STAINING, PRACTICAL AND THEORETICAL 



French (1926) azur C tissue stain, some samples of azur C did 

 not work satisfactorily when the solutions were first made, but 

 they improved with age. This fault was overcome by adding a 

 very small proportion of methylene violet (Bernthsen) to the azur 

 C, which is a lower oxidation product of methylene blue. 



The azurs, A, B and C, normally contain a small proportion of 

 methylene violet. It would appear from French's statement that 

 solutions of azur C on standing undergo further oxidation with the 

 production of an increased amount of methylene violet. Possibly 

 the pH of the latter dye, which is considerably higher than that 

 of any of the other thiazine dyes or of any other basic dye of any 

 group, may have some bearing on its staining effects on the 

 nucleus of the malarial parasite, etc. 



(4) There is very little difference in the pH ranges between 

 the acid and basic triphenylmethane dyes commonly used in 

 histology. 



(5) It has already been suggested (page 7) that basic dyes of 

 around the same molecular weight as pyronin Y and methyl 

 green might be used in place of these two for differentiating 

 between RNA and DNA. As will be seen from the tables here, 

 toluidine blue, used by Korson (195 1) in place of pyronin Y for 

 staining RNA, not only has a molecular weight very near to that of 

 pyronin Y, but apparently its pH is very close to that of pyronin Y 

 also. Pyronin B has a pH even closer to pyronin Y but there is 

 an appreciable difference between the molecular weights of these 

 two dyes. The former dye is unsatisfactory as a substitute for 

 pyronin Y as a stain for RNA. 



Methyl green has a molecular weight of 458 and a pH of 5-6. 

 In selecting dyes on their molecular weights, or more precisely 

 on the mass of their individual dye-ions for research, as suggested 

 by E. Gurr (i960), it might be as well, in certain cases, to take 

 the pH into consideration also, 



(6) Tables II to VI given below may possibly serve to show 

 whether further study and division of Table I, into mon-, di-, 

 tris-azo and other dyes listed therein are likely to be of interest 

 to individual readers. It is not, however, considered necessary 

 to make further extensions here, as this is something which can 

 be done quite readily by the reader himself should he be inter- 

 ested. 



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