The power of tears to wash away irritants in the eye is symbolically extended to all parts of the physical and psychic structure. Weeping is thus a defence against narcissistic injury, and as a defence its aim is regressive. Since it appears in the fourth post-natal week its goal must be a retreat to the amnion, the fluid of which closely resembles tears in composition. Heilbrunn speculates that tears are not shed during the first four weeks of life because sleep affords sufficient possibilities for regression before cerebration is stimulated by the exigencies of life (and also before the lachrymal glands have further developed). Weeping may become pathological when a decisive infantile trauma renders the patient hypersensitive to later narcissistic injuries.