NERVES. 



[ 457 ] 



NERVES. 



the nerve-tube, which forces out the white 

 substance. BoiHng the nerves in absolute 



Fig. 516. 



Human nerve-tubes, showing tubes of various sizes ; 

 some with a single, others with a double outline ; some 

 varicose, others with the white substance in a granular 

 state. 



Magnified 350 diameters. 



alcohol, with the subsequent addition of 

 caustic alkali, or in acetic acid, when cry- 

 stals of fat separate from the white substance 

 (fig. 615, 1), will answer the same purpose. 

 Treatment with strong nitric acid, and after- 

 wards with potash, causes the white sub- 

 stance to exude, and the axial fibre being 

 dissolved, the yellow sheath is left empty 

 and very distinct. Solution of corrosive 

 sublimate has also been recommended. The 

 axial band is best seen in nerves treated 

 with strong acetic acid, cold absolute alcohol, 

 aether, chromic acid, &c. 



Chemically the sheath and axial band 

 consist of a proteine compound, and the 

 white substance of a mixture or compound 

 of fat with a proteine substance. 



Inthecerebro-spinal nerves, the nerve-tubes 

 are aggregated into bundles, and surrounded 

 by an envelope of areolar tissue, called the 

 neurilemma, in which blood-vessels ramify, 

 thus corresponding with the arrangement of 

 the primitive fibrillse of muscle. Sometimes, 

 towards the terminations of the nerves, the 

 nem-ilemma appears as a homogeneous 

 membrane with elongated nuclei. 



The nerves rarely branch; they usually 

 terminate in loops. 



In the gray, sympathetic, or ganglionic 

 nerves, the fibres of which are sometimes 



called gelatinous fibres, the nerve-tubes are 

 smaller and paler than those of most of the 

 cerebro-spinal nerves, and scattered through 

 a more copious areolar sheath or neurilemma 

 of mostly longitudinal fibres(Remak's fibres), 

 containing numerous elongated nuclei (fig. 

 517). 



Fig. 517. 



From the human sympathetic. A. Portion of a gi-ay 

 fibre treated with acetic acid : a, fine nerve-tubes ; A, nu- 

 clei of Remak's fibres. B. Three ganglion- globules, one 

 with a pale process. 



Magnified 350 diameters. 



Nerve- cells, nerve-corpuscles, or ganglion- 

 globules are nucleated cells, most numerous 

 in the cineritious or dark portions of the 

 nervous centres, and in the ganglia, but 

 sometimes met with in the trunks and termi- 

 nal expansions of nerves, as the retina, &c. 

 They are furnished with a delicate outer 

 coat or membrane (fig. 518, la); this is 

 easil}^ seen in the cells of the ganglia, but 

 wdth difficulty in those of the central organs. 



They are rounded, elongate, pyriform, or 

 angular (fig. 518). Some of them are sim- 

 ple, others furnished with one, tw o, or more 

 simple or branched processes, by which they 

 are connected with nerve-tubes : hence thev 

 are described respectively as uni-, bi-, or 

 multipolar. Their contents are a soft, tena- 

 cious, and elastic mass (fig. 518, 3), consist- 

 ing of a clear, homogeneous, proteine basis, 

 and a number of larger and smaller granules, 

 as well as a nucleus. In size they are very 

 variable, fi'om 1 -5000 to 1 -500" . The granules 

 are sometimes colourless, at others yellow, 

 brown or black ; and occasionally these are 

 aggregated to form a mass. 



Intermingled with the cells in the cineri- 

 tious matter of the nervous centres, is a 

 finely granular pale substance, resembling 

 that within the cells, also aggregations of 

 free nuclei. 



The ganglia consist of nerve-tubes either 

 separate or united into bundles, intermingled 



