XVII.] NERVE-FIBRES. 2 1 3 



set in, but it is also applicable to nerve-fibres that have undergone degenera- 

 tion, e.g., after section of a nerve, constituting Wallerian degeneration. It 

 will also detect any degenerated fibres in an ordinary nerve. 



16. Isolated Schwann's Sheath. Place a stretched nerve of a frog in the 

 following lluid for twenty-four hours in the dark : 



Boveri's Fluid. 



Silver nitrate ( i per cent.) . . . 10 cc. 

 Osmic acid (i per cent.) . . . 10 ,, 



Wash it in water, and place for twenty-four hours in very dilute caustic 

 potash (2-3 drops of a concentrated solution in 15 cc. water). Tease in 

 glycerine. The axis-cylinder shrinks and Schwann's sheath may be traced as 

 a continuous sheath without any interruptions at the nodes. 



17. Nerve-Fibres of the Spinal Cord. These are devoid of Schwann's 

 sheath, but they possess both Ranvier's nodes and incisures of Lantermann. 

 Boveri's fluid may stain both. It is evident then that these two structures 

 have no relation to Schwann's sheath, but are related entirely to the myelin. 

 The cylinder-cones are readily isolated by Schiefferdecker's methyl-mixture 

 (p. 26). 



18. Degeneration of Nerve-Fibres. This is readily studied in the rabbit. 

 The skin is first disinfected with solution of corrosive sublimate, and then the 

 median and ulnar nerves are exposed on the inner aspect of the upper arm, 

 the nerves divided, and the wound sealed with collodion (C. Huber). 1 In 

 different animals the nerves are excised 2, 3, 4, . . . 8 or 10 days after the 

 operation. The excised nerves are kept extended on wood and fixed for 

 twenty-four hours either in Hermann's fluid (Lesson XXXV.) or the picro- 

 osniium mixture of Benda, prepared by saturating a I per cent, solution of 

 osniic acid with picric acid and filtering. They are then washed in water and 

 hardened in alcohol. The sections are stained with safranin and light-green. 

 Besides showing the usual degeneration phenomena, they show mitotic division 

 of the nuclei of Schwann's sheath, showing that these proliferate. 



LESSON XVIII. 



NERVE -GANGLIA, NERVE -CELLS, AND PERI- 

 PHERAL TERMINATIONS OF MOTOR NERVES. 



Spinal Ganglia. Harden a spinal ganglion of a cat or dog in 

 2 per cent, ammonium bichromate for three weeks, and subse- 

 quently in alcohol. Make transverse and longitudinal sections 

 of the ganglion, stain with logwood or carmine, and mount in 

 balsam. 



1. L.S. Mammalian Spinal Ganglion (L). (<.<.) Note the cap- 



1 Archivf. mik. Anat., xl. p. 409, 1892. 



