(Beraisa): If a woman always sees every other day (at dawn, she follows an 18-day cycle of seven days of Nidah and 11 days of Zivah):

She is permitted (to have Bi'ah on) the entire eighth day (including night eight) and the (following, i.e. ninth) night, and four more nights within the 18 days (the nights following days 10, 12, 14 and 16. Clearly, the seven days of Nidah are forbidden. Of the remaining days (of Zivah), the odd days (9, 11,... ) are forbidden (during the day), for she sees then. The even days are entirely forbidden, for then she is Shomeres Yom k'Neged Yom. Rashi - the night after 18 is also permitted. We counted only the (four) nights within the 18 days. R. Chananel explains that she always sees in the middle or at the end of the night. Bi'ah is forbidden the entire night (after 18) for it is Samuch l'Vestah (she will become Nidah this night).

(In this and all the coming cases, all sightings are at the beginning of night. Recall that one who saw Dam Zivah (once) is Shomeres Yom k'Neged Yom. To become permitted she will need one (or sometimes seven) clean day(s). Even though she may immerse the next day, Bi'ah is forbidden, lest she see later in the day, retroactively making her a Zavah and disqualifying the immersion. The same applies if she saw two consecutive days. If she sees three consecutive days, she is a full Zavah, and she cannot immerse until counting seven clean days.) If she sees every other night, she is permitted only the eighth day. (She sees on every odd night of Yemei Zivah. All Yemei Zivah she is Shomeres Yom k'Neged Yom.)

If she alternates seeing two days (really, nights), and then has two clean days, she is permitted on the following entire days -- 8, 12, 16 and 20. (The two days following each of these she sees, and the third day she is Shomeres Yom k'Neged Yom.)

Question: Day 19 should be permitted, for Shimur is not needed for day 18! (It is day 11 of Zivah. She cannot become a Zavah!)

Answer #1 (Rav Sheshes): (The Mishnah (72a) calls one who has Bi'ah after immersing on the morrow of a sighting on day 11 a glutton for Bi'ah.) Our Beraisa teaches that this is forbidden.

Answer #2 (Rav Ashi): Granted, Shomeres Yom k'Neged Yom does not apply to day 11 of Zivah. However, day 10 requires Shemirah, and day 11 of Zivah (18 overall) was not valid Shimur because it was not clean. (Therefore, she must be Shomer the next day, i.e. 19.)

If she alternates seeing three days, then has three clean days, she is permitted only two days in her entire life. (She sees on days eight and nine. Day 10 she is Shomeres Yom k'Neged Yom. Days 12 and 13 are permitted. Afterwards she becomes a Zavah for life, for she never has seven clean days.)

If she alternates seeing four days, then has four clean days, she is permitted only one day (in her life, i.e. day eight. Afterwards she becomes a Zavah forever.)

If she alternates seeing five days, then has five clean days, she is permitted only three days (eight, nine and 10. Afterwards, she becomes a Zavah forever.)

If she alternates seeing six days, then has six clean days, she is permitted only five days (eight through 12. Afterwards she becomes a Zavah forever).

If she alternates seeing seven days, then has seven clean days, she is permitted seven days out of every 28 (the first seven days of Zivah. Afterwards she becomes a Zavah. After the next seven clean days, she becomes Nidah the next night.)

If she alternates seeing eight days, then has eight clean days, she is permitted 15 days out of every 48. (Her first clean day is Shimur for day eight. Her next seven clean days she is permitted. She becomes Nidah on day 19. The next of her eight clean days is the seventh day of Nidah. Her next seven clean days she is permitted. She becomes Zavah afterwards. After seven clean days she immerses. She is permitted on the eighth clean day, and then she becomes Nidah.)

Question: She is permitted only 14 days (of these 48, for (even) clean days of Nidah cannot be Metaher from Zivah! Rashi - she became Zavah on day 35. When she sees on day 37, this begins seven days of Nidah amidst Zivah. Such days do not count towards seven clean days. Therefore, she starts counting clean days only from day 44. She does not have seven clean days to become Tahor before day 48! Tosfos - on day 17 (day 10 of Zivah) she became Shomeres Yom k'Neged Yom. She saw also on day 18. She was Nidah from days 19 through 25, none of them (even day 25, which was clean) counts as Shemirah for day 17. Therefore she must be Shomer day 26. It is forbidden.)

Answer (Rav Ada bar Yitzchak): Since the Tana permits 15 days out of 48, this teaches that clean days of Nidah can Metaher from Zivah (just like days of Tum'as Leidah do):

Question: If a woman was Yoledes b'Zov, can clean days during the (seven or 14) days of Tum'ah (for a boy or girl) count towards the seven clean days she must count?

