Niddah 71 - A Woman Who Died
If a woman died, and then a "reviit" (about 5 ounces) of blood oozed from her uterus, this is not blood of niddah , because the woman did not sense it leave. However, it carries the ritual impurity of a stain. It also has the ritual impurity of a corpse, and has the capacity to make people and items under the same roof ritually impure. Rabbi Yehudah disagrees: since it is not blood niddah, it does not have this ritual impurity. And, if there is less than a "reviit" of it, it has no ritual impurity of a dead either. The first teacher agrees that it is not blood niddah, and if so, why does he assign any impurity to it? He and Rabbi Yehudah disagree about "is vs. becomes": is uterine blood ritually impure while in the uterus, or does it becomes so when it comes out.
A woman who has given birth and who is in her "pure" days, when even if she sees blood, this does not render her ritually impure (thirty-three days for a boy, and sixty-six for a girl) has the right to eat the second tithe, just like any "immersed today" person - who was impure, went to a mikveh this day, and is awaiting for sunset to become completely pure. This is considered her "extended day" of waiting for complete purity. Afterwards, she brings her childbirth sacrifice, goes to a mikveh, and then she resumes eating the sacrifices.
Art: Johann Georg Meyer von Bremen - Dressing the Baby