A Dictionary of Medicine was, some time since, published by Dr. Motherby, and continued, in successive editions, by him and Dr. Wallis, When a new work of this kind was required by the public, it was supposed that it was requisite only to add the modern improvements to the ancient structure: nor was it suspected that what had received the sanction of the public, in five successive editions, could be wholly contemptible. It was, however, soon discovered that the substance was no less erroneous, than the form was unpleasing; that, to render it instructive, without offending the reader of taste and education, required more attentive care than was necessary for a simple revisal. The discovery was not, however, made before a part of the first volume had been printed, which has occasioned some of the unconnected sentences of the former work, and some of the disgraceful references, to remain. When the defects appeared, in their fullest view, the whole was examined with a severer scrutiny, and the subjects investigated in the original authors; nor was a single opinion allowed to remain, which had not the support of authority or experience. The work is, consequently, to be considered as original, and the names of Motherby and Wallis are consigned to the oblivion, from which they had, for a time, escaped, though their labours have been lately copied, often servilely, in publications professedly original.

If the necessary extent of a work of this nature be considered, it will be at once obvious that the bulk should not be unreasonable, and it has been consequently limited to two quartos The requisite additions were supposed sufficient to supply the rejected parts of the folio. But absurdity mocks calculation, and numerous observations and disquisitions, at first studiously retrenched, might, we found, have been retained, since much space was gained by the smallness of the type, and the size of the page; more, by avoiding controversies, employing a concise, comprehensive style, increased vigilance in detecting absurdity and error. Though the utmost care was exerted to avoid its necessity, an Appendix thus became expedient; and, when once admitted, every means of increasing its utility was adopted. The words suppressed were few; but it soon appeared that numerous additions and corrections might be useful. In a long period, destined to the study and practice of a profession, under circumstances which brought every new production before his eyes, and called for his decision, the author thought that the principal questions were decided in his mind, and had little doubt of rendering his work consistent. After the lapse of several years, however, subjects must assume a different, hue; and the medical questions are too numerous for constant recurrence. When therefore, the subjects were again reviewed, some facts appeared in a different light, and it was by no means proper that truth should be sacrificed to consistency. The change of opinion was, however, pointed out in the concluding article; and, by the assistance of the Appendix, the references were not only better compacted, but the inconvenience from these variations was avoided. The minuter errors, which inadvertently crept in, before the imperfections of Dr. Motherby were fully discovered, are by this means also corrected, and the whole work is rendered more regular and consistent. It is not, therefore, an appendix, but amendments, that might make a part of another edition. The author becomes a critic on himself, and, he thinks, has sometimes proved a severe one. For this reason, he has changed the title of the additional part, and styled it, "Second Thoughts,"curae Posteriores.

A new work of this kind, from the peculiar circumstances of the era, was required. Since the last publication of any tolerable compendium of medicine, no inconsiderable progress had been made in every branch. Every quarter of the globe, and the new continent, if Australasia merits this name, have been visited, with anxious care, by the eager votaries of natural knowledge; and the highest Andes have not escaped the researches of Humbolt and his coadjutors. From these investigations medicine and natural history have gained considerable advantages; and if new remedies have not added to the length of lists already-crowded, we have ascertained, in many instances, the true botanical relations of those formerly known; and, from the improvement of the natural system, in the hands of Ventenat, the successor and pupil of Jussieu, the first of the French botanists, we can, in many instances, supply what accidents, or the chances of war, may for a time deny.

Chemistry, during this interval, has become a new science, and the refinement of its analysis has been applied to the most important purposes of medicine. We now know, with the most minute accuracy, the nature of the blood, and the greater number of animal fluids: we know, too, that the circulating mass is scarcely changed by diseases, once supposed to reside exclusively in it. The natural and morbid states of the secreted fluids are also, by the application of this science, more easily understood, and we are thus taught to disregard many imaginary sources of terror.

The difference between the animal and vegetable mixed, and again, between vegetables and minerals, is now, also, more clearly defined: the limits of each are ascertained; and. though, in the progress of our knowledge, we find nature, as usual, passing, by almost undis-tinguishable shades, from one to the other, we can assert, with some confidence, from what points they diverge, and where they coincide. If we find the fibrin in bran, and the prussic acid in bitter almonds, we cannot, for a moment, mistake them for animal substances: if we discover the phosphoric acid in the human body, and the kali in the leucite, we shall not mistake one for a mineral, nor the other for a vegetable.

In the analysis of the vegetable substances used in medicine, and in ascertaining the real chemical nature of mineral preparations, whose utility has been established by the most extensive experience, the same science has lately become most beneficial to mankind. These acquisitions have improved and simplified our pharmacopoeias; nor are our formulae now crowded with heterogeneous, discordant ingredients, our mineral waters loaded with imaginary and incongruous impregnations, or disgraced by contradictory powers. We approach the era when the vegetable principles will be still more clearly understood, when the gum and the resin will not be the ultimate results of our analysis; but we shall, probably, be able to offer only the rudiments of such investigations, under the additions to the article Cortex Peruvianus.