52 NERVE. 



the slightly bulbous enlargement which precedes the constric- 

 tion of each end. Find a second node along the same 

 fibre, observe also that the medullary sheath now shows the 

 incisures distinctly, owing to slight shrinkage of its substance. 

 The nuclei stained pink occupy depressions in this sheath, 

 and are best seen in profile view. There is one nucleus to 

 each internode (Ranvier). The axis cylinder may project from 

 the broken end of a fibre. 



Nerve treated with nitrate of silver. Fresh nerve is placed in 

 \ P.C. AgNO s for 20 minutes, then transferred to 30 p - c - alcohol in 

 sunlight until darkened. Tease a piece of the nerve in glycerin. 



(II) Find Ranmer's crosses, nodes where the brown stain- 

 ing exhibits the axis cylinder and nodal cement substance 

 coloured, roughly cross-shaped. The staining may extend along 

 the axis cylinder, and then is disposed as transverse markings 

 (Frommann's strise). This disposal of the stain indicates 

 the existence, around the axis cylinder, of material corres- 

 ponding to the cement at the node. Incisural outlines may 

 be indicated. 



Large nerve. T.S. Sciatic or ulnar, man. (p. 11, s. 22, c. P., m. B.) 

 (L] The large rounded areas are bundles of nerve fibres. The 

 perineurium around each bounds them with a sharp out- 

 line ; between and embracing them is loose connective tissue, 

 epineurium. (H) The perineurium is a lamellated structure 

 consisting of several layers, between which there are nuclei and 

 lymph spaces. Internally to this sheath are the nerve fibres 

 mostly seen in transverse section. Each nerve exhibits a stained 

 axis cylinder, around which is the medullary sheath. 



This sheath varies in its appearance with the method of 

 preparation. If long hardened in Miiller's fluid it is more 

 homogeneous and shows, here and there, concentric outlines, 



