Zavim, Chapter Five, Mishnah Five
1) If an unclean person rests upon part of an object fit to lie upon, or a clean person rests upon part of an object fit to lie upon, it becomes unclean.
2) If part of an unclean person rests on an object fit to lie upon, or part of a clean person rests upon an object fit to lie upon, it remains clean.
3) Thus we find that impurity enters it and goes out of it by its lesser part.
4) Similarly, if a loaf of terumah was placed upon an object fit to lie upon [that was unclean] and there paper in between, whether it was above or below, it remains clean.
5) Similarly, in the case of a stone with scale disease it remains clean.
a) Rabbi Shimon pronounced such a case unclean.
Section one: There are two situations referred to here. In the first case most of the zav (the unclean person) is resting on part of a clean object that is fit to lie upon. In the second case, most of the clean person is resting upon part of an object fit to lie upon that has been defiled by a zav. In both cases the impurity is conveyed, either to the object in case one or the person in case two. The mishnah will explain below in section three that the impurity of the zav can enter the entire object through the small part of the object upon which the zav lies. It can also go out of the object through the small part of the object upon which the pure person lies.
Section two: But if only a small part of the unclean person is on the object or only part of the clean person is on the unclean object, then he remains pure, because the object is only defiled if it bears most of the weight of the zav (see 4:4). Similarly, the pure person is not defiled unless the impure object bears most of his weight.
Section three: This section provides the rule that explains section oneimpurity can go in and out of the object fit to lie upon even threw a small part of that object.
Section four: The word “similarly” does not really belong here. It is missing in some versions of the Mishnah.
In mishnah 3 we learned that impurity through “carriage”being carried without touchingis conveyed only to a human being by an object upon which a zav has lain. So if a loaf of terumah is either on top of an object which a zav lied upon or that object is on top of it, and there is a piece of paper separating them so that they don’t touch, the loaf of terumah remains pure. The loaf of terumah is impure only if it touches the object.
Section five: The same is true if the loaf of terumah is on top of a stone that has contracted a “nega”scale disease. As long as the paper prevents contact, the loaf is pure.
Rabbi Shimon says that in this case the loaf of terumah is impure. A stone with a nega conveys impurity through being in an ohelovershadowing. Since the stone overshadows the loaf or vice versa, the loaf is impure.