PUSTTJLANTS AND CAUSTICS 57 



after some days generally dry up, protecting the parts until 

 the new epidermis forms. Biniodide of mercury, canthar- 

 ides, mustard, acetic acid, turpentine, and ammonia, are the 

 vesicants commonly used in veterinary practice. 



PUSTULANTS inflame the deep-seated cutaneous tissues, 

 especially the orifices of the sweat glands, cause exudation 

 of leucocytes and raise pustules. These are the effects of 

 croton oil, tartar emetic, mercury biniodide ; and also of 

 cantharides, mustard, and other active vesicants, when 

 applied with sufficient friction. 



CAUSTICS combine with the water and albumin of the 

 tissues, with which they are brought into contact, kill the 

 cells, and cause the separation of a slough. Those producing 

 extensive sloughing receive the title of escharotics. Caustics 

 are exemplified by the concentrated mineral acids, glacial 

 acetic, carbolic, and chromic acids, concentrated alkalies, 

 antimony chloride, arsenic, bromine, and the soluble salts 

 of the heavy metals. 



Caustics are used to destroy parasites or virus in infected 

 wounds, and for this purpose penetrating fluid caustics are 

 sometimes preferable to solid. They are employed for 

 opening abscesses, and for removing warts and other 

 growths, especially when so deep-seated and vascular that 

 they cannot be safely extirpated by the knife. (See also 

 Astringents and Styptics.) 



But besides these more direct actions, they develop more 

 complex and vital reparative effects. Applied, for example, 

 to indolent or callous ulcers, they stimulate the trophic 

 nerves and blood-vessels in the zone adjacent to the dead 

 or dying cells, promote healthy nutrition, and thus hasten 

 healing. Lightly used, they condense soft, spongy, exuber- 

 ant granulations, and hasten the cicatrisation of sinuses. 

 These beneficial effects on morbid processes thus result, not 

 only from direct action on the diseased tissues, but also 

 from indirect reflex action on surrounding parts ; in other 

 words, from counter-irritation. 



SETONS are sometimes substituted for blisters or firing, and 

 are frequently preferred to firing on account of their being 

 less apt to blemish. The seton consists of a piece of tape 

 or cord, and is usually inserted by means of a seton needle. 



