I was searching for southern biscuit recipes and stumbled on these quinine Biscuits. I began to wonder which of my characters might want to use them, and just what were they used for anyway. Although the advertisement pretty much sums it up. So, I set out exploring a little about quinine biscuits. Enjoy!
Quinine Biscuits.—One of the London bakers has introduced a dietetic novelty in the shape of quinine biscuits. They are small, extremely well made, and have a pleasant and delicately bitter flavor, not too strongly pronounced, which is exactly what a club man seeks in his sherry and bitters. Each biscuit is estimated to contain one-fourth of a grain of quinine, and for delicate stomachs, or where it is desirable to disguise medicine as much as possible, or to combine food with medicine in a perfectly agreeable form, these biscuits are likely to become very popular.—English Journal.
Source: Medical Record ©1872
Note that while this was published in a London journal it was reprinted in several American Medical journals.
Here's a link to Wiki with some basic information about quinine and it's uses.