FINE NEKVE-FIBKES. 



427 



The medulla is rapidly and invariably altered by the application 

 of cold water, of most acids, &c. This change consists principally 

 in a coagulation of it, sometimes occurring from without inwards, 

 and involving the entire thickness, or only its outermost layer. In 

 the latter case, the nerve-fibres of dou- 

 ble contour lines are produced; in 

 the former, the contents become ap- 

 parently wholly grumous or opaque. 

 The neurilemma gives the single con- 

 tour line. Sometimes, also, the me- 

 dulla accumulates into larger masses 

 in places, and thus the frequently de- 

 scribed varicose appearance of the 

 nerve-fibres is produced. (Figs. 275 

 and 273.) In this change the neuri- 

 lemma participates ; but in all those 

 mentioned, the axis-fibre takes no 

 part. By pressure, the medulla may 

 be made to assume all possible forms. 



2. The Fine Nerve-Fibres. 

 The finest nerve-fibres (Fig. 298, 3) 

 are only ^^QQ of an inch in diame- 

 ter; and in these neither neurilemma 

 nor medulla can be demonstrated, 

 only the axis-fibre being apparently 

 present. Most of them are, however, 

 TO ^oo" to S-QQ-Q of an inch; but these 

 also have no proper medulla i. e. are 



J T1 J T> 1 rupted by pressure, while the neurilemma 



nOW-medullated. But they Contain remains, g. The same, with varicosities. 



between the axis-fibre and the neuri- h - Various appearance of the meduiiaand 



, _ . axis-fibre, forced out of the neurilemma by 



lemma a Substance Sometimes resem- pressure, t Broken end of an axis-fibre 



bling the axis-fibre of other nerves, with the medulla Cl08ed over " * Lateral 



. bulging of medulla and axis-fibre from 



and Sometimes more Clear. These pressure. I. The same, more complete, g'. 



are often called pale nerve-fibres, as Vari . co " fibre , 8 : r of ous sizes> fron \ the 



cerebellum. (Magnified 320 diameters.) 



they have only a single contour line. 



In the nervous centres, also, they frequently present a varicose ap- 

 pearance. (Fig. 275, g'.) 



It has already been seen, however, that a nerve-fibre may be me- 

 dullated, coarse, and have a neurilemma, in one part of its course, 



A. Diagram of a tubular fibre of a spinal 

 nerve, a. Axis-fibre. t>. Inner border 

 of medulla, c, c. Its outer border, d, d. 

 Neurilemma. B. Tubular fibres, e. In a 

 natural state, showing the parts as in a. 



f- The medulla and axis-cylinder inter- 



