The River of Seven Stars (1924)

Arthur
Friel, relentlessly curious, funded his own mission to find the white
Indians of Venezuela. Along the way, he dealt with the severe tropical
heat and humidity, diseases like yellow fever and beri-beri, and
assorted vicious and deadly creatures packed so densely that they just
about trip over each other -- giant anacondas, jaguars, leaping spiders,
fire ants, snakes of every description, and poisonous centipedes. Then,
also, there were the Mayorunas, cannibals and head hunters who
occasionally poison the streams because of 'real or imaginary enemies'.
Friel found the white Indians, but they were not what he expected. He
made it home and became one of the most popular writers for Adventure
magazine during the 1920s and 1930s.