But, though such statements are admitted to be correct in theory, it remains still to be considered whether they form a fitting basis for a classification of medicines. Now it will be observed that no theory of action enters into such an arrangement, but merely the tendency of the action of each medicine is considered; and as each medicine has naturally many distinct tendencies, it comes therefore under many different heads. But the chief practical use of a classification seems to be, that we may quickly learn from it the general action or effect of a medicine; so that, if it is stated to have many different tendencies, and is ranged under no one particular head, we can gain from this no very distinct practical information respecting it. In an arrangement of the kind that we have last examined, the most important result is the chief point considered. Thus it is rendered useful. And in one of the third kind, where the mode of operation is the great thing taken into account, as each remedy has only one primary operation, and according to this is classified, we gain from its designation some useful information respecting it. It may sometimes come under another head in its secondary operation, but only according to the primary should it be classed, the other term being supplementary. The designations founded on local tendency are further of an indefinite character, because they do not denote the kind of action exerted. Of such a kind is the classification adopted by Dr. A. T. Thomson, founded on that of Dr. Murray. He divides what he calls _Vital remedies_ into one division that acts on the nervous system, a second that affects the secerning system, and a third that influences the muscular and sanguiferous systems. This is certainly a step in the right direction. Nerve-medicines seem to have no relation to those that act on the glands, though connected with them as Stimulants by Dr. Murray. They are thus separated. Tonics are also separated from Stimulants, and included with those which act on the muscular and sanguiferous systems. This seems to me to be a correct view of their action. I do not consider that they act primarily on the nerves, but on the blood. Dr. Thomson places Astringents beside them. Though alike in some points, as with regard to their tendency to affect the condition of muscular fibre, yet there appears to be very little agreement in the mode of operation of Tonics and Astringents. There is not altogether much similarity between Quina and Sulphuric acid. I will now transcribe the chief divisions adopted in the classification of Eberle, which seems to have been the prototype of that one since so ably elaborated by Dr. Pereira. EBERLE'S CLASSES.