Makhshirin, Chapter Six, Mishnah Seven
1) The following cause neither uncleanness nor susceptibility to uncleanness:
2) Sweat, rotten secretion, excrement, blood issuing with any of these, liquid [issuing from a child born in the] eight month.
a) Rabbi Yose says: except its blood.
3) [The discharge from the bowels of] one who drinks the water of Tiberias even though it comes out clean.
4) Blood from the slaughtering of cattle and wild animals and birds that are unclean, and blood from bloodletting for healing.
5) Rabbi Eliezer declares these unclean.
6) Rabbi Shimon ben Elazar says: the milk of a male is clean.
Section one: These liquids don’t cause either susceptibility or uncleanness. Some of them are still pretty yucky though.
Section two: Rotten secretion is something like pus. Blood that comes out with pus or with excrement doesn’t cause impurity or susceptibility.
The rabbis considered a child born at 8 months to be one who would surely die. The child is in a sense considered dead even before he actually dies (remember they had no way to really care for such children). Liquid such as urine and spittle that comes from the child before he dies does not cause impurity or susceptibility, as it would for a viable child. Rabbi Yose says that the blood of such a child does cause impurity.
Section three: I guess drinking the waters of Tiberias will make you sick. While the water causes susceptibility once it passes through a person’s body and comes out the other end (not as urine) even if it simply passed right through him, it doesn’t cause susceptibility.
Section four: As we learned in mishnah five, only the blood from slaughtering a clean animal causes susceptibility. Also blood from a bloodletting that he wants to let another animal drink. If he is just bloodletting for healing then it doesn’t cause susceptibility.
Section five: Rabbi Eliezer holds that all of these liquids do cause susceptibility.
Section six: Evidently men can occasionally secrete small amounts of milk from their breasts. Rabbi Elazar says that such milk is pureit doesn’t cause susceptibility.