METACHROMASIA 



197 



METHYL VIOLET 



Metachromasia, see Metachromatism. 



Metachromatism (metachromasia) is the 

 property of certain dyes to stain (G., 

 meta, beyond) the usual color (G. 

 chroma). The action of some impure 

 methylene blues is sometimes cited as 

 an example. Thus polychrome (many 

 colored) methylene blue stains some 

 objects blue and certain granules red- 

 dish. This methylene blue is however 

 a mixture of methylene blue and methyl- 

 ene red. The latter dye accounts for 

 the staining beyond. Orcein colors 

 nuclei blue and cytoplasm pink. Safra- 

 nin stains nuclei in its ordinary solution 

 color (red) and the ground substance of 

 cartilage that of its free color base 

 (orange). Michaelis (Lee, p. 136) 

 thinks that the appearance of the color 

 base is not occasioned by the alkalinity 

 of the objects stained. The red stain 

 of mucin by thionin can be altered to 

 blue by alcohol and be shifted back to 

 red by water. For colored plates show- 

 ing metachromatic staining of mast 

 cells, see Maximow, A., Arch. f. mikr. 

 Anat., 1913, 83 (1), 247-289. Meta- 

 chromasia of acid dyes is increased by 

 adding strychnine, quinine or clupein 

 and of basic dyes by gum arable or other 

 negatively charged colloid (Bank, O. 

 and Hungenberg de Jona, H. G., Proto- 

 plasma, 1939, 32, 489-516). The dis- 

 tinction between "true" and "false" 

 metachromatic staining with toluidine 

 blue is fully described by Sylvan, B., 

 Acta Radiol., 1945, Suppl. 59, 100 pp. 



Metacresol Purple. See Hydrogen Ion In- 

 dicators. 



Metallurgic Microscope. Since the mate- 

 rials routinely studied are opaque the 

 light is reflected vertically down upon 

 them through the objective. This in- 

 strument is of little use in biology and 

 medicine. 



Metamyelocytes, see Leucocytes, develop- 

 mental series. 



Metanil Yellow (CI, 138)— acid yellow R, 

 orange MNO or MN, soluble yellow OL, 

 tropaeolin G, yellow M — An acid mono- 

 azo dye employed in the Masson tech- 

 nique, see Foot, N. C., Stain Techn., 

 1933, 8, 101-110. 



Methacrylate. Plastic for mounting ali- 

 zarin-red-S preparations. (Holcomb, 

 R. C. and Apterman, P. M., J. Tech. 

 Methods, 1944, 24, 21-24). 



Methyl Alcohol, see Elementary Bodies. 

 It is much used in many techniques. 



Methyl Benzoate. Refractive index close 

 to that of cedar wood oil. It can be 

 used in place of immersion oil. In 

 addition it is a substitute for absolute 

 alcohol and an excellent clearing agent 

 but it is expensive. See Ceresin 

 imbedding. 



Methyl Blue (CI, 706)— cotton blue, Hel- 

 vetia blue — Widely used. Recom- 

 mended for connective tissue by Lillie, 

 R. D., J. Tech. Methods, 1945, No. 25, 

 47 pp. See Mann's Methyl-Blue Eosin 

 and staining of Elementary Bodies. 



Methyl Blue-Eosin, see Mann's. 



Methyl Eosin (CI, 769). The methyl ester 

 of eosin Y, see Eosins, choice of. 



Methyl Green (CI, 684) — double green, 

 light green — This basic triphenyl meth- 

 ane dye is crystal violet (he.xa-methyl 

 pararosanilin) into which a seventh 

 methyl group has been incorporated. 

 Conn (p. 130) points out that this is 

 loosely bound so that some methyl or 

 crystal violet is always present with the 

 methyl green to which circumstance the 

 metachromatic properties of the dye are 

 partly due. Methyl green is not as 

 stable as most dyes and cannot therefore 

 be kept too long in the powdered state. 

 It is very similar to Ethyl Green. 



Methyl Green-Pyronin (Pappenheim). Sec- 

 tions of formalin-Zenker fixed tissues 

 are stained about 6 min. in : methyl 

 green 0.5 gm.; pyronin Y, 0.5 gm.; ale. 

 2.5 cc; glycerin 20 cc; aq. dest. 0.5% 

 carbolized 100 cc. Rinse in aq. dest.; 

 dehydrate in acetone; clear in cedar 

 oil followed by xylol and mount. Opti- 

 mum time of staining must be deter- 

 mined experimentally. A brilliant 

 stain particularly for lymphocytes and 

 plasma cells. Very useful for spleen 

 and lymph nodes. (Slider and Downey 

 in McClung's Microscopical Technique, 

 p. 342). 



Modification of Scudder (Stain 

 Techn., 1944, 19, 39-44) gives good 

 results on tissue sections and bacteria 

 and has been used for identification of 

 2 types of nucleic acids (Taft, E. G., 

 Exper. Cell Research, 1951, in press). 

 Dehydration of stained material with 

 tertiary hiilyl alcohol gives better results 

 than with ethyl alcohol. 



Methyl Orange (CI, 142)— gold orange MP, 

 helianthin, orange III, tropaeolin D — 

 A slightly acid mono-azo dye widely 

 employed as an Indicator. 



Methyl Red (CI, 211). A slightly acid 

 mono-azo dye widely used as an Indica- 

 tor. See also Carter, J. S., J. Exp. 

 Zool., 1933, 65, 159-179 for vital staining 

 of rabdites of Stenostomum with 

 methyl red. 



Methyl Salicylate (oil of Wintergreen) is 

 employed in Spalteholz Method of 

 clearing. 



Methyl Violet (CI, 680)— dahlia B, gentian 

 violet, Paris violet, pyoktaninum coeru- 

 leum — Exists in various shades 2R, R, 

 B, 2B, 3B, etc., depending upon propor- 

 tions of the mixture of tetra-, penta- 

 and he.xa-methyl rosanilins. R indi- 



