RECURRENT SENSITIVITY. 789 



after destruction of portions of the spinal cord (in birds), that the ventral roots 

 were still found, when examined by the microscope, to contain a few unde- 

 generated myelinate nerve fibres ; these could be traced to the arachnoid and 

 pia mater. Schafer discovered that in the cat there are in the lumbar 

 ventral roots a few nerve cells ; these cells resemble the smaller of the cells of 

 the spinal root ganglion ; the number of these cells and the number of sound 

 fibres remaining in the ventral spinal root, peripheral to its place of section, 

 do not in many cases tally. A phenomenon somewhat similar to the slight 

 sensitivity exhibited by the peripheral end of a severed ventral root, is met 

 with on stimulating the peripheral ends of certain motor peripheral nerves 

 after severance of the nerve nearer its origin. The branches of the facial of 

 the dog, when examined in front of the parotid gland, exhibit it, unless the 

 trigeminus is severed. The phenomenon is the more marked, the more peripheral 

 the region of the nerve examined. Fibres can be traced by the degeneration 

 method to loop back from the fifth nerve into these branches of the seventh. 



Bell's l and Magendie's 2 observations, in so far as they dealt with the 

 afferent channel, dealt with it only as a channel for exciting signs of sensation. 

 Volkmann, 3 later, showed that the dorsal root is also the channel for evoking 

 reflex action after decapitation, and under circumstances, therefore, which 

 there is reason to think exclude sensation. The discrimination between the 

 functions of the roots was discovered, as above stated, in mammals. Wagner, 4 

 Stannius, 5 and Moreau 6 found it to apply in fish ; J. Miiller 7 and Panizza 8 

 established it for the frog; and Panizza 8 and Schiff 9 for the bird. 



The dorsal spinal root has been stated above to be a purely afferent tract 

 of fibres. It does appear to be so in most animals; in some forms, how- 

 ever, it contains a few fibres which have origin in intraspinal cells, perhaps of 

 efferent function, v. Wijhe 10 holds that the ventral spinal roots of Amphioxus 

 contain some afferent fibres. I n have brought forward some evidence in the 

 same direction regarding the roots of the third, fourth, and sixth cranial 

 nerves of mammals. 



The histologists Ramon y Cajal 12 and v. Lenhossek 13 have, by use of the 

 method of Grolgi, discovered in the dorsal (afferent) spinal root, nerve fibres 

 arising from cells in the grey matter of the spinal cord itself. This discovery 

 made in the chick has been extended to the cord of certain teleosteans. 14 The 

 nerve cells which give origin to these fibres of the dorsal root lie for the most 

 part in the dorsal portion of the ventral grey horn. They are multipolar, 

 and the microscopists describe them as " motor." This suggests exception 

 of the Bell-Magendie law of direction of transmission in the spinal nerve roots, 

 and calls to mind the recent account 15 of peripheral effects following excitation 

 of the distal ends of the dorsal spinal nerve root of the frog. Steinach and 

 Wiener detected visceral effects, Horton-Smith detected effects on skeletal 



1 "An Idea of a New Anatomy of the Brain," 1811, republished in "An Exposition 

 of the Natural System of Nerves," London, 1824. 



2 Journ. de physiol. ex})er., Paris, 1822. 



3 Arch.f. Anat., Physiol. u. wissensch. Med., 1838, S. 15 ; ibid., 1841, S. 354. 



4 ' Handworterb. d. Phys.," 1846, Bd. iii. S. 366. 



5 'Das periph. Nervensyst. d. Fisch.," Rostock, 1849. 



6 Compt. rend. Soc. de biol., Paris, 1858-1860. 



7 ' Handbncli d. Physiol.," 1834. 



' Richerche sperimentali sopra i 

 'Lehrbuch. d. Physiol.," Lahr, 



nervi," Pavia, 1834. 



. 1858. 



10 Verhandel. d. k. Akad. v. Wetensch., Amsterdam, January 1897. 



11 Proc. Roy. Soc. London, 1897. 12 Anat. Ann., Jena, 1890, 8. 112. 



13 Ibid., S. 360. Later confirmations by Retains, Biol. Untersuch., Stockholm, 1892, 

 Bd. v. ; v. Gehuchteii, Anat. Anz., Jena, 1893, S. 215 ; J. Martin, Cellule, Lierre and 

 Louvain, 1895. 



14 v. Gehuchten. 



15 Steinach, Lotos, 1893, Bd. xiv. ; Steinach and Wiener, Arch. f. d. ges. Physiol., 

 Bonn, Bd. Ix. S. 593 ; Horton-Smith, Journ. Physiol., Cambridge and London, vol. xxi. 

 p. 101. 



