REGENERATION OF VAGUS. 665 



The depressor consists chiefly of medium fibres, the other varieties 

 being also represented. 



Gaskell 1 pointed out that numerous non-medullated fibres appear 

 in the vagus immediately below the ganglion trunci vagi. If the view 

 given above (p. 663) be accepted, namely, that the nerve cells of the 

 ganglion of the trunk are posterior root cells, it follows either that 

 afferent fibres may become non-medullated a long way from their 

 endings, or that the efferent pre-ganglionic fibres do. 



In the sympathetic system it can hardly be doubted that pre- 

 ganglionic fibres may become non-medullated a considerable distance 

 centrally of the cells to which they run (cf. above, p. 650), and, in 

 consequence, we may fairly assume that the same may be the case with 

 the similar fibres of the vagus. 



Degeneration. What has been said with regard to the degeneration 

 of sympathetic fibres (p. 652) holds in general for the autonomic fibres 

 of the cranial nerves. It may be noted that, as the vagus is a com- 

 paratively large nerve, the absorption of degenerative products, after 

 the nerve has been cut, goes on much more slowly than in the cervical 

 sympathetic. Clumps and granules and granular cells may be con- 

 spicuous for two or three months. The irritability of the vagus is lost, 

 as a rule, at any rate, on the fourth to fifth day after section of the 

 nerve. 



Schiff 2 stated that the vagus in the dog lost its inhibitory power on the 

 heart on the fourth or fifth day after section of the nerve. According to the 

 same observer, acceleration of the heart can in most cases be obtained by 

 stimulating the peripheral end of the cut nerve, five, seven, and even fourteen 

 days after the nerve has been cut. 



Arloing, 3 who holds, as did Schiff, that cardiac accelerator fibres are 

 present in the vagus, finds that in the dog the accelerator fibres are irritable 

 on the fifth day, but that the cardiac inhibitory and the motor oesophageal 

 fibres have lost their irritability. In the donkey he finds that the accelerator 

 fibres retain their irritability about eight days after section, and that the motor 

 oesophageal fibres may be still effective thirteen days after section. He states 

 also that, in the donkey, the sciatic nerve, eight days after section, may still 

 cause contraction of the blood vessels of the hind-leg. 



Regeneration of vagus. A recovery of function, after section of 

 the vagus, has not been observed so far as regards its autonomic fibres, 

 but not many observations have been made on the matter. We should, 

 of course, expect that the vagus, when cut in the neck, would take a 

 considerable time to regenerate, since the distance from the point of 

 section to the peripheral structures is considerable. 



In an experiment on a cat, 1 4 obtained no effect on stimulating the peri- 

 pheral end of the vagus twelve months after section, although the nerve had 

 largely regenerated, and contained numerous medullated fibres. Tuckett 5 did 

 not find regeneration of the oesophageal fibres of the vagus in the rabbit 231 

 days after section of the nerve. According to Vanlair, 6 the recurrent 

 laryngeal in the dog recovers its functions about eleven months after section 

 of the cervical vagus. 



1 Journ. PhysioL, Cambridge and London, 1886, vol. vii. p. 19. 



2 Arch./, d. ges. PhysioL, Bonn, 1878, Bd. xviii. S. 172. 

 '-' Arch, de pliysiol. norm, et path., Paris, 1896, p. 75. 



4 Journ. PhysioL, Cambridge and London, 1895, vol. xviii. p. 283. 



5 Ibid., 1896, vol. xix. p. 297. 



6 Arch, de physiol. norm, etpafii., Paris, 1894, p. 217. 



