Years fled and the boy David grew up to manhood. One day he told his parents that he wished to be a medical missionary, and go to the people in the east and south, tend the sick, and preach to any who would listen. In order to procure means for his studies he had to save up his earnings at the factory, and when the time was come he went with his father to Glasgow, hired a room for half-a-crown a week, and read medicine. At the end of the session he went back to the factory to obtain money for the next winter course. Finally he passed his examination with distinction, and then came the last evening in the old home and the last morning dawned. His father went with him to Glasgow, took a long farewell of his son, and returned home sad and lonely. Livingstone sailed from England to the Cape, and betook himself to the northernmost mission-station, Kuruman in Bechuanaland. Even at this time he heard of a fresh-water lake far to the north. It was called Ngami, and he hoped to see it one day. From Kuruman he made several journeys in different directions to gain a knowledge of the tribes and their languages, to minister to their sick and win their confidence. Once when he was returning home from a journey and had still 150 miles to trek, a little black girl was found crouching under his waggon. She had run away from her owner because she knew that he intended to sell her as a slave as soon as she was full-grown, and as she did not wish to be sold she determined to follow the missionary's waggon on foot to Kuruman. The good doctor took up the frightened little creature and provided her with food and drink. Suddenly he heard her cry out. She had caught sight of a man with a gun who had been sent out to fetch her and who now came angrily to the waggon. It never occurred to Livingstone to leave the defenceless child in the hands of the wretch. He took the girl under his protection and told her that no danger would befall her henceforth. She was a symbol of Africa, the home of the slave-trade. And Africa's slaves needed the help of a great and strong man. Livingstone understood the call and worked to his last hour for the liberation of the slaves, as Gordon did many years later. He strove against the cruel and barbarous customs of the natives and their dark superstitions, and hoped in time to be able to train pupils who would be sent out to preach all over the country. In one tribe the medicine-men were also rainmakers. Livingstone pointed out to the people of the tribe that the rainmakers' jugglery was only a fraud and of no use, but offered, if they liked, himself to procure water for the irrigation of their fields, not by witchcraft but by conducting it along a canal from the neighbouring river. Some rough tools were first hewn out, and he had soon the whole tribe at work, and the canal and conduits were laid out among the crops. And there stood the witch-doctors put to shame, as they heard the water purling and filtering into the soil.