Blood

Space inside our arteries is fully utilized. At every heartbeat, a higher blood pressure literally compacts millions of red blood cells into massive trains of oxygen that quickly flow throughout our body. And the tiny space inside our red blood cells is not wasted, either. In healthy conditions, more than 95 percent of their oxygen capacity is utilized. The reason blood is so incredibly efficient is that our red blood cells are not dedicated to specific organs or tissues; otherwise, we would probably have traffic jams in our veins. No, they're shared. They're shared by all the cells of our body. And because our network is so extensive, each one of our 37 trillion cells gets its own deliveries of oxygen precisely when it needs them. Blood is both a collective and individual form of transportation.