248 SOME PALE FIBRES ARE FROM THE SYMPATHETIC. 



essential and separate anatomical constituent of every 

 individual dark-bordered fibre must be given up. 

 For, as I showed in 1860, several dark-bordered 

 fibres and fine fibres might run together in the same 

 matrix, PL VII, fig. 2. The opinion that the fine 

 fibres which I hold to be nerve-fibres running in the 

 same sheath with the dark-bordered fibres, are not 

 nerve-fibres at all, but modified connective tissue, is, 

 however, still entertained by many observers, but the 

 nature of these fibres is proved by the fact of their 

 continuity with true dark-bordered fibres. The fine 

 fibre may in many instances be followed in one direc- 

 tion to its ultimate distribution, and in the other to 

 a large dark-bordered fibre.* 



2*35. Some pale fibres are from the sympathetic. 

 Many of the pale fibres accompanying the dark-bor- 



* The different and incompatible views existing between 

 continental observers and myself are in some measure due to 

 this sheath question. The so-called sheath is not a " tube" or 

 " membrane," or " tubular membrane," which contains the 

 other constituents of the nerve-fibre ; nor is it a sheath which 

 invests them, but it is simply a transparent matrix, in which 

 nerve-fibres, coarse and fine, are imbedded. The so-called 

 sheath is not formed as a special structure to invest the nerve- 

 fibres, but it results from changes occurring in the nerve-fibres 

 themselves. This " sheath" or " tubular membrane" of the so- 

 called dark-bordered fibre precisely corresponds to the transpa- 

 rent connective tissue, in which the fine nerve-fibres are im- 

 bedded. It is a form of connective tissue, and in many situa- 

 tions where nerves existed at an earlier period, nothing but this 

 so-called sheath remains. All the soluble fatty matters have 

 disappeared, and this material, which is not readily absorbed, 

 is left behind. Vessels may waste, and ducts and glands may 

 waste, and leave behind them the same sort of transparent con- 

 nective tissue. Moreover, as I have before stated, it is alto- 

 gether a fallacy to suppose that near the peripheral distribu- 

 tion, every single branch of nerve-fibre is surrounded by its own 

 separate sheath. Most of the drawings of the so-called axis- 

 cylinder near the terminal distribution of the nerves seem to me 

 to b.e diagrammatic, founded rather upon a theoretical idea of 

 the constitution of the nerve-fibre than upon the results of 

 actual observation. 



