There has not been in the materia medica, a general system; this science has been governed by the different theories that have successively predominated in medicine; each has, if I may so express myself, flowed back upon it. Hence the vagueness and uncertainty that it presents at this day. An incoherent assemblage of incoherent opinions, it is perhaps of all the physiological sciences, that which best shows the caprice of the human mind. What do I say? It is not a science for a methodical mind, it is a shapeless assemblage of inaccurate ideas, of observations often puerile, of deceptive remedies, and of formulæ as fantastically conceived as they are tediously arranged. It has been said that the practice of medicine was disgusting; I add further, that it is not in some respects the study of a reasonable man, when its principles are derived from the greatest part of the works on the materia medica. Take away those medicines, the effect of which is known only by accurate observation, as evacuants, diuretics, sialagogues, anti-spasmodics, &c. those consequently that act upon a particular function; what knowledge have we of the remainder? It is, without doubt, extremely difficult at present to class remedies according to their modus operandi; but it is undeniable that all have for their object, the restoration of the vital forces to the natural type, from which they have been driven by disease. Since the morbid phenomena may be considered as different alterations of these forces, the action of remedies should also be viewed as the means by which these alterations are to be brought back to the natural type. Upon this principle, each of the properties has its class of appropriate remedies. 1st. We have seen that there is in inflammations an increase of organic sensibility and insensible contractility; diminish then this increase by cataplasms, fomentations, and local baths. In some dropsies, in white-swellings, &c. there is a diminution of these properties; raise them by the application of wine and all those substances that are called tonics. In every species of inflammation, suppuration, tumours of different kinds, ulcers, obstructions; in every alteration of secretion, exhalation, or nutrition, the remedies act peculiarly upon the insensible contractility, to increase, diminish, or alter it in some way. All those that are called resolvents, tonics, stimulants, emollients, &c. act upon this property. Observe, that these remedies are of two kinds: 1st. general; as wine, ferruginous substances, oftentimes the acids, &c.; these re-animate insensible contractility, and give tone to the whole system: 2d. particular; thus this property is separately excited by nitre in the kidnies, mercury in the salivary glands, &c.