1. By exciting an impression on the nervous system.
2. By modifying the cuticular discharge.
3. By being absorbed into the circulation.
In considering the different forms of external applications, it will appear that, for their extemporaneous construction, preparation, and application, the same scientific knowledge, practical skill, and pathological acumen will be required, as we have already stated to be so indispensably requisite to enable the physician to prescribe, and the pharmaceutist to prepare the various remedies intended for internal administration; although in regard to the former, it may be stated generally that the prescriber will more frequently be called upon to exercise that species of knowledge and address which enables the practitioner to impart a convenient and efficient consistency to his remedy; for an external application is far more dependent upon this circumstance for its efficacy, than one intended for internal use.
LOTIONES:
Remedies of a liquid nature, designed for external application.
Under this generic term, which strictly signifies a wash, may be comprehended several species of medicines, calculated for the fulfilment of different indications, as Embrocationes, Collyria, Fomenta, Linimenta, &c. In some instances these applications are entirely local in their effects, as where a morbid action of the skin is changed by a stimulating lotion, as exemplified in the cure of Psora by the decoction of Hellebore, or the relaxed vessels of the tunica conjunctiva of the eye, by an astringent collyrium; in other cases, they operate upon parts not in contact with the remedy, through the medium of sympathetic communication, as where cholic and disorders of the bowels are abated by the application of warm fomentations to the surface of the abdomen, or where paralytic affections are relieved by pumping cold water on the part affected.
Embrocationes. These, as the term[[307]] denotes, are compositions of spirit, decoctions, infusions, or other liquids, applied by sprinkling or rubbing them on an affected part.
Linimenta[[308]] are understood to differ from embrocations in consistence, the former being of an oily, or mucilaginous density, which increases their efficacy by imparting a certain emollient power, in addition to their other virtues. In popular language, however, liniment and embrocation are generally considered synonymous terms. They constitute a valuable class of remedies, and the observations which Dr. Percival has offered on their utility well merit the attention of the medical practitioner. “Volatile and antispasmodic liniments are highly useful remedies, and it is to be lamented that external applications of this kind are not more frequently employed, for there is just reason to apprehend that powerful effects might be expected from them in various diseases.” In chronic affections of the viscera, such applications appear highly serviceable, not only from the friction to which they give origin, but from the influence of that species of sympathy which appears to depend upon the mere proximity and continuity of parts, and which, as Sir Gilbert Blane has observed, is particularly displayed “in the containing on the contained parts, as that of the integuments on the subjacent viscera.”
Collyria[[309]].—Liquid applications to the eyes. The Pharmacopœia Chirurgica contains several different formulæ for lotions of this kind, some of which are simply astringent, while others combine also the virtues of a stimulant.