Yosef Karo, Shulchan Aruch — 38: Laws of the lung's appearance
“ An opinion says that's if it looks like palm branches.Rema: And some say even if it's white like egg white it's treif (MHRY"V) (ערוך ערך כחל ורוקח וע"פ) and that's the practice. 2 Any of these Mar'ot (appearances) do not invalidate it until it's inflated and he rubs it by hand, and if it changes to a permitted appearance it's permitted, but if it retains its appearance it's forbidden (all the poskim excluding R"Y in Tos.) 3 There is an opinion that these Mar'ot do not invalidate unless the change is in the skin because of it, and not because of Mugla (pus) inside it. ”
