Although medicines which produce the same ultimate effects by modes of operation obviously different, cannot be considered SIMILAR, in the sense affixed to the term in the present section, yet if these different modes of operation be not physiologically incompatible with each other, the union of such remedies may not only be admissible, but even useful; and it will, accordingly, constitute an object of inquiry in a succeeding section. (III. A.)
C.—By combining the Basis with Substances of a DIFFERENT NATURE, and which do not exert any Chemical influence upon it, but are found, by experience, to be capable of rendering the Stomach, or System, or any particular organ, more susceptible of its action.
Thus it is that the system is rendered more susceptible of the influence of Mercury, by combining it with Antimony and Opium.[[245]] Where the stomach is insensible to impressions, the exhibition of Opium previous to, or in combination with, any active medicine, often assists its operation; this is remarkably striking in some states of mania, when emetics will fail, unless the stomach be previously influenced and prepared by a narcotic; indeed, in ordinary cases of inirritability of stomach, the addition of a small quantity of opium will often render an emetic active.[[246]]
So again the system, when it is in that particular condition which is indicated by a hot and dry skin, is unsusceptible of the expectorant powers of Squill, unless it be in union with antimony or some powerful diaphoretic, (Form. 134.) Squill is by no means disposed to act upon the urinary organs, when exhibited singly; but calomel, and some other mercurial preparations,[[247]] when in conjunction with it, appear to direct its influence to the kidneys, and to render these organs more susceptible of its operation; (103, 106.) Upon the same principle, Antimonial Wine quickens the operation of saline cathartics (69); Opium increases the sudorific powers of Antimony (124); and the purgative operation of Jalap is promoted by Ipecacuan (84). Dr. Aikin asserts that fifteen grains of the former purgative when combined with two or three grains of the latter root, will purge more than double that quantity of Jalap when administered without such an adjunct.
Sir John Pringle speaks of the advantages which may be obtained by combining an alkali with a bitter infusion, by which the diuretic effects of the former will be increased, while the latter is calculated to remove any gastric debility, and to impart a general tone to the body: there is no doubt but that Bitters, from their invigorating influence upon the primæ viæ, (see page 78) increase the effects of remedies whose operation is connected with changes in transitu, or with absorption, as in the exhibition of certain diuretics;[[248]] they also frequently render the stomach and bowels more susceptible of bodies that act by impression, as purgatives, emetics, &c.
We may discover the operation of such a principle in some of the more active compounds presented to us by nature: many herbs owe their efficacy to a cause of this kind. Elaterium, as I have ascertained by experiment, contains a purgative element, sui generis, (Elatin) and a bitter principle, which in itself is quite inert, and yet its presence in the compound renders the alimentary canal more susceptible of the impression of the active ingredient, and therefore increases its force. See Extract. Elaterii. The history of Senna will afford some interesting facts in farther elucidation of this subject; the leaves of this plant, like Elaterium, appear to contain an active principle, in combination with a bitter, which latter ingredient, although destitute of purgative properties, considerably increases those of the former; for if this be removed, as happens when Senna is transplanted into the south of France, the purgative principle is weakened, but may be again restored by the artificial addition of some bitter extractive. The fruit or pods of Senna[[249]] contain only the purgative principle, and are therefore comparatively feeble, unless the defect be compensated by art. Dr. Cullen has observed that a much smaller quantity of the leaves is required for a dose if they be infused in company with some bitter plant; and it has been found that the watery infusion of Rhubarb is rendered more purgative by the addition of Calumba.
The experiments of Seguin have established beyond all doubt that the active principle of vegetable astringents is a peculiar element, to which the name of Tannin has been given; but the efficacy of this ingredient is undoubtedly enhanced by the presence of the gallic acid with which it is usually associated, although this acid, when separated from the native combination, is incapable of producing the least astringent effect; that peculiar flavour which we so commonly experience in unripe fruits, and which we designate by the term acerbness, is the result of a combination of the astringent principle with some vegetable acid. The relative sweetness of sugar, when in different degrees of purity, depends upon the operation of the same law of combination; pure sugar, as Dr. Mac Culloch has very justly observed, however paradoxical it may appear, is not so sweet as that which is impure; the sweetness of melasses, compared with that of refined sugar, is too well known to require more than a bare mention; the vegetable extractive matter in this case, increases the effect of the saccharine principle with which it is combined; for the same reason grapes, differing very materially in their proportion of saccharine matter, may seem to the taste equally sweet, and such in fact is the case on comparing the luscious grapes of Spain, with the Chasselas of Paris; and yet the vinous produce is entirely different, the result of the one being a sweet and luscious wine, while that of the other is hard and dry, because, in truth, these grapes contain very different proportions of sugar; and however powerfully the extractive matter may modify the effects of this principle upon the palate and organs of taste, it cannot alter the quantity of alcohol resulting from its fermentation.[[250]] Crystallized sugar also appears less sweet to the taste than loaf sugar, but this may depend upon the different state of aggregation, and, consequently, the different degrees of solubility possessed by the sugar in these two forms.
In some cases, the addition of certain bodies will induce the absorbents to admit and carry into the circulation remedies which, in a more simple state, they would reject as injurious; this position is supported by the fact of mercury being more readily absorbed when in combination with animal matter, see Ung: Hydrarg: and it is probable that iron, in the form of a tanno-gallate, will be more acceptable than when presented in a more purely mineral state: see Ferri Sulphas.
Does it not therefore appear from the preceding remarks, that certain elements exist in the composition of vegetable remedies, as furnished by nature, which, although individually inert, confer additional strength and impulse upon the principle of activity with which they are associated.[[251]]
The solutions of saline cathartics appear likewise to gain an accession of power and celerity of operation by impregnation with Carbonic acid gas, depending probably upon the intestines thus receiving a degree of distention favourable to the action of the salt, (19, 23.) Certain it is that the operation of emetics, as well as that of glysters, is materially increased by the stimulus of distention.