One can show his nega to a Kohen and gain, and one can show his nega to a Kohen and lose. How so? Someone was confirmed tamei and the symptoms disappeared, [but] he did not succeed in showing it to the Kohen before it covered him completely, is tahor, whereas had he shown it to the Kohen, he would be tamei. [On the other hand, someone who had] a baheres with nothing in it, [but] he did not succeed in showing it to the Kohen until it covered him completely is tamei, whereas had he shown it to the Kohen, he would be tahor.

A boil or a burn is tamei for [no more than] one week [unless it has one of these] two symptoms: white hair or expansion. What is considered a boil? [If] he was injured by wood, or by stone, or by olive peat, or by the waters of Tiberias, [or by] any heat not caused by fire, this is a boil. What is considered a burn? [If] he was burnt by coal, or by ash — any heat caused by fire — this is a burn.