212 



INNERVATION. 



[CHAP. vin. 



fibrillse. Acetic acid dissolves the fibre, leaving the nuclei un- 

 changed. These fibres, containing nothing analogous to the white 

 substance of Schwann, are devoid of that whiteness which charac- 

 terises the tubular fibre ; and it would seem that the gray colour of 

 certain nerves depends chiefly upon the presence of a large propor- 

 tion of the gelatinous fibres. Hence they are sometimes called 

 gray fibres. 



The mode of connexion of the gelatinous fibres with the elements 

 of the nervous centres is, as yet, quite unknown. They are found, 

 in considerable numbers, in what are called the roots of the sym- 

 pathetic, or the communications of that nerve with the spinal 

 nerves : it has been supposed by Valentin that they are continuous 

 with certain elements of the vesicular nervous matter. 



These fibres are smaller, in general, than the tubular fibres ; 

 their diameter ranges between the -g^Vo an ^ ^ ne ~*~o^o f an mcn - 

 They resemble very much the fibres of unstriped muscle. 



Of the Vesicular Nervous Matter. This is distinguished by its 

 dark reddish gray colour, and soft consistence : it is found in the 

 nervous centres, but never in nerves, properly so-called, and it is 

 always supplied by a considerable plexus of blood-vessels. 



The essential elements of the 

 gray nervous matter are vesicles 

 or cells, containing nuclei and 

 nucleoli. They have been also 

 called nerve or ganglion globules. 

 The wall of each vesicle consists 

 of an exceedingly delicate mem- 

 brane, containing a soft but te- 

 nacious finely granular mass. The 

 nucleus of the cell is generally 

 , eccentric, much smaller than the 



Nerve-vesicles from the Gassenan ganglion of . . 



the human subject: a. A globular one with de- containing VCSlclC. and adherent 

 fined border ; b. its nucleus ; c. its nucleolus. d. ... 



Caudate vesicle, e. Elongated vesicle, with two to SOmC part of its interior. Its 

 groups of pigment particles. /. Vesicle surround- 

 ed by its sheath, or capsule, of nucleated particles, structure IS apparently the same 

 g. The same, the sheath only being in focus. * , .. 



Magnified 300 diameters. a s that of the Outer VCSlcle. The 



nucleolus is a minute, remarkably clear, and brilliant body, also 

 vesicular, inclosed within the nucleus. It forms a most character- 

 istic and often conspicuous part of the nerve- vesicle. 



The ordinary or prevailing form of these elements is that of 

 a globular vesicle. So soft and compressible are they, how- 

 ever, that a good deal of diversity of shape is manifest in them, 

 by reason of the compression they suffer as they lie packed 



