BALANTIDIUM COLI 89 



0. ranarum, being more like a barrel in shape. It is much rarer 

 than the other two. All three varieties are furnished with numerous 

 similar, small, round nuclei (fig. 26, c). 



Although the Opalina are of most frequent occurrence, two other 

 much smaller Infusoria are sometimes met with in the intestine of 

 E. temporaries and E. esculenta. They are Balantidium entozoon and 

 Nyctotherus cordiformis (fig. 26, a and b), which belong to the order 

 Heterotricha, and are closely related to the intestinal Infusoria of 

 man. This order is characterized by the possession of a uniform 

 covering of similar cilia and by an " adoral zone/' a row of larger 

 cilia or membranelles, which runs along the peristome from the 

 anterior extremity of the parasite to its oral opening. In Nycto- 

 therus the mouth continues as a long cytopharynx, and the adoral 

 zone is prolonged to its end. The arrangement and the movements 

 of the cilia should be noted, as well as the action of the contractile 

 vacuoles, of which Nyctotherus possesses one, while four are present in 

 B. entozoon (not represented in fig. 26, a). In Nyctotherus there is also 

 a short anal tube, situated at the posterior end, close to the contractile 

 vacuole. The macronucleus in Nyctotherus is bean-shaped and the 

 micronucleus lies close to its hinder concave surface. In Balantidium, 

 it is round, and is, as a rule, easier of detection, being situated within 

 the curve of the macronucleus, which is very much bent, varying in 

 shape from that of a kidney to that of a horse-shoe. 



Cover-glass preparations of the whole organism are fixed in alcoholic 

 solution of mercuric chloride and stained with haematoxylin, counter- 

 staining with eosin. The finer details, such as the insertion of the 

 cilia and the structure of the nucleus, are only to be seen in sections, 

 which should be stained with iron-hsematoxylin. 



(b) Balantidium coli. 



Opportunities for the study of the parasitic Infusoria of man are 

 rare in this country. B. coli, the best known of these and, on account 

 of its pathogenic significance, the most important, is principally found 

 in the north-east of Europe. Occasionally, though this is rare, fresh 

 material may be obtained in East Prussia. There is a Balantidium, 

 however, which is invariably present in the rectum of swine and 

 which is so similar to the parasite found in man, that the two 

 organisms have, up to now, been considered identical. 



The rectum should be tied at both ends before removal and it 

 should be taken from the carcase immediately after slaughter. It 

 should be wrapped in a thick cloth to prevent cooling during transit 

 from the slaughter-house to the laboratory, and the examination 

 should be made as soon as possible certainly upon the same day. 



