When the basic-aniline stains are used a saturated water or concentrated alcoholic solution (1½-2 per cent in 40 per cent alcohol) may be employed as stock-solution and diluted 1:5 or 1:10, as desired. The sections are stained 3-5 minutes, then differentiated in absolute alcohol, cleared in xylol, and mounted in balsam. Methylene-blue is used by some workers as a nuclear stain contrasted with eosin for tissues fixed in Zenker’s solution, giving better effects with this fixation than the hæmatoxylins. =Unna’s alkaline methylene-blue formula= is employed (methylene-blue 1 grm., carbonate of potassium 1 grm., water 100 cc.). Dilute 1:10 or 1:5 for staining. Stain 10-15 minutes, wash quickly in water, differentiate in 95 per cent alcohol; dehydrate in absolute, clear in xylol, mount in balsam. When celloidin sections are used, 95 per cent alcohol may be used for dehydrating, blotting on the slide with several changes of xylol. The =nucleolus= has an affinity for the acid stains. With the modifications of the Romanowsky methylene-blue-eosin methods the nucleolus stains red, the nucleus blue. II. DIFFUSE OR PLASMA STAINS. The most commonly used diffuse stains are eosin, erythrosin, acid fuchsin, orange G, and picric acid. They are practically never used alone, but are employed as contrast-stains to the nuclear stains. Eosin, orange G, acid fuchsin and picric acid may be used as counterstains for hæmatoxylin; picric acid is used as the best contrast to the carmines, while eosin and orange G are employed as counterstains for methylene blue. The combination of hæmatoxylin and eosin is by far the best general staining method for laboratory and diagnostic work, except for tissues fixed in Zenker’s solution; for these the combination of methylene blue and eosin is preferable. Ammonia carmine is sometimes used as a diffuse stain for bone and the central nervous system. The majority of the diffuse stains wash out easily in water, alcohol and xylol, hence sections thus stained should not be allowed to remain too long in these fluids. a. =Eosin.= Two forms of eosin are obtainable, one soluble in water, the other in alcohol. Saturated solutions of both kinds should be kept as stock solutions and diluted as occasion demands. For use after hæmatoxylin a ½ per cent solution is advisable; with Zenker’s fixation a more dilute solution may be used, as tissues so fixed stain intensely in eosin. If used as a contrast-stain to methylene-blue, eosin is used first in a 5 or 10 per cent solution, as the basic nuclear stain takes out some of it. Some workers express a preference for the aqueous solution of eosin, others for the alcoholic; the alcoholic solution stains more uniformly and with less differentiation than the other. Eosin is particularly good as a contrast-stain for tissues containing red blood cells when fixed in formol, mercuric chloride or Zenker’s.