As opium is a very complex substance, made up of numerous principles which differ remarkably among themselves, it will conduce to a better understanding of its actions to consider, first, opium as a whole, and then follow with some details regarding its individual constituents.

The physiological effects of opium are best studied as respects—1, small medicinal doses; 2, full medicinal doses; 3, lethal doses.

1.   The preparations of opium have a disagreeable, bitter, and. rather nauseous taste. Dryness of the mouth and fauces, huskiness of voice, and diminution in the sense of taste, occur in a short time after administration of the drug has begun, and continue during the whole period of its influence. To the dryness succeeds a viscid secretion, which contains excrementitious matter having a foul odor. When opium does not produce nausea, the appetite may not be impaired, may be even increased; but the rule is that the desire for food is lessened by opium. The secretion of mucus, and of the special glandular apparatus of the gastro-intestinal mucous membrane, is lessened by opium, and hence the digestion and the peristaltic movements are less active. The excretions being thus locked up, dullness and hebetude are experienced, the skin looks muddy, the tongue is coated, and the breath is offensive. When the influence of the opium ceases, it not infrequent-ly happens that the constipation is succeeded by relaxation of the intestines, and rather profuse and fetid evacuations, and increased urinary discharges, take place.

The action of the heart becomes stronger, and the arterial tension rises. When opium agrees, the sense of fatigue vanishes, and muscular movements become more rapid and easy. The face flushes a little, the pupil contracts slightly, the conjunctivae may be somewhat injected, and the expression of the eye more brilliant. At this stage the ideas flow more rapidly, but are less sustained and orderly. The appreciation of time, the sequence of events, and the sense of moral fitness, are diminished. The cerebral excitement is, after a period which varies in different individuals, succeeded by calm, by drowsiness, and sleep when it occurs is usually disturbed by visions and dreams, often of a frightful character. In most subjects, after the sopor has passed off, headache, vertigo, confusion of mind, nausea, constipation, and muscular hebetude, are experienced.

2.   When full medicinal doses are administered, the symptoms above described occur in a more intense degree. The stage of cardiac stimulation and of cerebral excitement is of much shorter duration; and the stage of intoxication and sopor not only comes on more quickly, but is much more pronounced. At first the pulse is increased in frequency and the respiratory movements are more rapid; but the cardiac pulsations soon diminish in number and force, and the respirations become sighing in character and more shallow. There is also present decided dryness of the mouth, fauces, and larynx, and swallowing becomes somewhat difficult and the voice grows husky. Nausea and vomiting, or at least weight and oppression of the epigastrium, ensue. Confusion of ideas, vertigo, somnolence, are succeeded by deep sleep, contracted pupils, slow and relaxed pulse, slow and snoring respirations, a perspiring skin, and, in many persons, an intense general pruritus, which, however, is more harassing at the nasal orifices.

Persons not habituated to the use of opium usually experience, after a full medicinal dose has expended its force, very distressing sequelae, referable to the cerebro-spinal system. The most important of these after-effects are headache, confusion of mind, vertigo—which is especially severe on assuming the erect posture—nausea, retching and vomiting, complete anorexia, and constipation. A mild but defined hepatogenic jaundice not infrequently occurs, and the urine is tinged with the coloring-matter of the bile.

3. A lethal dose of opium causes but a transient excitement; the stage of narcosis quickly supervenes, and the functions of animal life are often rather abruptly suspended. The patient soon lapses into a condition of insensibility, with a slow and feeble, or, it may be, rapid and feeble, action of the heart; slow respiration, shallow and quiet or stertorous; face at first flushed, but soon becoming shrunken, pallid, and cyanosed; skin wet; pupils minutely contracted and insensible to stimulation; unconsciousness profound, with muscular relaxation and abolition of reflex movements. This state of opium narcosis is with difficulty distinguished from alcohol narcosis, from cerebral haemorrhage —especially in the pons—and from uraemic coma. An attentive consideration must be given to all available facts in the history of the case, to the surroundings of the patient, and to the odor of the breath or other excretions, for the symptoms of one of the states above mentioned may be represented in another, even to the inequality of the pupils, since a case of opium narcosis has been reported in which such inequality existed.

There are no characteristic structural alterations produced by opium. The brain presents the appearance known as the "wet brain" by pathologists; the subarachnoid spaces and the ventricles contain an abnormal quantity of serum; the intra-cranial veins are engorged, and the puncta vasculosa are somewhat more numerous. The right cavities of the heart and the large venous trunks are usually distended with soft coagula. These appearances are largely due to the mode of dying. In consequence of the diminishing frequency of the respiratory movements, the blood is imperfectly decarbonized, and the capillary circulation of the lungs is impeded. The action of the heart being weak and the resistance a fronte increased, it is obvious that venous stasis must take place.

It is necessary now to consider somewhat more minutely the nature and degree of the action of opium on the different organs and systems of the body. It will save space and avoid repetitions to study these actions in connection with the several principles contained in opium.