378 



BIOLOGY. 



[BOOK vi. 



The nervous fibres continue direct with the cells. They are 

 in some sort tentacles which these project to connect themselves 

 with the other organs. 



The fundamental part of every nervous fibre is a very thin 

 filament solid and flexible (Fig. 68, h). This filament, called 

 cylinder axis, cylindraxis, is chemically constituted by a quater- 

 nary azotised substance. It continues direct with the granulous 

 content of the nervous cell. This filament is the truly essential 

 part of the nervous fibre : it is the soul thereof. It is the con- 

 ducting portion, the telegraphic wire which puts the nervous 

 cell in relation with the other organs. 



In the complete fibre the axile filament is enveloped by a 

 protecting manica. It occupies then the centre of a tube, of 



Nervous fibres magnified 350 times ; e, fine fibre ; /, fibre of middle size ; g, broad fibre 

 with dark edge, and in the fresh state, taken from the nerve of a rabbit ; h, fibre of the 

 spinal marrow of man ; visible therein are the bright cylinder axis and the contracted 

 sheath ; i, analogous fibre of the brain of man : k, passage from the fixed cerebral fibre 

 to the sheathed fibre; fibre taken from the brain of the torpedo. 



an elastic sheath, filled with a sort of viscous oil. This sub- 

 stance, which Kolliker has compared with turpentine, but which 

 belongs rather to the family of fat bodies, is transparent. Like 

 all transparent bodies, rich in carbon, it strongly refracts the 

 light. Also, under the microscope, the nervous fibres with oily 



