The intracaecal inoculations yielded positive results in diagnosis of human amoebiasis when the clinical manifestations were obscure and the amoebae in the discharges so few and atypical as to make such an examination unsatisfactory.
Other Intestinal Amoebae.—It is a remarkable fact that one of the most common of the intestinal amoebae, Endolimax nana, has only recently been reported (Wenyon and O’Conner in 1917). In the examination of the stools of American soldiers Kofoid found it present in 28% of his examinations while E. coli was present in 23% of cases and E. histolytica in 9.3%. In examining 156 British soldiers Dobell noted its presence in 33% of them. The general view is that it is not pathogenic but its great importance is in the possibility of its being mistaken in its cyst form for E. histolytica. The living amoeba averages about 8 microns but in stained specimens it is somewhat smaller. In freshly passed faeces the amoeboid motion is sluggish and the nucleus indistinct. This amoeba is best identified by haematoxylin stained specimens when the nucleus shows a measurement of about 2 microns with a large eccentric karyosome which exhibits a variety of form. Unless perfectly fresh material is stained the degenerative changes in the amoebae may give a signet ring appearance of karyosome and ring nucleus. Such an appearance may suggest the limax nucleus. The mature cysts are usually oval, but sometimes round, and contain 4 nuclei, but when newly formed may only have one nucleus. The nucleus is large in the uninucleate form (up to 3 microns) but in the quadrinucleate forms it is about 1.2 microns with a large eccentric mass of chromatin. Chromidial bodies are rarely, if ever, present in these cysts.
Iodine Cysts.—These bodies which stain a deep brown colour when treated with iodine are now recognized as amoebae and have been named Iodamoeba bütschlii. They are most probably nonpathogenic. It is a small amoeba (9 to 13 microns, rarely up to 20 microns) and shows the sluggish movements of E. coli. The nucleus is very difficult to discern, thus differing from E. coli. In stained specimens it has a vesicular nucleus about 2 microns in diameter with a fairly large central karyosome. The cysts are spherical or oval, often of irregular outline and are about 10 microns in diameter. The nucleus is large and eccentrically placed and has a karyosome which tends to show as a peripherally placed mass. There is almost always present a large glycogen mass in the cyst which stains intensely with iodine.
Dientamoeba Fragilis (Jepps and Dobell 1918).—A rare binucleate amoeba averaging 8-9 microns in size. Nuclei show a fairly large, central granular karyosome and no peripheral chromatin. Strands of linin may be seen radiating from karyosome to nuclear wall. This organism is said to be frequently mistaken for Blastocystis when the vacuoles coalesce leaving a thin ring of cytoplasm. Cysts unknown. Considered nonpathogenic. Recently Kofoid and Swezy reported another species of amoeba parasitic in man, Councilmania lafleuri. The adult and cystic stages resemble in many respects the E. coli. Adult said to ingest red blood cells. Stated to be pathogenic but that more evidence is needed on this point.
Human Experiments.—Recently Walker and Sellards have published a most important paper.
The experiments were made in men who had been under observation for years at Bilibid Prison, whose food was cooked and the water they drank distilled. Moreover, there were complete records of examination for intestinal parasites, including entamoebae. They were under complete control and the existence or possibility of natural infection with amoebae was reduced to a minimum. All the men fed pathogenic amoebae were volunteers and each signed, in his native dialect, an agreement to the conditions of the experiment.
The first series of experiments was with cultural amoebae, in order to refute statements that amoebae cultivated from water or other nonparasitic sources, as well as from dysenteric stools, are capable of living in man parasitically or of producing dysenteric symptoms. Twenty feeding experiments on ten men were made by Walker and Sellards with cultures of amoebae without the development in a single instance of dysentery or the finding of such amoebae in the stools upon microscopical examination. In 13 cases they recovered the amoebae in cultures from the faeces from the first to the sixth day, but never afterwards. They stated definitely that cultural amoebae are nonpathogenic.
The next experiments were with Entamoeba coli. In the 20 cases fed with material containing Entamoeba coli there was a uniform failure to recover them culturally and in no instance was dysentery produced. Seventeen became parasitized as the result of a single feeding in from one to eleven days, the entamoebae being found in the stools and persisting in their appearance in the stools for extended periods. They concluded that Entamoeba coli is an obligate parasite, nonpathogenic, and cannot be cultured.
The third series of 20 feedings, carried on by Walker alone, was with Entamoeba histolytica. The material was mixed with powdered starch or magnesium oxide and given in gelatin capsules. In these experiments they obtained tetragena cysts in the stools of men fed only motile Entamoeba histolytica, and motile Entamoeba histolytica in the stools of men who were fed only tetragena cysts and, finally, an alternation of motile E. histolytica and tetragena cysts in the stools of a man having a recurrent attack of amoebic dysentery.
Results.—Seventeen of the men became parasitized after the first feeding; 1 required three feedings, and 2, who did not become parasitized at the first feeding, were held as controls. The average time for parasitization was nine days. Only 4 of the 18 parasitized men developed dysentery, which came on after twenty, fifty-seven, eighty-seven, and ninety-five days, respectively, after the ingestion of the infecting material.