THE REPAIR OF A NERVE 419 



they carried out careful dissections that they convinced them- 

 selves that union with the central nervous system had occurred. 

 The new nerve fibres which grow into the peripheral segment 

 from other nerves divided in the operation, often do so by 

 a devious and contorted course. If the number of medullated 

 nerve fibres in the peripheral end is small, then the connection 

 with central fibres was found to be slight; and in cases where 

 no connection occurred then medullated nerve fibres were entirely 

 absent. Bethe admits a variability in the number of medullated 

 fibres, and this, though easily explicable on the view that such 

 fibres come by accident from the central ends of divided nerves, 

 is not accounted for at all by the autogenetic theory. 



Another admission which Bethe makes also weakens his 

 view. He admits that auto-regeneration does not occur in adult 

 animals. He does not, however, state at what age animals lose 

 their power of auto-regeneration, nor explain how it is that 

 after a certain date an animal repairs a divided nerve in the 

 exactly contrary manner to that it would have adopted if the 

 nerve had been cut before that date. The difference which 

 exists between young and adult animals is quite easily accounted 

 for in accordance with Wallerian views ; it is simply due to the 

 greater ease with which reunion with central nerves occurs 

 in young and actively growing animals, 



Bethe's views have been contested not only by Langley 

 and Anderson, but also by Lugaro, by Kolliker, by Cajal, by 

 Marinesco, by Mott, and Edmunds in conjunction with myself, 

 and by numerous others. 



I may mention a few of the experimental results which have 

 come out of the renewed work elicited by the promulgation 

 of the autogenetic theory. 



(i) It is possible entirely to prevent reunion with the central 

 ends of divided nerves. In our own work we accomplished this 

 by removing a long stretch of the main nerve experimented 

 with, by making the skin incision as small as possible, and 

 by inclosing the top end of the peripheral segment in a cap 

 of sterilised gutta-percha. Under such circumstances no auto- 

 regeneration occurs. 



(2) Pieces of nerve may be transplanted under the skin, 

 and in time a few fully formed medullated fibres appear within 

 the degenerated bundle of fibres. This is adduced by Kennedy 

 as undoubted evidence of auto-genesis, but, again, is easily 



