A baheres the size of a gris that contained a michyah less than a lentil — [if] the baheres expanded, it becomes tamei; [if] it receded, it becomes tahor. [If] the michyah expanded, [the baheres] becomes tamei. [If the michyah] receded, R’ Meir renders it tamei and the Sages render it tahor, because a nega does not expand inwards.

A baheres larger than a gris contained more than a lentil of living skin — [if] they grew or receded, [the baheres] is tamei, as long as they do not recede below the minimum size.