These are remedies acting on bodies foreign to the system, but within it They embrace the five classes of

1. Antacids, which neutralize acid in the stomach, or elsewhere in the system;

Absorbents, which, by absorbing acrid or irritating matters, prevent or diminish their irritant action;

3. Solvents, which effect the solution in the stomach of substances otherwise insoluble;

4. Disinfectants, which chemically destroy noxious and fetid exhalations; and

5. Parasiticides, which are destructive to the lower forms of animal and vegetable existence, seated in the human body, and acting injuri-ously upon it. These include the two subclasses of a. Anthelmintics, which favour the expulsion of worms from the bowels; and b. Antizymotics, which are destructive of those microscopic organisms which support fermentation, and thus probably cause and sustain the proper zymotic diseases.

The following is a tabular view of the foregoing classification; the ultimate classes being in italics.

Systemic Remedies. General remedies. Stimulants.

Permanent stimulants. Astringents. Tonics. Diffusible stimulants. Arterial stimulants. Cerebro-nervous stimulants. Nervous stimulants. Cerebral stimulants. Spinal stimulants. Sedatives.

Arterial sedatives. Ccrebro-nervous sedatives. Nervous sedatives. Cerebral sedatives. Spinal sedatives. Alteratives. Local remedies.

Affecting the functions. Emetics. Cathartics. Diuretics. Diaphoretics. Expectorants. Cholagogues. Emmenagogues. Uterine motor-stimulants. Sialagogues. Errhines. Affecting the organization. Rubefacients. Epispastics. Escharotics. Operating mechanically. Demulcents.

Emollients. Diluents.

Protectives.

Antacids.

Absorbents.

Solvents.

Disinfectants.

Parasiticides.

Anthelmintics.

Antizymotics.

The plan of arrangement here presented does not claim to be perfect, It is, however, in the best judgment of the author, as little objectionable as any that has been proposed, and perhaps as nearly perfect as the present state of our knowledge on the subject permits. It is but partially original. In forming it, the author has preferred adopting what seemed to him best in preceding systems of classification, and modifying where modification was called for by the progress of knowledge, to any presumptuous attempt to supersede, by crude novelties of his own, plans which have in their favour the matured observation of ages, and the judgment of the soundest thinkers of past times. The present plan is a classification of results, of facts well known and generally admitted, which must remain true, whatever changes the progress of discovery may hereafter make in our views of the operation of remedies. It does not profess to explain the modes in which the results are produced. For a classification upon this principle we are not yet prepared. Our knowledge of the precise modes in which medicines act is yet too uncertain to admit of any system of arrangement, founded upon their re-semblance in this respect; and it may be confidently predicted that any such system will prove unstable, as it must rest upon a fluctuating basis.

The attention of the reader is particularly requested to a few considerations, which are necessary to a proper understanding of the scope of the present arrangement. I have said that the classification is not perfect. In the first place, the remedies attached to the several classes, while they agree in the possession of the particular property which characterizes the class, often differ very much in other respects, end in some Instances are applicable to very different purposes. The rule which I have adopted is to classify them, as far as possible, according to their most distinctive property, or that for which they are most valuable therapeutically, and then, in the description of each remedy, to refer to all its other remedial properties and applications, so that its individual character may be well understood. In many instances, the operation of the remedy is altogether peculiar, except in the single point in which it conforms with the other individuals of its class. Thus, while the salts of lead are astringent, they are in every other respect quite specific in their manner of affecting the system.

Again, it not unfrequently happens that a remedy, belonging to one class, has additional powers which serve to rank it in another. In such cases, the remedy is considered in both classes; being treated of at large in that with which its most important therapeutic character would rank it, and in the other only so far as may concern its categorical position. Thus, digitalis is a powerful nervous sedative, and is more strongly characterized, and probably more used as such than in any other capacity; but it is also a very efficient diuretic. It is, therefore, treated of in general, among the nervous sedatives; while, among the diuretics, it is again referred to, but only in relation to the property which attaches it to that class. Indeed, there are some remedies which, in this manner, may be ranked in several classes; as the antimonials, for example, which, while they are chiefly arterial sedatives, belong also to the emetics, diaphoretics, and expectorants. Nor is there any inconvenience in considering medicines in this way. In therapeutics, it is not any particular medicinal substance or remedial agent that we have in our minds, but the condition of disease calling for certain remedial influences; and it is important that our knowledge should be so arranged in the memory as most readily to suggest what particular remedy may be best calculated to exert this influence. This object will certainly be better attained by ranking all the remedies together calculated to meet each indication, and to have them thus associated in our minds, than by having the whole character of each body, in all its different relations and applications, impressed upon us in one exclusive view. Thus, it will be more useful practically, when we have occasion for an arterial sedative, emetic, expectorant, or diaphoretic, to have tartar emetic associated with each of these classes in our recollection, than to know it only as an anti-monial, having a great diversity of properties, and thus to be compelled to think over it, along perhaps with a number of other bodies, in order to ascertain whether any one of these properties may suit our present purpose.

In reference to the modes of operating of the several remedies in producing the effects which serve to classify them, I shall offer and enforce those views which seem to me most in accordance with reason and experience, not omitting, however, to allude to others which may have been advanced, and wishing always to be understood as considering our knowledge upon this point to be in great measure provisional, and liable to be materially modified in the progress of discovery.