Weigert’s modification of Gram’s method, as given above for the staining of fibrin, is the best for the staining of bacteria that stain by this method. (See Fibrin, Chapter XXVI.) The differentiation with aniline-xylol is slower and safer than with alcohol. Acetone-xylol (1:5) has been recommended in place of aniline-xylol. Wolbach recommends the use of a 5-10 per cent colophonium-alcohol for differentiation. Contrast staining with watery Bismarck brown, dilute carbol-fuchsin or eosin may be carried out if desired. The aniline-xylol may be saturated with eosin and the section stained during the differentiation. _Carbol-gentian-violet_ may be used instead of aniline-gentian-violet; it keeps much better than the latter. Staining by Gram’s Method (Gram-positive). Staphylococcus pyogenes aureus. Staphylococcus pyogenes albus. Staphylococcus pyogenes citreus. Streptococcus pyogenes. Micrococcus tetragenus. Diplococcus pneumoniæ. Bacillus aërogenes capsulatus. Bacillus of diphtheria. Bacillus of anthrax. Bacillus of leprosy. Bacillus of tetanus. Bacillus of tuberculosis. Bacillus of rhinoscleroma. Bacillus of mouse septicæmia. Bacillus of swine erysipelas. Oïdium albicans. Mycelium of actinomyces. 2. BACTERIA NOT STAINING BY GRAM’S METHOD. For the bacteria belonging to this class Löffler’s methylene-blue, carbol methylene-blue, a watery solution of methylene-blue or gentian-violet, Leishman’s or Wright’s modification of Romanowsky’s methylene-blue eosin method (see page 290), Unna’s alkaline methylene-blue solution preceded by eosin after Zenker’s fixation (see page 260), aniline gentian-violet, Zieler’s method and carbol fuchsin are most commonly used as stains. Wolbach advises the use of a 5-10 per cent acetone-colophonium solution for the differentiation of Gram-negative bacteria in tissue fixed in formol. 1. =Löffler’s Methylene-blue.= 1. Saturated alcoholic solution of methylene-blue 30 cc.; potassium hydrate solution (1 in 10,000) 100 cc. 2. Stain 5 minutes to 24 hours. 3. Wash in water. 4. Differentiate in 1 per cent acetic acid, 10-30 seconds. 5. Wash in 90 per cent alcohol, 2-5 minutes; dehydrate in absolute alcohol; clear in xylol; mount in balsam. 2. =Gentian-violet.= 1. Stain sections in a 2 per cent watery gentian-violet for 5-20 minutes. 2. Wash in water. 3. Decolorize in 70 per cent alcohol until stain ceases to come away. 4. Dehydrate in absolute alcohol; clear in xylol; balsam. 3. =Zieler’s Method.= 1. Fix in Orth’s solution, or any fixing solution except those containing osmic acid; imbed in paraffin or celloidin. 2. Stain in Pranter’s solution (orcein D 0.1 grm., hydrochloric acid 2.0 cc., 70 per cent alcohol 100 cc.) for 8-24 hours. 3. Wash rapidly in 70 per cent alcohol. 4. Wash in water. 5. Stain in polychrome methylene-blue 10 minutes to several hours.