Before quitting the present subject, it deserves notice, that there is frequently a _chemical_ condition of the stomach that may interfere with the mild operation of a medicine, and may therefore require consideration: this is particularly exemplified in the action of those antimonial preparations which are liable to become emetic and drastic by the presence of an acid; it is, for this reason, very eligible to guard such substances with antacid adjuncts. See _Antimonii Sulphuretum_, and _Form. 125, 128_. There is also, upon some occasions, an irritable state of the _primæ viæ_ depending upon a deficient secretion of mucus, which renders even small doses of any active medicine mischievous; mucilaginous decoctions in such a case will offer the readiest _corrigent_; see _Scammonia_. The vinous infusion of _Colchicum_ appears to act more violently when acid is present in the stomach; small doses of _Magnesia_ may therefore precede, and accompany its exhibition, with advantage. III. TO OBTAIN THE JOINT OPERATION OF TWO OR MORE MEDICINES. A. _By uniting those substances which are calculated to produce the_ SAME ULTIMATE RESULTS, _although by totally different modes of operation_. It has been already stated, (_page 152_), that we may frequently combine substances together whose modes of operation are dissimilar, with considerable advantage, provided they be not physiologically incompatible with each other. We may illustrate this subject by a reference to the operation of purgatives; a series of medicinal substances may be produced, each of which has the property of exciting catharsis, but by a very different mode of action; one for instance stimulates the muscular fibres of the intestines; a second acts upon the exhalant vessels, and mucous glands; and a third exerts its influence upon the neighbouring organs, so as to produce an increased flow of their secretions into the bowels; but since such modes of action are quite compatible with each other, they may be simultaneously established, not only without any loss of efficacy, but with the most decided advantage; suppose, for instance, we administer a substance which, either from its insolubility or peculiar nature, acts exclusively upon the muscular fibres of the alimentary canal, its peristaltic motions will be undoubtedly thus increased, and the contents of the bowels evacuated, but the operation will be slow, and probably accompanied with considerable _tormina_; now it is evident that if to such a remedy we add those which can produce an increased flow of serous fluids, the effect will be both quicker and easier. _The infusion of Senna_ is thus quickened and corrected by _Soluble Tartar_. In the same manner various substances included in the class of diuretics, which, although different, still if they be not adverse in their operation, may be conjoined; _Digitalis_ and _Potass_ are not similar, nor are they