Chapter IV 

 STAINING WITH CONTRAST DYES 



The correlation between tissue elements and particular classes 

 of dyes serves as a working basis for the selection of combinations 

 of contrast dyes. The composition of organic materials may be 

 regarded as comprehensive groups of carbohydrates, carbohy- 

 drates and proteins, or only proteins. Carbohydrates are stained 

 more readily with basic dyes but proteins are differentiated more 

 easily with various types of acid dyes. This initial relation be- 

 tween tissues and stains implies : ( 1 ) acid dyes for embryonic or 

 mature animal tissues and meristematic parenchyma, (2) basic and 

 acid dyes for stem, root, or leaf, and (3) basic dyes for sections of 

 wood. As a general rule the greater the inherent difference in 

 cellular structure the greater should be the chemical differences of 

 the dyes present in the combination. 



The selection of any combination of two or more dyes de- 

 pends not so much on whether the section is animal or plant tissue 

 as on whether the section consists of similar or unlike substances. 

 In most sections of animal tissues, fungi, and meristems, the varia- 

 tions are usually between types of proteins. These similar sub- 

 stances provide different colors more easily in mixtures of closely 

 related acid dyes. Although the color of nuclei may be intensified 

 with basic stains, clear contrasts of protein elements are better in 

 acid dyes with basic properties, that is, direct dyes which possess 

 an amino radical. Whenever cellulose assumes a dominant part of 

 vascular plants a basic dye is necessary. Then, the red basic 

 Rhodamine 6G, Safranine, Acridine Red, or Basic Fuchsine may 

 be used with a counterstain such as Aniline Blue, Niagara Sky 

 Blue, Fast Green, or Haematoxylin. 



Many stains either lack a suitable counterstain or they dif- 

 ferentiate with few other dyes. Sun Yellow, a direct dye, gives 

 a clear contrast with Niagara Sky Blue or New Methylene Blue, 

 but blends on plant tissues into a dull gray-violet with Methyl 

 Violet. Biebrich Scarlet, an acid dye, differentiates sharply with 

 either of the blue dyes or the violet basic dye. 



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