HOST-PARASITE RELATIONS: INTESTINAL PROTOZOA 



will live for three days. Rees (1927), however, while 

 working in the writer's laboratory, discovered that these 

 ciliates do not round up at room temperature if kept 

 under anaerobic conditions ; that they will continue to live 

 at room temperature for as long as 10 days; that wash- 

 ings from trucks in which pigs were hauled contained 

 trophozoites that lived at room temperature for 14 hours ; 

 and that active specimens could be recovered from solid 

 feces of the pig that had been passed at least 4 hours. 

 There is thus abundant opportunity for the living tropho- 

 zoites to reach the digestive tract of man after they are 

 passed by the pig. This is particularly true when a per- 

 son works with pigs as in the case of a butcher ( Cordes, 

 1921). Cysts are more resistant. Ohi (1924) states that 

 when kept moist at room temperature they will live for 

 2 months; when dried in the shade, i to 2 weeks; and 

 when exposed to direct sunlight, 3 hours. They with- 

 stand bile 15 days ; urine, 10 days ; gastric juice, 12 hours ; 

 5 per cent carbolic acid, 3 hours ; i per cent carbolic acid, 

 4 hours; and 10 per cent formalin, 4 hours (Ohi, 1924). 

 Distribution and localisation within the host. B. Coli 

 must reach its habitat in the large intestine by way of the 

 mouth, stomach and small intestine. It may be ingested 

 either in the trophozoite or cyst stages and is no doubt 

 passively carried through the digestive tract by peris- 

 talsis and other movements of the host. Primary distribu- 

 tion and localization within the host is thus brought 

 about by the host without any effort on the part of the 

 ciliate. Where excystation takes place is not known. It 

 is easy to understand why B. coli becomes localized at 

 first in the large intestine since it has no special means of 



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