Niddah 67: Immersion During the Day When Women are not Safe At Night

Today's daf discusses when a woman should immerse in the mikva.  We know that a woman who is niddah begins counting from the first day of menstruation.  She can immerse at the end of the seventh day, even if her bleeding continues through the week, but Rav teaches that this immersion that must be at the end of the day.  If she waits until the next day, she is permitted to immerse during the day.  Rabbi Yochanan disagrees, noting that her daughter might see this behaviour and believe that it was proper behaviour on the wrong day.

The rabbis discuss exceptions to the rule that women immerse in the evening of their last day:

• Rav Idi says that immersion should be done on the eighth day in Neresh when lions roam that area during the day
• Rav Acha bar Yaakov says that immersion should be done on the eighth day when thieves are in Pappunya 
• Rav Yehuda says that immersion at Pumbedita should happen during the eighth day due to the cold at night
• Rava says that the guards at the city gates of Mechoza are not trustworthy and thus women can immerse on the eighth day at night

The principle is that when there is danger at night, women can immerse during the day following her seventh day of niddah.