1) HALACHAH: MAKING A "MUM" IN ORDER TO HEAL A SICK BECHOR
OPINIONS: The Mishnah records three opinions about the permissibility to let blood of an ill Bechor in order to save its life when doing so will make a blemish in the Bechor. Rebbi Yehudah maintains that it is forbidden, even if the animal will die if its blood is not let. The Chachamim maintain that one may let blood of an ill Bechor in order to save its life, but only from a part of the body where the bloodletting will not create a permanent Mum. Rebbi Shimon maintains that one may let blood even from a part of the body where a cut will create a Mum. The Gemara (34a) explains that Rebbi Shimon maintains that a Davar she'Eino Miskaven is permitted, and therefore one may let blood from the animal in such a place as long as he has no intention to cause a Mum in the Bechor (see TOSFOS DH Ileima).
In the Beraisa (33b), Rebbi Meir says that one may let blood of a Bechor only from a part of the body where a cut will not create a Mum. (Rebbi Shimon's opinion in the Beraisa is like that of the Chachamim in the Mishnah.) The Chachamim in the Beraisa permit one to let blood even from a part of the body where a cut will create a Mum, but they do not permit the animal to be slaughtered after a Mum was made in such a way. Rebbi Shimon permits one to let blood even from a part of the body where a cut will create a Mum, and he permits one to slaughter the animal if such a Mum is made. Rebbi Yehudah in the Beraisa prohibits letting blood anywhere on the animal, even though the animal will die if its blood is not let.
What is the Halachah with regard to letting blood of an ill Bechor? If one is permitted to let its blood, from which part of the body may the blood be let?
Moreover, what is the Halachah if a Mum is made? May the animal be slaughtered based on that Mum or not?
(a) TOSFOS (DH Ileima) and the ROSH (5:4) understand that the Mishnah and Beraisa are discussing two different cases. The Beraisa is discussing a case in which the animal certainly will die unless blood is let from part of the body where a cut creates a Mum. Since the animal is mortally ill, it is already considered to have a Mum. In such a case, the Chachamim agree that one is permitted to make a [second] Mum in order to save the animal's life, but they maintain that the Mum that is made does not permit the animal to be slaughtered (because of a Gezeirah lest others think that it is permitted to make a Mum in an unblemished Bechor).
The Mishnah, in contrast, is discussing a case in which it is not a certainty that the animal will die from its condition if blood is not let from a place where a cut creates a Mum. In the case of the Mishnah, the Chachamim and Rebbi Shimon disagree about whether a Davar she'Eino Miskaven is permitted. Since the Chachamim maintain that it is not permitted, they rule that one may not let the blood from a part of the body where a Mum might be made.
As Shmuel says in the Gemara, the Halachah follows the view of Rebbi Shimon in the Mishnah, who maintains that a Davar she'Eino Miskaven is permitted. Therefore, one may let blood from a part of the animal where a cut causes a Mum to form, as long as he has no intention to create a Mum.
The Rosh rules that the Halachah also follows the view of the Chachamim and Rebbi Shimon in the case of the Beraisa. One is permitted to inflict a Mum on an animal that will otherwise die. Since the animal is mortally ill, it is considered to have a Mum already, and one may make a second Mum on a blemished Bechor. However, with regard to slaughtering the animal based on the Mum inflicted in such a manner, the Rosh rules like the Chachamim; the Bechor may not be slaughtered on the basis of this Mum, but rather one must wait for another Mum to form in order to slaughter the Bechor. The Halachah follows the view of the Chachamim in this regard, because their opinion is that of the majority. (The Rosh discusses at length why Shmuel says that the Halachah follows Rebbi Shimon of the Beraisa, even though his opinion is not the Halachah in all respects.)
(b) The RAMBAM (Hilchos Bechoros 2:13), however, understands that the Mishnah and Beraisa are discussing the same case, and that the Halachah follows Rebbi Shimon who says that one is permitted to make a Mum unintentionally in a Bechor in order to cure it, and one is permitted to slaughter and eat the Bechor as a result of that Mum.
HALACHAH: The SHULCHAN ARUCH (YD 313:6) rules that one is permitted to let blood from an ill Bechor as long as he does not intend to make a Mum (that is, Davar she'Eino Miskaven is Mutar). If the bloodletting causes a Mum, the animal may be slaughtered. The BEIS YOSEF and KESEF MISHNEH explain that the Shulchan Aruch follows the opinion of the Rambam.
