What is the purpose of adding cane sugar to an aqueous mounting medium?

• A. To prevent bleeding of aniline dyes into surrounding medium
• B. To fix tissue to slide
• C. To increase mounting medium viscosity
• D. To dehydrate tissue

Answer: (A)

The main idea is to keep the stain from diffusing out of the tissue once it’s placed in the mounting medium. An aqueous mounting medium can allow water-soluble dyes to migrate into the surrounding medium, which bleeds the color beyond the tissue margins. Adding cane sugar (sucrose) raises the osmolarity and increases the viscosity of the medium, creating a less favorable environment for dye diffusion. This helps lock the aniline dyes in place and preserves crisp, defined staining around the tissue. It isn’t about fixing tissue to the slide or dehydrating tissue; those are accomplished by other steps, not the mounting medium. So the purpose is to prevent dye bleed into the surrounding medium.