OPIUM. 191 



The action of opium upon the centres of several of the 

 viscera has been partly described under the previous heads. In 

 addition to this, it depresses the afferent (including the sensory) 

 nerves of all organs, and acts upon many of the viscera 

 directly. 



The heart is temporarily accelerated by opium, in part 

 through the cardiac centre, in part through its intrinsic 

 ganglia. Thereafter, or with fuller doses, it is slowed by 

 stimulation of the vagus in the medulla and heart. Finally, 

 the cardiac vagus is depressed or paralysed; but by this 

 time the intrinsic ganglia are so depressed that acceleration is 

 impossible, and the action remains infrequent, whilst very 

 feeble. Very rarely death occurs by sudden cardiac failure. 



The vessels, dilated through the centre, as described, are 

 not directly influenced by opium, either in their muscular coats, 

 or in their peripheral nerves. 



Whilst the respiratory movements of the chest are im- 

 paired 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 

 dyspnoea! excitement (hyperpnrea) , 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 ano- 

 dynes, on the other hand. Speaking broadly, it is used in 



