70 



color). A bluish-purple indicates too great a reduction. Wash in distilled water 

 for an hour or so. 



If it is desired to make a teased preparation, transfer to glycerin in which 

 the fibers may be cautiously teased apart, taking care not to separate them too 

 much. Permanent mounts may be made in glycerin or glycerin-jelly. 



If sections are called for, dehydrate, clear (xylene method, 52), and imbed in 

 paraffin. Celloidin may also be used. 



With fresh tissue the treatment by formic acid may cause too 

 marked a swelling and distortion ; in which case the Ranvier method 

 [30] may preferably be used. 



195. Tigroid substance (Nissl's bodies). The stainable sub- 

 stance in the cell body of nerve cells resembles the chromatin of 

 the nucleus in its reactions, staining with basic stains of which a 

 number are suitable. Alcohol, Carnoy's fluid ( 26, 27), mercuric 

 chlorid, or formalin may be used as fixers, preferably one of the first 

 three. Methylene blue or toluidin blue are the usual stains. 



196. NissPs Method (modified). Imbed in paraffin or cel- 

 loidin tissue that has been fixed in 95% alcohol or Carnoy's fluid; 

 cut the sections rather thick, 15 to 20^. The sections may either be 

 fastened to the slide or carried on as free sections. Stain the sec- 

 tions in a 1% aqueous solution of methylene blue or toluidin blue 

 for 5 to 10 minutes, heating it until it steams. Permit it to cool, 

 rinse in water, dehydrate and differentiate in absolute alcohol, clear 

 with oil of cajuput and xylene and mount in xylene balsam. The 

 nerve cells and nuclei will be stained blue, all else colorless. In the 

 cell-bodies of the nerve cells, the tigroid substance will be stained. 

 Should the stain not be selective enough, differentiate for a few 

 seconds before dehydrating with a mixture of anilin 1 part, 95% 

 alcohol 9 parts. 



If celloidin is used for imbedding, it should be remembered that 

 it should be dissolved away in the differentiation (absolute alcohol). 



197. H eld's Method (modified). Fix in mercuric chlorid 

 (or as for Nissl's method), imbed in paraffin, cut sections 5 to 10^ 

 and stain 15 minutes in 1% solution of erythrosin in 67% alcohol, 

 rinse, stain 10 minutes in 1% aqueous solution of toluidin blue, dif- 

 ferentiate briefly in 1 /10th% alum solution, dehydrate rapidly in 

 95% and absolute alcohol, clear in xylene, mount in balsam. Alka- 

 line methylene blue or Nissl's soap solution (y&% methylene blue in 

 1/5% soap solution) may be used in either of these two methods if 

 desired. 



