Susan Abookire, an internist and professor at Harvard Medical School, had a cure for all that ailed me. "Find a being. The being might be a tree or rock," she told me. "Greet it as you would a friend. You might want to introduce yourself. You may want to share something with that being." I was participating, somewhat skeptically, in a forest bathing session Abookire was leading at Harvard's Arnold Arboretum for seven young doctors. It's part of resident training ... which is looking for ways to reduce stress and burnout within the profession. She explained that just by standing among the trees, we were inhaling essential tree oils called phytoncides and aromatic plant compounds called terpenes. "There's several studies now showing that inhaling phytoncides boosts our immune system, and specifically our natural killer-cell numbers and activities go up," she said. Breathing in tree scents fights infection, prevents cancer and protects against dementia. Qing Li, a professor at Japan's Nippon Medical School ... told me, "the larger the trees, the higher the tree density, and the larger the forest area, the greater the effects of forest bathing." More phytoncides and more terpenes, more benefit. He also believes we profit from inhaling negative ions (found in abundance near waterfalls) as well as a microorganism found in the soil, Mycobacterium vaccae. He recommends spending two to four hours in the forest walking at a slow pace ... and paying attention to your senses.