MAN INFECTED FROM PIGS 267 



bowed or kidney - shaped, and a small, spherical 

 micronucleus (Fig. 50, A, b) is somewhere in its 

 neighbourhood, often in contact with it. The organ- 

 ism possesses two contractile vacuoles for the excre- 

 tion of liquid waste, but no permanent cell anus 

 exists. When the Balantidium is removed from the 

 intestine, it often contains numerous drops of mucus, 

 and sometimes red blood-corpuscles have been seen 

 within it. The multiplication is brought about by 

 simple division of the free forms into two, and the 

 division is not repeated until these two are full 

 grown. At times conjugation occurs. Spherical 

 thick-walled cysts (Fig. ,50, B) also are formed, and 

 with motile forms are found in stools of dysenteric 

 patients. Balantidian dysentery at one time was 

 common in the Philippine Islands, where amoebic 

 dysentery also was rife, and they still occur there. 



Balantidium coli is a constant parasite of pigs, in 

 which it does not seem to do much injury, but 

 from the pigs it can reach man. Numerous cysts 

 are found in the pigs' excrement, which is used in 

 the cultivation of the land. The cysts thus get 

 scattered, and can contaminate both water-supply 

 and vegetables and fruit, whence the parasites reach 

 man. If the recipient of the cysts is thoroughly 

 healthy, no harm may accrue. But if the intestine 

 be at all deranged, the parasites produce further 

 irritation and penetrate the epithelium and lie in 

 the layers below it, looking very like Entamceba 

 histolytica. It is of interest to note that some strains 

 of Balantidium coli are less virulent than others. 

 Balantidium minutum is about one-fifth the size of 



