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Nidah 55

1. "EVEN MESAMA" OPINIONS: The Gemara suggests we might think that just as a Nidah is Metamei b'Even Mesama so too her blood should be Metamei b'Even Mesama. The Gemara cites a Limud to refute this and concludes that blood does not have Tum'as Mishkav u'Moshav nor does it have Tum'as Even Mesama. Dam is, however, Metamei b'Masa.

   Which objects are considered to be Tamei with Even Mesama (which applies only to Nidah, and becomes only a Rishon l'Tum'ah) although they are neither Mishkav u'Moshav (which only applies to a Nidah and becomes an Av ha'Tum'ah) nor Masa (which applies to Neveilah as well as to Nidah, and becomes only a Rishon l'Tum'ah)?

   1. According to RASHI, anything which is suited for siting upon is Metamei b'Mishkav u'Moshav when placed under a Nidah. Even Mesama is an extension of Masa, and applies even to objects which are not suited for sitting upon. It is different from the normal Tum'as Masa, since generally only something which is fit to be moved by the Nidah becomes Tamei through Masa, while something lying on a very heavy stone which is above the Nidah cannot be moved by her (since the stone is too heavy to carry).

   2. According to Rabbeinu Tam (in Tosfos Eruvin 27a DH Kol), an Even Mesama is such a heavy stone that the weight of the Nidah above it in no way adds any noticeable pressure to any of the objects which are below it. Any objects below the stone become Rishonim. It is not the same as Masa, since Masa requires moving the object that is carried by the Nidah, and not just carrying it (as Rashi explains in Chulin 21b).

   3. TOSFOS (Eruvin 27a DH Kol and in our Sugya) disagree with Rabbeinu Tam. They explain that we are dealing with a case where there is an object which is suited for sitting upon, however there is an enormous boulder is between it and the Nidah. Any objects which are fit for sitting upon which lie below the stone will become a Rishon l'Tumah not an Av ha'Tumah. (That is, Even Mesama is an extension of Mishkav u'Moshav).

2. HALACHAH: CORNEAL TRANSPLANTS
   • Question: Chazal decreed that skin is Tamei to prevent people from "making human skin into spreads." Why would it have been permitted to do such a thing had they not enacted their decree? One may not derive benefit from any part of a dead human body (Avodah Zarah 29b)! (TOSFOS DH Shema)

   • Answer:
     1. People are more careful to keep themselves Tahor than to keep the other Mitzvos of the Torah. (Tosfos -- this seems to be Tosfos' intent in our Chulin 122a as well.)
     2. One may derive benefit from the skin of a cadaver. (ibid. -- Rashi in Chulin ibid. seems to agree to this approach, DH Dvar Torah.)

        The difference between Tosfos' two answers is very important in determining the halachic permissibility of certain transplants. It is now common practice to replace damaged corneas with those of cadavers. Since the cornea can be classified as skin, and it is not necessarily "Pikuach Nefesh" to replace the cornea (especially if it is damaged in only one eye), it is important to determine whether or not one may use the skin of a dead person. (Even if the cornea was taken from a non-Jewish corpse, the SHULCHAN ARUCH (YD 349:1) prohibits the derivation of benefit from a non-Jewish corpse as well as a Jewish one.)

        Harav Yekusiel Greenwald in his "KOL BO AL AVEILUS" and the SERIDEI ESH (2:120) permit corneal transplants based on the answer in Tosfos that allows one to benefit from the skin of a dead person. Others disagree, asserting that a cornea is flesh and not skin, while yet others permit the operation on the grounds that using a cornea for a transplant is considered Shelo ke'Derech Hana'asan. (see Rav Ovadyah Yoself in YABI'A OMER, 3:20)

        The MISHNEH LE'MELECH (end of Hil. Avel) brings an interesting proof to permit the derivation of benefit from the skin of a cadaver. David betrothed his wife Michal with 100 Philistine foreskins, removed from Philistine warriors that he killed in battle (Shmuel II 3:14). Obviously, it is permitted to derive benefit from the skin of the dead!