1) HALACHAH: THE FIVE-DAY WAITING PERIOD BEFORE THE COUNT OF SEVEN CLEAN DAYS
OPINIONS: The Gemara discusses the status of a woman who was "Poletes Shichvas Zera." The Gemara concludes that a discharge of Shichvas Zera is Metamei the woman and cancels her count of seven clean days (if she had been counting them). However, it cancels her count only when it is discharged within 72 hours after she had relations.
Does the Gemara's discussion refer to any type of discharge of Shichvas Zera, or only to the specific Shichvas Zera of a man who was Tamei?
(a) RABEINU TAM (cited by the ROSH 4:1) asserts that the Gemara is discussing a woman who discharges the Shichvas Zera of a Zav. He proves this from the statement that "Dayah k'Bo'alah" -- it is enough to make her like her husband. Just as Shichvas Zera cancels only one day of her husband's seven-day count, it cancels only one day of her count. When does a man count seven clean days? He counts seven clean days when he is a Zav. Rabeinu Tam understands, therefore, that the Gemara is discussing specifically a woman who has a discharge of Shichvas Zera after having relations with a Zav.
(The other Rishonim understand that when the Gemara says "Dayah k'Bo'alah," it is not referring specifically to her husband. It means that, in general, when a man who is counting seven clean days because of Zav becomes Tamei with Shichvas Zera, the Shichvas Zera cancels only one day of his count. It does not mean that the man with whom she had relations was a Zav.)
The Rosh questions Rabeinu Tam's explanation. The verse from which the Gemara proves that an emission of Shichvas Zera cancels a clean count refers to every case of Poletes Shichvas Zera, and not just to a woman who had relations with a Zav. Moreover, it is evident from various other statements of the Gemara here that the Gemara is discussing normal marital relations, and not relations with a man who is a Zav.
(b) The RA'AVAD maintains that a woman who is Poletes Shichvas Zera loses her count of seven clean days only with regard to handling Taharos, but not with regard to being permitted to her husband.
The Rosh has difficulty with this opinion as well. He objects to the possibility that a woman's count can be canceled for one thing (handling Taharos) but not for another (being with her husband), and that she can maintain two separate counts. The Rosh refutes all of the Ra'avad's proofs.
(c) RABEINU YONAH (cited by the Rosh) explains that the Gemara refers to all women who have a discharge of Shichvas Zera. Since every woman who is Poletes Shichvas Zera becomes Tamei and her count of seven clean days is canceled, every woman who has relations must be concerned that she might unknowingly have a discharge of Shichvas Zera, and therefore she may not start counting seven clean days until 72 hours have passed after having relations. This is the conclusion of TOSFOS (33a, DH Ro'ah) as well.
HALACHAH: The Gemara's discussion about a woman who is Poletes Shichvas Zera has important practical ramifications in Halachah. The Halachah requires a woman who sees even the smallest amount of blood to count seven clean days. This is based on the teaching of Rebbi Zeira (66a), who states that Jewish women accepted upon themselves to observe the laws of a Zavah upon seeing any blood, even when they do not see blood for three consecutive days. Since a Zavah must count seven clean days, every woman who sees any amount of blood must count seven clean days. When, though, does she begin counting these seven clean days?
1. The SHULCHAN ARUCH (YD 196:11) rules that a woman who expels Shichvas Zera and experiences a flow of blood afterwards must wait 72 hours before she begins counting seven clean days. He gives an example of a woman who had relations on Motza'i Shabbos and saw blood afterwards. Even if the blood stopped immediately, she must wait until Thursday to begin counting seven clean days. She may not begin the count on Wednesday, because she might have expelled Shichvas Zera on the preceding night (Tuesday night) at an hour that was still within 72 hours of the time at which she had relations on Motza'i Shabbos, and thus the entire day (Tuesday night to Wednesday) is unfit to be counted as a clean day.
