Substances whose application diminishes the force of cohesion in the
particles of the solid matter of the human body, and thereby renders
them more lax and flexible.
According to this definition, which we derive from Dr. Cullen, the
primary operation of emollients would appear to be purely mechanical,
for they are insinuated into the matter of the solid fibre, and either
diminish its density, or lessen the friction between its particles; this
explanation will undoubtedly apply to those emollients which consist of
unctuous bodies, and which are introduced into the animal fibre by
friction; but it is evident that the beneficial effects of _Cataplasms_
and _Fomentations_ cannot be so explained; for in these instances, none
of the materials can be absorbed through the entire cuticle; and yet the
relaxation and consequent ease which such warm applications produce on
inflamed surfaces is very considerable, but it must be wholly attributed
to the relaxing effects of warmth and moisture upon the extreme vessels
of the surface, propagated by _contiguous sympathy_ to the deeper seated
organs.
The operation of those substances which afford relief to excoriated
surfaces by their bland qualities, as mucilaginous lotions in
erysipelatous affections, is too obvious to require explanation.
Having thus investigated the manner in which medicinal substances
produce their effects upon the living system, we shall be better
prepared to appreciate the advantages which are to be derived from their
combination with each other, and to escape the too common error of
uniting in one formula, remedies which are rendered adverse by the
incompatibility of their physiological actions.