Barbecued Buffalo Sandwiches

In a heavy skillet cook the buffalo and onion, stirring often until the buffalo is brown and tender. Stir in the ketchup, water, celery, lemon juice, brown sugar, Worcestershire sauce, salt, vinegar, and dry mustard, and heat to boiling. Reduce the heat, and simmer covered for 30 minutes. Serve on toasted wheat buns.