This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol1", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
Remedies are divided primarily into those which operate upon the system, and those upon extraneous bodies accidentally contained within the system. The former division embraces the great body of remedies; the latter includes only five or six classes, which are retained for the sake of practical convenience; as it is desirable that the physician should have the substances belonging to them associated together in his memory.