This constitutes by far the most obscure part of the subject of medicinal combination, and must ever continue so until we become better acquainted with the laws which govern the action of medicinal substances upon the living system. That the most valuable effects, however, are really produced by such arrangements, we have the testimony of long experience, and examples are furnished in the valuable and well-known operation of many officinal preparations; thus the “_Pulvis Ipecacuanhæ compositus_” contains as its active elements, _Opium_ and _Ipecacuanha_; and yet, in well regulated doses, it neither possesses the narcotic operation of the former, nor the nauseating effects of the latter; they appear to be mutually lost, and converted into a powerful diaphoretic: so again, the emetic operation of _Sulphuret of Antimony_, and the specific influence of _Calomel_, are changed by combination with each other, giving rise to a remedy eminently distinguished for its powers as an alterative. Dr. Bree observes that _Tincture of Squills_ combined with _Extract of Henbane_, and the _Nitric Acid_, have been proved by much experience to be expectorant and sedative in a paroxysm of asthma, although each article, uncombined, had been given without success. See _Form. 139_. The efficacy of _Hemlock_, in quieting Pulmonary irritation, has been frequently adverted to in the course of this work; I have to state, in this place, that its value, on such occasions, is generally enhanced by combination with _Ipecacuanha_.