Niddah 35 - First Discharge
A male's "zivah" discharge is usually a sign of a particular internal ailment, and some say, it is a spiritual disease, just like a "metzora" - leper - was a spiritual ailment. However, occasionally it can be caused by one of the seven conditions: food, drink, carrying a load, jumping, illness, or a sight or thought of a woman.
Rav Huna said that even when it is caused by a stimuli, it has all the laws of a regular zivah, and causes one to be ritually impure, just like semen emission, based on the Torah phrase, " This is the law concerning the zav and one from whom semen was emitted ." Rav Huna's opinion is challenged with four different challenges, but he successfully answers all.
So how is zivah defined? Rav Huna gives the criteria: it is similar in consistency to water of barley dough; it issues from a limp organ, whereas semen issues from an erect one; it is runny and resembles the white of a spoiled egg, whereas semen is viscous and resembles the stark white of an unspoiled egg.
Definition: Niddah and Zavah Cycles
A woman's initial monthly discharge renders her a niddah. Seven days after that she may immerse in a mikveh and be again permitted to her husband.
The next eleven days after that are potential "zivah" days. Any discharge during these days renders her a "zavah." If the discharge lasted for one or two days, she is called "minor zavah" and needs only to wait for another day free of discharge, and can go to a mikveh. However, three days of discharge render her a "major zavah." She needs to observe seven clean days, immerse in a mikveh, and in the time of the Temple bring an offering. After that, the new cycle begins, where the next discharge will render her a niddah.
This is the Torah law, but in later generations, due to the difficulty of observing the day counts of niddah and zivah, the custom has become to treat any discharge as requiring seven clean days after it.
Art: Gilbert Gaul - Man Carrying Sticks at Dusk