Lecturer's Précis - Descartes (1662)

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First published online 10:46 GMT 11th March 2002, Copyright Derek J. Smith (Chartered Engineer). This version [2.0 - copyright] 09:00 BST 8th July 2018


Descartes' "Animal Spirits"

The French philosopher René Descartes (1596-1650) gave an early description of the reflex in his posthumously published book "A Treatise on Man" (Descartes, 1662). Here is how he explained - with the aid of a diagram - the phenomenon:  

Descartes (1662): Here is Descartes' description of the spinal withdrawal reflex. The fire, A, produces inner vibrations of some sort in the skin of the foot, B, which then propagate up the nerve tube to the brain (just to the left of the blue hashed line), where they would open a pore in one of the brain ventricles, F, releasing what he called "animal spirits". These animal spirits travel back down the nerve tube in order to pull the foot away from the fire. This explanation was compatible with what was already known about spinal anatomy from the available anatomy textbooks (eg. Vesalius, 1543), and was not greatly improved upon until Sir Charles Bell and François Magendie discovered in the early years of the 19th century that the sensory and motor pathways occupied different bundles within the spinal cord (see Bell, 1811). 

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Redrawn from a black and white public domain electronic image from Descartes (1662). This version Copyright © 2002, Derek J. Smith.