492 GENERAL THERAPEUTIC MEASURES 



degrees of potency. There first appears redness of the skin^ accompanied 

 by some burning or pain (rubefacient action)^ and if the irritation pro- 

 gresses there is a serous exudate poured out into the mucous layer of the 

 skin. This leads to swelling and edema. Greater irritation causes more 

 exudation of serum and an elevation of the epidermis in a circumscribed 

 area or areas, and the formation of blebs or blisters (vesication) . If the 

 irritation ceases at this point, the blisters break open and their contents 

 dry on the surface, covering the parts with a thick scab. Synchronous 

 with vesication we observe a similar process attacking the hair follicles. 

 The hairs are loosened and fall, but as the papillse are usually unaffected, 

 the growth of hair is. soon renewed. The recovery of hair is facilitated 

 by the application of grease to parts. Certain agents cause circumscribed 

 inflammation of the gland orifices of the skin, with the formation of pus- 

 tules (pustulants), as croton oil, aind these create necrosis of the hair 

 papillae, and, therefore, permanent loss of hair. If the irritant is severe, 

 suppuration follows vesication ; or, if an ordinary irritant is applied with 

 violent friction, is covered with a bandage, or placed over an already in- 

 flamed part, the same result happens. The terms referring to the degree 

 of action inherent in agents are as follows : 



1. A rubefacient, causing hyperemia. 



2. A vesicant, or epispastic, inducing blistering. 



3. A pustulant, creating pustules. 



4. An escharotic, or caustic, occasioning death of the tissues. 



The same agent, as has already been pointed out, may produce one 

 or more of these actions according to circumstances. The inner aspect of 

 limbs and the flexures of joints are peculiarly sensitive, owing to the thin- 

 ness of the skin over these areas. If a counter-irritant is rubbed properly 

 into the skin it may penetrate into the mucous layer. 



Reference has been made to the local influence of irritants. We will 

 now direct attention to their remote effect. It is certainly known that 

 irritation of the surface decidedly affects distant organs. Brown-Sequard 

 noted contraction of vessels in one arm when the other was immersed in 

 cold water. Severe burns of the surface are followed by duodenal ulcers. 



The influence of counter-irritants may be partially summed up in 

 reflex action; i.e., the production and conduction of an impulse from the 

 periphery to nerve centres, thereby modifying the nerve functions and 

 blood supply in distant parts. 



The skin is commonly the point of application. It normally is an 

 organ of protection, respiration, secretion and special sense, and, through 

 its medium, a regulator of temperature, responding to such natural stimuli 

 as heat, cold, moisture and dryness. Such an unnatural and considerable 

 stimulation as is produced by counter-irritants consequently creates very 

 sensible alterations in the bodily functions. Extensive counter-irritation 

 causes the breathing to become slower and deeper by reflex stimulation 

 of the respiratory centre, and also by making the respiratory movements 

 more painful, if the application be made to the chest wall. The circula- 

 tion is likewise affected by stimulation of the vagus and vasomotor cen- 

 tres, and both the force of the heart and blood pressure are increased, 



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