GENERAL ACTIONS 473 



depressed the lower reflex centres are free and unchecked. 

 Opiates kill by respiratory arrest. Medicinal doses are 

 analgesic and antispasmodic, diminish the several secre- 

 tions, excepting those of the skin, and, in combination 

 with other drugs, are sometimes used as calmatives for 

 horses and dogs. They are frequently applied locally to 

 relieve irritability and pain, but experimentally it has 

 been found that they have no effect on either sensory or 

 motor nerve-endings, so that local application is of little 

 value. 



GENERAL ACTIONS. When administered by the mouth, 

 opiates slightly augment the secretion of the salivary and 

 gastro-intestinal glands with which they are brought into 

 contact. Full doses cause some amount of gastric irritation, 

 occasionally producing vomiting in man and dogs (partly 

 by central action), but shortly, and more notably and per- 

 manently, they diminish gastro-intestinal secretion and 

 movement. 



After absorption, full doses induce primary, usually brief, 

 stimulation, followed by depression and paresis of the central 

 nervous system. In veterinary patients the prominent 

 phenomena are agitation, unrest, inco-ordinate, generally 

 manege, movements, diminished sensibility to pain, indis- 

 position for voluntary movement, and, in toxic doses, con- 

 vulsions, coma, and death by respiratory arrest. Moderate 

 doses dilate the blood-vessels of the skin and quicken heart 

 action, and this is more notable in horses than in man. But 

 repeated full doses slow heart action in all animals. Moder- 

 ate doses affect respiration and render it shallow, slow, and 

 then irregular. The rectal temperature is temporarily 

 raised ; skin temperature from increased transpiration is 

 reduced ; but lethal doses, depressing the heat-producing 

 centres, eventually lower the general temperature. Opium, 

 morphine, and narceine diminish all secretions excepting 

 those of the skin and kidneys, their effect on the latter organs 

 being variable. By lessening reflex activity, and depressing 

 all sensory nerve cells, they are notable antispasmodics. 

 The effect on the iris varies in the different animals. In 

 man the pupil is typically contracted to pinhole size. In 

 the horse and cat it is dilated throughout, whilst in the 



