Why is there always a blood shortage?

With its direct connection to the heart, its vivid hue (from wine-dark to cherry bright and cobalt blue), and its spilling in both birth and death, blood has historically served as a metaphor for humanity, as Susan Lederer, a professor of medical history and bioethics at the University of Wisconsin-Madison, argues in her 2008 book, Flesh and Blood. “Write with blood, and thou wilt find that blood is spirit,” wrote Friedrich Nietzsche in the 1880s. “All the soarings of my mind begin in my blood,” wrote Rainer Maria Rilke in 1921. “Blood is memory without language,” added Joyce Carol Oates, more recently.