Kelim, Chapter Eighteen, Mishnah Six
Our mishnah continues to deal with a bed that has contracted midras impurity. In order to understand this mishnah we should note that there is a difference between “midras impurity” and “contact with midras.” Midras impurity is a “father of impurity” and it defiles other things. “Contact with midras” is a first degree impurity and its defiling powers are limited.
A bed that had contracted midras impurity:
1) If a long side of it was broken and then he repaired it, it still retains its midras impurity.
2) If the second side was also broke and then he repaired it, it becomes pure from midras impurity but is unclean by virtue of contact with midras.
3) If before one could manage to repair the first side the second one broke, the bed becomes clean.
Section one: If the long side broke and then he repaired it, the bed still retains its madras impurity.
Section two: However, if the second long side broke and then he repaired it as well, the bed sheds its original midras impurity because it is considered new. In other words, when does a repaired bed become a new bed? When both long sides were fixed.
Although the original midras impurity is gone, the bed does have a lesser degree of impurity because it was in contact with something that had midras impurity. I shall explain. When the first long side was repaired and put back into the bed it contacted impurity from the rest of the bed. And even when the second side broke, and the bed lost the impurity it had by being in contact with a zav, it does not lose the impurity it had by being in contact with other impure parts of the bed. This is because the bed continued to be usable.
Section three: If both sides were broken at the same time, then the bed is completely pure, even from contact with midras. This is because when both sides are broken, the bed cannot be used.