108 Staijis and Siauiing (chap. 10) 



used if followed by a well-ripened hematoxylin. If the solution is un- 

 ripened, then the mordant should include a substance of considerable 

 oxidizing power, a ferric or chromitim salt. The value of two solutions 

 lies in the fact that the dye can be preceded by a salt, which can not be 

 used in combination with the dye in a single solution. Ferric chloride, 

 when added to an ammonia-ripened hematoxylin, will throw down a 

 precipitate of ferric hydroxide. Double mordanting can be profitable. 

 A mordant followed by a solution of hematoxylin containing a mordant 

 gives excellent results. The mordants for separate use are: ammoniimi 

 or potassium alum, ferric ammonium alum (2-3 drops of HCl increases 

 contrast), and ferric chloride (HCl increases contrast). They yield the 

 following colors with hematoxylin: ammonium alum, bright blue 

 nuclei; potassium alum, lilac or violet; chrome alum, cold gray blue; 

 iron alum, blue to black. [Cole, 1943) 



Relative to the use of metals with hematoxylin, the following list of 

 tissue elements and the metals effectively used on them may be of prac- 

 tical interest. {Mallory, 1938) 



Nuclei: aluminum, iron, tungsten 



Myelin sheaths: chromium, iron, copper 



Elastic fibers: iron 



Collagen: molybdenum 



Fibroglia, myoglia, neuroglia, epithelial fibers: tungsten 



Axis cylinders: lead 



Mucin: iron 



Fibrin: tungsten 



Lakes, formed by mordant and dye, can be used progressively, but 

 ^vhen mordant and dye are used separately, regressive staining usually 

 is more effective. In progressive staining the stain is added to the tissue 

 until the correct depth of color is reached. In regressive staining, the 

 sections are overstained and excessive amounts are removed by one of 

 the following methods. 



'& 



Method 1: By Use of Excess Mordant 



With an excess of free mordant present outside of the tissue, the 

 mordant-dye complex in the tissue is broken up, and, since the amoiuit 

 of mordant in the tissue is small in comparison with that in the differ- 

 entiating fluid, tlie dye moves out of the tissue into the latter. (If tiie 

 tissue is left long enough in the fluid, it is concei\able that most of the 

 dye could move out of it into the excess mordant and the sections be- 



