During the Middle Ages the long-ignored axioms and formulæ of Hermetic wisdom were assembled once more, and chronicled, and systematic attempts were made to test their accuracy. To Theophrastus of Hohenheim, who called himself Paracelsus (a name meaning "greater than Celsus"), the world is indebted for much of the knowledge it now possesses of the ancient systems of medicine. Paracelsus devoted his entire life to the study and exposition of Hermetic philosophy. Every notion and theory was grist to his mill, and, while members of the medical fraternity belittle his memory now as they opposed his system then, the occult world knows that he will yet be recognized as the greatest physician of all times. While the heterodox and exotic temperament of Paracelsus has been held against him by his enemies, and his wanderlust has been called vagabondage, he was one of the few minds who intelligently sought to reconcile the art of healing with the philosophic and religious systems of paganism and Christianity.
Paracelsus was a great observationalist, and those who knew him best have called him "The Second Hermes" and "The Trismegistus of Switzerland". He traveled Europe from end to end, and may have penetrated Eastern lands while running down superstitions and ferreting out supposedly lost doctrines. From the gypsies he learned much concerning the uses of simples, and apparently from the Arabians concerning the making of talismans and the influences of the heavenly bodies. Paracelsus felt that the healing of the sick was of far greater importance than the maintaining of an orthodox medical standing, so he sacrificed what might otherwise have been a dignified medical career and at the cost of lifelong persecution bitterly attacked the therapeutic systems of his day.