96 THE ESSENTIALS OF HISTOLOGY. 



in studying the endings of nerve-fibres, and the structure of the central 

 nervous system. 



It is further shown by this method that each nerve-cell is an ana- 

 tomically independent element, consisting of the cell-body with its 



p 



-my 



vty 

 -ff 



FIG. 113. DEGENERATION AND REGENERATION OF NERVE-FIBRES IN THE RABBIT. 



(Ranvier. ) 



A, part of a nerve-fibre in which degeneration has commenced in consequence of the section, 

 fifty hours previously, of the trunk of the nerve higher up ; my, medullary sheath be- 

 coming broken up into drops of myelin ; p, granular protoplasmic substance which is 

 replacing the myelin ; n, nucleus ; g, primitive sheath. B, another fibre in which 

 degeneration is proceeding, the nerve having been cut four days previously ; p, as 

 before ; cy, axis-cylinder partly broken up, and the pieces inclosed in portions of myelin. 

 C, more advanced stage of degeneration, the medullary sheath having almost disappeared, 

 and being replaced by protoplasm in which, besides drops of myelin, are numerous 

 nuclei which have resulted from the division of the single nucleus of the internode. D, 

 commencing regeneration of a nerve-fibre. Several small fibres, t't", have sprouted from 

 the somewhat bulbous cut end, 6, of the original fibre, t ; a, an axis-cylinder which h.is 

 not yet acquired its medullary sheath ; s, ', primitive sheath of the original fibre. A, C, 

 and D are from osmic preparations ; B from an alcohol and carmine preparation. 



nucleus, the ramified "protoplasmic" processes or dendrites, and the 

 tierve-process which becomes the axis-cylinder of a nerve-fibre. It will 

 therefore be easily understood that when a nerve is cut, part of the 

 axis-cylinder will be cut off from the cell to which it belongs, and from 



