DBUGS AOTJNG ON THE SKIN 63 



Caustics, or Escharotics, are agents which, when locally- 

 applied, lead to so great a degree of irritation that the 

 vitality of tissues is destroyed, e.g., nitric acid, caustic potash 

 and the white-hot iron. 



Uses. — Irritants are often called counter-irritants when 

 they are used against (counter) existing irritation or inflam- 

 mation by reflexly causing contraction of vessels in congested 

 or inflamed underlying parts. Thus a blister on the chest 

 leads to contraction of the vessels in the inflamed pleura 

 and relieves pleuritis. • Counter-irritants are, therefore, 

 employed locally to overcome internal congestion and 

 inflammation. Rubefacients are often applied over the 

 whole surface of the body (mustard and turpentine) to dilate 

 superficial vessels and equalize the circulation in colds, 

 chills and internal congestions. Vesicants are used to alter 

 the circulation and nutrition of adjacent parts and to secure 

 resolution and absorption of inflammatory products in joint 

 and periosteal disorders. (For details see Counter-irritants, 

 p. 69 G ) 



(2) Locally contracting superficial vessels. 



Astringents are drugs which, when locally applied, make 

 the tissues drier and denser and lessen secretions. Their 

 action is probably dependent on various factors : partial 

 coagulation of the albuminous fluids of the tissues ; coagu- 

 lation of morbid secretions ; removal of water ; and contrac- 

 tion of the muscular coat of the blood vessels. They are 

 local irritants with the exception of lead acetate and bismuth 

 salts. The astringents are : 



Lead Adrenalin 



Aluminum Tannic acid, and drugs contain- 



Zinc ing it 



Salts \ Silver Hydrastis 



Copper Cocaine 



Ferric Antipyrin 



Bismuth Ether ) On evapora- 



' Hamamelis Methylene chloride ) tion 



Ergot (Cold) 



Styptics, or Hcemostatics, are drugs which arrest hsemor- 



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