278 Drs. Mott and Halliburton and Mr. Edmunds. [June 12, 



and a large sensory bundle in the leg were traced up into the main sciatic 

 trunk, and by dividing the sheath they could be easily separated in the trunk 

 for a considerable distance. A small piece of the upper and lower ends of 

 both the motor and the sensory bundle were then removed, placed in Marchi's 

 fluid, and examined in sections as before. 



There was a noticeable difference between the amount of medullation in 

 the motor and sensory nerves, that in the latter being, as is usually the case, 

 more advanced. Both, however, showed at their upper ends numerous 

 myelinated fibres ; whereas at the lower end, which was 4 or 5 inches distant, 

 myelination was much less distinct. We illustrate these appearances by the 

 figures on the accompanying plate, which show high and low power views of 

 transverse sections of the motor trunk at the two levels. 



This second cat, although it was killed a week later than the first, showed 

 less advanced myelination. We have called attention in our previous work 

 to the difficulty of assigning any exact dates, even in the same species of 

 animal, to any particular stage of the regeneration process. The dates vary 

 within somewhat wide limits with the vital reaction of different animals. In 

 the case of the two cats we are at present concerned with, the first animal was 

 a young and lively one, whereas the second animal was large, lethargic, and 

 older. It is therefore not surprising that regeneration should have been 

 more rapid in the first than in the second case. 



It can hardly be doubted that the medullary sheath is a developmental 

 appendage of the axis cylinder ; it appears in the fibres of the central nervous 

 system where the neurilemma is absent ; it degenerates with the axis 

 cylinder when a nerve-fibre is cut, and completeness of function is associated 

 with its appearance in development and with its reappearance in 

 regeneration. 



We therefore think we are justified in concluding that the late appearance 

 of the medullary sheath in those portions of the regenerating fibres which 

 are most distant from the place where the nerve was originally cut is a con- 

 clusive piece of evidence in favour of the view that the new nerve-fibres have 

 grown from the central end in a peripheral direction. 



Von Biingner,* von Nbtthaft/f Stroebe,t and Wieting§ all agree that the 

 formation of nerve-fibres takes place more rapidly near the junction than at 

 the periphery. 



* 'Ziegler's Beitrage,' vol. 10, p. 321 (1891). 

 t ' Zeitsch. f. Wissen. Zool.,' vol. 55, p. 376 (1892). 

 J ' Centralbl. f. path. Anat.,' vol. 4, p. 49 (1893). 

 § 'Ziegler's Beitrage,' vol. 23, p. 63 (1898). 



