“It was just a few small red dots,” I would recount to innumerable sympathetic nurses. They—the dots, not nurses—clustered together on my son’s smooth slim neck. I stroked them as I dressed him after the bath. My inner hypochondriac was oddly quiet. Larry, my son, was well, throwing himself through the world with speed, joy, and curiosity. The next day I took him casually to our general practitioner to get these curious freckles checked. Then everything started to tilt. How do I weave it all together? In a string of Facebook posts? In a small impersonal room opposite a stranger while I sip a glass of water? In a series of dark jokes with my husband in the kitchen late at night? In snatches of awkward conversation with friends? In dreams from which I wake gasping? By scouring the sentences of authors and archives? From the discoveries of Paul Ehrlich to the scattered words of Emily Dickinson to the constant mechanical chugging of the IV pump, this interdisciplinary essay delves into the medical and cultural history of blood and bone marrow to tell an acutely personal story.