Niddah 63: Blood Stains and Establishing Menstrual Cycles

The Gemara cotinues to discuss the seven substances that remove blood?

1. Tasteless saliva: that which has been in one's mouth overnight; it contains several chemicals/enzymes that help with cleaning
2. Liquid from String Beans comes from chewing up those beans using the warm saliva of one's mouth
3. Urine: must be fermented for three days
4. Natron: Alexandrian
5. Borit: sulfer, one type of ice plant
6. Casmonian earth: earth that is "pull out, stick in"; the meaning is not decidedly defined
7. Potash: found in the shell of a pearl and removed with an iron stick

Some notes:

• if soap is applied after these seven substances and the stain disappears, the item remains ritually impure because of uncertainty - the stain might have disappeared at that point anyway
• the rabbis compare this with the discharge of a zav into a ceramic bowl where the discharge creates ritual impurity everywhere if it is heated and ritual impurity when touched

A first Mishna from today's daf is introduced: A woman has a regular menstrual cycle if she recognizes the start of menstruation by time or by physical sensation.  The sensations might be sneezing, yawning, shuddering, feeling a secretion, etc.  If this happens three cycles in a row, she has established a pattern has a regular cycle.

A second Mishna is introduced: a woman who experiences these signs of menstruation does not have to be named ritually impure retroactively.

Our third Mishna describes a woman who tastes something (onions, garlic, pepper, etc.) which provokes menstruation.  The rabbis debate the meaning of being able to do this three times in a row.

Finally, our fourth Mishna: if a woman menstruates on the fifteenth day of her cycle and then deviates to the twentieth day, she is not permitted to have intercourse with her husband between the fifteenth and twentieth day.  If this happens twice, she is not permitted to her husband on the fifteenth or the twentieth.  If it happens three times, she is permitted to her husband from the fifteenth until the nineteenth at which point the twentieth is a day for herself.