236 PHYSIOLOGY CHAP. 



the periphery (perhaps by chemical stimuli deriving from the 

 degenerative processes). 



Some remarkable experiments have recently been carried out 

 upon the embryos of various cold-blooded animals with a view 

 to solving the origin of nerve - fibres. The results cannot, 

 however, be taken as conclusive for either theory. Such are the 

 experiments of Braus and Banchi (1905), who transplanted limb 

 buds into the bodies of tadpoles, and the observations of 0. 

 Schultze (1904-5) on the histogenesis of the peripheral nerves 

 in tadpoles. These yield data that decidedly favour the 

 autogenous theory. On the other hand, Harrison (1904-6) found 

 in amphibian larvae that after excising the neural crest, from 

 which all the cells of Schwann for sensory and motor nerves are 



FIG. 149. Diagrammatic. Regenerative changes at the central end of a nerve-fibre, close to the 

 section. (Perroncito.) a, normal axis-cylinder composed of a bundle, of fibrils; b, swelling, 

 from or above which the regenerating fibres grow out ; c, portion of axis-cylinder undergoing 

 degenerative changes, close to the section ; <l, d", young fibrils sprouting from the axon, which 

 leave the nerve-fibre through the neurolemma ; d', new fibres running backward in a spiral ; 

 e , fi Oi Q'I 9"> ''i h', h", different forms of buds and regenerating fibres. 



derived, the axis -cylinders still develop, but remain destitute 

 of sheaths. 



When, in 1900, it was still possible in the absence of specific 

 histological tests to question the existence of the regeneration 

 of axis-cylinders in cut nerves, Purpura examined them with 

 Golgi's silver nitrate method and obtained decisive results. At the 

 extremity of the central stump of a divided nerve, between the 

 normal medullated fibres, he observed the presence of nude axis- 

 cylinders that stained black and were associated with a number 

 of ramifying varicose nerve - fibrils, of a markedly embryonic 

 character. These fibrils invaded the cicatricial tissue between 

 the two stumps, running through it in all directions, and 

 interlacing in a most complex fashion. At a later period the 

 peripheral stump is also invaded by fine branching nerve-fibrils, 

 which differ from those which run in the scar by following a 

 longitudinal course between the residues of the old degenerated 



