James Cook, a retired coal miner from Letcher County, doesn't go anywhere without his oxygen tank."I'm on it 24/7 now," he said. "It started out, I was on it at nighttime."He brought it with him to the Appalachian Citizens' Law Center in downtown Whitesburg, a constant reminder of the battle he's fighting at 54 years old. Cook is suffering from the effects of black lung.The progressive disease is caused by inhaling coal and rock dust, and rates …