This section is from the "Elixirs And Flavoring Extracts. Their History, Formulae, & Methods of Preparation" book, by John Uri Lloyd. Also available from Amazon: Elixirs and flavoring extracts,: Their history, formulae, and methods of preparation;
It has been shown by Prof. Emil Scheffer that pepsin is incompatible with alcohol. By an elaborate series of experiments Prof. Scheffer demonstrated that even the amount of alcohol which exists in sherry wine prevents the wine from dissolving pepsin from the mucous membrane of the pig's stomach (Journal of Pharmacy, 1870). In connection with this portion of our subject, we quote from Prof. Scheffer's writings as follows: "After these experiments I do not hesitate to say that the so-called wine of pepsin does not contain any pepsin at all, and that all the medical virtue of it has to be attributed to the wine itself."
In continuance, 1872, the same author shows that solution of ammonio-citrate of bismuth is incompatible with pepsin, and hence he concludes that the benefit derived from the use of elixir of pepsin and bismuth was due to the alcohol or the bismuth salt. Notwithstanding these facts, it is well known that elixirs containing pepsin and bismuth associated are among the most popular. Let us now consider another phase of the subject. If hydrochloric acid is added to solution of ammonio-citrate of bismuth, as is well known, a precipitate immediately results. Here we have an additional incompatible, for hydrochloric acid is usually employed in making solutions of pepsin, and we might be led to argue therefrom that both the pepsin and the bismuth are probably absent from elixir of pepsin and bismuth, and hence that the value of this elixir depends upon the alcohol only. We have been somewhat successful in overcoming the incongruities we have just named by substituting acetic acid for hydrochloric acid in the preparation of the pepsin liquid, thus permitting it to be mixed with the bismuth solution without precipitation of bismuth, and also the apparent solution of pepsin in the presence of ammonio-citrate of bismuth.
(It is by no means certain that such a solution of pepsin is injured, regarding its digestive power, by the substitution of acetic acid for hydrochloric acid. True it is that to dissolve albumen artificially hydrochloric acid is necessary, but the juices in the stomach may render it unnecessary. See elixir of pepsin.)
We use the term "apparent solution of pepsin," for although the pepsin undoubtedly disappears, it does not necessarily follow that it dissolves and remains active pepsin. Perhaps it is so modified as to be devoid of digestive value and still remain dissolved. Upon the other hand, even if this is the case, it. is barely possible that such a pepsin is only paralyzed, and that its vitality will return when it is taken into the stomach. Were it not true that these combinations are demanded by physicians, we might even ignore them altogether.