Thomas Willis' iatrochemistry and the activity of matter

This article presents a comprehensive study of Thomas Willis' chemistry and matter theory. Willis' medical and chemical views rest on the assumption that matter is both active and endowed with life. He resorted to chemical principles, which he interpreted in corpuscular terms, to account for physiological processes, including those occurring in the brain and in the nervous system. He combined anatomical research with the chemical investigation of organic fluids, giving a central role to spirits, which he saw as active particles of matter. Willis deployed analogies between chemical apparatuses (and processes) and physiological phenomena, as attested by his study of the brain and of the nervous system. He saw muscular motion, sensation and imagination as the result of chemical reactions triggered by animal spirits, i.e. by volatile and active corpuscles generated by the distillation of blood in the cerebral cortex. Furthermore, he posited that elementary forms of reasoning are reducible to matter, namely to the activity of animal spirits.