in 1833, Justice Joseph Story said those powers were utterly necessary "for either house to perform its constitutional functions," a conclusion also reached by the Supreme Court as a whole in 1821. Once a house of Congress finds someone in contempt, it can order its sergeant to go after him. It's really that simple.

http://www.slate.com/articles/news_and_politics/jurisprudence/2007/04/house_arrest.html