It has been a subject of popular inquiry, how far the habitual use of Snuff may prove beneficial or injurious; and whether the habit, when once fully established, can be discontinued with impunity? It may be remarked that Snuff, by habitual use, soon ceases to produce the effect of an Errhine, for which reason its discontinuance cannot, generally, be regarded as likely to be attended with any danger; in those cases, however, in which the discharge is perpetuated, a contrary judgment should be pronounced, for all artificial discharges become constitutional by long continuance, and can therefore be seldom checked with impunity. Dr. Cullen states, from experience, that “whenever the nasal discharge has been considerable, the laying aside the custom of taking snuff has been productive of evil.” EPISPASTICS. _Vesicatories._ _Blisters._ 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. Blisters may act— 1. AS DERIVATIVES, i. e. _by producing a derivation of the circulation from the inflamed and engorged vessels of the neighbouring organs to the blistered surface_. This mode of operation was long overlooked by the physicians, who ascribed all the beneficial effects of a blister to the evacuation which it produced, while the humoral pathologist, moreover, considered the matter so discharged to be of a morbific nature. That such agents owe their salutary tendency to causes independent of their powers as evacuants, is at once rendered evident by the relief which they afford, when used only as Rubefacients.