It was hard work, forcing the long shallow boat against the rapid current of the stream, whose unknown source is somewhere among the famous diamond regions of Brazil. It was plain sailing for three hundred leagues from the Amazon, from whose majestic volume the little party of explorers had turned southward more than a month before. The broad sail, which was erected in the centre of the craft, swept it smoothly along over the narrowing bosom of the Xingu, between luxuriant forests and past tribes of strange-looking Indians, who stood on the banks staring wonderingly at the extraordinary beings, the like of which many of them had never seen before.Occasionally the explorers put ashore, and, using only the language of signs, exchanged some of the beads and gaudy trinkets for the curious articles of the savages. Endless varieties of fruit were so abundant that it was to be had for the simple trouble of plucking; while the timid natives stood in such awe of their visitors, that the thought of harming them never entered their minds.But ominous changes were gradually noted by our friends, as they steadily ascended the mysterious stream. At first the natives fled at their approach, and failed to understand the signs of comity, or were so distrustful of the strangers that they refused to meet their advances. Fleeing into the woods or high hills, they peeped out from their coverts, uttering strange cries and indulging in grotesque gestures, the meaning of which could hardly be mistaken. Had there been any misapprehension on the part of the visitors, there was none after several scores launched their arrows at the boat, as it glided away from the shore and up stream. The aim was wild and no one was struck, but when Professor Ernest Grimcke, the sturdy, blue-eyed scientist of the party, picked up one of the missiles and carefully examined it, he made the disturbing announcement that it was tipped with one of the deadliest of known poisons.The other members of this exploring party were Fred Ashman, a bright, intelligent American, four-and-twenty years of age; Jared Long, an attenuated, muscular New Englander in middle life, and Aaron Johnston, a grim, reserved but powerful sailor from New Bedford, who had spent most of his life on whaling voyages. Professor Grimcke and Ashman were joint partners in the exploring enterprise, Long and Johnston being their assistants.In addition, there were three native servants, or helpers, known as Bippo, Pedros and Quincal. They had been engaged at Macapa, near the mouth of the Amazon. They were rather small of size, the first-named being the most intelligent, and in that warm, tropical climate wore no clothing except a strip of native cloth around the loins. Ashman had striven to teach them the use of firearms, but they could never overcome the terror caused by the jet of fire and the thunderous explosion when the things were discharged. They, therefore, clung to their spears, which, having honest points, cannot be said to have been very formidable weapons in their hands, even though each native was able to throw them with remarkable deftness and accuracy.The sail that had served the explorers so well, where the Xingu was broader and with a slower current, became useless, or at least proved unequal to the task of overcoming the force of the stream. Consequently they had recourse to the broad-bladed oars, with which they drove the canoe swiftly against the resisting river, cheered by the oft-repeated declaration of the Professor, whose spirits never flagged, that the harder it proved going up stream, the easier must it be in descending, and that the arrangement was much better than if the condition of affairs were reversed.