ציטירנדיקער פּירוש אויף ויקרא 20:18

1. From "its source" (which means the uterus). From what is written, "he has laid bare her flow and she has exposed her blood flow" (Lev. 20:18), Chazal learned that she is not impure unless the blood comes from the "source", i.e. the uterus.

The Laws of Niddah
"When a woman has a discharge, her discharge being blood from her body, she shall remain in her impurity seven days" (Leviticus 15:19). Our sages learnt from explication of the verses that not all blood flows render the discharger impure, but specifically those of uterine blood (a braita from Torat Kohanim). The Ri"f writes in the second chapter of Tractate Shevuot, and the Rosh at the end of Niddah, and this is his language: "'When a woman has a discharge' (ibid.) -- I could have thought any flow of blood would be impure. The Torah teaches therefore 'he has uncovered the source [uterus] of her blood' (Leviticus 20:18) -- teaching regarding the blood that it speaks only of uterine blood."

And that which is written, "not all blood which comes from the uterus is impure, only five specific kinds of blood", is a gezeira shava: "It could be that all appearances of discharge will be impure? But to contradict this, the Torah teaches "blood" -- and blood is only red. When it says "her bloods", it teaches that many bloods are impure -- the red, the black, the saffron-hued, the muddy-water coloured, and the colours of mixed wine. The meaning is in chapter "every hand" (Niddah 19a), since it says "her bloods" "her bloods", behold there are four types. An explanation: since it says "and she revealed the source of her bloods" (Leviticus 20:18), behold there are two here. "And she will be pure from the source of her bloods" (Leviticus 12:7), behold there are two here. Behold four; and are there not five? We teach: this black is only faded red.

ערות הארץ means THE NAKEDNESS OF THE LAND — from which side it might easily be conquered. Of similar meaning are, (Leviticus 20:18) “He hath made naked (הערה) her fountain”; (Ezekiel 16:7), “naked and עריה) bare”. Indeed all forms of this root ערה signify “uncovering”). Onkelos renders it by “the breach (בדקא) of the land”, similar to (2 Kings 12:6), “the breach (בדק) of the house”— the defective places in the house — but he was not particular to translate according to the wording of the text (i.e. literally).

כי תהיה זבה AND IF A WOMAN HAVE AN ISSUE — One might think that this means: if there be an, issue from any limb of her body (e. g. ear, nose)! It, however, states in a law referring to this matter, (Leviticus 20:18) “and she hath uncovered the fountain of her blood” — only that issue of blood therefore makes her unclean which comes from her fountain (Sifra, Metzora Parashat Zavim, Section 4 2).