Edward Stone (natural philosopher) piece of bark from a willow tree and was struck by its extremely bitter taste. Knowing that the bark of the Peruvian cinchona tree − from which quinine (used in the treatment of malarial fevers) is derived − has a similarly bitter taste, he surmised that the willow might also have therapeutic properties. Stone's interest in willows was due to the ancient "doctrine of signatures" – whereby the cause of a disease offers a clue to its treatment. According to Stone: "As this tree delights in a moist or wet soil, where agues chiefly abound, the general maxim that many
Therapeutice Specialis ad Febres Periodicas Perniciosas who first systematically studied the effect of cinchona in the treatment of malaria, wrote a book which he titled "Therapeutice Specialis ad Febres Periodicas Perniciosas". One highlight of the "Therapeutice Specialis" is the drawing "tree of fevers", where different fevers, such as branches of the tree, are divided into categories: on the left, those that respond to cinchona, are shown as branches covered with bark, while on the right are those for which cinchona is ineffective, and are depicted as denuded leafless branches. Torti clearly identified cinchona as a specific therapy for intermittent fevers, as opposed to continued fevers, which