The _Historical Introduction_, comprehending the substance of the lectures delivered before the Royal College of Physicians of London, from the recently established chair of Materia Medica, has been prefixed to the work, at the desire of several of the auditors; and I confess my readiness to comply with this request, as it enabled me at once to obviate any misconception or unjust representation of those remarks which I felt it my bounden duty to offer to the College. It will be observed that the work itself is divided into two separate and very distinct parts, the _First_ comprehending the principles of the art of combination,—the _Second_, the medicinal history, and chemical habitudes of the bodies which are the subjects of such combination. These comprise every legitimate source of instruction, and to the young and industrious student, they are at once the LOOM and the RAW MATERIAL. Let him therefore abandon those flimsy and ill-adapted textures, that are kept ready fabricated for the service of ignorance and indolence, and by actuating the machinery himself, weave the materials with which he is here presented into the forms and objects that may best fulfil his intentions, and meet the various exigencies of each particular occasion. J. A. P. _Dover-street, January, 1820._ HISTORICAL INTRODUCTION. COMPREHENDING THE SUBSTANCE OF SEVERAL LECTURES DELIVERED BY THE AUTHOR BEFORE THE _ROYAL COLLEGE OF PHYSICIANS_, FROM THE CHAIR OF MATERIA MEDICA, In the Years 1819–20 and 21. “_It has been very justly observed that there is a certain maturity of the human mind acquired from generation to generation, in the_ MASS, _as there is in the different stages of life in the_ INDIVIDUAL _man;—What is history when thus philosophically studied, but the faithful record of this progress? pointing out for our instruction the various causes which have retarded or accelerated it in different ages and countries._” _Historical Introduction, p. 4._ HISTORICAL INTRODUCTION. AN ANALYTICAL INQUIRY INTO THE MORE REMARKABLE CAUSES WHICH HAVE, IN DIFFERENT AGES AND COUNTRIES, OPERATED IN PRODUCING THE REVOLUTIONS THAT CHARACTERISE THE HISTORY OF MEDICINAL SUBSTANCES. “_Historia quoquo modo scripta delectat._”