1) THE OBLIGATION TO BURY A FETUS
OPINIONS: In the Mishnah (56b), the Tana Kama states that the Beis ha'Teme'os (the place where women stay when they are Nidos) of Kusim is Tamei with Tum'as Ohel, because the women bury their stillborns (Nefalim) there. Rebbi Yehudah says that the Kusim do not bury their Nefalim, but rather they throw them out and wild animals take them away.
The Gemara asks what the Kusim's source is for not burying their Nefalim. The Gemara answers that they learn this from the verse, "Do not move your neighbor's boundary which was set in place by the previous generations" (Devarim 19:14). As Rashi mentions, the Sifri explains that this verse teaches the prohibition to sell a family burial plot ("Gevul"). The Kusim expounded this verse to mean that "anyone who is entitled to an inheritance is also entitled to a burial place (Gevul)." Since Nefalim do not inherit (see 44a, where the Mishnah and Gemara teach that a one-day-old baby inherits, but a fetus does not), they also do not receive a burial place.
What is the conclusion with regard to the requirement to bury a Nefel?
(a) The MAGEN AVRAHAM (OC 526:20) cites the HAGAHOS MAIMONIYOS who rules that there is no requirement to bury a Nefel. However, the Magen Avraham questions this ruling from the Gemara here, which says that it was the Kusim who did not bury Nefalim, implying that Jews are required to bury Nefalim. (See Gemara on 69a, and Tosfos to 39a, DH d'Ihu.)
The CHAZON ISH (OC 133:2) defends the opinion of the Hagahos Maimoniyos who says that Jews are not required to bury Nefalim. When the Gemara asks from what verse the Kusim derive that a Nefel does not need burial, the Gemara does not mean that the Kusim contrived this Derashah and it is not true. Rather, this Derashah is a genuine Derashah. The Gemara is asking on what Derashah do the Kusim rely to leave their Nefalim in the house. Even though this Derashah is true, the Jews nevertheless conduct themselves with holiness and purity and they bury their Nefalim or deposit them into pits, while the Kusim leave their Nefalim in their homes.
(b) The Magen Avraham rules that we are obligated to bury Nefalim, as he infers from the Gemara here. The CHOCHMAS BETZALEL cites further proof for the Magen Avraham's opinion from the words of RASHI (DH Mai). Rashi explains that the Gemara is asking, "What verse did the Kusim expound so that they do not bury their Nefalim?" Rashi apparently understands that the Gemara is asking a question according to Rebbi Yehudah, who maintains that the Kusim did not bury their Nefalim at all. The Tana Kama, however, maintains that even the Kusim buried their Nefalim. Accordingly, we certainly should bury Nefalim.
The MISHNAH BERURAH (OC 526:49) quotes some Acharonim who maintain that it is a Mitzvah to bury a Nefel. He cites (in SHA'AR HA'TZIYUN) the BEIS MEIR who writes that although it is a Mitzvah to bury a Nefel, this requirement is not due to the honor of the living or the dead, but rather it is because the corpse should not be left around to cause Kohanim to become Tamei.
The Magen Avraham adds that it seems apparent from the Gemara here that the prohibition against leaving a dead body without burial overnight ("Lo Salin," Devarim 21:23) applies to Nefalim as well. The Chochmas Betzalel cites RAV YEHONASAN EIBSHITZ in BINAH L'ITIM who suggests that the Magen Avraham's source is Tosfos (56b, DH Kovrin), who says that the Kusim would leave their Nefalim in their homes only temporarily, and they would later bury them in the cemetery. In this way, the Kusi women were able to use the Beis ha'Teme'os without becoming Tamei from the Nefalim there. The Magen Avraham may have understood that the reason why they buried the Nefalim was in order not to transgress "Lo Salin."
However, the Binah l'Itim rejects this possibility, because we certainly do not learn Halachos from the Kusim.
