Kommentar zu Niddah 2:5

החדר והעליה והפרוזדור – the inner part of the female genitals/upper end of the vagina/uterus {חדר) from within, and the forepart of the female genitals/lower end of the vagina/uterus(פרוזדור) from without, both of them are one next to the other, with the inner part of the female genitals/upper end of the vagina/uterus(חדר) to the side in back of it, and the lower end of the vagina/uterus in front of it, and an upper chamber (עליה) built o top of both of them, and there is an hole/perforation (נקב) between it and the lower end of the vagina/uterus called a לול/a passage from the vestibulum vaginae, and sometimes blood comes from the upper chamber to the lower end of the vagina/uterus (פרוזדור) via the passage from the vestibulum vaginae (לול) . And the sides/walls of the womb are below in the middle of the lower end of the vagina/uterus (פרוזדור) and through there the blood exits.

Introduction Today's mishnah distinguishes between pure and impure blood that flow from various sources in a woman's body.

דם החדר טמא – that is the interior of the womb from where the menses are discharged (המקור) .

The sages spoke of a woman through a metaphor: A chamber, a vestibule and an upper chamber. The blood of the chamber is unclean, If blood is found in the vestibule, and there arises a doubt about its character, it is deemed unclean, because it is presumed to have come from the source. Building upon their analogy of a woman as a "house" (see mishnah one) the rabbis use a "house" metaphor to describe a woman's anatomy. There are many disagreements as to what parts of the anatomy these actually refer to. I will use Maimonides interpretation.

ספיקו טמא – it is [ritually] impure from doubt of a definite impurity/defilement.

There are three parts to a house and to the woman's anatomy. The "chamber" is equivalent to her uterus. The "vestibule" is the vagina. And the upper chamber is the cavity that contains the ovaries and fallopian tubes.

שחזקתו מן המקור – but we don’t say that perhaps it (i.e., the blood) comes from the upper chamber (עליה) for the blood of the upper chamber is pure, but they made it as if it definitely comes from the interior of the womb where the menses are discharged(המקור) . But these words [apply] when it is found from the vestibulum vaginae (לול) and internally to the side of the upper end of the vagina/uterus(חדר) , but if it (i.e., the blood) is found from the vestibulum vaginae (לול) and outwards, it is not impure a definitive defilement to burn it - but it is a doubtful defilement to hold it in abeyance, for two [types] of blood go out through that passage – the blood of the upper end of the vagina/uterus (חדר) and the blood of the upper chamber (עליה) – and we don’t know which comes (see also Maimonides’ Mishneh Torah, Hilkhot Issurei Biah, Chapter 5, Halakhot 3-5).

Blood that comes from the chamber is unclean. This is the source of menstrual blood. The implication in this mishnah is that if the blood comes from the upper chamber, it is clean. I am not entirely sure how it could be determined if the blood came from the upper chamber.

If blood is found on the vagina, and it is unclear whether it came from the uterus or not, the blood must be treated as unclean because it must be presumed to come from the "source" which is another word for the uterus. The practical implication of this is that if the woman touches terumah, the terumah is unclean and may not be eaten, but it is not burned. Only certainly impure terumah is burned.