A. By which the efficacy of the remedy is enhanced.
After the views which have been submitted in the progress of the present inquiry, it is evident, that the form in which a remedy is administered may exert some influence upon its medicinal effects; for additional proofs of this fact, and for more particular directions, see Decocta, Infusa, Tincturæ, Misturæ, Pilulæ, Pulveres, &c.
When a substance, or a combination of substances, requires the addition of some other one, for the purpose of imparting a convenient, agreeable, or efficacious form, a vehicle should always be selected, whose effects will be likely to correspond with the intention of the other ingredients. This precept may be exemplified by a reference to Form. 80, 134, and others, the key-letters of which announce the modus operandi of their respective vehicles.
B. By which its aspect or flavour is rendered more agreeable.
It should ever be the object of the practitioner to accommodate, as far as he is able, the form and flavour of his medicines to the taste and caprice of his patient, provided always that he does not compromise their efficacy, and which often appears to be nearly connected with those sensible qualities which render them disgusting and objectionable.
Some medicines are more grateful to the stomach, as well as more efficacious in their operation, when exhibited in the state of effervescence. To effect this we have only to introduce an alkaline carbonate into the formula, and to direct a portion of some vegetable acid to be added just before it is swallowed. We must, however, take care that the ingredients are of a nature not likely to be decomposed by the alkali, in the first instance, or by the neutral salt, which is formed, in the second. See Form. 27, 82, 86.
C. By which it is PRESERVED from the spontaneous decomposition to which it is liable.
It is sometimes adviseable to add an ingredient for the purpose of preventing the sudden decomposition of a medicine; thus is the Compound Tincture of Cardamoms added to the Compound Decoction of Aloes, in order that the latter may be preserved a longer period without change. The addition of sugar will prevent ointments from becoming rancid. Vegetable infusions, that are susceptible of mouldiness, are best preserved from such deterioration by some aromatic addition. For the knowledge of this fact we are indebted to Dr. Mac Culloch, who in a very interesting paper, lately published in the Edinburgh Philosophical Journal[[273]] has observed, that perfumes, such as Essential Oils, &c. will prevent the production and growth of those minute cryptogamous vegetables, upon which the phenomenon of mouldiness depends.[[274]]
Such are the objects which are to be attained by combining several substances in one Formula, and such the laws by which these compositions are to be regulated; but unless a physician can satisfactorily trace the operation of each element in his prescription to the accomplishment of one or more of the objects which I have enumerated, SIMPLICITY should be regarded by him as the greatest desideratum. I was once told by a practitioner in the country that the quantity, or rather complexity of the medicines which he gave his patients, for there never was any deficiency in the former, was always increased in a ratio with the obscurity of their cases; “if,” said he, “I fire a great profusion of shot, it is very extraordinary if some do not hit the mark.” Sir Gilbert Blane[[275]] has given us a similar anecdote; “a practitioner being asked by his patient why he put so many ingredients into his prescription, is said to have answered more facetiously than philosophically, in order that the disease may take which it likes best.” A patient in the hands of such a practitioner has not a much better chance than the Chinese Mandarin who, upon being attacked with any disorder, calls in twelve or more physicians, and swallows in one mixture all the potions which each separately prescribes!
Let not the young practitioner however be so deceived; he should remember that unless he be well acquainted with the mutual actions which bodies exert upon each other, and upon the living system, it may be laid down as an axiom, that in proportion as he complicates a medicine, he does but multiply the chances of its failure. Superflua nunquam non nocent: let him cherish this maxim in his remembrance, and in forming compounds, always discard from them every element which has not its mode of action clearly defined, and as thoroughly understood.