From Faith, Madness, and Spontaneous Combustion

Our immune systems, and only our immune systems, prevent us from becoming everyone else all at once.  We are who we are only because we defend ourselves every moment of every day.  And who we are is everything.  We are pieces of others.  Portraits painted somewhere between our brains and thymuses.  We are the dirt we've eaten and the songs we've sung.  We are the light of stars and darknesses old beyond imagining.  We are at once spontaneous fires and sacred water.  We are faith and forgiveness.  We are our own deaths and we are the eternal thoughts of others.

-- Gerald Callahan, Faith, Madness, and Spontaneous Combustion:  What Immunology Can Teach Us About Self-Perception (New York:  St. Martin's, 2002), p. 227