NERVOUS SYSTEM. (NERVE.) 



599 



in the cerebro-spinal system, the grey fibres are 

 less numerous, and are seen as grey fasciculi 

 lying in the larger mass of white fibres." 



Neither Retzius nor Muller has given a 

 clear description of these organic fibres as seen 

 by them. Muller quotes and adopts Remak's 

 account of the microscopic examination of these 

 fibres. " They are," according to the latter 

 anatomist, " much more minute than the cere- 

 bro-spinal fibres ; they are perfectly homo- 

 geneous, that is to say, not composed, as far 

 as can be distinguished with the microscope, of 

 a tube and contained portion ; and are so pale 

 and transparent that in a strong light they are 

 not visible ; lastly, a completely characteristic 

 appearance is produced by the small roundish 

 or oval bodies which here and there beset their 

 surface." They are almost gelatinous in their 

 nature ; they have on their surface the appear- 

 ance of fine longitudinal lines, and are easily 

 resolved into very fine fibres.* 



Schwann seems to confirm this description, 

 and to regard the organic fibre as a less per- 

 fectly developed state of the nerve-tube of the 

 cerebro-spinal system. 



Henle in his description of the grey or soft 

 nerves gives the following account of these fibres 

 (Jig. 334). They areflatfibres,very clear, of homo- 



Fig. 334. 



Gelatinous nervous fibres from a soft nerve in the 

 Calf (from Henle.) 



A, fibre resolving itself into fibrillaj. 



B, A fibre doubled on itself, shewing the flattened 

 character. 



C, Two fibres lying in juxtaposition. 



u, a, a, nuclei. 



c, a nuclear fibre (Kernfaser.) 



d, a fibrilla. 



geneous appearance, in diameter from 0.002 to 

 0.003 of aline (g^th to 10 Lth of an inch), with 

 numerous nuclei of cells, round and oval, most 

 of them laid flat, and arranged at nearly equal 

 distances, many presenting regular nucleoli, 

 and pointed at their opposite poles. Their 

 longest diameter is generally parallel to the 

 longitudinal axis of the nerve. Sometimes one 

 of these fibres resolves itself into more delicate 

 fibnllse, resembling the primitive fibre of cellu- 

 lar tissue. Acetic acid dissolves them, and 

 leaves the nuclei untouched. Henle admits 

 that the greyish colour of the nerves depends 

 on the quantity of these fibres ; the greater the 



* Miiller's Physiology, translated by Baly, p. 

 720, and Remak Obs. anat. et microscop. de sys- 

 tem, nervos. structure. 



number of nerve-tubes, the more the bundle 

 resembles an ordinary cerebro-spinal nerve. In 

 the roots of the sympathetic the number of the 

 grey fibres is in large proportion, there being 

 four to six of them for one nerve-tube, so 

 that each nerve-tube appears surrounded by the 

 nucleated fibres.* 



Valentin, who admits the existence of fibres 

 of a similar kind to those described by Henle, 

 maintains that they are continuations of the 

 sheaths of the globules which exist in the gan- 

 glia, and which are prolonged from them into 

 the nervous trunks, and they serve as an enve- 

 lope or protecting sheath to the cerebro-spinal 

 nerve-tubes. Henle, who had formerly regarded 

 these fibres as nerves distributed to the con- 

 tractile cellular tissue and to vessels, (" the 

 slight developement of the nerves of these 

 tissues seeming to correspond to the imperfec- 

 tion of their contractile power,") now expresses 

 great doubts as to their nature and office, and 

 proposes to call them gelatinous nervous fibres; 

 " a name," he says, " which has no other end 

 but to designate their presence in certain nerves, 

 in the same way as we continue to call the 

 fibres of cellular tissue, which are met with in 

 tendons, tendinous fibres." 



Muller conjectures that they may serve the 

 purpose of establishing a communication be- 

 tween the ganglia; in short, that they are so 

 many commissures between these centres.^ 



Purkinje and Rosenthal describe the organic 

 nerve-fibre as the same as the central axis of 

 the cerebro-spinal nerve-tube deprived of its 

 investing membrane, and from comparing the 

 sympathetic fibres with the cerebro-spinal fibre 

 in the young embryo, they state their opinion 

 that the latter, in an early stage of develope- 

 ment, is identical with the former, but they do 

 not appear to recognise, as llemak did, any 

 continuity between these organic fibres and the 

 ganglionic globules. J 



Volkmann and Bidder have lately put for- 

 ward an examination of this question ; and 

 these observers maintain the existence of a 

 series of fibres peculiar to the sympathetic and 

 distinct from those of the brain and spinal cord. 

 Their work, however, contains many statements 

 so much at variance with those of preceding 

 writers, and with what I have myself seen, that 

 I am led to entertain a strong suspicion that 

 there must have been some fallacy affecting 

 their observations throughout. 



The sympathetic fibre, according to these 

 writers, differs from the cerebro-spinal fibre in 

 the following particulars; it exhibits at its mar- 

 gin a single contour, instead of the double one 

 which is so constant a feature of the cerebro- 

 spinal fibre, especially when examined some 

 time after death ; the distinction between a 

 containing tube and the pulpy contents is not 

 manifest ; the fibre has sometimes a greyish 

 aspect, which the authors regard as independent 

 of any admixture with material foreign to that 

 of the nerve-fibre itself; it is much smaller 

 than the cerebro-spinal fibre, nearly one-half; 

 in the cerebro-spinal as well as the sympathetic 



* Henle, Alftemeine Anat. 



t Archiv. 1839, p. ccv. 



j De Formatione granulosa, Vratislav. 1839. 



