Commentary for Niddah 4:3

דם מכרית וכו' בית שמאי מטהרין – but even though that [regarding] her spit and her urine, the School of Shammai agrees with the Sages that decreed upon them to be like those with gonorrhea for all their matters, even so, her blood is pure, for the Rabbis reserved for her that it would be a means of recognition of their Rabbinic [ritual] impurity, in order that they would not burn heave-offering or Holy Things upon them.

The blood of a Gentile and the clean blood of a metzoraat (a woman with scale: Bet Shammai declares clean. And Bet Hillel holds that it is like her spittle or her urine. The menstrual blood (or zivah blood, blood that flows when a woman is not supposed to be menstruating) of a Gentile is, according to Bet Shammai, pure. This is because the chapters in Leviticus that discuss this issue are addressed to "the children of Israel" (Leviticus 15:2). "Clean blood" is the blood that flows from a woman during the period after childbirth following her time of impurity. For a boy, she is impure for a week and then pure for 33 days and double that amount of time for a girl. According to Bet Shammai, even if the woman is a metzoraat, who is impure, her blood is pure during this period, just as the blood of any woman is pure during this period. Bet Hillel disagrees on both of these issues. Concerning the blood of Gentile women, while Bet Hillel agrees that it is not impure by virtue of Torah law, they hold that the rabbis declared it impure (it would be impure derabanan). Just as they declared that other fluids that come from a Gentile's body are impure, urine and spittle, so too is their menstrual blood. This means that it defiles when moist, but not when dry, as do urine and spittle. Similarly, the rabbis hold that the "clean blood" of a metzoraat defiles like her spittle and urine when wet and not when dry. We could summarize the debate in the following way: Bet Shammai considers this blood not to be like the other fluids that come from the body, urine and spittle. Therefore, for both of these women, their urine and spittle can be impure while their blood is pure. Bet Hillel groups the blood with the other fluids, and just as urine and spittle are impure, so too is blood.

ודם טהור של מצורעת – but even though that the discharges of a woman leper such as her spit and urine are primary sources of ritual impurity like that of someone with gonorrhea, even so, her blood of purity (i.e., the vaginal bleeding experienced by a woman from eight to forty days after giving birth to a boy and from fifteen to eighty days after giving birth to a girl) is pure, for it is not a discharge, for we require that which is similar to spit (i.e., secretion of the mouth) which is formed in globules on being discharged (see Tractate Niddah 56a).

The blood of a woman after childbirth who did not immerse [in a mikveh]: Bet Shammai says it is like her spittle or her urine, But Bet Hillel says: it conveys uncleanness both when wet and when dry. Seven days after the birth of a boy and 14 days after the birth of a girl a woman is supposed to go to the mikveh, and subsequent blood will be pure. If she does not go to the mikveh, Bet Shammai says that this blood is like other liquids in her body it will defile when wet and not when dry. This is because she is still unclean, even though her blood is clean (i.e. the blood doesn't defile because it is blood, but rather because it is bodily fluid). Bet Hillel says that the blood is like menstrual blood i.e. it defiles because it is blood and not just because it is a fluid. This means that it will defile even when dry.

כרוקה וכמימי רגליה – that defile while moist but do not defile while dry. But this recognition is what is used regarding the blood of a heathen woman which defiles according to the Rabbis who decreed upon them that they would be like those with gonorrhea for all their matters, whereas the Israelite women (i.e., Jewish women) blood defiles moist and dry, and that of the heathen [which defiles] moist but not dry, like her spit and her urine that do not defile dry. But the blood of a woman leper also, even though her blood is not an issue/spring, she has the law of a spring upon her, for the All-Merciful included her from Scripture as it is written for a male, to include the leper to his discharge/issue and for the female, to include the female leper to her discharge/issue, and we state that her discharge/issue is suspicious, for if you wish you can say the rest of the discharges, we derive it from the male, and since we include the [male] leper to his discharges, we include the female leper with her discharges, for there is something analogous to it in the male, but to her blood, there is nothing [like it] in the male, for since the All-Merciful included her blood, that it would be like her spit and like her urine, if so, just as her spit and her urine defile moist and don’t defile when dry, so too her blood is like this.

They agree that if she gave birth while in zivah, it conveys uncleanness both when wet and when dry. Both houses agree that if she gave birth while in a state of zivah, meaning while she was impure due to non-menstrual blood, her blood defiles as would menstrual blood, until she goes to the mikveh, after seven days for a boy and 14 days for a girl. In other words, the fact that this is supposed to be "clean blood" does not get her out of the fact that she had unclean blood before she even gave birth.

דם היולדת- that passed the days of [ritual] defilement of a menstruant woman who did not immerse [as yet in the Mikveh].

בית שמאי אומרים כרוקה וכמימי רגליה - it defiles when moist but does not defile when dry. But even though it is blood of purity, the All-Merciful ties it to days but these were filled, but not to make it defiled also because of a discharge because it doesn’t form globules on being discharged, nevertheless, the Rabbis decreed [ritual] defilement upon her, for since she did not immerse [in a Mikveh], she is [ritually] impure/defiled, as a decree that after seven [days] is like within seven [days]. But however, it was not decreed that that it would be defiled [both] moist and dry like before the seven [days], for just as there is recognition that they knew that his defilement is according to the Rabbis.

ובית הלל אומרים מטמא לח ויבש – for his [ritual] impurity is from the Torah all the time that he didn’t immerse [in the Mikveh]. For the School of Hillel holds that the All-Merciful ties days and ritual immersion, all the while that she didn’t immerse, her blood after the seven [days] is like that of before the seven days.

ומודים ביולדת זוב – it at the time of her giving birth she had a flux, she would need to count seven clean days prior to becoming [ritually] pure, but if she gave birth and didn’t count [seven clean days], the School of Shammai agrees with the School of Hillel that her blood is impure moist and dry even though the seven days following her giving birth to a male had passed or two weeks for a female, for the blood of a woman with a flux always remains in its impurity from the Torah until she counts seven clean [days].