or Ague, is characterized by this, that the febrile paroxysm is followed by a period of intermission, again succeeded after a certain interval by the febrile stage; the period of intermission and the febrile stage recurring at certain intervals, so long as the disease lasts. Ague displays itself under three distinct forms,—1st, Quotidian, in which the fever passes through its stages, and recurs again every 24 hours; 2d, Tertian, having a period of 48 hours; and, 3d, Quartan, having a period of 72 hours. In the Quotidian the feverish paroxysm begins early in the morning; in the Tertian about noon, and in the Quartan, from three to six in the afternoon. When the disease is fully formed, each feverish attack consists of three stages, the cold, the hot, and the sweating. The cold stage commences with a sense of coldness running down the back, the whole body feels cold, the nails turn blue, the features collapse, and the skin assumes the rough shrivelled appearance usually induced by cold; severe shivering, with chattering of the teeth, rapidly follows and continues for a considerable time, attended with a painful sense of constriction round the temples, aching pains in the back, and frequently with sickness and vomiting. This stage, after a period lasting from half an hour to two hours and a half, is followed by the hot stage, during which the pulse rises, the skin becomes hot and parched, there is intense headache, thirst, and other symptoms of high fever: this stage lasts from three to eight hours. Gradually a gentle moisture appears on the skin, which soon amounts to copious perspiration; and the sweating stage, after continuing for a varying period, is followed by a complete remission, during which, excepting a sense of weakness, the patient feels as if restored to perfect health.

Agues are peculiar to all undrained localities, and are virulent or dangerous apparently just in proportion to the warmth of the country. In Britain, before the general drainage and improvement of the soil ague was one of the regular diseases; but now it is quite rare, being only occasionally met with in some undrained localities. In all countries it chiefly manifests itself during the autumn, when the great heat of the sun raises malarious exhalations from the undrained soil. This malaria may be carried by currents of air to great distances; and many instances are recorded where ships' crews, many miles from the African coast, have been struck down with ague from encountering a current of air blowing off the marshy coast. Formerly the treatment of this disease gave great trouble, but since the discovery of the alkaloids which reside in the Peruvian barks, its treatment has been greatly simplified, as it is found that these alkaloids, given at certain intervals, not only cure the disease, but that, if administered to those exposed to the malarious exhalations, they prevent the attacks of the disease altogether. Quinine is the best known of these alkaloids, but it has been found that the other alkaloids in the Cinchona barks, viz., cinchonine and quinidine, are equally efficacious, while they have the additional recommendation of being considerably cheaper. Five grains of any of these alkaloids every third hour, till three doses are taken, generally suffices to remove mild cases of ague. In malarious districts, however, it is desirable to continue to take at least one dose daily for a short time to prevent a relapse. In severe cases doses of 15 or even 20 grains are often given with great advantage. In some old or obstinate cases, or in which quinine has not been given in sufficiently large doses, arsenic has been found a valuable agent. When the disease is not checked, it leads to various organic alterations of the organs, which it is unnecessary to particularize; it may only be mentioned that the chief of these consists of enlargement of the spleen, well known in malarious districts by the name of ague cake. Those who have once suffered from this disease are extremely liable to a recurrence of the paroxysms on exposure to wetting, to east winds, or to malarious exhalations.