viii. B, 5 Walke)-: Experimental Balantidiasis 343 



the entrance of Balantidium coli into the tissues, but that in 

 no one of the relatively large number of parasitized monkeys 

 in which such lesions existed have the balantidia taken advan- 

 tage of them to enter the tissues. 



In their entrance into the tissues of the intestine the balan- 

 tidia pass through the healthy epithelium. No necrosis or ul- 

 cerations of the epithelium are apparent, only a pushing aside 

 of the cells or, at most, a mechanical rupture of the epithelium 

 exists. In every case the entrance was effected through the 

 epithelium between, and in no case within, the tubules. In 

 monkey 10, parasitized for thirty-eight days with Balantidium 

 coli suis, some of the balantidia are just penetrating the epithe- 

 lium and others are in the mucosa between the tubules and, to a 

 less extent, in the submucosa and in the blood vessels of the 

 submucosa (Plates I, II, and III). In this case they were not 

 found in the muscularis. In monkey 31, parasitized for forty- 

 two days and, according to my assistant who performed the 

 necropsy, showing no intestinal lesions, the balantidia were found 

 in the muscularis and in the mesenteric lymph glands (Plates 

 IV and V). 



Therefore, these experimental infections have shown that both 

 Balantidium coli hominis and Balantidium coli suis are capable 

 of penetrating the sound intestinal epithelium and of wandering 

 widely in the sound tissues of the mucosa, submucosa, muscularis, 

 blood vessels, and mesenteric lymph glands. 



In these early infections the balantidia are found singly or 

 in scattered groups, evidently in the process of migration rather 

 than of active multiplication in the tissues. In consequence, 

 there is as yet little injury to the tissues beyond some mechanical 

 rupture; and usually even this is wanting; the parasites, which 

 are capable of amoeboid movements, pass between the cells like 

 migrating leucocytes. Moreover, there is in these early cases 

 little cellular reaction in the vicinity of the single parasites 

 and no extensive cellular infiltration of the tissues. At a 

 later period an active multiplication of the balantidia takes 

 place in the tissues, forming nests or colonies (Plates VI and 

 VII) which, by their multiplication, aided probably by the secre- 

 tion of a ferment, produce cellular reactions, necrosis of the 

 tissues, and finally open ulcerations, which are advanced by the 

 secondary invasion of intestinal bacteria. 



That Balantidium coli is able, without the aid of bacteria, to 

 produce abscesses and ulcerations of the intestine of infected 



