For the source text click/tap here: Bava Kamma 11
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Our Daf cites another ruling from Ulla in the name of Rabbi Elozar: When a placenta comes out from a woman (during a miscarriage) partly on one day and partly on the next day, the counting of the days of tumah (even without blood; if it is a male child, she is tamei for seven days – for a female, it is fourteen) begin with the first day (when the placenta starts to emerge).
Rava said: Since we are concerned (that the majority of the fetus emerged on the first day), we rule her to be tamei from the first day, but the actual counting only begins with the second day.
The Gemora asks: What is the novelty that Rava is teaching us? It cannot be that even a portion of an emerging placenta contains part of a fetus in it, for we have already learned in a Mishna: If a partial placenta came out of an animal (before it was slaughtered), the entire placenta is unfit for consumption.
This is because the placenta is a sign of a fetus in a woman and it is similarly a sign of a fetus in an animal (and we are concerned that a majority of the fetus emerged from the animal; accordingly, we would consider that the fetus was born already and it will not be permitted for consumption by the slaughtering of the mother).
We explore the history of the placenta in antiquity and nomenclature as well as the recently discovered critical role it plays in maternal immunity and genetics.