The peculiar powers of opium are represented chiefly in the morphine which it contains. In opium of good quality the proportion of morphine is from ten to fifteen per cent. The actions of the other principles contained in opium differ widely; and as they all possess some activity, the sum of their effects must so far influence the result that the powers of opium and morphine must vary somewhat in kind as well as in degree. One sixth of a grain of morphine is about equivalent in activity to one grain of average opium.

In general terms, it may be stated that morphine differs from opium in the following respects:

Morphine is less stimulating, less convulsant, and more decidedly hypnotic and anodyne than opium.

Morphine constipates less and affects the contractility of the bladder more than opium.

Morphine has less diaphoretic action and produces much more pruritus than opium.

The physiological action of morphine is best studied as administered subcutaneously. In a short period—from a few seconds to a few minutes—after the insertion of an ordinary dose—one sixth to one fourth of a grain—under the skin, the symptoms of morphine narcosis begin. A sense of heat and flushing of the face—after, in most subjects, a very transient pallor—fullness of the head, giddiness, tinnitus aurium, and frequently nausea, are experienced. Deep-seated epigastric pain is often felt, and loud borborygmi occur. The vertigo may be so considerable as to render walking uncertain and staggering, or to render the upright position impossible. Injection of the conjunctivae and contraction of the pupils occur at the same time the cerebral effects are experienced. The lips have a bluish appearance, the mouth and tongue become dry, swallowing is painful, and the voice has a husky tone. When these physiological effects are produced, pain and spasm are relieved, and an indescribable feeling of content takes possession of the mind. A condition of somnolence in many persons, in others of extreme wakefulness, with intense mental activity, is experienced. When sleep occurs, it is usually deep but not calm, the respirations are slow, noisy, and labored. Not infrequently the sleep is disturbed by dreams and visions, or the individual passes into a somnambulistic state, from which he is aroused with difficulty. The action of the heart is diminished in frequency, but a decided rise takes place in the arterial tension. On ophthalmoscopic examination, a marked increase in the vascularity of the retina, and blurring of the papillae, can be discerned.

Soon after a hypodermatic injection has been practiced, itching of the nose, and often of the whole cutaneous surface, is experienced. The skin is at first dry, but, after a time, diaphoresis begins and is sometimes profuse. The relaxation of the skin is coincident with a fall in the arterial tension. The secretions of the mucous surfaces are at first arrested, as well as those of the skin. If the morphine be administered after a full meal, digestion is suspended for a time. The intestinal movements are also arrested for a short period, and constipation is therefore produced; but, very frequently indeed, no change takes place in the time in which the alvine discharges occur, or in their number. Partly in consequence of the increased action of the skin, the quantity of urine discharged is lessened, and, at the same time, difficulty is encountered in its emission. When the desire is felt, an interval of less or greater duration elapses before the flow begins, and, as the contractile power of the bladder and of the ejaculatory muscles is diminished, the discharge is feeble and slow, and the last drops linger in the urethra.

With the decline of morphine narcosis a majority of subjects, probably, experience headache, confusion of mind, anorexia, and nausea.

When a lethal dose of morphine has been administered by any mode, profound narcotism quickly ensues; the pulse becomes slow and feeble, or rapid and feeble; the respirations also become very slow and shallow; the skin cold and sweating; the face pale, cyanosed, and ghastly; the conjunctivae deeply injected; the pupils minutely contracted, and reflex movements entirely abolished. Respiration ceases before the action of the heart, as a rule, but in some instances very sudden death ensues from paralysis of the heart.

Half a grain is the smallest dose of morphine which has proved fatal to an adult. Five cases, according to Taylor, have been recorded in which one grain of the muriate caused death.

A consideration of the symptoms produced in man by morphine, and the results of experiments on animals, prove that it chiefly affects the cerebro-spinal functions. In the lower animals, the spinal more; in man, the cerebral more than the spinal functions. Morphine first raises and afterward lessens the action of the heart and arteries; first stimulates the pneumogastric end-organs and cardiac motor ganglia, and afterward paralyzes both. It causes death chiefly through paralysis of the muscles of respiration.