(R. Yitzchak): If Pigul, Nosar or Tamei was brought up on the Mizbe'ach, the Isur goes away.

(R. Zeira): The case is, it caught fire.

Question (R. Yitzchak bar Bisna - Beraisa - Acherim): "V'Tum'aso (his or its Tum'ah) Alav" refers to one (i.e. a person) whose Tum'ah can cease (through immersion). It does not refer to Tamei meat, for its Tum'ah never goes away.

According to R. Yitzchak, meat can become Tahor!

Answer #1 (Rava): The Tana means that Tum'as Basar never goes away through immersion.

Objection: The verse does not mention immersion. The Tana says that the Tum'ah cannot cease through any means!

Answer #2 (Ravina): "V'Tum'aso Alav" refers to one (i.e. a person) whose Tum'ah can cease while he is intact. It does not refer to meat, for its Tum'ah does not cease until some of it is missing (burned).

(Beraisa): "V'Tum'aso Alav" refers to a Tum'as ha'Guf;

R. Meir: It cannot refer to Tamei meat, for "v'Tum'aso Alav" refers to one whose Tum'ah can cease. Tum'ah of meat never goes away.

Pesachim 21b: If Chametz was charred before the time (of Isur), it is permitted even after Chametz is forbidden.

45b (Beraisa): One must be Meva'er (destroy) moldy bread, because one can grind it up and use it to ferment other dough. (Therefore, it is forbidden like Se'or (sourdough, which is used to ferment other doughs);

R. Shimon ben Elazar says, this is if it is being kept (for fermenting, which is) for the sake of eating. Kofes Se'or (a block of heavily leavened dough) which was designated for sitting is Batel.

Inference: Only R. Shimon says that it is Batel. The first Tana holds that even 'Bitul' (designation for sitting) does not help for a k'Zayis (it is still considered Chametz)!

(Beraisa): If bread became moldy and is not fit for people to eat but dogs would eat it, it has Tum'as Ochlim if it is k'Beitzah (the size of an egg), and (even if it is Terumah) it may be burned with Tamei (Chametz) on (Erev) Pesach;

R. Noson says, it does not have Tum'as Ochlim.

The following Mishnah is unlike R. Noson.

(Mishnah): The general rule is, anything (that was initially) fit for people to eat is Mekabel Tum'ah as long as dogs would eat it.

Avodah Zarah 67b (Beraisa): "Lo Sochlu Chol Nevelah la'Ger (...Titnenah va'Achalah)" - it is called (and forbidden like) Neveilah only if a Ger (Toshav) would eat it.

Rif (Pesachim 14a): If something is spoiled and dogs would not eat it, it ceases to be a food. It is like earth.

Ran (DH Tanu): Why is Bi'ur required (if people cannot eat it, but dogs would eat it)? A Neveilah not proper for a Ger to eat is not a Neveilah (Avodah Zarah 67b)! We permit detrimental absorptions, even of Chametz during Pesach! Here is different, since it can be used to ferment other doughs. The Gemara says that Se'or is not proper to eat, and even so the Torah forbids it for this reason (Beitzah 7b). The Mechilta says so.

Rif and Rosh (Pesachim 14a, 3:4): A Tosefta says that if flour was put into a bandage for the eye or the body, it is exempt from Bi'ur. If a Melugma (plaster put on a wound) spoiled, it is exempt from Bi'ur.

Ran (DH Melugma): The Tosefta exempts Melugma from Bi'ur when it spoiled before Pesach. This is like Chametz charred before the time (of Bi'ur). It is permitted after the time. If it spoiled during Pesach, if it spoiled before becoming Chametz, this is like Chametz charred before the time. The Isur does not take effect on it, so it is exempt from Bi'ur.

Rambam (Hilchos Chametz 1:2): The Isur of Chametz and Se'or is the same.

Ra'avad: There is a difference. If Chametz was spoiled to the point that dogs would not eat it, it is exempt from Bi'ur, but one must be Meva'er such Se'or, for one can grind it up to ferment other doughs. A Tosefta obligates Bi'ur of moldy bread for this reason. It must discuss bread of Se'or. We would not need this reason for Chametz!

Rambam (4:10): If flour was put into a bandage for the eye or the body or Tri'ak (a special potion), one may keep it during Pesach, for it lost the form of Chametz.

Rebuttal (Ra'avad): This is wrong. He heard this from elsewhere. This is not the reason.

Rambam (11): If bread became moldy and spoiled so that dogs would not eat it, or Melugma spoiled, it is exempt from Bi'ur.

Ra'avad: The Yerushalmi says that this is when it spoiled and later became Chametz.

