This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol1", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
On the secretions its influence is especially worthy of notice. Most of them are diminished by it, perhaps all occasionally; but some are at times promoted, and one, that, namely, of the surface, generally so. The mucous secretion is almost invariably diminished. Hence, in part, the remarkable dryness of the mouth, nostrils, and fauces, which characterizes the action of opium. The same deficiency probably exists throughout the alimentary canal, contributing to the thirst which is among its prominent symptoms. There is often also a feeling of dryness in the conjunctiva from the same cause. The secretion of the salivary glands is certainly diminished, and probably that also of the pancreas. The secretory function of the liver is much impaired by a continued use of the medicine, as may be known by the light-coloured passages from the bowels. This I have very often noticed; and it is one of the effects which the physician will have most frequently to counteract. There can be little doubt that a single dose produces a proportionate effect. The kidneys are variously affected. In the greater number of instances their secretion is diminished, especially when the patient is warm in bed; but I have sometimes known it to be powerfully promoted, particularly by the salts of morphia. Indeed, I have seen few diuretics act more copiously than this for a short time; and the effect generally takes place in the course of the first hour or two after the administration of the medicine. It is most apt to occur when the skin is kept cool.
The diaphoretic effects of opium are well known. I seldom, however, witness this effect when the patient is walking about. When he is warmly covered in bed, it is extremely common; and sometimes the discharge is profuse. It docs not usually come on until the patient has slept for some time, and is most copious towards the end of the period of sleep. It is very common to awake in the morning bathed in sweat. This diaphoretic property is greatly increased by the addition of ipecacuanha.
The itching sensation in the skin which opium is apt to produce may be referred to in this connection. It is sometimes attended with prickling, and may occur in any part of the body. It is often very annoying to the patient, and may even prevent sleep. In some instances, it is attended with a miliary, erythematous, or urlicarious eruption; but this effect is relatively rare; at least I have seldom noticed it.
The stomach may be at fast moderately excited by opium; but the effect soon ceases, and is followed by a marked diminution of its function. The appetite is diminished, and the digestion impaired. These effects may be ascribed perhaps in part to a diminution of the secretion of gastric juice and mucus; but are probably mainly dependent on a want of the accustomed influence from the nervous centres, and the diminished call for food from the nutritive function.
The bowels are generally constipated. This is among the most constant effects of opium, though it is not invariable. It probably depends on different causes, among which may be mentioned the diminished secretion of bile, of pancreatic liquor, and of mucus, and the diminished supply of chyme from the stomach; but the chief cause is probably a deficiency of influence from the organic nervous centres, through which the muscular coat becomes enfeebled, and, as it were, partially paralyzed.
The activity of the nutritive process is much diminished; and consequently less food is required. This is much more obvious from the habitual use of opium, than from a single dose; but there can be no doubt that the latter produces the same effect in a proportionate degree. It docs not follow that emaciation must take place. On the contrary, the body often retains its weight, and sometimes even gains under the continued use of the drug, if not taken in great excess. This is explained by the consideration, that the normal disintegration of the tissues is diminished equally with nutrition, and even in a greater degree.
Not only the voluntary muscles, and those of the alimentary canal, suffer a diminution of their power in the second stage of the action of opium, but those of the bladder also, so that there is occasionally some difficulty in passing the urine from this cause; but the effect is seldom obvious, unless from very large doses.