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When azo coupling of tissue with freshly diazotized sulfanilic acid at 20-25 mM concentration in a bicarbonate solution is followed by acid washing and staining with dilute azure A or safranium O solutions at pH 1, the azo coupling sites in tissue are demonstrated with green to greenish black or red colors of sufficient intensity to render the method useful for the study of the distribution of reactive proteins. Erythrocytes react more strongly by this method than with most other diazonium salts. The method also affords a procedure for creating readily demonstrable sulfonic acid groups in tissue sections, for the study of their reactions in comparison with those of ester sulfuric acid groups.
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Lillie et al. (1966) studied this question.
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