2. The REMA writes that the practice followed by Ashkenazim is that the woman adds an extra day of waiting before she counts seven clean days, whether she saw a flow of blood or found a stain of blood on her clothing. This is based on the ruling of the TERUMAS HA'DESHEN (#245). The Terumas ha'Deshen rules that we must take into account the possibility that the woman had relations near the end of the day on Sunday, during Bein ha'Shemashos, and she also saw blood at that time. The woman might assume that Bein ha'Shemashos is considered daytime, and since relations took place during Bein ha'Shemashos, it is no different from having relations at the beginning of that day (Motza'i Shabbos, the night after Shabbos). She will mistakenly begin her count on Thursday when, in truth, Bein ha'Shemashos might be night (Sunday night), and thus the 72-hour period does not conclude until Wednesday night. Since she might be Poletes Shichvas Zera on Wednesday night and be Tamei for all of Thursday, she must wait until Friday to begin her count of seven clean days. (See DIVREI CHAMUDOS on the ROSH 4:2.)
The SHACH (YD 196:20) maintains that the Terumas ha'Deshen's ruling that a woman must wait five days to begin her count applies even when her husband was out of town and they did not have relations, and there is no concern that she will be Poletes Shichvas Zera ("Lo Plug Rabanan"). Moreover, some communities adopted the custom that a bride, who counts seven clean days and immerses before her wedding, must wait five days before she begins counting seven clean days. The TAZ (YD 196:7) argues with the custom that a bride must wait, asserting that there is no reason for her to wait since she never had relations. Rather, she may begin her count of seven clean days as soon as her flow of blood stops.

42b----------------------------------------42b

2) HALACHAH: THE CRY OF AN UNBORN BABY
QUESTION: The Gemara relates that a man asked Rava whether he may perform a Bris Milah on Shabbos. Rava, suspecting that the question was not so simple, asked the man to explain the case. He told Rava that his son was born on Shabbos, but he heard the baby crying earlier during the delivery, on Erev Shabbos. What day is considered the day of birth, Erev Shabbos or Shabbos? Rava answered that if the baby was heard crying, then that shows that his head had already exited the Prozdor and the birth occurred on Erev Shabbos. Consequently, the Bris may not be performed on Shabbos.
It is clear from the Gemara that the cry of a newborn baby is considered the beginning of the baby's birth.
The NODA B'YEHUDAH (YD 2:120) was asked whether a woman is considered to be Tamei when her husband heard the cry of the baby in her womb while she was sleeping, and later no indication of birth was found. Do we assume that the baby's head emerged from the birth canal, and since blood always accompanies the opening of the birth canal, his wife is a Nidah? Perhaps, it is unrealistic to consider that the baby's head emerged from the womb without the various stages of birth occurring, and without even waking its sleeping mother, and the mother is Tahor. What is the Halachah?
ANSWER: The NODA B'YEHUDAH rules that not only is the woman considered a Nidah, she is even considered a Yoledes (and she is Tamei for two weeks due to the possibility that the child is a female). His ruling is based on the Gemara here that states that a baby's cry can be heard only when the baby is considered born according to Halachah.
However, the Noda b'Yehudah agrees with the one who asked the question that it is highly unlikely that a woman would be able to remain asleep during such a birth. Therefore, in practice, he rules that since the wife remained asleep, she is Tamei only mi'Safek, out of doubt.
3) ONE WHO EATS A "NIVLAS OF TAHOR"
QUESTION: The Gemara discusses the question of whether the "Beis ha'Beli'ah" (the place in the throat where swallowing occurs), where a Nivlas Of Tahor is Metamei the person who eats it, is considered "Belu'ah" ("swallowed up" deep in the body) or "Beis ha'Setarim" (a covered, hidden place in the body, but not as deep as "Belu'ah").
The Gemara explains that the difference between the two is in a case in which one person puts a k'Zayis of Nivlas Of Tahor into the throat of a second person. If the Beis ha'Beli'ah is considered Belu'ah, then the Tum'ah is considered Tum'as Belu'ah and it does not make the second person Tamei. If the Beis ha'Beli'ah is considered Beis ha'Setarim, then the second person does become Tamei, because even though Tum'ah in Beis ha'Setarim is not Metamei through Maga (contact), it is Metamei through Masa (carrying).
RASHI (DH Tum'ah) explains that Tum'ah Belu'ah is considered as though it does not exist, and therefore it is not Metamei through Maga or through Masa. In contrast, Beis ha'Setarim is merely like folds in the body, and thus the Tum'ah there is not annulled. Even though it is not Metamei through Maga, it is Metamei through Masa since the person with the Tum'ah in his Beis ha'Beli'ah is still carrying the Tum'ah.
