METHYLENE AZURE 



198 



MICRODISSECTION 



cates reddish and B bluish. 2B is the 

 one which Conn (p. 123) regards as most 

 satisfactory whenever methyl violet, 

 or one of the redder types of gentian 

 violet, is requested. (It is Commission 

 Certified.) The pure hexamethyl com- 

 pound is called crystal violet — a dye 

 much in demand. See Hydrogen Ion 

 Indicators. 



Methylene Azure (CI, 923) . A basic thiazin 

 dye long recognized as a component of 

 Polychrome Methylene Blue. Conn 

 (p. 76) says that the term, methylene 

 azure, should be discarded because it 

 is composed of three components Azure 

 A, B, and C which see. 



Methylene Blue (CI, 922)— Swiss blue- 

 Conn (p. 80) says that this basic thiazin 

 dye is theoretically tetra-methyl thio- 

 nin but the homologues of lower 

 methylation are practically always 

 present ; he lists the following grades : 

 methylene blue BX, B, BG, BB, and 

 methylene blue chloride. The last 

 named is Commission Certified and least 

 toxic. Methylene blue Med. U.S.P. 

 is required to be zinc free and is also 

 satisfactory. New methylene blue N 

 (methylene blue NN) is a basic dye of 

 the same type but of a slightly greener 

 shade. Conn (McClung, p. 595) states 

 that it was apparently in certain lots 

 of prewar methylene blue. Methylene 

 blue O is the same as toluidin blue O 

 which resembles azure A, a component 

 of methylene azure produced by poly- 

 chromizing methylene blue. Another 

 of the series is methylene blue GG but 

 it has no particular advantage. Prob- 

 ably no dye, other than hematoxylin and 

 eosin, is more widely used. The oxida- 

 tion products of methylene blue are 

 described by Holmes, W. C, Stain 

 Techn., 1926, 1, 17-26 and the influence 

 of pH on staining of plasma cells and 

 lymphocytes by Kindred, J. E., Stain 

 Techn., 1935, 10, 7-20. Its cytological 

 action has been fully studied by Lud- 

 ford, R. J., Arch. f". exp. Zellf., 1935, 

 17, 339-359. It is an excellent counter- 

 stain for Acid Fast Bacilli. See Poly- 

 chrome Methylene Blue, Loeffler's 

 Alkaline Methylene Blue, Nerve End- 

 ings, Phloxine Methylene Blue, Mac- 

 Neal's Tetrachrome, Pancreas, Pro- 

 tozoa, etc. For use of methylene blue 

 as a supravital stain fixed with ammo- 

 nium molybdate, see Lillie, p. 245. 



Methylene Blue NN, see New Methylene 

 Blue N. 



Methylene Blue T 50 or T Extra, see Toluidin 

 Blue O. 



Methylene Blue Eosinate, see May-Griin- 

 wald fixative and stain. 



Methylene Green (CI, 924). This basic 

 thiazin dye is mono-nitro methylene 



blue. Conn (p. 86) says that it is oc- 

 casionally employed as a substitute for 

 methyl green and gives good results as 

 counters tain for eosin. 



Methylene Violet. Commission Certified. 

 This feebly basic thiazin dye is, as 

 Conn (p. 86) explains, formed whenever 

 methylene blue is heated with a fixed 

 alkali or alkali carbonate. It may be 

 purified by recrystallization but little 

 is to be gained. The dye is not much 

 used. 



Metrial Gland. This is a transitory struc- 

 ture of unknown function in the mouse 

 appearing at approximately the 8th d.n}' 

 of pregnancy. Failure of its cells to 

 take up trypan blue seems to eliminate 

 the hypothesis that it is active in phago- 

 cvtosis (Lobo, B. A., and Atkinson, 

 W. B., Anat. Rec, 1946, 94, 77). 



Micelle (dim. of L. Mica a crumb, micella, 

 micellae). Term introduced by Nageli 

 in 1884 for then hypothetical structural 

 units of the cell. 



Michiavello Stain. See Rickettsia. 



Microchemical Reactions. For the 

 microscopic identification of particular 

 elements or substances some micro- 

 chemical reactions are available but it 

 is difficult to sharply distinguish them 

 from other techniques not usually styled 

 microchemical. An attempt is made to 

 list them under the objects demon- 

 strated : Lead, Iron, Vitamin C, Peroxi- 

 dase, etc. Many are generally known 

 under personal names. See for exam- 

 ple: Axenfeld (proteins), Burchardt 

 (gold) , Carr-Price (vitamin A) , Feulgen 

 (thymonucleic acid), Gmelin (bile pig- 

 ments), Lilienfeld-Monti (phosphorus), 

 Millon (tyrosin), Romieu (proteins), 

 Schiff (aldehydes), Vulpian (epineph- 

 rine), etc. 



Microdissection. In the selection of this 

 method for use in any particular problem 

 it is well to bear in mind several con- 

 siderations. It is of particular value 

 in the direct examination of large cells 

 easily isolated, like sea urchin eggs, 

 and of tissues that exist in thin sheets, 

 like highly vascularized membranes 

 which can be easily approached in the 

 living state without serious injury. 

 The data to be secured relate chiefly 

 to the responses of the cells to the 

 mechanical stimulus of the microneedle, 

 to the character of the connections be- 

 tween fibers, cells and parts of cells as 

 determined by their resistance to at- 

 tempts to separate them and to the 

 physical consistency of cellular and 

 nuclear membranes and of cytoplasm 

 and nucleoplasm. Moreover individual 

 cells can be isolated by microdissection 

 just as Barber was able to isolate single 

 bacteria by the pipette which he intro- 



