This section is from the book "Materia Medica: Pharmacology: Therapeutics Prescription Writing For Students and Practitioners", by Walter A. Bastedo. Also available from Amazon: Materia Medica: Pharmacology: Therapeutics: Prescription Writing for Students and Practitioners.
There are two vegetable substances that possess the peculiar property of abolishing the appreciation of bitter taste. They are yerba santa (eriodictyon), a leaf, and gymnemic acid, a whitish powder which is soluble in water, dose, 5 grains (0.3 gm.).
The syrup of yerba santa, dose, 1 dram (4 c.c.), has been much employed as an addition to bitter medicines, especially quinine. It lessens the appreciation of bitter taste, but in swallowing hardly acts rapidly enough to check the taste of a bitter substance mixed with it; in fact, to get the real anti-bitter effect, it is necessary to hold the yerba santa preparation in the mouth for several minutes before the bitter is taken. Yerba santa is itself bitter and very astringent. It contains tannic acid in abundance, and it is largely by forming the insoluble tannate that it lessens the bitterness of quinine and other alkaloids.