Irving Hardesty 345 



sections stained by this method the framework supporting the myelin 

 appears arranged in the form of concentric lamella}. The different 

 lamellae, however, cannot be followed as distinct and individual mem- 

 branes, for they apparently anastomose with each other and are further 

 connected by still finer threads or branches. The structure is better de- 

 scribed as a lamellated reticulum in the meshes of which the myelin is 

 contained. Were it fibrillar in structure, lamellation could not appear 

 in both transverse and longitudinal section. In longitudinal section the 

 meshes of the reticulum appear considerably elongated in the direction 

 of the long axis of the nerve fiber. 



At the periphery of the fiber there is a slight condensation of this 

 lamellated reticulum, giving under certain conditions the appearance of 

 a membrane (jj. Figs. G and 7), but close examination of the uncollapsed 

 sections shows this membrane continuous with the more open network 

 further in. This explains the difficulty with which the membrane is 

 seen and the disputes concerning its existence, for consisting of but a 

 condensed peripheral portion of the reticulated framework, the meshes 

 of which are intimately occupied by the myelin throughout, the mem- 

 brane is really continuous with the framework and therefore necessarily 

 seems to adhere closely to the myelin. The breaking of the medullary 

 sheaths in the fixed preparations consists, of course, of a breaking of the 

 framework, and in the usual osmic "acid and Weigert preparations espe- 

 cially, one could hardly expect to see the apparent membrane except in 

 fortunate cases where the myelin is crushed or shrunken away from the 

 periphery in such a way as to expose it. Quite frequently in the teased 

 corrosive-osmic preparations the broken end of a fiber showed frayed por- 

 tions of the framework of the sheath as indicated in Figs. 5 and 6, fr. 

 These appearances are due to the myelin having l^een washed out of the 

 meshes of a short extent of the framework by the action of the water in 

 teasing and are prol)al)ly not to be seen except in preparations teased by 

 water. 



The lamellated reticulum also usually shows a slight condensation 

 about and upon the axone of tlie medullated fiber. This corresponds to 

 the second thin layer of neurokeratin as described by Hatai. It probably 

 corresponds to the axolemma frequently mentioned in the books. Being 

 of the same nature and formed in the same way as the peripheral mem- 

 brane, the usual difficulty with which it is seen is perhaps due to the 

 same reason as that given to explain the difficulty with which the per- 

 ipheral membrane is seen. 



In the longitudinal sections of the fibers of the spinal cord it is seen 

 that even the heavier lamella? of the framework do not run uniformly 



