Okay, I've run out of prostitute-related material for the moment. I'm sure I will find more in the months to come. I found the following story by following @historyweird on Twitter, and reading their blog found here. The quotations come from the original source in The General Homeopathic Journal, vol. 113, 1886.
So you know how the French are really, really good at bread, right? Like, no matter what they do, it's the one thing they could never screw up. Well, you're wrong. In 1886, a German naturalist and hygienist named Dr. Gustav Jager visited Paris and was instructed to visit this local boulangerie [bakery] for its magically magical delicious magic bread. He went to the bakery and found that the deliciousness of the bread was in equal and opposite measure to how nasty the shop smelled.
He wrote: "The neighbours of an establishment famous for its excellent bread, pastry and similar products of luxury [have] complained again and again of the disgusting smells that prevailed there, which penetrate into their dwellings". Now he, being a hygienist, was like, "Well, this is going to end well." Cholera soon broke out in the area and city officials inspected everyone's buildings and the water supplies, because you could usually trace cholera outbreaks back to a single source, like a contaminated well. What they found horrified people. That bakery got its water from a pond connected to the sewer, instead of just using wells like sane people. They'd been making poop-bread, y'all. And poop-bread is apparently SCRUMPTIOUS.
Gustav wrote: "Chemists have no difficulty in demonstrating that water impregnated with 'extract of water-closet' has the peculiar property of causing dough to rise particularly fine, thereby imparting to the bread the nice appearance and pleasant flavour which is the principal quality of luxurious bread".
So whenever someone makes really delicious food but won't tell you the secret ingredient, just know that it's probably 'extract of water-closet' and go home.