Opium is the chief member of the second division of Narcotics, which consist of medicines that, in their action on the heart, are about intermediate between Stimulants and Sedatives, and in their secondary action, on the intellectual functions produce in them, the condition of sleep (p. 239.) Opium produces at first some stimulation, and exhilaration of the mind, with a full pulse, and general febrile excitement. This soon subsides, and is succeeded by drowsiness and sleep. Large doses cause slowness of the pulse, slow and difficult breathing, and coma. If a small dose of Opium be continually repeated, the stimulant action may be maintained for a time, and the Narcotic effect prevented. But whenever it is taken habitually, the dose will require to be gradually increased, or the desired effect will not be produced, for the system is induced by degrees to tolerate the remedy in larger and larger quantities. Given in moderate doses, it powerfully relieves pain, and controls nervous irritability. Though it always tends to produce sleep, its anodyne effect may take place without its soporific action. It is useful in the painful inflammations of the serous and mucous membranes. But it tends to cause congestion of the brain. It should thus be generally avoided in brain-disorders; and, on account of its primary stimulant action, it should only be very cautiously used, or altogether avoided in cases of high fever, where there is a hot dry skin, or a full and hard pulse. The system may sometimes be prepared for it by antiphlogistic treatment; or Tartar Emetic or Ipecacuanha may be conjoined with the dose of Opium. Ipecacuanha and Opium are combined in Dover's powder. Opium is a Diaphoretic; but it diminishes all the other secretions, and most especially that of the bowels. In the treatment of fevers and inflammations it is often combined with Calomel, for the purpose of preventing the latter from passing out by the bowels, and of allaying at the same time the nervous excitement and pain.