Researches on the Intestinal Protozoa of Monkeys and Man. I. General Introduction, and II. Description of the whole Life-History ofEntamoeba histolyticain Cultures

Abstract

A pure strain ofEntamoeba histolyticahas been isolated and cultivated, and an attempt has been made to study and describe its whole life-history in detail.This strain (K. 28 c) was derived from the dysenteric dejecta of a kitten experimentally infectedper osby means of typical cysts from the faeces of a monkey (Macacus sinicus). It has now been under continuous cultivation for about 20 months (220 serial subcultures), and its developmentin vitrohas been uniform throughout.Methods have been devised, and are here described, whereby any desired stage in the life-history of this strain—amoebae, cysts, and all intermediate stages (including encystation and excystation)—can be readily procuredin vitroat will.Detailed study has shown that the trophic amoebae multiply in cultures by simple binary fission only, as they do in their natural hosts. Their mode of division is briefly described.Encystation also occursin vitrojust as it does in the bowel, with formation of characteristic precystic amoebae and the final production of typical quadrinucleate cysts.Excystation has been carefully studied, and it has been found that a single quadrinucleate, amoeba escapes from each cyst through a minute perforation in its wall. An account is given of this remarkable process, which has not been described previously.The 4-nucleate excysted (metacystic) amoeba has been found to produce a new generation of trophic forms by a complicated series of nuclear and cytoplasmic divisions, which are described in detail for the first time. The final result of this subdivision is the production of eight uninucleate amoebulae by each quadrinucleate amoeba hatched from a cyst.These amoebulae are young trophic amoebae, and not gametes or conjugants. No sexual phenomena of any sort have been observed during the metacystic itages: and the life-history ofE. histolytica, as visiblein vitro, is thus wholly sexual.A development similar to that here described in the case of StrainK. 28 c has been found to occur in many other cultivated strains ofE. histolytica— including a strain isolated directly from man, and a human strain experiaentally implanted in a monkey (M. sinicus) and recovered therefrom in pure culture. There are therefore good reasons for concluding that the development were described is not abnormal, and that it is probably closely parallel to that which occurs naturally inside man.