This class of medicinal agents formerly comprised a much wider range of
forms than it at present contains; such as numerous _Epithems_;
_Vapours_; _Aromatic Bags_; _Medicated Quilts_, _&c._
The external remedies of the present day may be divided into two orders,
viz.
1. Those whose effects are entirely _local_, as exemplified in the
application of certain _refrigerating_ embrocations, _stimulating_
cataplasms, and _astringent_ unguents.
2. Those which excite general effects, or produce an influence upon
parts remote from those to which the remedy is more immediately
addressed, as illustrated by the operation of mercurial liniments
and unguents, or by the general tonic effects of adhesive
plaisters.
With respect to the former of these divisions it is unnecessary to
multiply our remarks; the objects which they embrace belong more
particularly to the department of surgery, and from the investigation of
the different modes and forms of external application we shall hereafter
derive very ample and instructive illustrations. In considering the
objects of the latter division, a very interesting and important
question immediately suggests itself for our consideration—How far a
medicinal substance, when locally applied to the surface of the body,
may be capable of affecting the general system, or some of its more
remote parts?—the experienced practitioner will feel no hesitation in
admitting numerous proofs of the existence of such agency; and it would
seem probable that topical applications may produce general effects by
several distinct modes of operation, viz.