The slightest glance at the history of the doctrines which have been taught relative to the nature and the seat of fever from remote antiquity, and more especially a consideration of the variety and even the contrariety of the received opinions respecting both, in the present day, but too clearly shew that if the ancients were in error, there cannot be many points with regard to which the moderns are right, since there is scarcely one in which they are agreed. Further observation and investigation are therefore not yet superseded. There is as yet no uniformity of opinion among physicians even whether the primary seat of the disease be in the fluid or the solid parts of which the body is composed. Scarcely is the most ancient doctrine respecting it of which we have any record, that it consists in a morbid derangement of the fluids, and that the excitement which attends it is the result of an effort of Nature to expel the poison received into or generated within the system, obliterated from the imaginations or banished from the reasonings of physicians. When indeed we see a patient in the latter stage of some of the forms of fever with his dark or leaden skin, pouring forth its peculiar and fetid exhalation; with his foul tongue, his offensive breath, his vitiated and almost putrid secretions and excretions, we can understand why this doctrine should have taken a firm hold of the human mind and should have been able to maintain its ground through many centuries. Yet when the phenomena came to be observed with the accuracy with which we know that they were observed and recorded, and examined with the acuteness with which we have abundant evidence that some of the most powerful minds reasoned upon them, we may justly wonder that the order of the events, together with their great variety and opposite nature did not sooner suggest doubts of the accuracy of the theory and give to the inquiries of these celebrated men a new direction. But so far was this from being the case that when Hippocrates, considering the increased heat as the essence of fever, founded his division of the varieties of the disease upon this principle, whence his _causus_ or burning fever, his _leipyria_, or fever with the parts externally cold and internally hot, and his _epialus_, or mild fever, with a simultaneous feeling of heat and cold; when he ascribed these different forms of fever to the superabundance of one or other of the four humours, blood, phlegm, yellow and black bile, and considered the disease as the result of a contest on the part of Nature to expel the morbid humour, or to render it inert or harmless by the process of concoction, the mind of Galen so many centuries afterwards, was so well satisfied with this hypothesis, that his powerful genius contented itself with the mere amplification of the conjecture and the addition of similar conjectures of his own. Whence assigning the different sources by which a morbid heat, which he also