In the Advertisement to the First Volume it is stated that, by the advice of the Council of the Sydenham Society, I had restricted the history which I gave of professional opinions on the various subjects treated of in the course of my work to what is properly called the period of ancient literature, and to this rule it will accordingly be observed that I have generally adhered, except in a few instances, where a departure from it seemed to be demanded for the sake of illustration, or for some other special object. But in dealing with the subject-matter of the present volume, namely, the Materia Medica and Pharmacy of the ancients, it became apparent to me from the first that a different plan of proceeding was indispensable, otherwise the usefulness of the whole work to the ordinary reader would be very much impaired. It is well known how frequently the nomenclature of the sciences connected with these subjects has changed, and what differences of opinion have prevailed with regard to many of the substances used in the practice of medicine by the ancients. In order, therefore, to render the information contained in this and the preceding volumes of ready access for practical purposes, it appeared to me necessary to bring down the annotations to modern times, so that one might see at once what is the exact import of the ancient terms of art, and what the medicinal substances mentioned in the course of the work actually were, according to the nomenclature of the present age. Accordingly it will be found that the Commentary in this volume abounds in references to modern authorities, and contains a variety of materials collected, not only from the earlier herbalists and commentators on Dioscorides, Theophrastus, and other ancient authors, but likewise from recent writers on Botany, Mineralogy, and the Materia Medica, in illustration of the various articles which are treated of in this work. And I have much satisfaction in having it in my power to state that the plan now described has the authority and sanction of the Council, who gave it their entire approval. To Dr. Pereira I owe my grateful acknowledgment for much valuable advice and assistance received from him on this part of my work; but at the same time it is fair to him to state I have no right to make him in anywise responsible for opinions herein advanced which may turn out to be erroneous.