The task of harvesting the secrets of Brazil's vast Amazon rain forest that could help in the battle against cancer largely falls to Osmar Barbosa Ferreira and a big pair of clippers.
In jungle so dense it all but blocks out the sun, the lithe 46-year-old shimmies up a thin tree helped by a harness, a strap between his feet, and the expertise gained from a lifetime laboring in the forest.
A few well-placed snips later, branches cascade to a small band of researchers and a doctor who faithfully make a long monthly trip to the Cuieiras river in Amazonas state in the belief that the forest's staggeringly rich plant life can unlock new treatments for cancer.
They may be right.
About 70 percent of current cancer drugs are either natural products or derived from natural compounds, and the world's largest rain forest is a great cauldron of biodiversity that has already produced medicine for diseases such as malaria.
But finding the right material is no easy task in a forest that can have up to 400 species of trees and many more plants in a 2.5-acre (1-hectare) area, and in a country where suspicion of outside involvement in the Amazon runs strong.
If we had very clear rules, we could attract scientists from all over the world, said the doctor, Drauzio Varella, with a mix of enthusiasm and frustration. We could transform a big part of the Amazon into an enormous laboratory.
As it stands, though, foreigners are barred from helping oncologist Varella and the researchers from Sao Paulo's Paulista University, who are among a tiny handful of Brazilian groups licensed to study samples from the Amazon.
Varella, 66, believes his high profile has helped. He is a well-known writer and television personality who shot to fame in 1999 with a book and subsequent hit movie based on his work as a doctor in a brutal Sao Paulo prison called Carandiru.
But a move by his team in the 1990s to partner with the U.S. National Cancer Institute produced a storm of accusations of bio-piracy and for years it has been blocked from the international cooperation and funding that could increase the chances of finding the Holy Grail of a cancer cure.
Their work has also been regularly delayed by bureaucratic demands, once stopping their collections for two years.
In more than a decade of searching, the group has brought back 2,200 samples from this tributary of the mighty, tea-dark Rio Negro (Black River) to its laboratory in Sao Paulo, of which about 70 have shown some effect against tumors. Just those samples have given the team enough analysis work for 20 years, said Varella, a lanky marathon runner whose younger brother died of cancer.
If we can find 70, imagine what a big university with international resources could do -- they could screen for an absurd amount of diseases, said Varella, who still spends part of his time treating prisoners in Sao Paulo.
As well as the impact this could have on human health, it could bring resources for preservation and to improve the quality of life of people who live here.
Ironically, it was a foreigner who inspired Varella to begin his search. Robert Gallo, a U.S. researcher and leading AIDS expert who co-discovered the HIV virus, asked Varella during a trip to the Amazon in the early 1990s if anyone was researching the medical potential of the forest.
Among the natural products being used to fight cancer today is Taxol, a chemotherapy drug that comes from the bark of the Pacific yew tree.
David Newman, head of the Natural Products Branch of the U.S. National Cancer Institute, said several promising cancer drugs derived from natural sources as varied as a deep-water sponges and microbes are currently going through clinical trials. Often the natural compounds are tweaked or mimicked to better fight cancer cells.
It's a detective story and a jigsaw puzzle, but you don't know how many pieces there are or what the picture looks like, he said. In one teaspoon of soil from the Amazon, you find over a thousand microbes that have never been isolated.
Out of an estimated 80,000 species of flower-bearing plants in the Amazon, only about a fifth have been identified.
Newman said progress in Brazil has been greatly hampered by the inability of companies to patent a natural product under legislation passed in the 1990s, leaving no incentive to invest in research.
He cited the example of a Brazilian viper snake whose venom proved vital to the development of blood pressure drug captopril in the 1970s, a find that might not have happened under today's laws.
Further analysis of the promising compounds found by Varella's team has been held up while the university waits for access to a nuclear-magnetic resonance machine that can isolate the active elements.
We're still a long way from discovering an actual medicine that could cure a type of cancer but we have strong signs that some plants have substances that inhibit the growth of tumors, said Mateus Paciencia, a bearded 34-year-old botanist.
Their main hope is that growing concern over the environment and increasing government efforts to slow the destruction of the Amazon by ranchers and loggers will turn the tide in favor of sustainable forest industries, of which they say their work is a prime example.
There is nothing more sustainable than this, said Paciencia. We take a kilogram worth of samples from a tree that weighs a ton and get an extract that lasts 10 years.
As he hung from a tree trunk, Ferreira said his relationship with the forest had been transformed by his job. He used to cut down trees with a chainsaw and sell the lumber in the city of Manaus, about 80 km (50 miles) down river from the research site.
I think we'll find a medicine, and it won't take too long, he said. If I deforest, I'm killing not just one plant but destroying a lot of other plants as well. So the job we're doing here is much better.