232 RESEARCH IN PROTOZOOLOGY • 



b. Excystation. No one knows in what part of the digestive tract 

 excystation occurs, how long a time is required to bring it about, 

 nor what factors are responsible for the process. An easy method 

 to study excystation is to inject cysts into the stomach of labo- 

 ratory animals through a rubber catheter attached to a syringe and 

 then examine the stomach and intestinal contents at intervals of 

 about an hour. Work in vitro might also succeed, as it has in the 

 case of excystation in certain amoebce and flagellates. 



c. Pathology and Pathogenesis. The pathology of the lesions due 

 to B. coll in man is fairly well known but the origin of the lesions 

 (pathogenesis) is still in doubt. Walker (1913) states that balan- 

 tidia, when they come in contact with a solid object, do not back 

 ofif and try another direction, as Paranicvcimii does, but attempt to 

 bore their way through ; he suggests from this that balantidia bore 

 their way mechanically into the tissues of the intestinal wall. An- 

 other possible method of tissue invasion is that of dissolution of 

 the cells by the secretion of cytolytic enzymes. If a laboratory 

 animal can be found that can be infected with balantidia and in 

 which these ciliates are pathogenic, this problem can be studied 

 efifectively by setting up infections and observing the formation of 

 the lesions in the early stages. Neither guinea-pigs nor pigs seem 

 to be injured by balantidia although Brumpt (1909) obtained 

 lesions in a young pig which he infected with balantidia from 

 monkeys. Scott finds that balantidia invade the tissues of guinea- 

 pigs after the death of the host, but this is of little value in study- 

 ing pathogenesis in living tissue. Perhaps young pigs or monkeys 

 might be used for studies on pathogenesis. 



The effects of balantidia on other body tissues and upon the 

 physiological processes of the host are little known. Laboratory 

 animals, for example, monkeys, that are known to be susceptible, 

 could be infected and the chemical constitution of the blood and 

 changes in the cellular content of the blood studied. 



d. Carriers. The carrier condition exists in infections with B. 

 coli as in most other protozoan diseases. Do the balantidia live as 

 harmless commensals in the lumen of the gut during the carrier 

 period, or do they attack the tissues, but not severely enough to 

 induce symptoms ? What constitutes the resistance of the host dur- 

 ing the carrier period and what changes are effective in breaking 

 down this resistance? These are primarily physiological problems 

 involving both the host and the parasite. The results obtained by 



