The Torah prohibits the consumption of blood and imposes the punishment of karet (excision) on anyone who disregards the prohibition. However, there is a disagreement about the minimum amount a person must consume to become liable to this punishment. Most sources state that the minimum is the volume of a kezayit (an olive, approximately 20cc). However, in Yevamot 114b, the minimum amount given is a revi’it (approximately 86cc) – four times the volume of an olive.
In Responsa Binyan Tzion (#49), Rav Yaakov Ettlinger was asked a question relating to this law. A person was ill, and was directed by his doctor to drink animal blood daily. To avoid doing something normally punishable by karet, Rav Ettlinger advised him to eat less than the minimum amount required for liability. However, it was unclear to the rabbi whether this minimum was a kezayit or a revi’it. Some say that the two different measurements apply to two different cases: one is the minimum for eating coagulated blood, and the other for free-flowing blood. However, Rav Ettlinger rejected this distinction.
We may resolve this dispute with a text recently printed by Yad HaRav Herzog (publisher of this book), which lists variant readings of Talmudic texts. There we find that even though the minimum amount is a revi’it in our standard Vilna Talmud version of Yevamot (as well as in the Soncino and Venice Talmuds, which were the basis of the Vilna Talmud), nevertheless, in six manuscripts the amount that appears is a kezayit. The text found in Beit HaBechirah of the Meiri (1249-1306), which was not available in the time of Rav Ettlinger, reads kezayit as well.
Now that we are aware of these textual variants, we can easily resolve the contradiction without resorting to casuistic distinctions (pilpulim).