Which tissue serves as the control for Mayer's mucicarmine staining?

• A. Unautolyzed small intestine, appendix or colon
• B. Autolyzed tissue
• C. Fresh spleen
• D. Liver with fat

Answer: (A)

Mayer's mucicarmine stain highlights mucin by staining it a red color, with nuclei counterstained blue. To interpret this stain reliably, you need a positive control tissue that naturally contains mucin in preserved goblet cells. The small intestine, appendix, and colon are rich in goblet cells and provide a clear mucin signal when the tissue is well preserved. Using unautolyzed tissue ensures the mucin remains intact; autolyzed tissue can lose or alter mucin, leading to misleading results. Tissues like the spleen or liver with fat lack the goblet-cell mucin pattern this stain is meant to demonstrate, so they aren’t appropriate positive controls. Thus, unautolyzed mucin-containing tissue from the small intestine, appendix, or colon serves as the best control for Mayer's mucicarmine staining.