200 



PROTOZOAN PARASITISM 



that the pig is the main source of spread. It is also 

 a parasite of the intestine of monkeys. 



It is transferred in the encysted phase from the 

 feces of swine, probably of man, and possibly of mon- 

 keys, to man by ingestion of contaminated sub- 

 stances or, perhaps, directly from hand to mouth. 



Fig. 31. — Balanfidium coli. 



Drawings of trophozoite and cj'st from specimens stained by iron- 

 haematoxylon. x 550. 



Balantidium coli is a large organism, by compari- 

 son to other alimentary tract protozoa, the original 

 description of Malmsten giving it a size of 60 to 100 

 microns long by 50 to 70 microns wide, small and large 

 forms occurring in individual infections, according 

 to Craig (1926). 



It is roughly pearshaped, the narrower end being 



