"Not quite," contradicted Dr. Cloyd, still smiling. "To Mersey, my patient, troubled by his delusion and using all his craft to persuade both of us of its reality, the unsatisfactory answer would be the satisfactory one." * * * * * Mersey's voice laughed. "Dr. Cloyd, I salute you. I will leave your world with a tremendous respect for you--and completely unsure of whether you believe in my existence." "Thank you." "I am leaving, you know," Mersey's voice replied. The traveler by now was resigned to letting the patient be his medium and speak his thoughts. Thus far, he had spoken them all truly, if somewhat excessively. The traveler thought he knew why, now, and expected Mersey to voice the reason for him very shortly. He did. "I'm leaving because I must report failure and advise my people to look elsewhere for a new home. Part of the reason for that failure I haven't yet mentioned: "Although it might appear that I, the visitor, am manipulating Mersey to speak the thoughts I wished to communicate, the facts are almost the opposite. My control over either Mersey's body or mind is practically nil. "What you have been hearing and what you hear even now are the thoughts I am thinking--not necessarily the ones I want you to know. What has happened is this, if I may borrow your theory: "My mind has invaded Mersey's, but his human vitality is too strong to permit him to be controlled by it. In fact, the reverse is true. His vitality is making use of my mind for its own good, and for the good of your human race. His own mind is damaged badly, but his healthy body has taken over and made use of my mind. It is using my mind to make it speak against its will--to speak the thoughts of an alien without subterfuge, as they actually exist in truth. Thus I am helplessly telling you all about myself and the intentions of my people. "What is in operation in Mersey is the human body's instinct of self-preservation. It is utilizing my mind to warn you against that very mind. Do you see? That would be the case, too, if a million of us invaded a million minds like Mersey's. None of us could plot successfully against you, if that were our desire--which, of course, it is--because the babbling tongues we inherited along with the bodies would give us away." The doctor no longer smiled. His expression was grave now. "I don't know," he said. "Now I am not sure any longer. I'm not certain that I follow you--or whether I want to follow you. I think I'm a bit frightened." "You needn't be. I'm going. I'll say good-by, in your custom, and thank you for the hospitality and pleasures your world has given me. And I suppose I must thank Mersey for the warning of doom he's unknowingly given my people, poor man. I hope you can help him." "I'll try," said Dr. Cloyd, "though I must say you've complicated the diagnosis considerably." "Good-by. I won't be back, I promise you." "I believe you," said the doctor. "Good-by."