Historians of medicine have set up a difference between two “schools,” the so-called iatromechanists, who like Descartes attempted to explain biological function in purely mechanical terms, and the so-called iatrochemists, who like [Thomas] Willis interpreted bodily functions in terms of chemical reactions. Despite much historical eclecticism, the difference remains analytically useful. It is no accident that iatrochemistry was able to take on and theorize mental disease or disturbances in the interaction between mind and body in a way that the iatromechanists simply were not; the etiology of mental diseases could simply not be explained satisfactorily in purely mechanical terms.

Helmut Illbruck, Nostalgia: Origins and Ends of an Unenlightened Disease