STAINING 741 



for fat, the intra vitam staining of nerve tissues with methylene blue, etc. 



Mordants. The successful application of a dye requires tTiat~the 

 tissue shall have a chemical affinity for the stain. This affinity may be 

 either natural or artificial, e.g., eosin will color nearly all tissues under 

 any ordinary conditions without the aid of any other reagent ; the colora- 

 tion is, however, largely a physical phenomenon, due to inhibition 

 of the dye; hematoxylin, on the other hand, stains ordinary tissue but 

 slightly, but its action is much enhanced by first acting upon the tissue 

 with alum or a similar reagent. The alum, in this case, serves as a 

 mordant. 



A mordant should have a strong affinity for both the stain and the 

 tissue. Hence it is that, after a tissue has been once stained by the 

 aid of a mordant, it may be decolorized, partially or completely, by the 

 second application of the same or another mordant of equal strength. 



SINGLE STAINS WITH NUCLEAR DYES 



Hematein. Hematein is the active principle of the dye, hema- 

 toxylin, obtained by extracting logwood. Hematein is derived from the 

 solutions of hematoxylin by oxidation, either by chemical reagents or by 

 prolonged exposure to the air. As a dye it must be combined with a 

 mordant, which, most frequently, is some form of alum. The following 

 formulas are recommended: 



Alum Hematein (Mayer) : 



Alum hematein (Griibler's) 0.2 grin. 



95 per cent, alcohol 5 c.c. 



Saturated aqueous solution of ammonium 



alum 100 c.c. 



About 10 grm. of alum are required for this solution. The hematein 

 should be first dissolved in the alcohol, with gentle heat if necessary, 

 and afterward added to the warm solution of alum. The fluid is ready 

 for use in two or three days, but will increase in strength for several 

 weeks ; it then requires dilution. 



Bohmer's Hematoxylin: 



Hematoxylin 0.5 grm. 



Absolute alcohol 5 c.c. 



Saturated aqueous solution of potassium alum 100 c.c. 



