The most complete and detailed study of a specific medical case in Chaucer is the account, in The Knight's Tale, of Arcite's injury, his gradually developing symptoms, the diagnosis of their underlying causes, the treatment applied, and the patient's eventual death. Boccaccio's Teseide describes the youth's accident but does not record the attempts of the physicians to save his life: the entire passage is an interpolation by Chaucer. The probable source of the poet's remarkably accurate knowledge of medicine is revealed by an examination of the medical chapters of the greatest of mediæval encyclopedias, the Speculum Majus of Vincent of Beauvais.