For the source text click/tap here: Avodah Zarah 68
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Rav Sheishes answered: Usually, Rav holds that if a forbidden item imparts a detrimental taste to the mixture, it is permitted. However, a mouse is a novel law, as people think it is repulsive, yet even so, the Torah specifically forbids it. It therefore forbids other things as well even though it imparts a detrimental taste to the mixture. The Rabbis asked Rav Sheishes: If this is so, whether it is moist or dried out it should transmit tumah!? However, the Mishna says that it only transmits tumah if it is moist (i.e. alive in normal conditions) and not if it is dried out!?
The Gemora replies: According to this, semen should also transmit tumah both when it is moist and dry. However, the Mishna says it only transmits tumah when it is moist. It therefore must be that the Torah only said it transmits tumah when it is in a form where it can fertilize, as opposed to when it is dry.
We explore the transition from Bible to Talmud in attitudes to semen and seminal emission.