מסכת כלים

פרק יח משנה ה

NB:  The bed of the mishna was made of four boards and four leg posts.  Two long boards went along the sides, and two short boards were at the ends of the bed.  The two ends of each of the four boards were held by a socket in a leg post.

A bed

that was tamei midras (from having borne the weight of a zav, zavah, niddah or yoledes),

if a short board was removed

and two legs (that were on either end of that short board),

it is tamei (as the bed can still be slept upon, even though it is now tilted downward on the end from which the legs and board were removed);

if a long board and two legs (that were on either end of it were removed)

it is tahor (as the bed is now unusable, being that it is now titled to its side);

Rabbi Nechemie rules that it is tamei (he held that since it could be propped up against a wall or on another object, the bed is not considered broken).

If two diagonal tongues were cut off (these tongues were wooden pieces that were under each of the legs),

if two legs are cut off

(one handbreadth from each) diagonally

or one lowered [the bed to a height] less than one handbreadth (in this case, the middle of the bed will sag on to the groung)

it is tahor.

A bed

that was tamei midras (from having borne the weight of a zav, zavah, niddah or yoledes),

if a long board broke and one fixed it

it is tamei midras.

If the second [long board] broke and he fixed it (after having replaced the broken first board)

but is tamei from contact with midras. (in other words, the bed is no longer a progenitor, an av hatumah, but is now one level below that, a rishon, because each component of the bed, in addition to its status as tamei midras for being a bed, had a separate status as an item connected to something tamei midras, which was never lost as they were always a part of a usable utensil);

If he did not have a chance to fix the first board

before the second board broke

it [the bed] is tahor (completley, because while missing both long boards, it was unsuitable for use, and so lost all tumah).