STRUCTURE OF NERVE-FIBRES. 



87 



nodes, where it may be observed stretching across the interruption in 

 the medullary sheath, and it may also sometimes be seen projecting 

 from a broken end of a nerve-fibre. It is longitudinally striated, being 

 really made up of exceedingly fine fibrils (ultimate fibrils, fig. 102), 

 which are darkly stained by chloride of gold. Staining with nitrate of 

 silver produces a curious transversely striated appearance in the axis- 

 cylinder, but it is not known if this indicates a pre-existent structure. 

 Kiihne has described a special reticular sheath of the axis-cylinder 

 lying within the medullary sheath, and composed of a peculiar chemical 

 substance termed neurokeratin. The reticulum is, however, produced 

 within the substance of the medullary sheath, probably by the action 

 of reagents. 



Non-medullated fibres. Intermingled with the medullated fibres 

 there may always, even in the cerebro-spinal nerves, be found a certain 

 number of pale fibres devoid of the dark double contour which is 



FIG. 105. SECTION OF A PART OF THE MEDIAN NERVE (HUMAN). (DRAWN AS SEEN 

 UNDER A LOW MAGNIFYING POWER.) (From Landois after Eichhorst.) 



ep, epineurium, or general sheath of the nerve, consisting of connective-tissue bundles of 

 variable size separated by cleft-like areolse, with here and there blood-vessels ; pe, lamel- 

 lated connective-tissue sheaths (perineurium) of the funiculi ; ed, interior of funiculus, 

 showing the cut ends of the medullated nerve-fibres, which are embedded in the con- 

 nective tissue within the funiculus (endoneurium). 



characteristic of the presence of a medullary sheath. There are the 

 non-medullated fibres, also called, after their discoverer, fibres of Remdk 

 (fig. 104). They frequently branch, which the medullated fibres 

 never do except near their termination, and they are beset with 

 numerous nuclei which perhaps belong to a delicate sheath. The 



