This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol2", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
The fruit of Cydonia vulgaris, or the common quince tree, yields seeds, the coriaceous envelope of which abounds in mucilage, which they yield with great facility to boiling water. When the infusion is evaporated to dryness, the residue is found to be soluble in water, and therefore to differ from the mucilage of flaxseed, and from tragacanth. From pure gum or arabin it differs in some of its relations. it is, therefore, considered peculiar, and by Dr. Pereira has been called cydonin. Two drachms of the seeds impart sufficient viscidity to a pint of water.
Mucilage of quince seeds is made use of exclusively as an external remedy, being applied in Great Britain to erysipelatous inflammation, inflamed hemorrhoids, cracked lips, sore nipples, and especially to the eyes in ophthalmia. in this country it is seldom used; its place being supplied by the demulcent to be next noticed, and the mucilage of sassafras pith. As it yields copious precipitates with the acetate and Subacetate of lead, it cannot be employed in connection with them.
A Decoction (Decoctum Cydonii, Lond.) was directed by the London College to be made by boiling two drachms of the seeds for ten minutes in a pint of water. This is the preparation used as above mentioned. it does not keep well. Quince seeds have been omitted in the British Pharmacopoeia.