Figure 1.1: Descartes’ depiction of a reflex Descartes believed that reflexes occur through purely mechanical means. In describing this figure, Descartes (1637/1972) suggested that the fire causes movement in the nearby particles of skin, pulling on a “thread” (that runs “C” to “C” along the back) going to the brain, which, in turn, causes a pore to open in the brain, allowing fluid to flow through a “small conduit” to the muscles that withdraw the foot. What Descartes called a “thread” and a “small conduit” are today called nerves, and we now know that nerves operate through electrical means, not through physical pulling or the shunting of fluids.