In 1913 he traveled through South American countries to speak before learned bodies which had invited him to come before them.  Afterwards, with his son Kermit, some American naturalists, and Colonel Rondon, a brave and distinguished Brazilian officer, he made a long trip through the wilderness of Brazil, to hunt and explore.  Some of the country through which they traveled was little known to white men; some of it absolutely unknown.  They hunted and killed specimens of the jaguar, tapir, peccary, and nearly all of the other strange South American animals.

In February 1914, they set out upon an unknown stream called the River of Doubt.  They did not know whether the exploration of this river would take them weeks or months; whether they might have to face starvation, or savage tribes, or worse than either, disease.  They surveyed the river as they went, so as to be able to map its course, and add to geographical knowledge.  Strange birds haunted the river, and vicious stinging insects annoyed the travelers.  They constantly had to carry the canoes around rapids or waterfalls, so that progress was slow.  Some of the canoes were damaged and others had to be built.  Large birds, like the curassow, and also monkeys, were shot for food.  The pest of stinging insects grew constantly worse,—­bees, mosquitoes, large blood-sucking flies and enormous ants tormented them.  The flies were called piums and borashudas.  Some of them bit like scorpions.

Kermit Roosevelt’s canoe was caught in the rapids, smashed and sunk, and one of the men drowned.  Once they saw signs of some unknown tribe of Indians, when, one of the dogs belonging to the party was killed in the forest, almost within sight of Colonel Rondon, and found with two arrows in his body.  The river was dangerous for bathing, because of a peculiar fish—­the piranha—­a savage little beast which attacks men and animals with its razor-like teeth, inflicts fearful wounds and may even kill any unfortunate creature which is caught by a school in deep water.  Some members of the party were badly bitten by the piranhas.

As their long and difficult course down the river continued, and as their hardships increased, one of the native helpers murdered another native—­a sergeant—­and fled.  Roosevelt, while in the water helping to right an upset canoe, bruised his leg against a boulder.  Inflammation set in, as it usually does with wounds in the tropics.  For forty-eight days they saw no human being outside their own party.  They were all weak with fever and troubled with wounds received in the river.  Colonel Roosevelt (who was nearly fifty-six years old) wrote of his own condition: