"They are called Bohooma," said Abdul, "and none but these people are allowed to attend the herds. The privilege descends from father to son; and if the herds are captured by neighboring tribes and carried off, the herders go with them, and remain in the same employment as before. They never carry weapons of any kind, or take part in battle, and nothing but death can separate them from their herds." As they proceeded south our friends found that the rains were more frequent, and water-proof garments were constantly needed. Doctor Bronson had made careful provision for this emergency, so that there was comparatively little suffering in consequence, save that the humidity of the climate induced fevers, which did not spare a single member of the party. The medical knowledge of the Doctor was of great use at this time, and as there was a plentiful supply of sulphate of quinine in the medicine-chest, and each of the travellers had a pocket-case constantly within reach, the suffering was reduced to a minimum. The boys endorsed the statement of previous travellers that rain and humidity are the chronic condition of Central Africa. They found the clouds a relief rather than otherwise, as the rays of the sun are excessively warm, especially in the middle of the day, when they become almost insupportable. The high elevation at which they were travelling made the nights very cold. An abundance of thick clothing prevented their suffering from the chilly nights, but their porters and attendants had no such protection, and were wretchedly miserable all the time the sun was below the horizon. [Illustration: EFFECT OF A LONG RAIN IN AFRICA.--ANIMALS SEEKING SAFETY.] While they were at dinner, on the second evening after leaving Foueira, the conversation naturally turned upon the peculiarities of the region they were traversing. "It is only within the present century," said the Doctor, "that we have definitely ascertained the geography of the interior of Africa. It was formerly supposed to be a mountainous region, sloping steadily away to the sea; and there was a tradition, as I have before told you, of the great rivers of Africa rising near each other and flowing in different directions, as the water is carried from the roof of a house. "The explorations of Livingstone, Burton, Speke, Du Chaillu, Cameron, Baker, and others have demonstrated that the centre of the continent is a vast plateau, or table-land, elevated from two thousand to four thousand feet above the level of the sea. There are mountains in the centre, and in various parts of this plateau, eight or ten thousand feet high, and there is a rocky rim or edge nearly all the way around it, with occasional openings, through which the rivers find their exit." Frank was pushing aside his tea-saucer, when the Doctor paused and told him to invert it on the table.