Maseches Temurah, Chapter 1, Mishnah 3. Until now we have established that sanctity can be transferred from one animal to another by means of temurah. Now the question arises: what is the law regarding part of an animal, a single limb? And what is the law regarding an offspring that has not yet been born, a fetus still inside its mother?
Two introductions before learning the Mishnah:
Clarifying the terms: "eiver" or "eivarim" - a limb of the animal, such as its leg. "Ubar" (spelled with an ayin) - a complete animal that has not yet been born, the offspring in its mother's womb.
The dispute about consecrating a limb: There is a dispute elsewhere in Shas concerning a person who consecrates an animal but does not consecrate all of it, saying instead that the leg of this animal shall be an olah - does the consecration take effect? According to Rabbi Yosei, and likewise according to Rabbi Shimon, the consecration does take effect, and not on the leg alone: once the leg becomes consecrated, the entire animal becomes consecrated along with it as an olah. But according to Rabbi Meir and Rabbi Yehudah, one who consecrates the leg has accomplished nothing at all.
An aside that is not part of the main subject: everyone agrees that if a person consecrates a limb upon which life depends - a limb the animal needs in order to survive, such as the heart, which if removed would cause it to die on the spot - then when he says about his animal that its heart shall be an olah, the heart becomes consecrated and the animal becomes consecrated along with it. But this is not the subject of our Mishnah.
The words of the Mishnah:
"Ein memirin eivarim v'ubarin" - the Mishnah takes for granted that a person can consecrate a fetus in its mother's womb. Therefore, one who has a consecrated fetus and comes to make a temurah for it, saying that in place of the fetus the leg of a certain animal shall come - the temurah does not take effect.
"V'lo ubarim v'eivarim" - and likewise the reverse: one who has a consecrated animal and comes to transfer the sanctity of one of its limbs onto a fetus that has not yet been born - this is ineffective.
"V'lo eivarim v'ubarim bishlamim" - one does not bring a limb, and one does not bring a fetus that has not yet been born, and apply to them the sanctity of shelamim, that is, of a complete consecrated animal. The reason: a limb is not an animal and is not called an animal, and likewise a fetus, an animal that has not yet been born, is not yet called an animal.
"V'lo shelamim bahem" - one who has a consecrated animal cannot exchange one of its limbs for a whole non-sacred animal, and likewise he cannot transfer its sanctity onto a fetus, onto an unborn offspring, since these are not called "an animal." That is the entire halachah, and it is straightforward.
The view of Rabbi Yosei:
Rabbi Yosei follows his own approach, that one who simply consecrates a single limb thereby consecrates the entire animal, and therefore in temurah as well one can transfer sanctity onto a limb. One who has a consecrated animal can bring another animal and say that the sanctity of the consecrated animal shall pass onto the leg of the new animal - and the temurah takes effect, since once the leg becomes consecrated the entire animal is drawn along with it.
However, this does not apply in the opposite direction: a person cannot say that the sanctity of that one leg of the consecrated animal shall pass onto a whole new animal, since the leg by itself is not sufficient to transfer the sanctity. But a whole consecrated animal is sufficient to transfer sanctity even onto a single leg, and from there the sanctity spreads throughout the entire body.
And this is how Rabbi Yosei reasons: in the ordinary laws of hekdesh, not in temurah, one who says that the leg of this animal shall be an olah - all of it is an olah, and not only the leg becomes consecrated but the entire animal. So too in temurah: one who says that the leg of the new, non-consecrated animal shall be a temurah in place of the consecrated animal he has - the temurah takes effect, and the entire animal becomes consecrated and not only its leg, because the sanctity spreads from the leg to the rest of the body.
The halachah:
The halachah does not follow Rabbi Yosei, and a person cannot consecrate a limb by means of temurah. The halachah follows Rabbi Meir and Rabbi Yehudah, that one who consecrates - not by way of temurah - a vital limb of an animal, one upon which life depends, such as the heart, the entire animal becomes consecrated. But even they agree, and so the halachah has been ruled, that one who says that the heart of this non-sacred animal shall be a temurah for this consecrated animal - his words are ineffective.
In summary: In this Mishnah we learned that temurah does not take effect on limbs or on fetuses, neither in this direction nor in that direction, because a limb is not called an animal and a fetus that has not yet been born is not called an animal. We examined the view of Rabbi Yosei, who holds that just as one who consecrates a limb thereby consecrates the entire animal, so too one can effect temurah through a limb, and the sanctity spreads from it throughout the whole body, and we noted that the halachah does not follow his opinion.