BENZOPURPTJRIN. 71 



p. 102). Quinolein should be dissolved in alcohol of 36 strength (i.e. 90 

 percent.), and the solution diluted with an equal volume of water. (If the 

 alcohol were taken dilute in the first instance, the blue would not dissolve.) 

 The solutions employed for staining should be very weak, as quinolein 

 stains very powerfully. 



After staining, wash and mount in glycerin. When first mounted, nuclei 

 will be seen to be stained a fine violet, nerves of a grey-blue, smooth muscle 

 blue, protoplasm blue, fat deep blue. But after twenty-four hours in the 

 glycerin, the aspect of the preparation is changed ; the nuclei have become 

 colourless ; the protoplasm remains blue, and is seen to contain granulations 

 stained intensely blue ; nerves remain grey blue, but frequently contain 

 granulations stained blue. Quinolein, in a word, has the property of 

 staining fatty matters an intense blue. 



If the stained preparations be treated with solution of potash of 40 per 

 cent, strength, the differential reaction is produced immediately ; the nuclei 

 are unstained, protoplasm, nerve, and muscle tissue are pale blue, and fatty 

 matters deep blue. 



It is, perhaps, not generally known that if tissues be stained slowly (for 

 some hours) in very dilute aqueous solution of quinolein as directed for 

 methyl violet (ante, 107), and then be mounted in balsam, a fairly precise 

 and permanent nuclear stain may be obtained. 



Quinolein is useful for staining Infusoria, which in dilute solution it 

 stains during life. On this point, see the methods of Certes (post, Part II). 



Other Anilins. 

 (The order adopted is Red, Yellow, Green, Blue, Black). 



112. Saurefuchsin (Fuchsin S., Acid Fuchsin), a Fuchsin in which the 

 colouring principle is an acid, instead of being a base as in ordinary fuchsin- 

 It is only made by the " Badische Anilin und Soda Fabrik." It may be 

 obtained from Griibler or the other providers of histological reagents. It is 

 a powerful diffuse stain, having a special affinity for axis cylinders, and is 

 chiefly used for staining nerve centres. See the Chapter on Nerve Centres, 

 in Part II. 



113. Congo Red (Congoroth). See Griesbach, in Zeit.f. wiss. MiJc., 

 iii, 3, 1886, p. 379. Also an " acid " colour, in the sense in which that 

 appelative is given to Suurefuchsin. The aqueous solution, however, has a 

 neutral or alkaline reaction. It becomes blue in presence of the least trace 

 of free acid (hence Congo is a valuable reagent for demonstrating the presence 

 of free acid in tissues, see the papers quoted 1. c.). A diffuse stain, much of 

 the same nature as that of Saurefuchsin, and like it seems to be at present 

 chiefly useful for staining axis-cylinders. See the Chapter on Nerve Tissue, 

 in Part II. It may also be used for staining some objects during life (see 

 ante, 93). 



114. Benzopurpurin, according to Griesbach (I. c.), another 

 "acid" colour, very similar in its results to Congo red. 



