Daffy's Elixir was one of the most popular patent medicines in Britain -- and it sold for nearly 300 years, which is amazing considering these types of products were often a flash in a pan. But what makes this product different than others we’ve talked about this snake oil season, other than its longevity, is that its ingredients list wasn’t kept secret -- it was a novel idea to publish ingredients for patent medicines at a time when most products didn’t even put that information on the label. And manufacturers seemed to be okay with that -- maybe because no one could actually prove ownership.