260 Drs. Mott and Halliburton and Mr. Edmunds. [June 12, 



Since we commenced our work, the subject has risen into considerable 

 prominence, and numerous papers have been published on the question. 

 Some investigators, like Purves Stewart, and Ballance,* in this country, and 

 Bethef in Germany, have advanced the view that the new nerve-fibres have a 

 peripheral origin, while others, like Langley and Anderson,$ and S. Bamon 

 Cajal,§ have defended the older Wallerian doctrine. In Cajal's paper a very 

 complete bibliography of the large number of investigations devoted to the 

 enquiry is also given. 



We ventured to suggest in the preliminary notice of our work that the 

 manifest activity of the neurilemmal cells is related in some degree, pro- 

 bably nutritionally, to the successful repair of a divided nerve, for in situations 

 like the central nervous system, where the neurilemma does not exist, not 

 only is the removal of degenerated myelin a very slow process, but, as is 

 well known, regeneration does not occur. When the nerve is regenerated, 

 and conducts impulses, the elongating strands of neurilemmal cells are seen 

 to be situated outside the new axis cylinder, and in longitudinal view the 

 latter is thus frequently concealed ; but on transverse section the axis 

 cylinder is seen to be quite distinct and separate within this sheath, 

 although the neurilemmal nuclei retain an abnormal thickness for some 

 time.|| 



The idea that the sheath is nutritive has been advanced in a somewhat 

 modified form more recently by Graham Kerr. IF He points out that there 

 are three main views regarding the development of motor nerves in 

 vertebrata : — 



1. Each nerve-fibre develops as an independent outgrowth from a ganglion 

 cell, which gradually grows outwards and finally becomes united to its special 

 muscle. This view is associated especially with the name of His, and is 

 favoured by the majority of embryologists. 



2. The nerve trunk is regarded as multicellular in origin, and consists at 



first of a chain of cells, in the substance of which the nerve-fibres are 



developed later as fine strands passing continuously from one cell body to 

 t 



* ' The Healing of Nerves,' Macmillan and Co., 1901. 



t 'Neurol. Centralbl.,' January, 1902, p. 60; ' AUgenieine Anatomia und Physiologie 

 des Nervensystems,' Leipzig, 1903. 



X ' Journ. of Physiology,' vol. 31, p. 418 (1904). 



§ " Mecanismo de la regeneraci6n de los Nervi6s," ' Trabajos del Laboratio de 

 investigaciones biologicas de la Universidad de Madrid,' vol. 4, pp. 119 — 210 (1905) ; 

 " Mecanisme de la Regeneration du nerf," ' Compt. rend. Soe. de Biol.,' vol. 59, p. 420 ; 

 " Critique de la theorie de l'autor6gen6ration," ibid., p. 422. 



|| This is well illustrated in fig. 30, p. 464, of our 'Phil. Trans.' paper. 

 IT " On some Points in the Early Development of Motor Nerve Trunks and Myotomes 

 in Lepidosiren," by J. Graham Kerr, 'Roy. Soc. Edin. Trans.,' vol. 41, pp. 121—128 (1904). 



