Kelim, Chapter Twenty-Three, Mishnah Four
1) A bier, the mattress and the pillow of a corpse are susceptible to the uncleanness of midras.
2) A bride’s stool, a midwife’s stool, and a launderer’s stool on which he piles the clothes:
a) Rabbi Yose says: it is not regarded as a seat.
Section one: The fact that these three things are used for a dead body does not make them susceptible to midras uncleanness. However, the Tosefta explains that women sit on these when they wail over the dead. Therefore they are considered seats and they are susceptible to midras impurity.
Section two: These stools are not sat upon for comfort, just so that one doesn’t have to be on one’s feet. The bride sits in the chair only as part of the bridal procession. The midwife sits on the stool so that she may assist in the birth. The launderer sits on the stool while he launders and folds the clothes. Since these are not used for comfort, they are excluded from being susceptible to sitting impurity.