No. 3-] PERIPHERAL NERVES. 715 



experiments dealing with resection and subsequent implanta- 

 tion of a nerve segment, and a study of the microscopical 

 appearances presented, may, for the sake of clearness, be sum- 

 marized as follows : — 



I. After primary implantation of a segment of a nerve trunk 

 between the resected ends of a peripheral nerve, the implanted 

 portion, the entire peripheral stump, and about ^ctm. of the 

 central stump degenerate. 



II. The myelin and axis cylinders of the implanted nerves 

 are absorbed within the first ten days after the operation. 

 The absorption takes place more slowly in the peripheral 

 degenerating portion of the nerve, and in the degenerated part 

 of the central stump. 



III. The degenerated fibres of the implanted segment and 

 injured nerve present essentially the same structural appear- 

 ance, collapsed sheaths containing a nucleated band of proto- 

 plasm. The nuclei are, however, less numerous in the degen- 

 erated fibres of the implanted part than in the degenerated 

 fibres of the peripheral and central stump of the injured 

 nerve. 



IV. Regeneration begins in the central stump, and proceeds 

 centrifugally. It consists in a down-growth of the axis cylin- 

 ders of the nerve fibres of the central end, through the central 

 wound, the implanted segment, the peripheral wound, and the 

 peripheral portion of the injured nerve. 



V. By the end of the twenty-first day, some of the down- 

 growing axes have reached the central wound. 



VI. By the end of the thirty-seventh day, the greater propor- 

 tion of the down-growing axes have passed the central wound ; 

 some few have passed through the implanted segment and the 

 peripheral wound, and have reached the upper end of the 

 peripheral part of the nerve. There is some return of irritabil- 

 ity to this part of the nerve as shown by the presence of reflex 

 movement on stimulation with strong induction shocks. 



VII. By the end of the 120th day, regeneration extends to a 

 short distance below the middle of the forearm, and to the mus- 

 cular branches of the flex. carp. ul. and flex. prof. dig. (in experi- 

 ments involving the ulnar). Many of the new axis cylinders 



