Masechet Chullin, Perek Tet, Mishnah. The Mishnah is now going to talk about the Tum'ah (ritual impurity) of bones and marrow bones. The Mishnah says, “Kolit ha-met ve-Kolit ha-mukdashim”—the marrow bones of a dead person and the marrow bone of a korban (offering) that was pigul (disqualifying intent) or notar (left over past its time)—“ha-nogea bahen bein setumim (closed) bein nekuvim (punctured) Tamei (impure).” If somebody touches them, whether they were closed or punctured, that person is Tamei, as we will continue to learn in the Mishnah. A marrow, a piece of marrow inside a bone, cannot make something Tamei unless the bone was punctured. Here, though, it doesn't need to be punctured because the bone itself is Tamei, and that's what's emitting the Tum'ah with a dead person or a korban of a pigul or notar animal. The bone is what's causing the Tum'ah. The Torah tells us clearly that the bone of a dead person is Tamei, and when it comes to pigul and notar, Chachamim (Sages) made a decree that if you touch this type of meat, the Kohen (priest) would become Tamei. The idea behind that is that they wanted to make sure the Kohen was going to be very on top of making sure the korban doesn't become pigul or get left uneaten and become notar. So we extended the decree onto the bones that are part of the korban as well. If someone touches them, they become Tamei.
If somebody touches a marrow bone of a Nevelah (animal carcass) or a marrow bone of a Sheretz, a creepy crawler that's mentioned in the Torah—there are eight of them—while they're closed, since only their meat, not the bones, is Tamei, then there's no way to touch the meat inside because the bone was all closed up; it wasn't opened, it wasn't punctured. But if they were punctured, even a little bit, a person becomes Tamei from touching the meat or marrow inside by putting even one of his hairs through the hole to touch the meat. The bones make a person Tamei by touching them, since the bones are considered the Shomer (protective covering) of the meat, which is on the inside. So once the marrow or meat on the inside, which is Tamei, is accessible, the bones become its Shomer, and they also transfer Tum'ah.
The ruling that a marrow bone that's closed off doesn't transmit Tum'ah in certain situations is based on the ruling that something that cannot transmit Tum'ah by being touched cannot transmit Tum'ah by being carried either. Here we'll give the background and basis for this halacha (Jewish law): minayin she-af ba-masa (carrying)—where do we know that something that cannot transfer Tum'ah by being touched automatically cannot transfer Tum'ah by being carried? We learn it from what the Torah tells us about a Nevelah, where the pasuk (verse) says, “ha-nogea ve-ha-noseh”—someone who touches and someone who carries—they should become Tamei, which we're comparing carrying to touch. That means: “et she-ba lichlal maga (touch) ba lichlal masa”—something that could create a state of Tum'ah while being touched could come to a state of Tum'ah by being carried; “lo ba lichlal maga lo ba lichlal masa”—but something that does not come to the state of making Tum'ah through touch, like the marrow of a closed bone, also does not come to the point where it could become Tum'ah through carrying.