Cook the tripe the day before using. Wash thoroughly, place in kettle and cover with water. Boil 8 hours. Remove the tripe. When cooled, cut into pieces about 1/2 inch square. The next day wash the veal knuckle, cover with 3 quarts of cold water and simmer about 3 hours, removing scum as it rises. Remove meat from bones and cut into small pieces. Strain the broth and return to kettle. Add the bay leaf and onion and simmer about 1 hour. Then add the potatoes, which have been cut in squares, and the pot herbs. Add the meat and tripe and season with salt and cayenne pepper (if desired). Make dumplings by combining the finely chopped suet, flour, salt and enough water to permit rolling the dough into dumplings, about the size of marbles. Flour well to prevent sticking and drop into the hot soup. Cook 10 minutes, add some chopped parsley and serve at once.