NERVE 



605 



An analysis of the sciatic nerve of man gave in round numbers : 



Water - 66 per cent. 



ICerebrin, lecithin, choles- \ 

 terin, and fatty acids - 17 

 Proteids and glutin - J 34 per cent. 

 Other substances - - i j 



The only difference between living and dead nerve which has 

 made out with any degree of 

 certainty is that the former is 

 neutral or faintly alkaline, and 

 the latter acid, in reaction. 



Degeneration and Regen- 

 eration of Nerve. Nerve- 

 fibres are ' bound in the 

 bundle of life ' with the 

 nerve - cells from which 

 their axis-cylinders arise ; 

 the connection between 

 cell and axon once 

 severed, the nerve-fibre 

 dies inevitably. We shall 

 see later on that changes 

 also occur in the nerve- 

 cell whose axon has been 

 divided from it, although 

 they are of a different 

 nature (rather a slow 

 atrophy than an acute 

 degeneration), and do not 

 necessarily lead to the abso- 

 lute destruction of the cell. 

 Thus, we must regard the 

 neuron not only as a mor- 

 phological unit, a single 

 cell from nucleus to re- 

 motest end - brush, but 



also as a functional and nutritive unit, the fortune of 

 any portion of which is not indifferent to the rest. The 

 acute changes that occur in severed nerve-fibres are most 

 conveniently studied in the peripheral nerves, although 



FIG. 187. DEGENERATION OF NERVE- 

 FIBRES AFTER SECTION (BARKER, alter 

 THOMA). 



I, normal fibre ; II, degenerating fibre ; 

 III, further stage of degeneration ; S, neuri- 

 lemma; m, medullary sheath ; A, axis- 

 cylinder ; L, incisure ; R, node ; mt, drops 

 of myelin; a, remains of axis cylinder ; 

 w, proliferating cells of neurilemma. 



