74 



NORMAL HISTOLOGY. 



FIG. 88. 



sheath the axilemma (Kiihne) ; other authorities regard this 

 appearance as an artificial production. Since every axis-cylinder 

 is connected with the corresponding process of a nerve-cell, 

 axis-cylinders may be regarded as direct continuations of the 

 ganglion-cells, their component fibrilke 

 forming uninterrupted paths which con- 

 nect the periphery with the presiding 

 nerve-centres. On approaching its ter- 

 mination, the axis-cylinder splits into 

 smaller bundles of component fibrillse ; 

 these groups subsequently divide, until, 

 finally, the naked ner- 

 FIG. 8. yous threads reach their 



ultimate destination as 

 the terminal arborizations. 

 The nerve-fibrillae not in- 

 frequently exhibit nu- 

 merous minute fusiform 

 enlargements or vari- 

 cosities along their 

 course, giving to the 

 fibrils a characteristic 

 beaded appearance, es- 

 pecially after gold-stain- 

 ing. 



The medullary sub- 



Medullated nerve-fibres : A , 

 teased in salt solution, x, shortly 

 after death ; y, a node of Ranvier ; 

 2, post-mortem distortions of med- 

 ullary substance. B, an isolated 

 stained fibre ; a, axis-cylinder ; r, 

 node of Ranvier; m, medullary 

 substance ; n, neurilemma, beneath 

 which a nerve-corpuscle is seen in 

 the lower segment. 



Uujv x 



Gold-stained axis- 

 cylinder (a), showing 

 component fibrillae ; 

 b, varicose nerve- 

 fibrillas near their 

 termination. 



^Ljtf*v*~ stance, or white matter 



of Schwann, surrounds the axis-cylinder, and forms the most con- 

 spicuous investment of the fibre. The existence of a narrow lym- 

 phatic cleft described as lying between the medullary substance and 

 the axilemma is still uncertain. The medullary substance consists 

 of two parts : one of these occurs as a delicate reticulated frame- 

 work, composed of a resistant material probably resembling neuro- 

 keratin (Kiihne and Ewald) ; the other fills the interstices of the 

 reticulum and appears as a semi-fluid, highly refracting, fatty sub- 

 stance the myelin which affords protection to the enclosed axis- 

 cylinder. Other authorities regard the reticulated framework as 

 the effect of reagents, citing the variability in the appearances of the 

 net-work as opposed to its presence as a normal constituent of the 

 coat. 



At regular intervals along the medullated nerve-fibres well-marked 

 annular constrictions occur ; these are the nodes of Ranvier, and 

 mark the fnterruption of the white substance of Schwann at certain 

 points. 



