STAINING BACTERIAL CAPSULES

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Abstract
A modification of Muir''s method is descr., which consistently gives good results, and yields more well-defined capsules than the original method.[long dash]Prepare light suspensions in tap water, and allow a loopful to dry on a well-roasted cool slide (do not spread the film); fix by gentle heat; place a small rectangle of filter paper on the slide to cover the film and oversaturate it with carbol fuchsin; heat by passing 14 times (7 sec.) through a flame, or until steam rises (the paper keeps the stain in place on the film); when the slide is cool, after about 30 sec. on the bench, wash off the paper and excess stain; apply Muir''s mordant for 5-15 sec.; wash well in running water; re-stain for 30 sec. with any suitable staining soln. containing methyl alcohol. The following staining solns. have given good results: [long dash](1) methyl hydrate 50 ml., basic fuchsin 1% aqueous soln. 50 ml.; (2) methyl hydrate 50 ml., methylene blue 1% aqueous soln. 50 ml.; (3) a mixture of Nos. 1 ; nd 2 in the proportion 2:1. The contrast between the red cell and the blue capsule appears to be better with No. 3 than with No. 2. The better definition given by this modification than by the original method appears to be due to the omission of the treatment with ethyl alcohol after the 1st staining operation. Capsules have been well differentiated with soln. No. 3 in beef-peptone agar cultures of the following bacteria: Aerobacter cloacae Escherichia coli Seratia marcescens Klebsiella pneumoniae Eberthella typhosa Proteus vulgaris Pseudo-monas pictbrum Pseudomonas aeruginosa; of Neisseria catarrhalis on lactose agar; Vibrio amylocella on starch agar and in cellulose mineral salts medium; of Bacillus megatherium in broth and on potato glucose agar, of a "rope" Bacillus on potato glucose agar; and spp. of Nitrobacteria in mineral salts liquid medium. Capsules of cultures on beef peptone agar appear to stain more intensely after 3 or 4 days, than earlier. The films were examined-with light from a 100 watt lamp. The capsules of some bacteria, e.g., Neisseria, may be seen better if a ground-glass screen be used under the condenser.

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