Motus Tonicus : Georg Ernst Stahl's Formulation of Tonic Motion and Early Modern Medical Thought

This paper places in multiple contexts Stahl's formulation of tonic motion, a contractive and relaxative movement of body tissues that was thought to moderate the circulatory blood flowing through their porous structure. The paper analyzes Stahl's theory, elucidates its role in connecting his physiology and pathology, and situates its formulation in his conceptual development as well as the intellectual history of early modern medicine. The theory was at first a post-Harveyan attempt to explain occasional uneven blood flows; it was then expanded to account for the mechanism of blood circulation and metabolism, and formed a fundamental part of Stahl's effort to present a theory of animal heat and fever that would replace the traditional Galenic and fermentational theories. Tonic motion constituted the most important device that counteracted the ineluctable, unceasing corruption of the body, as dictated by its chemical nature; it thus qualified as the preeminent form of what Stahl considered vital motions.