The first and most appropriate procedure in preparing tissue for microscopic examination is the choice of which component?

• A. Fixative
• B. Embedding medium
• C. Staining protocol
• D. Section thickness

Answer: (A)

Fixation is the first step because it preserves tissue architecture and halts decay, creating a stable material that can withstand the subsequent processing steps. A fixative, typically formalin, cross-links proteins and inactivates enzymes, preventing autolysis and degradation so the cells and their relationships remain intact. Once fixed, the tissue can be dehydrated, cleared, and embedded, which won’t be reliable if the tissue were allowed to decompose first. After embedding, thin sections can be cut and then stained to reveal cellular detail. Section thickness and staining protocols are important later steps that rely on having well-fixed tissue to begin with.