V] STAINING UN-IMBEDDED SECTIONS 41 



clove oil and mount. The section when in 95 p.c. 

 alcohol should neither be markedly blue nor markedly 

 red ; if it is blue, stain it again with eosin, passing it 

 more quickly through the alcohols ; if it is red, leave it 

 in the alcohol till the red colour is fainter. The nuclei 

 are stained with hsematoxylin, the cell substance and 

 most other tissue with eosin. Nearly all tissues give 

 good results when stained in this way. 



A 1 p.c. aqueous solution of eosin stains more quickly than the 

 alcoholic solution given above ; in it, a second or two will probably 

 be sufficient to stain the section. 



If the tissue has been hardened in Muller's fluid, potassium 

 bichromate, or by brief treatment with osmic acid, the haemo- 

 globin of the red corpuscles which in these cases is usually 

 preserved will be stained orange with eosin. 



9. After-staining with picric acid. Picric acid may be used 

 after any other stain. It is perhaps best after carmine or 

 hsematoxylin l . The section is stained and treated in the usual 

 way up to 75 p.c. alcohol (the hsematoxylin stain should be deep, 

 since the picric acid will much lessen it). From this it is removed 

 to a watch-glass containing picric acid, e.g. 2 p.c. in 95 p.c. alcohol. 

 After staying about two minutes in this, it is placed in 95 p.c. 

 alcohol and moved about till a faint yellow tinge only is left. It 

 is then transferred to clove oil and mounted. 



Picric acid stains red corpuscles brilliantly when the haemo- 

 globin is preserved, it stains also elastic tissue and the horny 

 layer of the skin ; it stains muscular tissue more readily than 

 white fibrous tissue, and striated duct cells more readily than 

 the alveolar cells of glands. In slight excess it stains the whole 

 section. 



10. Hcematoxylin and rubin S 2 with picric acid. Stain with 

 hoematoxylin. After the section has been passed through alcohols 



1 A piece of arytenoid cartilage may be taken. 



2 Kubin S is the acid-magenta or saure-fuchsin made by a par- 

 ticular Firm, and considered by some workers to give the best stain. 



