In alchemy - זרע Zera - Entity of Semen - in a male or female sexual organs, is the crystallization of שמים-Shamayim, the fiery waters of Genesis. Thus, זרע Zera - Entity of Semen is the outcome of the two polarities of אש-Esh fire, namely, איש-Ysh man and אשה-Ysha woman, from their - ראש-Rosh - head.
So, - ראש-Rosh - is אשר-Asher, the fire of Binah, the Holy Spirit, who abides in - זרע Zera - Entity of Semen - the crystallization of - שמים-Shamayim - the Genesic fiery waters of the earth, our physicality.
And when a [איש-Ysh] man [reaches orgasm] emits [זרע Zera] semen from him, then he has to bathe with [Genesic] water all his flesh, and be unclean until the evening.
And a [אשה-Ysha ] woman who copulates, with a [איש-Ysh] man, emitting [זרע Zera] semen [reaching orgasm], both have to bathe with [Genesic] water, and be unclean until the evening. Leviticus 15:16, 18
It is written, 'and the evening and the morning were day, one.' The evening arises out of darkness [uncleanness] and the morning from light [of שמים-Shamayim] and from the conjunction [of woman and man] the day is formed." - Zohar