xxxviii.] FRESH TISSUES. 399 



. Stain others with acid methyl-green or picro-carmine. 



Make cover-glass preparations (p. 140). 



Before staining pass the cover-glass three times through the flame 

 of a Bunsen-burner. 



16. Medullated Nerve-Fibres. Expose the sciatic nerve. 



(a.) Tease out a few fibres and show them fresh in normal 

 saline. Seal up the preparation with paraffin wax. 



(b.) Tease a piece in i per cent, osmic acid, cover with a watch- 

 glass, and after half an hour mount in glycerine. This 

 blackens the myeline. A part of this may be stained 

 in picro-carmine (p. 206). 



(c.) Tease a piece in .5 per cent, silver nitrate for Ranvier's 

 crosses (p. 207). 



(<?.) Harden a piece of nerve in alcohol for a quarter of an 

 hour. Tease, place in ether for 10 minutes, transfer to 

 alcohol. Stain with logwood and mount in glycerine. 

 This shows the axis-cylinder and nuclei of sheath. 



(e.) Place a piece of fresh nerve in collodion to show axis- 

 cylinder. This preparation only lasts for a short time 

 (p. 211). 



(/.) Show with silver nitrate the endothelial sheath on one of 

 the small nerves to be found in the dorsal lymph-sac, 

 stretching between the back muscles and the skin 

 (p. 207). 



17. Peripheral Nerve-Cells. Use the rapid gold chloride 

 (p. 79) or methylene-blue method (p. 222). 



(a.) Cells along course of aorta. Cut out the abdominal part 



of the aorta. 



(/>.) Cells of sympathetic (p. 216) or 

 (f.) Cells of spinal ganglia, or other ganglia (p. 215). 

 (<l.) Interauricular septum of the heart. The heart must be 



distended and kept fixed in this position (p. 233). 



18. Retina. Carefully dissect out the eyeball, remove retina. 

 (a.) Place a part in i per cent, osmic acid and then make 



teased preparations. One should show the pigmented 



epithelium, rods with outer segments blackened, pieces 



of the several layers, the glistening fatty globule 



rendered brownish. 

 (b.) Harden a piece in absolute alcohol and tease in very 



dilute eosin. Mount in glycerine. 

 (c.) Place small pieces in very dilute methylene-blue (p. 222) 



to show the nervous elements,, Mount it in picro- 



glycerine (p. 222). 



19. Blood- Vessels. A new frog will be required. Proceed as 

 directed at p. 230. 



