Midrasch zu Wajikra 13:43

3) (Vayikra 13:43) "And the Cohein shall see him, and, behold, a rising of the plague-spot, reddish-white, (is in his karachath or in his gabachath"): We are hereby taught that a rising confers tumah intermixed. And whence (is the same) to be derived for the other appearances? From (Vayikra 13:42) "a reddish-white plague-spot in his karachath or in his gabachath … as in the appearance of the leprosy of the skin of the flesh." Just as this [karachath] confers tumah intermixed, so the leprosy of the skin of the flesh confers tumah intermixed, and just as the skin of the flesh confers tumah plain, non-intermixed, this, too, confers tumah plain, non-intermixed. "the skin of the flesh": (which requires a quarantine of) two weeks.

4) (Why is this Scriptural analogy [hekesh] needed?) Does it not follow by induction (mah matzinu)?, viz.: Tumah is conferred here (in the instance of karachath), and tumah is conferred in (the instance of) the skin of the flesh. Just as the skin of the flesh, two weeks, here, too, two weeks.

5) Or, perhaps go in this direction: Tumah is conferred here, and tumah is conferred in (the instance of) boil or burn. Just as boil or burn, one week, here, too, one week.

6) Let us see what it [karachath] most resembles. We derive something which confers tumah through michyah [i.e., karachath], from something which confers tumah through michyah [i.e., skin of the flesh], and this is not to be refuted by boil or burn, which do not confer tumah through michyah. — But, perhaps go in this direction: We derive something [karachath] which confers tumah through two signs (michyah and spreading) from something [boil or burn] which confers tumah through two signs (spreading and white hair), and this is not to be refuted by skin of the flesh, which confers tumah through three signs (white hair, michyah, and spreading). It must, therefore, be written "as the appearance of the leprosy of the skin of the flesh" — two weeks. "leprosy": (the size of) a garis (see Section 4, Chapter 7:9). Now does this not follow by induction. (Why make special mention of "leprosy" to this end?) Tumah is conferred here [karachath] and tumah is conferred through boil or burn. Just as boil or burn, the size of a garis, here, too, the size of a garis!

6) If in the end we will include a returning plague-spot (even if it does not spread), what is the intent of "And the Cohein shall come and he shall see, and, behold, the plague-spot has spread"? — Leave it (i.e., This is not the place of this verse. It does not refer to post-removal and scraping, but to spreading at the end of the second week, as in 7) below.) Or, once we have learned that if the plague-spot returns and blossoms in the house (even if it does not spread, it is tamei), then, if we see it returning on the same day (of the plastering), it should be declared tamei (and razed immediately)! It is, therefore, written (Vayikra 13:39) "And the Cohein shall return" - (Vayikra 13:43) "and if the plague-spot returns." Just as the "returning" there, is at the end of one week, so, (the returning) here, is at the end of one week.

7) No, this may be true of boil or burn, which confer tumah through white hair, and the size of the white hair requires no space, so that a garis suffices for the size of the boil or burn, as opposed to karachath and gabachath, which confer tumah through a michyah, which requires the size of a lentil, (so that they should be of greater size than a garis relative to the michyah in order to confer tumah). This is refuted by skin of the flesh, which confers tumah through a michyah and confers tumah (even) by the size of a garis.

8) No, this may be true of skin of the flesh, which confers tumah through three signs, as opposed to karachath and gabachath, which confer tumah through only two signs, so, the Torah, having been relatively lenient with them, perhaps they must be greater than a garis to confer tumah. It must, therefore, be written (re karachath and gabachath) "Leprosy," (to teach that they confer tumah even if they are only) the size of a garis.

11) They said in the name of R. Yishmael: "Blight leprosy" is written of garments, and "blight leprosy" is written of houses. Just as with garments, remaining the same and spreading in the second week was equated with spreading in the first week, so with houses, remaining the same and spreading in the second week was equated with spreading in the first week. (Vayikra 13:43) "after the house has been scraped and after it has been plastered": What is the intent of this? (i.e., it is known that there is no removing without scraping and plastering.) For I might think that there is no returning (of the plague-spot) and razing except after spreading in the first week. Whence do I derive for inclusion returning (of the plague-spot) after spreading in the second week and after remaining the same in the second week (that both require removing, scraping, and plastering, and, if it returns thereafter, razing)? From (Vayikra 13:43) "after he removed the stones …" Let it not be written "after scraping" and "after plastering." Is there removing without scraping and plastering? Why, then, is it mentioned? To include a returning (plague-spot) after spreading in the second week and after remaining the same in the second week.