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. ON THE THEORY AND ART OF PRESCRIBING. “_To know “That which before us lies in daily life, “Is the prime wisdom._” MILTON. ON THE THEORY AND ART OF PRESCRIBING. OF MEDICINAL COMBINATION. “_Variorum mixtura novas sæpe vires generet, in simplicibus nequaquam reperiundas longe saluberrimas._” GAUBIUS.