iv GENEEAL PHYSIOLOGY OF NEBVOUS SYSTEM 235 



corresponds with the theory which regards a ganglion cell and 

 its processes, not as a morphological and functional unit, but 

 as a syncytium, i.e. the result of the fusion of a number of 

 neuroblasts arranged in a chain. On this hypothesis the cells 

 of the neurolemma represent the residues of the neuroblasts 

 from which the nerve -fibres originated, and after section of 

 the nerve they reassume their character of neuroblasts by 

 multiplying and hypertrophying in the form of spindle-shaped 

 embryonic cells, and regenerate the nerve-fibre discontinuously 

 and simultaneously in the different parts of the cut nerve. This 

 theory is supported by Benecke, Tizzoni and Cattani, Huber, 

 v. Blingner, Galeotti and Levi in particular, and it has been 

 reinforced by recent morphological and experimental observations 

 of Bethe. 



Bethe, unlike the earlier workers, prevented the two stumps 

 of the divided sciatic in dogs and rabbits from joining, and 

 examined the peripheral stump six to nine months later by 

 physiological and histological methods. When the experiment 

 was carried out on adult animals he noted an increase of 

 protoplasm in the neurolemma, with differentiation into an 

 axial filament and a peripheral sheath, but was unable to detect 

 fibrils in the former or myelin in the latter. The nerve was 

 thus partially regenerated, but was found on stimulation to be 

 inexcitable and incapable of conducting. 



Bethe obtained different results on experimenting with young 

 animals, in which the regenerative capacity of the tissues as 

 a whole is much greater. Of four young dogs and one rabbit 

 operated on he observed in 3 cases not only complete morpho- 

 logical regeneration, but also functional recovery of the isolated 

 peripheral nerve (i.e. one not reunited with the central stump). 

 On stimulating with induced currents that were too weak to 

 produce 'direct excitation of the muscle, the leg muscles were seen 

 to contract freely. 



Langley and others, however, objected to Bethe's conclusions 

 that this was not a true autogenous regeneration of the nerves, 

 and that the regeneration of the peripheral stump must depend 

 on its uniting with the central end of other adjacent nerves 

 that had been divided in the operation. The tendency mani- 

 fested even by nerves that are situated at a distance, and that 

 supply other muscles, to unite with the peripheral ends of cut 

 nerves, so as to re-establish the conductivity of the fibres, is 

 in fact very marked. This enigmatical fact, that nerve -fibres 

 emerging from the centre and in normal connection with it 

 grow towards peripheral organs that have been denervated, has 

 been attributed by some neurologists who deny autogenous 

 regeneration to a kind of neurotaxis, i.e. to the capacity of 

 denervated organs to attract the nerve-fibres that grow towards 



