The unnecessary multiplication of books on the same subject may be said, with propriety, to be a great evil; and, therefore, in undertaking the compilation of the following Work, which in its arrangement and plan coincides very closely with the Edinburgh New Dispensatory, it has been my endeavour to render it essentially so different from that work, as to prevent it from being placed under this reproach. But the plan of that volume, which is nearly the same as was originally adopted by Dr. Lewis, with some little alterations, has become so familiar to the profession, and is so well adapted for the purposes of a Dispensatory, that I have thought it prudent not to deviate from it. I trust, however, that the alterations and the additions which I have introduced, particularly in the history of the different articles of the Materia Medica, will give a legitimate value to the London Dispensatory; and, without a wish to detract from the high character of its precursor, will enable it to excite a new interest in the branch of the science of medicine of which it treats; and especially to turn the attention of the student towards Medical Botany, which has been so unaccountably neglected, as to be almost regarded as unnecessary in the education of a physician.

Indeed, although it has always been admitted that a correct knowledge of Materia Medica and Pharmacy can be obtained by those only who possess a previous knowledge of Botany and Chemistry, yet neither the Dispensatories nor the systems of Materia Medica published in this country have described plants in a scientific manner; or noticed, in their descriptions, those characteristics which botanists have fixed on as the only means by which a plant, that is not familiar to the reader of a description of it, can with certainty be known, when he wishes to possess it, or is in any doubt regarding it when it is obtained. From the want of this degree of accuracy in the descriptions of plants, many valuable remedies, used by the inhabitants of one part of the world, have been lost to those of another part, where they are, nevertheless, indigenous; or, instead of the proper plants, other species of the same genera, which possess little or no virtue, have been employed; and even plants, not in any respect medicinal, but highly deleterious, have been used as remedies, merely from their bearing names in common or in pharmaceutical language similar to those of some medicinal plants.

To prevent this evil, therefore, I have added to the usual account of each vegetable substance the characters of the genus to which the plant belongs, as they are given by Willdenow, in his excellent edition of the Species Plantarum; and have also given detailed descriptions of each in the language employed by modern botanical writers.

In the performance of the task of compilation, I have endeavoured to bring together as much useful information, regarding each of the substances treated of, as could be crowded into a small space; and to obtain it have had recourse to every work of reputation to which I could gain access. For the liberality of Sir Joseph Banks, who, through the kind interference of Dr. Gartshore, opened to me the door of his princely collection, I have to return my most grateful thanks; as I obtained information there which I could not otherwise have procured, and some which has never before, I believe, been given to the public in an English garb. Of this nature, in particular, are the observations of Zea on the medicinal species of Cinchona, extracted from the Annates de Historia Natural; those of Humboldt on the same subject, and on some other South-American plants, from his splendid work entitled Plantae Aequinoctiales; and Willdenow's description of the Heracleum gummiferum, which 1 have translated from the Hortus Berolinensis. Information has also been sought for, and obtained, from other sources besides books: and I have received from individuals engaged in the drug trade some notices regarding the forms in which drugs are imported, and the modes of selecting them; which I hope will prove useful.

The botanical descriptions of the plants have been selected chiefly from Martyr's edition of Miller's Gardener's Dictionary; the last edition of Woodvilles Medical Botany; Smith's Flora Britannica; Soicerby's English Botany; the Flora Peruviana; Rheede's Hortus Malabaricus; and the Flora Danica; but in every instance when the living plants could be obtained, - which was the case with the greater number of the indigenous plants, and many exotics also, - the descriptions have been either drawn up from nature, or those adopted have been carefully compared with the plants themselves, and any errors corrected. For other information on this part of the subject, the excellent work of Gartner de Fructibus; Ber-gins' Materia Medica a Regno Vegetabili; Murray's Apparatus Medicaminum; Alston's Materia Medica; and the Linnean and the Philosophical Transactions, with the best books of travels, have been consulted.