Whilst the respiratory movements of the chest are impaired through the centre, so that they become feeble and tend to cease, the afferent nerves of breathing - that is, the branches of the vagus arising in the lungs and passages - are also depressed. Thus reflexion is dulled or arrested at its very origin, and dyspnoeal excitement (hyperpnoea), cough, spasm, and other reflex respiratory acts are rendered more difficult or altogether prevented. At the same time, the bronchial secretions are diminished or inspissated by the action of the drug upon the glands, and the activity of pulmonary circulation is lowered with the general blood pressure, and by the weakening of the respiratory movements. The total effect of opium upon the respiratory functions is thus powerfully depressant.

The biliary and glycogenic functions of the liver are affected by morphia, which causes pale stools or even jaundice, and remarkably diminishes the amount of sugar in diabetes. Hepatic and general metabolism is reduced in activity, the amount of urea and probably of carbonic acid excreted being distinctly diminished. The temperature rises for a time, and then falls, apparently varying with the blood pressure.

4. Specific Uses

The hypnotic and anodyne effects of opium constitute it by far the most valuable drug of its kind, and the most im-portant article of the whole materia medica. It is constantly employed to induce sleep, relieve pain, and calm excitement; this combination of properties giving opium a great superiority to chloral and other simple hypnotics, on the one hand, and to aconite, belladonna, quinine, and other direct or indirect anodynes, on the other hand. Speaking broadly, it is used in sleeplessness due to pain; in the insomnia of exhaustion, overwork, fever, or insanity; and in the restlessness and anxiety of visceral disease; the quantity, combinations, and time of administration being carefully arranged. In delirium chloral is often preferred, especially in delirium tremens; hut opium is more suitable in the delirium of mania, and in the later stages of fevers, when the temperature is falling and the respiration and circulation are not oppressed. It has been recommended, however, in heat-pyrexia, combined with quinia.

There are but few kinds of pain that cannot be relieved by opium; hut whether it be wise to administer it in every instance is another question. The unbearable pains attending the passage of renal and biliary calculi, the pains of neuralgia, acute rheumatism, and cancer; of fractures, dislocation, and other injuries, area few examples of conditions in which opium is essential. In all cases when pain is urgent, and its seat accessible, the hypodermic method should be chosen. In gout it is to he used only when the pain is excessive, as it tends to aggravate the cause. In hysterical pain it is less valuable. Other local visceral pains will be noticed presently. The pain and shock of operations are constantly treated with a full dose of opium.

No use is made of the action of opium on the iris and ciliary nerves.

As an antispasmodic, opium is less employed for various reasons, e.g. in epilepsy and other convulsive diseases; hut it relieves some cases of spasmodic asthma, whooping-cough, and spasmodic stricture of the urethra.

The violent spasms and pains of certain diseases of the cord may yield to no other form of treatment than morphia injected hypodermically.

From its action on the medulla, opium has been recommended as an antidote to belladonna, which is so far its physio-logical antagonist, as we shall see (page 198); hut it must always be used with great caution, and only in the stage of excitement.

The practical points connected with the vital centres will be noticed under the heart, vessels, and respiration.

In disease of the heart, opium is of great value to relieve pain, anxiety, and distress, whilst, as we have seen, it is a dangerous cardiac depressant. Towards the end of most cases of cardiac disease, the greatest discrimination is called for as to when opium may or may not he given. The safe rule is to trust to other anodynes entirely, such as belladonna, direct and indirect stimulants, and measures for relieving the circulation; but it is equally true that in some cases of heart disease un-speakable relief and permanent benefit may be obtained by the hypodermic injection of morphia. This subject must be studied in books on the practice of medicine.

From its soothing effect upon the vessels and circulation generally, opium is a haemostatic of the first order, but requires to be used with judgment. In haemoptysis, it is given in small doses, to relieve cough, to depress the circulation slightly by Blowing and weakening the heart and dilating the vessels, and to relieve the mind of the anxiety which aggravates the bleed-ing. In intestinal haemorrhage it is of great value, arresting, as it also does, the movements of the bowel. It is best given combined with lead or preparations containing tannic acid.

The soothing influence of opium on the bronchi, lungs, the afferent nerves, and the centre of respiration, accounts for its extensive employment in cough, pain, dyspnoea, and other dis-tressing symptoms in the chest. Its power here is unquestion-able; but for this very reason the danger of it is great. Cough and dyspnoea are frequently beneficial acts, and are not to be arrested in a routine fashion by sedatives, but, if possible, by the removal of their cause. When cough is due to some irre-movable condition, such as growth in the lung or bronchi, pressure, or a remote (reflex) irritation, or to excessive irrita-bility of the nerves and centre, opium is indicated, and may be given with benefit. On the other hand, in cough and respira-tory distress with abundant secretion, as in the bronchitis of the old and infirm or of the very young and feeble, opium leads to retention and inspissation of the products, aggravation of the cause, and asphyxia, and is on no account to be given. Between these extremes lies every variety of case in which opium may suggest itself, e.g. in phthisis and recurrent bronchial catarrh. The rule here should be on no account to prescribe opium unless other means have failed, such as the many expectorants, and attention to food, warmth, etc.; and that, when given, opium must be ordered in small doses com-bined with expectorants, such as ammonia and ipecacuanha, which will prevent dangerous depression of the local nerves and centres. In acute inflammation of the pleura, or pleuro-pneumonia, it may be necessary to relieve severe pain in the chest, harassing cough, sleeplessness, and mental distress by morphia hypodermically. For asthma, opium must be ordered with the greatest hesitation, as the opium habit is readily acquired in this disease. Its employment in haemoptysis has been already noticed.