The Mishna discusses the laws of nullification regarding yayin nesech (wine used for idolatry) that becomes mixed with permitted wine. It distinguishes between wine mixed with wine (min b'minu—same substance), which is forbidden in any amount, and wine mixed with water (min b'she'eino mino—different substance), which is prohibited only if it imparts taste.

Rav Dimi quotes Rabbi Yochanan as saying that if one pours yayin nesech from a barrel into a pit of kosher wine, each drop is immediately nullified upon contact. The Gemara raises three challenges to Rav Dimi's interpretation based on the Mishna, and resolves them by reinterpreting the cases in the Mishna. Rav Yitzchak bar Yosef offers a narrower understanding of Rabbi Yochanan's ruling—limiting it to pouring from a jug into a barrel, but not from a barrel into a pit.

Ravin also transmits a halakha in Rabbi Yochanan's name regarding a mixture that includes a forbidden item combined with both a similar and a different substance. In such a case, the forbidden item is nullified by the different substance (e.g., yayin nesech mixed with wine and water), while the similar substance is viewed as if it is not there. Rav Shmuel bar Yehuda also quotes Rabbi Yochanan, but there are two versions of his statement. In one version, he disagrees with Ravin and limits the ruling to cases where the different substance was present first. In the other version, his comment refers to the Mishna, and he actually agrees with Ravin.

A debate between Chizkiya and Rabbi Yochanan also concerns a case where a forbidden item is mixed with both a similar and a different substance. What is the underlying basis of their disagreement?

Rav and Shmuel dispute the position of Rabbi Yochanan and Reish Lakish regarding whether the distinction between mixtures of the same type and mixtures of different types applies universally to all prohibited items, or only to yayin nesech and tevel (untithed produce). The Gemara explains why the rabbis would have adopted a stricter approach with those two prohibitions.