460 



NERVOUS SYSTEM 



A 



difference of opinion in regard to the physiology of the so-called 



gelatinous nerve-fibres. Some anatomists have regarded them simply 

 A B as elements of connective tissue, and 



others have described them as axis- 

 cylinders surrounded with a nucleated 

 sheath ; but the fibres do not present 

 the lines of Fromann when treated 

 with silver nitrate. While elements 

 of connective tissue may have been 

 mistaken for true nerve-fibres, there 

 are in the nerves, particularly in those 

 belonging to the sympathetic system, 

 fibres resembling the nerve-fibres of 

 the embryo. These are the gelati- 

 nous nerve-fibres, or fibres of Remak. 

 All the nerves have this structure 

 until about the 

 fifth month of in- 

 tra-uterinelife, and 

 in the regenera- 

 tion of nerves after 

 division or injury, 

 the new elements 

 ordinarily assume 



this form before they arrive at their full development. 

 The gelatinous nerve-fibres present the following 



characters : They are invested with a delicate neuri- 



lemma, are flattened, with regular and sharp borders, 



grayish, pale and fibrillated, with very fine granules 



and a number of oval longitudinal nuclei, a charac- 

 teristic which has given them the name of nucleated 



nerve-fibres. They branch frequently. The diameter 



of the fibres is about g^Vo f an mc ^ (3 P\ 1 ne 



nuclei have nearly the same diameter as the fibres 



and are about y^Vo ^ an mcn ( 2O A*) m length. 



They are finely granular and present no nucleoli. 



The fibres are rendered pale by the action of acetic 



acid, but they are slightly swollen only, and present, 



in this regard, a marked contrast with the elements of connective tissue. 



They are found chiefly in the sympathetic system and in that particular 



portion of this system connected with involuntary movements. They 



usually are not found in the white filaments of the sympathetic. 



CY-- 



Fig. 98. Nodes of Ranvier and lines of Pro- 

 maun (Ranvier). 



A, intercostal nerve of the mouse, treated 

 with silver nitrate, X2OO. B, nerve-fibre from 

 the sciatic nerve of a full-grown rabbit, X 600 ; 

 A, node of Ranvier; M, medullary substance 

 rendered transparent by the action of glycerin ; 

 CY, axis-cylinder presenting the lines of Fro- 

 mann, which are very distinct near the node. 

 The lines are less marked at a distance from 

 the node. 



Fig. 99- Fibres of Re- 

 mak, X 300 (Robin). 



With the gelatinous 

 fibres of Remak, are seen 

 two of the ordinary dark- 

 bordered nerve-fibres. 



