METANIL YELLOW. 73 



Here it may merely be mentioned that the majority of the 

 authors who recommend these combinations proceed by stain- 

 ing first with the eosin and then with the nuclear stain, and 

 that the majority also employ alcoholic solutions of eosin. I 

 am by no means convinced that this practice is the best. As 

 regards the anilins, at all events, good results are certainly 

 obtained by staining first with the nuclear stain (gentian 

 violet, for instance) and washing out (sections) for a few 

 seconds or a minute or two in a tolerably strong aqueous solu- 

 tion of eosin, and then dehydrating with alcohol and mounting 

 in balsam. If the eosin is too much extracted by the alcohol 

 or clearing agent, these should be used charged with a little of 

 the colour. Bosin stains may also be kept in glycerin, if this 

 be perfectly neutral or, better, slightly alkaline (which may 

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

 chloride), and also charged with a little eosin. 



117. Bengal Rose (GRIESBACH, Zool. Am., 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. 



118. 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-carmin, alum-carmin, hasmatoxylin, 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. 



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

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

 1887, p. 448 ; see also Journ. Roy. Mic. 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 