2) A YISRAEL WHO INTENTIONALLY INFLICTS A "MUM" UPON A "BECHOR"
QUESTION: The Mishnah discusses a case in which one purposely blemishes his Bechor. Rebbi Eliezer maintains that the Bechor may never be eaten. The Chachamim maintain that this blemish does not permit the Bechor to be eaten, but a subsequent blemish (that comes naturally) does permit the Bechor. RASHI (DH ha'Tzorem) writes that the Mishnah refers to a case in which a Kohen inflicts a Mum on the animal's ear. Similarly, Rashi in Gitin (44a, DH Im Timtzi) writes that the Mishnah here refers to a Kohen who makes the Mum.
Why does Rashi say that the Mishnah refers only to a Kohen who makes a Mum? The prohibition against slaughtering a Bechor when a Mum was inflicted intentionally should also apply in a case in which a Yisrael inflicts the Mum. In the case of a Safek Bechor, the Yisrael may keep the animal until the Kohen brings proof that the animal is definitely a Bechor. In such a case, the Yisrael must leave the animal to graze in the pasture until it develops a Mum. Once it develops a Mum, the Yisrael may slaughter it and eat it. If, before the animal naturally develops a Mum, the Yisrael intentionally inflicts a Mum in the animal, the prohibition of the Mishnah should apply, and the Yisrael should not be permitted to eat the animal! What forces Rashi to explain that the Mishnah refers only to a Kohen who inflicts a Mum?
ANSWERS:
(a) The MAHARIT ALGAZI (#43, DH Hineh) first suggests that since it is clear from the Gemara that the prohibition of the Mishnah is a penalty instituted by the Rabanan, it could be that Rashi follows the view of the RAMBAM (see Hilchos Avos ha'Tum'ah 16:1, and Hilchos Tum'as Mes 9:12) that the rule that of Safek d'Oraisa l'Chumra (that one must act stringently when in doubt about a Torah law) is only mid'Rabanan; that is, even though the Torah permits the doubt in a case of a Safek, the Rabanan decreed that one must act stringently in a case of a Safek d'Oraisa (see Insights to Bechoros 28:2). Accordingly, if the Mishnah would have been discussing a case of a Yisrael who inflicted a Mum upon a Safek Bechor, then the Isur to inflict the Mum would have been only an Isur d'Rabanan. Since the penalty not to eat a Bechor that was intentionally blemished is itself only mid'Rabanan, it is unlikely that the Rabanan would have instituted the penalty for someone who transgresses an Isur d'Rabanan.
However, the Maharit Algazi rejects this suggestion, because it is clear that Rashi does not agree with the Rambam, and he maintains that the rule of Safek d'Oraisa l'Chumra is indeed d'Oraisa. The TESHUVOS MAHARIT (YD 2:1) and PRI CHADASH (beginning of "Rules of Sfek Sfeika," after YD 110) cite several proofs that Rashi maintains that a Safek d'Oraisa is forbidden mid'Oraisa. One proof is from the words of Rashi in Yevamos (88b, DH Heichi Dami), where Rashi writes that even for a Safek Isur there is no need for an extra verse to teach that Beis Din may force the person not to transgress the Isur. This implies that Rashi maintains that a Safek d'Oraisa is forbidden mid'Oraisa.
(b) Therefore, the Maharit Algazi suggests a different explanation for the words of Rashi here. If the animal was definitely a Bechor but was still in the possession of the Yisrael who gave it a Mum, it is not logical at all to penalize him by prohibiting the animal; why should the Kohen suffer as a result of the prohibited act of the Yisrael?
However, if the Yisrael inflicted a Mum on a Safek Bechor, which he is not required to give to a Kohen (as mentioned above), or if a Yisrael receives a Bechor as an inheritance from his mother's father who was a Kohen (in which case the Yisrael, nowadays, does not have to give it to a Kohen, since there is no Beis ha'Mikdash in which to offer the Bechor as a Korban), then even if the Yisrael inflicts the Mum, a penalty is imposed on the Kohen as well, and the animal is forbidden. When Rashi writes that the Kohen made the Mum, his intention is to exclude a case of a Bechor that was still in the possession of a Yisrael (in which case an intentionally-inflicted Mum made by the Yisrael does not prohibit the Bechor to the Kohen). (See MINCHAS CHINUCH 18:9, DH v'Ayin.)