Magid Mishneh: The Rif and Rambam omitted the Yerushalmi, because it discusses when it became Chametz during Pesach, and then we require that it spoil before becoming Chametz. The Tosefta discusses when it spoiled before Pesach, so when Pesach comes, the Isur of Chametz does not take effect on it, for it is spoiled. It is like moldy bread that dogs cannot eat, which surely became Chametz before becoming moldy. Perhaps dogs would not eat a spoiled Melugma, and therefore the Rif and Rambam wrote Stam (that it is exempt from Bi'ur).

Rosh (ibid.): The Yerushalmi says that if a Melugma became Chametz and afterwards spoiled, one must be Meva'er it. Rav Hai Gaon says that since one need not be Meva'er a Melugma that spoiled, all the more so we exempt Tri'ak in which they mix in dry minced Chametz with meat of Afah (a viper?).

Shulchan Aruch (OC 442:2): If bread became moldy and spoiled so that dogs would not eat it, or Melugma spoiled, it is exempt from Bi'ur.

Beis Yosef (DH ha'Kilur): The Tur holds like the Rosh, who did not distinguish between becoming Chametz before Pesach or during Pesach.

Mishnah Berurah (9): The Shulchan Aruch permits when it became moldy before the time of Isur. If it became moldy after the time of Isur, one must be Meva'er it, even if it is so moldy that dogs would not eat it, since he needed to do Bi'ur before it became moldy.

Mishnah Berurah (10): If dogs would not eat it, it is exempt from Bi'ur, for it is like earth. If dogs would eat it, even though people would not eat it, one must be Meva'er it like proper Chametz, since it can be used to ferment other doughs.

Mishnah Berurah (11): Melugma is an (ointment put on a) bandage made from flour, figs and similar ingredients. One chews them and puts them on the wound.

Mishnah Berurah (12): Also Melugma must spoil to the point that dogs would not eat it. If it fermented and then spoiled, one may not keep it (during Pesach). Rather, it spoiled before Pesach, like we said about bread. If it spoiled before it fermented, it is permitted even during Pesach, for this is like bread that became moldy before the time of Isur.

Kaf ha'Chayim (25): It seems that 'after the time of Isur' is after six hours (on Erev Pesach). However, Mekor Chaim (4) says that it means during Pesach. If it spoiled after six hours, one may keep it and it is permitted after Pesach.

Kaf ha'Chayim (26): The Torah obligates Bi'ur even after people cannot eat it, unless it spoiled before it became Chametz.

Kaf ha'Chayim (27): Mekor Chaim says that bread was a proper food before it became moldy, therefore it is forbidden until dogs would not eat it. If a Chametz dough became moldy and people would not eat it, this is Chametz Nuksheh (and it is permitted), for it was never a food. Magen ha'Elef forbids, for it could be used to to ferment other doughs.

Shulchan Aruch (9): If Chametz became moldy before the time of Isur to the point that dogs would not eat it, or it was burned (Rema - before the time) and charred to the point that dogs would not eat it, one may keep it during Pesach.

Beis Yosef (DH ): Tosfos (21b DH Charcho) says that the Chametz was charred to the point that dogs would not eat it. If not, it is not permitted, just like bread that became moldy. Also the Rosh (2:1) says so. The Ran adds that if it was charred only after the time of Isur, the Isur does not go away until it is totally burned.

Magen Avraham (14): Even though people would not eat it, it is forbidden because it can be used to ferment other doughs. We do not distinguish between Chametz and Se'or. This is unlike the Ra'avad.

Gra (DH Chametz): The Ra'avad holds that one is always obligated to be Meva'er Se'or. His text did not say Kofes Se'or, rather, Pas Se'or. The Halachah does not follow R. Shimon ben Elazar. We can reject his proof. The case is, it was spoiled to the point that dogs would not eat it. However, Hagahos Maimoniyos brings a Tosefta that says that Se'or is what ferments other things, and Chametz is what was fermented through something else. It is called Se'or once dogs would not eat it.

Bi'ur Halachah (DH Chametz): The Magid Mishneh and Kesef Mishneh defend the Rambam, who permits even Se'or once dogs would not eat it. The Gra supports the Ra'avad form the Tosefta. The Pri Chodosh concluded that the Halachah follows the Ra'avad. How can the Rambam answer the Tosefta?! We must say like the Kesef Mishneh says, that even though the Torah obligates for Se'or even though dogs would not eat it, this is when it spoiled due to overfermentation. (This is like Chametz into which something very sharp was poured, and it cannot be eaten due to the sharpness. It did not cease to be a food.) If it became moldy to the point that dogs would not eat it, even if it were not so fermented, we can say that it is like earth. The Kesef Mishneh says that even the Ra'avad obligates only Bi'ur (after it is so moldy), but he exempts one who eats it. The Pri Megadim left this difficult, due to the Tosefta. We can answer that like I said. Even if the Ra'avad obligates one who eats it, the Rambam can distinguish between when it is inedible due to overfermentation or due to moldiness.