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



activities of the surrounding sheath, the protoplasm behaves just as it does iu 

 ontogenetic development ; it grows — probably slowly — and so gaps are 

 bridged over ; as soon as it becomes continuous, nerve impulses begin to play 

 backwards and forwards in its substance and cause again a differentiation 

 into fibrils. As part of the impulse tracks persist at the central stumps of 

 the fibrils, the regenerated parts of the fibrils will naturally develop in exact 

 continuity with these. 



We have reproduced Professor Graham Kerr's views at some length 

 because they support, in an entirely independent manner, our own views on 

 the nutritive properties of the nerve sheath. Whether, however, such 

 nutritive control is able to act so far as to produce actual flbrillse we are 

 extremely doubtful. Graham Kerr admits that in a degenerated and 

 regenerating fibre the protoplasmic strand can only be demonstrated with 

 extreme difficulty, and he further admits the necessity of union with the 

 central stump to ensure functional regeneration. In our own experiments, 

 as will be more fully described later, we have never seen anything of the 

 nature of an axis cylinder or neuro-fibrillee in the peripheral segment of 

 a divided nerve, provided connection with the central end is successfully 

 prevented. 



Graham Kerr further emphasises the fact that his observations apply to 

 one animal only, and that he does not wish to draw general conclusions from 

 them as to what occurs in other vertebrates. He, however, points out that 

 Bethe's observations on the chick, although apparently supporting the cell- 

 chain view, are in no way irreconcilable with the observations he chronicles. 

 With regard to the view he advances that the original nerve trunk exists 

 from the first as a link which stretches in length with the growth of the 

 animal, it appears to us that it is incapable of explaining how a gap an inch 

 or so long can be bridged across when one excises, as we have done in some 

 of our experiments, a portion of nerve of that length. The union that occurs, 

 often very rapidly, even when the ends are not sutured together, must 

 be due to growth of nerve fibres from the central to the peripheral stump or 

 in the reverse direction. 



In a paper published by the veteran histologist, von Kolliker,* shortly 

 before his death, the theory that regeneration can occur in the peripheral end 

 of a cut nerve without connection or control from the central end is very 

 vigorously criticised. Kolliker himself was instrumental many years ago in 

 putting forward the view that the nerve sheath, known as the neurilemma, is 

 a secondary formation in the mesoblast into which the axons penetrate, and 

 in his later years became an exponent of the neuron theory. It is mainly 

 * ' Auat. Anzeiger,' vol. 25, p. 1 (1904). 



