“Well, my dear fellow, to begin at the beginning we should have to analyze personality--and human personality is a mystery I confess myself unable to explore. You are aware, however, that there are people who have double personalities--even triple and multiple personalities--which differ utterly. For some reason which eludes us, one of these submerged personalities in an individual may suddenly come to the top. He, or she, entirely forgets the personality which was theirs up to that moment, forgets name, relations, every circumstance of life--and is completely someone else, quite new. There is a recent case, exhaustively studied, of a young woman with four such personalities--over which she has not the slightest control, and which differ profoundly, mentally and morally. I mention this merely to show you how unstable personality may be.” “These are pathological cases,” interposed Vincent. “My fiancée was a thoroughly well-balanced woman.” Chassaigne nodded. “Before the war when you last saw her. She must have gone through great stress since. But let us continue. Under hypnotism a person is extraordinarily susceptible to the suggestions of the operator. He will carry out perfectly any rôle indicated to him. The reason is that in the hypnotic condition the conscious personality is put to sleep and the subjective mind--the dream-creating consciousness which is independent of the will--is paramount. That subjective mind possesses little if any power of origination, but it has a startling faculty of dramatizing any suggestion made to it. Tell a hypnotic that he is President Wilson at the Peace Conference and he will get up and make a speech perfectly in character, amazingly apposite, expressing ideas that are normally perhaps quite alien to his temperament. Tell him that he is Napoleon at the Battle of Waterloo and he will act the part with a reality that is impressive. He believes himself actually to be Napoleon. Under hypnotism, then, the personality which is mirrored in the Ego--which you believe to be the essential, unchanging you--may be utterly changed----” “Yes,” objected Vincent. “But that is only during the hypnotic trance. It is not permanent.” “Wait a moment,” said Chassaigne. “Suggestions made during the hypnotic trance may and do persist after the subject has awakened from it. I may, for example, suggest to the hypnotized person that when he wakes he will have forgotten his native language--and he will forget it. If he knows no other, he will remain dumb until I remove the suggestion. I may suggest to him that a person actually in the room is not there--and he will not perceive him. I may suggest that in a week, a month, a year, at such and such an hour, he will perform some absurd action--and punctually to the moment, without understanding the source of his impulse, he will perform it. Post-hypnotic persistence of suggestion is a scientific fact.” “Then--in this case?”