The Song of the Cell: An Exploration of Medicine and the New Human

by Siddhartha Mukherjee

blood speaks to everyone and everything: it is the central mechanism of long-distance communication, of transmission, in humans. Be it hormones, nutrients, oxygen, or waste products, blood delivers and connects—talks—to every organ and from one organ to the next. It even speaks to itself: its three cellular components, red cells, white cells, and platelets, in particular, engage in an elaborate system of signaling and cross talk. Platelets band together to form a clot. A single platelet, in isolation, cannot congeal into a clot, but millions of platelets, in conjunction with proteins in the blood, collaborate to seal a bleeding site. White blood cells have the most complex system of all: they signal one another to coordinate an immune response, the healing of wounds, fighting microbes and surveying the body for invaders as a system of cells. Blood is a network. As with M.K., the young pneumonia patient with immunodeficiency, the collapse of one piece of the net can lead to the collapse of the whole net.