Nazir

R. Hisda, citing Rab, said: [A priest] if his father was decapitated, must not defile himself for him, For what reason? The text says for his father,  meaning when he is whole and not when he is defective.  R. Hamnuna said to him: In that case, suppose [the father] were travelling through the valley of 'Araboth  and robbers cut off his head, would you also maintain that [the son] is not to defile himself for him?  — He replied: You raise the question of a meth mizwah!  Seeing that we consider it his duty [to defile himself under such circumstances] to strangers,  how much more so is this true of his father! But is this considered a meth mizwah? Has it not been taught: A meth mizwah is [a corpse] with none to bury him. Were he able to call and others answer him,  he is not a meth mizwah;  and here this man has a son?  — Because they are travelling on the road, it is as though he had none to bury him. An objection was raised [from the following]: [It has been taught,] For her may he defile himself  signifies that he may defile himself for her herself but not for one of her limbs; for he may not defile himself for a limb cut off [even] from his father  whilst still alive; but he may search for a bone the size of a barleycorn.  Now what means 'he may search for a bone the size of a barleycorn'? Surely that if there is a small part missing [he may nevertheless defile himself]?  — No. The author of that statement is R. Judah. For it has been taught.' R. Judah said that he may defile himself for her, but not for her limbs; for he is forbidden to defile himself for limbs severed from his father whilst still alive; but he may defile himself for limbs severed from his father after death. But R. Kahana taught amongst [the Baraithas of] R. Eliezer b. Jacob [the following one]: 'For her may he defile himself,' but he must not defile himself for limbs, thus excluding an olive's bulk of [the flesh of] a corpse, or an olive's bulk of nezel  or a spoonful of rakab.  It might be thought that he is also forbidden to defile himself for the spinal column, or the skull, or the greater part of the bodily frame [of his sister's corpse]  or the majority [of its bones],  but since it is written, and say unto them,  it follows that Scripture has permitted you an additional defilement.