VIII, B, 5 Walker: Experhnental Balantidiasis 339 



with by the fact that many of the parasitized monkeys did not 

 become infected and by the death of a number of the monkeys 

 during the course of the experiments. The deaths of these mon- 

 keys were probably due in most cases to the close confinement in 

 small cages and to improper food. In consequence of these un- 

 foreseen complications and in consideration of the fact that the 

 symptoms and pathology of the later stages of infection with 

 Balantidi'um coli have been adequately studied in human cases, 

 it was decided to confine the investigation to the parasitization 

 and early stages of infection which are in need of elucidation. 



Post-mortem examination, with special reference to lesions in 

 the large intestine and to the presence of balantidia in the 

 intestinal contents, was made of each monkey that died or that 

 was killed after feeding or rectal injection with balantidia. In 

 every case where a colitis or ulcerations of the large intestine 

 were present, pieces of the tissues were fixed and subjected to 

 a histological examination for cellular changes and for the 

 presence of balantidia. 



These experiments are summarized in Table I. 



Of the 13 monkeys fed encysted balantidia from the pig, 12 

 became parasitized; and of the 4 monkeys that received rectal 

 injections of motile balantidia from the pig, none became para- 

 sitized. Only 1 monkey was fed encysted balantidia from man 

 and he did not became parasitized. Four monkeys received rectal 

 injections of motile balantidia from man, and of these 2 became 

 parasitized. Therefore 12, or 70.6 per cent, of the monkeys fed 

 or injected with Balantidium coli suis; and 2, or 40 per cent, 

 of the monkeys fed or injected with Balantidium coli hominis, 

 became parasitized. The smaller percentage of monkeys para- 

 sitized with the balantidia from man may be due to several 

 causes: to the smaller number of experiments with material 

 from this source, that the infective material contained few^er 

 balantidia, and to the fact that most of the experiments with 

 the human strains were with motile forms administered by rec- 

 tal injection. 



In pigs parasitized with balantidium the parasites appear rather 

 constantly in the encysted stage in the formed stools, and often 

 in enormous numbers. On the other hand, in parasitized man 

 the balantidia are rarely found in the encysted stage in formed 

 stools, but usually only in the motile stage in diarrhoeal stools, 

 and then often at irregular intervals. In monkeys. Table II 

 shows the number of stool examinations made on different days 

 of each animal that became parasitized and the number of positive 

 and negative findings for balantidia. 



