The distribution upon this continent, and especially in the -United States, of the endemic form of dysentery is, at present, difficult to estimate. If we ac cept this variety as synonymous with tropical and amcebic dysentery, a much closer study of the disease than yet made will be necessary in defining the limits of its prevalence. Cases have been re ported from Maryland, Massachusetts, Pennsylvania, Texas, Ohio, Alabama, and Georgia. But it seems probable that many of the so-called sporadic cases oc curring in this country, and, perhaps, not a few of the epidemic ones, may be shown to be of this kind. With the exception of the investigations of the disease car ried out in Egypt, Germany, Austria, and Italy, the American cases above referred to have been the most thoroughly studied.
The epidemic form of dysentery is oftenest confined to a single locality, a village or a town, with no extension to the country around. Instances are not rare in which the epidemic attacks a single detached establishment, such as a prison, a hospital, a poor-house, a sol diers' barracks, or, under certain circum stances, a ship, while there are no cases of dysentery outside these, or merely oc casional cases (Hirsch). It happens much more rarely that the disease achieves a greater diffusion, and most rarely do pandemics arise. Mention has already been made of the prevalence of dysentery as an epidemic disease, espe cially in earlier historical times. Great epidemics have not appeared in recent years. The countries which have been most severely visited are Italy, France, Ireland, Denmark, and Norway and Swe den. In the United States, dysentery in an epidemic form, except during the War of the Rebellion, has not in late years reached serious proportions. According to Woodward, it prevails annually among the civil populations in all parts of the United States. It occurs both in the form of sparodic cases and of small local epidemics which fasten upon different districts in different years.
Sporadic dysentery, which is distin guishable both from the endemic and the epidemic forms, is of very uncertain oc currence. This variety of dysentery is attributed by Kartulis to the action of mechanical and chemical irritants upon the intestine, and arises as a secondary condition in the course of other diseases, such as acute, infectious, and chronic dis eases of the heart, kidneys, and liver. By most writers the occasional cases of dysentery met with in all countries arc included under this term.
Various telluric conditions have, from time to time, been supposed to influence the prevalence of dysentery. Of late years the search has been made for micro organisms to the action of which the disease might be attributed. With what success this line of investigation has been pursued will be stated in other parts of this article. It is a well-known fact, and one borne out by the best statistics, that both the epidemic and the endemic forms prevail especially during the hot seasons. Great diurnal variations of temperature —warm days and cold nights—have been supposed to predispose to the develop ment of the disease, but in Egypt the facts observed are in direct opposition to this view. The degree of atmospheric moisture seems without influence: Hirsch states that, of 126 epidemics of dysen tery, 65 occurred during moist weather and 61 during continued drought. The elevation and configuration of the sur face seem also without particular signifi cance, although low-lying and marshy localities are more subject to visitations than high and dry ones.
There is good reason to believe that the dissemination of the virus of dysen tery takes place, in large part, through the water. And, although the same con clusive evidence of water-infection has not been brought for this disease as has been brought for cholera, yet there are many convincing observations at hand which bear out this belief. Numerous outbreaks both of the endemic and epi demic varieties, among troops and in habitants of towns, have been traced di rectly to contaminated drinking-water; and the replacement of the polluted by a wholesome supply has been quickly fol lowed by a cessation in the spread of the disease. Observations which indicated a more contagious character, a transmis sion from person to person, are not want ing. But whether, in these instances, the virus may not have been carried. by water, wash-linen, or food is not certainly known.
The demonstration of parasitic organ isms bearing an etiological relation to dysentery has been done certainly only for the endemic variety. Several differ ent bacterial organisms have been de scribed in association with the epidemic dysentery. The proof of their essential causal relationship with the disease has yet to be brought. The several micro organisms will be considered with their respective diseases.