Although these sketches were not intended for the profession, yet they may prove of some utility to the pupil who commences the arduous study of medicine. They may convince him, that great names, however justly respected and renowned, do not constitute a sufficient basis, on which to rest a satisfactory and conclusive judgment; and, as Locke has justly observed, that "_reverence or prejudice must not be suffered to give beauty or deformity to any of their opinions_." He will find that of which further experience will subsequently convince him, that medical investigation is too often founded upon analogy and hypothesis--but let not this painful and disheartening impression arrest his progress, or deter him from seeking to assist his judgment by collecting "the scattered parts of truth," for in speaking of hypothesis, Dr. Crichton has thus expressed himself: "There is a period in knowledge, when it must be indulged in if we mean to make any progress; it is that period when the facts are too numerous to be recollected without general principles, and yet, where the facts are too few to constitute a valid theory. If the exterior form of an edifice is often the principal motive with men for examining its internal structure; so it is in science, that the splendour of an hypothesis, and the desire of proving its solidity, are more frequent motives for research than a mere love of knowledge." Notwithstanding our boasted progress in scientific pursuits, and our supposed approach to perfection, there never perhaps was a period, since the fanciful days of Paracelsus, Agrippa, and Van Helmont, when more deceitful and fascinating reveries were indulged in than at the present _enlightened_ moment, nor more ingenuity and disingenuousness displayed in seeking to give substance to a vision or overthrowing its baseless fabric. It is painful to be obliged to admonish the would be legislators of our belief, in the words of the sceptical Bolingbroke: "Folly and knavery have prevailed most where they should be tolerated the least, and presumption has been excused most where diffidence and candour are on many accounts the most necessary. "Quale per incertam lunam sub luce maligna Est iter in Silvis." _Hanwell Lunatic Asylum, Dec. 1838._ INTRODUCTION.