CHAP. VIII.] 



TUBULAR FIBRE. 



209 



Within the edge of the tubular membrane, on each side, are seen 

 two thicker and darker lines (A, c, c, b), which appear to mark the 

 outer and inner limits of an inner ^.52. 



layer of different composition and 



refracting power, and which is ^ 



generally known as the white sub- 

 stance of Schwann. This forms 

 a tube within the tubular mem- 

 brane. Within the white sub- 

 stance of Schwann is a transpa- 

 rent material, occupying the axis 

 of the nerve-tube (A, a). This 

 has been called by Remak the 

 flattened band; but a better name 

 for it is that of axis cylinder, em- 

 ployed by Rosenthal and Pur- 

 kinje. 



It is evident, that the whole of 

 the matter contained in the tubu- 

 lar membrane is extremely soft, 

 for it is found to yield under very 

 slight pressure, and may be rea- 

 dily made to pass from one part 

 of the tube to another. When 

 pressed out (B, h to /), it is apt to 

 assume more or less the appear- 

 and form of globules, which 



\ 



d 6 h c d 



. Diagram of tubular fibre of a spinal nerve : 



ln 



Tubular membrane. B. Tubular fibres; e, 

 natural state, shewing the parts as in 



, -i f , /. The white substance and axis cylinder inter- 



the Same Characters OI OUt- rupted by pressure, wlule the tubular membrane 



i . i ,1 n ,-1 remains, a, The same, with varicosities. h. Va- 



Which they possessed in the rious appearances of the white substance and axis 



, -i . , , -I -i cylinder forced out of the tubular membrane by 



nerve-tube : that IS, they have a pressure, i. Broken end of a tubular fibre, with 



, , -i j j v the white substance closed over it. k. Lateral 



transparent interior, bounded by bulging of white substance and axis cylinder from 



0,1 -i 4 pressure. /. The same more complete, g'. Vari- 



a layer OI tllC White Substance C ose fibres of various sizes, from the cerebellum. 



/ o i 1 i i . 3 c. Gelatinous fibres from the solar plexus, treated 



Ot bchwanil, marked by its dOU- wlth acetic acid to exhibit their cell-nuclei. Band 



blc contour. It would appear c 



that the latter structure is particularly apt to form a coating or 

 film over the central material, and thus to isolate it from sur- 

 rounding tissues. This tendency may be understood by a reference 

 to fig. 52, h to /. 



When the nerve-tube is placed in aether, the white substance 

 is in part immediately dissolved, and a number of oil-like globules 

 appear both within and without the tubular membrane (fig. 53, b). 

 Probably its margarine is dissolved, and the elaine set free in the 



VOL. i. p 



