ANILINE DYES 31 



for a few minutes, and then to the sulphurous acid again, always 

 washing in water between the two changes. 



/. Wash thoroughly in water, and mount in the usual way in 

 balsam. 



ANILINE DYES 



The substances known as aniline dyes are derivatives of coal tar, 

 but not always of aniline. These dyes have become of great 

 importance in all kinds of biological work. The number of 

 different compounds is very large, and only a few of the most 

 common can be mentioned. None but the purest dyes should be 

 used, and those manufactured by Grubler can be recommended. 

 They are sold in the form of powders. American agents for 

 Grubler 's dyes are Eimer & Amend, of New York city. It is 

 simplest to classify the dyes as basic or acid. Fuchsin, methylene 

 blue, gentian violet, and safranin are basic dyes. They have an 

 affinity for nuclei and for bacteria. Eosin, picric acid, and acid 

 fuchsin are acid dyes, tending to stain tissues diffusely. The use of 

 eosin and picric acid has been described on pages 28 and 29. 



Certain cells have granules in their protoplasm. The granules 

 of some cells manifest an affinity for basic dyes (basophile, S and y) , 

 others for acid dyes (acidophile or eosinophile, ), and others 

 for a mixture of the two (neutrophile, *), and others still for both 

 the acid and the basic (amphophile, ft). 



It is best to keep on hand saturated alcoholic solutions of these 

 dyes, from which waterj r solutions may be made when needed, 

 by adding a few drops of the alcoholic solution to a small dish 

 filled with water. 



The basic dyes may be used as nuclear stains as follows : 



a. Stain sections in a strong watery solution of the dye five 

 minutes or more. The sections will be somewhat overstained. 



5. Wash in one per cent, acetic acid a few seconds. 



c. Alcohol. Dehydration must be done rapidly, as alcohol 

 extracts the color from the tissues. It must, nevertheless, be 

 thorough, as xylol, which is used in the next step, only mixes with 

 strong alcohol. 



d. Xylol. This agent is the one used to clear specimens after 

 staining with basic aniline dyes, because most of the oils slowly 

 dissolve out the aniline colors. 



e. Balsam. 



Among the dyes used in this manner, SAFRANIN is to be espe- 



