate) cysts, but not in those which are mature.8. The process of excystation is described for the first time, and closely resembles that seen inE. histolytica. The entire protoplasmic contents emerge as a single 4-nucleate amoeba through a minute pore in the cyst wall.9. Metacystic development—not previously studied —consists in simple division, by successive cytoplasmic bipartitions without division of the nuclei, into 4 uninucleate amoebulae. These grow into trophic amoebae once more.10. The whole life-history is thus asexual, with no gametes, conjugation, or autogamy, at any stage.