176 PLASMA STAINS WITH COAL-TAR DYES. 



298. Picric Acid. Picric acid gives useful plasma stains after 

 carmine and hsematoxylin. The modus operandi consists merely in 

 adding picric acid to the alcohols employed for dehydrating the 

 objects. 



Picric acid has considerable power of washing cut other anilin 

 stains ; and in combination with hydrochloric acid it very greatly 

 enhances the power with which this acid washes out carmine stains. 

 It should, therefore, not be added to the acidulated alcohol taken 

 for differentiating borax-carmine stains, or the like, but only to the 

 neutral alcohol used afterwards. It has the great quality that it 

 can be used for staining entire objects, and is much indicated for 

 such objects as small Arthropods or Nematodes, mounted whole. 



It can in some cases be employed by dissolving it in the solution 

 of another dye (see Picro-carmine, LEGAL'S alum-carmine, 221, 

 etc.) ; or (for sections) by dissolving it in the xylol or chloroform 

 used for clearing. 



Though picric acid is a useful ground stain, it is at most a rough 

 one, being very diffuse. It stains, however, horn, chitin, muscle^ 

 and erythrocytes, with special energy. 



According to FKOHLICH (Zeit. wiss. Mik., xxvii, 1910, p. 349) 

 picraminic acid (from Griibler & Hollborn) has some advantages 

 over picric acid. 



299. VAN GIBSON'S Picro-Saurefuchsin (from Zeit. wiss. Mik., 

 xiii, 1896, p. 344). To a saturated aqueous solution of picric acid 

 are added a few drops of saturated aqueous solution of Saurefuchsin, 

 until the mixture has become garnet-red. Or (Trans. Amer. Micr. 

 Soc., xix, 1898, p. 105) to 100 parts of the picric acid solution add 

 5 parts of 1 per cent, solution of Saurefuchsin. After staining 

 (sections only), rinse with water, dehydrate, and clear in oil of 

 origanum. 



OHLMACHER (Journ. Exper. Med., ii, 1897, p. 675) adds 0-5 per 

 cent, of Saurefuchsin to a saturated solution of picric acid which 

 has been diluted with an equal quantity of water. He uses this 

 after previous staining w r ith gentian violet. 



RAMON Y CAJAL recommends 0-1 grm. of Saurefuchsin to 100 of 

 saturated solution of picric acid (SCHAFFEE, Zeit. wiss. ZooL, Ixvi, 

 1899, p. 236). 



HANSEN (Anat. Anz., xv, 1898, p. 152) adds 5 c.c. of 2 per cent, 

 solution of Saurefuchsin to 100 c.c. saturated solution of picric acid, 

 and for staining adds to 3 c.c. of the mixture one-third of a drop of 



2 per cent, acetic acid, stains for a few minutes or hours, rinses in 



3 c.c. of water with 2 drops of the acidified stain added, dehydrates 



