The work now offered to the medical public, while it aims to present whatever in Therapeutics and Pharmacology is directly and practically important to the physician, is intended also to be an exponent specially of what the author himself knows and believes on the subjects of which it treats. Its value, therefore, must depend greatly on the opportunities which he has possessed of acquiring knowledge, and forming just views upon these subjects; and upon this point, consequently, they for whom the work is intended have a right to be informed.

Almost from the commencement of his professional life, the author has given peculiar attention to this branch of medical knowledge. For a period of about thirty years, before 1850, when he was transferred to the professorship which he now occupies, he was engaged in teaching Materia Medica, first as a private lecturer, and afterwards successively in the Philadelphia College of Pharmacy, and the University of Pennsylvania. His position, therefore, rendered constant investigation into the properties, effects, and uses of remedies necessary, in order at once to do justice to his pupils, and avoid discredit to himself. Most of those whom he now addresses are probably aware that he is one of the authors of the U. S. Dispensatory. To provide the original materials for his portion of that work, and to gather from time to time the knowledge requisite for its maintenance upon a level with the progressive condition of medical science, unremitting diligence was essential in prosecuting inquiry and investigation in the whole field of Pharmacology. In addition to the ordinary professional opportunities, he has, for about twenty years, held the office of one of the physicians of the Pennsylvania Hospital, which has given him facilities for testing the value of remedies greater than any amount of private practice could afford. Few persons have had greater advantages or stronger inducements than himself for acquiring the knowledge requisite for the production of a work of this kind. Of the extent to which he has availed himself of these opportunities, and his ability to make a proper use of them, the reader will form his own opinion, either from what he may find in this Treatise, or from what he may know of former works of the author.

In preparing the present work for the press, the author claims to have been actuated, in part at least, by motives higher than those of personal credit, or pecunlary advantage. Though he pretends to no insensibility to these ordinary influences, he believes that he is obeying a call of duty in laying before the profession those results of his research, experience, and reflection upon the subject of Therapeutics, which have heretofore been confined to the narrower limits of classes of medical students. His former lectures constitute the chief substance of the present Treatise, though considerably extended, and much elaborated. Perhaps he may be laying himself open to a charge of overweening self-estimation, in supposing that he can add to the existing mass of knowledge, or improve existing views in this department of medicine, in a degree which may justify the publication of a book like the present; but he is unwilling to leave the world without giving some degree of permanency to what he has so long taught, and consoles himself with the consideration that, should the work prove of less value to the profession than he ventures to hope or anticipate, it is not likely to do serious injury, and, at the worst, will be merely superfluous.

A few words of explanation may be necessary to a correct appreciation of the character of the Treatise. Though aiming at considerable fulness in all that concerns the effects of remedies, the nature of their operation, and their therapeutic application, it has no pretension whatever to be considered as a complete exposition of the Materia Medica, properly so called. Of the natural and commercial history, the sensible and chemical properties, and the pharmaceutical preparation of drugs, the author has endeavoured to select such parts as are of direct and immediate interest to the medical practitioner, and without a knowledge of which, he can scarcely be said to be prepared to enter upon the duties of his profession. All, therefore, that is said on these points may be considered as, in the opinion of the author, requiring the particular notice of the student. He has given much attention to this branch of the subject, in reference both to the general value and the accuracy of the facts stated; having, in many doubtful instances, practically verified their correctness. In the prosecution of investigations for this purpose, he has pleasure in acknowledging his indebtedness to Professor William Procter, Jr., who has, at his suggestion and request, performed many experiments in relation to the chemical properties, reactions, and incompatibilities of the medicines described.

The work will not be found rich in formulas. Nothing would have been easier than to attach numbers of prescriptions to every important medicine described. But the author has always considered that a multiplication of these precise combinations is productive of much more injury than good. It leads to an indolent reliance on mere authority, by sparing the trouble of thought; and greatly conduces to an empirical and routine practice, neither creditable to the physician, nor profitable to the patient. The author has preferably sought to give principles, by which the physician. himself may construct formulas, suitable to each special occasion. He has endeavoured to point out, in reference to each medicine, the peculiar circumstances which render its use appropriate, and the modifications in dose or form which it must undergo, to adapt it to the varying circumstances of different cases, or of the same case at different times. He has also Called attention to the medicines with which, in each special case, it may be appropriately combined, to aid or qualify its operation. With this knowledge, and that of the pathological condition to be corrected, the educated physician will be qualified to form much more appropriate associations or combinations of medicines, and to regulate much more correctly the proportions of the several ingredients in correspondence with the indications, than any formulary can possibly do for him ; nor can any medical man be considered as duly instructed, until he is capable of constructing such formulas for his own purposes.

To any one familiar with the author's Treatise on the Practice of Medicine, it will be obvious, in the perusal of the present work, that the same great principles of pathology pervade both, and constitute in fact the very basis of whatever belongs to the general subject of Therapeutics in the latter. The author has avoided an elaborate representation of these principles on the present occasion; as it would render necessary a repetition of much that is contained in his observations on general pathology in the former Treatise, to which, therefore, he would respectfully invite the attention of the reader, if desirous of information on the subject.

Finally, it is proper to state that, on a comparison of this work with the Treatise on the Practice, upon the one hand, and the U. S. Dispensatory on the other, there will be found not a little that is common to it and one or both of the others; but this overlapping, at the borders, of Treatises on closely allied subjects is absolutely essential to a full and consistent view of each, and is nothing more than is found in all conterminous sciences, not only in the great complex science of medicine, but throughout the whole circle of human knowledge.

This is probably the last professional Treatise of the author; as, with its publication, he will have exhausted what he has had to communicate in those departments of medicine to which he has given a special attention; and advancing years warn him that the time is fast approaching, when a failure of faculties, or the termination of life, will render labour in any new field impracticable. He asks for it only the same kindly consideration which he has had occasion to acknowledge for his other works, and which has bound him to the profession by the strong ties of gratitude, in addition to those of duty and affection.

Philadelphia, August, 1856.