Burying Blood Masses, Fetal Impurity, and Reviving Prohibitions

How the Talmud defines fetal development for firstborn status and impurity, and whether nullified substances can reawaken.

Burial of a Discharged Blood Mass

If a mother animal expels a חררת דם (cake of congealed blood), it does not convey carcass impurity through touch or carrying. The Gemara asks why the owner must bury this mass if it is not an impure carcass. The Gemara resolves that the discharge is treated as an offspring, but its impurity is negated through ביטול ברוב (nullification by a majority).

The mass must still be buried to publicize exemption from firstborn status for future offspring. The Shulchan Arukh codifies this rule in practical law. If an animal discharges such congealed blood, she is exempt from בכורה (firstborn status), and the blood mass must be buried.

שפעה חררת דם פטורה מהבכורה והחררה תקבר לפרסמה שהיא פטורה מהבכורה

If she discharged a mass of congealed blood, she is exempt from firstborn status, and the mass must be buried to publicize that she is exempt from firstborn status. (Shulchan Arukh, Yoreh De'ah 315:7)

Impurity From an Expelled Placenta

The Gemara cites a mishnah regarding a woman who miscarries a שליא (placenta) inside a house. Even if observers do not detect an actual fetus within the placenta, the entire house contracts טומאת מת (corpse impurity). Although Rabbi Shimon suggests the fetus may have dissolved prior to emerging, the Rabbis rule strictly.

The halachic basis is that no placenta exists without fetus, creating a legal certainty of impurity. The Rambam codifies that a house containing an expelled placenta is definitely impure based on this presumption. The Sefer Mitzvot Gadol similarly rules that this presumption establishes definite corpse impurity.

הָאִשָּׁה שֶׁהִפִּילָה שִׁלְיָא הַבַּיִת טָמֵא וַדַּאי. חֲזָקָה הוּא שֶׁאֵין שִׁלְיָא בְּלֹא וָלָד

When a woman discharged a placenta, the house is certainly impure. It is an established presumption that there is no placenta without a fetus. (Mishneh Torah, Defilement by a Corpse 25:10)

Fetal Head Size and Impurity Thresholds

A stillborn fetus in the womb does not convey impurity through פתיחת הקבר (opening of the womb) until its head rounds. The Gemara concludes that for a human fetus, the head must reach the size of a skein of warp threads. For an animal, the threshold is the larger skein of woof threads.

The Rambam rules that if a woman in labor walks between houses and miscarries, the first house remains pure if the head reached this warp-skein size. A woman could not walk unaided once her womb opened that widely. The Gemara also notes that earth from a בית הפרס (a field with a plowed grave) or the Diaspora conveys impurity at the size of a large sack-makers' skein, which the Rambam codifies as well.

Reawakening of Nullified Substances

Fish brine bought from an עם הארץ (an unlearned person not trusted with purity) can be purified by connecting its water to a mikveh. Rabbi Yirmeya limits this remedy to dipping bread, forbidding adding the brine to a cooking pot with other water. When the nullified minority of impure water meets additional water, the impurity finds its kind and is חוזר וניעור (reawakened).

The Gemara supports this revival principle from the laws of impure תרומה (priestly gift) that fell into pure non-sacred produce. Commentaries analyze whether this revival applies generally to dietary prohibitions. The Peleti notes that the Rema maintains that nullified matter is reawakened upon finding its kind across halacha.

An animal's discharged blood mass is buried to mark firstborn exemption, while fetal discharges convey corpse impurity based on strict developmental thresholds and presumptions.

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