— 49 



Lesson Xlil. 

 PERIPHERAL NERVES. 



(a) Fresh Medullated Nerve. 



Tease u piece from the sciatic nerve of a froi: in noniuil salt 

 solution. Before covering arrange the fihres as straight as possiljlc. 



Examine under high power, employing one of the 

 smaller openings in tlie diaphragm. Observe the axis 

 cylinder, seen as a light band passing down through the 

 center of the fibre. It is surrounded by a thin glistening 

 layer usually of a light green color, the medullary sheath; 

 around this is the neurilemma. Find the nodes of Ran- 

 vier; search for the nucleus of an internodal segment. 

 Some of the fibres may show the segments of Lantermann. 



(b) Medullated Nerve Fibres Stained in Osmic 



Acid. 



The sciatic of a frog was fixed for 24 hours in a ]% solution of 

 osmic acid. Tease very carefully in gum glycerine. 



Examine under high power. The medullary sheath is 

 stained deeply black by the osmic acid. The nodes of 

 Ranvier are ver}" clearly seen in this preparation. 



(c) Medullated Nerve Fibres Stained in Hsem- 



atoxylin. 



A small cerebro-spinal nerve was hardened in a saturated 

 aqueous solution of picric acid for 48 hours, washed for several days 

 in 70% alcohol, teased, and stained in Boehmer's luematoxylin for 

 about one hour. Tease thoroughly in gum glycerine. 



Study under high power. The axis cylinder appears 

 as a deeply stained cord passing through the center of the 

 libre. The medullary substance has a reticulated appear- 

 ance. The internodal nuclei are also stained. Sketch as 

 seen under high power. 



4. 



