It is easily forgotten that in the century of Shakespeare and Marlowe there was no scientific or rational physiology as we now understand these disciplines. The era was of magic and witchcraft; insubstantial notions of the spiritus animalis were rife, and irrational speculation abounded. The genius of Thomas Willis (1621–75) took medicine several stages forward. Willis showed that the cerebral cortex covered many subcortical centres that join the two hemispheres. The cortical grey matter, he thought was responsible for animal spirits, the white matter distributed the spirits to the body, governing movement and sensation. Willis, like Descartes, still believed that man had an immaterial, reasoning soul. Bodily activity was governed by a corporeal soul, in two parts: “...the animal Spirits flowing from the Medullary substance into the nerves, are as it were rays diffused from the light itself, and the other Spirits everywhere abounding in the Fibres . . . perform the acts both of the sensitive and locomotive Faculty” (Willis, 1681, p126).

The vital soul was the “flame” in the blood, and the sensitive soul was the animal spirit diffused …