Talmud - Niddah 17b נידה י״ז ב׳

Therefore, even if the earthenware vessel was full of items as small as mustard seeds, only a few of which touched the sides of the vessel or the impure item inside it, all the items inside the vessel are rendered ritually impure. Likewise, with regard to snow that passes through the vessel’s airspace, all of it becomes impure.

MISHNA: A woman’s reproductive organs are composed of different parts, and the halakhic status of blood that emerges from one part differs from the halakhic status of blood that emerges from another part. The Sages stated a parable with regard to the structure of the sexual organs of a woman, based on the structure of a house: The inner room represents the uterus, and the corridor [perozdor] leading to the inner room represents the vaginal canal, and the upper story represents the bladder.

Blood from the inner room is ritually impure. Blood from the upper story is ritually pure. If blood was found in the corridor, there is uncertainty whether it came from the uterus and is impure, or from the bladder and is pure. Despite its state of uncertainty, it is deemed definitely impure, due to the fact that its presumptive status is of blood that came from the source, i.e., the uterus, and not from the bladder.

GEMARA: Rami bar Shmuel and Rav Yitzḥak, son of Rav Yehuda, were learning tractate Nidda in the study hall of Rav Huna. Rabba bar Rav Huna found them sitting and saying an interpretation of this mishna: The room, i.e., the uterus, is the inner part of the reproductive organs, and the corridor is the outer part. And the upper story, the bladder, is built, i.e., found, above them both. And there is an open vestibule between the upper story and the corridor.

They continued: If blood is found from the opening of this vestibule and inward toward the uterus, i.e., inside the vagina, there is uncertainty whether it came from the uterus and is impure, or from the bladder and is pure, but its state of uncertainty renders it definitely impure. If it is found in the area from the opening of this vestibule and outward, on the outer surface of the vulva, the blood is more likely to have come from the bladder, through the urethra, and therefore its state of uncertainty renders it pure.

Rabba came and said to his father, Rav Huna: With regard to the halakha of blood that is found from the vestibule and inward, did the Master say to us that its state of uncertainty renders it impure, as I heard in the study hall, from which it may be inferred that this is a case of uncertain impurity? But didn’t we learn in the mishna: The blood is impure due to the fact that its presumptive status is of blood that came from the source, i.e., the uterus? This indicates that it is a case of definite impurity. If so, the mishna cannot be referring either to blood found from the vestibule and inward or from the vestibule and outward.

Rav Huna said to his son Rabba: This is what I said: If the blood was found from the vestibule inward it is definitely impure, as it is presumed to come from the uterus. This is the case mentioned in the mishna. If the blood was found from the vestibule outward its state of uncertainty renders it impure. Although it can be claimed that if this was blood from the uterus it would not have been found in this area, it is possible that when the woman bent over, the blood went from the uterus into this area. Consequently, she is impure due to the uncertainty.

Abaye says: What is different about a situation where the blood was found from the vestibule outward, where its state of uncertainty renders it impure? The reason for that halakha is that perhaps the woman bent over and leaned forward, and the blood came from the room, i.e., the uterus. If so, in the case where the blood was found from the vestibule inward, concerning which you ruled that she is definitely impure, you can also say that it is possible that the woman staggered backward and as a result the blood came from the upper story to the back of the canal. Accordingly, she should be impure merely out of uncertainty.

Rather, Abaye says: If you follow the concern, i.e., if your ruling of halakha is based on a concern that the blood might have moved due to the woman leaning forward or backward, then in both this case and that, whether the blood is found in the inner or outer section of the canal, the source of the blood is uncertain. And if you follow the presumption based on where the blood found in a particular place is usually from, then blood found from the vestibule inward is definitely impure, whereas blood found from the vestibule outward is definitely pure.

Rabbi Ḥiyya teaches: Blood that is found in the corridor is considered definite menstrual blood, and therefore if she engages in intercourse, both she and her partner would be liable as a result of this blood to receive karet for entering the Temple intentionally when ritually impure, or to bring an offering for entering unwittingly. And one burns teruma due to it, if the woman touches such produce. And Rav Ketina says: It is impure merely as a matter of uncertainty; therefore, the woman is not obligated, due to that blood, to bring an offering for entering the Temple when ritually impure, and one does not burn teruma on its account.

The Gemara discusses the relationship between this dispute and the previous statements of amora’im. According to this formulation, i.e., option, that Abaye stated: If you follow the concern that the blood might have moved due to the woman leaning forward or backward, there is uncertainty whether the blood was found in the inner or outer section of the canal, this supports the opinion of Rav Ketina, who likewise deems blood found in the canal impure due to uncertainty. And this option suggested by Abaye contradicts the opinion of Rabbi Ḥiyya, who deems the blood definitely impure.

According to that formulation that Abaye stated: If you follow the presumption that blood found in the inner section is definitely impure, while blood found in the outer section is definitely pure, this supports the opinion of Rabbi Ḥiyya, whose ruling that the blood is definitely impure is understood as referring to blood found in the inner section.

Traduction : The William Davidson digital edition of the Koren Noé Talmud, with commentary by Rabbi Adin Even-Israel Steinsaltz.

Nidah 17b explores ritual impurity through vessel contamination laws and the mishna's house analogy for female reproductive anatomy and blood sources.