For fifty years, Theodore Turquet de Mayerne served as a royal physician in France and then in England. Historians have long recognised him as a brilliant practitioner and chemical Galenist, but this book is the first major study of his remarkable Latin casebooks, the ‘Ephemerides Morborum’ (Diaries of Disease). Interpreting the casebooks in the light of Mayerne's own theoretical writings and of contemporaries such as Jean Fernel, the book is a cultural history of medical perception. It shows how Mayerne crafted a medical portrait for his patients, moving from evaluation, through diagnosis, prognosis, and therapeutics, and focuses on those moments when theory and practice merged to form an integrated medical outlook that served as the basis for action. Convinced that his innovations had the sanction of Galen and Hippocrates, Mayerne added chemical principles to humoral medicine, a greater empiricism to a more rational approach to medicine, and an interventionist therapeutics to a more cautious view of therapy, thus forging a complex synthesis that bore certain structural similarities to baroque culture and art.