726 



NEUROLOGY 



matter of Schwann, and by some it is believed to be produced by the action of 

 the reagents employed to show it. 



The medullary sheath, or white matter of Schwann (Fig. 631), is regarded as being a 

 fatty matter in a fluid state, which insulates and protects the essential part of the 

 nerve the axis-cylinder. It varies in thickness, in some forming a layer of extreme 





v,V Incisure 



]i-4i Node of Ranvier 



y 



FIG. 030. Medullated nerve fibers. X 350. 



Incisure 



Neurolemma 



Medullary sheath 

 Axis-cylinder 



FIG. 631. Diagram of longitudinal sections of medullated 

 nerve fibers. Osmic acid. 



Axis-cylinder 

 Neurolemma 

 Medullary sheath 



FIG. 632. Transverse sections of medullated nerve fibers. 

 Osmic acid. 



FIG. 633. Diagram of medullated nerve fibers 

 stained with osmic acid. X 425. (Schafer.) R. 

 Nodes of Ranvier. a. Neurolemma. c. Nucleus. 



thinness, so as to be scarcely distinguishable, in others forming about one-half the 

 nerve fiber. The variation in diameter of the nerve fibers (from 2 to 16/z) depends 

 mainly upon the amount of the white substance, though the axis cylinder also 

 varies within certain limits. The medullary sheath undergoes interruptions in its 

 continuity at regular intervals, giving to the fiber the appearance of constriction 



