The Rambam on Fetal Remnants, Measures, and Nullification

How the Rambam rules on fetal impurity, skein measurements, and the revival of nullified mixtures.

The Disintegrated Fetus and Nullification

The Gemara investigates whether an unformed discharge or an afterbirth transmits ritual impurity. If a discharged mass of congealed blood exempts future births from firstborn consecration, it implies a valid offspring existed. Yet the baraita teaches that it does not defile through contact or carrying.

Rabbi Yoḥanan explains that the fetus is nullified in the majority of the surrounding blood. He equates this with Rabbi Shimon's view concerning a human afterbirth, where a fetus allegedly liquefies before exiting and becomes entirely nullified.

The Presumption of a Human Offspring

The Rambam rejects Rabbi Shimon's exemption and adopts the majority rabbinic view. When a woman discharges an afterbirth, the house contracts corpse impurity without doubt.

The Rambam establishes that legal certainty governs the discharge. A woman who miscarries an afterbirth must also observe the postpartum impurity periods for both male and female births. The Mishneh LaMelech notes that the majority of placentas contain an offspring, thereby overriding the prior presumption of purity.

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

When a woman discharged a placenta, the house in which she was located is certainly impure. It can be presumed that there is no placenta without a fetus. (Mishneh Torah, Defilement by a Corpse 25:10)

Reconciling Conflicting Standards of Dissolution

The Lechem Mishneh notes an apparent contradiction in the Rambam's codification. The Rambam rules that an animal discharging a mass of blood transmits no carcass impurity, following Rabbi Eliezer ben Yaakov. Yet he rejects Rabbi Shimon regarding a human afterbirth.

The Lechem Mishneh resolves this by explaining that all Sages agree an animal fetus inside congealed blood was thoroughly dissolved and nullified at the start of birth. By contrast, the Rabbis dispute Rabbi Shimon regarding human afterbirth because they maintain the fetus did not dissolve completely.

The Three Measures of the Skein

The Gemara cites three distinct measurements based on a yarn skein: warp thread, woof thread, and a sack-maker's skein. The Rambam applies the warp skein to determine when a deceased human fetus causes tent impurity upon the opening of the womb. If the head rounded to this size, a walking mother could not have opened her womb without collapsing, rendering the previous room pure.

For an animal, the Rambam diverges from Rashi and the Ra'avad. Rather than applying the woof skein to carcass impurity, he rules that rounding like a woof skein is required to exempt the subsequent birth from firstborn status. Finally, he adopts the sack-maker's skein as the minimum volume of foreign earth that defiles.

אֲבָל אִם הֶעֱגֵיל רֹאשׁ הַנֵּפֶל כְּפִיקָה הַבַּיִת הָרִאשׁוֹן טָהוֹר שֶׁאִלּוּ נִפְתַּח רַחְמָהּ שָׁם לֹא הָיְתָה יְכוֹלָה לְהַלֵּךְ עַל רַגְלֶיהָ.

If, however, the head of the non-viable fetus rounded like a skein, the first house is pure, for had her womb opened there, she would not have been able to walk on her feet. (Mishneh Torah, Defilement by a Corpse 25:9)

Fish Brine and Reawakened Impurity

The Gemara rules that fish brine bought from an עם הארץ (an unlearned person) may be purified through השקה (contact with a mikveh). The Rambam codifies the qualification of Rabbi Yirmeya: this purification is effective only if one dips bread into the brine.

If placed into a cooking pot containing water, the minority of water in the brine joins the pot's water, reawakening the nullified impurity. Similarly, regarding impure heave offering falling into pure produce, the Rambam follows the Rabbis: the mixture is nullified, but must be consumed dry or kneaded without susceptible liquid because the original heave offering cannot be identified with certainty.

בַּמֶּה דְּבָרִים אֲמוּרִים לִטְבּל בָּהֶן פַּת. אֲבָל לִקְדֵרָה מָצָא מִין אֶת מִינוֹ וְנֵעוֹר וְנִמְצְאוּ רֹב הַמַּיִם טְמֵאִים.

When does the above apply? When one seeks to dip bread in it. If, however, one adds it to a pot, like finds its like and is reawakened, and the majority of the water is found to be impure. (Mishneh Torah, Defilement of Foods 16:5)

Practical Implications

In practical halakha, any discharged human placenta definitively renders an enclosed shelter impure and imposes double birth-impurity intervals upon the mother.

For livestock, an aborted mass exempts later offspring only if it reached the dimension of a woof skein. Furthermore, brine from an unverified source purified by immersion remains restricted to dry usage without additional liquids.

The Rambam presumes an unobserved fetus defiles definitively, applies the woof skein to bekhorah exemption, and bars reawakening nullified liquids in a pot.

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