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. 
Nervous Fibres. 
Of these, there are two different forms: a, the common 
white nervous fibres ; 4, 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 
