THE MACHINERY OF THE BRAIN 247 



was right ; each root served as a pathway for a definite 

 class of message. Bell was excited by his discovery ; 

 so he well may have been, for he had succeeded in show- 

 ing not only why spinal nerves had two roots, but that 

 the ordinary nerves of the body contained fibres of two 

 kinds : one which carried messages outwards, and another 

 inwards. There was, in his opinion, a circulation of nerve 

 messages. His great service, however, was in showing 

 men a method by which the machinery of the nerve 

 system of the human body could be unravelled. 



Bell tried to discover Nature's secrets in much the 

 same way as detectives follow up a criminal clue. He 

 tried to explain appearances. Now, almost at the same 

 time, or a little later to be quite accurate, as Bell was 

 making his discoveries in England, a great French physio- 

 logist — Magendie — set out to discover why spinal nerves 

 had two roots. He went about his work in quite a 

 different way to that pursued by Bell ; he made no 

 preliminary guesses. He started away by cutting first 

 one root, then another, and noting exactly what happened. 

 He proceeded to collect facts by pure experiment and 

 observation. His proofs that the nerve roots serve 

 different functions were more convincing than those which 

 Bell had brought forward, and hence we often find that 

 men who have no sympathy with the detective way of 

 finding out Nature's secrets give the whole credit of this 

 important discovery to Magendie. 



In 1826, when Charles Bell was reaping some of the 

 rewards of his labours, there was another arrival in 

 London which demands our attention for a moment. 

 Dr Marshall Hall, a very clever and alert Englishman, 

 suddenly abandoned his practice in Nottingham and 

 settled as a physician at No. 15 Keppel Street, near the 

 British Museum. We are to visit him there and witness 

 a discovery which shed a new light on the nervous 

 system. We find him in his consulting room, with his 

 eye glued to a microscope, watching the capillary circula- 

 tion in a lizard's lung. He has occasion during his 

 research to cut off the lizard's tail, and is surprised to 



