Why does the Mishnah say that Tum'as ha'Tehom is not Tahor if the Nazir was
Tamei with Tum'as Mes at the time he immersed in the water? Even if he was
Tamei with Tum'as Sheretz, he should be considered to have a Chezkas Tamei
and the Tum'as ha'Tehom should prevent him from becoming Tahor!
(a) The simple understanding of the Mishnah is that the Chezkas Tamei can
affect him only if he was Tamei with the same type of Tum'ah as the Tum'as
ha'Tehom (i.e. Tum'as Mes). If, however, he was Tamei with a different type
of Tum'as, such as Tum'as Sheretz, then the Chezkas Tamei cannot make him
acquire a different Tum'ah, that of Tum'as ha'Tehom (Tum'as Mes).
(b) However, REBBI AKIVA EIGER suggests a different explanation for the
Mishnah. The Gemara later (64b) says that if the Nazir Tamei -- on the
seventh day of his Tum'ah, after his Tiglachas but before sunset of that
day -- came across Tum'as ha'Tehom, he is *not* considered to be b'Chezkas
Tamei, because "sunset occurs by itself," and it is as if he is lacking
nothing to make him Tahor. TOSFOS (DH Amar Abaye, and the ROSH and RABEINU
AZRIEL as cited by the SHITAH MEKUBETZES) adds that Tevilah in a Mikvah
(when no Tiglachas is needed) is also not considered something that is
lacking to make a person Tahor, because the Mikvah is right there and it is
"b'Yado," in his ability, to immerse himself. The only thing that can give
the Nazir a Chezkas Tamei is the lack of his Tiglachas; if he did not yet
have his Tiglachas of the seventh day, he is considered b'Chezkas Tamei.
Rebbi Akiva Eiger suggests that if the Nazir is only Tamei with Tum'as
Sheretz, then he does not have to be Megale'ach and thus he is not
considered lacking anything to become Tahor (all he has to do is immerse in
a Mikvah and wait for sunset, which are considered insignificant actions),
and that is why Tum'as Sheretz does not give the Nazir a Chezkas Tamei to
make him Tamei with Tum'as ha'Tehom.
Rebbi Akiva Eiger points out that there is an important practical difference
between these two explanations. What would be the Halachah in a case where a
Nazir -- who was immersing in water over a Tum'as ha'Tehom -- was immersing
in order to become Tahor from the Tum'ah of a Revi'is Dam or of a Rova Kav
Atzamos? Although these Tum'os are the same type of Tum'ah that comes from
k'Zayis of a Mes (i.e. Tum'as Mes), nevertheless a Nazir who becomes Tamei
from a Revi'is Dam or a Rova Kav Atzamos does not need to be Megale'ach
(54a). According to the first explanation, the Nazir should have a Chezkas
Tamei, since it is the same type of Tum'ah. In contrast, according to
Tosfos, as cited in the second explanation, who says that only the lack of
Tiglachas could give him a Chezkas Tamei, this Nazir (who became Tamei with
Revi'is Dam or Rova Kav Atzamos) should be Tahor from Tum'as ha'Tehom since
he does not have a Chezkas Tamei!
(See ME'IRI, who writes clearly that the Nazir is considered b'Chezkas Tamei
only if he had the type of Tum'ah that is Soser his Nezirus. This implies
that he is learning like Rebbi Akiva Eiger's second explanation, that it is
only the lack of Tiglachas that makes the Nazir have a Chezkas Tamei.)