Talmud Shabbat 133a:18
When the eighth day of a baby’s life occurs on Shabbat, he must be circumcised on that day. Therefore, one performs all the necessities of the circumcision, even on Shabbat: One circumcises the foreskin, and uncovers the skin by removing the thin membrane beneath the foreskin, and sucks the blood from the wound, and places on it both a bandage [ispelanit] and cumin as a salve.
I really disagree with this practice after circumcision, and believe it borders on child abuse, as it is a tradition of men rather than biblical. Circumcision is mentioned numerous times in the bible, but sucking the wound is never mentioned once. Indeed, Zipporah's circumcision is described in detail, where she casts the useless skin away with disdain, as if it were indeed the sinful nature Colossians 2:11 explains the foreskin represents.