Dr. Fordyce first established the existence of the singular and important law, that a combination of similar[[241]] remedies will produce a more certain, speedy, and considerable effect than an equivalent dose of any single one; a fact which does not appear to have been known to any ancient physician. The earliest mention of it that I can find is by Valisnieri, the favourite pupil of Malpighi, who filled the medical chair at Padua in 1711, nearly ninety years before Fordyce published his valuable memoir on the combination of medicines, but he does not attempt any generalization[[242]] of the subject; he merely states, as the result of careful experiments, that twelve drachms of Cassia Pulp are about equivalent in purgative strength to four ounces of Manna; and yet, says he, if we give eight drachms of Cassia Pulp, in combination with four drachms of Manna, we obtain double the effect! How, adds the professor, can this possibly happen? Surely the very contrary ought to obtain, since four drachms of Cassia are much more than equivalent to an equal weight of Manna; the strength of the former being to that of the latter as 8 to 3.
The truth of this law of medicinal combination must be continually felt by the practitioner in the ordinary routine of his practice, viz.
Narcotics will better fulfil the intention of allaying irritation and pain, when composed of several of such medicines in combination, than when they consist of any single one, even should the dose, in this latter case, be increased. See Formulæ 3, 4, 5.
Antispasmodics acquire increased efficacy by the application of the same principle. Form. 20, 21, 22, 23, 24, 25.
Bitter Tonics are also thus exalted, see Form. 39, 40, 41. The beneficial effects, however, which arise from combinations of this kind will admit of a satisfactory explanation upon another principle; we may, for instance, consider them as medicines, differing from each other in their composition, and producing by their union an assemblage of bitter, astringent, and aromatic principles.
Aromatic and Diffusible Stimulants. There are perhaps no remedies which receive greater mutual benefit be intermixture with each other, than the individuals which compose this class; for they not only thus acquire increased force and efficacy, but at the same time they lose much of their acrimony; if, for instance, any one spice, as the dried capsule of the Capsicum, be taken into the stomach, it will excite a sense of heat and pain; in like manner will a quantity of Black Pepper; but if an equivalent quantity of these two stimulants be given in combination with each other, no such sense of pain is produced, but, on the contrary, a pleasant warmth is experienced, and a genial glow felt over the whole body; and if a greater number of spices be joined together, the chance of pain and inflammation being produced is still farther diminished. The truth of this law is also strikingly illustrated, as Dr. Fordyce has observed, by that universal maxim in cookery, never to employ one spice, if more can be procured; the object, in this case, being to make the stomach bear a large quantity of food without nausea.[[243]] This same principle also finds an illustration of its importance, as it regards the class of stimulants, in the following preparations of our Pharmacopœia, viz. “Pulvis Cinnamomi Compositus; Infusum Armoraciæ compositum; Infusum Aurantii Compositum; Spiritus Lavendulæ compositus; Tinctura Cinchonæ composita; Tinctura Valeriana Ammoniata; and the Confectio Opii, the elegant and scientific substitute for the celebrated Mithridate or Theriaca. The practitioner is also referred to Form. 45, 47, and to Allii Radix.”
The local action of these stimulants would appear to be placed under the dominion of the same law, and perhaps the origin of the custom, so long observed, of mixing together the varieties of snuff, may thus receive a plausible and philosophical explanation; certain it is that by such combination the harsh pungency of each ingredient will be diminished, whilst the general potency of the application, in exciting the nerves, will be increased, and rendered more grateful; the same principle will direct the formation of safe and efficient plaisters and lotions; the Emplastrum Cumini of the London, and the Emplastrum Aromaticum of the Dublin Pharmacopœia, offer examples of its judicious application.
Astringents. For illustrations see Form. 51, 58.
Emetics are certainly more efficient when composed of Ipecacuan united with Tartarized Antimony, or Sulphate of Zinc, than when they simply consist of any one of such substances in an equivalent dose. See Form. 63, 65.
Cathartics not only acquire a very great increase of power by combination with each other, but they are at the same time rendered less irritating in their operation; the Extractum Colocynthidis compositum affords an excellent example of a compound purgative mass being much more active and manageable, and less liable to irritate, than any one of its components separately taken. Additional examples of this fact are furnished by Formulæ 70, 76, 78, 79, 81, 88. In many cases, however, the fact of purgatives thus accelerating and correcting each other’s operation may be explained by considering them as substances endowed with different powers, as already demonstrated, (p. 88), and which will be more fully considered in the third division of this Essay.