MELANINS 



149 



METHYL BLUE 



See Dopa Reaction for melanogen in 

 n!o];in<il.lasts. 



Melanoblasts, see Dopa Reaction. 



Meldola's Blue, son Naphthol Blue R. 



Mercuric Chloride (corrosive sublimate) 

 in various combinations is an excellent 

 fixative. It can be used in saturated 

 aq. sol. plus 5% acetic acid or in satu- 

 rated ale. sol. with the sam(! amount of 

 acetic acid. See (1) with formalin, 

 glacial acetic and phj^siological saline 

 for Centrosomes, (2) sat. in 0.9% aq. 

 sodium chloride for Megakaryocytes, 

 (3) sat. in 70% alcohol + 5% acetic 

 for Mitosis, (4) sat. aq. + equal parts 

 2.5% aq. potassium bichromate for 

 Neutral Gentian, (5) sat. aq. with equal 

 parts abs. alcohol for Thymonucleic 

 Acid, and (6) with nitric acid for Urea. 

 The mercuric chloride is removed from 

 the sections by Lugol's iodine solution. 

 See also fi.vatives of Zenker, Gilson, 

 Rabl and Petrunkewitsch. Zinc chlo- 

 ride is suggested as substitute for 

 mercuric chloride in Zenker's fluid 

 (Russell, W. O., J. Techn. Methods & 

 Bull. Int. Asso. Med. Museums, 19-11, 

 21,47). 



Mercurochrome 220. Trade name for di- 

 brom-oxy-mercuri-fiuorescein. Can be 

 used as substitute for eosin (Baldwin, 

 W. M., Auat. Rec, 1928, 39, 229) but 

 it has little to commend it. 



Mercury, microchemical tests for. 



1. Method of Almkvist-Christeller. 

 Fix tissues 2 days in sat. aq. picric acid, 

 100 cc. ; 25% nitric acidl cc, saturated 

 with H2S gas, filtered after 1 day. After 

 fixation wash in running water for 24 

 hrs. Imbed in paraffin. Mercury ap- 

 pears as black ppt. of sulphide. Lison 

 (p. 102) explains that it is necessary to 

 make parallel tests for iron because this 

 method changes iron into the black sul- 

 phide which could be mistaken for the 

 sulphide of mercurv. Simonet (M., 

 Arch. d'Anat. Micr.,''l929, 25, 372-381) 

 uses instead fixation for 10 hrs. in equal 

 parts alcohol and chloroform, 100 cc, 

 -f- nitric acid, 2 cc. the mixture satu- 

 rated with HoS by bubbling. 



2. Method of Brandino (G., Studi 

 Sassari, 1927, 5, 85). Fix in formalin 

 or in alcohol. Treatment of sections 

 with 1% sol. of diphenylcarbazide which 

 forms with mercury a violet ppt. Gives 

 results with organs of persons killed by 

 mercury poisoning kept in formalin 

 17 years (Lison, p. 102). 



Intravenous injections of colloidal 

 solutions of mercury in rabbits are 

 described by Duliamel, B. G., C. rend. 

 Soc. dc Biol., 1919, 82, 724-726. 

 Mesentery spreads, sections and cultures. 

 Maximow, A., Arch. f. exper. Zellf., 

 1927, 4, 1-42 (nice colored plates). 



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 polj'chrome (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 ])y 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 arabic or other 

 negatively charged colloid (Bank, O. 

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

 plasma, 1939, 32, 489-516). 



MetacrescI Purple. See K)'drogen Ion In- 

 dicators. 



Metallurgic Microscope. Since the mate- 

 rials routinely studied are opaque the 

 light is reflected verticailj'' down upon 

 them through the objective. This in- 

 strument is of little use in biology and 

 medi'''iRe. 



Metamyelocytes, see Leucocytes, develop- 

 mcritfil SGriGS 



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. 



Methacryiate. 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, 



