550 CLASSIFICATION AND MORPHOLOGY OF AMEBA 



color. They are not elevated but rather depressed, and contain 

 necrotic material in their interior. Such foci are also found in the 

 depth of the liver tissue, not reaching up to the surface. In these 

 areas, as in the cecal pouches, large numbers of amebae are found. 

 According to Smith's observations these are very numerous in the 

 affected tissues in recent cases or when the disease is at its height. 

 They disappear, however, from areas where degenerative and necrotic 

 changes are much advanced. The most frequent appearance pre- 

 sented is that of round homogeneous bodies with a sharply defined 

 single contour. Within the parasites situated a short distance away 

 from the centre is a group of minute granules probably representing 

 nuclear chromatin. The Amoeba meleagridis is generally between 

 8 to 10 micra in diameter, sometimes between 12 to 14 micra. The 

 tissue reaction against the invading protozoa leads to the formation of 

 giant cells, and the parasites are often seen in their protoplasm. This, 

 however, is a process of phagocytosis on the part of the tissue cells, 

 because the Amoeba meleagridis is evidently not an intracellular 

 parasite, but it penetrates between the cells, which it destroys by the 

 intercellular invasion. The life cycle of this organism has not yet 

 been studied. 



BALANTIDIUM COLI. 



The subphylum infusoria is not of great importance as far as 

 microorganisms pathogenic to higher animals and men are concerned. 

 From what is known today, there is one infusorium which may produce 

 disease in man and which is frequently a parasite in the intestines of 

 the hog, from which it probably occasionally invades the large intes- 

 tines of man. This infusorium is the Balantidium coli. It can 

 generally be obtained for the purpose of study in the intestinal con- 

 tents of the hog. The organisms belong to the subphylum infusoria, 

 class ciliata, order heterotrichida, family bursaridse. Infusoria 

 possess cilia as a motor apparatus and a macronucleus and micro- 

 nucleus. The members of the family to which balantidium belongs 

 generally have a short, pocket-like body. Their chief characteristic 

 is a peristome, which is not a mere furrow, but a broad, triangular, 

 deeply excavated area, which ends at a point at the mouth. 



The body of Balantidium is oval or egg-shaped. It possesses a 

 short gutter or funnel-shaped peristome which is continued into a 

 short esophagus. The body is externally lined by a fine skin or 

 pellicula, under which an alveolar ectoplasm is found. The whole 

 exterior is covered by fine cilia. The entoplasm is cloudy and contains 

 droplets of mucus and fat. In it two contractile vacuoles are also 

 situated. The anus of the infusorium is indicated by a prominence 

 in the protoplasm. It is, however, always fused except during the 

 act of expelling waste material. The macronucleus is kidney- or 

 bean-shaped, and contains much chromatic material. The micro- 



