The application of this principle is highly important in practice, directing us in the choice of the different purgatives, according to the objects which we may wish to fulfil by them, and pointing out safe and easy methods by which we may increase, diminish, retard, or accelerate their operation; it thus enables us to construct new and powerful combinations, by imparting to established remedies fresh activity, or by mitigating the acrimony and violence of arrangements in other respects efficacious and eligible.
In the exhibition of solid substances, their mechanical state of division may be capable of modifying their operation, from the influence which this condition must necessarily exert upon their solubilities, although I am by no means disposed to assign to it the importance which Gaubius has ventured to express, “Sunt quæ ruditer pulverata alvum, subtilius vero urinas, aut alios humores movent;” and Ray, speaking of the Asarum (Hist. p. 208) has the following remark—“Quo tenuius est tritum, eo magis urinas movere, minus autem alvum ducere creditur;” and Linnæus[[268]] observes that this same plant, when exhibited in the state of very fine powder, uniformly acts as an emetic, but that when coarsely powdered it always passes the stomach, and becomes cathartic. M. Virey has made a similar observation with respect to Hellebore,—“L’Hellebore pulverisé fait vomiter; concassé il purge; et en decoction prolongée, il en devient sudorifique ou diuretique.” I have endeavoured under the article Pulveres to establish some useful precepts upon this subject, to which I beg to refer the reader.
The influence of solubility upon the medicinal energies and specific effects of remedies, may be farther illustrated by a comparative examination of the virtues of the Acetate and Sub-acetate (Goulard’s Extract) of Lead: the former preserves its solubility and integrity under any degree of dilution, while the latter, when slightly diluted with the purest water, in consequence of the carbonic acid diffused through it, gives out a copious precipitate; the acetate therefore is undoubtedly the more immediately active application as a preparation of lead, but it is nevertheless perhaps less adapted to remove inflammation and abate irritation than the turbid mixture of the sub-acetate, since the slow and gradual action which is ensured by the latter is more desirable than the instantaneous operation of the same remedy, applied in a more soluble form: the popular injection for gonorrhæa, consisting of a mixed solution of Sulphate of Zinc and Acetate of Lead, probably owes much of its value to the insoluble precipitate of Sulphate of lead which necessarily takes place, and which, from becoming entangled in the mucus of the urethra, produces a more permanent stimulus than what could have happened from a soluble salt: (Form. 62) thus again the Sulphuret of Antimony, and some other preparations of that metal, of slow solubility, establish a more permanent influence than Tartarized Antimony, and may be preferable to it in cases where immediate and active evacuations are not required.
Of remedies composed of vegetable tonics, the useful application of this principle is also apparent. Thus the addition of alkalies, or lime-water, to the infusions of Gentian, &c. or to the decoctions of Bark, by rendering their extractive and resinous principles more soluble, increase their elegance, and exalt their virtues, (Form. 39, 41,) although this law admits of an important exception to be hereafter explained. A knowledge of this principle likewise offers many useful hints connected with the successful exhibition of active remedies; it points out the medicines which require dilution in order to promote their operation, and those whose too speedy and violent effects may be retarded and checked by an abstinence from all potation. Thus, in the exhibition of Diuretics likely to become cathartic or diaphoretic, no liquid should be given for at least an hour after their administration; the same caution applies with respect to the Compound Powder of Ipecacuan, which has a strong tendency to excite vomiting. When the remedy has passed out of the stomach, then the ingestion of fluids may, and ought to be encouraged.
To Sir Francis Milman the profession is highly indebted for hints concerning the importance of accompanying the exhibition of Diuretics with plentiful dilution,[[269]] the arguments he adduces elucidate in a very satisfactory manner the view which has been just taken of the Influence of Solubility.
The influence of solubility[[270]] in increasing the virulence of a poisonous substance, has already been illustrated very fully (page 135,) and it has also been shewn under what circumstance it may be admissible. When these active substances are administered as remedies, in small doses, the precept respecting their solubility is even more important, for in such cases the smallness of the quantity places their operation more immediately under the control of various incidental agents; destroy the solubility of a medicine, and you will probably divest it of those properties which render it useful. Nitrate of Silver, by coming in contact with a Muriatic Salt, is rendered quite inert, and may be discovered unaltered in the fæces of persons to whom it has been administered. See Argenti Nitras.
Under the article Plumbi Acetas the practitioner will also find that the conjunction of this substance with any sulphuric salt, at once deprives it of its valuable properties as a remedy in Hæmopthysis.
Some practitioners, whose opinions I always receive with respect, have considered these views respecting the influence of solubility as savouring too much of the refinement of theory, and instances have been suggested which would appear to invalidate their pretensions; upon examination, however, it will be found that such exceptions are but apparent, and depend upon the solvent action of the gastric fluid. Thus the Protoxide of Iron would appear to be soluble in the fluids of the stomach, and is consequently an active medicine, whereas the Peroxide of the same metal, being insoluble under such circumstances, requires to be combined with an acid, as in the Tinctura Ferri Muriatis, to render it efficacious. The same remark will probably apply to the oxides of antimony.
I shall conclude this section upon the influence of Solubility, by the relation of an anecdote which may tend to confirm the justness of the views I have offered, more satisfactorily perhaps than any additional arguments derived from a scientific examination of chemical and medicinal facts; in as much as it presents us with a practice, the utility of which has been discovered by unassisted experience, and must consequently be independent of theory. The American Indians, whenever they undertake a long journey, and are likely to be destitute of provisions, employ Tobacco for the purpose of counteracting the uneasy sensations of hunger, and in its preparation for such a purpose they adopt an expedient for modifying its powers, and protracting its effects, which affords an instructive illustration of the influence of solubility; it consists in combining the juice of Tobacco, with the pulverized shells of snails, cockles, and oysters;[[271]] the mass is dried, and formed into pills, of a convenient size to be held between the gum and lip, which being gradually dissolved and swallowed, fulfil the intention required.[[272]]