OPINIONS: The Mishnah states that one who touches the "Kulis" (femur) of a dead person becomes Tamei. The Gemara infers that the Kulis is Metamei only through Maga (touch) and not through Ohel from the fact that the Mishnah says only that one becomes Tamei by touching it.
The Gemara asks that if there is marrow inside the bone, then the Tum'ah should exude and be Metamei b'Ohel. The Gemara answers that there is not a k'Zayis of marrow inside the bone. The Gemara then asks that even if there is less than a k'Zayis of marrow inside, if marrow inside of a bone can be "Ma'aleh Aruchah," then it should still be Metamei b'Ohel.
What is the meaning of marrow that can be "Ma'aleh Aruchah"?
(a) RASHI (DH v'Iy) explains that even when there is no marrow inside the bone, the marrow is able to rejuvenate itself and then nourish the outside of the bone, causing (in a living person) skin to grow on the flesh of the limb. Accordingly, the bone should be considered a proper limb which is Metamei b'Ohel. The Gemara answers that the Tana of the Mishnah maintains that marrow inside a bone does not nourish the flesh on the outside of the bone to cause skin to grow (in a live person).
TOSFOS (DH v'Iy) writes that the reason why Rashi explains that there is no marrow in the bone at all is that if it is necessary for a small amount of marrow to be present in order to regenerate the skin, then the Gemara should have answered simply that the Mishnah is discussing a case of a bone with absolutely no marrow. It must be that even when there is no marrow in the bone, the marrow still is able to rejuvenate and then cause skin to grow.
(b) TOSFOS, however, disagrees with Rashi's explanation. When there is no marrow at all in the bone, the marrow cannot rejuvenate. The reason why the Gemara does not answer that the Mishnah is discussing a Kulis with no marrow is that every Kulis has at least a small amount of marrow in it.
Later, however, when he explains Rebbi Yochanan's opinion in the case of a Kulis with dry marrow, Rashi (DH Neveilah) writes that when there is some marrow in the Kulis, it causes the skin to grow. Why does Rashi say that the skin regenerates only when there is some marrow in the bone, if he maintains that even when there is no marrow in the bone the marrow itself rejuvenates itself and causes skin to grow?
Rashi's words may be understood based on a question asked by the RAN. The RAN asks that if flesh regenerates even when there is no marrow in the bone, then how can Rebbi Yochanan assert that a Kulis that contains dry marrow is Tahor? Dry marrow should be no worse than no marrow, and it should rejuvenate itself and cause skin to grow! The LEV ARYEH explains that it is apparent that the Amora'im disagree about this point. When the Gemara initially suggests that marrow causes skin to regenerate, it refers to even when there is no marrow in the bone at all (for, otherwise, the Gemara would have suggested that the Mishnah is discussing a case of a Kulis that contains no marrow, as Tosfos says). Rebbi Yochanan, however, who says that a bone with dry marrow is Tahor, disagrees with the Gemara's assumption and maintains that there must be at least a small amount of moist marrow in order for the skin to regenerate. Accordingly, when Rashi explains the words of Rebbi Yochanan, he writes that there must be a small amount of marrow in order for the skin to regenerate. (M. KORNFELD)
OPINIONS: The Gemara discusses the circumstances in which a human Kulis is considered an Ever (limb) of a Mes, which can be Metamei b'Ohel (see previous Insight). An Ever is defined as an entire bone on which there is enough flesh (or marrow) to cause its skin to regenerate in a live person (see Kelim 1:5). The Gemara answers that marrow does not cause skin to regenerate.
According to the Gemara, it seems that it should be forbidden to attach the limb of a dead person to the body of a living Kohen. Since the Kohen will be touching the limb at all times, and he will be in the same room as the limb, he will be causing himself to be Tamei, which a Kohen is not allowed to do. Moreover, the Mishnah in Ohalos (1:1) says that even an Ever Min ha'Chai (a limb removed from a living person) is Metamei like a limb of a Mes. This is the Halachah as recorded by the RAMBAM (Hilchos Tum'as Mes 3:1) and SHULCHAN ARUCH (YD 369:1).
Accordingly, it should be prohibited for a Kohen, who has lost a limb, to have his own limb reattached or to receive a limb from a dead body. It is obvious that in a case of mortal danger, it is permitted to reattach the limb of a Kohen in order to save his life, even though he will transgress the Isur of becoming Tamei both through Tum'as Ohel and through Tum'as Maga. What is the Halachah in a case in which there is no Piku'ach Nefesh involved, such as when a Kohen suffers the severing of a finger, and his life is not in danger as a result? Is it permissible to reattach the finger?
(a) RAV AVRAHAM-SOFER AVRAHAM suggests that because the finger is supposed to be attached to the Kohen's body, it should not have a status of Tum'ah.
The TZITZ ELIEZER (13:90) rejects this logic. The Gemara in Nidah (70b) questions whether the son of the Shunamis woman whom Elisha revived from the dead (Melachim II 4) would be Metamei people who come in contact with him. The Gemara answers that only a dead person is Metamei with Tum'as Mes, and not someone who is now living. This implies that while he was dead, he indeed would have been Metamei even though he was going to be revived. Moreover, the TESHUVOS CHASAM SOFER (YD 337) explicitly states that the Gemara does not question whether he needed to be sprinkled with the ashes of the Parah Adumah to become Tahor after he was revived, because it is obvious to the Gemara that he required Taharah since he touched himself while he was dead.
