Our views as to the etiology and epidemiology of bacillary dysentery have been fairly definite for at least twenty years, while those relating to amoebic dysentery, notwithstanding the important researches of Kartulis, Councilman and Lafleur, Schaudinn and others have remained rather chaotic until quite recently. _The Term Dysentery._—By the term dysentery we understand a symptom-complex of more or less characteristic stools and more or less characteristic pains. As a rule the stool is composed of one or more teaspoonfuls of greenish yellow or dirty brown mucus, the altered blood being intimately admixed with the mucus, or we may have a whitish to grayish muco-purulent mass with streaks or flecks of blood on the outside. These mucoid masses may be found suspended in serous, sanguineous or more or less feculent discharges which are usually small in amount and passed with much frequency. The terms tormina and tenesmus are the ones used to designate the characteristics of the pains of dysentery, tormina for the griping colicky pains, which center about the umbilicus or run in the direction of the large intestine, and tenesmus for the painful spasmodic contractions of the sphincter ani to which is due the sensation of lack of ability to complete the act of defecation leading to straining and justifying Manson’s description “glued to the commode.” It is usually stated that the nearer the dysenteric process is to the rectum, the greater the tenesmus and the nearer to the caecum, the greater the tormina. THE MODERN CLASSIFICATION OF DYSENTERIES IS BASED ON ETIOLOGY RATHER THAN UPON CLINICAL MANIFESTATIONS Owing to the great importance of the two main kinds of dysentery, amoebic, or that caused by _Entamoeba histolytica_, and bacillary, or that caused by some strain of _Bacillus dysenteriae_, we shall consider them separately from the other causes of the dysenteric symptom-complex. =A. Dysenteries caused by animal parasites.= _Protozoal dysenteries._ 1. Amoebic dysentery (_Entamoeba histolytica_). 2. Flagellate dysenteries (_Lamblia intestinalis_, _Trichomonas intestinalis_ and _Chilomastix mesnili_). While in adults these intestinal flagellates usually cause only a diarrhoea, with at times marked nervousness, they may produce dysenteric symptoms in young children. The onset in children under three years of age may be insidious and attended with fever. The stool contains much mucus with only a little blood.