116 



Biological Stairis 



storage as a result of which the two dyes may become almost 

 identical optically. Their great similarity is well brought out by 

 comparing Curve 1 (toluidine blue) and Curve 2 (Azure A) in 

 Fig. 12 on p. 108. Ball and Jackson (1953) have recently shown by 

 chromatography that toluidine blue O seems to be a mixture, and 

 suggest that this may account for much of the observed variation 

 between samples. 



Although not a common textile dye, toluidine blue is more easily 

 prepared than thionin or azure A — a fact of considerable im- 

 portance, since in many procedures it may be substituted for one 

 or the other of these dyes. It may be employed like azure A as a 

 nuclear stain for sections of fixed tissue; and may be substituted 

 for thionin in staining frozen sections of fresh tissue. It is a valu- 

 able general nuclear stain, being ordinarily employed in 0.3-1% 

 aqueous solutions. It is widely employed in stains for Nissl gran- 

 ules and chromophylic bodies and has been proposed in a great 

 variety of special procedures. Well known among the latter is 

 Pappenheim's panchrome stain (of which it is an important in- 

 gredient) and the Albert stain which is at present widely replacing 

 methylene blue in the diagnosis of diphtheria. It has use as a 

 chemical reagent in the standardization of heparin and as a histo- 

 chemical reagent in determining thymonucleic acid. 



PROCEDURES RECOMMENDED BY THE COMMISSION IN WHICH THIS STAIN IS USED 



j30 



NEW METHYLENE BLUE N 



Synonym: Methylene blue NN. 



c. I. NO. 917 



CH3"CH3 



H 



\ 



I 



/ 



CH3 



CH, 



CH3CH, 



N 



'iN" 



CI 



C18H22N3SCI; Mol. Wt. 347.897 



{A basic dye; absorption maxima about \636.Ii], 588.) 



Solubility at 26° C: in water 13.32%; in alcohol 1.65% 



