GEMARA

(Mishnah): If one enters Beis ha'Menuga carrying his clothes on his shoulder or his sandals or rings in his hands, he and his Kelim are Teme'im immediately;

If he enters wearing his clothes, sandals or rings (on the proper fingers), he is Tamei immediately, and his Kelim are Teme'im only after he tarries the time needed to eat a half loaf of bread;

We gauge the time to eat wheat bread (not barley), reclining, with an accompaniment on the bread.

RISHONIM

Rambam (Hilchos Tzara'as 16:6): If three by three (fingers) of a Tahor Talis entered Beis ha'Menuga it becomes Tamei. The same applies to a Kli Cheres if its interior entered. Other Kelim do not become Tamei until the majority enters. This is if no one was wearing the Kelim.

Rambam (ibid.): If a Yisrael entered Beis ha'Menuga wearing his clothes, sandals or rings, he is Tamei immediately, and his Kelim are Teme'im only after he tarries the time needed to eat three eggs of wheat bread with an accompaniment on the bread. It says "Ha'Shochev...veha'Ochel ba'Bayis Yechaves Begadav". Surely, Tum'as Begadim does not depend on eating! Rather, it teaches that the Shi'ur for how long one must lie down is like the time needed to eat. The Shi'ur for lying, sitting or standing is the same.

Rambam (ibid. 7): If he entered carrying his clothes on his shoulder or his sandals or rings in his hands, he and his Kelim are Teme'im immediately. One saves only Kelim that he is wearing. Similarly, if an animal or Nochri entered wearing Kelim, the Kelim become Temei'im immediately. A Nochri is not Mekabel Tum'ah, just like an animal.

ACHARONIM

Mishneh l'Melech (Hilchos Tzara'as 16:6): In the Tosefta (Nega'im 7:6,7) Chachamim say that the Shi'ur to enter to become Tamei is three by three (fingers). R. Nechemyah requires the majority. If an entire garment is only three by three, I am unsure about whether or not it becomes Tamei when the majority enters. Perhaps it is a stringency to Metamei when three by three enters even if it is not the majority. (Or, perhaps three by three is always needed.)

Eliyahu Rabah (Nega'im 13:8) and Chazon Ish (Nega'im 10:16 DH Shi'ur): If the majority enters it becomes Tamei, even if this is less than three by three.

Question (Mishneh l'Melech, ibid.): The Ra'avad says that the majority of a person must enter because the minority is not considered Bi'ah. The same applies to a Kohen or Nazir entering Ohel ha'Mes, entering the Mikdash, and Benei Yisrael entering Eretz Yisrael (to obligate Hafrashas Chalah). However, "Ve'Hevi'um la'Shem" teaches that a Korban must be entirely in the Azarah, and "B'Vo'am El Ohel Mo'ed" requires the Kohen to be entirely in the Ohel Mo'ed (Zevachim 26a). It is not clear why one who enters Ohel ha'Mes becomes Tamei even for entering one limb.

Answer (Kovetz Shi'urim Pesachim 44b 187): Tosfos (Nazir 43a DH b'Vayis) says that we consider Ohel ha'Mes to be full of Tum'ah, therefore even partial entry is Metamei. A Nazir is not Chayav for "Al Nefesh Mes Lo Yavo" until his majority enters. Tum'as Beis ha'Menuga does not depend on Ohel, so we cannot say that it is as if it is full of Tum'ah. It would seem that a limb entered into Ohel ha'Mes could be a Yad to make the person Tamei, just like a bone of a Mes brought into an Ohel is a Yad for Tum'as Ohel even if the flesh is outside.

Question (Mishneh l'Melech, ibid.): Toras Kohanim asked a contradiction between two verses. One connotes that one who enters Beis ha'Menuga is not Metamei Begadim. Another says that there is Tum'as Begadim for eating or sleeping there. The conclusion is like our Gemara. What forced the Toras Kohanim to conclude this? Perhaps any garment that enters becomes Tamei independent of the person, and the latter verse teaches that someone in Beis ha'Menuga is Metamei Kelim that he touches at the time, even if they are outside the house!

Answer #1 (Mishneh l'Melech): Rashi says that "Yechaves Begadav" always refers to Tum'as Begadim, i.e. what he is wearing at the time. Therefore, we cannot learn to Metamei anything else.

Note: Perhaps the verse is Metamei garments he is wearing that are outside the house (e.g. a shoe)!

Mishneh l'Melech (ibid.): However` this answer does not help for those Meforshim who say that "Yechaves Begadav" refers to what he is wearing or touching at the time!

Answer (Mishnah Acharonah Nega'im 13:9 DH Ad): Whenever the Torah discusses Tum'as Begadim it says "Yechaves Begadav". This connotes what he is wearing. We learn that the same applies to what he touches at the time. even if they are outside the house; no other verse is needed for this.

Minchas Chinuch (Sof Mitzvah 177 DH v'Ilulei): It seems that only outer Begadim that do not touch the person are saved from Tum'ah (until the time to eat a half loaf), but not what touches the person. Some say that a Zav is Metamei only Begadim that he touches.