_Opium and opiates._--There seems to be no agreement among experimental physiologists regarding the manner in which opium produces its effects upon the body. By some it is ranked as a stimulant; by others it is considered a sedative. These different opinions are probably due on the one hand to differences in the dose and strength of the opiates employed, and on the other to idiosyncrasies on the part of the individuals subjected to experiment. The soporific effect of the drug appears to result from its direct action upon the substance of the brain. Under its influence the blood tends to accumulate in the veins, and loses its bright arterial hue. Small doses are said to contract the capillaries of the body, while they are dilated by excessive doses of the drug. From this it may be inferred that opium acts, like many other narcotics, as an irritant of the tissues when given in minute quantity, and as a paralyzing agent when a certain relative amount is exceeded. The experiments of Curci[47] indicate that under the influence of irritating doses of morphia the brain becomes hyperæmic. Opium is a remarkably complex substance, no less than nineteen different alkaloids having been separated from it. Of these, however, only one has stood the test of therapeutical experiment--morphia. Several other constituent alkaloids, notably _codeia_, have been lauded as hypnotics, but they are, at their best, far inferior to morphia, and may well be omitted from the list of sleep producers. But, though the soporific properties of opium are chiefly due to the morphia which it contains, there are certain points of difference between the action of the two medicines that often render a choice desirable. According to Stillé and Maisch,[48] morphia does not stimulate circulation and the nervous system as much as opium, and its narcotic effects are less decided and speedy, though its after effects are more enduring. Opium increases the bodily temperature and sense of heat; morphia produces the last effect, but diminishes the temperature. Opium at first increases the frequency of the pulse, while morphia diminishes it. Opium is of the two the less liable to excite nausea and vomiting; hence the superiority of the tinctures and aqueous solutions of opium when nausea is specially feared. Of all the remedies for the relief of pain opiates are the most effectual. Before the introduction of the alcoholic hypnotics and the bromides, they constituted the principal agents in the treatment of insomnia. Even at the present time they are indispensable for the relief of all forms of sleeplessness dependent upon pain. A combination of chloral hydrate, sodium bromide, and morphine forms one of the most generally useful hypnotic compounds ever employed.