THE REPAIR OF A NERVE 427 



covery that the first kind of sensation to return is of a vague 

 nature, which he terms protopathic ; he associates this with the 

 activity of the fine medullated fibres which replace the de- 

 generated ones at an early date ; return of protopathic sensibility 

 begins about the eightieth day. The more elaborate sensations 

 and power to localise them accurately return much later, and 

 this epicritic sensibility, as Head terms it, is usually not perfect 

 until months, or even years, have elapsed after the regeneration 

 started. 



By this time, as was shown by experiments on animals, 

 the fine nerve fibres which subserve protopathic sensation are 

 largely admixed with a later growth of larger nerve fibres, and 

 he believes that epicritic sensation is subserved by these. He 

 also postulates that the three kinds of sensation (deep, proto- 

 pathic, and epicritic) are related to different kinds of end-organs 

 in the peripheral structures. 



Granting that earlier observers had been led into errors 

 by not being acquainted with Head's discoveries, and that many 

 cases of supposed early recovery can be explained in the manner 

 already indicated, there remains a small residuum of cases in 

 which such explanations do not hold, and in which early 

 recovery appears to have been an undoubted fact. Of these, 

 I would particularly refer to some cases recorded by Dr. 

 Kennedy of Glasgow, in which the return of sensation of some 

 sort, especially to painful stimuli, was a matter of only a few 

 days. In these cases due care appears to have been taken to 

 exclude any bias of the patient's own mind. He admits that 

 such cases are rare ; from his own point of view auto-regenera- 

 tion would therefore appear to be an unusual phenomenon. 

 Granting that the early recovery was genuine, it seems to me 

 there is a much more probable explanation than that of auto- 

 regeneration. They are doubtless instances where extremely 

 rapid growth of new axis cylinders from the central into the 

 peripheral segment of the nerve took place. Dr. Kennedy's 

 cases appear to be happy examples of the date of the secondary 

 suture being such that the usual impediments to repair were 

 minimal. The preparatory work of the neurilemmal cells in 

 the distal portion of the nerve had evidently reached that 

 stage when they were most fitted to receive the new axis 

 cylinders, and by their metabolic activity favour the onward 

 growth of the fibrils at a rapid rate. The examination of 



