Hi
I'm looking for a fantasy book I've read probably about 20 years ago. The main characters are westerners, a man and a woman, who survived a plane crash (?) in the South America jungle, in some hidden valley, the woman looses her finger (thumb?), she pees on it to disinfect the wound. They find a Chinese community (Zheng He expedition descendants?) living medieval Chinese life with all beliefs, cast system etc (i'm not sure). They (the Chinese) found some kind of a fungus (or maybe a herb?) that has some unique psychosomatic features, it's used extend the consciousness (like LSD), it's highly valued and connected with those people beliefs, it also enables body regeneration (if you really want to). That how the heroine regrows her finger. Chinese also have pet monkeys, that are very intelligent, they have a limited speech (one asks here master for a cookie) and reportedly use fire in the wilderness. The main characters live with this people for some time, plan to return to the civilization, they steal one of the monkeys to show them to the world. The monkey started to die of dehydration, they trying to five it water but it chokes, then a native explains them they don't drink water like we do, they just lick the droplets from their whiskers