The day was warm and sunny, and after lunch I took Tricia into the woods behind the house to explore with her the places I remembered from my own childhood. A dark stream ran through the woodland, and leaves were yellow-green against the fast-moving clouds and blue sky. I pointed out, as my father had to me, the warblers darting among the oaks and maples. The stream swirled lazily over rocks and sodden logs, and for a while we sat upon a boulder and watched the water flow. "Did you know there are tiny creatures in that water?" I asked. "Animals that you can’t see?"
Tricia lowered her face toward the pool beneath us. "Are there?"
My father had demonstrated the existence of the invisible teeming life by taking a sample of creek water and showing me slides under a microscope. I remembered the elaborate bulbous forms of protozoa and the bizarre wriggling cilia that waved in the droplets of water. "How do you suppose we could tell whether such creatures were there?" I asked.
Tricia continued to stare into the water. "By the fish," she said.
"The fish?"
"I can see fish, and the fish have to eat something smaller than they are, and those things must eat something smaller…"I nodded and laughed at what seemed so logical, and at myself for thinking I should believe only what I could see with my own eyes.