After the cryostat sectioning, wash slides with 1x PBS for 5 times for 5-10 minutes. Prepare X-gal staining solution.
Timing is critical.
Don't let the slides to dry up because the tissue will break up if it's too dry. The purpose of drying slides on the slide warmer is to warm up slides for them to react with X-gal solution. If the slides are too cold, the X-gal solution will precipitate. Add enough of X-gal solution to cover tissues on the slides. Usually 1000 m l of solution can cover 5 slides.