248 THE ENGINES OF THE HUMAN BODY 



notice that each time he touched it with a needle the 

 tail wriggled. There was nothing new in this observation ; 

 men had done and seen the same thing before. The 

 question, however, which Marshall Hall asked himself 

 was new. " Why," he asked, " should the muscles of 

 this detached piece of tail contract when I merely touch 

 the skin ? " He observed that the lower end of the 

 spinal cord lay within the amputated part ; he destroyed 

 the cord, and then on touching the skin as before, nothing 

 happened ; there was no wriggling. He then went on 

 to carry out researches which showed that the spinal cord 

 was not merely a nerve cable, as physicians then supposed, 

 but the seat of a machinery which could start and control 

 many purposive muscular movements. He showed that 

 this machinery was set going by messages carried to it 

 by ingoing or afferent nerve fibres, and that orders were 

 dispatched along outgoing or motor fibres. He unfolded 

 a reflex action — a " touch-button " machinery — in the 

 spinal cord and brain stem. His discovery could not 

 have been made if Charles Bell had not shown the way, 

 but of the two discoveries Hall's proved the more 

 important. 



We have not yet finished with young medical men 

 arriving in London and promptly setting out to make 

 important discoveries about the nervous system. In 

 1845, when Dr Marshall Hall had become one of the 

 most successful and most maligned physicians in London, 

 Dr Augustus Waller commenced the practice of his pro- 

 fession in Kensington. He had pursued his studies in 

 Paris and learned the value of the compound microscope 

 — then being perfected — as an instrument for unravelling 

 the secrets of the human body. While waiting for 

 patients, he occupied his leisure hours in studying the 

 almost transparent tongue of the frog to discover how 

 juices of the food reached the terminals of the nerves of 

 taste. On one occasion he was surprised to notice that 

 the fibres of a nerve, which he had divided a few days 

 before, were rapidly becoming broken up — undergoing 

 degeneration. He noted that the degeneration ceased 



