Commentary for Eduyot 1:7
בֵּית שַׁמַּאי אוֹמְרִים, רֹבַע עֲצָמוֹת מִן הָעֲצָמִים, בֵּין מִשְּׁנַיִם בֵּין מִשְּׁלֹשָׁה. וּבֵית הִלֵּל אוֹמְרִים, רֹבַע עֲצָמוֹת מִן הַגְּוִיָּה, מֵרֹב הַבִּנְיָן אוֹ מֵרֹב הַמִּנְיָן. שַׁמַּאי אוֹמֵר, אֲפִלּוּ מֵעֶצֶם אֶחָד:
Beth Shammai say: A quarter [of a kav] of the bones [of the dead], whether from two or three, [cause tent-uncleanliness. And fewer than a quarter cause uncleanliness only by touching or carrying, but not in a tent. And Beth Shammai hold that a quarter of a kav cause tumah (uncleanliness) even if they are from many dead.] And Beth Hillel say: A quarter (of a kav) of the bones of the body. [That is, from the body of one dead man and not from many dead. And, even from one dead man, there is no tumah unless there be in the quarter of a kav either] the majority of the built [i.e., the majority of the built of the body] or the majority of the number [of the bones of a man — one hundred and twenty-five, a man's bones numbering two hundred and forty-eight.] Beth Shammai say: Even one bone. [i.e., If one bone of the dead man fills a quarter of a kav, it causes tent-uncleanliness. The halachah is in accordance with Beth Hillel.]
Bartenura on Mishnah Eduyot
English Explanation of Mishnah Eduyot
And Beth Hillel says: “A quarter-kav of bones from a corpse, either from [the bones which form] the greater portion of the [body’s] build, or from the greater portion of the number [of the body’s bones].
Shammai says: “Even from a single bone.”
This mishnah begins to list disputes between Beth Shammai (the school of Shammai) and Beth Hillel (the school of Hillel). The rest of the chapter will contain disputes between these two schools.
Numbers 19:14 teaches that if a person dies in a tent things that are in the tent, including the people, can become impure, even though they have not touched the dead body. Our mishnah discusses how many bones must be in the tent for them to be considered a dead body which will cause ritual impurity.
According to Beth Shammai, a quarter-kav of bones will transmit impurity, as long as they come from at least two or three different bones. Beth Hillel agrees that a quarter-kav of bones is enough to cause impurity but they state that the bones must either come from the greater portion of the body (the hips, thighs, rib cage and spine) or from a majority of the number of bones in the body, considered to be 248. If there is a quarter-kav but they come from only one limb or many limbs but not a majority of the number or from the greater portion, they do not transmit impurity.
Shammai himself is even stricter than Beth Shammai, for he holds that a quarter-kav from one bone transmits impurity.