PHYSIOLOGY OF NERVE 269 



be briefly summarised as consisting of the degeneration of that 

 part of the nerve fibre which has been cut off from the appropriate 

 nerve cell. Whether the " neurone theory " is anatomically exact 

 or no, as far as this particular physiological problem is concerned, 

 the degeneration exactly follows the law. 



There is no such unanimity as to the events occurring subse- 

 quently. Under certain circumstances, to be considered shortly, 

 the degenerated part of the nerve fibre is regenerated, and the 

 particular point on which controversy has arisen is the source of 

 the new nerve fibres. 



There are three possible ways in which such fibres might 

 arise. 



I. They could grow downwards from the central end of the 

 divided nerve, as Waller originally described in 1850. 



II. They could be formed in situ from the cells in the peripheral 

 portion, and then grow up towards the spinal cord. 



III. They could wander in from the central end of other cut 

 fibres, to which they originally did not belong. 



Each of these possibilities must now be considered. 



I. While this source of the new nerve fibres is regarded by 

 most observers as at least the usual one, it must be remembered 

 that there are certain conditions which must be fulfilled before 

 regeneration can take place in this manner. 



(a) The peripheral and central ends of the divided nerve must 

 be brought into some sort of connection. This is usually done 

 by apposition and suture of the two cut ends ; but where there 

 has been loss of nerve substance, and a gap is left, this can be filled 

 by another nerve from the same individual, which is naturally the 

 best method, or failing this, by the interposition of some other 

 tissue. This can be either plain catgut, or a nerve from an- 

 other animal, the results are about equally good in both cases 

 (Kilvington 28 ), and Marinesco ( M ) has shown that an alien nerve is 

 absorbed%s a foreign body and presents no advantages over catgut. 



(6) The negative side of the condition is interesting. If the 

 cut end of the peripheral part be enclosed in a rubber cap or 

 stitched to some part of the body where nerve fibres are scarce, 

 such as the peritoneum ( M ), no regeneration occurs at all. This is 

 one of the arguments against the growth of the new fibres from 

 the peripheral end, as we shall see presently. 



(c) The portion of the spinal cord from which the nerves 



