Permanent metachromatic effect of 1,9-dimethyl-methylene blue on acidic mucopolysaccharides of mastocytes

The 1,9-dimethyl-methylene blue (SERVA) has a very strong metachromatic reaction with sulphated mucopolysaccharides of mastocytes at pH = 1 (Tris-HCl buffer). This metachromasia is retained also at increasing pH (2.5-5), and is not affected either by the quality or by the concentration of the ions present (1/240 M Tris-HCl, and 0.2 M phosphate buffer). The smears do not need any special mounting medium, only Canada balsam. The metachromasia is preserved for a considerable length of time.