NERVE INJURIES 131 



secondary suture are trustworthy. As we have seen 

 already, there are many fallacies in testing sensation, 

 and since these have been recognized there is no 

 evidence that such immediate return of sensation 

 has been proved to occur in any well-authenticated 

 case. Patients are often over-sanguine as to the 

 benefit of operations, and may deceive themselves. 

 The .irritation of the stump by the stitches may 

 induce sensations referred to the surface. It is 

 certain that in most cases improvement after second- 

 ary suture is not more but less rapid than after 

 primary suture. 



(c). Bethe and others have found that if a nerve 

 is divided and not sutured, but a gap is left which 

 prevents union, after a year or two a few medullated 

 fibres may be seen in the degenerated peripheral 

 segment, and feeble muscular contractions of the 

 paralysed muscles may follow stimulation. He took 

 this to indicate that peripheral regeneration had 

 occurred. Langley and Anderson have, however, 

 proved that these few medullated fibres are derived 

 from some other nerve in the limb, which has grown 

 down the old path, in obedience to the mysterious 

 chemical attraction which is presumably the cause 

 of central regeneration. Thus if the sciatic nerve 

 was divided and the upper part cut away, any 

 medullated fibres found in the tibial nerves will 

 degenerate after section of the anterior crural or 

 obturator. The observation thus becomes strong 

 evidence in favour of the theory of central regener- 

 ation. 



There is indeed abundant proof in favour of the 



