SPECIAL NEUROLOGIC.\L STAINING METHODS 39 



in neurofibrils) it may be best to abbreviate the dehydration, and 

 block and cut without infiltration with celloidin. 



(2) Pieces are first placed in 95-per-cent. alcohol or in absolute 

 alcohol (32° to 40° C.) for twenty-four hours. For neurofibrils it is 

 better to add from 0.25 c.c. to i c.c. of ammonium hydrate to each 

 10 c.c. of the alcohol. They are then treated with silver nitrate i per- 

 cent, or 1.5-per-cent., as in (i). This method gives better pictures 

 of the cell processes and axis cylinders and a better fixation of the 

 cells. 



(3) Pieces are first placed in distilled water 100 c.c, formalin 

 20 c.c, ammonia i c.c, for twenty-four hours at 32°-4o° C, washed 

 in water twelve to twenty-four hours, and then treated with silver 

 nitrate i-per-cent. or 1.5-per-cent., as in (i). This method gives 

 pictures of the terminations of nerve fibres on the periphery of nerve 

 cells and their dendrites (end-feet or end-buttons of Auerbach). 



In general it is best to avoid, in the above methods, any excessive 

 exposure to the light while the pieces are in the silver bath (especially 

 when the pieces are very small), though they may be brought into 

 the light for examination and while being transferred to the reducing 

 fluid. 



Nissl's Method 



This method is useful for studying the internal structure of the 

 nerve cell. It depends upon a rapid fixation of the tissue, its sub- 

 sequent staining with an aniline dye, and final decolorization in 

 alcohol. 



The aniline dye most commonly used is methylene blue. There 

 are many variations and modifications of Nissl's method. The 

 following is simple and gives uniformly good results: 



Specimens are first fixed in mercuric-chlorid solution (page 8), 

 in formalin (lo-per-cent. aqueous solution), or in absolute alcohol, 

 and embedded in celloidin. 



Thin sections are stained in a i-per-cent. aqueous solution of 

 pure methylene blue (Griibler). The sections are gently warmed in 

 the solution until steam begins to be given off. They are then 

 washed in water and dift'erentiated in strong alcohol. The degree of 

 decolorization which gives the best results can be learned only by 

 practice. Several alcohols must be used, and the last alcohol must 

 be perfectly free from methylene blue. The sections are cleared in 



