Two nesakim, one inside the other, are separated by a row of hair. [If the row of hair] split in one place, [the affected person] is tamei. [If it split] in two places, he is tahor. How wide must the opening be? Two hairs wide. [If the row of hair] split in one place [the width of] a gris, [the nesakim] are tahor.

One who had a nesek with blond hair [is confirmed] tamei. [If] black hair grew [in the nesek, the afflicted person] becomes tahor. Even if the black hair falls out, he remains tahor. R’ Shimon ben Yehudah says in the name of R’ Shimon: Any nesek that was once tahor will never be tamei. R’ Shimon says: Any blond hair that was once tahor will never again be tamei.