338 The Philippine Journal of Science ms 



time, being kept in rooms in the animal house; others were 

 freshly purchased by this Bureau and were presumably recently 

 captured. No spontaneous infections with Balantidiv.m coli have 

 evet been discovered in the large number of monkeys that have 

 been used in the biological laboratory. Owing to the fact that 

 in infections of monkeys with this protozoan the parasites rarely 

 appear in the stools, it was considered useless to attempt to 

 control their freedom from natural parasitization by microscopic 

 examination of their stools. The monkeys were kept in indi- 

 vidual cages throughout the course of the experiments. 



These monkeys were either fed or injected rectally with the 

 faeces containing the balantidia, depending upon the stage of 

 development of the parasites. If the balantidia were encysted, 

 as was more frequently the case when they came frojn the pig, 

 a portion of the faeces containing the cysts was mixed with the 

 food of the monkey. On the other hand, motile balantidia, which 

 are more frequently found in human stools, were injected rectally, 

 since it is believed that the parasites in this unprotected stage 

 are incapable of withstanding passage through the stomach. 

 The diarrhoeal stool, diluted if necessary with physiological salt 

 solution, was given as a high rectal injection through a rectal tube 

 attached to a large syringe. Repeated feedings were given in 

 many cases in order to insure parasitization of the experimental 

 animal, which could not be readily determined by stool examina- 

 tions on account of the infrequent appearance of the parasites 

 in the faeces, and because the monkeys sometimes refused to eat 

 the infective food. That repeated feedings are not necessary, 

 however, to secure parasitization of monkeys with balantidia 

 is proved by the fact that several animals which were fed or 

 injected rectally only once became parasitized. 



Balantidium coli suis was used in more of these experiments 

 than Balantidium coli hominis because human cases that showed 

 a sufficient number of the parasites in their stools were not 

 frequently obtainable, and, moreover, it was especially desired 

 to determine the parasitism and pathogenesis of the balantidium 

 of the pig for the monkey. 



Following the feedings or rectal injections, the stools of the 

 monkeys were saved daily, or at frequent intervals, and examined 

 macroscopically for diarrhoea or dysentery and microscopically 

 for the presence of balantidia. 



At the beginning of the investigation it was planned to kill 

 the experimental animals at regular intervals in order to study 

 the progress of the infection, but this intention was interfered 



