133 



Weigert Hematoxylin Methods, for differentiating myelinic nerve 

 tracts, and (d) the Chrome-silver Impregnation Methods, to bring out 

 the form of the cells and differentiate the amyelinic nerve-fibers. 



These have their greatest value when used in conjunction with 

 more general staining methods, which supplement the first and give 

 a basis for the correct interpretation of the appearances produced by 

 the second method. In addition, there are other stains helpful in 

 bringing out the finer structure of the cells. 



§ 136. The 'Weigert hematoxylin methods. These meth- 

 ods all involve (a) mordanting the tissue with a chromium or cop- 

 per salt, (^) staining (over-staining) with a strong hematoxylin 

 stain, and (;-) decolorizing (differentiating) the sections in a 

 bleacher until the myelinic fibers are blue, all else (except blood) 

 white to brown. 



§ 137. The following method is serviceable : Harden the tis- 

 sue in a 3% aqueous solution of potassium dichromate for about 2 

 weeks, and in a 5% aqueous solution for an equal period (§ 31). 

 Imbed in collodion ; parafSn may be used if the piece of tissue is 

 small. The sections should not be thicker than 25/*. Wash the 

 sections in water (§§ 68-70) and (a) Mordant them 1-12 hours in a 

 half-saturated aqueous solution of copper acetate ; rinse them 

 well in water and {b) Stain them for 1-24 hours (until black) in 

 Weigert's hematoxylin (§ 83) ; rinse well in water and (c) Differ- 

 entiate in the Weigert's bleacher (Formula: Water, 200 c. c. ; 

 borax, 2 grams ; potassium ferricyanide, 2.5 grams). Watch the 

 differentiation carefully and when the cinerea has become a golden 

 brown and the myelinic fibers a rich blue, stop the action and wash 

 the sections in water, running or changed several times, for at least 

 Y2 hour. Dehydrate, clear, and mount in alkaline balsam (best) 

 (§158). If the specimens are to be left for some time before mount- 

 ing, place them in 95% alcohol with .sodium carbonate added to 

 render it alkaline. 



§ 138. Pal's method may be uised if it is desired to stain the 

 nerve cells subsequently. 



Harden the tissue thoroughly in solutions of potassium dichro- 

 mate (3% solution, 2 weeks ; 5%, 2 weeks or so). Imbed in collo- 

 dion (paraffin, if the sections are small). Stain the sections in Wei- 

 gert's hematoxylin (§ 83) until a blue black ; rinse in tap-water. 



