There are [stringencies] that apply to living skin which do not apply to expansion, and there are [stringencies] that apply to expansion which do not apply to living skin: Living skin renders tamei initially, and renders tamei with any appearance. There are [stringencies] that apply to expansion: Expansion renders tamei with any amount, renders all negaim tamei, [and renders tamei] outside the nega, which is not the case with living skin.

There are [stringencies] that apply to white hair which do not apply to living skin, and there are [stringencies] that apply to living skin which do not apply to white hair: White hair renders a boil-nega and a burn-nega tamei, [renders tamei] whether together or spread apart, whether surrounded or not. There are [stringencies] that apply to living skin: Living skin renders tamei on a bald area on either the back or the front of the head, whether changed [by the nega] or not, prevents one who turns completely white [from becoming tahor], and renders tamei with any appearance, which is not the case with white hair.

Two hairs that are turning black at the root and white at the top are tahor [i.e. they are not symptoms of tumah]; if they are turning white at the root and black at the top they are tamei. How much of the hair must be white? R’ Meir says: Any amount. R’ Shimon says: Long enough to be cut with a pair [of scissors]. [If] it is one [hair] that splits [so that it] appears to be two [hairs], it is tahor. A snow-white nega that has white hair or black hair is tamei; we are not concerned that the black hair reduces the size of the baheres [until it is too small to become tamei], because [the hair] does not have any substantive [thickness].

A baheres the size of a gris has a strip [of nega] extending from it. If [the strip] is two hairs wide, it connects the baheres to white hair or to expansion, but not to a section of living skin. Two beharos have a strip [of nega] connecting them. If [the strip] is two hairs wide, they combine, and if not, they do not combine.