(a) I don't understand the tuma'a of EVEN MESAMA, and the two Rashi's & Tosfos don't really clear it up.
Are there nafka minas? Or is it davka an "even" and davka on poles?
(b) What is actually the hava mina, since you could say that since an EVEN is not m'yuchad for sitting, it couldn't become tamei medras; it's too heavy for heset; it's a stone (w/o a kibul, apparently) so it itself cannot be nitma; and being an ohel is only by a mes.
Are there other mekorot to look in to understand this better?
Many thanks,
Tuvya Marcus, Jerusalem, Israel
(a)
1. Tosfos asks on Rashi: Why must it be a stone? Even if a board was on the poles, everything underneath the board should also be Tamei! The Chidushei ha'Ran answers that the reason, according to Rashi, why it says it is a stone is to teach us the Chidush that even though the Zav sits on a stone which is not Mekabel Tum'ah -- and one might have thought that the stone would prevent the Tum'ah from going through since it separates between the Tum'ah and the vessels underneath -- nevertheless the Tum'ah does go through and the vessels underneath become Tamei.
2. This answers your question that it is not Davka an "Even" but rather despite the fact that it is an "Even" which separates, the Tum'ah still goes through. If the Zav would be sitting on a board it would be more obvious that the Tum'ah goes through to the vessels.
3. It does not have to be Davka on poles. According to Rashi, it is sufficient for it to be on anything which lifts the stone above the vessels underneath it, and the Chidush is that even though the stone does not weigh down on the vessels below, the vessels still become Tamei.
(b) This also explains what the Havah Amina was. One might have thought that a stone, because it cannot become Tamei, would also prevent the Tum'ah from passing through from the Zav to the vessels below the stone.
(c) Another important source is the Rambam in Hilchos Tum'as ha'Mes (1:6) who writes that "Tum'as Masa" -- Tum'ah through carrying -- means that a person carries the Tum'ah and it is not necessary that he should touch it. The Rambam writes that even though there is a stone which separates between the person and the Tum'ah, he still becomes Tamei. According to this, the chidush of Even Mesama is that the Tum'ah does not have to touch the Tahor in order to make it Tamei.
Kol Tuv,
Dovid Bloom