NERVE 697 



there after regeneration has been much debated. All are agreed 

 that nerve-fibrils sprout from the central stump, and the weight 

 of evidence is in favour of the long-accepted view that it is by 

 the growth of these fibrils along the peripheral stump that the 

 new axons are formed, and that all the changes in the distal 

 portion of the nerve, however important for directing and 

 perhaps sustaining the growth of the central fibrils, are subsidiary 

 to this. But some maintain that the outgrowing central fibrils 

 meet and unite with corresponding fibrils sprouting from the 

 peripheral stump, and that the new axis-cylinders arise from 

 the fibrils of the axial strand. It is said that very shortly after 

 being brought into connection with the central portion of the 

 same or of another nerve by careful suturing the spindle cells 

 begin to lengthen, and form non-medullated fibres, like those of 

 the sympathetic. Four weeks after union the afferent fibres, 

 although still non-medullated, are capable of being stimulated 

 mechanically and electrically, and of conducting impulses 

 towards the centre. .In about eight weeks they become medul- 

 lated, but at first are of small calibre (Head and Ham). Bethe, 

 the most strenuous defender of the inherent regenerative power 

 of the isolated peripheral stump (autogenetic theory) , has even 

 stated that complete regeneration occurs in young animals in 

 nerves entirely separated from their centres. The controversy 

 turns largely upon the precautions judged necessary to prevent 

 the ingrowth of central fibres. And while it is comparatively 

 easy to make sure, by removing a large part of it, that the central 

 end of the nerve under observation shall remain completely 

 unconnected with the peripheral end, it is often a matter of the 

 greatest difficulty to prevent the union of the distal stump with 

 central fibres from other sources e.g., from the nerves cut in 

 the wound. There is no doubt that many of the results which 

 seemed to favour the autogenetic theory were due to this cause. 



A fact of great physiological interest, and also of practical im- 

 portance, in connection with the anastomosis of nerves for the 

 relief of certain forms of paralysis, is the bifurcation of axons in 

 regeneration, when the conditions are such that the axons of the 

 central stump are offered more than one path along which to 

 regenerate. If, for instance, a limb nerve-trunk containing motor 

 fibres is cut, and its central end sutured both to its own distal end 

 and to the distal end of an adjacent nerve- trunk, the sum of the 

 nerve-fibres in the two distal trunks after regeneration has occurred 

 is greater than the number of fibres in the central stump (Kilvington) . 

 That this is due to splitting of axons is shown by the fact that an 

 axon reflex (p. 809) can be elicited on dividing one of the distal 

 trunks and stimulating its central end after complete separation 

 of the proximal or parent stem from the central nervous system. 

 Even when the second path offered to the regenerating motor axon 



