No. 3.] PERIPHERAL NERVES. 70 1 



are not numerous ; they, as a rule, occupy a central position in 

 the collapsed sheath, and are surrounded by the protoplasm. 

 Between the degenerated fibres are found spindle-shaped con- 

 nective tissue cells and polynuclear leucocytes in larger number 

 than the figure would lead one to infer ; and not unfrequently 

 capillaries or small arterioles filled with red and white blood 

 cells are met with. PI. XXXIV, Fig. 5, represents a portion 

 of a typical nerve fibre taken from the peripheral ulnar nine 

 days after the operation for implantation. A comparison of 

 this with PI. XXXIV, Fig. 4 (portion of implanted segment 

 of the same dog), shows that in the degenerating fibres of the 

 peripheral ulnar segment, the absorption of the myelin has not 

 advanced nearly so far, while the proliferation of the nuclei is 

 more marked than in the fibres of the implanted segment. 

 That this proliferation of the nuclei takes place after the 

 manner of a typical mitosis has been shown by Torre, Biinger, 

 Stroebe, and myself in a former article, and I am, at this time, 

 able to corroborate the observation already recorded. The 

 peripheral end of the central ulnar stump degenerates to the 

 extent of about ^ ctm. The degeneration is essentially the 

 same as observed in the peripheral ulnar. Between the central 

 end of the implanted segment and the peripheral end of the 

 central ulnar stump is seen a layer of embryonic connective 

 tissue, composed largely of branched and spindle-shaped con- 

 nective tissue cells and polynuclear leucocytes enclosed in the 

 meshes of a very loose fibrous reticulum. A narrow layer, of 

 similar structure, unites the peripheral end of the implanted 

 segment and the peripheral ulnar. 



From the ninth to the twenty-first day very little structural 

 change worthy of mention is observed in the fibres of the im- 

 planted segment. In long. sect, of this tissue, removed twenty- 

 one days after the operation, hardened in Muller's fluid, and 

 stained in anilin blue and safranin, the collapsed sheaths are 

 not well made out. In teased preparations {see PI. XXXIV, 

 Fig. 7) they appear as narrow tubes, often compressed and 

 containing a small amount of protoplasm and here and there a 

 nucleus. Between the fibres are found connective tissue ele- 

 ments and leucocytes. In the peripheral ulnar of the above 