Answer (Rav Kahana - Beraisa): If a woman saw blood for two days (of Zivah), and miscarried on the third day, and she is unsure what she miscarried, she is Safek Zavah, Safek Yoledes. She brings a Korban, but it is not eaten. (Rashi - the case is, she did not have labor pains on the two days. She is also Safek Yoledes b'Zov, i.e. if blood came out before the birth. Aruch la'Ner - she does not bring two Korbanos (for Yoledes b'Zov), since it is a Sefek Sefeka (two doubts). Tosfos (21a) - the case is, she had pain. The Tana holds that Dam Koshi applies to Nefalim, so if she is a Yoledes, the Dam was not Dam Zavah, so one Korban suffices.)

Clean days of (Tum'as) Leidah count towards the seven clean days she must count. (Tosfos - if she is a Yoledes, it was not b'Zov, so she does not need seven clean days. Nevertheless, this is a good proof, for if clean days of Leidah did not count towards seven clean days (for a real Yoledes b'Zov), we would decree that they do not count here.)

Objection (Rav Papa): Perhaps she may count only the second week of Tum'as Yoledes, for perhaps Tum'as Yoledes does not apply then, i.e. perhaps she did not give birth to a female!

Answer (Rav Huna brei d'Rav Yehoshua): Surely, the chance that she is Yoledes Nekevah is as great as the chance that she is Yoledes Zachar! (We must be concerned for both.)

Rav Kahana's answer stands.

If she alternates seeing nine days, then has nine clean days, she is permitted eight days out of every 18. (The first clean day she is Shomeres Yom k'Neged Yom. The next eight days are permitted. She becomes Nidah the next night.)

If she alternates seeing 10 days, then has 10 clean days, the number of days she is permitted (three, all the clean days except for seven clean days she must count) equals the number of days of (seeing Dam) Zivah (all the days of blood except for seven days of Nidah);

The same applies if she alternates seeing 100 or 1000 (days of blood and clean days). The number of permitted days equals the number of days of Zivah (all the days of blood or clean days, except for seven).

(Mishnah): Dam Nidah and flesh of a Mes are Metamei whether they are moist or dry;

The following are Metamei only if they are moist -- Zov (emissions of uncooked semen from the Ever), Ni'a (thick mucus or spit) and (thin) spit (of a Zav, Nidah or Metzora), a Sheretz, a Nevelah, and semen;

If they are dry, but can become moist again if they are soaked, they are Metamei.

Question: Within what time must they become moist again?

Answer: This must be within 24 hours of soaking in lukewarm water.

R. Yosi says, if dry flesh of a Mes cannot become moist again, it is Tahor.

(Gemara - Question): What is the source of this? (The Gemara first shows that it is Tamei, and then shows that this is even if it is dry.)

Answer (Chizkiyah): "Veha'Davah b'Nidasah" -- Madveh (Dam Nidah, which is Metamei her) is like her -- just like she is Metamei (through Masa (moving) and Maga (touching)), also her blood is.

Question: "Davah" connotes flowing. What is the source regarding dry Dam Nidah?

Answer (R. Yitzchak): "Yihyeh" teaches that it keeps its status (even when it is dry).

Question #1: Perhaps we learn only about blood that was initially moist and became dry. What is the source for blood that was dry from the beginning?

Question #2 (Mishnah): If a woman miscarried (something resembling) a scab, hair, earth or red mosquitoes (Aruch - worms), if they dissolve in water, she is Nidah.

What is the source of this?

Answer: "Yihyeh" is a Ribuy, it includes all of these.

Suggestion: Just like she makes a Mishkav or Moshav an Av ha'Tum'ah (if she sits on it) to be Metamei people and their garments, also her blood should!

Answer #1: It is unreasonable to learn this from the Hekesh, since "sitting" does not apply to blood.

Rejection: If not for a verse, we would have learned Tum'as Mishkav u'Moshav regarding a stone (from a house with Tzara'as), even though 'sitting' does not apply to it!

(Beraisa) Suggestion: A Kal va'Chomer should teach that Even Menuga'as makes a Mishkav or Moshav (an Av ha'Tum'ah to be Metamei people and their garments)!

A Zav is not Metamei through Bi'ah (entering a room), yet he makes a Mishkav or Moshav. Even Menuga'as is Metamei through Bi'ah. All the more so it should make a Mishkav or Moshav!

Rejection: "Ha'Zav" teaches that a Zav makes a Mishkav or Moshav, but Even Menuga'as does not.

Answer #2: Just like "ha'Zav" excludes Even Menuga'as from Tum'as Mishkav u'Moshav, "Asher Hi Yosheves Alav" excludes her blood.

Suggestion: ("Even Misma" is a rock too heavy to be moved, or that is supported on pegs.) Just like she is Metamei through Even Misma (if she sits on it, she is Metamei garments underneath. Alternatively, if her Mishkav is under the rock, it is Metamei a Tahor who sits on the rock), also her blood should be!

Rejection (Rav Ashi): "Veha'Nosei Osam" is a Mi'ut (to exclude this).