The specificity of certain drugs to particular diseases had been highlighted at least since the seventeenth century. Perhaps the best-known example is the efficacy of Peruvian bark, the predecessor of quinine, in the treatment of intermittent fevers or malaria (Figure 1) [5]. Yet, such specificity remained a mysterious phenomenon. As one sceptical author put it in 1797:… as to specifics, if their idea be explicable by supposing an admiral sent down channel, across the Bay of Biscay, and up to the Mediterranean, with express orders to attack the Maltese, but with the strictest charge not to molest any other state whatever; I cannot conceive any medicine such a specific as to conform most punctually with such orders, to act vigorously against one particular gland or humour of the body, without in the least affecting or disturbing any other … [6].