The classification of drugs and remedial agents is a theme regarding which the many writers upon and teachers of medicine have shown a wider diversity of opinion, perhaps, than upon the physiological action and medical uses of individual remedies. The fact that therapeutics is far from being an exact science, and the rapid advance in our knowledge of normal physiological processes, of pathological conditions, and the systematic action of drugs, are sufficient explanation of the ever-changing judgments of our best observers concerning the action of certain medicinal agents under given conditions.

It follows that from time to time, as appears in reviewing the literature of the subject, different writers, in their attempt to keep pace with the advancement of knowledge, have devised various systems of classification.

In earlier days, when the therapeutist culled from the fields his simples for the cure of disease, there was naturally created a strong tendency toward a botanical classification. So far was the system pushed that in certain so-called schools of medicine the authority of Scripture was invoked, it being proclaimed as an axiom that "the leaves of the tree were for the healing of the nations "(Rev. xxii. 2). This eclecticism, strange as it may seem to-day, was the outgrowth of the Thompsonian or Botanical system of therapeutics. On the other hand, as an evolution of the old alchemic school, an attempt was made to found a classification by explaining the remedial action of all medicines upon a purely chemical basis.

With the advent of more modern methods of study, applied to the physiological action of drugs upon the animal economy, came the physiological classification, in which the effects of remedial agents were explained upon rational grounds.

It is hardly necessary to state that coexistent with these various endeavors to attain a philosophical method of classification, complicating them and perplexing their votaries, the dominating principle of empiricism held universal sway, setting at defiance in many instances the cardinal maxims of rational therapeutics, the rational therapeutist even to-day welcoming as a last resort the cruder, though often efficient, empirical method.

Some authors, perceiving the inutility of the older systems, have contented themselves with a mere alphabetical arrangement of medicinal agents, regardless of their origin, natural affinities, mode of preparation, and physiological action.

Taking all the conditions into consideration, it seems the wisest plan for beginning students of medicine to so arrange the various drugs in use as far as possible along lines of therapeutic efficiency; and inasmuch as the trend of modern therapeutics is becoming more and more physiological, a combination of the physiological and therapeutic systems is here adopted. Many inconsistencies are inevitable in any classification, yet such a method of grouping is deemed the most satisfactory for students and practitioners alike.