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Abstract
When the periodic acid-Schiff stain is followed by a counterstain of 1% tartrazine O in 1% acetic acid, mastocyte granules turn to a brick-orange color. Pharyngeal and intestinal mucus remain unchanged and gastric mucus is only slightly affected. The best results were obtained after fixation in Cajal-De Castro fluid (95% ethanol, 50 ml; distilled water, 50 ml; chloral hydrate, 5-10 gm; and nitric acid, 5 ml).