The hematopoietic system plays roles that are crucial for survival of the host: delivery of oxygen to tissues, arrest of accidental blood leaking from blood vessels, and fending off of invading microbes by humoral, cell-mediated, and phagocytic immunity. The activity of the hematopoietic system is staggering: daily, a normal adult produces approximately 2.5 billion erythrocytes, 2.5 billion platelets, and 1 billion granulocytes per kilogram of body...