When a nuclear counterstain is desired, put the sections in water after 4; then stain in hæmatoxylin; differentiate quickly in acid alcohol; wash in water; place in weak ammonia or lithium-carbonate solution; wash in water; transfer to slide; blot; mount in glycerin gelatin. Sudan III and scarlet R stain the smallest particles of fat yellowish-red to deep scarlet; scarlet R on the whole gives the best results. The contrast with the blue nuclei when stained with hæmatoxylin gives beautiful preparations. 3. =Staining of Fat with Indophenol.= Stain sections with lithium-carmine; wash; then stain 20 minutes in a saturated solution of indophenol in 70 per cent alcohol. Fat blue; nuclei red. 4. =Staining of Fatty Acids and Soaps.= _a. Benda’s Method._ Fix in 10 per cent formol. Transfer tissue to Weigert’s copper-fluorchrom mordant (neutral copper acetate 5 grms., fluorchrom 2.5 grms., water 100 cc.; boil and add 5 cc. of 36 per cent acetic acid) in the incubator for 2-4 days. Cut on the freezing-microtome. Stain sections in sudan III or scharlach R, and then in hæmatoxylin. Nuclei are blue, normal fat red, necrosed fat green due to formation of fatty acid copper salt. Soaps give the same reaction when converted into insoluble salts by fixing in formol saturated with calcium salicylate. Through comparison of tissue hardened in this way with another portion fixed in formol alone soaps and fatty acids may be differentiated. _b. Smith’s Method._ Stain in concentrated water solution of Nile blue sulphate for 10 minutes. Fat stains red, nuclei dark blue, protoplasm light blue, fatty acids dark-blue. Differentiate in 1 per cent acetic acid; wash in water; mount in glycerin-gelatin. =X. FIBRIN.= Fibrin stains with the acid aniline dyes, except in areas of necrosis containing diffused chromatin, under which conditions it stains deep blue with hæmatoxylin. In Van Gieson’s mixture it stains yellow or brownish; in Mallory’s reticulum stain it stains red, and with Mallory’s chloride of iron hæmatoxylin it is grayish to dark blue. The best selective method by far is Weigert’s, and it is the only really practical method giving a good differentiation. 1. =Weigert’s Fibrin Stain.= I have obtained the best results by making this stain as follows: 10 cc. of aniline oil and 100 cc. of water are shaken together violently for several minutes, and then filtered through a moist filter. The filtrate must contain no drops of aniline. Add to the filtrate sufficient dry gentian-violet or methyl-violet to produce a metallic shimmer on the surface of the solution after the dye is dissolved by shaking. The solution will keep for several months.