Nature of Staining Action 111 



The majority of dyes do not stain metachromatically, but are ortho- 

 chromatic in action. This means that their action is direct and predic t- 

 able under normal conditions; if it is a blue dye, it stains blue, if it is a 

 green one it stains green, and so forth. 



Structure of Synthetic Dyes^ 



The synthetic (coal tar or aniline) dyes are derivatives of benzene, all 

 built on the benzene ring. When certain chemical groups, called 

 chromophores, are attached to a benzene derivative, the compound ac- 

 quires the property of color and is known as a chromogen. A chromogen, 

 however, still is not a dye. It has no affinity for tissues, will coat them 

 only mechanically, and can be easily removed by mechanical means. 

 The compoinid must also contain a gTOup which gives it the property 

 of electrolytic dissociation (the formation of cations and anions in solu- 

 tion). This auxiliary group, known as an auxochrome, furnishes the 

 required salt-forming properties. As mentioned above, most of the dyes 

 are sold as salts and are stable powders tmtil put into solution, then 

 becoming acidic or basic by dissociation. 



Nomenclature of stains has no absokite conformity. The color may be 

 used — orange G, Martitis yellow; or perhaps some chemical term — 

 methyl green and so forth. If the term is followed by a letter or nmneral 

 (Sudan III, I\', ponceau 2R, 4R), one dye is being distingtiished from 

 a related one. B indicates a more bluish color, Y or G a more yellowish 

 color, WS means water soluble; and A, B, C distinguish among certain 

 azures. 



Nature o£ Staining Action 



Biologists and biochemists argue concerning the nature of staining 

 action — is it chemical, physical or a combination of both? If chemical, 

 this can mean that some parts of the cells are acid and others alkaline, 

 the former tending to combine \vith cations and the latter with anions. 

 There is an absorption and diffusion of the dye penetrating the cellular 

 elements, combining with them and remaining there in a state of more 

 or less chemical combination. This action can be combined with physi- 

 cal action, where there is an adsorption of the dye, an attraction of plus 

 and minus charges for each other and a condensation of the dye on the 

 surface of the cell parts. Minute particles of the dye are deposited on 



^ For a complete discussion of d)LS, consult Conn, 1953 or Gurr, 19G0. 



