The practice of medicine has been detailed with unusual care. The plans of the most approved and scientific authors have been carefully considered, and, whatever science or empiricism has at different eras suggested, is carefully noticed, with those distinctions which may render the discovery more useful and effectual. To accumulate every medicine which has been recommended, in the manner of Lieutaud, would not be difficult; but to discriminate the circumstances, in which alone each plan will be effectual, is not equally easy, though such discrimination can only render the directions valuable or salutary. A real dogmatic practice, viz. pursuing indications, arising from the knowledge of a proximate cause, would gratify the pride of science, and be most advantageous to the patient. The expectation is, however, vain; for in very few instances can an immediate cause be established. Though this, however, be beyond our attainment, we can, in many cases, ascertain general principles, which will assist our practice. Whatever be the cause of fever, for instance, the balance of the circulation is evidently disturbed; and to restore the equilibrium contributes very essentially to the cure. It has been a great object, through the whole work, to ascertain such principles; but they often fail, and the physician must then pursue, under proper regulations, the juvantia and Icedentia which observation has ascertained. When the medicine is determined, the form is easily adjusted; but, except in a very few instances, what are styled formulae are omitted. These are the refuge of ignorance, indolence, or quackery. Every one can transcribe what is printed, and every old woman will eagerly affix a name to a disease: few will venture, from a class of medicines, to select the particular remedy or the dose. If it were possible always to discriminate the circumstances in which the different plans are advisable, formulae might be added; but, to those who can distinguish, they are useless, and to others furnish a weapon, which may be fatal, rather than salutary. The alternative is too dangerous; and, while the disposition to quackery pervades every individual, from the highest ranks to the meanest, while those who claim distinction, in other sciences, arrogate it in this also, what may prove mischievous must be concealed.

Surgery has many advantages, when compared with the practice of medicine. The objects are often before the eyes of the surgeon; the changes daily conspicuous, and show not only the state of the organ, but often of the constitution. If the object be beyond his sight, the touch will assist; and, in the most doubtful cases, the inductions are fewer, the conclusion more certain. When an operation is to be performed, as the situation of every part is known, he is ready, in every emergency; and, having obtained, by experience, a steady command of his hand, his eye, and his mind, he can meet every difficulty unruffled. Yet, as in anatomy, description cannot go far. The eye must witness the conduct of some more experienced practitioner; and operations on the dead subject must assist in giving a steadiness and a command of minute muscular exertion. As practical surgery is viewed in different lights, the directions may appear too general or too minute; but, where description could best avail, it has been most full and particular.

There is one step between the practice of medicine, and the particular remedies, too cursorily passed over by the authors on the materia medica, viz. the therapeutics, or those general doctrines respecting medicines nearly related, which may facilitate our judgment in the selection. As a subdivision of the theoretical course in universities, it has not generally obtained a sufficient share of attention: in Dr. Cullen's Materia Medica it has had an unusual portion; but it is there subservient to his own system, and not so general in its views as the importance of the subject demands. It may be added also, that the extensive associations, usually styled classes of medicine, are too indiscriminate to direct the practice. Subordinate groups are necessary, and these, in imitation of Dr. Duncan, have been added; but the orders are in a great measure new, and are carefully connected, on one hand, with the particular remedies, and, on the other, with the indications of cure.

The means employed for the Cure of diseases are either natural or chemical, By the former are meant those productions of nature which require no preparation, or only the separation of the more active from the more inert portions; chiefly the vegetable or animal substances, since there are few mineral productions which do not require some process to adapt them for use. The vegetable kingdom offers numerous remedies, of very unequal value, uncertain origin, or variously mixed and adulterated. To attain the desired purpose, or to avoid injury, it is first necessary to ascertain the real plant from which the medicinal portion is procured: a circumstance not easy, in a kingdom supposed to consist of more than 60,000 species. The investigations, however, of Linnaeus himself, of his pupils Bergius. Murray, and Thunberg, have greatly facilitated the task: and the lacunae have been, in a great measure, filled up by the labours of Sir Joseph Banks, Mutis, Loueiro, Des Fontaines, Bruce, La Marck Cavanilles. and Roxburgh. Few now remain, whose parent plant has not been accurately and scientifically distinguished. To refer, then, to the Linnaean system, especially in its most improved form, lately published by Wildenow, is sufficient to identify the plant. As, however, the tern from the pen of Wildenow is uncommon, and not yet complete, a reference to the Species Plantarum, a work in every hand, has been preferred, and Wildenow, or later observers, have only been referred to, when it did not appear in the earlier work of Linnaeus himself. No modern naturalist of credit has escaped attention in this department. The system of Linnaeus is not only useful, in identifying the plant, but on account of its numerous references, to each observer who has treated of it: among the rest, to Caspar Bauhine. This author is the link between ancient and modern naturalists; and, under the appellation which he assigns to each plant, we may discover its name in the works, not only of the ancient physicians, but of the ancient botanists, at least so far as the identity of the plant can be ascertained. It has been usual to transcribe the specific character; but, without the generic, it would be of little value, and to add, also, the synonyms of C. Bauhine would make every trifling article disproportionally long; so that the species plantarum is only noticed. As the botanical relations of plants are supposed to be connected with their medical powers, the natural orders have been particularly attended to.