190 NERVE INJURIES 



(primary suture) or many months later (secondary 

 suture), medullated nerve will in time be repro- 

 duced and the function restored. There are two 

 schools of interpretation. The one holds that the 

 central cut end buds out new fibres which find 

 their way down the old track to their old destina- 

 tions. This is the theory of central regeneration. 

 The other school contends that the severed piece 

 of nerve, after degenerating, eventually recovers 

 itself, and the continuity of its fibres is restored, 

 though admittedly very few of them, if any, acquire 

 a medullary sheath. It onl}^ needs, according to 

 this school, that the nerve thus regenerated should 

 be put into continuity with its old stump for its 

 function to return and the medullary sheath to 

 develop. This is the theory of peripheral regenera- 

 tion. 



The arguments in favour of the latter theory were 

 as follows : — 



(a) . A nerve is cut across, and the cut ends are kept 

 apart. After some months, it is said, long beaded 

 fibres may be demonstrated by suitable staining 

 methods, running continuously the whole length of 

 the nerve. They are not, in ordinary, surrounded by 

 a medullary sheath. 



It is objected to this that more reliable staining 

 methods show only the discontinuous fibres which 

 make up ordinary white fibrous tissue ; and that no 

 nerve elements are present at all in the degenerated 

 piece of nerve thus cut off from its trophic centre. 



{h). It has been claimed repeatedly that if in 

 man a nerve is divided and not sutured for many 



