Prejudice, superstition, and fancy, have greatly extended the list of vegetable remedies: but in a work of this kind, though every absurdity has not a claim to considerable attention, yet the most ridiculous medicines only should be wholly omitted. There are, therefore, very few which have not shared some notice. In enumerating their virtues, it was difficult to avoid the exaggerated commendations of some authors, or the sceptical, contemptuous tone of others. In many instances, therefore, the praises of the former have been adopted, with marks of hesitation, doubt, or disbelief, sufficiently pointed; and those who have not travelled over the dreary waste of forgotten authors, would be surprised at the number of supposed properties omitted.
The animal substances are few, and their sources sufficiently known. It is sufficient, therefore, to have referred, in general, to the Systema Naturae, and, in the lower orders of animated nature, to Sonnini's Continuation of Buffon's Natural History, or the minuter French naturalists, in the Memoirs of the Institute, the Annals of the National Museum, and the numerous tribe of monographists. Natural history has, indeed, of late, approached more nearly the confines of medicine. The latter is strictly the history of the human body and mind, in their natural and morbid state, and comparative anatomy, with its physiology, is the link which unites man to the lower orders, whose structure and whose functions are often beyond the reach of our investigation. The deficiencies are those of our knowledge; for, when this is extended, the chain is less broken, the connections more obvious. The natural history of the lower orders has, however, been little cultivated in this kingdom. It is singular that an animal, so extensively useful as the leech, has never been scientifically described in our language, except in these pages, and the hydatis, so common a source of disease, is by no means generally known to be an animal To identify the few mineral bodies which are used without preparation, we have referred to the system of the judicious and accurate Hauy, which well merits an English dress; but the greater number, which form a valuable part of the materia medica, require a careful, and often an operose, preparation. Medicine, in these cases, calls in chemistry to her aid; nor is the assistance confined to the mineral kingdom. It has been hinted that, in vegetable bodies, different means are employed to separate the more active from the inerter portions, often to change the form, or to concentrate their virtues. This art has been employed from the time of Galen, and has been styled Galenical, in opposition to chemical, pharmacy; which treats of the necessary operations in preparing medicines, more strictly chemical. On the latter subject we greatly want a system co-extensive with the present state of chemical knowledge. Dr. Duncan's New Dispensatory is a most valuable work in this line; but as its subjects are so numerous, he is often compelled to be more concise than we could wish. The lacunae, in this part of the subject, have therefore been filled up from the works of the latest and best chemists, particularly from that valuable collection, the Annales de Chimie.
The utility of chemistry, however, is not confined to the preparation of remedies. Its light has illuminated the most obscure recesses of the medical science. The nature of the animal fluids, in a state of health and disease, has been illustrated by the more refined analysis of modern chemistry, and, by its assistance in the practice of medicine, we guard against those mixtures which might weaken or destroy the virtues of the different ingredients in a formula. It may appear that this part of our subject has been expanded to an extent, which the real connection of chemistry with medicine will scarcely justify, and that chemical disquisitions occasionally trench on medical ones. In the progress of the work, in the moment of writing, the connection, however, became daily more striking; and as this, we trust, is not the ephemera of a day, it was necessary to give the younger reader every advantage of which he might, at a future period, avail himself. Till near the conclusion of these pages, there was, however, no chemical system to which we could refer. Dr. Thomsons Chemistry, a very valuable work, embraced a most extensive outline, and Dr. Aikin's Chemical Dictionary had not appeared. Neither, however, was applicable to medical inquiries, and it was necessary, not only to explain the chemical relations, but to apply them, so far as they would admit, to the principal object.
When we spoke with disrespect of the mechanical physicians, it was not with a design of depreciating the utility of natural philosophy; Though we do not calculate, with Borelli. the momentum of muscular action; with Sanctorius and Keil, the proportion of the surface of the lungs to that of the whole body; with Bellini, the acceleration or retardation of the motions of fluids, circulating through vessels passing off at different angles; yet this science will be found highly useful. The human body, though an animated machine, is constructed on the justest and most nicely balanced mechanical principles: of these the surgeon, in reducing luxations and fractures, will require a minute knowledge. The eye is a most curious optical, the ear an exquisite acoustic, machine; and the human voice, both in compass, variety, and clearness of tone, excels every musical instrument. At present, indeed, our attention is chiefly directed to the evolution and communication of heat, to the effects of the electrical and Galvanic fluids, if they really differ, and their very striking relations to that principle with whose mobility our life is most intimately connected. Indeed the relation of Galvanism to the minuter component parts of bodies has rendered it an agent of peculiar power, in the hands of the analytical inquirer; and we are indebted to Mr. Davy for one of the most important steps, in this branch of science, which has added lustre to any era. Yet all these are accessary sciences, and only of value, in the present work, so far as they assist the explanation of diseases, or direct the practice of medicine. We do not offer these volumes as a dictionary of physics, or of natural history, although they contain a larger share of each than is to be found in many works, which have been distinguished by this title. We do not offer it as a continuation of Dr. Motherby's Dictionary, which, with all its faults, has been unmercifully pillaged, without acknowledgment.