Reference for Menachot 48:12

קמץ מן ראשון שניהם אינן נאכלין

One might prove it, however, from the subsequent [Mishnah] which reads: R'Jose agrees that where two sheets lay folded one above the other and one that had an issue sat upon them, the upper has contracted midras uncleanness, and the lower has contracted midras uncleanness and also uncleanness by reason of contact with midras uncleanness.

Jastrow