"We must go," said Dorothy. "Father and Mother have gone on a half-hour ago." There were tears in all eyes as Doris and Dorothy sprang into their saddles. "Good-by! Good-by!" they called as the mules started forward. Since they were babies, Doris and Dorothy Shelton had lived in Tibet, the land that is called "the roof of the world," because it is higher than any other country in the world. They had taken many trips, clinging to the backs of their mules as they went almost straight up on the rough mountain roads, but the journey on which they were starting now, as the sun rose from behind the snow-capped mountains, was to be the most thrilling of all. [Illustration: THE SHELTON FAMILY CROSSING THE MOUNTAINS OF TIBET Mrs. Shelton and the girls are in the chairs carried by barefoot coolies.] They soon overtook their mother and father and the servants. In front of the party rode guards, for the country was full of robber bands. Then came six mule drivers driving the twenty-five mules that were loaded with tents, baggage, and food. Following the mule drivers Mrs. Shelton rode in a sedan chair fastened to two poles which rested on the shoulders of four carriers who wore fine, bright-red turbans and long robes of grey _pulu_ or wool, which were tied about the waist. In the party were Andru, Drashi, and Shen-si, the three servants who had helped to care for Doris and Dorothy since they were babies. Last of all, on a mule strong enough to carry his two hundred and thirty pounds, rode Dr. Albert Shelton. Everyone in Batang knew "Big Doctor Shelton," and everyone loved him. Seventeen years before this time, when he left the medical school in Kansas, he looked over a map of the world to find the place that needed a doctor most. There was not a town in Kansas that did not have a doctor in it or near to it, and in some of the towns there were many doctors. "I should like to go to a place where there are no other doctors," he said. "Well, then," said a friend, "go to Tibet. That is the place for you, because in all Tibet there is no doctor. But you may not get there alive. The Dalai Lama, who is the head of everything in Tibet, government and Buddhist Church, lives in Lhasa, the capital, and he will not let any Christian missionary or doctor come within the walls of his city. Some have tried to go, but most of them were killed." The more Albert Shelton thought about the land without a doctor, the more he wished to go there. He talked to his young wife, and she wanted to go, too, so one day they took a steamer from San Francisco and crossed the Pacific Ocean to China where a boat carried them a thousand miles up the Yangtze River. Then they went still farther on a little Chinese house-boat pulled by thirty men who walked along the bank. After the house-boat had gone up the river for nearly two months, they stepped off on shore and rode on the backs of mules for seven hundred miles.