154 CHAPTER 17. 



Though in a far less degree than mineral, Vegetable tonics are power- 

 ful for good or for evil, and the effects which they are producing require 

 to be carefully watched. 



305. Blisters. 



Blisters, by means of their irritant action, produce inflammation of the 

 true skin, and as a result, effusion of the watery parts of the blood. 

 This effusion appears in the form of vesicles or blisters, which raise up 

 the cuticle from the skin underneath. 



Blisters are used either as local stimulants ; or as irritants with a view 

 of causing an altered, and it may be a healthier action; or as counter- 

 irritants. 



When the first or mere stimulant action is desired, the blistering 

 liquid is applied sparingly. By such stimulation more blood is brought 

 to the part affected, and increased action is the result. With this view 

 blisters are applied to indolent wounds and ulcers, to parts from which 

 the hair has fallen off, and to the coronet in order to stimulate the 

 growth of the hoof. When an irritant effect is desired, as in some cases 

 of sprains of tendons or ligaments, the blistering liquid is applied more 

 freely. When increased irritation is sought for, the liquid is applied 

 freely over a considerable extent of surface. 



The agents in use for the purpose of producing stimulation or irrita- 

 tion are of various degrees of severity, from the temporary superficial 

 redness caused by simple friction to the deep and severe action of the 

 actual cautery. 



Irritants, under which are included all classes of blisters, are much 

 used in Veterinary practice, and are so important that we deem it neces- 

 sary to devote a separate chapter to the consideration of their action and 

 uses, to which the reader is referred for further information on this 

 subject. See Chapter 19. 



306. Caustics or Eschar otics. 



Caustics act by chemically decomposing solid tissues and the fluids. 

 This action destroys the vitality of the part. They are therefore much 

 used in cases of unhealthy granulations, otherwise called proud flesh. 



Although they destroy the structure with which they come in imme- 

 diate contact, yet they cause irritation and increased action in the adja- 

 cent parts. Hence they are often made use of for the cure of indolent 

 wounds and ulcers. 



Some of them possess the property of uniting with albuminous matters, 

 which renders them effectual in coagulating blood and thus stopping 

 haemorrhage, and likewise in producing an eschar or scab over painful 

 or irritable sores or wounds. 



Caustics differ much in intensity. Those in common use are nitrate of 

 silver, otherwise called lunar caustic, bluestone or sulphate of copper, 

 sulphate of iron and zinc, sulphuric and hydrochloric acids, arsenic, 

 corrosive sublimate, terchloride of antimony, and the hot iron or actual 



