Comentario citado sobre Levítico 15:5

A general principle was stated by Rabbi Joshua: anyone that defile garments while still in contact [with their source of uncleanness] also defiles foods and liquids so as to become [unclean] in the first grade, and the hands so that they become [unclean] in the second grade; but they do not defile people or earthenware vessels. Rabbi Joshua formulates a general principle meant to aid in determining the level of impurity of certain people mentioned in the Torah. The Torah says about certain people, for instance one touched by a zav, that he must wash his clothes (see for instance Leviticus 15:5-11, 21-22, 27). When he is actually touching the zav or something the zav laid upon, his level of impurity is relatively high. He defiles food and liquids so that they have first degree impurity. And if he touches the hands of another person he gives them second degree impurity (we will return to the topic of hand impurity in the next tractate). However, he doesn't defile people or earthenware vessels, as was stated in section one.

עושה משכב ומושב – all utensils that are under it, and even if they are one hundred, defiles man and defiles clothing, as it is written (Leviticus 15:5): “Anyone who touches his bedding shall wash his wash his clothes,[bate in water, and remain impure until evening].”

A zav defiles the objects that are lain upon (or sat in five ways, so that they defile people and garments: by standing, sitting, lying, hanging or leaning. A zav can defile things that are lain upon or sat upon (such as chairs and couches) even though he hasn't touched them. The things that he defiles will then defile other people and clothing (see Leviticus 15:5-6). The five ways are: standing (he stands on the object, even if he doesn't touch it. Sitting and lying (even without touching). "Hanging" refers to a case where the zav is hanging because of the couch or chair. For instance, the chair is on one end of a balance and the zav on the other. If the zav is lifted up by the heavier chair, the chair is now impure. These five things are called "midras hazav." The chair or couch is now a "father of impurity" and it will defile other people and garments. Note that simply touching something is not sufficient he must do one of these five things.

His bedding - [from the verse] "those persons who touch his bedding" [Leviticus 15:5]. By scriptural decree, stolen bedding is excluded, in that it cannot become a primary source of impurity that is able to render people impure.