Michael Harner: The Way of the Shaman

"Instead of just observing what happened to the Conibo after they consumed the soul-vine ayahuasca, Harner imbibed the hallucinogen himself. 
It is obvious that not all anthropologists would be willing to take such a risk, but it is also clear that by becoming a participant instead of just an observer, he was able to learn more than he ever could have by just sitting on the sidelines and taking notes."
From The Holographic Universe by Michael Talbot.