XVIL] 



NERVE- FIBRES. 



2O7 



FIG 



appear as flattened bands with oval nuclei at intervals in their 

 course. They are non-medullated nerve-fibres, which, as they 

 have no myelin, are not blackened by the osmic acid. 



(/.) A small quantity of connective tissue and capillaries. To 

 get a good view of the incisures and nodes, the best plan is to 

 stretch the sciatic or other nerve of a frog on a match before 

 placing it in osmic acid. In this way the fibres are kept straight, 

 and the cylinder-cones pulled asunder as far as possible, thus 

 making the incisures wide and distinct. 



3. Ranvier's Crosses (H). Rapidly tease out on a dry slide one 

 of the branches of the sciatic nerve (frog), and stain it for five 

 minutes with .3 per cent, solution 



of silver nitrate. Wash off the 

 silver, apply a drop of glycerine, 

 and expose it to daylight. It 

 rapidly becomes brown. 



(a.) Observe the fibres, but at 

 each node will be seen a brownish- 

 hlack cross (fig. 186); the silver 

 nitrate diffuses into the nerve-fibre 

 only at the nodes, stains tho 

 cement joining one internode with 

 another, thus making the trans- 

 verse bar of the cross, and as it 

 diffuses along the axis-cylinder it 

 stains some cement substance on 

 the latter, and thus makes the 



vertical bar of the cross. Occasionally a number of transverse 

 (fig. 187) lines Frorcmann's lines are seen on the axis-cylinder, 

 i.e., on the vertical bar of the cross (p. 210). Place a sciatic nerve 

 of a frog for twelve hours in i per cent. AgN0 3 , and keep it in 

 the dark. Wash and harden in absolute alcohol, and mount 

 in balsam. The crosses and lines are then seen with great dis- 

 tinctness. 



4. Endothelial Cells of the Perineurium. Intercostal, or other 

 Small Nerve. (i.) It is well also to stain with silver nitrate one 

 of the small intercostal nerves of a rat or some other small nerve. 

 Stain the whole nerve in silver nitrate. 



(ii.) Open the abdomen of a frog, remove the abdominal viscera, 

 so as to expose the nerves coining from the vertebral canal. Pour 

 on the nerves .3 per cent, silver nitrate. After three minutes, cut 

 out the nerves and place them for half an hour in fresh .3 per 

 cent. AgNO r Wash in distilled water, tease a piece in glycerine, 

 and expose it to light. 



(a.) The crosses are seen as before, but above them is the 



lO. 186. Nerve 

 with Ranvier's 

 Crosses. Silver 

 nitrate, x 30. 



187. Nerve- 

 Fibre. . Node 

 and cross of Ban- 

 vier with Fro- 

 mann's lines, x 

 200. Silver nit- 

 rate. 



