COUNTER-IEEITANTS 703 



The hair should be clipped from an area to be blis- 

 tered, the skin washed with soap and water, and the animal 

 tied up or restrained in some way from biting the part. It 

 is the custom to cover immediately the surrounding parts 

 with grease, but protection from the acrid discharge can be 

 secured more effectively by frequent sponging with soap 

 suds and water; or painting the skin, under the blistered 

 surface, with a solution of resin in alcohol. Grease is not 

 so good a protective, since it is a solvent for cantharides. 

 Vaseline should be applied following the active stage. 



Caustics or Escharotics are agents which destroy tissue. 

 They comprise such substances as the caustic alkalies, min- 

 eral acids, silver nitrate ; iron, zinc and copper sulphates ; 

 ferric, zinc and mercuric chlorides ; carbolic acid, arsenic, 

 together with the actual cautery. They are indicated in the 

 treatment of exuberant granulations, moibid growths, septic, 

 sloughing and necrotic parts, pyogenic membranes, fistulous 

 tracts, and for the destruction of poisons, as in rabid dog and 

 snake bite. Escharotics stimulate and modify nutrition in 

 unhealthy wounds and ulcers. Many form chemical com- 

 pounds with the tissue elements. Heat oxidizes animal 

 tissues, and also coagulates albumin and abstracts water 

 from them. 



The alkalies produce greasy compounds with the pro- 

 teids, sapouify the fats and withdraw water from the tissues. 

 They are the most widely destructive agents. Silver nitrate 

 forms an insoluble albuminate with the tissues to which it is 

 applied, and protects the underlying structures from further 

 action. It is most superficial in its action, but possesses 

 specific properties in altering the condition of unhealthy 

 wounds for the better. Extreme heat, exemplified by the 

 white-hot iron, acts as a counter-irritant in stimulating 

 reflexly the nervous system ; in increasing the vascularity of 

 surrounding parts, and in favoring revulsion of blood ; in 

 aiding absorption and resolution, and in relieving pain apart 

 from its direct destructive effect. Caustics may be applied 

 in either the solid or liquid state, and in various forms, as 



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