Midrash su Levitico 13:9

1) (Vayikra 13:9) ("A plague-spot of leprosy, if it be in a man, then he shall be brought to the Cohein. (Vayikra 13:10) And the Cohein shall see, and, behold, a white se'eth in the skin, and it has turned the hair white, and the healthiness (michyah) of living flesh within the se'eth"): "a plague-spot of leprosy": What is the intent of this? From "and, behold, a white se'eth" we learn that a se'eth becomes tamei with a michyah. Whence do we derive the same for the other appearances? (From "a plague-spot of leprosy.") — But does this not follow (even without the verse)? viz.: If we find all of the other appearances to be similar to se'eth vis-à-vis becoming tamei through white hair, let them be similar to se'eth vis-à-vis becoming tamei through michyah. And, furthermore, it follows a fortiori, viz.: If all of the appearances are similar to se'eth to become tamei through white hair, which does not confer tumah in karachath (back of the head) and gabachath (front of the head, viz. Vayikra 13:42-43), how much more so should they be similar to se'eth to become tamei through michyah, which does confer tumah in karachath and gabachath! — No, if all of the other appearances are similar to se'eth to become tamei through white hair, it is because white hair confers tumah in shechin (boils) and michvah (burns). Should they then be similar to se'eth to become tamei through michyah, which does not confer tumah in shechin and michvah! It must, therefore, be written "a plague-spot of leprosy" (to tell us that they do become tamei through michyah. And just as a se'eth is an um (a generator of leprosy), so is a bahereth an um. And whence do we derive the same for the other appearances? From the same a fortiori argument (as above) and from the same answer, viz. (It is derived) from "a plague-spot of leprosy."

2) "if it be": from the pronouncement on (see Section 1:2). "in a man": to include the plague-spot appearing in all of the man — that the michyah makes him tamei (i.e., even though if all of the man turned white he is tahor (viz. Vayikra 13:13), still, if there is a michyah in the plague-spot, he is tamei because of the michyah.) Now (why is a verse needed to tell me this?) does it not follow a fortiori? viz.: If a michyah causes tumah in a small bahereth (the size of a garis), how much more so does it cause tumah in a large bahereth (which covers his entire body! — No, this may be true of a small bahereth, which is a sign of tumah. Would you then say the same for a large bahereth, which is not a sign of tumah! Since it is not a sign of tumah, (we would say that) a michyah should not cause tumah in it. It must, therefore, be written "in a man," to include a plague-spot appearing in all of the man — that the michyah makes him tamei.

3) If they called the Cohein to see one plague-spot, and there erupted in it another plague-spot (before he quarantined or confirmed the first), whence is it derived that he examines it? From "and the Cohein shall see, and, behold (connoting something novel) a se'eth." "and it has turned the hair white": (only if) it has turned the hair white), and not a neighboring spot. How so? If one had a bahereth the size of a garis with white hair in it, and the bahereth disappeared and left the white hair in its place, and the bahereth returned —