804 THE SPINAL CORD. 



in the opposite afferent root is very slight, inconstant, and whether 

 significant of discharge of impulses appears doubtful. 1 



EEGENERATION OF THE AFFERENT BOOT FIBRES. 



Leaving aside the old question of the regeneration of peripheral ganglia 

 as presenting no observations with methods adequate to settle it, 2 there 

 is the related one concerning regeneration of the afferent spinal roots. Eich- 

 horst and Naunyn, 8 after transection of the spinal cord, found nerve fibres 

 traversing the cicatrix, which they considered traceable to an afferent root 

 adjacent, being able to follow them to a spinal ganglion. After extradural 

 section of the afferent root, a partial regeneration has been observed. 4 Chi- 

 pault 5 has obtained in three puppies regeneration of the severed roots when 

 they were sutured together immediately after section, the times elapsing 

 between severance and suturing and the autopsy being from three to six 

 months. The dorsal spinal columns, since they consist of afferent root fibres 

 almost entirely, should show evidence of regeneration. There is, however, 

 none such recorded. 1 6 looked for signs of regeneration in a monkey's cord, 

 in which the dorsal columns alone had been transected four months previously, 

 but found no evidence of regeneration, although the scar was very limited in 

 the longitudinal extent of the cord. Thirty-three days after section of the 

 lumbar afferent roots proximal to their ganglia, I was surprised to meet, in the 

 spinal stumps of the severed roots, numbers of minute myelinated fibres, less 

 than 4 /x, in diameter, presenting the same appearance as the young nerve fibres 

 in regenerating peripheral nerves. The ganglia had been excised, so that the 

 new fibres could not be due to out-growth from them. The question of the 

 regeneration of the afferent root is not without practical importance. Kegenera- 

 tion of the peripheral fibre the cellulipetal conducting fibre of the afferent 

 root cell is a well-established fact, and is found to occur quite well in even 

 advanced adult life. As tested by functional results, it takes place more 

 quickly than the regeneration of the axon of the motor root cell. 7 



SKETCH OF THE FUNCTIONAL ANATOMY OF MEDIATE SPINAL SYSTEMS. 



Although the two root cells, afferent and efferent, may suffice for 

 certain reflex actions, it is probable that for most, even purely spinal, 

 reflexes they are by themselves an insufficient apparatus. It is there- 

 fore convenient, before dealing with spinal reflexes in general, to consider 

 other elements in the neural mechanism of the cord. Among the 

 spinal cell systems, including in the word " cell " not only the cell body 

 (perikaryon) but also all the nerve fibres which are its branches, there 

 can be distinguished on the one hand the root systems and on the other 

 the mediate systems. It is possible that the two root systems are them- 

 selves connected together, and that the simplest reflex arc is formed by 

 their direct linkage. But in many cases the reflex reaction seems to 

 occur through one part of the afferent root system acting on a distant 



1 E. M. Sowton, Proc. Roy. Soc. London, 1898, vol. Ixiv. p. 354. 



2 The problem does not seem to have been touched in this half of the century. 

 Valentin, " De functionibus nervorum cerebralium," 1839 ; Dupuys et Dupuytren, Bull. 

 Acad. de mdd., Paris, 1843-1844, p. 355 ; Schrader, "Exp. circa regenerat. in'gangl. nerv. 

 vuln. illatis in animal, institute," Gottingen, 1850 ; Walther, " De regenerat. gangliorum," 

 Bonn, 1853. 



3 Arch.f. exper. Path. u. PharmaTcol. , Leipzig, 1874, Bd. ii. S. 377. 



4 Kahler, Prag. med. Wchnschr., 1884, S. 301. 



5 "'Etudes de chirurgie meilullaire," Paris, 1893. 



6 Journ. Physiol., Cambridge and London, 1893, vol. xiv. p. 271. 



7 Ibid., 1894, vol. xvii. p. 218. Of. Kennedy, Phil. Trans., London, 1898, and Trans. 

 Roy. Soc. Edin., 1899. 



