v SPINAL CORD AND NEEVES 295 



cord, like those of the brain, have a long course in the sympathetic 

 chain and plexuses, after which they re-enter by the spinal roots 

 of a region higher or lower than that under observation. 



An indirect proof of the Bell-Magendie law is afforded by the 

 Wallerian degenerations that take place in the two spinal roots 

 after section. As we saw in the last chapter (see p. 232), when 

 a mixed nerve is divided the peripheral part that is severed 

 from the centre degenerates, while the proximal part connected 

 with the centre remains unchanged for a long time, and may grow 

 and regenerate the cut nerve. Waller found that after section of 

 the dorsal root (between the spinal ganglion and the cord) the 

 central, but not the peripheral part degenerates ; after section of 

 the ventral root, on the contrary, the peripheral, but not the 

 central part degenerates. So that the afferent fibres of the 

 posterior root have their trophic centre in the cells of the spinal 

 ganglion, and the efferent fibres of the ventral root have their 

 trophic centre in the cells of the grey matter of the cord. This 

 observation agrees with, and therefore confirms, our physiological 

 knowledge of the dissimilar character of the fibres which constitute 

 the two roots. 



Wallerian degeneration also confirms the phenomenon of 

 recurrent sensibility. Schiff (1850) was the first to see that 

 after cutting the ventral root certain fibres in the central stump 

 degenerate, while a corresponding number in the peripheral stump 

 remain intact. Since these are recurrent fibres, it is clear that 

 those which are separated from their trophic centres in the central 

 stump degenerate, while those which are left in connection with 

 their centre in the peripheral stump remain intact. 



Wallerian degeneration also confirms the fact that a certain 

 number of centrifugal (vaso-dilatator) fibres emerge with the dorsal 

 roots. If this is a genuine exception to the Bell-Magendie law, 

 section of the dorsal roots should give rise to a form of degeneration 

 which is not in strict correspondence with Waller's law, i.e. there 

 must be some intact fibres in the central stump and some 

 degenerated fibres in the peripheral stump. Different authors, 

 however, obtained different results by this method. Vejas, Max 

 Joseph, Gad, Morat and Bonne obtained positive results as above ; 

 Sherrington, Singer and Miinzer, Gabri, on the other hand, found 

 the central stump completely degenerated, and the peripheral stump 

 intact, precisely according to Waller's law. In order to settle the 

 controversy, Tarulli and Panichi (1902) resumed the study of the 

 degenerations consequent on section of the dorsal roots, and made 

 a number of experiments on different parts (cervical, dorsal, and 

 lumbar) of the dog's cord. The degenerations were followed out 

 by the method of March i or of Weigert-Pal, both on cross-sections 

 of the root-stumps and on teased bundles of nerves, in order to 

 study the fibres lengthways. The result was constant ; in the 



