Niddah

R. Johanan stated: In three instances  did the Sages follow the majority rule  and treated them as certainties, viz., the 'source', the 'placenta' and the 'piece'. The 'source'? The case already spoken of.  The 'placenta'? Concerning which we have learnt: If a placenta  is within a house, the house is unclean;  and this is so not because a placenta is regarded as a child but because generally there is no placenta without a child in it.  R. Simeon said, The child might have been mashed  before it came forth.  A 'piece'? For it was taught:  If a woman aborted a shaped  hand or a shaped foot she  is subject to the uncleanness of birth,  and there is no need to consider the possibility  that it might have come from a shapeless body.  But are there  no others?  Is there not in fact the case of nine shops  concerning which it was taught: If there were nine shops  all of which were selling ritually killed meat and one shop that was selling nebelah  meat and a man bought some meat in one of them and he does not know in which of them he bought it, the meat is forbidden on account of the doubt;  but if  meat is found,  the majority rule is to be followed?  — We  speak of uncleanness;  we do not discuss the question of a prohibition.  But is there not the case of the nine [dead] frogs among which there was one [dead] creeping thing  and a man touched one of them and he does not know which one it was that he touched, where he is unclean on account of the doubt if this occurred in a private domain,  but if it occurred in a public domain such a doubtful case is regarded as clean; and if one  was found  the majority rule is to be followed?  — We  deal with the uncleanness of a woman; we do not discuss general questions of uncleanness. But is there not the following case of which R. Joshua b. Levi spoke: If a woman crossed a river