viii, B, 4 Walker and Sellards: Entamcebic Dysentery 305 



ulcerative colitis, although no dysentery had manifested itself 

 during the five months the monkey had been infected. There- 

 fore, so far as these experiments have gone, it appears that latent 

 balantidiasis in the monkey may be due to several different 

 causes, namely: (1) In certain cases to the failure of the balan- 

 tidia to penetrate the tissues of the intestine, (2) in other cases 

 to the chronicity of the ulcerative process, and (3) to the fact 

 that more or less extensive colitis and ulceration may exist in 

 the intestine of the infected animal without any dysenteric 

 symptoms. It is conceivable, indeed probable, that the latency 

 of entamcfibic dysentery is due to similar causes. 



Notwithstanding that the prevalence of latent infections has 

 caused the results of the experimental infections with Entamoeba 

 histolytica to appear less clean-cut than the results with the 

 Amoebae and with Entamoeba coli and has rendered the nonpara- 

 sitized controls of these experiments inconclusive, nevertheless, 

 I am of the opinion that these experiments supply evidence 

 which, when considered with the morphological, clinical, and 

 pathological data, is sufficient to establish beyond a reasonable 

 doubt the etiologic relationship of Entamoeba histolytica to 

 endemic tropical dysentery. 



In the first place, it is to be noted that the uniformly negative 

 results of the feeding experiments with the Amoebse and Enta- 

 moeba coli suffice to exclude them once for all from the etiology 

 of this disease. Therefore, the question of the etiologic factor 

 must lie between Entamoeba histolytica and some unidentified 

 microorganism present in dysenteric stools. 



If the entamoebae are only commensals, the multiplication of 

 which is favored by the dysenteric conditon and which invade 

 the dysenteric lesions as a secondary infection, it would be ex- 

 pected that the common Entamoeba coli would be most frequently 

 associated with the disease; on the contrary, it is the relatively 

 rare Entamoeba histolytica only that is constantly found in the 

 stools and lesions of entamcebic dysentery. 



Post mortem, the entamoeba are found not only in the lesions, 

 but in the sound tissues underlying the lesions, where they are 

 usually the only microorganisms demonstrable. They penetrate 

 between the cells of the sound mucosa, the submucosa, and even 

 of the muscularis, where by their migrations and multiplication, 

 aided probably by the secretion of a ferment, they produce histol- 

 ysis. They are found in the lymph spaces and in the blood 

 vessels in which they are carried by the way of the portal circu- 

 lation to the liver and give rise to abscesses as sequelae to the 

 intestinal infection. In these liver abscesses, which are usually 



