The psychological work of the physician does not begin with his curative efforts. Therapy is always only the last step. Diagnosis and observation have to precede, and an inquiry into the causes of the disease is essential, and in every one of these steps psychology may play its role. The means of psychodiagnostic are not less manifold than those of psychotherapy. Moreover there the technique may be more complex and subtle. The whole equipment of the modern laboratory ought to be put at its disposal. Perceptions and associations, reactions and expressions ought to be examined with the same carefulness with which the conscientious physician examines the blood and the urine. A particular difficulty of the task more or less foreign to every other medical inquiry is the intentional or unintentional effort of the patient to hide the sources of the trouble and to mislead as to their true character. Too often he is entirely unconscious of the sources of trouble or else he has social reasons to deceive the world and himself, and ultimately the physician. And yet no psychical treatment can start successfully so long as the patient is brooding on secret thoughts at the bottom of his mind. The desire to hide them may often be itself a part of the disease. It is surprising how often unsuspected vistas of thoughts and impulses and emotions are opened by an inquiring analysis where the direct report of the patient does not awaken the least suspicion. In the field of insanity, naturally the physician at once goes to an examination on his own account, but in the borderland regions of the psychasthenics and hysterics and neurasthenics, the intellectual clearness of the patient too easily tempts one into trusting the sincerity of his story; and yet the most important ideas clustering perhaps about love or ambition, about vice or crime, about business failure or family secrets, about inherited or acquired diseases may be cunningly withheld and may frustrate every psychotherapeutic influence. Where suspicion is awake and mere confidential talk and persuasion seem insufficient, the physician may feel justified in the interest of his patient in drawing the thoughts out of their hiding-place by artificial means. Skill, tact, and experience are needed there.