GEORGE BERNARD / SCIENCE PHOTO LIBRARY GEORGE BERNARD / SCIENCE PHOTO LIBRARY
Nervous reflex arc. Engraving of a man standing next to fire with half his nervous system visible, taken from the first European textbook of physiology, Rene Descartes' De Homine (1662). The fire triggers a nervous impulse which travels up to the brain, into another nerve fibre and back to the leg muscles. The leg jerks away from the pain without any conscious thought in a reflex arc. Descartes (1596-1650) was a French mathemati- cian and philosopher. He based De Homine on the idea of a human machine made by God to be almost identical to a real person. This allowed him to explain the body mechanically without the restric- tions of contemporary theology and physiology.
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