The Gemara states that Abaye rules that Beis ha'Beli'ah is considered Belu'ah, while Rava rules that it is considered Beis ha'Setarim. Since the Halachah always follows Rava when he argues with Abaye (with the exception of the six cases mentioned in Bava Metzia 22b), it follows that the Neveilah of a Tahor bird is Metamei the person before it is considered swallowed up (that is, before the act of eating is considered to have taken place).
This is difficult to understand. The Halachah is that the Neveilah of a Tahor bird is Metamei only when it is in the Beis ha'Beli'ah, and not when one merely touches it without it entering the mouth. This Tum'ah is transferred specifically through eating. How, then, can it be Metamei the person before he eats it?
Moreover, the RAMBAM (Hilchos She'ar Avos ha'Tum'os 3:1) states that the amount of Nivlas Of Tahor that must be in the Beis ha'Beli'ah in order to make a person Tamei is a k'Zayis (see Zevachim 70a). The Shi'ur of a k'Zayis is always associated with prohibitions of eating. This implies that the Tum'ah of Nivlas Of Tahor comes about as a result of eating. How, then, can it be Metamei the person before he eats it?
ANSWER: RAV CHAIM SOLOVEITCHIK (Hilchos She'ar Avos ha'Tum'os 3:1) explains that the Halachah that a Nivlas Of Tahor is Metamei in the Beis ha'Beli'ah is not related to eating; rather, it is a specific Halachah in the laws of Tum'ah. He proves this from the Rambam's words that a Nivlas Of Tahor "is Metamei in the Beis ha'Beli'ah." In all of the Torah's prohibitions of eating, there is never a specific place in the digestive tract where the act of eating must occur. Rather, the prohibition is on the act of eating. Accordingly, the prohibition of eating is always transgressed after swallowing. While the forbidden food is still in the Beis ha'Beli'ah, the prohibition has not yet been transgressed.
Rav Chaim cites the Gemara in Kesuvos (30b) that says that when a non-Kohen eats Terumah and it is still in the Beis ha'Beli'ah, he is not yet Chayav. After it has passed through the Beis ha'Beli'ah, he becomes Chayav, and this is considered "after Achilah." This proves that there is no place per se at which one transgresses an Isur of Achilah, but rather the Isur is the act of eating the prohibited food. If the Tum'ah of eating a Nivlas Of Tahor would be a Halachah in the laws of eating (that is, the Halachah would be that one who eats a Nivlas Of Tahor becomes Tamei), then it would not be appropriate to discuss a specific place in the body that the Neveilah must reach in order for it to make the person Tamei. The fact that one becomes Tamei only when the Neveilah is in the Beis ha'Beli'ah shows that this law is a specific Halachah in the laws of Tum'ah. The law of Nivlas Of Tahor is a special Gezeiras ha'Kasuv that teaches that when the Neveilah is in the Beis ha'Beli'ah, which is the place where the act of eating occurs, it is Metamei the person, but the act of eating itself is not what is Metamei the person.
This also explains why the Shi'ur for Nivlas Of Tahor is a k'Zayis, even though a k'Zayis is normally the Shi'ur for prohibitions of eating, and Nivlas Of Tahor is a law in Tum'ah, not a law in eating. The Rambam writes that we derive from the verse, "Any Nefesh (soul) who shall eat a Neveilah or a Tereifah..." (Vayikra 17:15), that one becomes Tamei for eating a Nivlas Of Tahor only when the Neveilah reaches the "Beis ha'Nefesh," the place where the soul is sustained, which is the Beis ha'Beli'ah, where the food that sustains the soul is swallowed. The Rambam writes that the verse says "who shall eat" in order to teach the Shi'ur necessary to make him Tamei. The Shi'ur is a k'Zayis, which is the quantity that is considered "eating." It is evident from the Rambam's words that the law of Nivlas Of Tahor is a specific Halachah in the laws of Tum'ah, but that the Shi'ur necessary for it to apply is a k'Zayis, as derived from the words in the verse, "who shall eat." (See also KEHILOS YAKOV, Taharos #34.) (D. BLOOM)

OTHER D.A.F. RESOURCES
ON THIS DAF