Dostay of the village of Yasma was of the students of Beis Shammai, and [he] said: I heard from Shammai the Elder that it never conveys tumah until it is like [the volume of an] egg.

And in what [case] did they say: “Any [agent] that leavens, spices, or generates a prohibited mixture of chullin and terumah is to be treated with stringency”? A type in a like type. To be treated [sometimes] leniently and [sometimes] stringently? A type in an unlike type. How so? Sourdough of wheat that fell into a dough of wheat, and there is enough of it to leaven, whether there is enough to nullify in one hundred and one and whether there is not enough to nullify in one hundred and one, it is forbidden. [If] there is not enough to nullify in one hundred and one, whether there is enough of it to leaven or whether there is not enough of it to leaven, it is forbidden.