Change of phase is a well-recognised feature in the course of certain of the psychoses. In manic-depressive insanity it is on the phasic variation of the affective state that the separation of that type of mental disorder is based. So, also, in many cases of the chronic psychoses phase changes occur as the disorder progresses, and as the patient fits in new experience and builds up fresh mental content on the basis of the already existing delusional state.