CHAPTER IV 



INTESTINAL INFUSORIA 

 I. Balantidium colt 



I. MORPHOLOGY 



Balantidium coli (Fig. i8), which lives in the large 

 intestine, is the only ciliate known with certainty to be 

 an inhabitant of man. It is very large compared with 

 other human protozoa, ranging from 30/1 to 200^1 or more 

 in length and from 20/x to 70/i in breadth. The usual 

 range in size is 50/ito 70/zlong by 40/x to 6o/twide. This 

 extraordinary range in size may be due in part to herita- 

 bly diverse races as regards size but is more probably 

 the result of the presence of specimens in various stages 

 of growth. The organism seems very little modified by 

 its parasitic habit being very similar in structure to 

 Paramcecium caudatum. It is in general oval in shape, 

 but broader at the posterior end and more pointed at the 

 anterior end. Cilia emerge from minute basal granules 

 beneath the cuticle; cover the entire surface; and are 

 arranged in parallel rows. Near the anterior end is a 

 funnel-shaped cytostome, which can be expanded and 

 contracted and into which food particles are driven by 

 the surrounding cilia which are longer than on the rest 

 of the body. An excretory pore, the cytopyge, is located 

 near the posterior end. The cytoplasm is separated into 



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