The most satisfactory methods at the present time for the staining of capsules of bacteria are those of Welch and Hiss. The method of Welch depends on the precipitation, by glacial acetic acid, of the mucin composing the capsule. The acid is then replaced by aniline gentian violet, which is added repeatedly, and finally washed with a 2 per cent. solution of sodium chlorid. Hiss employs ascitic fluid in making the smear. After drying and fixing in the flame, the film is covered with a 5 per cent. solution of gentian violet, stained for a few seconds and then washed with a 20 per cent. solution of copper sulphate.
The present method is an application of the principle involved in the India-ink "stain" for the Spirochæta pallida. The latter was adopted by Hecht and Wilenko early in 1909 and reported by Frahwald.1
The chief difficulty in the demonstration of bacterial capsules by the various stains proposed is the same as
RULISON ET. A NEW METHOD OF DEMONSTRATING THE CAPSULES OF BACTERIA. JAMA. 1910;LIV(18):1426–1427. doi:10.1001/jama.1910.92550440001001c
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