Has not experience fully established the value of many medicinal combinations, which, at the time of their adoption could not receive the sanction of any chemical law? We well remember the opposition, which on this ground was for a long time offered to the introduction of the _Anti-hectic Mixture_ of Dr. Griffith,—the _Mistura Ferri Composita_ of the present Pharmacopœia, and yet subsequent inquiry has confirmed upon scientific principles the justness of our former practical conclusion; for it has been shewn that the chemical decompositions which constituted the objection to its use, are in fact the causes of its utility (_see Mist. Ferri_,); the explanation, moreover, has thrown additional light upon the theory of other preparations; so true is the observation of the celebrated Morveau, that “_We never profit more than by these unexpected results of Experiments, which contradict our Analogies and preconceived Theories_.”
Whenever a medicine is found by experience to be effectual, the practitioner should listen with great circumspection to any _chemical_ advice for its correction or improvement. From a mistaken notion of this kind the _Extractum Colocynthidis compositum_, with a view of making it chemically compatible with _Calomel_, has been deprived of the _Soap_ which formerly entered into its composition, in consequence of which its solubility in the stomach is considerably modified, its activity is therefore impaired, and its mildness diminished.[115]
On the other hand, substances may be medically inconsistent, which are chemically compatible, as I shall have frequent opportunities of exemplifying. The stomach has a chemical code of its own, by which the usual affinities of bodies are frequently modified, often suspended, and sometimes entirely subverted; this truth is illustrated in a very striking manner by the interesting experiments of M. Drouard, who found that Copper, swallowed in its metallic state, was not rendered poisonous by meeting with oils, or fatty bodies; nor even with _Vinegar_, in the digestive organs. Other bodies, on the contrary, seem to possess the same habitudes in the stomach as in the laboratory, and are alike influenced in both situations by the chemical action of various bodies, many examples of which are to be found under the consideration of the influence which solubility exerts upon the medicinal activity of substances; so again, acidity in the stomach is neutralized by _Alkalies_, and if a _Carbonate_ be employed for that purpose, we have a copious disengagement of _Carbonic acid gas_, which has been frequently very distressing to the patient; lastly, many bodies taken into the stomach undergo decompositions and changes _in transitu_, independent of any play of chemical affinities from the hidden powers of digestion, some of which we are enabled to appreciate, and they will accordingly form a subject of investigation in the course of the present work.