Zevachim Daf 79 זבחים דַף 79

Rava summarizes the Biblical rules of bitul: אמור רבנן בטעמא – the Rabbis said that the halachah of one type of mixture is determined by flavor; ואמור רבנן ברובא – the Rabbis said that another type of mixture is determined by majority, ואמור רבנן בחזותא – and the Rabbis said that a third type of mixture is determined by appearance. He explains: מין בשאינו מינו בטעמא – the law of one kind of food mixed with something not its own kind is dependent on flavor (i.e., if forbidden flavor is discernible in the mixture, it is Biblically prohibited, despite being a minority of the mixture). מין במינו ברובא – The law of one kind of food mixed with something of its own kind is determined by majority (i.e., the forbidden substance becomes בטל by a simple majority of permitted food). היכא דאיכא חזותא במראה – Where there is a law related to appearance, such as tevilah in a mikveh (which does not depend on taste), the mixture’s status is determined by appearance.

On the previous Daf, Reish Lakish said that איסורין nullify each other in a mixture. Rebbe Elazar disagrees: כשם שאין מצות מבטלות זו את זו – just as mitzvos do not nullify one another , כך אין איסורין מבטלין זו את זו – so too forbidden items do not nullify one another. Rather, ביטול only applies to a mixture of permitted and forbidden substances. The source that mitzvos do not nullify each other is Hillel, as a Baraisa states: אמרו עליו על הלל הזקן – they said about Hillel the Elder שהיה כורכן בבת אחת ואוכלן – that he would wrap them (the פסח, the מצה, and the מרור) together and eat them, because the passuk says: על מצות ומרורים יאכלוהו – together with matzos and bitter herbs they shall eat it (the pesach). We see that Hillel was not concerned that the flavor of the מרור would nullify the flavor of the matzah.

The Mishnah on the previous Daf taught that if korban blood was mixed with blood of פסולים – invalid [korbanos], it is all spilled into the אמה – canal. The same applies to blood mixed with an animal’s דם התמצית – last blood (after the lifeblood ceases to flow). Rebbe Eliezer rules the blood valid. All agree that if the Kohen applied the דם without asking, it is valid. This machlokes is explained in two ways: Rav Zevid says they argue about גוזרין גזירה במקדש – whether we make decrees in the Mikdash. The Tanna Kamma says they decreed to spill out blood mixed with invalid blood, even where there is not enough to nullify the valid blood, to prevent a mixture from being used where there is enough invalid blood to nullify the valid blood. Rebbe Eliezer says they do not disqualify korbanos to prevent such mistakes. Rav Pappa says all Tannaim agree we make such גזירות in the Mikdash, but argue about דם התמצית מצוי לרבות על דם הנפש – whether it is common for the last blood to be more than the lifeblood. The Tanna Kamma considers it common, so a decree was enacted, and Rebbe Eliezer holds it is uncommon, so no decree was necessary. According to Rav Pappa, Rebbe Eliezer only argues in the case of דם התמצית.