Rambam - 1 Chapter a Day

Uterine bleeding of a nidah, a zavah, or a woman in childbirth, imparts impurity whether it is moist or dry. Nevertheless, the discharge of a zav, his saliva, and his semen impart impurity only when moist. If, however, they are overly dry, they do not impart impurity.

To what extent must these substances be dry not to impart impurity? If they would return to their natural state after being soaked in lukewarm water for 24 hours, they impart impurity as if they were moist. If they would not return to their natural state after this, they are considered as having been dried out, even if the water was lukewarm at the outset even though it was not lukewarm at the end of the 24 hour period. All of these matters are part of the received tradition.

When flax was spun by a woman in the nidah state, one who moves it is pure. If it was moist, it imparts impurity because of the saliva from her mouth.

When a zav places his mouth on a cup and then changes his mind and decides not to drink from it, one who moves the cup remains pure. If the zav drank even the slightest amount from it, a person who moves it is impure because of the liquid from the mouth of the zav.

When a zav bites into a piece of bread or an onion, a person who moves them is considered pure. If he bites into a zucchini or a cucumber, one who moves them is impure, because of the liquid from the mouth of the zav which becomes mixed with them.

When the shells of beans and vetch were cut off by a gentile, one who moves them is impure, because gentiles are considered like zavim in all contexts, as will be explained. The ruling concerning shells in the marketplace depends on the majority.

When impure blood becomes mixed with water, the entire mixture is pure if there is no appearance of blood. If such blood becomes mixed with pure blood and/or with wine, we consider the wine and the blood as if they were water.

Similar laws apply if impure saliva becomes mixed with water. If the saliva remains a viscous entity as is its natural state, it is impure. If it is reduced to nothing in the water and it is no longer visible as a distinct entity, everything is pure. If it becomes mixed with other saliva, we consider the pure saliva as if it was water.

Similarly, when the urine of such an impure person becomes mixed with water, if it is no longer visible as a distinct entity, the entire mixture is pure. If not, it is impure. If it is mixed with wine or pure urine, we consider the wine or the pure urine as if it was water.

If the urine of a Jew becomes mixed with the urine of a gentile, the ruling is determined by the majority. What is implied? When there is a urinal into which both gentiles and Jews would urinate, if the majority of those who use the urinal are gentiles, all its contents are impure. If the majority are Jewish, all its contents are pure. If equal numbers use it, all its contents are impure. Similarly, if the urine of one gentile is mixed with the urine of one Jew, the ruling is determined by the majority.

Urine can be borrowed from Jews in all situations. We do not suspect that it is from a nidah, for Jewish women were not suspect to save their urine when in the nidah state.

When a urinal into which a zav or a zavah would urinate was washed once or twice, the fluid with which it was washed is deemed impure. After the third washing, whether it was washed with water or other urine, the fluid is pure, because it can be assumed that none of the impure urine remained.

When at the conclusion of the seven spotless days she is required to count, a zavah felt that she had already begun to urinate, but nevertheless contained herself, descended to a mikveh immersed herself, and only urinated after the immersion, the status of the urine is in doubt. It is unresolved whether we consider the urine as if it had emerged originally while she was a zavah or after it actually emerged when she is pure. Similarly, if a gentile woman who had already begun to urinate, but nevertheless contained herself, converted, immersed herself, and only urinated after the immersion, the status of the urine is in doubt. It is unresolved whether we consider the urine as if it had emerged originally and it is considered as the urine of a gentile woman or after it actually emerged, and is considered as the urine of a pure Jewish women.

Canaanite maidservants and servants contract impurity due to zivah, nidah, and childbirth, like Jews do. Gentiles, by contrast, do not contract impurity; not through zivah, nidah, or childbirth according to Scriptural Law, as can be inferred from Leviticus 15:2 which states: "Speak to the children of Israel and tell them: 'A man should he experience a discharge.'" Implied is that the children of Israel contract impurity through zivah, but not the gentiles.

Our Sages, however, decreed that all gentiles impart impurity like zavim in all contexts, both males and females, provided the male is nine years old or more and the female is three years old or more. They did not decree that children under these ages contract impurity, for the primary reason for the decree is that a Jewish child will not be involved in sodomy with gentiles and there is no concept of sexual intimacy for children of younger ages.

When this decree was instituted, they did not decree against the semen of a gentile. Instead, the semen of a gentile is pure, as is its status according to Scriptural Law. Why was a decree not instituted to render it impure? To make it known that the gentiles' impurity is of Rabbinic origin. For everyone knows that if their status as zavim was Scriptural in origin, their semen would be impure like the semen of a zav. And since they know a gentile's impurity is of Rabbinic origin, they will not burn terumah and sacrificial food to which they imparted impurity.

Thus we can infer that all of the following: a gentile male's zav discharge, a gentile woman's nidah blood, her zivah blood, and the blood that comes at childbirth, a gentile man and a gentile woman, even though they are pure from any uterine bleeding and discharges, the saliva of gentiles, their urine, the couches on which they lie, the saddles on which they ride, and one who has relations with a gentile woman are all primary sources of impurity according to Rabbinic Law.

Therefore, one is not liable for entering the Temple or partaking of sacrificial food if one contracted impurity from one of these sources, nor is terumah burnt if it contracted impurity from such a source. All of them do, however, impart impurity to people and implements through physical contact and impart impurity to a person when carried as a zav does in all contexts. It is just that the impurity is of Rabbinic origin, as stated above.

Blood from a gentile woman's uterine bleeding is considered as her saliva and her urine and it imparts impurity when moist, but not when dry.