Kelim, Chapter Nineteen, Mishnah Six
1) If a mattress was wrapped around a bed and a corpse touched them, they are subject to a seven-day uncleanness;
a) If they are taken apart they are still subject to a seven-day uncleanness.
2) If a sheretz touched them they are subject to an evening uncleanness;
a) If they are taken apart they are still subject to evening uncleanness.
3) A bed from which the two longer sides were removed and two new ones were prepared for it but the original sockets were not changed:
a) If the new sides were broken the bed retains its uncleanness,
b) But if the old ones were broken it becomes clean, since all depends on the old ones.
Section one: In this case the mattress is impure because it too came into contact with a corpse, and not just because it became part of a bed that had corpse impurity (as in yesterday’s mishnah). Therefore, even when it is taken apart from the bed, it still retains its corpse impurity.
Section two: The same is true if the bed and mattress become defiled with evening uncleanness through contact with a sheretz. Since the mattress was also defiled, it retains its impurity even when removed from the bed.
Section three: One removed the two longer sides of the frame of a bed and he made new ones to replace them. But since he did not change the sockets of the bed, if the new ones break he can still replace them with the old ones. If he puts the new ones in and they break, the bed regains its old impurity. In other words, it’s not a new bed if the old bed can still be reconstituted.
But if the old ones are broken, then the bed cannot be reconstituted and it is pure.
As the mishnah notes, the purity of the bed depends on the existence of the old ones, not the new ones.