It would be ungenerous not to express my warmest acknowledgments to those Gentlemen who have endeavoured to extend the usefulness of this Performance, by translating it into the language of their respective countries. Most of them have not only given elegant translations of the Book, but have also enriched it with many useful observations; by which it is rendered more complete, and better adapted to the climate and the constitutions of their countrymen. To the learned Dr. Duplanil of Paris, physician to the Count d’Artois, I lie under particular obligations; as this Gentleman has not only considerably enlarged my Treatise, but, by his very ingenious and useful notes, has rendered it so popular on the Continent, as to occasion its being translated into all the languages of modern Europe. I have only to add, that the book has not more exceeded my expectations in its success, than in the effects it has produced. Some of the most pernicious practices, with regard to the treatment of the sick, have already given place to a more rational conduct; and many of the most hurtful prejudices, which seemed to be quite insurmountable, have in a great measure yielded to better information. Of this a stronger instance cannot be given than the inoculation of the small-pox. Few mothers, some years ago, would submit to have their children inoculated even by the hand of a Physician; yet nothing is more certain, than that of late many of them have performed this operation with their own hands; and as their success has been equal to that of the most dignified inoculators, there is little reason to doubt that the practice will become general. Whenever this shall be the case, more lives will be saved by inoculation alone, than are at present by all the endeavours of the Faculty. INTRODUCTION. The improvements in Medicine, since the revival of learning, have by no means kept pace with those of the other arts. The reason is obvious. Medicine has been studied by few, except those who intended to live by it as a trade. Such, either from a mistaken zeal for the honour of Medicine, or to raise their own importance, have endeavoured to disguise and conceal the art. Medical authors have generally written in a foreign language; and those who were unequal to this talk, have even valued themselves upon couching, at least, their prescriptions, in terms and characters unintelligible to the rest of mankind.