This is not a bag of blood. Granted, it did begin as a blood donation, drawn from the arm of a volunteer donor in Massachusetts. Within hours of collection, though, that precursory pint of warm whole blood had been centrifuged, fractionated and decanted into a red blood cell concentrate laced with a cocktail of chemical buffers and nutrients. The ruddy yield, shown here, is one chilled unit of processed blood product, suitable for a patient desperately in need of red cells. Such units—screened, packaged and tracked through their life cycles in keeping with the dictates of the U.S. Food and Drug Administration—are manufactured with assembly-line efficiency to optimize the safety and utility of a precious, limited resource.