Recognition of the pneumococcus depends upon its morphology, the fact that it is Gram-staining, and the presence of a capsule. Numerous methods for staining capsules have been devised, but few are satisfactory. Buerger's method is excellent. It is especially useful with cultures upon serum media, but is applicable also to the sputum. Smith's method usually gives good results, as does also the more simple method of Hiss (p. 263). The sputum should be fresh--not more than three or four hours' old. * * * * * {37} Buerger's Method for Capsules.--(1) Mix a few drops each of the sputum and blood-serum on egg-albumin solution (egg-albumin, distilled water, equal parts; shake and filter through cotton). Make thin smears from the mixture and just as the edges begin to dry, cover with Müller's fluid (potassium bichromate, 2.5 gm.; sodium sulphate, 1.0 gm.; water 100 c.c.) saturated with mercuric chlorid (ordinarily about 5 per cent.). Gently warm over a flame for about three seconds. This rapidly fixes the bacteria while still living. (2) Rinse very quickly in water. (3) Flush once with alcohol. (4) Apply tincture of iodin for one to two minutes. (5) Thoroughly wash off the iodin with alcohol and dry in the air. (6) Stain about three seconds with weak anilin-gentian-violet freshly made up as follows: Anilin oil, 10; water, 100; shake; filter; and add 5 c.c. of a saturated alcoholic solution of gentian violet. (7) Rinse off the stain with 2 per cent. solution of sodium chlorid, mount in this solution, and examine with a one-twelfth objective. Buerger suggests a very useful variation as follows: After the alcohol wash and drying, the specimen is stained by Gram's method (p. 39), counter-stained with aqueous solution of fuchsin, washed, and mounted in water. The pneumococcus holds the purple stain, while all capsules take on the pink counter-stain. Smith's Method.--This somewhat complicated, but not difficult, method is very useful as a routine stain for the sputum. It brings out well all cells and all bacteria except the tubercle bacillus. (1) Make thin smears, dry, and fix in a flame in the usual manner. (2) Apply anilin-gentian-violet a few seconds, gently warming until steam rises. (3) Rinse in water. (4) Apply Gram's iodin solution for thirty seconds. {38} (5) Wash in 95 per cent. alcohol until the purple color ceases to come off. (6) Wash with equal parts of ether and absolute alcohol, or with ether and absolute alcohol successively. (7) Apply a saturated aqueous solution of eosin for a minute or two. (8) Rinse off the eosin with Löffler's methylene-blue, then cover with the methylene-blue, and heat until steam rises. (9) Wash in water. (10) Rinse quickly with absolute alcohol. (11) Apply xylol a half minute or longer. (12) Mount in balsam.