NER VE 695 



continuity, but is not cut, no distortion of the motor and sensory 

 ' patterns ' of the nerve in other words, no ' straying ' of 

 the fibres from their old paths can be detected on regeneration. 

 When the nerve is cut and then sutured, a certain amount of 

 distortion of the pattern is inevitable. The mechanical apposi- 

 tion of central and peripheral stumps is, of course, much more 

 nearly perfect in the crushed nerve than in the cut nerve, however 

 exact the suturing may be (Osborne and Kilvington). That, 

 however, the degenerated peripheral stump directs the growth 

 of the axons from the central stump in some other than a merely 

 mechanical way is evident from the experiments of Langley on 

 regeneration of the cervical sympathetic in the cat after section 

 below the superior cervical ganglion. The nerve contains fibres 

 of various functions which reach it from the upper thoracic 

 nerves. The anterior roots of the first and third thoracic nerves 

 supply the cervical sympathetic mainly with fibres which end 

 in the ganglion around cells that give off dilator fibres for the 

 pupil. The fibres connected with the cells in the ganglion 

 which send vaso-motor fibres to the vessels of the ear are for the 

 most part contained in the anterior roots of the second and fifth 

 thoracic nerves ; and the fibres connected with the cells that 

 give origin to the pilo-motor fibres for the hairs of the face and 

 neck in the anterior roots of the fourth to the seventh . Stimula- 

 tion of any one of the upper thoracic roots accordingly causes 

 a specific effect, \vhich, according to Langley, is in general the 

 same after regeneration as before section of the cervical sym- 

 pathetic. We must assume, therefore, that each regenerating 

 fibre seeks out either the ganglion cell with which it was originally 

 connected, or one belonging to the same class. No mere mechanical 

 guidance of the growing axons by the old neurilemmas will 

 suffice to explain this selective growth. It is necessary to 

 postulate, in addition, an attraction of a chemical or physico- 

 chemical nature (chemiotaxis), dependent upon a specific rela- 

 tion between the new axons and the scaffolding of the peripheral 

 stump or the ganglion cells. But it is not possible at present 

 to form any very precise conception of the properties on which 

 the chemiotactic phenomena depend. And the specificity is 

 not an absolute one. Under certain conditions these pre- 

 ganglionic nerve-fibres (that is to say, nerve-fibres running from 

 the spinal cord to end around the sympathetic ganglion cells) 

 can form connections with nerve-cells of a different class e.g., 

 pupillo-dilators with cells whose axons end in the erector muscles 

 of the hairs. Further, after section of the sympathetic above 

 the superior cervical ganglion, the post-ganglionic nerve-fibres 

 (i.e., the fibres coming off from the cells of the ganglion) may 

 also, if the opportunity be favourable during regeneration, ex- 



