HOST-PARASITE RELATIONS! INTESTINAL PROTOZOA 



Philippine Islands, China, Formosa, Cuba, South Amer- 

 ica, the United States, and from other countries. Mc- 

 Donald (1922) records them in 68 per cent of 200 pigs 

 from the western United States and Ohi (1925) found 

 from 36 to 96 per cent of the pigs at Taiwan in Southern 

 Formosa infected, the incidence depending on the sea- 

 son, there being a higher percentage parasitized in sum- 

 mer than in winter. It is generally admitted that the 

 species that occurs in the pig is the same as that in man. 

 That two species are present in the pig is claimed by 

 McDonald (1922) who describes one type that corre- 

 sponds in size and other characteristics to Balantidium 

 coli of man and another type which he has named Balan- 

 tidium suis; this type averages the same as B. coli in 

 length but is one-third less in breadth and possesses a rod 

 or sausage-shaped macronucleus at least one-half the 

 length of the body instead of a bean-shaped macronu- 

 cleus about one-third the length of the body as in B. coli. 

 How extensively B. suis is distributed among pigs geo- 

 graphically cannot be stated. B. suis has not been recorded 

 from man, all specimens thus far described being of the 

 B. coli type. 



B. coli has been considered for many years a natural 

 parasite of the pig and an accidental parasite of man. 

 This is indicated by the widespread infection among pigs 

 and the usual absence of pathogenic effects in these ani- 

 mals; whereas in man the infection is rare and is often 

 accompanied by severe pathological conditions. The in- 

 testinal wall of the pig is apparently very seldom attacked 

 by B. coli. Brumpt (1909), however, records one case 

 in which a pig was given an injection of material rich in 



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