One night last April, Karen Ann Quinlan, 21, went to bed saying she was not feeling well. She never woke up. Stricken with a still undiagnosed malady (perhaps the result of mistakenly mixing a tranquilizer and drinks), she has remained in a coma ever since. One side of her permanently damaged brain shows almost no sign of functioning while the other gives off only slight but steady signals visible on an electroencephalogram. Last week, unwittingly, Karen Ann became the focus of the continuing legal-medical-ethical controversy over how to define death.

In Limbo. For...