Mechanism, vis motiva, and Fermentation: a Reassessment of Borelli’s Physiology

Abstract According to the standard view, Borelli was a strict mechanist who sought to explain organic processes by resorting to invisible mechanisms. This paper aims to show that his outlook on living organisms as contained in De motu animalium was far more nuanced than historians have maintained. Borelli resorted to vis motiva as the source of activity of corpuscles, a notion that was at odds with strict mechanism. He identified motive force with spirits, namely with self-moving particles of matter. Borelli combined anatomy and mechanism and integrated the latter with chemical experiments and analogies. Like most late–seventeenth century physiologists, Borelli resorted to fermentation to account for several physiological processes such as digestion, generation, and muscular motion. He distinguished two kinds of fermentative processes: a slow one, as in the case of digestion, and a quick one, as in the case of the presumed effervescence of the blood which he maintained was the cause of muscular movement.