Scientists have found evidence of a poison used as anesthesia on 600-year-old surgical tools, which may rewrite the history of anesthesia. The tools, which date back to the ming dynasty or 14th/15th century, were found to carry traces of a toxic plant or lethal toxin that was likely used as a topical anesthetic. The discovery was made in china and is considered one of the earliest chemical evidence of anesthesia, although the exact details and implications are still being reported.