VIII, B. 5 Walker: Experimental Balantidiasis 341 



of the balantidia to appear in the stools of the experimental 

 animal. And they demonstrate that Balantidium coli suis be- 

 haves, w^ith reference to its appearance in the stools of the 

 parasitized monkey, as does Balantidium coli hominis. 



Monkeys 10, 35, and 43, two of which had and 1 of which had 

 not become parasitized with the balantidia, had a diarrhoea or 

 slight dysentery just before death; but, as will be seen from the 

 post-mortem examinations, the dysentery was probably due to 

 other causes than the balantidium infection. None of the other 

 monkeys had diarrhoea or dysentery during the time they were 

 under observation. However, as will be seen from the histo- 

 logical examinations of infected monkeys, the ulcerative process 

 of this infection is probably extremely chronic, and conse- 

 quently no dysenteric symptoms would be expected in these early 

 stages of infection. 



Post mortem, a number of the monkeys, whether killed or 

 dying naturally, showed a colitis and sometimes ulcerations, 

 which histological examination showed not to be due to balan- 

 tidium infection. These lesions, at first misleading, were soon 

 cleared up by the histological study of the tissues, and have 

 served the useful purpose of comparison with the lesions pro- 

 duced by Balantidium coli, and for determining the part played 

 by lesions of other etiology in the entrance of the balantidia into 

 the tissues of its host. 



A comparison of the gross lesions in the intestine of monkeys 

 having an early balantidial infection with those having a colitis 

 due to other causes has shown that the balantidial infection 

 is characterized chiefly by the inconspicuousness of the lesions, 

 which consist simply of reddened areas of the mucosa with 

 or without punctiform hsemorrhages, sometimes so slight as to 

 be overlooked, but no exudate or ulcerations; while the colitis 

 of other etiology usually presents a catarrhal, diphtheritic, or 

 haemorrhagic exudate, frequently associated with ulcerations. 



One, or 50 per cent, of the 2 monkeys parasitized with Balan- 

 tidium coli hominis showed balantidia in the tissues post 

 mortem. The negative animal had been parasitized only thirteen 

 days when it died, while the one which showed balantidia in the 

 tissues had been parasitized forty-two days when the post-mor- 

 tem examination was made. Of the 13 monkeys parasitized 

 with Balantidium coli suis, 1, or 7.7 per cent, showed balantidia 

 in the tissues post mortem. This is a smaller per cent of in- 

 fections than with the balantidium from man, but it is to be borne 

 in mind that the series of animals parasitized with the latter 



