Medicines produce two distinct effects : one termed the primary, or iu some eases, as when given to a healthy person, the physiological effect; the other secondary, or curative, which can only take place when there exists a disease to be removed. The former is generally uniform or constant ; the latter too often variable and uncertain. To lessen the of uncertainty in the latter and most important of the two kinds of action, many zealous medical men have instituted experiments with different medicines on themselves or others ; while chemists have carefully investigated the chemical composition of the articles, and sought to discover their active principles, or to explain their modes of action. Notwithstanding these valuable aids, thera peutics is still the most imperfect of all the departments of medical science, partly from the difficulties inherent in the subject, and partly from inability in medical men to weigh correctly the evidence respecting the effects of medicines. The union of several articles in one prescription, by which we attempt by one stroke to remove several symptoms, tends still further to obscure the results, and to vitiate the conclusions which may be drawn. The polypharmaey of the ancients has been in a great measure abandoned, but still it must be confessed that simplicity in prescribing is not 'sufficiently studied. (Holland's Medical Notes and Reflexions on Medical Evidence, and on Methods of Prescription.') On the opposite hand, the attempts to isolate the supposed active principle of many vegetable remedies, and to administer it apart from the others, though in some instances advantageous, by diminishing the size of the dose, or concealing the unpleasantness of the taste, have not produced the consequences expected; for example, in most cases cinchona bark administered in some of the old prepara tions will be found a more valuable tonic than quinine. The superiority
of many mineral waters, which contain a variety of ingredients in a state of extreme dilution, over the exhibition of the saline materials in a hew quantity of liquid, seems to militate against the practice of excessive concentration.
The introduction of new substances Into the lIateria Medics, by the discovery of new plants, or by the progress of chemistry, may supply deficiencies in the catalogue of remedies. But less benefit to mankind will flow from a multiplication of remedies, than from the establish. merit of clear and scientific rubes for their administration. livery improvement hi anatomy and physiology will promote the advance ment of therapeutics, by leading to greater precision in the employment of medicines. For nothing is more certain than that medicinal substances act upon special parts of the body, in preference to others, and in many instances on those which aro diseased rather than on those which are sound. The careful investigation of the modes of action of medicines is worthy of the best faculties and energies of medical men, and every contribution to this department of science should be regarded as an incalculable benefit conferred on mankind.
(Pereira's Elements of Materia Medico ; Vogt. Lehrhuch der wtakodynasnik, and Headland Os the Actions of dncdidnea.)