We are in Chapter 2, Mishnah 1. From here on, the Mishnah begins recording testimonies from various figures from the period right after the Destruction, and the first of them is Rabbi Chanina, the Deputy Kohen Gadol. The deputy was the right hand of the Kohen Gadol and stood at his right side, and if the Kohen Gadol became tamei on Yom Kippur and could not perform the service, the deputy would take his place. Rabbi Chanina served as deputy at the time of the Destruction, and now he comes to testify about what he saw, and from his testimony we learn halachos in the coming mishnayos.
Altogether he testified to four things, and so the next three mishnayos will be devoted to them. Our first mishnah deals with matters of tumah and taharah, and it also appears in Maseches Pesachim (Chapter 1, Mishnah 6).
Background: the levels of tumah:
Tumah, which is a halachic and spiritual reality, generally spreads from an av hatumah ('av' in the sense of a source) to what the Mishnah calls a v'lad - an offspring. How does this work? If an av hatumah touches wine, the wine becomes a rishon - one level removed from the source; and if that wine touches bread, the bread becomes a sheni - two levels removed from the source. How far does this chain continue? That depends on the type of food:
Chullin and ordinary foods: reach only the level of sheni, and there is no such thing as a shelishi in them.
Terumah (the gift given to the kohen) and things whose halachic status is like Terumah (such as challah): can become a shelishi, three levels removed from the source.
Kodashim (the meat of offerings or a meal offering): can even become a revi'i, four levels removed from the source, and that is the maximum.
It is forbidden to cause kodashim or Terumah to become tamei, and we must be careful about this. On the other hand, there is an obligation that if kodashim became tamei, such as the meat of an offering, they are taken outside the area of the Beis HaMikdash and burned.
Hence the question our mishnah addresses: if tamei sacrificial meat is going to be burned anyway, may one burn meat that became tamei at the level of shelishi together with meat that is a rishon? After all, if they touch one another, the rishon will turn the shelishi into a sheni - that is, it will increase its tumah. And since one generally may not cause kodashim to become tamei, is it permitted when they are slated for burning in any case?
The language of the Mishnah: "Rabbi Chanina S'gan HaKohanim he'id arba'ah devarim" - Rabbi Chanina, the Deputy Kohen Gadol, testified to four things, and this is the first of them. "Mimeihem shel kohanim lo nimne'u milisrof es habasar shenitma bi'vlad hatumah im habasar shenitma b'av hatumah" - throughout all the years that the kohanim served in the Beis HaMikdash, they never refrained from burning meat that became tamei from a v'lad. ('V'lad' means a child, as opposed to an 'av'; in many mishnayos it refers to a rishon, and here it refers even to lower levels.) The meat became tamei from a v'lad and became a shelishi, and now it is burned alongside other meat that touched an av hatumah and became a rishon. The rishon is liable to touch the shelishi and make it a sheni, and even so Rabbi Chanina testifies that the kohanim were not concerned about this and it was permitted - "af al pi shemosifin tumah al tumaso" - even though they are adding tumah onto its tumah, that is, even though they are indeed raising its level of tumah from shelishi to sheni.
Rabbi Akiva's addition:
Rabbi Akiva teaches something even greater: not only is it permitted to raise the level by one degree, from shelishi to sheni, but it is permitted to raise it by two degrees. The case he brings deals with Terumah rather than kodashim, but the rules are identical.
Tevul yom: a person who was tamei (a zav, for example) and immersed in a mikvah that day. Until the sun sets, meaning nightfall, he is called a tevul yom, and his status is that of a sheni. Therefore, if a tevul yom touches Terumah, the Terumah becomes a shelishi - a situation that is not proper to bring about in the first place, but if it happened, it happened.
Tumah from a corpse and metal utensils: As a rule, direct contact lowers things by one level - an av touches something and it becomes a rishon, a rishon touches something and it becomes a sheni, and so on. However, with the tumah of a corpse, whose source is the avi avos hatumah - the body itself or a significant part of it - whoever is exposed to it through contact, through carrying (bearing its weight), or through ohel (being in the same room with it) becomes an av hatumah called a tamei meis, and he transmits the level of rishon to things. But there is a separate rule based on a verse: a metal utensil does not go down a level. If a tamei meis touches a metal utensil, the utensil too becomes an av hatumah and not a rishon. It follows that if the person touched a metal spoon, the spoon becomes an av hatumah, and if the spoon then touches oil of Terumah, the oil becomes a rishon.
The case in the Mishnah: a menorah holding small lamps into which oil is placed to be burned, and the lamps are made of metal rather than earthenware. If someone who is tamei from contact with a corpse touched them, the lamps become an av hatumah (a primary source of tumah). With Terumah, a kohen is permitted to benefit from its burning, and here we have Terumah oil that became a 'third degree' through contact with a tevul yom - it may no longer be eaten, but it may be burned and one may benefit from its burning. When the kohen pours that third degree oil into the metal lamp, which is an av hatumah, the oil becomes a 'first degree' through its direct contact with the av - that is, it is raised two levels at once. And this is Rabbi Akiva's point: even this is permitted. He is therefore more lenient than Rabbi Chanina, the deputy Kohen Gadol, since he permits raising the level by two degrees and not only by one.
The wording of the Mishnah: "Hosif Rabbi Akiva" - Rabbi Akiva added, and said: "Mimeihem shel kohanim lo nimne'u mehadlik es hashemen shenifsal b'tevul yom" - throughout all the years that the kohanim served in the Beis HaMikdash they never refrained from kindling Terumah oil that had been disqualified through the touch of a tevul yom. 'Disqualified' in the context of Terumah means that it became a 'third degree', the last and most removed level. "B'ner shenitma b'tmei mes" - in a metal lamp that became tamei through direct contact with someone tamei from a corpse, so that the lamp too is an av hatumah, and the third degree oil placed inside it becomes a first degree. And even so they did not refrain, "af al pi shemosifin tumah al tumaso" - even though they are raising the level of its tumah from third degree to first degree.
In summary: we learned the first testimony of Rabbi Chanina, the deputy Kohen Gadol, that when sacred items are going to be burned in any case, we do not refrain from burning them together and adding tumah to their tumah, and we learned Rabbi Akiva's addition regarding Terumah, that one may add even two levels of tumah. In practice the Rambam cites both opinions, so this leniency is accepted as the halachah.
In the coming Mishnayos we will continue with the rest of the matters about which Rabbi Chanina, the deputy Kohen Gadol, testified.