In his masterful story `A River in Egypt`, David Means paints a portrait of a moment. Cavanaugh and his young son are suspended; trapped in what a nurse calls `the sweat chamber`, where the boy will be tested for cystic fibrosis.Cavanaugh has brought distractions - spasmodic action figures, malformed toy trucks - but they do little to alter the frustration of the sick child screaming, or to alleviate the anxiety of the time spent waiting for `some exactitude in the form of a diagnosis`.