One who touches a sheretz, or semen, or [one who touches] that which contracted tumah from a corpse, or [one who touches] a metzora during the days of his counting, or purification water of an amount insufficient for sprinkling, or an ani-mal carcass, or the [contaminated] saddle [of a zav] contaminates one and invalidates one.  This is the rule: Any-thing that touches one of the avos hatumah [listed] in the Torah contaminates one and invalidates one, except for a person. Once it sep-arates, [it also] contaminates one and invalidates one.

A man who has discharged semen is like one who has touched a sheretz, and a man who has cohabited with a niddah is like one who has touched a corpse. However, a man who has cohabited with a niddah has a stringency over [one who has touched a corpse], for he contaminates a couch and seat [with a] light form of tumah [enabling them] to contaminate food and beverages.

These invalidate terumah: One who eats food which is a rishon [letumah], and one who eats food which is a sheni [letumah], and one who drinks liquids that are tamei; one whose head and the greater part of his body enter into drawn water, and a tahor person [in the event that] three login of drawn water fall upon his head and the greater part of his body; and a scroll [of Scripture], and [unrinsed] hands, and a tevul yom, and food and utensils that became contaminated by [tamei] liquids.

[If] one gathered portions of challah with the intention of separating [them later], and they clung together, Beis Shammai say: [It is considered] a connection in regard to a tevul yom. But Beis Hillel say: [It is] not [considered] a connection. Slices of dough that cling to one another, or loaves that cling to one another, [if] one baked a flat cake on top of [another] flat cake [and they became stuck together] before they have formed a crust in the oven, froth of water that is hollow the first froth of split beans [porridge], and the froth of new wine, R’ Yehudah says: The same applies to [froth] of rice. Beis Shammai say: [It is considered a] connection for a tevul yom. Beis Hillel say: [It is] not [considered] a connection. However, [Beis Hillel] agree in [the case of] all other sources of tumah, whether light or severe.