Il6 NORMAL HISTOLOGY. 



their normal form, staining the myelin black. In apply- 

 ing this agent it is necessary to maintain the nerve in a 

 state of gentle tension, because it is otherwise somewhat 

 contracted and distorted. This is done by gently stretch- 

 ing the nerve the sciatic of the rabbit will answer along 

 a bit of wood which has been whittled away at one side, 

 so that the nerve may lie free. It is fastened by the ends 

 to the wood by threads. The nerve thus prepared is im- 

 mersed for twenty-four hours in an aqueous solution of 

 osmic acid (r to TOO), then washed, and a small bit care- 

 fully teased apart longitudinally in glycerin. In such a 

 preparation nearly all the structures in the fibre can be 

 readily seen : the constrictions and nuclei, the medullary 

 sheath stained black, the incisures of Schmidt, and where, 

 as will almost always occur in some parts of the specimen, 

 the medullary sheath has been broken across, or the seg- 

 ments pulled asunder, or the myelin has contracted at 

 the constrictions, the neurilemma, and axis cylinder. 

 Not infrequently, if the teasing has not been very care- 

 fully done, the segments of the medullary sheath are 

 broken across in many places and separated, giving the 

 fibre a beaded appearance. 



Nerve-Fibres Stained with Acid Fuchsin (Van Gieson's 

 method). A bit of nerve is hardened for from three to 

 five weeks in Mtiller's fluid, washed slightly in water, 

 and then further hardened in alcohol. A strand of the 

 nerve is then teased apart on a slide in water. The 

 water is absorbed with filter-paper, and a drop or two of 

 a saturated aqueous solution of acid fuchsin is placed on 

 the preparation and allowed to act for two to five 

 minutes. The preparation is then washed with water, 



