The Regurgitated Knife: Demonic Power and the Boundaries of Nature in Early Modern Medicine

Confronted with the possibility of demonic illness, the physician Johann Weyer (d. 1588) writes that the physician’s work ends and the priest’s work begins when the “evil” of an illness “surpasses natural limits.” This limit, delineating the domain of medicine from that of ecclesiastical healing, was as imprecise as it was absolute. This article uses the regurgitated knife and related symptoms associated with demonic illness to explore how diverging understandings of demonic and natural action informed medicine in sixteenth-and seventeenth-century Europe. During this period, many physicians joined demonological discourse in order to justify expansive claims to medical authority through a naturalistic redefining of demonic power. These theories of the demonic and the natural were situated in debates over the boundaries of nature and the limitations of natural operations, providing a glimpse into the fluidity of these categories and the disciplinary boundaries aligned with them in the early modern period.