Chemical Agents. 53 



ides, quicklime, barium chloride), the corrosive salts of the heavy 

 metals (salts of antimony and mercury, zinc chloride, zinc sul- 

 phate, chromate of potassium, etc.), the poison of the beetle Lytta 

 vcsicatoria, cantharidin, snake venom, the poison of the sting glands 

 of bees, wasps and hornets, the salivary secretion of gadflies, 

 stinging flies and mosquitoes, and the so-called acria or acrid medi- 

 caments derived from a number of plants (croton oil, mezereum, 

 etc.). A number of poisons, volatile or gaseous in form, may 

 also cause dermal or mucous membrane irritation, especially to 

 the lining of the respiratory tract during inhalation (irrespirable 

 gases). Should these irritant and corrosive substances be ab- 

 sorbed and be conveyed by the lymph paths into the blood and 

 internal organs, they may cause, in addition to their local effects, 

 associated disturbances of the heart and nervous system, the liver 

 and kidneys. Substances inducing degenerations of these paren- 

 chymatous organs may be spoken of as parenchymatous poisons, 

 their effects depending chiefly upon alterations of tissue meta- 

 bolism, regressive nutritive changes and formation of precipitates 

 in the tissues. Among this group phosphorus belongs, capable 

 of causing extensive fatty degeneration of tissues, especially the 

 liver. Corrosive sublimate, chromic acid, cantharidin, which pro- 

 duce marked changes in the renal parenchyma, are also irritants. 

 The production of argyria, the impregnation of the tissues with 

 minute black particles of silver after long continued administration 

 of nitrate of silver, may be thought of as a similar process ; 

 and lead is an excellent example of parenchymatous poisons, 

 producing, as it does, a wide range of disturbances, palsies, de- 

 generations and both local and general pathological results. 



The so-called hccmic poisons act principally by depriving the 

 red blood corpuscles of their power to act as conveyors of oxy- 

 gen, by inducing their disintegration, liberating and breaking up 

 haemoglobin or causing thrombosis. Some in addition may cause 

 lesions at the point of introduction, and perhaps directly influence 

 the nervous system. Some of them are gases entering the blood 

 through inhalation, others are in solution and are derived per- 

 haps from the intestine or from wounds. The best known blood 

 poison is carbon monoxide, a constituent of illuminating gas, 

 which enters into combination with haemoglobin to form carbon- 

 oxyd-haemoglobin, and thus prevents absorption of oxygen by the 

 blood and induces a tissue asphyxia. A characteristic feature of 

 CO poisoning is the bright, cherry-red color of the blood. Sul- 



