BALANTIDIUM COLI : HOST-PARASITE SPECIFICITY 



amined microscopically the balantidia are found to occur 

 in groups in the mucosa and submucosa where their food 

 probably consists of tissues dissolved by ferments they 

 secrete. They are located near the edges of the older 

 ulcers associated with living cells and within the blood 

 vessels. The more extensive ulcers involve the muscle. 

 The abscesses produced by the balantidia appear to be 

 sterile at first but become secondarily infected with bac- 

 teria when they rupture. Balantidia probably enter the 

 blood stream in cases of intestinal ulceration and may be 

 carried to various parts of the body but no secondary 

 sites of infection have been determined with certainty. 

 Nothing is known regarding immunity (active resist- 

 ance of the host) in cases of balantidial infection. 



4. HOST-PARASITE SPECIFICITY 



Host-parasite specificity appears to be less rigid in 

 B. coll than in any other protozoon that lives in man. 

 Soon after Malmsten (1857) decribed B. coli from man, 

 Leuckart (1861) reported it from pigs and the following 

 year Stein placed the ciliate in the genus Balanfidiitm 

 which had been established by Claperede and Lachmann 

 in 1858 with B. entocoon of the frog as the type species. 

 Since then what seems to be the same species has been 

 found in several species of primates, and infection ex- 

 periments have been carried on with various species of 

 lower animals which indicate the possibilities in this 

 direction. 



Pig. B. coli probably exists in pigs wherever these 

 animals are to be found. They have been reported from 

 pigs in Germany, Sweden, Russia, Italy, France, the 



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