Using Claude Bernard's concept that animals exist in an external and internal environment and extending this idea to the realm of psychology, the author discusses mourning as an adaptational process of the internal psychic environment to an altered external environment. The loss of a significant object causes a disturbance in object relationships that is seen as antiadaptational. In order to reestablish a state of ego equilibrium a mourning process is set in motion. Pollock describes acute and chronic stages of mourning: the acute stage is visible in animals and birds; the chronic stage requires a psychic organization of the human type. The cathexis of a new object is not part of the mourning process alone but is an indicator of the degree of resolution of the object loss in terms of the adaptational process.