430 PRUSSIC ACID 



ated on a platinum capsule it leaves no residue. Seheele's 

 acid, which is frequently used in veterinary practice, 

 contains four per cent, of hydrogen cyanide. 



ACTIONS AND USES. Prussic acid first briefly stimulates 

 and then paralyses all nerve structures with which it comes 

 into contact. A few drops of the diluted acid applied to 

 mucous or skin surfaces diminish or arrest sensation. It is 

 hence used as an analgesic for relief of irritation and pain, 

 especially of the skin, stomach, and throat. It is quickly 

 absorbed. Full doses paralyse the cerebro-spinal axis, kill 

 almost instantaneously by cardiac arrest, or somewhat 

 less suddenly by respiratory arrest. 



GENERAL ACTIONS. It stops protoplasmic movements 

 both in plants and animals, kills infusoria, checks oxidation, 

 and arrests fermentation (Brunt on). The anhydrous acid 

 applied to the skin, after momentary irritation, paralyses 

 and anaesthetises. The diluted acid applied to the skin or 

 mucous surfaces quickly penetrates and paralyses the nerve- 

 endings, impairing and destroying tactile sensation and 

 sensibility to pain. If the surfaces are freely moistened, 

 these effects usually continue for one or two hours. Its 

 volatility and rapidity of diffusion ensure quick absorption, 

 and poisonous doses promptly paralyse the central nervous 

 system. In moderate doses after absorption the primary 

 stimulant action is seen. Respiration becomes quicker and 

 deeper ; the heart beats slower from vagal stimulation, 

 but blood-pressure rises from the general vaso-constriction. 

 In a short time this stimulation passes into depression, 

 respiration becomes slow and weak, blood-pressure falls, 

 and the heart becomes progressively weaker. The further 

 effects depend on the dose. If small, the volatile drug 

 becomes diffused and excreted and recovery takes place. 

 When a large dose has been given, the respiratory, vaso- 

 motor, and spasm centres of the medulla, and the peripheral 

 afferent nerves, are early and notably affected ; and in all 

 mammalia death usually occurs within a few minutes. 

 When poisoning is not immediate, the central nervous 

 system is affected ; there is giddiness, staggering movements, 

 and a few slow inspirations, followed by rapid expirations 

 and irregular heart action ; convulsions, coma, anaesthesia, 



