Nuclear Division in the Trophozoites of Endamoeba Histolytica

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

A pure strain of Entamoeba histolytica has 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 infected per os by 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 development in vitro has 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 procured in vitro at 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 occurs in vitro just 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 of E. histolytica, as visible in vitro, is thus wholly sexual.

A development similar to that here described in the case of Strain K. 28 c has been found to occur in many other cultivated strains of E. 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.

Nuclear division in the trophic stages of Iodamoeba butschlii (Prowazek, 1912) Dobell, 1919

1. Study of the nuclear morphology of a large number of haematoxylin-stained specimens of Iodamoeba bütschlii has permitted description of the process of nuclear division in this organism.

2. The interphase nuclei of the trophozoites were classified into four types (types I to IV) depending on the distribution of the periendosomal granules. The development of the four types of interphase nuclei appears to follow the process of nuclear division.

3. During the early prophase stages the periendosomal granules are incorporated into the endosome. More than twenty small granules are formed from the organizing endosome.

4. In late metaphase stages more than ten, and probably twelve, granules can usually be counted per set of the daughter chromosomes.

5. The centrodesmus may extend beyond the nuclear boundary during the anaphase stages, while the nuclear membrane appears intact.

6. The periendosomal granules reappear by the end of telophase stages when the two daughter nuclei are nearly completely separated.

7. In the freshly separated daughter cell the nucleus may still retain the trailing tail and appear tadpole-shaped, but the periendosomal granules are usually arranged like those in the type I interphase nucleus.

8. The validity of the genus Iodamoeba is re-emphasized on the basis of the characteristic nuclear structures and the unique process of nuclear division as here described for I. bütschlii.