A HISTORY OF SCIENCE 



distribution of the spinal nerves had been an unsolved 

 puzzle. 



Bell's discovery was epochal ; but its full significance 

 was not appreciated for a decade, nor, indeed, was its 

 validity at first admitted. In Paris, in particular, then 

 the court of final appeal in all matters scientific, the al- 

 leged discovery was looked at askance, or quite ignored. 

 But in 1823 the subject was taken up by the recognized 

 leader of French physiology Francois Magendie in 

 the course of his comprehensive experimental studies of 

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

 jected to the most rigid experimental tests and found 

 altogether 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 fila- 

 ments 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 un- 

 recognized duality of function pertains to the entire 

 extra-cranial nervous system. Any impulse sent from 

 the periphery to the brain must be conveyed 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 corresponding message is 

 denied transmission as effectually as an electric cur- 

 rent is stopped by the section of the transmitting 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- 



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