Clean stomach bag thoroughly and leave overnight in cold water to which salt has been added. Turn rough side out. Put heart, lights, and liver in a pan. Bring to the boil and simmer for 1 1/2 hours. Toast the oatmeal on a tray in the oven or under the grill. Chop the heart, lights, and liver. Mix all the ingredients together with the suet, adding salt and pepper. Keep mixture sappy, using the liquid in which the liver was boiled. Fill bag a little over half full, as mixture needs room to swell. Sew securely and put in a large pot of hot water. As soon as mixture begins to swell, prick with a needle to prevent bag from bursting. Boil for 3 hours. Serve with mashed potatoes and mashed turnip. Serves 6-8