Zavim, Chapter Two, Mishnah Three
1) One who had [a discharge of] semen does not defile due to zivah for a period of twenty-four hours.
a) Rabbi Yose says: [only] that day.
2) A non-Jew who had a discharge of semen and then converted, he immediately becomes unclean due to zivah.
3) [A woman] who had [an issue] of blood, or had experienced difficulty [in childbirth], [the time prescribed] is twenty-four hours.
4) One who strikes his slave, the “day or two” is twenty-four hours.
5) A dog that eats a corpse’s flesh, for three days from one time of day to the same time of day, it is considered to be in its natural state.
Section one: As we learned in yesterday’s mishnah, if a man has a seminal emission, for the next twenty-four hours any zivah is attributed to the semen; he does not defile as does a zav.
Rabbi Yose says that this “grace” period is just during that day, the day on which he had a seminal emission. If the following day he has a flow of zov, he is impure, even if this is less than 24 hours after the seminal emission.
Section two: When a non-Jew converts, all of the things that happened to him as a non-Jew no longer count towards his status. So if he had a seminal emission before he converted, and then he converted, the seminal emission does not purify the zivah that he sees after he has converted (welcome to Judaism!). This is summed up by the saying that “a person who converts is like a newborn child.” He starts afresh and seminal emissions that he had as a non-Jew no longer count (bet you never knew that one before!).
Section three: A woman who sees menstrual blood defiles things that she has had contact with in the past 24 hours. This is a halakhah we saw throughout tractate Niddah.
A woman who has labor pains cannot be a zavah even if she has seen zivah. However, if there are 24 hours in which she doesn’t have pains and then she sees zivah, then she can be considered a woman who has childbirth while she is a zavah (there are special rules concerning this scenario, see Niddah 4:4).
Section four: The next two sections are here only because they deal with other cases in which a 24 hour waiting period is relevant. If a person strikes his slave and the slave is okay for 24 hours, and then he dies, the owner is exempt (Exodus 21:21). The rabbis understand “a day or two” to be a 24 hour waiting period.
Section five: If a dog eats the flesh of a human corpse, the flesh continues to defile as human flesh for three days, from the time of day in which it was eaten. After that, it no longer defiles because it is no longer considered to be human flesh.