I´ve recently read the first part of "The River of Doubt" by Candice Millard, a book about Theodor Roosevelt and his endeavour to follow the most dangerous river in the Amazon. Multiple times they were in danger, because of animals, diseases, attacks from tribes, the loss of their food and so on. And when I stopped reading the book, they hadn´t even managed to reach their final destination yet.
So I felt that the chapter about their Amazon travel has been too superficial, too. This has to be a vicious place. As much as I enjoyed reading about the different tastes of the tributaries, drinking riverwater had to have an effect on their digestive system. Having said that I still enjoy this book a whole lot.
I have found Humboldts
original diaries, but unfortunately only in German and in a terrible fond. Who knows, maybe it will get translated someday.