The U.S. Constitution doesn't mention corporations once. But if you want to talk about federal regulations, you have to talk about private enterprise, too. They're yin and yang, intertwined over centuries, locked in an eternal struggle. This week, we're tracing that history back to the 13 colonies, when corporations helped to create the basic framework of our democracy. And we hear how railroad companies, the country's first big homegrown corporations, regulated the people before the people regulated them.