CH. XIV.] 



DEGENERATION OF NERVE 



147 



axis cylinders which are cut off from their parent cells die, breaking 

 up into fragments ; the medullary sheath of each undergoes a process 

 of disintegration into droplets of myelin, which are ultimately 

 absorbed and removed by the lymphatics. At the same time there is 

 a multiplication of the nuclei of the primitive sheath. This degenera- 

 tive process begins to be visible microscopically two or three days 



t' ft' 



Fio. 153. Degeneration and regeneration of nerve-fibres. A, nerve-fibre, fifty hours after operation. 

 my, Medullary sheath breaking up into myelin drops, p, Granular protoplasm, n, Nucleus, g, 

 Primitive sheath or neurilemma. B, nerve-fibre after four days, cy, Axis cylinder partly broken 

 up and enclosed in portions of myelin. C, a more advanced stage in which the medullary sheath 

 has almost disappeared. Numerous nuclei, n", are seen. D, commencing regeneration ; several 

 fibres (t', t") have sprouted from the somewhat bulbous cut end (6) of the nerve-fibre, a, An axis 

 cylinder Avhich has not yet acquired its medullary sheath, s, s', Primitive sheath of the original 

 fibre. (Ranvier.) 



after the section has been made In the case of the non-medullated 

 fibres, there is no medullary sheath to exhibit the disintegrative 

 changes just alluded to; and the nuclei of the sheath do not 

 multiply ; there is simply death of the axis cylinder. The degenera- 

 tion occurs simultaneously throughout the whole extent of the nerve. 

 Ranvier's original diagram is reproduced in fig. 153. Fig. 154 is 

 drawn from a specimen of degenerated fibres stained by osmic acid ; 

 the myelin droplets are coloured black by this method. 



