In consequence of pressing engagements in the revision of his other works, which could not with propriety be postponed, the author has been compelled in some degree to neglect the present, which has now for several months been out of print. About seven years have elapsed since the second edition was given to the public; and, as this period has been one of extraordinary activity in the cultivation of medicine, it will be readily perceived that much labor was necessary, on the part of the author, to bring the work fully up to the level of the present time. For nearly a year, with a short intermission rendered unavoidable by family affliction and his own impaired health, he has devoted most of his time to this object; and the reader will perceive, by the additions made to the Treatise, and the numerous modifications necessary to keep pace with the advance of the science and the change of opinion, that the task of revision has been no sinecure. Besides many of minor importance, the following remedial substances have been treated of, and some at considerable length; to wit, coca, nitrous oxide, antimoniated hydrogen, gelsemium, calabar bean, bromine and its preparations, lithia and its carbonate and citrate, ozone, peroxide of hydrogen, permanganate of potassa, and sulphurous acid and the sulphites with carbolic acid in their antizymotic relations. The progress of the science has rendered advisable the formation of two new classes, in order prop-perly to arrange several substances of peculiar powers; one embracing the disinfectants, which now hold an important place among the means of encountering disease; and the other named antizymotics, because endowed with extraordinary powers in arresting fermentative processes, which are recognized as exercising a most noxious influence in the causation of disease. The size of the type used in the former editions has been so much reduced in the present, as to enable the quantity of matter contained in each page to be increased at least one-tenth; and yet, to accommodate the new material, it has been found necessary to add considerably to the bulk of the book. The subjects of subcutaneous injection, and of the introduction of liquids into the air-passages by bringing them to the state of fine spray, which are now for the first time fully considered in this Treatise, involve so large a number of substances in their practical application, that a constant watchfulness was necessary, in the revision, not to allow important medicines to pass unnoticed in this relation. The author is not aware that any topic, having a direct bearing upon the subject of the work, has been neglected in preparing it for the press; and he thinks he may justly say that, whatever may have been the merits of the former editions, as exhibiting the condition of the Materia Medica at the periods respectively when they were issued, the present will not be found to have deteriorated as representative of the existing state of the science. The author wishes once more to repeat the assurance of his warm interest in the advance-ment of the profession and its prosperity in all respects, and of his grateful feelings towards its members personally for the kindness which his labours have always received at their hands.

Philadelphia, Oct. 15th, 1867.

There are a few abbreviations used throughout the work which require explanation. The letters U.S., attached to a medicinal name or process, are to be understood as referring to the authority of the existing United States Pharmacopoeia; Br., to that of the first British Pharmacopoeia published in 1864; and Lond., Ed., Dub., to that of the last Pharmacopoeias published by the London, Edinburgh, and Dublin Colleges respectively, but now superseded by the British.

In an Appendix will be found tables showing the differences between the British Pharmacopoeia recently published, and the first edition of that work, published in 1864, which has been recognized throughout this Treatise as the British standard.

The reader is requested to supply two omissions, from inadvertence, in the following pages; one, of Moschus Moschiferus, the name of the animal described as furnishing musk (vol. i. p. 690), and the second, of Cephaelis Ipecacuanha, as the botanical title of the ipecacuanha plant (vol. ii. p. 465).