These convey tumah via touch or carrying, but do not convey tumah via ohel: a bone the size of a barleycorn; the land of the nations; a field in which a grave was plowed over; a limb [severed] from a corpse or a limb [severed] from a living body that is lacking sufficient flesh [to heal]; [and] a spine and a skull that are incomplete. How much is considered ‘‘missing’’ in the spine [for it to be considered incom-plete]? Beis Shammai says: Two vertebrae. But Beis Hillel says: Even one vertebra. And of the skull? Beis Shammai says: As [large as the hole] made by a gimlet. But Beis Hillel says: An amount which, if removed from a living person, would cause him to die. Which gimlet are they referring to? The small one used by physicians — these are the words of R’ Meir. But the Sages say: The large gimlet of the [Temple] chamber.

The cover of a grave and its support convey tumah if touched and through ohel, but not if they are carried. R’ Eliezer says: They do convey tumah if they are carried. R’ Yehoshua says: If underneath them there is earth from the graves, they convey tu-mah when carried, and if not, they do not convey tumah when carried. What is a support? That upon which the cover [itself] rests. However, a sup- port for a support is tahor.

These items are tahor if they become diminished: an olive’s volume of a corpse; an olive’s volume of netzel; a ladleful of corpse powder; a quarter [-log] of blood; a bone the size of a barleycorn; and a limb, [that was severed] from a living person, whose bone is incomplete.

A spine and a skull from two corpses; a quarter [-log] of blood from two corpses; a quarter [-kav] of bones from two corpses; a ‘‘limb’’ [severed] from two corpses; and a ‘‘limb’’ [severed] from two living persons — R’ Akiva declares [all these cases] tamei, but the Sages declare [them] tahor [from tumas ohel].