1. Sterilization,
2. Removal of the foreskin (circumcision) and
3. peri'a or removal of epithelium.
The fourth step is the Metziza, sucking the blood from the circumcision wound. The ritual of Metzitzah is found the Mishna, Masekhet Shabbat (19:2) as one of the steps involved in the circumcision rite.
Modern rabbis (Chatam Sofer) have observed that the rationale for the Metziza is hygienic.
According to Rabbi Mordechai Halperin, this action lowers the internal pressure in the tissues of the organ, in the blood vessels of the head of the organ and in the exposed ends of the arterioles that have just been cut. Thus, the difference between the pressure in the blood vessels in the base of the organ and the pressure in the blood vessels at its tip is increased.
In modern days, as our awareness of infections and sterilization procedures have increased, the rabbis dissent regarding the right procedure for the Metziza.
Some rabbis, notably Rabbi Sinai Schiffer of Baden, Germany, states in his Sefer Mitzvas Hametzitzah that most Russian (Lithuanian) rabbis categorically prohibit Metzitzah with a sponge etc. and require it to be done orally.
Most Modern Orthodox Rabbis, however, recommend to use a sterilized glass which fulfills the same mission and eliminates the risks of infections, herpes, HIV, etc.
Our own rabbi Eliyahu ben Hayim (Shelita), also recommends the Metzizta be done using a sterilized glass tube.
Click here to read the statement of the Rabbinical Council of America on the issue of Metzitza.