Menstrual Impurity

1. Shammai says: For all women it suffices [to reckon] their [period of menstrual uncleanness from] their time [of discovering the flow].

Hillel ruled: [Their period of uncleanness is to be reckoned retroactively] from the [previous] examination to the [last] examination, even if this was many days.

The sages say: [The law is] not like the words of these or the words of those, but [the women are deemed to have been unclean] during [the preceding] twenty-four hours when this lessens the period from the [previous] examination to the [last] examination, and during the period from the [previous] examination to the [last] examination when this lessens the period of twenty-four hours. For any woman who has a regular period, it suffices [to reckon her period of uncleanness from] the time she discovers the flow. And if a woman uses rags when she has marital intercourse, this is like an examination, which lessens either the period of the [past] twenty-four hours or the period from the [previous] examination to the [last] examination.

2. How [does the rule that] it suffices [to reckon her period of uncleanness from] the time she discovers the flow work?

If she was sitting on a bed and was occupied with ritually clean objects and then she leaves [the bed] and then sees [blood flow], she is unclean but the objects are clean. Even though they have said that she conveys uncleanness for a period of twenty-four hours [retroactively], she counts [the seven days of her menstruation] only from the time she observed the flow.