(See also TESHUVOS IMREI YOSHER (1:78) who cites another answer, in the name of the Maharit Algazi, for the question on Rashi. According to this answer, Rashi here and in Gitin is explaining the case according to the view of Rebbi Eliezer, who maintains that an intentionally-inflicted Mum prohibits the animal forever. According to Rebbi Eliezer, such a severe penalty applies only when a Kohen inflicts a Mum on a definite Bechor. According to the Chachamim, who maintain that one may not eat a Bechor based on a Mum that was inflicted intentionally but one may eat a Bechor after it gets a Mum naturally, the penalty applies both to a Kohen and to a Yisrael who made a Mum.) (D. BLOOM)
3) INTENTIONALLY INFLICTING A "MUM" UPON A BECHOR
QUESTION: The Mishnah discusses a case in which one purposely blemishes his Bechor. Rebbi Eliezer maintains that the Bechor may never be eaten. The Chachamim maintain that this blemish does not permit the Bechor to be eaten, but a subsequent blemish (that comes naturally) does permit the Bechor.
It is evident from the Gemara that Rebbi Eliezer's prohibition to eat the Bechor is a penalty mid'Rabanan. However, the Sifri quotes Rebbi Eliezer as saying that when one eats a Bechor that he intentionally blemished, he transgresses the Isur d'Oraisa of "Lo Sochal Kol To'evah" (Devarim 14:3)! How are the Gemara and the Sifri to be reconciled? (TOSFOS DH u'Mi)
ANSWERS:
(a) TOSFOS suggests that perhaps Rebbi Eliezer indeed prohibits the animal mid'Oraisa, and the wording ("u'Mi Kanis," "Ki Kanis") that the Gemara here uses when it explains Rebbi Eliezer's opinion is not exact (Lav Davka). It uses this wording only to compare Rebbi Eliezer's view with that of the Chachamim. The Chachamim, who argue with Rebbi Eliezer, learn other laws from the verse, and maintain that the prohibition to slaughter the Bechor based on an intentionally-inflicted Mum is a Kenas mid'Rabanan.
(b) Alternatively, Tosfos suggests that Rebbi Eliezer's Derashah in the Sifri is an Asmachta mid'Rabanan.

34b----------------------------------------34b

4) HOW CAN A NON-EXISTENT "NEGA" SHRINK?
QUESTION: The Gemara quotes the Mishnah in Nega'im (7:5), in which the Chachamim state that when a person transgresses and cuts off a Nega Tzara'as from his flesh, he remains Tamei "until the Nega shrinks to less than the size of a Gris."
If the Nega was already cut off, then how is it possible to wait for it to shrink to less than the size of a Gris?
ANSWERS:
(a) RASHI (DH O Ad she'Tisma'et) and RABEINU GERSHOM explain that the Mishnah means that a person remains Tamei unless the Nega was less than the size of a Gris before it was excised.
(b) TOSFOS (DH Ad she'Tifrach) explains that it is possible for a cut Nega to shrink when only part of the Nega was cut off, leaving less than a Gris (which is normally Tahor) on the body. If the remaining portion of the Nega decreased in size such that it would be less than the size of a Gris even if the first had not been cut off, then the Nega is Tahor.
5) PENALIZING THE OWNER'S HEIRS
QUESTION: The Mishnah (34a) discusses a case in which one purposely blemishes his Bechor. Rebbi Eliezer maintains that the Bechor may never be eaten. The Chachamim maintain that this blemish does not permit the Bechor to be eaten, but a subsequent blemish (that comes naturally) does permit the Bechor. Rebbi Yirmeyah asked Rebbi Zeira whether the heirs are prohibited from eating the Bechor when the owner intentionally made a Mum and then died. RASHI (DH u'Mes) explains that the question is whether the prohibition against eating the Bechor forever applies to the heirs, or only to the owner.
Why does Rashi learn that the Gemara's question applies only to the opinion of Rebbi Eliezer? The same question may be asked according to the opinion of the Chachamim, who penalize the owner of the Bechor and do not permit him to eat the Bechor until it develops another Mum. (RASHASH)
ANSWER: Perhaps Rashi understands that the prohibition against eating a Bechor on which a Mum was intentionally inflicted is not merely a Kenas mid'Rabanan (as TOSFOS suggests; see above, Insight #3), but rather it is an Isur d'Oraisa derived from the verse quoted in the Sifri, "Lo Sochal Kol To'evah" (Devarim 14:3). (Rashi understands that the prohibition against eating a Bechor with an intentionally-inflicted Mum is mid'Oraisa according to the Chachamim, and mid'Rabanan according to Rebbi Eliezer, the opposite of the first approach of Tosfos; see above, Insight #3.)
Consequently, according to the Chachamim it is obvious that the prohibition against eating the Bechor would apply to the heirs as well, since it is mid'Oraisa. The Gemara's question, therefore, applies only to the opinion of Rebbi Eliezer. Since he maintains that the Rabanan enacted a penalty not to eat such a Bechor forever, the Gemara asks whether the Rabanan penalized the heirs as well. (M. KORNFELD)

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