ENDEMIC (from en, among, and demos, the people), a term applied to diseases which affect numbers of persons shnultaneously, but so as to show a connection with locali ties as well as with their inhabitants. Endemic diseases are usually spoken of as con trasted with epidemic (q.v.) and sporadic (q.v.); the first term indicating that a disease infests habitually the population within certain geographical limits, and also that it is incapable of being transferred or communicated beyond those limits; while, on the other hand, a disease is termed epidemic if it is transmitted without reference to locality; and sporadic if it occurs in isolated instances only. The theory, accordingly, of E. diseases it, that they are in some way or other connected with the soil—the result of terrestrial influences, or poisons generated within the earth, or near its surface, and diffused through the air, so as to be weakened in proportion to the dis tance from the source of the poison. Such poisons are always observed to be more virulent in summer than in winter—more dangerous at night, when the vapors are concentrated on the surface of the soil, than in the day-time—more abundant in the plains, and in close confined places, than at a certain degree of elevation—more easily carried in the direction of the wind than in the opposite—and very often arrested altoo.ether by water, or by a belt of forest or other luxuriant vegetation. In all these 9 particulars, endemic are different from epidemic diseases, which bear no very obvious relation to the soil, end are not observed to be considerably modified either by the prevailing winds or the period of the day or night at which exposure to their influence takes place. The most marked type of an endemic disease is ague (q.v.) or intermittent fever, which has all the habits mentioned above, and is to so marked a degree a denizen of particular tracts of country as to lead to their being in some instances almost depop ulated. Many places in Italy are a prey to the aria cattiva or malaria, as it is popularly
called; and hence, no doubt, even more than for protection from human foes, the cus tom so prevalent in that country of building the villages on the tops of hills, so as to secure immunity from the poisonous vapors raised by the solar heat from the plains lying on either side at the base of the Apenn ines. Terrestrial miasms, or such poisons as generate E. diseases, are usually found in the neighborhood of marshy flats, or of uncultivated tracts of land at the confluence of rivers, or where a delta, or a wide chap nel subject to overflow, is formed at the upper end of a lake. In proportion, too, as the heat of the sun is greater, the tendency to nialarious emanations is increased; and in the tropics, accordingly, large tracts of jungle and forest are often rendered absolutely uninhabitable and almost impassable at certain seasons, by the invisible and odorless germs of intermittent, remittent. and even continued fevers (q.v.), which are more fatal and unmanageable than the most terrible epidemic pestilence to those who are exposed to them. Such diseases arc almost always sudden in their mode of attack, and they indicate the range of their influence by the number of persons attacked; but they are wholly free in most eases from the suspicion of communication by contagion (q.v.), which is so frequent in the case of epidemic diseases. The precise nature of the mala rious poison has never yet been discovered with any approach to exactness. It is known, Howeyer, to be almost invariably checked by drainage and cultivation of the soil; and hence many places in Europe, formerly very productive of E. diseases, have now ceased to be so, as in the. case of the Tuscan Maremina, and some parts of Kent and Essex, and of the Lothians in Scotland.