use a crowbar and a nail remover on the boards. a house that old might use cut nails to hold the boards down. sight along each joist to see which way the joist is cupped. what that means is each joist bends either up or down along its length. the cupped or up side should go up. if you have the opportunity to see a flat bed truck trailer, you'll see that the middle bends up, so that when a load is applied, the bed springs downward a little to support the load. same concept in a floor joist. the springy-ness is what gives the joist the property of holding a load.