While various ciliates may cause a severe type of dysentery it is very exceptional that others than _Balantidium coli_ do so. This oval ciliate is from 60 to 100 microns long by about 50 to 70 microns broad. It is a commensal of hogs and the disease in man is usually found in those having the care of hogs. Infections have been reported from various parts of the world, temperate as well as tropical regions. These ciliates may be found in the faeces of persons apparently well but in such cases symptoms may eventually appear. The parasites multiply in the submucosa and the pathologic process is similar to that observed in the large intestine in amoebic dysentery. The parasite is so large and has such an active motility that it would be impossible to fail to detect it in a microscopic examination of the faeces. Encysted parasites are round. The onset is rather insidious with diarrhoea which may be followed by dysentery. A severe form of anemia may be noted. Ipecac, emetine, arsenic and quinine appear to be of little value in the treatment, but Walker considers the organic silver compounds, as protargol, etc., of value. Methylene blue enemata (1-3000) and 2-grain pills by mouth have been recommended. [Illustration: FIG. 58.—Important pathogenic Protozoa of the intestinal tract. (1a) Motile _E. coli_. Note large amount of peripheral arrangement of chromatin in nucleus. (1b) Encysted _E. coli_. Note larger size than _E. histolytica_ cyst, 8 ring form nuclei and absence of chromidial bodies. (2) Motile _E. histolytica_ from acute dysenteric stool. Note histolytica nucleus with scanty chromatin. (3) Tetragena type of _E. histolytica_ from case of chronic dysentery. Note greater amount of chromatin and central karyosome with centriole. (4a) Preëncysted _E. histolytica_ from carrier. Note small size and heavy peripheral ring of chromatin in nucleus making this feature of chromatin in nucleus similar to the larger _E. coli_. (4b) Encysted _E. histolytica_ from dysentery convalescent. Note small size, 4 ring nuclei and a dark chromatin staining mass, “chromidial body.” (5a and 5b) Motile and encysted cultural amoebae from Manila water supply. (6a and 6b) Oocyst and sporozoite production in 4 spores of _Eimeria stiedae_. (7a and 7b) Oocyst with 2 sporoblasts and oocyst with 2 spores containing 4 sporozoites of _Isospora bigemina_. (8a and 8b) Vegetative and encysted _Trichomonas intestinalis_. (9a and 9b) Vegetative and encysted _Lamblia intestinalis_. (10) _Balantidium coli._ Illustrations of amoebae from Walker—others from Doflein.] 4. There are also dysenteric manifestations noted in the terminal stages of kala-azar (_Leishmania donovani_) and in algid pernicious malaria (_Plasmodium falciparum_). These conditions are taken up under the diseases kala-azar and malaria.