Niddah 55: Wet and Dry Sources of RItual Impurity

We begin a new Perek today and we carry on with the Mishna that begun yesterday.  We had learned that menstrual blood and the flesh of a corpse impart ritual impurity when they are moist.  Even if they are dried, the ritual impurity returns if the item is soaked in water for twenty-four hours.  

The rabbis discuss other sources of ritual impurities that can be transferred when wet or dry.  One of the examples is discussion about the secretions of a zav, a man with an STI.  The rabbis determine that his semen, mucous from the mouth or nose and spittle can impart ritual impurity only when wet.  

Why aren't tears one of the wet secretions that impart a zav's ritual impurity?  The Gemara repeats Rav's words: He who wishes to blind his eye shall have it painted by a gentile, and Levi stated that he who wishes to die shall have his eyes painted by a gentile.

Steinsaltz teaches us about kohl, the black-blue makeup used in Talmudic times.  Ti was used around the eyes to make them appear larger.  It was also used as medicine.  In the Talmud Yerushalmi, we learn that Rav did not use kohl but Levi did.  Kohl was made of mercury and it may have been used as a poison.