466 



THE XERVODS SYSTEM. 



Fig. I33-* 

 B c 



composition is, however, only apparent in the fibres of 

 a perfectly fresh nerve ; for, shortly after death, they 

 undergo changes which make it probable that their con- 

 tents are composed of two different materials. The internal 

 or central part, occupying the axis of the tube, becomes 

 greyish, while the outer, or cortical portion, becomes 

 opaque and dimly granular or grumous, as if from a kind 

 of coagulation. At the same time, the fine outline of the 

 previously transparent cylindrical tube is exchanged for a 

 dark double contour (fig. 133, B), the outer line being 

 formed by the sheath of the fibre, the inner by the margin 

 of curdled or coagulated medullary substance. The gra- 

 nular material shortly collects 

 into little masses, which distend 

 portions of the tubular mem- 

 brane, while the intermediate 

 spaces collapse, giving the fibres 

 a varicose, or beaded appearance 

 (fig. 133, c and D), instead of the 

 previous cylindrical form. 



The difference produced in the 

 contents of the nerve-fibres when 

 exposed to the same conditions, 

 has, with other facts, led to the 

 opinion now generally adopted, 

 that the central part or axis- 

 cylinder of each nerve-fibre differs 

 from the outer \ portion. The 

 outer portion is usually called the medullary or white 



* Fig. 133. Primitive nerve-tubules. A. A perfectly fresli tubule 

 with a single dark outline. B. A tubule or fibre with, a double contour 

 from commencing post-mortem change, c. The changes further ad- 

 vanced, producing a varicose or beaded appearance. D. A tubule or 

 fibre, the central part of which, in consequence of still further changes, 

 has accumulated in separate portions within the sheath (after Wagner). 



