Phenyl Methane Dyes 



169 



.6- 



400 



460 520 580 640 

 WAVELENGTH mu 



Fig. 22. Spectral curve of anilin blue W.S, 



700 



if the reaction becomes acid. It is not a specially valuable in- 

 dicator, however, partly because of the slowness with w^hich it re- 

 sponds to change in reaction, and partly because it is quite subject 

 to protein and other errors. In spite of these drawbacks it has 

 sometimes been used in bacteriological media, when accuracy is 

 not important and the slow response to acid production is of no 

 significance. 



Hendrickson, Baldwin, and Riker (1934) have employed it in 

 bacteriological media for a different purpose, the isolation of the 

 crown gall organism ; in their medium it holds fungi in check while the 

 desired organism absorbs the blue color and is thus easy to recog- 

 nize. For some reason not yet explained, those samples (apparent- 

 ly pararosanilin derivatives) which do not decolorize properly in 

 alkaline solution, fail to work in this medium, although the dye 

 does not serve in this instance as an acid-base indicator. 



By far the best known use of anilin blue, W.S., is as a counter- 

 stain in histology. Among its histological applications are: by 

 Stroebe and Huber (see Krause, 1926-7, p. 63) as a cytoplasm 

 stain preceding safranin; by Galli for axis cylinders; frequently by 

 botanists as a contrast for safranin in vascular plant tissue, or for 



