We may altogether conclude, that though the actions of many remedies may be partly elucidated by chemical considerations, it is impossible to account for the influence of all alike in this way. For at least the actions of nerve-medicines and of gland-medicines cannot be reasonably explained on any such hypothesis. 3. The most plausible explanations of the mode of operation of medicines have been founded on _vital_ or _general_ principles. By _vital_ I mean that these theories concern actions which could only take place in the living body. They may be termed _general_ principles, because the grounds on which they are based are neither mechanical nor chemical, but something different from both. The term _dynamical_ has sometimes been applied to an ill-understood vital action of this sort. Many different ideas have been broached to account thus for the action of medicines. Some, who have constructed very ingenious and plausible systems, have explained in different ways the operations of different groups of medicines. But when others have adopted a single inflexible hypothesis to account for the action of all alike, this is found, as might be supposed, to be of a very untenable character. I will now consider very briefly several such ideas; first, for the sake of clearness, dividing them into seven sections. I shall explain my meaning as I proceed. Different writers have supposed that the general operation of remedies in the cure of disease is conducted in these various ways. _a._ By degrees of stimulation. _b._ By counter-stimulation. _c._ By opposition. _d._ By similar agencies. _e._ By elimination. _f._ By alterative actions. _g._ By various counteractions. _a._ This idea has received the title of the "Brunonian Theory," from the name of its founder. It was promulgated by the famous Dr. John Brown at the close of the last century. He considered all diseases to arise from excessive or diminished "excitement." He was of opinion that all medicinal agents were stimulants, only that some acted so powerfully as to produce "indirect debility." These latter were to be used in sthenic, the others in asthenic disorders. But it is to be urged against this idea, that many sedatives produce no appreciable degree of "primary stimulation;" that alterative medicines are neither stimulant nor depressent; and that the actions of different therapeutic agents,--as, for example, of Opium, Mercury, and Rhubarb,--differ very much in quality, and not simply in degree, as Dr. Brown supposed. The principle, then, cannot be maintained.