Negaim, Chapter 6, Mishnah 1. Our mishnah completes a theme that has run through the discussion of sofek nega'im: doubtful cases in tzora'as, and when such a doubt is resolved leniently and when it is resolved strictly. The governing principle is this: "Kol sofek nega'im b'tchilah tohor, ad shelo nizkak letum'ah", every doubt in nega'im at the outset, so long as the person has not yet become bound up with tumah, that is, so long as no hachlatah has been pronounced upon him, leaves him tohor. "Mishenizkak letum'ah, sfeiko tomei." But once he has been declared a metzora muchlat, every doubt that arises afterwards regarding his status is resolved as tomei, for he stands with a chazakah of tumah, and a doubt cannot remove him from it. Our mishnah illustrates the second half of that rule.
The case
The mishnah's own language: "Mishenizkak letum'ah", once a person has been bound over to tumah, "sfeiko tomei." It then asks, "Keitzad?", how does such a case look? "Shnayim sheba'u eitzel kohen": a pair of men presented themselves for examination, "bizeh beheres kegris", the first carrying a beheres exactly a gris across, which is the smallest measurement that qualifies as a nega, "uvizeh kesela", while his companion carried one as wide as a sela, a noticeably larger mark. The kohen closed both of them up for a week of hesger, so that when the seven days ran out he could see whether either mark had undergone piso'yon, spreading.
"Besof shavu'a", when the week of hesger had run its course, and this is exactly the moment at which piso'yon takes legal effect, the kohen found "bizeh kesela va'od": the first man's mark now measured a sela with an additional area beyond it; "uvizeh kesela va'od", and the second man's mark measured the same. Each of them had unmistakably grown. The one who had entered with a sela now had a sela and more, which is a plain piso'yon. And the one who had entered with a gris had grown even further; a gris does not ordinarily stretch out to a sela within seven days, yet his had pushed past a sela. "Shneihem temei'im": each is pronounced tomei, and each becomes a metzora muchlat. This is precisely what the rule intends by a man who has been drawn into tumah: both are now held fast by tumah, each on the strength of the spreading established in his own case.
The doubt that arises afterwards
The mishnah continues: "Af al pi shechazru", even if the marks reverted, "lihyos kesela, shneihem temei'im." When the next week was over the kohen came to inspect them again, as he must with a muchlat, and found that each of the two spots had contracted until it measured precisely a sela. Weigh what that means for each man on his own. For the one whose original mark was a sela, the spreading has disappeared; he stands exactly where he began, and by right he should be released from his tumah. For the one whose original mark was only a gris, a sela still counts as growth, so his piso'yon remains in force and he stays a muchlat. The trouble is that the two have become mixed up with one another, and no one can any longer say which man is which. Since each already holds the status of a muchlat, and the uncertainty arose only after they had been caught by tumah, no doubt is able to release either of them. Both are left tomei.
"Ad sheyachzru lihyos kegris." Purification becomes available to them only if both marks shrink until neither is larger than a gris. At that point nothing remains to be clarified: whichever of the pair had started out with a gris is now demonstrably free of any spreading at all, and this holds all the more for the man who started out with a sela. With the uncertainty dissolved, both of them may be declared tahor.
The closing words
"Zeh she'amru: mishenizkak letum'ah, sfeiko tomei." The Mishnah signs off by pointing to this very case as the illustration of the principle stated by the Chachomim. A metzora who has already been declared muchlat on the basis of a genuine piso'yon, and who then becomes mixed up with another muchlat so that we can no longer tell which of them still carries his spreading and which of them should now be released, is not freed by the doubt. Both remain in their tumah until the facts themselves make the doubt disappear. Before hachlatah a doubt leaves a man tohor; once he has been drawn into tumah, his doubt is tomei.