The Chazon Ish writes that the Magen Avraham's source that "Lo Salin" applies to Nefalim is the fact that the Gemara needs a verse (Devarim 19:14) to exclude Nefalim from burial. (This is consistent with the Chazon Ish's understanding that the Derashah from the verse is genuine and is not the Kusim's mistaken way of understanding it.) This implies that if not for the verse, a Nefel would have the same status as an ordinary person with regard to burial. Accordingly, the Magen Avraham understands that just as a Nefel must be buried, it also must not be left overnight. (D. BLOOM)
2) HALACHAH: "TUM'AS NIDAH" AS A RESULT OF A SENSATION
OPINIONS: Shmuel derives from a verse (Vayikra 15:19) that a woman who feels no flow of blood come from her womb is Tahor mid'Oraisa, even if she finds a bloodstain. She is considered to be a Nidah only mid'Rabanan. A woman who feels a flow of blood come from her womb is Tamei mid'Oraisa, even if an internal examination shows no blood.
What does Shmuel mean when he discusses a woman who "feels" blood come out of her womb?
There are three basic definitions for the "Hargashah" which Shmuel mentions (as cited by the PISCHEI TESHUVAH YD 183:1).
(a) The SHULCHAN ARUCH (YD 190:1) and the REMA (YD 188:1) write that the woman feels her "womb opening." The Acharonim explain that this feeling is similar to the sensation felt when urinating. This concurs with the Gemara here that compares the two sensations.
(b) The RAMBAM (Hilchos Isurei Bi'ah 5:17 and 9:1) writes that the woman feels her body "tremble" with the flow of blood.
(c) The NODA B'YEHUDAH (YD 1:55) explains that she feels the "flow of a fluid" inside her body. The CHASAM SOFER (YD 1:145) cites his Rebbi who argues and rules that the feeling of a flow of fluid does not render a woman a Nidah mid'Oraisa. (Feeling dampness or a flow of fluid outside of her body certainly does not make her Tamei mid'Oraisa. See MAR'EH KOHEN 1:3.)
HALACHAH: The Poskim conclude that experiencing any of these sensations renders a woman a Nidah mid'Oraisa. When a woman does not experience one of these sensations, she is Tamei only mid'Rabanan.
If a woman finds blood during a Bedikah or when cleaning herself immediately after urinating, she is also Tamei mid'Oraisa, even if she does not experience any of these sensations. This is in accordance with the Gemara that says that the feeling of blood flowing from the womb can be obscured by the sensation of a Bedikah or of urination.
3) A "HARGASHAH" THAT GOES UNNOTICED
QUESTION: Shmuel rules that a woman who feels no flow of blood come from her womb is Tahor mid'Oraisa, even if she finds a bloodstain. She is considered to be a Nidah only mid'Rabanan. A woman who feels a flow of blood come from her womb is Tamei mid'Oraisa, even if an internal examination shows no blood. The Gemara questions Shmuel's ruling from a Beraisa. The Beraisa states that when a woman finds blood on her body and she is in doubt about whether she is Tamei, she is deemed to be Tamei. Why is she Tamei if she felt no blood come from her body? The Gemara answers that the Beraisa means that she is Tamei mid'Rabanan. Shmuel agrees that the woman is Tamei mid'Rabanan.
The Gemara earlier questions Shmuel's ruling from another Beraisa. The Beraisa states that when a woman bleeds often, the objects that she touches have the status that she has during the majority of her life. If she is a Nidah more often than she is Tahor, then those objects are Tamei. The Gemara asks why those objects are Tamei if the woman experienced no Hargashah. The Gemara answers that the woman may have had a Hargashah recently and did not notice it.
Why does the Gemara not answer its question from a bloodstain on the woman's skin in the same manner and say that she may have experienced a Hargashah but did not notice it? (TOSFOS DH Ketani)
ANSWER: TOSFOS explains that this answer applies only in the third case, in which the woman is Tamei for the majority of her days. In such a case, there is substantial reason to assume that she may have had a Hargashah without realizing it, since she is Tamei so often. However, in the case of a woman who finds blood on her body there is no reason to assume that she did not notice a Hargashah.