"I believe he was," Frank answered. "That being the case," said Fred, "he will do for a rhyme like this: "To James Buchanan came a letter From the King of Timbuctoo: That monarch said, 'I can't do better Than write Old Buck and Jim Buck too.'" "That will do," was the response; "and here's another to match it: "Sim and I went to the races, By the coach from Timbuctoo: When we went to book our places I said to him, 'Please, Sim, book two. '" Fred tried to compose something else on the subject, but the power of rhyming left him, and he gave up the attempt just as the Doctor returned from his conference with Abdul. CHAPTER XXI. TRAVELS OF DR ROHLFS.--THE TSETSE-FLY.--THROUGH UNYORO. "There's another brave explorer of the valley of the Niger," said Doctor Bronson as he resumed his seat after the conference with Abdul, "whom we should not omit from the roll of honor." "I know to whom you refer," said Frank. "Who is it?" Fred asked. "Dr. Gerhard Rohlfs," was the reply. "He is a German traveller, born near Bremen, in 1834, who graduated in medicine, and afterward entered the French army, and obtained the highest distinction open to a foreigner. His service was mostly in Algeria, where he learned the Arabic language, and in 1861 went to Morocco, where he assumed the character of a Moslem, and travelled a long distance in the Sahara desert." [Illustration: A VILLAGE ON THE GUINEA COAST.] "Quite right," said the Doctor, as Frank paused. "It was in that first exploration he was treacherously attacked and robbed by his guides in the desert, who left him for dead on the sands, with a broken arm. In 1864 he again travelled in Morocco, and a year later he started from Tripoli, in the disguise of an Arab, and went to Lagos, on the Gulf of Guinea, by way of Moorzook and other cities in that part of Africa. He passed Lake Tchad, and continued to the Niger, which he partially explored, together with the river Benoowe, which has already been mentioned. His name is familiar to many people in America, as he visited the United States in 1875, and lectured there on his travels. "He tells some interesting stories of his adventures," the Doctor continued, "while travelling in disguise. He had managed to make the Grand Shereef of Morocco his friend, and he secured letters that caused him to be received with distinguished honors in most of the towns and cities that he visited. As he spoke Arabic fluently, and knew all the Moslem prayers by heart, his religious faith was not often called in question. Occasionally, however, he was open to suspicion, and as he was among the most fanatical Moslems his life was in great danger. "At Tidikelt he was received very kindly by the prince to whom he had several letters of introduction. One day a Touareg sheik came to him and said,