Which type of fixatives changes the protein structure into a mesh-like network to enhance penetration of solutions into tissue?

• A. Coagulant fixatives
• B. Nonadditive fixatives
• C. Noncoagulant fixatives
• D. Glutaraldehyde

Answer: (A)

The effect described comes from coagulating (coagulant) fixatives. When these fixatives denature and precipitate proteins, they form a mesh-like, gelled network throughout the tissue. This protein network creates spaces within the tissue that allow solvents and reagents to move through more readily, improving penetration during subsequent processing and staining. In contrast, noncoagulant fixatives work mainly by cross-linking proteins without precipitating them, which does not produce the same porous mesh and can alter diffusion differently. Glutaraldehyde is a noncoagulant, cross-linking fixative, so it doesn’t form the mesh network that enhances penetration in the same way. Nonadditive fixatives aren’t the term used to describe this mesh-forming property.