METHODS OF STAIN TNG. 307 



five minutes. There is no danger of over-staining. It is a pure 

 nuclear stain, coloring the chromatin red. After staining, the sec- 

 tions are either washed, and are then ready for dehydration, or 

 they may receive a counterstain with picric acid, coloring the tissues 

 a diffuse yellow. This may be most readily accomplished by adding 

 a few small crystals of picric acid to the first dish of dehydrating 

 alcohol (see p. 313). 

 4. Borax-carmine. — 



The borax is dissolved in the water by warming, and the solution 

 allowed to cool ; the carmine is then stirred in and the alcohol added. 

 After standing twenty-four hours the solution is filtered into the 

 stock-bottle, a process that is exceedingly slow. 



Borax-carmine is used for the staining of little masses of tissue 

 before they are embedded. It is a nuclear dye, giving the chromatin 

 a red color. It is useful when paraffin-embedding is to be employed 

 and it is desirable to restrict the manipulation of the sections to a 

 minimum. 



Small pieces of hardened tissues, not over 5 mm. thick, are trans- 

 ferred from distilled water to the undiluted dye and allowed to stain 

 for twenty-four hours, or longer. After staining they are immedi- 

 ately placed in an acid alcohol, prepared by adding 5 drops of con- 

 centrated hydrochloric acid to 100 cc. of 70 per cent, alcohol. The 

 tissue should not rest on the bottom of the vessel containing the 

 alcohol, but upon crumpled filter-paper, so that the extracted excess 

 of coloring-matter may sink to the bottom. If the acid alcohol 

 around the specimen becomes colored, fresh portions of alcohol 

 should be used. The treatment with acid alcohol is continued until 

 no more color is given off from the specimen. It is then transferred 

 to 90 per cent, alcohol, in which it should remain for twenty- 

 four hours, after which it can be subjected to the dehydration neces- 

 sary for embedding. 



5. Orth's Lithio-carmine. — 



Carmine, " No. 40," 3 grams. 



Lithium carbonate, saturated aqueous solution, 100 cc. 



