THE MACHINERY OF THE BRAIN 249 



at the point of division ; from that point to the brain 

 the fibres remained intact. What proved still more 

 surprising to him was the fact, that presently the de- 

 generated fibres were replaced by a fresh set which grew 

 out from the end of the cut nerve. That was a new 

 light on nerves ; if they were cut, they withered and died 

 just as a branch did when it was lopped from a tree. 

 Like a branch, too, it could be replaced by the outgrowth 

 of a new one. No other structure of the body behaved 

 in that manner when divided. 



The discovery which finally revealed the machinery of 

 the nervous system was made not by medical men at all, 

 but the mechanicians who in the early thirties of the 

 nineteenth century converted the compound microscope 

 into an efficient instrument for research. Methods were 

 soon invented for cutting small slices of the brain and 

 spinal cord so thin and translucent that they could be 

 studied by the microscope. Then came the discovery 

 of staining, of treating microscopic sections with dyes 

 which brought out their structural pattern. These were 

 the means by which the structure of the nervous system 

 were unravelled. 



Although the discoveries which Schleiden and Schwann 

 hiftl made in Berlin in 1838-39 convinced everyone that 

 the human body, like all living matter, was made up of 

 innumerable microscopic units or cells, yet at first it was 

 difficult to believe that a nerve was made up of separate 

 particles or cells. When a nerve thread was teased out 

 by needles into its finest elements and these were 

 * examined under the microscope only delicate white fibres, 

 each about -^wcr °^ an mcn m breadth, were seen, packed 

 in bundles like wax tapers in a box. Each fibre had its 

 central wick or axis cylinder ; then came the wax- like 

 substance — myelin — which surrounded the wick ; then 

 the outer transparent wrapping or sheath. Nowhere did 

 the fibres seem to be interrupted or come to a sudden 

 end. A microscopic fibre, which commenced in the skin 

 of the sole of the foot or in the palm of the hand, seemed 

 to pursue an unbroken course until the spinal cord was 



