BALANTIDIAL DYSENTERY 589 



Balantidium (Paramecium) coli 



This is an intestinal parasite of swine, occasionally met with in 

 man in conditions associated with chronic diarrhoea and dysentery. 



Balantidial dysentery is very like amoebic dysentery, both 

 clinically and pathologically, and differential diagnosis is possible 

 only by microscopical examination of the stools. 



Bal. coli is a relatively large ovoid organism averaging 50 p to 

 70 /x in length, though larger and smaller individuals occur. The 

 body is invested with a delicate membrane and is relatively rigid 

 though capable of passive distortion. The membrane appears to 

 be striated owing to the presence of cilia which are set at an angle 

 to the surface and which they entirely cover. A small funnel- 

 shaped mouth, with longer cilia, is situated subterminally on the 

 ventral surface at the more pointed anterior end of the body, and 

 a pore or anus is sometimes visible at the posterior end (Plate 

 XXIII, u). Two contractile vacuoles are present in the cyto- 

 plasm one near the middle of the dorsal surface, and the other 

 near the posterior end. Two nuclei are situated at about the 

 centre of the body, a large kidney-shaped macronucleus and a 

 small spherical micronucleus lying in the concavity of the macro- 

 nucleus. The organism undergoes encystation ; the cysts are 

 smooth, thick-walled, spherical, or slightly ovoid, measuring 35 

 to 60 fj. in length. Both cysts and free forms are present in 

 numbers in the freshly passed faeces in balantidial dysentery. 



Ciliates resembling Balantidium may occur in water and saline 

 used in diluting faeces for examination, and must not be mistaken 

 for the organism. 



Class III. Mastigophora 



These are protozoa in which one or more permanent organs 

 serving for locomotion or food capture are present in the form of 

 flagella. As a rule the body is limited by either a cuticle or a 

 differentiation of the protoplasm into a firmer external portion or 

 periplast. One, two, or more flagella may be present, and when 

 multiple are arranged in various ways. Food-vacuoles may occur 

 in the protoplasm, also contractile vacuoles, but not in the para- 

 sitic forms. Various other granules, including chromatophores , 

 which generally contain chlorophyl, may be present. The nuclear 

 apparatus is usually double, consisting of a large principal or 



