The influence of opium upon the different organs and functions of the body may be thus enumerated:

On the Digestive Organs; it impairs appetite and the digestive process, causes thirst, diminishes the secretions from the whole mucous membrane, and induces constipation.

On the Brain and Nervous System the action of opium is most powerfully exerted, as is shown in the primary exaltation of the mental faculties and the subsequent sleep and coma; the pupils of the eyes become contracted, even to a point, when the patient is powerfully under the influence of the drug; the spine is sometimes affected, and tetanic symptoms occur, especially when opium is given to the lower animals, in whom the cerebral effect is less marked.

On the Vascular System; opium acts at first as a stimulant and then as a sedative, probably both effects are induced through the medium of the nervous system; when given in small doses, frequently repeated, the force of the circulation can be kept up for a long time.

On the Cutaneous System; opium causes free perspiration, an effect for which the drug is often prescribed, and which is much increased by combination with ipecacuanha, camphor, etc.

On the Secreting and Excreting Organs, with the exception of the skin, the effect of opium is to lessen their activity: the bile is diminished, as is seen in the pale-coloured faeces; the urine often becomes scanty, and also the saliva and buccal mucus.

On the Respiratory System, opium produces a sedative effect, diminishing the frequency of the respirations, and hence impairing the oxidation of the blood.

On the Sexual System, opium acts as a stimulant, especially in males, and has been employed in Eastern countries as an aphrodisiac.

Applied to the skin opium appears to possess some power of allaying pain, and is often added to fomentations. When the cutis is denuded, the opium and morphia salts become absorbed and produce constitutional effects. Applied also to the mucous membrane of the rectum in the form of suppository or enema, not only the local but the general symptoms of the drug are produced.

Opium is perhaps more extensively used than any other drug, and of such value is it, that it has been called the "gift of God" to man. It may be employed to allay pain and spasm, occurring in almost any condition of the system, as in the varieties of neuralgia, colic, during the passage of renal or biliary calculi, in tetanus and inflammations of various kinds; in short, pain, from whatever cause arising, is usually advantageously treated by opium.

In Inflammation it is given not only to assuage pain and spasm, but to control the disease; opium seems to have some power over the capillary circulation, which is advantageously made use of after depletion; perhaps this may be exercised through the medium of the nervous system; it is very commonly given, combined with calomel, in cases of inflammation, where it is valuable, not only for the influence it exerts over the disease, but also from its preventing the mercurial salt from running off by the bowels. Opium is given with tartar emetic, in several forms of inflammation. In inflammation of mucous membranes, opium may or may not be useful; when the air passages are affected, opium should be cautiously administered: but when the intestinal tube is involved, as in dysentery, its property of checking secretion and allaying irritability is of much value.

In Fevers opium may be sometimes used when nervous symptoms, as tremor and watchfulness, occur, attended with deficient power of the vascular system; it should always be given in small doses, and the effects watched. In intermittent fevers, or agues, opium sometimes suffices for the cure, when given before the time of accession of the cold stage; but there are other remedies which possess greater antiperiodic powers, without the narcotic properties; opium, however, may be occasionally used in intermittent cases with advantage.

In diseases of the Nervous System, when attended with increased vascular action, opium is generally injurious; but when there is defective power of the circulation, as in delirium tremens, and allied affections, then the value of this drug becomes very evident.

In Haemorrhages, opium is often useful, especially when there has been much loss of blood, and consequent arterial excitement; whether the drug is a direct astringent to the vascular system is doubtful; it is usually combined in such cases with acetate of lead, and gallic acid.

In Mucous Discharges, opium is often of service, especially in diarrhoea; sometimes also in leucorrhaea, etc.; but the condition of the system must be the guide to the administration of the drug in these cases; certain forms of ulcers, of a phagedaenic character, or occurring in very weak subjects, are greatly improved by the influence of this remedy.

In Urinary Diseases, to lessen the amount of urine, if excessive, as in diabetes; and to allay the irritability of the bladder, occurring in many affections of the urinary organs, opium is employed with advantage.

In Chest Affections, this drug should be used with caution; it often allays the cough; but when the respiratory function is seriously impaired, increased dyspnoea is sometimes produced by it; opium tends to diminish the expectoration, an effect at times desirable, but often injurious.

Opium is used in the form of suppository in painful diseases of the rectum and bladder, and chordee; also as an enema in similar cases. It may be applied to the skin in the form of fomentation, over painfully inflamed joints and other parts; and as a liniment or plaster in neuralgic, rheumatic, or other diseases.

Circumstances influencing the operation of Opium.

Age has great influence; children are much more affected than adults; much more than in proportion to the age; and opium must be given with the greatest care to infants and young subjects.

Certain individuals are peculiarly susceptible of the action of opium; and in some, great excitement and restlessness are produced, instead of calmness and sleep.

The presence of Disease often gives a resisting power to the influence of this drug, especially when great pain is present.

Custom or habit has perhaps the most marked influence on its action; by gradually increasing the dose, enormous quantities may be taken without any very evident effect being produced; the want of the drug in such cases is, however, most severely felt. The author knew a young man who took 60 grains of Smyrna opium night and morning, and frequently, in addition to this, 1 fluid ounce to 1 1/2 fluid ounce of laudanum during the day. If the drug be discontinued, and after a time the large dose at once resumed, poisoning may occur.

Action of Morphia Salts. Morphia appears to possess the anodyne and soporific powers of opium, and gives to the drug most of its valuable properties; at the same time it, as a rule, acts more agreeably, having less tendency to produce headache and nausea; it also is much less stimulant in its operation. Other substances contained in opium must impart to the crude drug some of its power, for although only about 10 per cent. of morphia exists in good opium, yet the alkaloid has not more than four times the strength. The different salts of morphia act in the same manner, when estimated by the amount of the alkaloid contained in them.