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1. We may presume that blood flows from one place to another, but we may not presume that it is taken from one place to another.
2. Rebbi Elazar b'Rebbi Yosi ruled in accordance with our Mishnah with regard to clothing used as a blanket.
3. If a woman was handling other types of blood, she may presume that a bloodstain that she finds is from that other blood.
4. A woman may presume that a bloodstain smaller than a Gris came from a different source and is not Tamei.
5. Rebbi Akiva ruled that even a cut that had formed a scab may be presumed to be the source of such a bloodstain.
A BIT MORE
1. For example, the Beraisa states that if a woman was bleeding from her neck, we may presume that the bloodstain on her clothing is not Tamei, as it could have fallen from the wound onto her neck and onto her clothing. However, if she had a wound on her shoulder, we do not presume that her hand touched the wound and then transferred the blood to the clothing on the lower parts of her body.
2. Any bloodstain on such clothing is considered Tamei, as people often turn the blanket during the night. When Rebbi Elazar b'Rebbi Yosi told the Chochmei Darom that he ruled this way, they concurred with him.
3. For example, if she was handling slaughtered animals or fowl, or she was near people who were handling such items, she may presume that the bloodstain on her clothing came from that blood.
4. This is because she might have killed (without realizing it) a louse, and the blood of the louse caused the stain.
5. Rebbi Akiva's ruling applies as long as it is reasonable that the scab could have opened up and started bleeding again. These leniencies (wherein we attribute the bloodstains to different sources of blood) are possible only because the law of bloodstains on clothing is mid'Rabanan in nature, and the Rabanan were entitle to dictate when their decree should be applied.
Index to Revach for Maseches Kerisus