342 The Philippine Journal of Science wu 



variety is very small from which to draw conclusions. The time 

 of parasitization before necropsy of the monkeys that did not 

 become infected with the balantidium from the pig varied from 

 thirty-four to one hundred fifty-two days, and in the infected 

 monkey it was thirty-eight days. 



These experiments, therefore, prove that both Balantidium 

 coli hominis and Balantidium coli suis are capable of invading 

 the tissues and becoming tissue parasites of the monkey. They 

 further show that only a small proportion of the monkeys para- 

 sitized with balantidia from either source become infected ; that 

 is, show the parasites in the tissues within the period of time 

 (from thirteen to one hundred fifty-eight days) during which 

 these animals were under obsei-vation. However, it is probable, 

 since in these early infections little or no gross lesions are 

 apparent, because only a few balantidia may have entered the 

 tissues, and since the sections made can include only an infin- 

 itesimal part of the whole intestine, that more of these para- 

 sitized monkeys were really infected. It is also to be borne in 

 mind that every one of the animals parasitized would be liable 

 sooner or later to become infected. The condition is exactly 

 similar to that found to prevail in entamoebic dysentery, in which 

 only about 22 per cent of men experimentally parasitized became 

 infected and developed dysentery (Walker and Sellards, 1913). 



Histological examination of sections of the large intestine of the 

 monkeys parasitized with Balantidium coli and showing a colitis 

 has disclosed well-marked difi'erences between those which did 

 and those which did not contain balantidia in the tissues. The 

 latter show either a catarrhal or diphtheritic exudate or ulcera- 

 tions, usually associated with polymorphonuclear leucocyte infil- 

 tration of the mucosa and submucosa. On the other hand, sections 

 of the intestine of cases of these early stages of infection with 

 balantidia show the epithelium intact, except for mechanical in- 

 jury due to entrance of the balantidia or to minute haemorrhages, 

 but no exudate or ulcerations. There is more or less congestion 

 of the blood vessels and the tissue infiltration, which is slight, 

 is of round cells and eosinophiles. 



Therefore, the lesions and cellular reactions in balantidial coli- 

 tis, in the early stage before complicated by secondary bacterial 

 invasion, are characteristic and are distinguishable from those 

 of colitis due to bacterial infection. Moreover, these cases have 

 demonstrated that lesions in the intestinal epithelium from bac- 

 terial infection or other causes not only are not necessary for 



