Reference for Keritot 30:2

הולך לו ערב פסח אצל הרופא וחותכו עד שמניח בו כשערה ותוחבו בסירא ונמשך ממנו והלה עושה פסחו והרופא עושה פסחו

THE AFFLICTED PERSON WOULD GO ON THE EVE OF PASSOVER TO THE PHYSICIAN, AND HE WOULD CUT THE LIMB UNTIL ONLY CONTACT OF A HAIRBREADTH WAS LEFT;<span class="x" onmousemove="('comment',' So long as the limb is not completely detached from the body it is clean.');">²</span>

Jastrow