246 THE ENGINES OF THE HUMAN BODY 



on the muscles of expression, beautifully illustrated by- 

 drawings done by his own hand. He found no warmth 

 of welcome in London, but he elbowed his way, and when 

 almost at the end of his resources had the audacity to take 

 the lease of a big ramshackle house in Leicester Square, 

 where he put up his plate, and spent almost his last 

 shilling in fitting the boy, who had to open the door for 

 patients who rarely came, with a blue coat bedizened with 

 brass buttons. He opened a private school for medical 

 students, and we are to visit him in 1811 while he is 

 giving his students a demonstration on the central nervous 

 system of the human body. We find him puzzling over 

 Nature's craftsmanship just as Hunter did. "Why," he 

 asks his students, " should a spinal nerve have two roots ? 

 If both serve the same office, then why are they not 

 united in one root?" He announced that he was con-' 

 vinced there were two roots because two pathways were 

 necessary — one for messages going out from the cord, 

 the other for messages coming in. He inferred that the 

 hinder root was for incoming or afferent messages, because 

 the nerves from the eyeball and from the ear, which had 

 to carry only incoming messages, ended, as posterior roots 

 did, on the hinder side of the brain-stem. The anterior 

 root must then be for the outgoing or efferent messages 

 which set muscles in movement. He concluded, on this 

 basis, that the hinder part of the spinal cord was con- 

 cerned in carrying messages to the brain, while its front 

 part was for conveying impulses from the brain to the 

 muscles. 



If Charles Bell had been an ordinary man he would 

 have remained satisfied with the guess he had made, but 

 he was an anatomical detective of the highest rank. He 

 followed up the clue he had thus hit upon. He pricked 

 or stimulated an anterior nerve root in a living animal ; 

 the muscles supplied by the nerve contracted ; pricking 

 the posterior root, he found, had no result. He then 

 cut the anterior root ; the muscles supplied by the 

 corresponding nerve were paralysed, but on cutting the 

 posterior root no definite effect was detected. His guess 



