External applications to the skin, which produce a serous or puriform
discharge, by previously exciting a high state of inflammation.
When these agents act so mildly as merely to excite inflammation,
without occasioning the effusion of serum, they are denominated
RUBEFACIENTS.
Various substances have at different times, been proposed for the
accomplishment of this object,—such as _Nitric Acid_, _Boiling Water_,
_Strong Acetic Acid_, _Tartarized Antimony_, &c. It is, however,
generally admitted, that no substance ever employed equals in efficacy,
or certainty, the _Cantharis Vesicatoria_, the common blistering, or
Spanish fly; and whose effects may serve to illustrate the _modus
operandi_ of this class of remedies.
By the application of a _Blister_, the extreme blood vessels are excited
into increased action, by which inflammation is occasioned, and the
exhalants made to pour out a thin serous fluid which separates the
cuticle from the true skin, and forms a vesicle or blister.
From this simple view of the subject it will appear evident, that
blisters may produce their salutary effects by several different modes
of operation; by a just estimate of which the practitioner will be
enabled to reconcile the discordant opinions which have been delivered
upon the subject, and to employ these agents with greater satisfaction
and advantage.