THE VITAL IMPETUS 123 



were delicate tubes in communication with the 

 ventricles, and which were provided with valves ; and 

 this outward flow corresponds to our modern efferent 

 nervous impulse. The afferent impulse was represented 

 by the action of the axial threads contained in the 

 nerve tubuli. When a sensory surface was stimulated, 

 these threads became pulled, and the pull, acting on 

 the wall of the cerebral ventricle, caused a valve to 

 open and allowed animal spirits to flow along the 

 nerve to all the parts of the body supplied by the 

 latter. In the effector organs, muscles or glands, this 

 influx of animal spirits produced motion or other 

 effects. This, in brief, was the physiology of Descartes. 



He spoiled it, says Huxley, by his conception of 

 the " rational soul." Fearing the fate of Galileo, he 

 introduced the soul into his philosophy of the organism 

 as a sop to the Cerberus of the Church. It was un- 

 worthy : a sacrifice of the truth which he saw clearly. 

 Is it likely that Descartes deliberately made part of 

 his philosophy antagonistic to the rest with the object 

 of averting the censure of the Church ? He was not 

 a man likely to rush upon disaster, but the conviction 

 that what he wrote had in it something great and 

 lasting must have made it hardly possible that he 

 should traffic with what he held to be the truth. 



The rational soul was something superadded to 

 the bodily mechanism. It was not a part of the body 

 though it was placed in the pineal gland ; a part of 

 the brain, which by its sequestered situation and rich 

 blood supply suggested itself as the seat of some 

 important and mysterious function. Its existence 

 was bound up with the integrity of the body, and on 

 the death of the latter the soul departed. But the body 

 did not die because the soul quitted it, it had rather 

 become an unfit habitation for the soul. Without 



