Psychotherapy became a set of skills common to several related professions. This process of widening the base of professional involvement in psychotherapy occasioned difficulty, often stirring interprofessional hostilities which persist today in the form of opposition to the use of medically-based techniques by persons without medical training. Traditional psychotherapy with children is adult-oriented, proceeding through interpretive and highly verbal psychotherapy, which does not appear to be relevant to the problems of childhood. Psychotherapy based on the medical or "disease entity" model has frequently been modified and has continued to develop, but it has always retained the basic assumption that internal psychodynamic conditions constitute mental illness and must be altered in order to bring about meaningful or lasting improvement. During the Middle Ages, however, the earlier beginnings of naturalistic and humane treatment were submerged as religious animism was revived in the treatment of persons thought to be "possessed.".