Descartes, Cardiac Heat, and Alchemy

René Descartes (1596-1650) insisted on a heat and light theory to explain cardiac movement, and used concepts such as distillation of the vital spirits, fermentation in the digestive process, and fermentation in the circulation of the blood. I argue that his theory of the body as a heat-exchange system was based on alchemical and natural philosophical notions of fire and light expounded by precursors and contemporaries who included Jean D'Espagnet, Jean Fernel, Jan Baptist van Helmont, and Andreas Libavius. Descartes endeavoured to mechanise their approaches, creating a theory in which fire and heat, a legacy from thermal explanations of physiology, were transformed into alchemical fire, and then into mechanistic or physicalist heat.