In ch.25, Catherine realized that, in England, "neither poison nor sleeping potions [were] to be procured, like rhubarb, from every druggist". I searched through the Pemberley archives, but all I could find was two brief references, including an old L&T post of Caroline's which mentions "a reference in JA's letters to "doses of Rhubarb" but this seems to be for biliousness, not for purging".

First of all, I didn't exactly know what "biliousness" was, so I went Googling and found the following definition at http://www.medterms.com/script/main/art.asp?articlekey=19438:

Biliousness: A term used in the 18th and 19th centuries pertaining to bad digestion, stomach pains, constipation, and excessive flatulence (passing gas). The quantity or quality of the bile was thought to be at fault for the condition. Hence, the name "biliousness." ("Bilious" derives from the French "bilieux," which in turn came from "bilis," the Latin term for "bile.") Biliousness was generally laid to high living. The "cure" was moderation and frequent visits to the doctor.