"The doctrine of the four elements seems to have continued undisputed till the time of the alchemists. These men, better acquainted than the ancient philosophers with the analysis of bodies, became convinced of the inadequacy of that doctrine to explain all the phenomena which were presented to their view. Hence they substituted in its stead a theory of their own; namely, that all bodies are composed of three elements, salt, sulphur, and mercury, which they distinguished by the appellation of the tria prima. To these principles, which were embraced by succeeding writers, Paracelsus added two more, phlegm and caput mortuum."