296 



NEBVE-TISSUE. 



remains unchanged in the shape of a reticulum, or, still more 

 probably, the myeline originates in a manner different from that 

 of fat viz., from the lifeless liquid contained in the meshes of 

 bioplasson. In specimens of medullated nerve-fibers the myeline 

 is often found exuded from the nerves in the form of numerous 

 slightly refracting formations with a concentric striation, which 

 is evidently caused by a slow oozing and aggregation of the 

 myeline. (See Fig. 125.) 



FIG. 125. MYELINE DROPS, OOZED OUT FROM THE 

 OPTIC NERVE OF A BULL. 



N, bundle of medullated nerve-fibers ; M, myeline drops ; F, fat-granules. Magnified 

 400 diameters. 



By staining fresh medullated nerve-fibers with a solution of nitrate of sil- 

 ver, the bundle was found to be covered by an endothelial coat. Each fiber 

 exhibits a series of marks, which correspond to the " annular constriction " of 

 Ranvier. The axis-cylinder at the point of constriction exhibits a number of 

 dark brown transverse lines (Frommann). Between every two constrictions 

 a transverse bar has been found, of a biconical shape, through the broadest 

 portion of which the axis-cylinder passes. Ranvier concludes from these 

 facts that each section of the nerve-fiber is a unit, a tubular cell, filled with 

 myeline, like a fat-globule, which he terms the inter annular segment, with an 

 oblong nucleus in its investing membrane. The axis-cylinder, according to 

 this author, pierces a series of interannular segments without interruption ; 

 while Engelmann, on the other hand, claims that each interannular con- 

 striction corresponds to an interruption of the axis-cylinder. This latter 



