174 



PHYSIOLOGY OF NERVE. 



[CH. xvi. 



like appendage on the back or nose of the rat gave rise to sensation. The 

 impulse thus passed from base to tip, instead of from tip to base, as formerly. 

 This experiment does not. however, prove the point at all ; for all the 

 original nerve-fibres in the tail must have degenerated, and the restoration 

 of sensation was due to new fibres, which had grown into the tail. Exactly 

 the same objection holds to another series of experiments, in which the motor 

 and sensory nerves of the tongue were divided and united crosswise. 

 Restoration of both movement and sensation does occur, but is owing to new 

 nerve-fibres growing out from the central stumps of the cut nerves. 



Chemistry of Nervous Tissues. 



The nervous tissues contain a large amount of water ; it is 

 present in larger amount (85 to 90 per cent.) in grey matter than 



in white matter (about 70 per cent.); in early than in adult life; in 

 the brain than in the spinal cord ; in the spinal cord than in nerves. 

 The solids contain : 



a. Proteids : these comprise about half the solid matter in grey 

 matter, and about one-third of the solid matter in white 

 matter and nerve. In other words, proteid is most abundant 

 where the cells are situated, which is what one would expect. 

 The proteids found are nucleo-proteid and globulin. 



b. Albuminoids: (i) neuro-keratin, contained within the white 

 substance of Schwann and forming the chemical basis of 

 neuroglia, the supporting tissue of the nerve-centres; (2) 

 nuclein, from the nuclei of the cells. 



c. Fatty materials : the most important of these is lecithin, a 

 complex fat containing phosphorus and nitrogen, in addition 

 to carbon, hydrogen and oxygen. The lecithin in the nervous 

 tissues is combined with cerobrin ; the compound so formed 

 is called protagon. 



d. Cerebrins : nitrogenous substances of unknown constitution 

 which yield a reducing sugar (galactose) on hydration. 



