Kommentar zu Negaim 9:2

אין מצטרפין – one-half a split [Cilician] bean of boils with one-half a split [Cilician] bean of burning do not combine [to make] a complete split [Cilician] bean.

A boil and a burn do not combine, nor do they spread from one to the other, nor do they spread from there to the skin of the flesh, nor does [a nega] on the skin of the flesh spread to them. If there is a boil the size of a half a split bean and a burn the size of half a split bean, they do not combine to form a nega the size of a split bean. Also, if a boil and a burn are right next to each other and the nega spreads from one to the other, it is not considered as having spread and it is pure. If the nega spreads from the boil or burn to other skin, or if a nega from other skin spreads into the burn or boil, it is not considered to have spread. Rather, the nega must spread within the boil or burn. Put simply: the burn and boil nega are considered completely separately from an adjacent nega.

ואין פושין מזה וזה – that if a boil and a burning are one next to the other, and in one of them is a bright white spot on the skin the size of a split [Cilician] bean, and he was shut up/isolated/quarantined, and at the end of the week, it spread to its neighbor or on the skin of the flesh, we don’t declare him a certified leper. And similarly, if the bright white spot was on the skin of the flesh and spread to the boil or to the burn, it is not considered spreading.

If they were festering they are clean. If the boil or burn is still festering, it is pure. This was explained in 6:8.

היו מורדין – that they didn’t heal properly and the skin did not have a scab on it, and it still produces secretion, we don’t defile it through plagues, as it is written (Leviticus 13:18): “When an inflammation (i.e., boil) appears on the skin of one’s body and it heals.,” but with a burning, it is written (Leviticus 13:24): "והיתה מחית המכוה"/ “and the patch from the burn is a dis-coloration, [either white streaked with rea, or white.]”

If they formed a scale as thick as garlic peel, such is the scar of the boil that is spoken of in the Torah. Leviticus 13:23 states, "But if the boil (inflammation) remains stationary, not having spread, it is the scar of the boil (inflammation); the priest shall pronounce him clean." The rabbis explain that this doesn't refer to a boil (or burn in v. 28) that have healed completely. Rather, a little bit of a scab seems to have formed on it. Since the bright spot didn't spread (see the verse) he is not isolated for a second week, as he would be for other negaim. Rather he is pronounced clean.

אע"פ שנעשה מקומו צלקת (even though spot became the rough, scabby surface/scar) – that it is recognized that there was a boil there or a burn and it is not equivalent to the rest of the skin of the flesh, nevertheless it is judged like the skin of the flesh, for after it became a strong scab.

If they were subsequently healed, even though there was a mark in their place, they are regarded as the skin of the flesh. If the boil or burn completely heals, it is treated like regular skin, even if a mark remains. If a new nega appears there, the nega is treated like a regular nega, and not one that formed in a boil or burn.