Place a fragment of the gray matter of the spinal cord or the 

 cortex of the cerebrum on a clean slide in a drop of J^% Congo Red 

 ( 113) or 1/10% eosin in formaldehyde dissociator; with the blade 

 of a scalpel crush the tissue, grinding it thoroughly with a rotary 

 movement, which will reduce it to small pieces. Gather the debris, 

 drain off the fluid, and add a drop of glycerin containing stain. 

 Cover and examine, tapping the cover sharply with the handle of the 

 scalpel to shake out the processes of the cells and free them from 

 surrounding matter. Examine, searching for cells with many and 

 long processes, and if a satisfactory preparation, seal according to 

 119. 



192. Isolation of Nerve Fibers, (a) For isolation of myel- 

 inic nerve fibers, with the preservation and blackening of the myelin, 

 and for amyelinic fibers, employ osmic acid dissociator ( 42). 



(b) For the isolation of myelinic nerve fibers with the removal 

 of the myelin for the demonstration of the axis cylinder, neuro- 

 lemma and framework of the sheath, fix nerves in Dichromate- 

 acetic or similar fluid one or more days, wash in water, pass up 

 through the alcohols, dehydrate, remove the myelin by placing the 

 tissue in a fat solvent, chloroform, for one or more days, 95% alco- 

 hol 1 day, pass through the alcohols to water, stain in Delafield's 

 hematoxylin 12 to 24 hours, wash in water, pass up through the 

 alcohols, dehydrate and place in clearer. Out of this the small bun- 

 dles of the nerve fibers may be teased apart with needles, care being 

 taken to keep the fibers as nearly parallel as possible. Mount in 

 balsam. 



193. Gold Chlorid Methods. These methods, which are 

 widely serviceable, depend upon the reduction of gold chlorid solu- 

 tions by the tissues through the agency of (a) sunlight or (b) various 

 chemical substances of which the acids, formic, acetic, citric, etc., 

 are particularly used. Either one or both of these agencies may be 

 used. Usually fresh tissue is used although the method may be 

 applied to fixed tissue, particularly as a neurofibrilla stain [6, 30]. 

 It is the method par excellence for staining motor nerve terminations 

 for which purpose the following method is serviceable. 



194. [21]. Fresh tissue or (better) tissue fixed in 10% formalin may be 

 used. Place small pieces of muscle containing the endings for 30 minutes in 10% 

 formic acid solution. Remove to 1% gold chlorid for 30 to 40 minutes, avoiding 

 direct sunlight; the tissue becomes yellow. Transfer again to a 2% formic acid 

 solution in which the tissue should remain for 1 or 2 days in the dark (rich purple 



