the application or medicinal powers of the substance in question. The term PHARMACOLOGIA, as applied to the present work, may therefore be considered as contradistinctive to that of PHARMACOPŒIA; for while the latter denotes the processes for _preparing_, the former comprehends the scientific methods of _administering_ medicinal bodies, and explains the objects and theory of their operation. The articles of the Materia Medica have been arranged in alphabetical order, not only as being that best calculated for reference, but one which, in an elementary work at least, is less likely to mislead, than any arrangement founded on their medicinal powers; for in consequence of the difficulty of discriminating in every case between the primary and secondary effects of a medicine, substances very dissimilar in their nature, have been enlisted into the same artificial group, and when several of such bodies have, from a reliance upon their unity of action, been associated together in a medicinal mixture, it has often happened that, like the armed men of Cadmus, they have opposed and destroyed each other. The object and application of the black marginal letters, to which the name of _Key Letters_ has been given, are fully explained in the First Part of the work, and it is hoped, that the scheme possesses a more substantial claim to notice than that of mere novelty: it will be perceived that in the enumeration of the officinal formulæ these letters are also occasionally introduced, to express the manner in which the particular substance, under the head of which it stands, operates in the combination. If any apology be necessary for the introduction of the medicinal formulæ, it may be offered in the words of Quintillian, who very justly observes, “_In omnibus fere minus valent præcepta quam exempla_;” or in the language of Seneca; “_Longum est iter per præcepta, breve et efficax per exempla_.” Under the history of each article, I have endeavoured to concentrate all that is required to be known for its efficacious administration, such as, 1. _Its sensible qualities._ 2. _Its chemical composition_, or the constituents in which its medicinal activity resides. 3. _Its relative solubility in different menstrua, and the proportions in which it should be mixed, or combined with different bodies, in order to produce suspension, or saturation._ 4. _The Incompatible Substances_; that is to say, those substances which are capable of destroying its properties, or of rendering its flavour or aspect unpleasant or disgusting. 5. _The most eligible forms in which it can be exhibited._ 6. _Its specific doses._ 7. _Its Medicinal Uses, and Effects._ 8. _Its Preparations, Officinal_ as well as _Extemporaneous_. 9. _Its Adulterations._ That such information is indispensible for the elegant and successful exhibition of a remedy, must be sufficiently apparent; the injurious changes and modifications which substances