STRUCTURE OF NERVOUS TISSUE. 



343 



form; and their mean size in the adult is from l-15th to l-10th of an inch in 

 length, and from l-26th to l-20th of an inch in breadth. They are attached 

 to the branches of the nerves on which they cluster, by slender peduncles, each 

 of which consists of a single tubular nerve-fibre, with one or more fine blood- 

 vessels, and a sheath of areolar tissue (Fig. 113, A, a, 6). The corpuscle itself 

 consists of numerous concentric capsules, of a delicate fibrous membrane, in- 

 closing each other like the coats of an onion, to the number, sometimes, of 

 between forty and sixty ; those which form the internal portion (c) being closer 

 together than those of the outer part (d). These capsules are kept apart by a 

 transparent fluid (probably albuminous), which also occupies the central cavity. 

 The nerve-fibre gradually loses its neurilemma as it passes through the series of 

 capsules, but still retains its dark double contour until it enters the cavity; from 

 that point, however, it presents the cha- 

 racters of the " gelatinous" fibres, being Fi g- H3. 

 pale, flattened, granular, and destitute of A B 

 a tubular envelop; and this it usually 

 retains as far as its termination. The 

 fibre usually ends in a sort of knob at the 

 farthest extremity of the capsule; some- 

 times, however, it bifurcates, and each 

 division ends in a similar knob; and 

 still more rarely, it separates into three 

 parts (/). The constant presence of 

 these bodies, in certain regions of the 

 body, in perfectly healthy individuals of 

 all ages, and even in the foetus, is quite 

 sufficient to negative the idea put for- 

 ward by Cruveilhier and others, that 

 they are morbid or accidental produc- 

 tions, probably resulting from pressure 

 applied to the nerves. On the other 

 hand, the suggestion of Pacini, adopted 

 by Henle and Kblliker, that they are 

 analogous in function to the electrical 

 organs of Fishes (to which they bear a 

 certain degree of structural resemblance), 

 has no sufficient evidence in its favor. 



345. The Chemical constitution of 

 the Nervous matter is peculiar, but has 

 not yet been satisfactorily made out. 

 An acquaintance with its general features 

 is of importance, however, in leading us 

 to recognize in the excretions the results 

 of its decomposition. The following, 

 according to L'Heritier, 1 is the relative proportion of the different constituents 

 in individuals of different classes : 



Water . ... 



Albumen 



Fat ... 



Osmazome 2 and Salts 



Phosphorus 



1 " Traite de Chimie Pathologique," p. 596. 



2 It is probable that, in the above analyses of L'Heritier, the Cerebric acid, which is 

 not soluble in ether, is included under the head of Osmazome ; for the analyses of Denis 



Human Pacinian Corptisdes: A, single corpus- 

 cle, highly magnified, showing a its peduncle, b its 

 contained nerve-fibre ; c, outer layers and d inner 

 layers of the capsule ; e, nerve-fibre become pale 

 in its passage through the interior of the corpuscle ; 

 /, its subdivision and termination : B, portion of 

 digital nerves with Pacinian corpuscles attached, 

 rather less than the natural size. 



