COMPOUND TUBULAR TISSUES. 



39 



Within the tubular mem- 

 brane lies a more opaque sub- 

 stance known as the ivhite 

 substance of Schivann^ and 

 within this again is a transpa- 

 rent material which has been 

 called the axis cylinder. The 

 whole of the contained sub- 

 stance is exceedingly soft, and 

 may be made to pass from one 

 part of the tube to another. A 

 bundle of nerve-fibres, sur- 

 rounded and connected by are- 

 olar tissue, constitutes a nerve. 



The other form of fibrous 

 matter is that which is seen in 

 the great sympathetic system, 

 and which is known as the 

 gelatinous nervous fi bre. These 

 fibres contain nothing analo- 

 gous to the white substance of 

 Schwann, and are devoid of 

 the whiteness which charac- 

 terizes the tubular fibre. The 

 gray colour of certain nerves 

 depends upon the presence of 

 a large proportion of gelatinous fibres, 

 called gray fibres. They are smaller 

 fibres, rancrinii from ^^4^^^ to 



Hence, they are sometimes 

 1 diameter than the tubular 

 4oVo o^^"inch. (Fig. 11 ) 



The remaining element of the nervous structure is what is called 

 the gray or vesicular. This is found in the nervous centres, but 

 never in the nerves, properly so called. It consists of cells or vesicles 

 containing nuclei and nucleoli. The walls of each vesicle are ex- 

 tremely thin and delicate, and contain a soft but tenacious granular 

 mass. In some vesicles we find a number of pigment granules ex- 

 terior to the nucleus, giving a dark colour to a portion of the vesicle. 



Another form of nerve vesicle, is that called the caudate, which 

 is characterized by one or more tail-like processes extending from 

 it. They contain nuclei and nucleoli, and pigment granules. These 

 caudate processes either serve to connect other vesicles, or else they 

 become continuous with the axis cylinder of the tubular fibres. 



* A. Diajrram of tubular fibre of a spinal norve :— a. Axis cylinder, h. Inner border of 

 white substance, c. r.. Outer border of white substance, d. d. Tubular membrane, b. Tu- 

 bular fibres ; e, in a natural state, showing the parts as in a. /. The white substance and 

 axis cylinder interrupted by pressure, while the tubular membrane remains, g. The same, 

 with varirnsities. g'. Varicose fibres of various sizes, from the cerebellum, c. Gelatinous 

 fibres from the solar plexus, treated with acetic acid to exhibit their cell-nuclei. 



