Negaim, Chapter 7, Mishnah 1. Until now we have been dealing with the beheres itself, its measurements and its simanei tumah. This Mishnah takes up a different question: which parts of a person's body are altogether outside the parshah of beheres, so that even a full-sized white discoloration appearing there carries no tumah.
The opening words set the agenda: "Eilu mekomos ba'adam she'einam mitam'in babeheres" - the following are the spots on a human body over which a beheres has no power to bring tumah.
The inner surfaces
"Toch ha'ayin, toch ha'ozen, toch hachotem, toch hapeh" - the inside of the eye, the inside of the ear, the inside of the nose, the inside of the mouth. The inside of the eye means the skin one sees when a person pulls down the lower lid or lifts the upper lid, as when something has gotten into the eye; that skin is exempt from beheres. So too the inner surfaces of the ear canal, of the nostrils, and of the mouth.
And what of the lips? The Tosfos Yom Tov points to an explicit ruling in the Tosefta, quoted also by the Rosh, that odem sfasayim, the reddish flesh of the lips, receives the same treatment as toch hapeh. He adds a reason for it from the Kesef Mishneh in Perek Vov of Hilchos Tumas Tzoraas, citing the Mahari Korkos: the Torah keeps repeating the phrase "or besaro," the skin of his flesh, and that very derivation also removes kaf haregel, the sole of the foot, from the parshah. Both are places that do not ordinarily meet the eye, since in the normal way of things a person holds his lips closed.
Wrinkles, and areas hidden by posture
"Hakmatim vehakmatim shebatzavor" - the wrinkles of the body and the wrinkles of the neck. The Tosfos Yom Tov explains that the Tanna spelled out the neck in the second clause precisely in order to clarify the first: do not think that only the wrinkles of the neck are excluded, on the grounds that they are hidden away in a manner that other wrinkles are not. Wrinkles anywhere on the body are meant, including, as the Tosfos Yom Tov notes, the folds of a very heavy person whose flesh doubles over on itself. One might have argued that such a person is unusual and should not be reckoned with; the Mishnah teaches otherwise, and all such folds are outside the tumah of beheres.
"Tachas hadad uveis hashechi" - underneath the breast and inside the armpit. Think back to the Mishnah in Perek Beis, which laid out the stances in which the kohen has a person examined: a woman stands as though nursing a child and as though working at a loom, and a man as though gathering olives off a tree. Those stances fix how much of the breast region and of the underarm counts as being in view; here the Mishnah teaches that whatever stays tucked away below the breast (dad here means the breast in its entirety) and deep in the hollow of the armpit cannot contract this tumah at all.
"Kaf haregel vehatziporen" - the sole of the foot and the nail. Regarding the nail, the Rav explains simply that it is not or basar; beheres is a tumah of the skin of the flesh, and a nail is neither.
Areas governed by other parshiyos
"Harosh vehazakon" - the scalp and the beard. The Rav explains that a beheres has no effect in these places because the Torah gave them a tumah of their own: nesek, which governs those parts of the head and face where hair grows. And should the hair be lost, they pass into yet another parshah, that of korachas and gabachas.
"Hashchin vehamichvah vehakedach" - these too have their own parshiyos. Shchin refers to damaged skin resembling the aftermath of a burn but produced otherwise: by a blow, by disease, by infection and the like. Michvah is produced by an actual burn, by direct contact with something hot. Kedach is really a form of michvah; some explain the distinction as burns caused by toldos eish, something heated by fire such as hot metal, as against michvah caused by fire itself, coals and the like.
While the wound is still open
"Hamordim" - as long as these wounds are still raw. The Rav explains that this means so long as they have not healed and have not raised a kerum, a membrane of new skin over them; they are still moist and running. In that state: "einam mitam'in banegaim", they are not rendered tomei as negaim; "ve'einam mitztarfin banegaim", nor do they combine with a nega (we have already learned that shchin and michvah, similar as they are, do not even combine with one another); "ve'ein hanega poseh lesocham", a nega spreading into them does not count as pisyon; "ve'einam mitam'in mishum michyah", healthy flesh appearing in them does not render tomei as michyah; "ve'ein me'akvin es hahofech kulo lovon", and they do not stand in the way of the halachah that one whose entire body has turned white is tohor. We learned that a beheres that spreads renders a person tomei, but if it spreads to cover his whole body he becomes tohor; an unhealed shchin or michvah that the whiteness did not cover is not considered an interruption.
Once they have healed
The Mishnah continues: "Chozar harosh vehazakon shenikrechu, vehashchin vehamichvah vehakedach shena'asu tzareves, harei eilu mitam'in banegaim" - if the head and the beard went bald, and if the shchin, the michvah and the kedach healed over and formed tzareves, scar tissue, they are now rendered tomei through negaim, that is, through a beheres of the four mar'os.
Nevertheless: "ve'einam mitztarfin banegaim". The Rav explains that head and beard do not join together, and none of these areas joins with ordinary skin. If there were half a gris of nesek on the head and half a gris of nesek in the beard, or half a gris of nesek and half a gris of nega on the skin of the flesh, they do not combine; and likewise half a gris of shchin together with half a gris of michvah do not combine to make up a full gris.
"Ve'ein hanega poseh lesocham" - a beheres spreading from ordinary skin into the scalp, the beard, a shchin or a michvah is not counted as pisyon. "Ve'einam mitam'in mishum michyah" - healthy flesh standing within a nega in these areas does not render tomei as michyah.
"Aval me'akvin es hahofech kulo lovon" - but here they do stand in the way of the person becoming tohor through his entire body turning white. The Rav explains: if the tzoraas broke out over his whole body, but the head and beard that had gone bald were left over and the tzoraas did not spread there, or the shchin, michvah and kedach that had healed into scar tissue were left over, he remains tomei until the whiteness spreads over those areas as well.
Where the hairy areas are judged as ordinary skin
The Mishnah's final clause returns to "harosh vehazakon" in a particular state: "ad shelo he'elu se'ar", before any hair has come up there, as with an infant whose scalp is still smooth or a young man whose beard has not yet appeared. The same clause includes "hadidulin shebarosh ushebazakon", small tags of bare skin jutting out on the scalp or in the beard region which grow no hair of their own. All of these, the Mishnah rules, are "nidonin ke'or habasar", treated exactly like plain skin of the flesh, and they are therefore fully liable to the tumah of a beheres.