הלכה על נזיר 98:5

From the laws of the commandment is that which they, may their memory blessed, said (Nazir 49b) that there is a [type of] impurity of a dead body that if the nazirite is made impure by it, he shaves and it interrupts his earlier [tally of] days, and begins to count the days of his naziriteness afterwards [from the beginning]; and there is [another type of] impurity of a dead body for which he does not shave and it does not interrupt his earlier days. [And the latter is such,] even though it is an impurity [that makes impure for] seven [days] (characteristic of impurity generated by a dead body); because it is not said about it, "and if he becomes impure for a soul," but rather (Numbers 6:9), "And if a dead body dies upon him" - which implies [only] when he becomes impure with impurities which are from the essence of the dead body. And these are the impurities for which the nazirite must shave: for a stillborn embryo, even if its limbs have not become attached to its tendons; for a kazayit from a dead body; for a kazayit of the discarded (netsel); for the bones that make up the numerical majority of the bones, even if they do not constiture one quarter of a kav; for half a kav of bones, even if they do not constitute the majority of its structure or their numerical majority, so long as all of the bones are from one dead body and not from two dead bodies; for a backbone coming from a dead body; for the skull of one dead body; for the [detached] limb of a living person that has [enough] flesh to grow back on a living person; for half a log of blood from one dead body; and for a fist-full of rotted remains of a dead body. And what is netsel? It is flesh of a dead body that is dissolved and has become rotten liquid. And the rotten remains (rakav) of a dead person only render impure if he is buried naked in a marble coffin and he is all complete. If one limb was lacking from him or if he was buried with his cloak or in a coffin of boneware or metal, [his remains] are not [considered] rakav. And they only spoke about rakav regarding a dead body alone, which excludes someone killed, as behold, he is missing his blood. If they buried two dead bodies together or they cut his hair or his fingernails and buried them with him, or if a pregnant woman died and she was buried [with] the embryo in her innards and so [too,] if [someone] ground the dead body until it became rakav, their rakav does not render impure until [the body itself] rots on its own. And so [too,] if he became impure from a quarter [of a kav] of bones that come from the backbone or from the skull in their tent, behold it is a doubt whether he is impure.