BALANTIDIUM COLI I SPECIFICITY 



This may be due not to the short length of association 

 between the two but to the infrequency of the associa- 

 tion; thus a period that has been long enough to bring 

 about an apparently harmless association in the pig may 

 not have been sufficient to accomplish this result in man 

 and monkeys. The life-cycle of B. coli is not fully known, 

 but there seems to be nothing peculiar about it that might 

 account for the weak host-parasite specificity of this 

 ciliate. 



187 



