"Marco Polo," continued the historian, "came as near to the land of the Wusun as any other European. Three centuries later a Portuguese missionary, Benedict Goës, passed through the desert near the city of the Wusun, and reported seeing some people who were fair of face, tall and light-eyed." Van Schaick turned to his papers. "In the last century," he said, "a curious thing happened to an English explorer, Ney Elias. I quote from his book. _An old man called on me at Kwei-hwa-ching, at the eastern end of the Thian Shan Mountains, who said he was neither Chinaman, Mongol, nor Mohammedan, and lived on ground especially allotted by the emperor, and where there now exist several families of the same origin. He said that he had been a prince. At Kwei-hwa-ching I was very closely spied on and warned against asking too many questions_." Van Schaick peered over his spectacles at Gray. "The Thian Shan Mountains are just north of this blind spot in the Gobi Desert where we think the Wusun are." The historian broke in eagerly. "Another clew--a generation ago the Russian explorer, Colonel Przewalski, tried to enter this blind spot from the south, and was fought off with much bloodshed by one of the guardian tribes." Gray laughed frankly. "I admit I'm surprised, gentlemen. Until now I thought you were playing some kind of a joke on me." Van Schaick's thin face flushed, but he spoke calmly. "It is only fair, sir, that you should have proof you are not being sent after a will-o'-the-wisp. A few days ago I talked with a missionary who had been invalided home from China. His name is Jacob Brent. He has been for twenty years head of the college of Chengtu, in Western China. He heard rumors of a captive tribe in the heart of the Gobi. And he saw one of the Wusun." He paused to consult one of his papers methodically, "Brent was told, by some Chinese coolies, of a tall race dwelling in a city in the Gobi, a race that was, they said, 'just like him.' And in one of his trips near the desert edge he saw a tall figure running toward him over the sand, staggering from weariness. Then several Chinese riders appeared from the sand dunes and headed off the fugitive. But not before Brent had seen that the man's face was partially white." "Partially?" asked Gray quizzically. "I am quoting literally. Yes, that was what Brent said. He was prevented by his native bearers from going into the Gobi to investigate. They believed the usual superstitions about the desert--evil spirits and so forth--and they warned Brent against a thing they called the pale sickness." Gray looked up quietly. "You know what that is?" "We do not know, and surmises are valueless." He shrugged. "You have an idea?" "Hardly, yet--you say that Brent is ill. Could he be seen?" "I fancy not. He is in a California sanitarium, broken down from overwork, the doctors informed me."