THE STORY OF NINETEENTH-CENTURY SCIENCE 



leader of French physiology Francois Magendie in 

 the course of his comprehensive experimental studies of 

 the nervous system, and Bell's conclusions were subject- 

 ed to the most rigid experimental tests, and found alto- 

 gether valid. Bell himself, 

 meanwhile, had turned his 

 attention to the cranial 

 nerves, and had proved 

 that these also are divisible 

 into two sets sensory and 

 motor. Sometimes, indeed, 

 the two sets of filaments 

 are combined into one nerve 

 cord, but, if traced to their 

 origin, these are found to 

 arise from different brain 

 centres. Thus it was clear 

 that a hitherto unrecog- 

 nized duality of function 

 pertains to the entire extra- 

 cranial nervous system. 



Any impulse sent from the periphery to the brain must 

 be convej^ed along a perfectly definite channel ; the 

 response from the brain, sent out to the peripheral 

 muscles, must traverse an equally definite and altogether 

 different course. If either channel is interrupted as by 

 the section of its particular nerve tract the correspond- 

 ing message is denied transmission as effectually as an 

 electric current is stopped by the section of the trans- 

 mitting wire. 



Experimenters everywhere soon confirmed the obser- 

 vations of Bell and Magendie ; and, as always happens 

 after a great discovery, a fresh impulse was given to in- 



402 



SIR CHARLES BELL 

 By permission of G. Bell and Sons, London 



