142 NERVOUS FIBRES. 



tended sense of the term, including the fibres of the brain and 

 spinal cord : 2d, globules, ganglion-globules, in addition to the 

 ganglia occurring in the brain and spinal cord. Our task is 

 to point out the relation which these two forms of elementary 

 structure bear to the elementary cells. 



Ne7*vous Fibres. 



Of these, there are two different forms : «, the common 

 white nervous fibres ; b, the gray, so-called organic fibres. 



a. White nervous fibres. They have the appearance of 

 fibres, which, when examined microscopically, exhibit very 

 dark margins, and these margins are produced by a substance 

 apparently identical with that which gives them their white 

 colour when examined with the unaided eye. Since the cause 

 of this colour does not appear to be situated in the whole 

 fibre generally, but to be confined to its external portion, this 

 latter may be termed the white substance of the nervous 

 fibres. The margin of a fibre generally presents a double 

 outline on both sides, so that it has the appearance of a 

 hollow tube, and the distance between the two outlines, 

 then, denotes the thickness of the white substance. According 

 to the researches of Remak, the white substance of every 

 nervous fibre may be removed by pressure, and an extremely 

 pellucid, pale band, which was previously surrounded by 

 the white substance, then remains, corresponding to that 

 which, previous to the manipulation, seemed to be the contents 

 of the tube. (See R. Remak, Obss. Anat. et Microsc. de Syst. 

 Nerv. Struc, Berol. 1838.) 



Two opinions with respect to the nervous fibres may be 

 deduced from the above observations ; either this pale band is 

 the proper nervous fibre, and the white substance only a 

 sheath (cortex) around it (this is the view taken by Remak), 

 or the nervous fibre is actually a hollow fibre, the wall of 

 which is formed by the white substance, the contents of which, 

 however, are not fluid, but composed of a tolerably firm sub- 

 stance, namely, the above-mentioned band. 



The history of the development of the nervous fibres must 



: 



