iv GENEKAL PHYSIOLOGY OF NEKVOUS SYSTEM 237 



fibres. Purpura holds that the newly found fibrils come from 

 the central end of the nerve, and, in fact, from the old axis- 

 cylinders. At a later stage, in place of the fibrils and arranged 

 like them, bundles of medullated nerve-fibres are found in the 

 cicatrised tissue and in the peripheral stump. 



Lastly, A. Perroncito (1908) made a careful histological study, 

 of the regeneration of cut nerves, using particularly Kamon y 

 Cajal's photographic method. He too concluded that the re- 

 generation of nerve- fibre is exclusively the work of the central 

 stump. He brought out the remarkable fact that regenerative 

 changes in the fibrils occur within a few hours of the injury in 

 the central end of cut nerve, far more rapidly than was formerly 

 supposed. The regenerative process is manifested by a numerous 



FIG. 150. Three nerve-fibres from central end of dog's sciatic at different periods after section. 

 The axon shows different forms of regenerating fibrils. (Perroncito.) The upper fibre comes 

 from a nerve divided six hours, the centre fibre seventeen hours, the lowest fibre forty-eight 

 hours previous to preparation. 



and varied formation of fibrils, derived from the central stumps 

 of the axis-cylinders which had degenerated for a greater or less 

 distance (but never more than a few millimetres) from the point 

 of section. This degeneration ceases at a point of the fibre which 

 does not, according to Perroncito but contrary to the opinion of 

 others, correspond with a node of Eanvier: at this point the 

 end of the axis -cylinder a few hours after section exhibits a 

 fusiform or cylindrical swelling, in which a fibrillary structure 

 is quite apparent (Fig. 149). The formation of new fibres, most 

 of which as they grow advance towards the periphery, proceeds 

 rapidly from this swelling or the part of the axis - cylinder 

 immediately above it. Some force their way through the neuro- 

 lemma into the old fibres. All of them exhibit characteristic 

 bulbous or spiral endings (Fig. 150). Twenty-four hours after 

 the lesion, in young animals, these regenerated prolongations have 

 already passed the confines of the old central stump, and penetrated 



