The phænomena of fever have not only received a new title, but several new terms have been adopted in detailing them, chiefly to remove the mistake into which the use of Dr. Brown's terms had led some of the author's readers, respecting his principles. A new order has likewise been given, and some new facts added, to the inquiry upon this subject. In the Account of the Yellow Fever of 1793, many documents, interesting to the public at the time of their first publication, are omitted; and many of the facts and observations, which related to the origin of the fevers of 1794 and 1797, now form a part of a separate inquiry upon that subject, in the fourth volume. The histories of the yellow fever as epidemics, and of its sporadic cases, have been published in the order in which they have appeared in Philadelphia, to show the influence of the weather upon it, and the impropriety and danger of applying the same remedies for the same epidemic, in different and even successive seasons. The records of the first cases of yellow fever, which have appeared in each of the twelve years that have been noticed, are intended further to show the inefficacy of all the means, at present employed, to prevent its future recurrence. In the fourth volume, the reader will find a retraction of the author's former opinion of the yellow fever's spreading by contagion. He begs forgiveness of the friends of science and humanity, if the publication of that opinion has had any influence in increasing the misery and mortality attendant upon that disease. Indeed, such is the pain he feels, in recollecting that he ever entertained or propagated it, that it will long, and perhaps always, deprive him of the pleasure he might otherwise have derived from a review of his attempts to fulfil the public duties of his profession. Considerable additions are made to the facts and arguments in favour of the domestic origin of the yellow fever, and to the Defence of Blood-letting. The Account of the Means of Preventing the Usual Forms of Summer and Autumnal Disease, appears for the first time in this edition of the author's Inquiries. Part of the facts intended to prove the yellow fever not to be contagious, were published in the sixth volume of the New-York Medical Repository. The reader will perceive, among many additions to them, answers to all the arguments usually employed to defend the contrary opinion. The Inquiry into the Comparative State of Medicine, in Philadelphia, between the years 1760 and 1766, and 1805, was delivered, in the form of an oration, before the Medical Society of Philadelphia, on the 18th of February, 1804. Some things have been omitted, and a few added, in the form in which it is now offered to the public.