Yosef Karo

“ But there's someone who prohibits it (which is what we do) .
3 If the disease is only in the white part, even though the rest of the kidney is healthy it's treif.
4 If there are stones in the kidney it's kosher.
5 A kidney that's shrunk is treif. And how much shrunken to be treif? Small beasts, up to and including half size is treif. Large beasts, up to and including an average size grape is treif. ”

“ And if blood is found in it then its rule is as for fluids. And if it's found full of fluid that has a bad appearance but isn't thick or cloudy but rather it looks crocus-colored like (date-) honey it's kosher. ”