Niddah

What is the length of an 'onah? — Resh Lakish citing R. Judah Nesi'ah  replied: A normal 'onah is thirty days; but Raba, citing R. Hisda, replied: Twenty days. In fact, however, there is no difference of opinion between them. One Master  reckons both the clean and the unclean days  while the other Master  does not reckon the unclean days. Our Rabbis taught: If over an old woman have passed three 'onahs  and then she observed a flow, it suffices for her to reckon her period of uncleanness from the time she observed the flow; if another three 'onahs have passed  and then she observed a flow, it again suffices for her to reckon her uncleanness from the time she observed it. If, however, another three 'onahs have passed  and then she observed a flow she is regarded  as all other women and causes uncleanness retrospectively for twenty-four hours or from the previous examination to the last examination. This  is the case not only  where she observed the flow at perfectly regular intervals  but even where she observed it at successively decreasing intervals or  increasing intervals.  [You say,] 'Even  where she observed it at successively decreasing intervals'. It thus follows  that there is no need to mention that this law  applies where she observed the flow at perfectly regular ones. But should not the law be reversed, seeing that where she observes a flow at perfectly regular intervals she thereby establishes for herself a fixed period and it should, therefore, suffice for her to reckon her period of uncleanness from the time she observed the flow? And should you reply that this  represents the view of the Rabbis who differ from R. Dosa in maintaining that even a woman who has a fixed period causes retrospective uncleanness for twenty-four hours,  [it could be objected:] Should not the order  have been reversed to read as follows: Not only where she observed the flow at successively decreasing intervals or increasing intervals  but even where she observed it at perfectly regular ones?  — Read: Not only where she observed the flow at successively decreasing intervals or increasing intervals  but even where she observed it at perfectly regular ones.  And if you prefer I might reply, It is this that was meant: This  does not apply where a woman observed the flow at perfectly regular intervals but only where she observed it at successively decreasing or increasing ones. Where, however, she observed it at perfectly regular intervals she thereby establishes for herself a fixed period and it suffices for her to reckon her uncleanness from the time she has observed the flow. And whose view does this represent? That of R. Dosa. R. ELIEZER RULED: FOR ANY WOMAN OVER WHOM HAVE PASSED etc. It was taught: R. Eliezer said to the Sages. It once happened to a young woman at Haitalu  that her menstrual flow was interrupted for three 'onahs, and when the matter was submitted to the Sages they ruled that it sufficed for her to reckon her uncleanness from the time she observed the flow. They replied: A time of emergency is no proof. What was the emergency? — Some say, It was a time of dearth,  while others say, The quantity of foodstuffs the woman had prepared  was rather large and the Rabbis took into consideration the desirability of avoiding the loss of the levitically clean things. Our Rabbis taught: It once happened that Rabbi acted in agreement with the ruling of R. Eliezer, and after he reminded himself observed, 'R. Eliezer deserves to be relied upon in an emergency'. What could be the meaning of 'after he reminded himself'? If it be explained: After he reminded himself that the halachah was not in agreement with R. Eliezer but in agreement with the Rabbis [the difficulty would arise:] How could he act according to the former's ruling even in an emergency? — The fact is that it was not stated whether the law was in agreement with the one Master or with the other Master. Then what is meant by 'after he reminded himself'? — After he reminded himself that it was not an individual that differed from him but that many differed from him, he observed 'R. Eliezer deserves to be relied upon in an emergency'. Our Rabbis taught: If a young girl who had not yet attained the age of menstruation  observed a discharge, after the first time it suffices for her to reckon her uncleanness from the time she observed it; after the second time also  it suffices for her to reckon her uncleanness from the time she observed it, but after the third time  she is in the same position as all other women  and  causes uncleanness retrospectively  for twenty-four hours or from her previous examination to her last examination. If subsequently three 'onahs have passed over her  and then she again observed a discharge it suffices for her  to reckon her uncleanness from the time she observed it.  If another three 'onahs have passed over her  and then again she observed a discharge it suffices for her to reckon her uncleanness from the time she observed it. But if another three 'onahs have passed over her  and she again observed a discharge she is in the same position as all other women  and causes uncleanness retrospectively for twenty-four hours or from her previous examination to her last one.  When, however, a girl had attained the age of menstruation,  after the first observation it suffices for her to reckon her uncleanness from the time she observed the discharge, while after the second time she causes uncleanness retrospectively for twenty-four hours or from her previous examination to her last examination.  If subsequently three 'onahs have passed over her  and then she again observed a discharge, it suffices for her to reckon her uncleanness from the time she observed it. The Master said,  'If subsequently three 'onahs have passed over her and then she again observed a discharge, it suffices for her to reckon her uncleanness from the time she observed it'.