The signification given to this term by different authors has varied very much indeed, some employing it to denote the whole range, and others only a particular department, of that branch of medical science which relates to the means employed for the prevention or in the treatment of diseases. Prophylactic or preventive, and remedial or curative means, may be referred to three principal divisions: 1st, The performance of manual operations; 2d, The regulation of what have been termed the non-naturals, as of diet, exercise, temperature, clothing, &c.; and, 3d, The employment of medicinal substances. Manual operations, as far as their mode of performance is concerned, fall under the domain of surgery; the regulation of the non-naturals is the object of dietetics and hygiene. As to the third division (medicinal substances), they may be considered either in reference to the sources from which they are derived, or to the modes in which they are prepared for medical use; or they may be considered, along with the other two classes of means, in reference to the immediate purposes for which they are employed in the treatment of diseases, and the indications which they are intended to fulfil. Now, the term materia medica has by some been understood as embracing the consideration of remedies in all these respects. But by others, and, as we conceive, more correctly, it has been limited to signify the natural and commercial history of medicinal substances. Those processes by which medicinal substances are fitted for use constitute the department of pharmacy, whilst the purposes for which remedies are employed form the objects of consideration in therapeutics. Some have employed the word pharmacology as a general term, to include the whole of the knowledge that has been obtained relative to remedies.

MATERIALISM is the name given to that speculative theory which resolves all existence into a modification of matter. (See METAPHYSICS.)