The Structure of Nerve-fibres. 13 



The evidence of this change of length is sometimes very complete. 

 Imagine a stretched elastic string placed in the long axis of a tube with 

 flexible walls. Release the string and so let its elasticity come into play. 

 As the string contracts, the flexible tube will become arranged as a spiral 

 curled around the axial string. Such a figure would be the reverse of the 

 appearance described above in which a straight tube enclosed a spiral string. 

 I do not say that I have seen evidence of tension so complete as this, but I 

 have frequently seen something similar, if something less. 



Thus when the process of teasing has left nerve-fibres arranged upon the 

 slide in undulating curves, the clot which forms within the intramyelin 

 material sometimes shortens to a length less than that of the fibre. In this 

 case the clot does not follow the curvature of the fibre, but passes straight 

 across from one point of maximal curvature to another. 



Sometimes this central coagulum may be seen to show the usual signs of 

 longitudinal strain in a viscous cord. It is faintly marked by fine lines in 

 the main direction of the strain, and has a finely fibrillated appearance 

 which has led to a belief that this central mass is formed by the agglutina- 

 tion of a number of originally separate " neuro-fibrils." There is, however, 

 nothing in the appearances seen in teased nerve-fibres to warrant such a 

 view. The most severe test to which this view can be put is to seek, in 

 terms of it, for an explanation of the alterations in length which this 

 central mass undergoes. Such an explanation would require not only an 

 imagination of separate fibrils, but also their new endowment with the 

 property of elasticity. 



In nerve-fibres teased in Ringer's solution these appearances are usually 

 distributed in a definite order. The immediate vicinity of the cut end is 

 granular, this granulation is succeeded by a tract of homogeneous intra- 

 myelin material, and then all the successive appearances due to a gradually 

 increasing degree of coagulation occur in the order given above. The order 

 in which the appearances are arranged is sometimes complicated by less 

 extensive and subsidiary sets of appearances of the same kind arranged 

 around interpolated nodes of Ranvier. 



This balancing of appearances around injured points and nodes of 

 Ranvier introduces a complexity into the description of the normal character 

 of teased nerve-fibres. If there is any hurry to identify some one of these 

 appearances as the " normal " one, it must be remembered that teased nerve- 

 fibres are traversed by the " current of injury " and must be expected to 

 exhibit evidence of consequent polarisation. 



