166 



PHYSIOLOGY OF NERVE 



[CH. XV. 



tracing nervous tracts, and ascertaining the nerve-cells from which 

 they originate. It must not, however, be regarded as an isolated 

 phenomenon in physiology ; it is only an illustration of the universal 



FIG. 182. Nerve-fibres from sciatic nerve of cat, four days after the nerve had been cut. This shows an 

 early stage of the degenerative process.. ' COO diameters. (Mott and Halliburton.) 



truth that any portion of a cell (in this case the axis cylinder process) 

 cut off from the nucleus of the cell degenerates and dies. 



If a nerve is simply cut, and allowed to heal, regeneration of 

 function in time occurs. This is hastened by the surgeon suturing 

 the cut ends of the nerve together. It must not, however, be supposed 

 that this is due to a restoration of the structure of the fibres in the 

 peripheral portion of the cut nerve. It is due to very fine new 

 nerve-fibres sprouting out from the central end of the cut nerve, and 

 growing distal wards. This is illustrated in D, fig. 181. When 



FIG. 183. These are fibres from the sciatic nerve of another cat, ten days after the nerve had been cut. 

 This shows the breaking-up of the medullary sheath in a marked way, and the intense black colour 

 the myelin droplets take with osmic acid. 600 diameters. (Mott and Halliburton.) 



regeneration does not take place, the central ends of the cut fibres 

 and the cells from which they originate undergo slow atrophic 

 changes (disuse atrophy). 



The view expressed by the earlier workers on nerve regeneration 



