STRUCTURE OF NERVE FIBRES. 155 



of turpentine. Transverse sections of the spinal cord are 

 admirably adapted to exhibit the extraordinary variations 

 that occur in the thickness of the axis cylinder, and the 

 methods of Pfliiger and Waldeyer are those which are best 

 adapted to bring the axis cylinder speedily into view in fresh 

 nerves. Pniiger's plan consists in adding a drop of collodion, 

 Waldeyer's in adding a drop of chloroform, to the preparation, 

 in as dry a state as possible, and covering with a thin glass. 

 The medullary sheath will then be found to have lost its 

 brilliancy, and in the greater number of nerve fibres the axis 

 cylinder appears very distinctly as a finely granular central fibre. 



We are in possession of extended observations by Bidder 

 and Volkmann,* in reference to the difference in thickness 

 existing amongst the peripheric medullated fibres, and espe- 

 cially between the cerebro-spinal and sympathetic fibres, which 

 is very considerable. 



A fourth form of nerve fibre may be added to those already 

 described, which also occurs in the peripheric nerves, but is 

 distinguished from the foregoing by the absence of the 

 medullary sheath, and is on this account usually described 

 as the peripheric non-medullated nerve fibre. These consist 

 of fibres composed of a thicker or thinner bundle of primi- 

 tive nerve fibrils, according to the kind of axis cylinder 

 present, united together by a nucleated sheath of Schwann. 

 All the branches of the olfactory nerve in the mucous mem- 

 brane of the nose of all Vertebrates consist of such non- 

 medullated nerve fibres. They are also of frequent occurrence 

 in the sympathetic, the branches of which, distributed to the 

 intestines, are often entirely composed of them ; as, for example, 

 the thick splenic nerves of Ruminants, which are often more 

 than a millimeter in diameter. It was here that Remak first 

 observed theni,-f- and hence the non-medullated sympathetic 

 fibres bear the name of Remak's fibres. Remak himself sub- 

 sequently called them ganglionic fibres.^ Some fibres show 

 the fibrillar structure much more distinctly than others, as was 



* Die Sellstandiykeit des Sympathischen Nervensy stems. Leipzig, 1842. 

 f Observations Anatomicce et Microscopicce de Systematis Nervosi Struc- 

 ture Berol., 1838. 



% Monatsberichte der Berliner Akademie, 1853, 12th May. 



O 



