NEEVE-TISSUE. 



291 



but G-erlach concluded that it must be present, and I positively 

 maintain its existence. The next layer is the myeline investment, 

 which, in thin sections, is invariably destroyed. In its place, a 

 delicate, knotty retictiliim is visible, to the existence of which 

 Kiihne and Ewald* first drew attention. These observers claim 

 that the reticulum in the myeline layer is horny or keratoid, 

 because it resists digestion with pepsine and tripsine. They also 

 traced in the gray substance a similarly resistant reticulum. In 

 the meshes of this reticulum the myeline is contained. The mye- 

 line investment in some nerves is very narrow, and in others 

 completely wanting. The next layer is a delicate sheath the 



FIG. 122. WHITE SUBSTANCE OF THE SPINAL CORD 

 OF A CHILD. TRANSVERSE SECTION. 



PE, connective-tissue offshoot of the pia mater the external periueurium ; PI, lateral 

 connective- tissue offshoots around the nerve-fibers the internal perineurium; M, oozed-out 

 myeline investment, with inclosing myeline sheath; A, axis-cylinder, with inclosing axis, 

 cylinder sheath. Magnified 600 diameters. 



axis-cylinder slieatli, discovered by L. Mauthner similar to the 

 myeline sheath. The center is occupied by the bright, homo- 

 geneous-looking, usually roundish axis-cylinder, from which 

 delicate radiating spokes emanate and go to the axis-cylinder 

 sheath. 



In longitudinal sections the axis-cylinder is plainly visible 

 only where the investing sheaths are stripped off, but where the 



* Verhandlungen der Heidelberger Gesellschaft, 1876. 



