136 STAINED PREPARATIONS 



stain in alcohol, while a third group stain with difficulty but after being 

 stained resist the action of the most powerful decolourizing agents. 



Bacteria are vegetable cells of which the greater part is occupied by the 

 nucleus (Biitschli) : they stain with those dyes which stain the nuclei of 

 vegetable cells, that is to say, the basic aniline dyes. 



Stains. Ehrlich divided dyes according to their action on cells into two 

 groups : basic dyes and acid dyes. 



Basic dyes are those in which the staining property depends upon a base 

 combined with a colourless acid. They are called selective dyes, because 

 they exhibit a marked selective affinity for nuclei and especially the nuclei 

 of vegetable cells. The basic dyes are the true micro-organic dyes. Those 

 most commonly used are the following : 



Violets, - 



Crystal-violet. 



Thionin (Lauth's violet). 



Gentian-violet. 



Methyl-violet B (Bale's violet). 



Methyl- violet 6B. 

 Paris violet. 

 Dahlia. 



Methylene blue. 

 Victoria blue. 

 Azur. 



ies ' ' Nile blue, or Capri's blue. 



Quinoline blue. 

 Unna's polychrome blue. 



I Fuchsin. 

 I Rubin. 

 I Safranin. 

 I Neutral-red. 



(Methyl- green. 

 \Malachite green. 



Bismarck brown, - Vesuvin. 

 Colin black, - - Indulin. 



In the acid dyes on the other hand the staining agent is an acid combined 

 with a coloured or colourless base. They are non-selective dyes and stain 

 all tissues indifferently . Fluorescein (phthalic ether of resorcin), eosin 

 (tetrabrom-fluorescein), aurantia, coccinine, acid fuchsin, tropseolin, magenta 

 8, orange Gr, and picro-carmine are the acid dyes in most common use. 



Note. The aniline dyes have intense staining properties, and should be carefully 

 handled; if the hands be stained accidentally they can be quite easily decolourized 

 with soap. The powders should not be shaken. 



Mordants. In dyeing, an intermediary agent is used to fix the dye more 

 firmly in the fabric. This intermediary agent is known as a mordant, and 

 combining both with the dye and with the tissue unites the two intimately 

 together. 



Mordants are also used in staining micro-organisms, and though their 

 mode of action is not as yet thoroughly understood, they undoubtedly increase 

 the affinity of the dyes for the cells and render the staining more rapid and 

 more lasting. The mordants in ordinary use are : 



Acids. Acetic acid. 



Phenol. Creosote. 



Tannin. 



Iodine in iodine-iodide solution. 



Bromine in iodine- bromide and bromine- bromide solutions. 



Perchloride of mercury. 



