Psychotherapy is the practice of treating the sick by influencing the mental life. It stands at the side of physicotherapy, which attempts to cure the sick by influencing the body, perhaps with drugs and medicines, or with electricity or baths or diet. Psychotherapy is sharply to be separated from psychiatry, the treatment of mental diseases. Of course to a certain degree, mental illness too, is open to mental treatment; but certainly many diseases of the mind lie entirely beyond the reach of psychotherapy, and on the other hand psychotherapy may be applied also to diseases which are not mental at all. That which binds all psychotherapeutic efforts together into unity is the method of treatment. The psychotherapist must always somehow set levers of the mind in motion and work through them towards the removal of the sufferer's ailment; but the disturbances to be treated may show the greatest possible variety and may belong to mind or body.