In ancient times, before the realisation of the importance of the action of the heart and circulation of blood, a person was deemed to have died when he stopped breathing. The reflecting surface of a mirror was held before the face of the sick person. Death was diagnosed when the mirror was not fogged by water vapour present in the breath. Later, irreversible cessation of respiration and of the action of the heart were established as the criteria for the diagnosis of death. In the middle of this century, attention was turned to the brain, which required much more energy than other organs. If its needs were not met for four minutes or more, irreversible damage to it followed. After a variable interval, the other organs failed and the person died. In the interim, there was a dead brain in a dying body.