(b) However, the Tzitz Eliezer concludes that a limb transplant is permitted for a Kohen, based on a statement of the SHACH (YD 157:3). The Shach discusses the Halachah that one is required to sacrifice all of his money in order not to transgress a negative commandment (Lo Sa'aseh). The Shach is in doubt about whether losing a limb (apparently where no question of Piku'ach Nefesh is involved) is the same as losing all of one's money. Must one give up a limb in order to avoid transgressing a Lo Sa'aseh? One of the sources for this doubt is the law with regard to Shabbos which states that the loss of a limb without Piku'ach Nefesh is not a reason to permit desecrating Shabbos by performing a Torah prohibition (in contrast to a case of Piku'ach Nefesh). Even though the Shach considers this possibility, he concludes that one may be lenient and one is not required to give up a limb in order to avoid transgressing a Lo Sa'aseh.
The PRI MEGADIM (in Mishbetzos Zahav OC 328:7) quotes the words of the Shach and gives a reason for why the Shach was able to rule leniently. It is possible that because Shabbos is a strict category of Halachah, one is forbidden to transgress a Torah prohibition even to prevent the loss of a limb (again, when there is no Piku'ach Nefesh involved). However, other Mitzvos do not have the same degree of stringency as Shabbos. Therefore, one is permitted to transgress a Lo Sa'aseh in order to prevent the loss of a limb. The Tzitz Eliezer cites other reasons to be lenient, but he concludes that the only reliable reason is that the Shach and Pri Megadim rule this way. Accordingly, a Kohen is permitted to transgress the Lo Sa'aseh of making himself Tamei in order not to lose a limb. (Y. MONTROSE)


OPINIONS: The Gemara teaches that there is a type of Tum'as Ohel that is Metamei with Tum'as Maga. The normal type of Tum'as Ohel is an independent form of Tum'ah that spreads through being sheltered by an Ohel, and it does not combine with any other form of Tum'ah. A second type of Tum'as Ohel is in the same category as Tum'as Maga. This form of Tum'ah occurs when a person touches half of a k'Zayis of a Mes while he shelters and makes an Ohel over a second half-k'Zayis. Since he is touching one half-k'Zayis and making an Ohel over a second half-k'Zayis, the two half-k'Zeisim make him Tamei with Tum'as Maga. This type of Tum'as Ohel, which is considered a form of Tum'as Maga, applies to a case of "Tum'ah Retzutzah." Tum'ah Retzutzah refers to a case in which there is less than a Tefach between the Mes and the covering above it. In such a case, the Tum'ah of the Mes penetrates the object and goes out the other side.
Rebbi Zeira in the Gemara here describes Tum'ah Retzutzah as being Tum'ah between two chests (between which there is less than a Tefach). What exactly is the case of Tum'ah Retzutzah here?
(a) RASHI (DH d'Chulah) and TOSFOS (DH Amar) explain that the two chests are resting next to each other, side by side, with less than a Tefach between them, and a piece of a Mes is situated in the small space between the two. The Tum'ah is considered to be Retzutzah (compressed), and therefore it spreads up and down without limit. (Rashi mentions that the chests are made of wood. Large wooden vessels (which are not made to be carried while full) are not Mekabel Tum'ah. Presumably, if the boxes would be Mekabel Tum'ah, then they could not "lock in" the Tum'ah which lies between them.)
According to Rashi's explanation, in what way does the presence of the two chests change how the Tum'ah spreads in such a situation? Tum'ah left in the open air also spreads directly up and down without limit (Ohalos 9:11)!
Rashi writes that "it is as if the entire space between the chests is filled with Tum'ah," and, therefore, if one puts his hand anywhere between the boxes, even towards the top of the space far away from the Tum'ah, he becomes Tamei. It seems that even the area between the boxes that is not directly over the Tum'ah is Tamei, because the Tum'ah is Retzutzah and spreads throughout the entire space.
However, RAV MOSHE SHAPIRO shlit'a states that this cannot be the intention of Rashi. We never find that Tum'ah Retzutzah spreads in any direction other than straight up and down. What, then, makes this Tum'ah Retzutzah different from any other form of Tum'ah left in the open air?
It must be that Rashi's intention is as follows. When Tum'ah rests in an open area beneath an Ohel, it is Metamei only through Ohel and not through Maga. In contrast, when an object of Tum'ah is "compressed" between two chests, one who makes an Ohel (with his body) between those chests and directly above the Tum'ah is considered to have touched the Tum'ah and is Tamei through Maga. If, however, he places his hand higher, above the level of the top of the chest, he also becomes Tamei, but not with Maga but with Tum'as Ohel of the ascending Tum'ah.
(b) The RAMBAM (in Perush ha'Mishnayos to Ohalos 4:2) explains that the two chests mentioned here are placed one above the other, and not next to each other. There is a small space of less than a Tefach between them, and in that space is a piece of a Mes. This form of Tum'ah Retzutzah (vertical) is the normal case of Tum'ah Retzutzah, whereby the Tum'ah is able to penetrate through the upper covering and rise upwards.
According to the Rambam's explanation, why does the Gemara need to mention two chests? For the case to be one of vertical Tum'ah Retzutzah, it suffices for the Tum'ah to be on the ground (and not on top of one chest) and for a chest (or other object) to be placed within a Tefach over the Tum'ah!
The SIDREI TAHARAH of the RADZINER REBBE explains that the Gemara is suggesting a case which is consistent with the words of the Mishnah in Ohalos (3:1), "That which touches a half-k'Zayis and covers a half-k'Zayis, or a half-k'Zayis covers it, is Tamei." When two chests -- one above the other -- both have a half-k'Zayis of Tum'ah clinging to their surfaces, they are both touching a half-k'Zayis, and, moreover, the upper one is covering a half-k'Zayis while the lower one is being covered by a half-k'Zayis! (M. KORNFELD)