“I sing the body elec­tric,” wrote Walt Whit­man. Let the poets praise the body’s gal­van­ic spir­it, moral incan­des­cence, and cur­rents of courage and pas­sion. To physi­cian-essay­ists Richard Selz­er and Frank Gon­za­lez-Crus­si goes the task of chron­i­cling the body’s short cir­cuits, frayed insu­la­tion, blown fus­es, and dead batteries.