106 ELEMENTARY PHYSIOLOGY. [x. 



e. Drops and fragments of the medullary sheath, 

 extending from the cut ends of the fibres and 

 shewing a double contour. 



Some non-medullated nerve-fibres will also be 



seen (cp. B). 



2. Cut off a similar piece of nerve and treat it in 

 the same way, but instead of adding a normal 

 solution, add a drop of chloroform, and irrigate 

 with chloroform as evaporation goes on. 



In the middle of the nerve-fibre the pale granu- 

 lar axis cylinder will be seen running through 

 the swollen and partially dissolved medullary 

 sheath. 



3. Take another piece of fresh nerve, and place it in 

 a small quantity of osmic acid 1 p.c. for ten 

 minutes, covering it up to prevent evaporation. 

 Remove it to a slide, and separate a small bundle 

 of fibres, putting the rest back in osmic acid ; 

 isolate the fibres as much as possible, add a drop 

 of water, and put on a cover-slip. If it is desired 

 to preserve the specimen the nerve should be 

 washed with water before teasing and mounted 

 in dilute glycerine. 



Select a nerve fibre which is isolated for a con- 

 siderable part of its length, and observe 



a. The medullary sheath, stained black with 

 osmic acid. 



b. The nodes of Ranvier. These will be 

 seen as short but distinct breaks in the me- 

 dullary sheath ; with Zeiss obj. D. oc. 2 they 



