92 METHYLEN BLUE, AND OTHER ANILINS. 



be brought about by the addition of 1 per cent, of sodium 

 chloride), and also charged with a little eosin. 



136. Bengal Rose (GEIESBACH, Zool Anz., No. 135, 1883, p. 172). 

 Bengal rose, or "Rose bengale," or "Bengal rosa," is an eosin dye. It is the 

 bluest of the eosin dyes as yet known, approaching in hue to fuchsin, but 

 possessing far greater brilliancy and purity of hue. In aqueous solution it 

 is useful for staining chromic acid objects, especially spinal cord, in which 

 the grey matter stains of a deep bluish red, and stands out boldly from the 

 less deeply coloured white matter. It is also useful for double and treble 

 stains, as will be explained below. 



137. Picric Acid. Not used alone as a stain, but one of the 

 most useful of all colouring agents as a secondary or ground- 

 stain. Nothing is easier than to stain with an alcoholic solu- 

 tion of picric acid tissues of which the nuclei have previously 

 been stained by borax-carmine, alum-carmine, hsematoxylin, or 

 an anilin stain. It should be borne in mind that picric acid 

 has considerable power of washing out other anilin stains ; 

 and that in combination with hydrochloric acid it very greatly 

 enhances the power with which this acid washes out carmine 

 stains. It does not otherwise affect any of the usual stains, 

 and may be most highly recommended as a useful though fre- 

 quently inelegant stain. 



138. Metanil Yellow (Metanilgelb). This colour has lately been 

 ^studied with great minuteness by GEIESBACH (Zeit. f. wiss. Mik., iv, 4, 



1887, p. 448 ; see also Journ. Roy. Hie. Soc., 1889, p. 464). It does not 

 appear to be worthy of having so much time spent on it from the practical 

 point of view, the interest of Griesbach's work lying rather in the region of 

 chemical theory. The practical outcome is that metanil yellow is a diffuse 

 stain with a certain affinity for various elements belonging to the group of 

 the connective tissues, and that with some other colours it gives sharply 

 differentiated double stains of certain preparations. These will be mentioned 

 in the proper places. 



139. Sauregelb (Echtgelb), Tropaeolin O., Crocein, Gold Orange, 



are all of them more or less diffuse yellow or orange stains, having certain 

 affinities for certain tissues, and may occasionally be found very useful for 

 double-staining, being good stains in their way (see GRIESBACH, Arch. /. 

 mik. Anat., xxii, p. 132). 



140. Iodine Green (" Hofmann's Griin "), see GRIESBACH, Zool. 

 Anz,, No. 117, vol. v, 1882, p. 406. The high praise accorded 

 to this stain by Griesbach has not been justified by the ex- 

 perience of other workers. The colour is now no longer 



