Organic Substances 69 



Fix tissues in alcohol or formalin-alcohol. Other fixatives 

 are also usable, but the background may be stained more or 

 less intensely. Stain nuclei with hematoxylin. 



Rinse slide in water; stain in mucicarmine for about 15 

 minutes; rinse in water, dehydrate, and mount. Some kinds of 

 mucus stain intensely red; others are much paler or may fail 

 to stain altogether. If staining time is prolonged, hyaluronic 

 acid and glycogen may become stained, although in a much 

 paler shade. 



The Metachromatic Staining of Acid Polysaccharides 



The concept of metachromasia.— It was observed simulta- 

 neously by Comil,^^ Jiirgens,^^ and HeschP^ in 1875 that 

 methyl violet stains amyloid red and other tissue structures 

 blue. This phenomenon— namely, the staining of certain tis- 

 sue components in a color different from that of the dye so- 

 lution itself— has been named "metachromasia" by Ehrlich.^^ 

 According to his nomenclature, the shade of the dye solution 

 is the orthochromatic shade; the different shade in which cer- 

 tain tissue elements stain is the metachromatic shade; the 

 substances which exhibit the property of staining in the 

 metachromatic shade are the chromotropic ( or metachromat- 

 ic) substances. It must be made clear that metachromasia 

 applies only to the cases in which both shades are produced 

 by a single dyestuff and not by a mixture of dyes. Some com- 

 mercial dyes may contain substantial admixtures, as impuri- 

 ties, of other related dyestuff s. 



The number of dyes exhibiting metachromatic properties is 

 large. However, only a few of them have practical impor- 

 tance. The list includes thionin, the azures, toluidin blue, 

 cresyl violet, and methyl violet. Methyl green, used for the 

 metachromatic staining of amyloid, owes its metachromatic 

 properties to its content of methyl violet. The most typical 



55. Comil, v.: Compt. rend. Acad. d. sc, 80:1288, 1875. 



56. Jiirgens, R.: Virchows Arch. f. path. Anat., 65:189, 1875. 



57. Heschl, R.: Wien. med. Wchnschr., 25:712, 1875. 



58. Ehrlich, P.; Arch. f. mikr. Anat, 13:263, 1877. 



