Instrumentation, Reagents, and Maintenance
Key instruments
Candidates should know the purpose and basic maintenance of the tissue processor, embedder, microtome, cryostat, water bath, and stainer. The processor moves tissue through timed stations; its risks are clogged lines, evaporated reagents, and incorrect timing. The microtome needs a sharp blade, secure block, and clean mechanism. The cryostat must be kept cold and defrosted appropriately; ice buildup ruins sections.
Reagents
Reagents degrade: alcohols absorb water, xylene becomes contaminated with alcohol and water, and hematoxylin oxidizes over time. Reagent rotation and replacement schedules are part of maintenance. Labeling with date and lot is essential.
Maintenance and monitoring
Routine maintenance includes cleaning, lubrication where specified, temperature checks, and logbooks. Preventive maintenance avoids failures; corrective maintenance fixes them.
Traps
Questions often confuse the processor with the embedder, or ask what happens if xylene is water-contaminated (poor clearing, milky fluid). Another trap is assuming reagents last indefinitely if unopened-expiry and storage conditions still matter. A frequent trap is forgetting that cryostat temperature affects section quality.
Worked rule
If clearing fluid turns milky, suspect water carryover: check alcohol steps and replace contaminated xylene. If sections smear in the cryostat, check temperature and ice buildup before blaming the blade.