Sifra 6.0.6

Tazria Parashat Negaim, Chapter 3

1) (Vayikra 13:11) ("It is old leprosy in the skin of his flesh. And the Cohein shall declare him tamei; he shall not quarantine him, for he is tamei.") "leprosy": This is a prototype (binyan av) for all leprosy as requiring a garis (the size of a Cilician bean, for tumah). "old": We are hereby taught that the michyah confers tumah if it preceded ([hence "old"] the se'eth). For (without the verse) would it not follow (that it should not do so, viz.): White hair is a sign of tumah, and a michyah is a sign of tumah. Just as white hair confers tumah only if it did not precede the se'eth, so michyah should confer tumah only if it did not precede the se'eth. It is, therefore, written "old," to teach us that it confers tumah if it preceded the se'eth.

2) "It (is leprosy"): This teaches us that it (also) confers tumah if it did not precede the se'eth. Now (even without the verse) would it not follow a fortiori that it does so, viz.): If white hair, which does not confer tumah if it precedes the se'eth (does confer tumah if it follows the se'eth), then michyah, which does confer tumah if it precedes the se'eth, how much more so should it confer tumah if it follows the se'eth! … It must, therefore, be written "It," to teach us that it confers tumah if it follows the se'eth.

3) See Chapter 2:6

4) But perhaps the meaning of (Vayikra 13:11) "he shall not quarantine him for he is tamei" is that a Cohein who is tamei shall not quarantine him, but a confirmed leper is quarantined (for a new eruption)! It is, therefore, written "for he is tamei." We are speaking of the inspected and not of the inspector.

5) (Vayikra 13:12) ("And if the leprosy blossom in the skin, and the leprosy cover all the skin of the plague-spot, from his head until his feet, to all the sight of the eyes of the Cohein") "blossom": This tells me only of its blossoming in all of him at once. Whence do I derive the same for its blossoming little by little? From (lit.) "if there blossom, blossom" (— in any manner.)

6) This tells me only (of blossoming similar to that in flowers), from bottom to top. Whence do I derive the same for (blossoming) from top to bottom? From "if there blossom, blossom" (— in any manner.)

7) This tells me only (of a blossoming) from an unclean plague-spot to a clean one. Whence do I derive the same for (the blossoming of) a clean one to an unclean one? From "blossom" (— in any manner.) "and if it blossom": R. Nechemiah says: If in the beginning it blossomed from an unclean spot to a clean one, it is clean; from a clean one to an unclean one, it is unclean.