The Gemara cites a dispute between Rabah and Rav Yosef with regard to whether a Nazir who is already Tamei is permitted to have contact with Tum'ah again. Rabah maintains that the Nazir is permitted to touch another corpse. Rav Yosef maintains that he is not permitted to touch another corpse.

Rabah clarifies his position and explains that a Nazir may touch another corpse only while he is in contact with the first. Rabah agrees that once he has released his hold of the first corpse, he is not allowed to touch another corpse, since that will add to his Tum'ah in the following way: A person who touched a corpse and is no longer touching it has the status of an ordinary Av ha'Tum'ah, and he will make someone who touches him a Rishon l'Tum'ah. If, however, the person is still touching the corpse, whoever touches him becomes an Av ha'Tum'ah. Therefore, everyone agrees that when a Nazir is no longer touching a corpse, he is prohibited from touching another corpse.

This prohibition has practical ramifications with regard to the prohibition which forbids a Kohen from becoming Tamei with Tum'as Mes, which applies even today. (The Gemara itself compares the Isur of a Kohen to touch a corpse with the Isur of a Nazir.) What are the Halachic ramifications of this Gemara for a Kohen today (who is considered Tamei already)?

(a) The Rishonim rule like Rabah because of the principle that whenever Rabah and Rav Yosef argue, the Halachah follows the view of Rabah (see Bava Basra 114b). Since Rabah rules that a Nazir is Chayav for becoming Tamei when he touches a second corpse while he is no longer touching the first, it follows that a Kohen should be prohibited to become Tamei from a corpse again (including Tum'as Ohel) unless he is still touching the first corpse. This is the ruling of the RAMBAM (Hilchos Nezirus 5:17, Hilchos Avel 3:4).

TOSFOS (43a, DH me'Hacha) and the ROSH (Hilchos Tum'ah #6) write that this is the source for the custom to designate a separate section in a cemetery for Kohanim, at the edge of the burial area. Although a male relative of a deceased Kohen is permitted to enter the cemetery in order to bury his relative since he is already touching the Mes (which a Kohen is permitted to do for a close relative), after the burial the Kohen will have to become Tamei again by walking over other graves in order to exit. At that time he will be adding to his Tum'ah -- which is prohibited -- since he is no longer touching a Mes. Consequently, the male relative of a deceased Kohen should not be permitted to enter the cemetery to bury the deceased. In order to avoid this problem, a separate section for Kohanim is designated at the edge of the cemetery so that the relatives of the deceased Kohanim will be able to exit the cemetery without having to walk over other graves.

(b) However, the ROSH (42b, DH Kan) suggests another interpretation of the entire Sugya here. The Rosh explains that it is Rav Yosef who distinguishes between a Nazir who is presently touching a corpse (Tum'ah b'Chiburin) and a Nazir who is not touching a corpse (Tum'ah she'Lo b'Chiburin). Rabah, who says that a Nazir does not transgress the Isur against becoming Tamei when he is already Tamei, maintains that even when he is not touching the first corpse at the time he touches the second, he still does not transgress the Isur.

The Rosh (Hilchos Tum'ah, loc. cit.) quotes RABEINU TAM who understands the Gemara in this way and rules like Rabah, that a Kohen does not transgress the Isur against becoming Tamei even when he is not touching the first source of Tum'ah at the time he touches the second (see Rabeinu Tam as cited by Tosfos in Shevuos 17a). The Rosh adds that the argument between Rabah and Rav Yosef appears to be the subject of a Machlokes Tana'im in a Beraisa (Avel Rabasi 4:15).

Even according to this lenient ruling, a Kohen who is already Tamei may not become Tamei again. The Rosh shows that the Beraisa in Avel Rabasi prohibits a second Tum'ah mid'Rabanan, even according to those who permit it mid'Oraisa. Moreover, it is clear from the Beraisa that on the following day, the Kohen is prohibited even mid'Oraisa from touching another Mes, since doing so will extend his Tum'ah another day and the Torah forbids adding to his Tum'ah.

The Rosh writes that according to this opinion, it is not necessary to designate a separate burial section for Kohanim at the edge of the cemetery. Since the Isur to become Tamei when he is already Tamei is only mid'Rabanan, the consideration of Kavod ha'Beriyos in this case overrides the Rabanan's prohibition and allows a Kohen to enter a cemetery to bury his relative, even though he will need to be Metamei himself in order to exit after the burial.

(c) The RA'AVAD (Hilchos Nazir, loc. cit.) understands the Gemara like the Rosh, that Rabah permits a Kohen to become Tamei a second time even when the Kohen is no longer touching the first corpse. The Ra'avad, however, is even more lenient in his ruling. He writes that since the Halachah follows the view Rabah, a Kohen who is already Tamei is permitted to touch a corpse l'Chatchilah (no Isur d'Rabanan prohibits it) and even on the day after he became Tamei the first time. The Ra'avad writes that for this reason, Kohanim nowadays cannot be obligated to refrain from sources of Tum'as Mes. (This is the way REBBI AKIVA EIGER and others understand the Ra'avad. See, however, DAGUL MEREVAVAH YD 372:2, and Insights to Yevamos 61:1:b.)