The Public are already in possession of many pharmaceutical compendiums and epitomes of plausible pretensions, composed with the view of directing the practice of the junior, and of relieving the occasional embarrassments of the more experienced practitioner. Nothing is farther from my intention than to disparage their several merits, or to question their claims to professional utility; but in truth and justice it must be confessed that, as far as these works relate to the art of composing scientific prescriptions, their authors have not escaped the too common error of supposing that the reader is already grounded in the first principles of the science; or, to borrow the figurative illustration of a popular writer, _that while they are in the ship of science, they forget the disciple cannot arrive without a boat_. I am not acquainted with any book that is calculated to furnish such assistance, or which professes to teach the GRAMMAR, and ground-work of this important branch of medical knowledge. Numerous are the works which present us with the detail, but no one with the philosophy of the subject. We have copious catalogues of formal recipes, and many of unexceptionable propriety, but the compilers do not venture to discuss the principles upon which they were constructed, nor do they explain the part which each ingredient is supposed to perform in the general scheme of the formula; they cannot therefore lead to any useful generalization, and the young practitioner, without a beacon that can direct his course in safety, is abandoned to the alternative of two great evils—a feeble and servile routine, on one hand, or a wild and lawless empiricism, on the other. The present volume is an attempt to supply this deficiency: and while I am anxious to ‘catch the ideas which lead from ignorance to knowledge,’ it is not without hope that I may also be able to suggest the means by which our already acquired knowledge may be more widely and usefully extended; and, by offering a collective and arranged view of the objects and resources of medicinal combination, to establish its practice upon the basis of science, and thereby to render its future career of improvement progressive with that of the other branches of medicine; or, to follow up the figurative illustration already introduced, _to furnish a boat, which may not only convey the disciple to the ship, but which may also assist in piloting the ship herself from her shallow and treacherous moorings_. That the design however of the present work may not be mistaken, it is essential to remark that it is elementary only in reference to the art of prescribing, for it is presumed that the student is already acquainted with the common manipulations of pharmacy, and with the first principles of chemistry. When any allusions are made to the processes of the Pharmacopœia, they are to be understood as being only supplementary, or as explanatory of their nature, in reference to