Corrosion and cleaning specimens are corroded in 10% ~ 20% sodium hydroxide or potassium hydroxide solution, or in 20% ~ 30% hydrochloric acid. The duration is usually five to seven days. If dilute hydrochloric acid is used, 5% ~ 10% pepsin can be added, the corrosion effect is better. The corrosive tissue around the blood vessels is then flushed with tap water at a slower rate for 24 to 72 hours.