What can be added to an aqueous mounting medium to prevent bleeding of aniline dyes into the surrounding medium?

• A. Cane sugar
• B. Glycerol
• C. Sodium chloride
• D. Water

Answer: (A)

The main idea is that dye bleed happens when dye molecules move from the tissue into the surrounding mounting medium. Making the mounting medium more viscous slows down this diffusion, keeping the dye in place. Adding cane sugar increases the viscosity of the aqueous mounting medium, creating a thicker, sugar-rich environment that hinders the movement of aniline dye molecules into the surrounding medium. That’s why it’s the best choice here. Glycerol also raises viscosity, but cane sugar is specifically effective at reducing dye diffusion in aqueous mountants. Water would promote diffusion, and sodium chloride doesn’t meaningfully prevent this dye migration.