From www.nutritionfacts.org, May 2011:
Americans consume about 5 billion hamburgers annually. Recently, pathologists at the Cleveland Clinic dissected hamburgers from eight major fast-food restaurants in the U.S. They found that the actual meat content of these samples ranged from 2 percent to 14.8 percent.
Cows' blood vessels, nerves, cartilage, and parasites (found in a quarter of the burgers sampled) were contained in the burgers, as well.
But the largest ingredient present was ammonia. Apparently, the meat industry injects ammonia into ground beef in order to kill any fecal bacteria on it. This ground beef is sold not only to major fast-food restaurants, but also to U.S. schools. Yuck!