James Keill, George Cheyne, and Newtonian physiology, 1690-1740.

Abstract

Mechanical explanations of human physiology proliferated in the seventeenth century. The anatomic and physiological discoveries made in the fifty years between Descartes's Traite de l'homme (written 1633) and Newton's Principia (1687) led to the playing of increasingly convoluted variations on this theme of the mechanical philosophy. In one variation, Giovanni Borelli and Lorenzo Bellini applied the new mechanics of Galileo and his followers to human anatomy, particularly to the description of muscular motion. In another, Boyle's mechanical chemistry was called upon to explain a variety of physiological functions from respiration to digestion to animal heat. Following in this pattern, Newtonian dynamics could have added yet another variation. But, as Newton himself was well aware, the possible existence of short-range forces analogous to gravity could rework the theme of the mechanical philosophy itself.' Newton had early recognized that short-range forces had obvious implications for physiological explanation; his 1692 essay "De natura acidorum" included several comments on this topic. In query 23 (known to us, from its position in later editions, as query 31) of the 1706 Opticks he presented several chemical examples of short-range attractions that related to animal function, such as fermentation,